Amorosi, A., Glaucony and Sequence Stratigraphy - a Conceptual-Framework of Distribution in Siliciclastic Sequences, Journal of Sedimentary Research Section B-Stratigraphy and Global Studies, 65 (4), 419-425, 1995.

Detailed analysis of recent literature on glaucony and selected case studies (Eocene, Isle of Wight; Miocene, northern Apennines) shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence, A reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony, including: (1) spatial distribution, (2) maturity (distinction between nascent, slightly evolved, evolved, and highly evolved glaucony), and (3) genetic attributes (differentiation of autochthonous from allochthonous, and intrasequential from extrasequential glaucony). Autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract (TST) and the lower highstand systems tract (HST), showing an upward increase (TST) and then decrease (HST) in abundance and maturity, The condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony, Allochthonous intrasequential (parautochthonous) glaucony can be present in the entire TST, HST, and lowstand systems tract (LST), generally showing lower concentration and maturity than its autochthonous counterpart, Al lochthonous extrasequential (detrital) glaucony is present mainly in the LST, its concentration and composition depending on the characteristics of the source horizon, The association between autochthonous and allochthonous (intrasequential and extrasequential) glaucony commonly exists in the LST and in the lower TST.

Bailey, G.W., and J. Rogers, Chemical oceanography and marine geoscience off southern Africa: Past discoveries in the post-Gilchrist era, and future prospects, Transactions of the Royal Society of South Africa, 52, 51-79, 1997.

In 1895/96, John D. F. Gilchrist was appointed marine biologist to the Cape Colony. During voyages extending as far as Walvis Bay and Maputo, he initiated studies of the marine geology and chemical oceanography of the shelf while mapping substrata for new demersal fishing grounds. The shelf sediments off the East Coast are controlled by wave processes along the inner shelf and by the poleward-flowing Agulhas Current along the outer shelf. In contrast, South Coast sediments of the eastern Agulhas Bank consist of wave-dominated, landward-coarsening modern (Holocene) terrigenous muds to sands on the inner shelf and relict wave-dominated shelly sands on the outer shelf, deposited during Pleistocene lowstands within glacial (hypothermal) periods. The Agulhas Current also appears to exert a controlling influence over the nutrient chemistry and, hence, primary productivity, on the East and South Coast margins. The surface waters of the Agulhas Current are nutrient-poor and most East Coast areas are consequently considerably less productive than their West Coast counterparts at the same latitude, but the underlying South Indian Central Water (SICW) is nutrient-rich. Recent findings suggest that the Agulhas Current may induce upwelling of nutrient-rich bottom water derived from SICW at sites such as the Natal Eight and off Port Alfred by kinematic upwelling, so enhancing the nutrient content of surface waters and increasing the potential for primary production there. A second physical process, which is also thought to be related to interaction of the Agulhas Current and bottom topography, is the dynamic shelf-edge upwelling of SICW onto the shelf along portions of the South Coast where the shelf is wider. It is uncertain whether this is continuous in space or time, but it is possible that the process may prime bottom waters for wind-induced upwelling in the south-western ice of capes along the South Coast. On the West Coast, the outer-shelf sediment consists of Holocene planktonic-foraminiferal ooze, reflecting the dominating influence of the equatorward-flowing Benguela Current. The middle-shelf sediment often consists of glauconitic sand, whereas the sediment of the inner shelf usually has a landward- coarsening and -thickening wedge of terrigenous muds to sands. Wind-induced upwelling is the dominant West Coast physical process of relevance to the sedimentology and chemistry of the inner shelf and overlying waters. In the southern Benguela, this is seasonal, resulting in seasonal variability in the abundance of nutrients and the resultant productivity of surface waters and associated biogeochemical processes, such as the appearance of oxygen-depleted bottom water. There is a northward decrease in the seasonality of these physical and biogeochemical processes along the West Coast, which is reflected in an increase in the reducing nature of the underlying organic-rich sediments between St Helena Bay and Walvis Bay. In the deep-sea environment of the Cape Basin, the clockwise poleward flow of bath the Antarctic Bottom Water (AABW) and the North Atlantic Deep Water (NADW) is reflected in a major zone of erosion of the sea floor, mantled by abundant ferromanganese nodules, at the foot of the continental rise, which is fed by margin-perpendicular slumps, debris flows and canyon-fed turbidity currents. The currents, driven by Coriolis Force, both swing left (east) into the Agulhas Passage between the Agulhas Bank and the Agulhas Plateau, before parting company in the Transkei Basin, where the AABW is forced eastwards by the northeast-shallowing contours of the Natal Valley. The E-W-orientated Agulhas Drift, a contourite drift, is being deposited on the left (north) side of the AABW. The NADW then heads into the Natal Valley to deposit margin- parallel contourite drifts at the foot of the continental slope as far north as Durban, where the Central Terrace and then the Mozambique Ridge steer the NADW first east and then south hack to the mouth of the Natal Valley.

Bennington, J.B., and R.K. Bambach, Statistical testing for paleocommunity recurrence: Are similar fossil assemblages ever the same?, Palaeogeography Palaeoclimatology Palaeoecology, 127 (1-4), 107-133, 1996.

Observations of the recurrence of similar fossil assemblages through long intervals of geologic time punctuated by rapid changes in both the composition and structure of fossil assemblages has recently resulted in the concept of ''coordinated stasis'' to describe this pattern in the behavior of paleocommunities through time. Coordinated stasis may imply the existence of ecological mechanisms that actively maintain particular community structures and thus have a significant impact on the process of macroevolution. However, before such mechanisms can be invoked, it must be shown that ecological stasis as observed in the fossil record is more significant than the persistence of similar community types due to the repeated reinvasion of recurring habitats from a persistent species pool (the ''null hypothesis'' for paleocommunity recurrence). Analysis of the relationship between communities and paleocommunities and an expansion of the ecological hierarchy at the community/paleocommunity level allows the creation of a rigorous definition of the entities composing the local paleocommunity (the samples collected within a stratigraphic horizon at a single locality), paleocommunity (groups of samples shown to be statistically identical), and paleocommunity type (groups of samples that are similar but can be shown to be statistically different). These definitions permit the development of the null model for paleocommunity recurrence and establish a base-level of variability within a local paleocommunity that permits rigorous statistical comparisons to be made between paleoecological samples at larger temporal and geographic scales. Paleoecological samples from four marine tongues in the Middle Pennsylvanian Breathitt Formation are used to analyze species abundance variability at several spatial and temporal scales and to lest for paleocommunity recurrence. Although recurrence of statistically identical local paleocommunities occurs at single localities and between localities within individual marine units, it is usually not detectable between marine tongues, suggesting that paleocommunity recurrence in the marine strata of the Breathitt Formation is the recurrence of paleocommunity types and does not falsify the null hypothesis.

Berne, S., G. Lericolais, T. Marsset, J.F. Bourillet, and M. De Batist, Erosional offshore sand ridges and lowstand shorefaces: Examples from tide- and wave-dominated environments of France, Journal of Sedimentary Research, 68 (4), 540-555, 1998.

Offshore sand bodies are described from many continental shelves in the world, as well as in the stratigraphic record, where they shelves in the world, as well as in the stratigraphic record, where they commonly are productive reservoirs. Same of these ancient sand bodies, initially interpreted as sand ridges, are now reinterpreted as lowstand shoreface deposits. Modern sand bodies, in contrast, have received relatively little attention with regard to reinterpretation of their origin, largely because of the lack of information about their internal structure. Improved techniques in acquisition and processing of very high- resolution seismic profiles, along with some shallow cores, allow us to reconstruct the architecture of "offshore sand bodies" from the Celtic Sea (tide dominated) and the Gulf of Lions (wave-dominated) shelves of France, in water depths of 100-170 m. In both areas, our investigations demonstrate that these particular sand bodies consist mainly of lowstand deposits (estuarine/deltaic systems, sharp based shorefaces), reworked during transgressions. In the Celtic Sea, intense erosion by combined waves and tidal currents resulted in the shaping of shore-oblique ridges by cannibalization of older lowstand deposits. In the Gulf of Lions, the shore-parallel orientation of the lowstand shorefaces has been preserved, leaving an ancestral sand body with reworked (transgressive) surface deposits. Understanding the architecture and distribution of offshore sand bodies requires taking into consideration not only the effects of relative sea-level changes and sediment supply, but also the role of hydrodynamical processes. The erosional sand bodies we describe represent a new category of outer-shelf sand bodies, a combination of the "autocyclic" examples described by Houbolt (1968) in the southern North Sea and the "allocyclic" lowstand shorefaces mainly described in the stratigraphic record of the Western Interior Seaway of North America. Our findings have applications for predicting the geometry of ancestral sand bodies and their orientation and position with respect to paleo-shorelines. The magnitude of erosional processes also implies that a large amount of shelf sediment (mainly sand) was transferred to the adjacent deep sea boor during the early transgression.

Blackwelder, B.W., I.G. Macintyre, and O.H. Pilkey, Geology of Continental-Shelf, Onslow Bay, North-Carolina, As Revealed By Submarine Outcrops, Aapg Bulletin-American Association of Petroleum Geologists, 66 (1), 44-56, 1982.


Boardman, M.R., and C. Carney, Origin and Accumulation of Lime Mud in Ooid Tidal Channels, Bahamas, Journal of Sedimentary Petrology, 61 (5), 661-680, 1991.

Mud layers have been found within the ooid sands of Joulters Cays and Lee Stocking Island, Bahamas. A 1.3-m vibracore extracted from 4 m water depth in the Lee Stocking tidal channel contains a lower unit of dark brown muddy sand (skeletal rich) overlain by two layers of ooid sands intercalated with two layers of creamy, white mud. The two upper mud layers are aragonite-rich, sometimes pelleted, and contain very few skeletal grains. The contacts between the ooid sands and mud layers are commonly sharp, but some contacts show evidence of burrowing and mud clast formation. A mud layer with similar textural, mineralogic and petrographic characteristics was recovered from a 16-cm core from a tidal channel on Joulters Cays, Bahamas. This mud layer was also enclosed within ooid sands. Mud in the Lee Stocking ooid tidal channel is apparently of two origins. Mud in the lower unit of the core contains a more equal distribution of aragonite and calcite (almost-equal-to 50% each) and abundant skeletal grains of normal marine origin, indicating that the lower unit is lagoonal. Mud that is interlayered with ooid sands in the same core is dominated by aragonite (almost-equal-to 80%) and contains little sand-sized material, suggesting that it is not a typical lagoon mud. SEM examination also confirms that this mud is quite different from the lagoonal mud found at the base of the core. C-14 dating of the mud from the lagoonal unit shows that this sediment was deposited in water depths of 2 to 3 m approximately 5000 years ago when sea level was 3 m lower than present. C-14 dating coupled with knowledge of Holocene sea level indicates that both the ooid sands and the mud layers were also deposited as subtidal sediments. The mechanism by which the mud layers are accumulated with ooid sands is problematic. Suspension by storms and transport to tidal channels is one possibility; however, evaluation of the data suggests an alternative explanation. The post-lagoon history of deposition of the tidal channel may include nearly continuous restriction during which mud layers were deposited. The restriction was possibly caused by the formation and maintenance of ooid sand barriers. Ooid sand deposition and burial of these layers may have accompanied barrier destruction.

Bodur, M.N., and M. Ergin, Holocene Sedimentation Patterns and Bedforms in the Wave- Current-Dominated Nearshore Waters of Eastern Mersin Bay (Eastern Mediterranean), Marine Geology, 108 (1), 73-93, 1992.

The distribution and bedforms of Holocene sediments in relatively high energy. wave-dominated nearshore waters of the eastern Mersin Bay (eastern Mediterranean) were investigated by high resolution seismic profiles, sidescan sonar records and surface sediment samples. High-resolution seismic reflection profiles show that the sedimentary column consists of two main sequences separated by a mid-reflector (R), showing irregular and erosional surface features, which is interpreted as the Late Pleistocene/Holocene boundary. The upper sequence which is seen as parallel to slightly divergent reflection configurations in a sheet-like to wedge-shaped geometry, approximates to Holocene deposits reaching up to 10 m in thickness about 2 km seaward of the shoreline, with a slight tendency to increase offshore. Seismic data indicate that the unconformity between the late glacial subaerial surface and the overlying post-glacial transgressive deposits occurs at depths of 1-10 m below the seafloor. Holocene sedimentation rates are estimated to be 10-100 cm per 1000 yr. Typical ridge-furrow systems cutting into beachrocks are apparently products of mechanical erosion at very shallow water depths. The lower seismic sequence underlying the reflector R may represent pre- Holocene deposits and is characterized by complex stratified reflection patterns, commonly showing hummocky to mounded and chaotic cut-and-fill facies. Sidescan sonar records indicate prominent features of these nearshore areas such as gravel waves between sand patches and beachrocks: The former are thought to have been produced as a result of the interaction of waves and currents on the sediment surface with an apparently westerly migration direction for sand, whereas the latter were formed during the lowstand of sea level in the Late Holocene. Muddy sand is the dominant sediment type in the nearshore waters of Mersin Bay (in depths less than 15 m) with local sand and gravel patches and beachrock outcrops.

Boyd, R., and C. Honig, Estuarine Sedimentation On the Eastern Shore of Nova-Scotia, Journal of Sedimentary Petrology, 62 (4), 569-583, 1992.

Vibracored sedimentary sequences and microfauna (foraminifera) were studied in Lawrencetown Lake, a small, wave-dominated estuary with minor fluvial input located on the Eastern shore of Nova Scotia. Seven lithofacies were identified on the basis of sedimentological characteristics, microfaunal assemblages, and stratigraphic relationships. These lithofacies can be grouped into three associations which define estuarine basin fill, channel cut and fill, and channel bypass subenvironments within the estuary system. Facies relationships indicate a cyclic pattern of estuarine sedimentation, controlled by fluctuating local sediment supply superimposed upon a regional transgression.

Bray, T.F., and C.H. Carter, Physical Processes and Sedimentary Record of a Modern, Transgressive, Lacustrine Barrier-Island, Marine Geology, 105 (1-4), 155-168, 1992.

High water levels, storms, and a sparse sand supply have led to the formation and episodic migration of this 30 km-wide, foredune-lacking, lacustrine barrier. Transgression is dominated by overwash and by channels cut during storms that transport sand to the lagoon. The barrier system is characterized by five environments: near-shore, foreshore, backshore/washover terrace, channel, and lagoon. The nearshore consists of irregular bars that overlie a Holocene peat and/or clay. The bars are characterized by low-angle stratification, and ripples, and landward-dipping tabular sets. The foreshore consists of a smooth, plane surface and internally by lakeward- dipping (3-degrees to 12-degrees) laminations that truncate one another and thin towards the berm. The backshore/washover terrace consists of a gently (1-degrees to 2-degrees) landward- dipping surface that changes at the lagoon margin to a steeply (30-degrees) landward-dipping surface. Stratification consists of subhorizontal, landward-dipping laminations and thin beds that are thinnest nearer the berm and gradually thicken toward the lagoon, and by avalanche foresets. Washover fans coalesce to form the terrace. The channels, which are commonly less than a few tens of meters wide and a meter deep, form during storms when wave energy is concentrated by refraction around nearshore bars. The channel facies consists of nearly horizontal beds and laminations of gravel and coarse sand. The lagoon consists of mud that overlies a Holocene peat; the lagoonal mud is eroded during transgression. The vertical sequence which is 1-2 m thick, consists from the base up of horizontal laminations of coarse sand and gravel of the channel facies, the landward- dipping foresets of the washover fan margin, and the gently landward-dipping laminations and landward-dipping avalanche foresets of the backshore/washover terrace. The preservation potential is considered low, although Pleistocene and Holocene coastal deposits have survived for up to 15,000 years in the Great Lakes region.

Bridge, J.S., and B.J. Willis, Marine Transgressions and Regressions Recorded in Middle Devonian Shore-Zone Deposits of the Catskill Clastic Wedge, Geological Society of America Bulletin, 106 (11), 1440-1458, 1994.

The shore zone of the Middle Devonian Catskill elastic wedge in New York State consists of (1) a storm-wave-dominated muddy marine shelf with sandy shoals; (2) sandy, tide-influenced channels with wave- and tide-influenced mouth bars; (3) sandy and muddy tidal flats, including channels, mouth bars, and washovers; and (4) muddy brackish bags, lakes, and flood plains. The spatial organization of these subenvironments suggests a wave- and tide-influenced deltaic shoreline. Meter- scale sequences can be related to processes such as lateral migration and filling of tidal channels, progradation of channel-mouth bars and tidal flats, and filling of coastal bays; these may be related to channel switching. Asymmetrical regressive-transgressive sequences that range from tens of meters to >100 m thick can be correlated over many kilometers with fully marine and fluvial deposits. Such sequences record a combination of eustatic sea-level changes and tectonically induced changes in sediment supply and subsidence rate. However, at present it is very difficult to determine the relative importance of these controls.

Brooks, G.R., Recent sedimentary development of Tampa Bay, Florida: A microtidal estuary incised into tertiary platform carbonates, Estuaries, 21 (3), 391-406, 1998.

Tampa Bay, a large, microtidal, clastic-filled estuary incised into Tertiary carbonate strata, is the largest estuary on Florida's west coast. A total of 250 surface sediment samples and 17 cores were collected in Tampa Bay in order to determine the patterns and controlling factors governing the recent infilling and modern sediment distribution, and to examine the results in terms of current models of estuarine sedimentation and development. Surficial sediments in Tampa Bay consist of three facies types, each occurring in a distinct zone: modern terrigenous elastic muds occurring in the upper bay and around the bay periphery; relict, reworked-fluvial, quartz-rich sands occupying the open portion of the middle bay; and modern carbonate-rich, marine-derived sands and gravels occupying the lower bay. Factors controlling sediment distribution include: sediment source and supply rate; bathymetry, which is a function of the antecedent topography; and the winnowing effect of wind-generated waves that prohibits modern accumulation in the shallow middle bay. These factors also play a major role in the recent infilling history of Tampa Bay, which has progressed in four stages during the Holocene sea-level rise. Recently developed models of estuarine sedimentation are based primarily on mesotidal to macrotidal estuaries in terrigenous elastic settings in which sedimentation patterns and infilling history are a result of the relative contribution of marine and fluvial processes. Tampa Bay differs in that it was originally incised into carbonate strata, and neither fluvial or marine processes are interpreted to be major contributors to modern sediment distribution. Tampa Bay, therefore, provides an example of an unusual estuary type, which should be considered in future modeling efforts.

Cacchione, D.A., D.E. Drake, J.T. Ferreira, and G.B. Tate, Bottom Stress Estimates and Sand Transport On Northern California Inner Continental-Shelf, Continental Shelf Research, 14 (10-11), 1273-1289, 1994.

Measurements of velocities and light transmission in the bottom boundary layer on the continental shelf off northern California demonstrate the importance of storms in the transport of sediment along the coast and offshore in this region. Time- series estimates of bottom stress obtained from a combined wave-current bottom boundary layer model in which wave and current measurements from the Geoprobe tripod were used as input show high stress values of 10 dynes cm-2 during two distinct storm events in early February and early March, 1991. These stresses induce significant offshore sediment transport, achieving maximum values of about 0.5 g cm-1 s-1. The net transport over the entire measurement period from 30 January 1991 to 13 March 1991 was along the coast toward the north and offshore. This transport pattern explains slow migration of low amplitude, broad crescentic dunes along and across this portion of the inner continental shelf.

Cacchione, D.A., P.L. Wiberg, J. Lynch, J. Irish, and P. Traykovski, Estimates of suspended-sediment flux and bedform activity on the inner portion of the Eel continental shelf, Marine Geology, 154 (1-4), 83-97, 1999.

Energetic waves, strong bottom currents, and relatively high rates of sediment discharge from the Eel River combined to produce large amounts of suspended-sediment transport on the inner continental shelf near the Eel River during the winter of 1995-1996. Bottom-boundary-layer (BBL) measurements at a depth of similar to 50 m using the GEOPROBE tripod showed that the strongest near-bottom flows (combined wave and current speeds of over 1 m/s) and highest sediment concentrations (exceeding 2 g/l at similar to 1.2 m above the bed) occurred during two storms, one in December 1995 and the other in February 1996. Discharge from the Eel River during these storms was estimated at between 2 and 4 x 10(3) m(3)/s. Suspended-sediment flux (SSF) was measured 1.2 m above the bed and calculated throughout the BBL, by applying the tripod data to a shelf sediment-transport model. These results showed initially northward along-shelf SSF during the storms, followed by abrupt and persistent southward reversals. Along-shelf flux was more pronounced during and after the December storm than in February. Across-shelf SSF over the entire measurement period was decidedly seaward. This seaward transport could be responsible for surficial deposits of recent sediment on the outer shelf and upper continental slope in this region. Sediment ripples and larger bedforms were observed in the very fine to fine sand at 50-m depth using a sector-scanning sonar mounted on the tripod. Ripple wavelengths estimated from the sonar images were about 9 cm, which compared favorably with photographs of the bottom taken with a camera mounted on the tripod. The ripple patterns were stable during periods of low combined wave-current bottom stresses, but changed significantly during high-stress events, such as the February storm. Two different sonic altimeters recorded changes in bed elevation of 10 to 20 cm during the periods of measurement. These changes an thought to have been caused principally by the migration of low-amplitude, long-wavelength sand waves into the measurement area. (C) 1999 Elsevier Science B.V. All rights reserved.

Cadee, G.C., Eider, Shelduck, and Other Predators, the Main Producers of Shell Fragments in the Wadden Sea - Paleoecological Implications, Palaeontology, 37, 181-202, 1994.

Seventy five per cent by weight of the > 2 mm carbonate fraction of Wadden Sea sediments consists of fragmented shells, thirty per cent > 8 mm and forty five per cent in the 2-8 mm fraction. Eiderducks (Somateria mollissima) feed mainly on mussels (Mytilus edulis) and cockles (Cerastoderma edule). Shells are crushed internally to fragments with a size-range from < 0.1 to 8 mm, twenty per cent were < 1 mm, sixty per cent 2-8 mm. One-third to one-half of the fragments in the 2-8 mm fraction in the sediments are due to eider predation alone. Other birds, crabs and fish probably produce the remaining fragments of this fraction. Shelduck (Tadorna tadorna) feed on the small gastropod Hydrobia ulvae; a varying amount (seventeen to thirty two per cent by weight) of shells was found intact in their faeces, but the remainder is fragmented. Around forty per cent by weight of Hydrobia shells in the Wadden Sea sediments is broken. This can be attributed to shelduck and other predators (e.g. knot) feeding on Hydrobia. Fragments in the > 8 mm fraction may also be produced by predators (shore crabs, oystercatchers). Physical destruction plays a minor role in the Wadden Sea. Shell fragmentation cannot be used as a measure of water turbulence. The high percentage of shell fragments indicates high predation pressure. However, the use of shell fragmentation to estimate predation pressure in fossil faunas is not possible, because some predators leave one (oystercatchers) or both valves (Asterias) intact. Despite high fragmentation fidelity of the death assemblage to the living fauna of the Wadden Sea is high. Physical destruction would leave only fragments of durable skeletons with low fidelity to the living fauna.

Callender, W.R., E.N. Powell, and G.M. Staff, Taphonomic Rates of Molluscan Shells Placed in Autochthonous Assemblages On the Louisiana Continental-Slope, Palaios, 9 (1), 60-73, 1994.

A mixed assemblage of lucinid and mussel shells were placed in mesh bags and left at a site of autochthonous death assemblage formation in a petroleum seep community on the Louisiana upper continental slope for a period of 3 yr. Upon recovery, the shells were assessed for taphonomic alteration and compared to a control assemblage of unaltered shells. The data verify a basic assumption of taphofacies analysis; that evidence of taphonomic processes preserved with the assemblage does in fact document the primary taphonomic processes that biased the assemblage from the original assemblage of living preservable organisms. Significant variability in taphonomic rates existed between shells from locations 10 m apart, as is typical of autochthonous assemblages, so that small-scale variability in the taphonomic process was important. Mussels were more severely altered than lucinids. Mussels were more heavily dissolved, had more altered edges, were more prone to fragmentation and exhibited greater weight loss (=carbonate loss) than did the lucinids. The estimated residence time for mussels on the continental slope is approximately 3 to 15 yr. Lucinids may be indefinitely preserved. The observed discrepancy between the dominance of lucinids at fossil seeps and the frequent dominance of mussels at recent seeps can be explained by biased preservation favoring the lucinids.

Caplan, M.L., and T.F. Moslow, Depositional origin and facies variability of a Middle Triassic barrier island complex, Peejay field, northeastern British Columbia, Aapg Bulletin-American Association of Petroleum Geologists, 83 (1), 128-154, 1999.

Middle Triassic strata of the Peejay field in northeastern British Columbia are composed of four regressive shorefaces, the youngest having been reworked by tidal inlets. Tidal-inlet sublitharenites and bioclastic grainstones form the best reservoir facies. These deposits form a series of shoreline- parallel, narrow sharp-based, linear sand bodies that eroded the paleoshoreface. The orientation, geometry, and internal sedimentology of these tidal-inlet facies suggest that the paleoshoreline was subjected to a wave-dominated paleohydrographic regime. Determining the processes responsible for forming a specific tidal inlet can provide information regarding waves, tides, and storms characteristic of the depositional setting. Knowledge of this paleohydrographic regime can aid in predicting the orientation and internal characteristics of tidal-inIet reservoir facies. Improved predictability of reservoir facies geometry and quality can have direct implications on hydrocarbon exploration and development strategies of these and similarly formed hydrocarbon plays of the Triassic in the Western Canada sedimentary basin and elsewhere.

Carr, D.L., and A.J. Scott, Late Pennsylvanian Storm-Dominated Shelf Sand Ridges, Sacramento Mountains, New-Mexico, Journal of Sedimentary Petrology, 60 (4), 592-607, 1990.


Carter, L., and K. Lewis, Variability of the modern sand cover on a tide and storm driven inner shelf, south Wellington, New Zealand, New Zealand Journal of Geology and Geophysics, 38 (4), 451-470, 1995.

The embayed coast, south of Wellington, is notorious for the severity of its storms and tides. Time-series side-scan sonar and sediment surveys, made of the bays and inner shelf over an 11-16 year period, show that the general locations of four main seabed types-(1) a modern, fine-medium sand cover, (2) a generally megarippled, coarse sand - fine gravel substrate, (3) a basal cobble-boulder deposit, and (4) greywacke basement- remain fairly stable despite considerable mobility at the edges of each deposit. The sand cover is best developed(1.5 m max. thickness) in the larger bays centred on Wellington Harbour entrance. Here it has undergone bouts of accretion (indicated by advances of cover edges) that have ended in erosion (with retreat of edges). Mobility of sand is induced on a daily to annual basis by tides reinforced by southerly swell and storm- driven currents. These high-frequency events are superimposed on annular to decadal variations that probably relate to the frequency of gales and storms, and to variations in sediment supply caused by local earthquakes, changes in land use, and climatic cycles. Outside the bays, on the open shelf, the combination of a more vigorous tidal flow and reduced sediment supply mean that the sand cover is much less extensive and more mobile. The seabed is predominantly coarse sand - fine gravel with a megarippled surface formed by southerly swell. Tides become progressively stronger to the west, and, in the Narrows of Cook Strait, currents are sufficiently powerful to keep sand in near-constant motion and erode the fine gravel down to underlying boulders and rock.

Chakraborty, T., Sedimentology of a Proterozoic Erg - the Venkatpur Sandstone, Pranhita-Godavari Valley, South-India, Sedimentology, 38 (2), 301-322, 1991.

Reappraisal of the Late Proterozoic Venkatpur Sandstone indicates that the bulk of the sandstone is aeolian in origin. Aeolian stratification types, namely (i) inverse graded translatent strata, (ii) adhesion laminae, (iii) grainflow strata and (iv) grainfall strata, are present throughout the outcrop belt. Nine facies have been identified that represent both aeolian and related aqueous environments within a well- developed erg. Cosets of large cross-beds at the Bellampalli section in the NW of the study area record dune fields in the interior of the sand sea. To the SE, at the Godavari River and Ramgundam sections, a progressive increase in the relative proportion of the flat-bedded to cross-bedded facies and intercalated non-aeolian facies delineates the transition from the dune-field to sand-sheet environment. An alternating sequence of aeolian and marine sediments at Laknavaram, in the extreme SE, marks the termination of the sand sea. Palaeocurrent data suggest that the NW-SE trend of the sections represents a transect across the sand sea in a direction normal to the resultant primary palaewind direction. Abundant horizontally stratified units in the Vankatpur Sandstone do not always represent the interdune sediments. On the basis of the thickness and geometry of the units, nature of bounding surfaces and associated facies sequence, the facies is variously interpreted to represent interdune, inland sabkha, sand sheet and coastal sand flat deposits.

Cheel, R.J., and D.A. Leckie, A Tidal-Inlet Complex in the Cretaceous Epeiric Sea of North- America - Virgelle Member, Milk River Formation, Southern Alberta, Canada, Sedimentology, 37 (1), 67-81, 1990.


Colman, S.M., J.P. Halka, C.H. Hobbs, R.B. Mixon, and D.S. Foster, Ancient Channels of the Susquehanna River Beneath Chesapeake Bay and the Delmarva Peninsula, Geological Society of America Bulletin, 102 (9), 1268-1279, 1990.


Demirpolat, S., Surface and Near-Surface Sediments From the Continental-Shelf Off the Russian River, Northern California, Marine Geology, 99 (1-2), 163-173, 1991.

There are two basic types of detrital sediments in the study area: modern and relict. Modern sediment consists mostly of sand on the inner shelf, and silt and clay on the middle shelf. The silt and clay overlie an older transgressive sand and extend northwest-southeast with an average thickness of 10 m. This unit pinches out toward the outer shelf, where relict detrital sand dominates with some authigenic glauconite. The detrital sand is much cleaner and darker than the inner shelf sand. The important heavy minerals of the sand fraction for detecting sediment dispersal patterns are biotite, hornblende, glaucophane and glauconite. Biotite and hornblende are abundant in the southern parts of the study area close to Point Reyes Beach, and decrease in abundance northward and offshore. Glaucophane is abundant close to the Russian River mouth, and decreases in abundance southward. Glauconite is abundant on the outer shelf, and decreases in abundance southward. There are two sediment sources for the inner and middle shelf: Russian River discharge and coastal erosion, particularly of beaches, headlands and cliffs in the southern part of the area. The sand-sized sediment of the Russian River is being deposited on the inner shelf between Salt Point (to the north) and Bodega Head (to the south). The Russian River silt and clay are confined to the middle shelf. Some of this silt and clay is being transported into Bodega Submarine Canyon. The coastal material is eroded in the south and transported northward, seaward and also into Bodega Submarine Canyon.

Dronkers, J., and A.G. Miltenburg, Fine sediment deposits in shelf seas, Journal of Marine Systems, 7 (2-4), 119-131, 1996.

From field observations it appears that the top layer of a shelf bottom in general exhibits an intricate geographical pattern of sediment formations. Sediments of different composition are confined in distinct regions. This contradicts the idea that current and wave forces stir up bottom sediment and disperse it in a random way over the shelf; the dispersal process is counteracted by sorting mechanisms. In this paper the bottom patterns of fine cohesive sediments are considered. A specific sorting mechanism is studied which may explain the patchy structure of fine sediment deposits. It is shown that fine sediments can be trapped in bottom deposits which contain a fine sediment fraction high enough to prevent pore water motion in the shelf bed. This mechanism opposes sediment dispersal away from existing deposits. It may also explain the formation or the preservation of mud patches, even in regions where the bottom shear stress is relatively high.

Dyke, A.S., J.E. Dale, and R.N. McNeely, Marine molluscs as indicators of environmental change in glaciated North America and Greenland during the last 18,000 years, Geographie Physique Et Quaternaire, 50 (2), 125-184, 1996.

Dated mollusc collections are classified in assemblages to map paleofaunistic zones. Hiatella arctica and Mya truncata account for almost half the records and comprise a restricted arctic assemblage. Arctic assemblages comprise 70% and arctic- dominated assemblages 80% of the database. Fifteen species dominate but 170 taxa are recorded. At last glacial maximum, the arctic zone extended from the Arctic Ocean to the Grand Banks. The boreal zone in the western Atlantic was compressed. The subarctic zone, which today dominates eastern Canada, was small. The boreal zone was extensive in the eastern Pacific where subarctic and arctic zones were compressed. Zones shifted northward during deglaciation and the arctic zone diversified when Bering Strait submerged 10.5-10.3 ka BP. Western Arctic molluscs during Younger Dryas time indicate shallow waters warmer than present. Major North Atlantic currents were established 9.5-9.0 ka BP. The subarctic zone extended to the head of Baffin Bay and a boreal zone became established in West Greenland 9-8 ka BP, with intensive changes about 8.5 ka BP. We relate the latter to the reduction of Mackenzie River discharge and in sea ice export to the North Atlantic as Laurentide ice withdrew from Mackenzie headwaters. The extended subarctic zone in Baffin Bay persisted until 3 ka BP and then retreated about 1000 km on the Canadian side. Boreal-subarctic molluscs in the Gulf of St. Lawrence before 9.5 ka BP derived from the glacial refugium. High boreal-subarctic molluscs farther north probably migrated from Europe. We postulate that the Labrador Current acts as a one-way valve for mollusc migrations at; glacial- interglacial scales.

Emery, K.O., J.M. Bremner, and J. Rogers, Hypsometry of Divergent and Translational Continental Margins of Southern Africa, Marine Geology, 106 (1-2), 89-105, 1992.

Flattenings that may be shelves formed by marine erosion/deposition or by slump masses are present on continental margins of southern Africa that border both the Atlantic and Indian oceans. Breaks in slope, indicated along sounding lines, suggest that a shallow terrace of the Atlantic margin has been warped downward from depths of about 130 m southward to about 200 m, and a deeper terrace lies between depths of about 150 m to about 440 m. Examination of contours and hypsometry (areas measured between depth contours) show widespread flattenings at about -65 and -95 m on the Indian Ocean margin and -125, -155, and -190 m along the Atlantic margin. Seismic profiles indicate that some of these and other more local flattenings are on slump blocks and thus are not correlatable for long distances. An additional complication is that sediment introduced by rivers is transported alongshore by wave-induced and oceanic bottom currents, and that their deltas are ephemeral.

Ercilla, G., B. Alonso, and J. Baraza, Post-Calabrian Sequence Stratigraphy of the Northwestern Alboran Sea (Southwestern Mediterranean), Marine Geology, 120 (3-4), 249-265, 1994.

The post-Calabrian sedimentary column of the northwestern Alboran Sea comprises three depositional sequences. The two older depositional sequences are defined by lowstand systems tracts (shelf-margin deltas, slope, base-of-slope, and basin deposits, and the Guadiaro channel-levee complex). In contrast, the most recent depositional sequence also includes transgressive (relict shelf facies) and high-stand (the Guadalmedina-Guadalhorce prodelta and hemipelagic facies) systems tracts. The stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea-level changes, variations in sediment supply, and sedimentary processes. The configuration of the depositional sequences is variable and their distribution is complex, as a result of the relative importance played by sea- level changes and tectonism through the area. The sequence boundaries are represented by polygenetic surfaces in the proximal margin, and by monogenetic surfaces in the distal margin and basin. Each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface, both developed during the previous sea-level cycle. The monogenetic surfaces correspond to unconformities and their correlative conformities, formed during sea-level lowstands. This pattern of depositional sequences developed in the margin and basin of the northwestern Alboran Sea shows differences with the Exxon Sequence Stratigraphy Model as traditionally applied: sea-level change control is essentially recognized through lowstand systems tracts, and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface, both developed during the previous sea- level cycle.

Field, M.E., Buried Strandline Deposits On Central-Florida Inner Continental-Shelf, Geological Society of America Bulletin, 85 (1), 57-60, 1974.


Flessa, K.W., A.H. Cutler, and K.H. Meldahl, Time and Taphonomy - Quantitative Estimates of Time-Averaging and Stratigraphic Disorder in a Shallow Marine Habitat, Paleobiology, 19 (2), 266-286, 1993.

We examined the radiocarbon age, taphonomic condition and stratigraphic position of shells of the venerid bivalve Chione spp. from the tidal flats of Bahia la Choya, Sonora, Mexico. Shells in Bahia la Choya are time-averaged. Thirty shells yielded radiocarbon dates from modern (A.D. 1950 or younger) to 3569 years before present. The median calendar age of inner flat shells is 483 years; the median age of tidal channel shells is 427 years. We interpret such long shell survival to be the result of frequent shallow burial. Such burial retards bioerosion of shells. The taphonomic condition of shells varied with environment. Shells from the surface of the inner flats were better preserved than shells from the tidal channel. Shells are more likely to be physically worn and biologically degraded in the waters of the channel than on the quieter and more frequently exposed inner tidal flat. Taphonomic condition is an unreliable indicator of a shell's time-since-death. Poorly-preserved shells on the inner flats tended to be old, but in general shell condition was much more variable than shell age. A shell's condition is more likely the result of its total residence time on the surface than its time-since-death (surface time plus burial time). Two composite short (44 cm and 50 cm) cores revealed varying degrees of stratigraphic disorder (the departure from perfect correlation between relative stratigraphic position and relative age). One of eight shells in the inner flats core was disordered; four of nine shells in the tidal channel were disordered. The actual age range of surface shells approximates the age range of shells in cores. Stratigraphic disorder is a consequence of both time-averaging and physical and biogenic mixing. Time-averaging controls the degree of precision possible in paleoecological studies. Environmental changes and ecological phenomena occurring within a span of 3500 years would not be recognized in deposits like those of Bahia la Choya. Time-averaging and stratigraphic disorder also constrain the temporal resolution possible in microstratigraphic studies of evolution. The extent of time- averaging and stratigraphic disorder will dictate an appropriate sample interval. In order to prevent temporal overlap between successive samples in deposits like Bahia la Choya, sample spacing should not be less than approximately 0.5 m.

Foyle, A.M., and G.F. Oertel, Seismic Stratigraphy and Coastal Drainage Patterns in the Quaternary Section of the Southern Delmarva Peninsula, Virginia, Usa, Sedimentary Geology, 80 (3-4), 261-277, 1992.

Seismic-stratigraphic analysis of the coastal zone and inner shelf of Virginia's southern Delmarva Peninsula has revealed three geochronologically significant surfaces of post-Tertiary age that impose a relative chronostratigraphic framework on Quaternary marine transgressive and regressive events. Characteristics of these surfaces indicate that two are sequence boundaries, and one is a ravinement surface. Lying at depths of 18-70 m (msl datum), the LP(b) surface (a late Pleistocene basal unconformity) represents the sequence boundary separating the Tertiary Chesapeake Group from the overlying late Pleistocene Nassawadox Formation. High relief (approximately 50 m) on the LP(b), surface is associated with large fluvial channels. Higher in the stratigraphic section, the LP(r) surface is found at depths of 6-28 m, and corresponds to a late Pleistocene transgressive, or ravinement surface. The surface dips southeastward with a regional dip of 0.04-degrees and has local relief of less than 2 m. The LP(r) surface may represent a ravinement which extended to the west side of the Chesapeake Bay prior to the development of the Nassawadox barrier spit. However, the LP(r) surface may steepen between the axis of the southern Delmarva Peninsula and the Holocene lagoon to form a shoreface attached to one of several known late Pleistocene shorelines. Lying at depths of 0-20 m, the H(b) surface is a basal unconformity that marks the Holocene sequence boundary. It deepens seaward, with maximum local relief of about 15 m, and has a topographic expression very similar to the present-day lagoonal drainage pattern. Maximum thicknesses of Holocene and Pleistocene sediments (12 and 70 m, respectively) are found above channels on the H(b) and LP(b) surfaces. The Pleistocene channels are large and limited in number and represent high-order channels of a drainage system that drained the Piedmont and Coastal Plain. The greater density of low-order stream channels on the H(b) surface suggests a relationship to much smaller drainage basins that were confined to the seaward part of the Coastal Plain east of the Delmarva Peninsula. These late Wisconsinan smaller H(b) channels do not re-occupy the former drain paths of the much larger high-order LP(b) channels.

Foyle, A.M., and G.F. Oertel, Transgressive systems tract development and incised-valley fills within a Quaternary estuary-shelf system: Virginia inner shelf, USA, Marine Geology, 137 (3-4), 227-249, 1997.

High-frequency Quaternary glacioeustasy resulted in the incision of six moderate- to high-relief fluvial erosion surfaces beneath the Virginia inner shelf and coastal zone along the updip edges of the Atlantic continental margin. Fluvial valleys up to 5 km wide, with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level, cut through underlying Pleistocene and Mio-Pliocene strata in response to drops in baselevel on the order of 100 m. Fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments (ancestral generations of the Chesapeake Bay), Complex incised-valley hh successions are bounded by, or contain, up to four stacked erosional surfaces (basal fluvial erosion surface, bay ravinement, tidal ravinement, and ebb- flood channel-base diastem) in vertical succession. These surfaces, combined with the transgressive oceanic ravinement that generally caps incised-valley fills, control the lateral and vertical development of intervening seismic facies (depositional systems). Transgressive stratigraphy characterizes the Quaternary section beneath the Virginia inner shelf where six depositional sequences (Sequences I-VI) are identified. Depositional sequences consist primarily of estuarine depositional systems (subjacent to the transgressive oceanic ravinement) and shoreface-shelf depositional systems; highstand systems tract coastal systems are thinly developed. The Quaternary section can be broadly subdivided into two parts. The upper part contains sequences consisting predominantly of inner shelf facies, whereas sequences in the lower part of the section consist predominantly of estuarine facies. Three styles of sequence preservation are identified. Style 1, represented by Sequences VI and V, is characterized by large estuarine systems (ancestral generations of the Chesapeake Bay) that are up to 40 m thick, have hemicylindrical wedge geometries, and occur within large, coast-oblique trending depressions (paleo-estuaries). Style 1 is dominated by fluvial through estuary-mouth depositional systems (Seismic Facies 1-4). Style 2 sequence preservation, represented by Sequences III and II, is dominantly an inner shelf and shoreface succession with a seaward-thickening tabular wedge geometry that does not exceed 15 m in thickness. These shoreface and inner shelf depositional systems of the upper transgressive systems tract (Seismic Facies 9) apd highstand systems tract (Seismic Facies 7 and 11) are not associated with paleo-estuaries. Style 3 sequence preservation is represented by Sequence I, the Holocene Sequence. It consists of lower transgressive systems tract fluival-estuarine, lagoonal, and tidal-inlet fill deposits (Seismic Facies 1-6, and 8) overlain by upper transgressive systems tract shelf and Shoreface sands (Seismic Facies 9). Style 3 has a crenulated wedge geometry, and is thickest beneath and seaward of the modern Chesapeake Bay mouth. It thins northward and landward onto Late Pleistocene interfluvial highs on the basinward side of the southern Delmarva Peninsula.

Gillespie, J.L., and C.S. Nelson, Distribution and control of mixed terrigenous-carbonate surficial sediment facies, Wanganui shelf, New Zealand, New Zealand Journal of Geology and Geophysics, 39 (4), 533-549, 1996.

Shallow-marine, mixed temperate, terrigenous-carbonate sediments are accumulating on the shallow to deep Wanganui shelf(c. 20-110 m water depth). From cluster analysis of textural and compositional parameters, five surficial sediment facies and five subfacies have been defined for the shelf. Facies 1 (Bivalve-beating [gravelly] sand), is a terrigenous- dominated,. shallow shelf facies (<50 m), incorporating Subfacies la (Sand)-a modern felsic sand prism-and Ib (Bivalve- bearing volcaniclastic gravelly sand)-modern to relict andesitic detritus and shell fragments. Facies 2 (Skeletal- dominated sandy gravel) comprises sediments containing >50% CaCO3, and occurs in the shallow to mid shelf region (c. 30-90 m) where: levels of terrigenous input are reduced, and substrates and hydraulic conditions are favourable for carbonate production. Facies 2 comprises Subfacies 2a (Bivalve- dominated sandy gravel), 2b (Bryozoan/bivalve-dominated sandy gravel), and 2c (Bryozoan/bivalve-dominated muddy sandy gravel and gravelly muddy sand). Facies 2 sediments are <c. 800 yr old. Facies 3 (Bivalve-bearing muddy sand) (75-110 m) contains moderate amounts of skeletal material (up to c. 3000 yr old) because of dilution by the terrigenous sediment that characterises Facies 4 (Mud) (85-110 m). The latter constitutes the northern reaches of the Cook Strait Basin mud depocentre and receives sediment from North and South Islands. Facies 5 (Micaceous sand) (95-105 m) is derived chiefly from west coast South Island material swept into Greater Cook Strait by wind- induced and oceanic currents. The overall pattern of surficial sediment facies distribution is determined by the interplay between factors controlling the separate terrigenous and carbonate fractions. These include Wanganui shelf's tectonic setting, the surrounding onland geology, storm-dominated hydraulic regime, bathymetry, and substrate type. The mixed terrigenous-carbonate shelf record affords a modern analogue for interpreting glacio-eustatic cyclothemic facies widely developed in uplifted Pliocene-Pleistocene deposits in onland Wanganui, as well as contributing to facies refinements in the developing model of nontropical shelf carbonate sedimentation.

Glover, C.P., and S.M. Kidwell, Influence of Organic Matrix On the Postmortem Destruction of Molluscan Shells, Journal of Geology, 101 (6), 729-747, 1993.

To examine the role of organic constituents in the destruction of calcium carbonate skeletons, we aged fresh shells of the bivalves Nucula sulcata (organic-rich nacreous aragonites with low crystallite surface areas) and Cerastoderma edule (organic- poor porcellaneous aragonites, high crystallite surface areas) under both sterile and non-sterile (''microbial'') conditions in aragonite-undersaturated, -saturated, and -supersaturated seawaters for periods up to 11 months. Deterioration was tracked by SEM and weight-loss, and compared to damage produced by reagents of specific effect. The same qualitative sequence of damage was observed in all tanks for both species, but rates of deterioration were greater than or equal to 2 x higher in microbial than in sterile tanks at a given saturation state, and were as high or higher in the microbial saturated and supersaturated tanks than in the sterile undersaturated tank. Damage to shell surfaces was limited almost entirely to loss of organic matrix, which eventually exposed and loosened surficial crystallites. Mineral dissolution in undersaturated tanks was apparently limited to crystallites occurring as loose particulate matter, as direct pitting of shell surfaces was rare. Shells of organic-rich aragonites did not suffer greater weight loss than those with organic-poor aragonites, but in microbial tanks they did suffer more rapid and intense microboring. The only macroscopic evidence of microstructural deterioration was a loss of surface sheen. The experiments show that intraskeletal matrix plays a more complex role in the persistence of calcium carbonate shells than generally appreciated, and that the dynamics of dissolution for fresh biogenic carbonates may differ significantly from the behavior of aged or organic-free carbonate grains used in most laboratory studies. Organics initially protect crystallites (evidenced by slow shell deterioration in sterile tanks): this may counterbalance the effects of undersaturated water and high crystallite surface areas for at least the first several months of aging. With progressive breakdown, however, organics increase shell vulnerability to crystallite-by-crystallite disintegration and, as a microbial substrate, appear to fuel dissolution and microboring. Organic-rich microstructures thus may ultimately have lower preservation potential than organic- poor types. Only after intercrystalline organics have been lost should shell destruction be dominated by mineralogy, microstructural surface area, and ion adsorption. The initial period of low mineral reactivity in fresh shells may help to explain why in situ sediments show lower dissolution rates than expected from laboratory measurements. The experiments also suggest that no aerobic environment should be considered as taphonomically or diagenetically neutral, since matrix decomposes in supersaturated waters and even under sterile conditions, albeit slowly. This overall vulnerability of organic-rich microstructures suggests the potential for systematic biases in the taxonomic and age-class composition of fossil datasets, since ecological groups and evolutionary lineages differ in their shells' microstructures, and since the proportion of organics within carbonate skeletons may vary both with latitude and through individual ontogeny.

Goodbred, S.L., E.E. Wright, and A.C. Hine, Sea-level change and storm-surge deposition in a late Holocene Florida salt marsh, Journal of Sedimentary Research, 68 (2), 240-252, 1998.

A 300-km length of west Florida's coastline is dominated by an open-marine coastal marsh system, Located along the central part of this sediment poor region, Waccasassa Bay is presently a broad, shallow embayment rimmed by an expansive Juncus roemerianus salt marsh, In this system, sediments were first deposited in a forested swamp from similar to 4400 to 1800 cal yr BP, Contemporaneously, large oyster reefs grew in the embayment near a paleo-river mouth. These deposits indicate a period of slow sea-level rise during the Late Holocene that correlates with the establishment or regression of other west Florida coastal systems. Circa 1800 cal yr BP, a rapid transgression of 2-4 km led to salt marsh growth over the former swamp, and a brackish marsh developed over a previously unflooded upland surface. Calculated rates of shoreline retreat are 10 to > 20 m/yr at this time and compare to < 3.0 m/yr during most of the Late Holocene. Timing of the event in Waccasassa Bay corresponds with transgressive sequences in other Atlantic and Gulf coast systems and supports a relative sea-level fluctuation ca. 1800 cal yr BP. Following this event, sediments overstepped during the transgression were reworked onto the low-lying tidal marsh, Rapid accretion along the shore edge outpaced sea-level rise and led to the local development of high intertidal and supratidal levees, Evidence indicates that storm-driven surge was the principal mechanism of sediment transport for these deposits, In Waccasassa Bay, storm surge deposition has played a significant role in marsh surface accretion, distinguishing the system from more typically tide- dominated wetlands, Within the past similar to 150 years, most of the supratidal environment became tidally inundated and there was a widespread transition into the modern salt marsh. This change and evidence from adjacent portions of the Florida coast implicate a rise in sea level within the past several hundred years.

Greenstein, B.J., and H.A. Moffat, Comparative taphonomy of modern and Pleistocene corals, San Salvador, Bahamas, Palaios, 11 (1), 57-63, 1996.

The taphonomic condition of the corals Acropora cervicornis and A. palmata obtained from two facies of the late Pleistocene Cockburn Town fossil reef was compared to that of modern, subfossil specimens of the same taxa collected from analagous environments. The extent of coverage by potentially preservable and preserved encrusting organisms (coraline algae, worm tubes, bryozoans and corals) and borer organisms (clionid sponges, lithophagid bivalves) was recorded. The degree to which the material had been abraded by a variety of processes was also recorded. Results revealed that the Holocene corals were significantly (alpha = 0.05) more degraded than those preserved in the Pleistocene facies, suggesting that the Pleistocene corals were exposed on. the sea floor for less time than the Holocene material currently residing on the sea floor. The recent history of the reefs from which the Holocene corals were collected suggests this interval to be less than ten years; however, sedimentologic evidence indicates that a single storm event buried and killed the Cockburn Town reef during late Pleistocene time. The taphonomic analysis presented here supports this conclusion.

Gross, T.F., and F.E. Werner, Residual Circulations Due to Bottom Roughness Variability Under Tidal Flows, Journal of Physical Oceanography, 24 (7), 1494-1502, 1994.

Tidal flows over irregular bathymetry are known to produce residual circulation flows due to nonlinear interaction with gradients of depth. Using the depth-averaged vorticity equations, the generation of residual vorticity and residual flows due to variation of the frictional coefficient are examined. The authors find that the contribution due to bottom roughness variations can be as large as that arising from gradients of depth and velocity. Specific cases are considered on the northern California shelf, Georges Bank, and the U.S. South Atlantic Bight. The generation of residual vorticity is a strong function of the length scales at which roughness or depth vary. Length scales of bottom roughness variation are commonly within the range of greatest effect (e.g., sand patchiness, cobbly outcrops, etc.). The site-specific cases show that the bottom roughness variability can generate as much residual circulation as that expected from depth variability. The implication for numerical modeling studies is that resolution of roughness variability is as important as resolution of topography at length scales comparable to the tidal excursion. Therefore higher-resolution models that seek to resolve flow patterns due to tidal scale topographic variability will also require similarly resolved bottom roughness variability.

Guillen, J., and P. Hoekstra, Sediment distribution in the nearshore zone: Grain size evolution in response to shoreface nourishment (Island of Terschelling, The Netherlands), Estuarine Coastal and Shelf Science, 45 (5), 639-652, 1997.

The natural sediment distribution in the littoral zone of Terschelling, The Netherlands was disturbed by a shoreface nourishment carried out off the central part of the island. The sedimentological impact of this shoreface nourishment, i.e. the grain size evolution and the sediment dynamics, is studied in order to increase understanding of coastal processes. The variability of the sediment during the study period is due to both natural processes and the nourishment. Immediately after implementation of the nourishment, the sediment distribution was measurably affected. The sediment supplied caused a coarsening (20-40 mu m) of the sediment in the zone directly affected by the nourishment. Six months after the nourishment, the grain size distribution across the profile was nearly the same as the original, and no significant effects of the nourishment could be recognized in the median grain size. Individual grain size fractions displayed a temporal evolution more complex than the median size, and significant changes, unrelated to the sand supplied, were observed. Results of the sediment analysis from the coastal zone of Terschelling indicate that the shoreface nourishment only had a short-term and very local impact on the sediment distribution. Some months after the nourishment, the former grain size distribution was re-established. This implies that the nourished sediment was quickly dispersed and mixed with the original deposits, and that it only represents a small part of the Volume of sediment involved in the dynamics of the littoral zone. On a yearly perspective, the natural variability of the sediment was higher than the changes caused by the nourishment. (C) 1997 Academic Press Limited.

Hald, M., and P.I. Steinsund, Distribution of Surface Sediment Benthic Foraminifera in the Southwestern Barents Sea, Journal of Foraminiferal Research, 22 (4), 347-362, 1992.

We have studied the distribution of living and dead benthic foraminifera in surface sediment samples in the southwestern Barents Sea. Based on the 13 most important benthic species among a total of 165 species, we have identified four assemblages (AS) using factor analysis: Nonion AS, Trifarina- Cibicides AS, Reophax AS and Epistominella AS. Generally, the faunal assemblages correlate well to summer bottom water temperatures and/or to sediment texture, carbonate content and organic carbon. The Nonion assemblage is positively correlated to the surface sediment pelite content and negatively correlated with the sediment carbonate content. The Trifarina- Cibicides AS correlates to the warmest bottom waters (about 5- degrees-C) and coarser sediments. The Reophax AS is found in colder waters (2-4-degrees-C) and correlates positively to the organic carbon content in the surface sediments. The Epistominella AS is influenced by reworking.

Harris, P.T., and P.E. Obrien, Geomorphology and sedimentology of the continental shelf adjacent to Mac Robertson Land, East Antarctica: A scalped shelf, Geo-Marine Letters, 16 (4), 287-296, 1996.

During the Quaternary, the Mac. Robertson shelf of East Antarctica was deeply eroded by glaciers and currents exposing the underlying basement, resulting in a scalped shelf. Major geomorphic zones are: (1) high-relief, ridge and valley topography (200-1400 m); (2) smooth sea floors associated with low-energy, depositional shelf valleys and basins (400-800 m); (3) low-relief, planated bank-tops (100-200 m); and (4) iceberg gouged and current reworked seaward-bank margins and upper slope (200 to <630 m). About 90% of the shelf's surface has net erosional conditions and about 10% is net depositional. The sedimentary processes and deposits may be common to large areas of the East Antarctic margin.

Hequette, A., and P.R. Hill, Storm-Generated Currents and Offshore Sediment Transport On a Sandy Shoreface, Tibjak Beach, Canadian Beaufort Sea, Marine Geology, 113 (3-4), 283-304, 1993.

Waves and currents were measured for three weeks in 3.4 and 5.0 m water depths on the sandy shoreface of Tibjak Beach, located on the eastern side of Kugmallit Bay in the Canadian Beaufort Sea. During the field study, five significant wind events resulted in strong shore-normal components of surface wind stress which induced sea level set-up at the coast. Because of the coastline configuration, storm surge conditions and horizontal pressure gradients varied along the eastern side of the bay as a function of small changes in wind direction. One of the westerly storms was responsible for raising the water level by 0.96 m above mean sea level in the nearshore zone. Northwesterly winds resulted in less significant storm surges at Tibjak Beach, but induced higher water levels to the south, near the head of the bay. During the northwesterly storms, strong seaward-directed near-bottom currents associated with downwelling conditions were observed. These currents, with mean velocity up to 0.49 m s-1, are believed to be primarily driven by wind-induced hydrostatic pressure gradients caused by the set-up of coastal waters. Once they began to develop, the seaward currents were directed offshore for periods of at least 6 to 9 consecutive hours; during one storm, near-bottom currents were flowing offshore for more than 18 hours. High wave orbital velocities were measured during these events which induced significant sediment remobilization as the threshold of sediment motion under oscillatory flow was largely exceeded. Because medium- to fine-grained sands prevail on the shoreface, a significant sediment transport load is probably moved down the shoreface by such currents during major events, thus contributing to offshore sediment dispersal.

Hequette, A., and P.R. Hill, Response of the Seabed to Storm-Generated Combined Flows On a Sandy Arctic Shoreface, Canadian-Beaufort Sea, Journal of Sedimentary Research Section a-Sedimentary Petrology and Processes, 65 (3), 461-471, 1995.

Wave and current measurements in 3.4 and 5.0 m water depths on a sandy shoreface of the Canadian Beaufort Sea showed that a down-welling circulation, accompanied by strong offshore- flowing near-bottom currents, develops during storm surges induced by northwesterly winds. Because fine to medium sand prevails on the shoreface, a significant sediment load is probably moved down the shoreface by such currents during major storms. A sidescan sonar profile recorded in 4.4 m water depth, the day after a storm with seaward-directed currents with mean velocity up to 0.49 m s(-1), revealed the presence of narrow bands of large ripples (0.7-0.8 m wavelength) with crests almost parallel to shore. On the basis of theoretical calculations relating the wavelength of wave-formed ripples to wave orbital diameter, the observed ripples were probably formed or reactivated during a storm in response to bed-orbital motion of surface gravity waves. On the sonograph, the ripple bands were separated by less reflective areas interpreted as current-parallel sand patches formed by seaward-flowing bottom currents. Cores taken on the shoreface at the end of the wave and current measurement period showed the presence of thick graded sand beds, which are thought to be the products of rapid deposition of sand from suspension during the waning phase of a recent storm. Such beds may be the modern analogues of graded sand beds in ancient wave-dominated sequences and could indicate waning storm sedimentation in shallow fetch-limited environments.

Hesp, P.A., M.J. Shepherd, and K. Parnell, Coastal geomorphology in New Zealand, 1989-99, Progress in Physical Geography, 23 (4), 501-524, 1999.

This article reviews coastal geomorphological research published in New Zealand or international journals which has been carried out in New Zealand during the past ten years. All coastal environments are covered, including tidal inlets, estuaries and lagoons, beach, surfzone, nearshore and shelf environments, and rocky coasts. Applied coastal studies are also covered. While the New Zealand coastal science community remains relatively small, a significant body of work has been carried out, much of it innovative and unique. However, with 11 000 km of very diverse coastline covering 13 degrees of latitude available for study there are many areas, geographical as well as disciplinary, that remain poorly researched.

Hilton, M.J., Sediment Facies of an Embayed Coastal Sand Body, Pakiri, New- Zealand, Journal of Coastal Research, 11 (2), 529-547, 1995.

A sedimentological investigation was conducted across the Pakiri-Mangawhai sand body located on the east coast of the Northland Peninsula, New Zealand. Nearshore, inner continental shelf and mid shelf depositional environments are recognised. The sand body extends seaward as a continuous accumulation of relatively mud-free unconsolidated sand from the landward extent of the coastal dunes to the 45 m isobath, approximately 4,500 m offshore, at the base of the inner shelf. The Pakiri- Mangawhai sand body is characterised by a regular pattern of morphological components and associated sediment types. In profile, the nearshore displays a concave geometry that extends to approximately the 22 m isobath, 1,500 m or so offshore. The inner shelf displays a convex or irregular profile and extends seaward of the nearshore to a break of slope at the 45 m isobath, approximately 4,500 m offshore, where the mid shelf commences. Nearshore gradients range between 0.4 degrees and 1.8 degrees, inner shelf 0.1 degrees to 0.6 degrees and mid shelf 0 degrees to 0.15 degrees. Three subtidal sediment facies are recognised. Nearshore sediments comprise fine, very well sorted sands of 2 phi (0.25 mm) mean grain size. Inner shelf sediments grade offshore from medium to coarse sands (Mz = 0.0- 0.5 phi, 0.71-1.00 mm) with some very coarse sand and fine gravel present. In contrast, the sediments of the mid shelf in Pakiri Bay are very fine sands (Mz = 2.0-2.5 phi, 0.177-0.250 mm), with a relatively high mud content (5-10%). Carbonate skeletal debris, derived mostly from mollusca, comprises a significant proportion of inner and mid shelf sediments, increasing offshore from 0-5% across the nearshore to 30% at the base of the inner shelf. The size-graded bed of the nearshore and inner shelf is consistent with diabathic sediment transport resulting in the preferential shorewards transport of the fine sand fraction of the sediments of the inner shelf. Shoaling gravity waves have the potential to disturb sediments to at least the base of the inner shelf, however, wind generated and other currents may also be significant. Sediment exchange between the mid shelf and inner shelf is unlikely and the Pakiri-Mangawhai sand body is in effect a closed sediment system. Sand mined from the nearshore must result in a net loss of sediment from the sand body, and the sand resource should be considered finite.

Kidwell, S.M., and K.W. Flessa, The Quality of the Fossil Record - Populations, Species, and Communities, Annual Review of Ecology and Systematics, 26, 269-299, 1995.

Paleontologists have always been concerned about the documentary quality of the fossil record, and this has also become an important issue for biologists, who increasingly look to accumulations of bones, shells, and plant material as possible ways to extend the time-frame of observation on species and community behaviors. Quantitative data on the postmortem behavior of organic remains in modern environments are providing new insights into death and fossil assemblages as sources of biological information. Important findings include: 1. With the exception of a few circumstances, usually recognizable by independent criteria, transport out of the original life habitat affects few individuals. 2. Most species with preservable hardparts are in fact represented in the local death assemblage, commonly in correct rank importance. Molluscs are the most durable of modern aquatic groups studied so far, and they show highest fidelity to the original community. 3. Time-averaging of remains from successive generations and communities often prevents the detection of shortterm (seasons, years) variability but provides an excellent record of the natural range of community composition and structure over longer periods. Thus, although a complex array of processes and circumstances influences preservation, death assemblages of resistant skeletal elements are for many major groups good to excellent records of community composition, morphological variation, and environmental and geographic distribution of species, and such assemblages can record temporal dynamics at ecologically and evolutionarily meaningful scales.

Kidwell, S.M., and K.W. Flessa, The quality of the fossil record: Populations, species, and communities (Reprinted from Annual Review of Ecology and Systematics, vol 26, 1995), Annual Review of Earth and Planetary Sciences, 24, 433-464, 1996.

Paleontologists have always been concerned about the documentary quality of the fossil record, and this has also become an important issue for biologists, who increasingly look to accumulations of bones, shells, and plant material as possible ways to extend the time-frame of observation on species and community behaviors. Quantitative data on the postmortem behavior of organic remains in modern environments are providing new insights into death and fossil assemblages as sources of biological information. Important findings include: 1. With the exception of a few circumstances, usually recognizable by independent criteria, transport out of the original life habitat affects few individuals. 2. Most species with preservable hardparts are in fact represented in the local death assemblage, commonly in correct rank importance. Molluscs are the most durable of modern aquatic groups studied so far, and they show highest fidelity to the original community. 3. Time-averaging of remains from successive generations and communities often prevents the detection of short-term (seasons, years) variability but provides an excellent record of the natural range of community composition and structure over longer periods. Thus, although a complex array of processes and circumstances influences preservation, death assemblages of resistant skeletal elements are for many major groups good to excellent records of community composition, morphological variation, and environmental and geographic distribution of species, and such assemblages can record temporal dynamics at ecologically and evolutionarily meaningful scales.

Kidwell, S.M., Time-averaging in the marine fossil record: overview of strategies and uncertainties, Geobios, 30 (7), 977-995, 1997.

The paleontologic reasoning that led to the recognition of time-averaged assemblages in the early 1970s, and to elaborations of the concept in the 1980s and 1990s, has now undergone considerable actualistic testing, primarily using marine mollusks. These studies have confirmed the fundamental elements of the concept, including paleontologic estimates of the absolute durations and short-term dynamics of time- averaging: despite the rapid rates of shell destruction that can be documented in modern environments, death assemblages in nearshore and shelf settings are age-mixtures that have commonly formed over thousands to tens of thousands of years. Although many more actualistic studies are needed to document environmental and taxonomic variation, the results so far greatly increase our confidence in the indirect sedimentologic, stratigraphic, and paleontologic evidence used to evaluate assemblages in the older fossil record. The strategy outlined for evaluating fossil assemblages stresses breadth of evidence, most particularly geological context and origins of the host interval. Numerous questions remain. One is whether a "taphonomic clock" operates. does damage, either on an individual shell or for an assemblage overall, accrue at a sufficiently steady rate that it can be used to estimate the relative age of a shell (i.e., if it is from one of the earlier or from one of the later generations to be incorporated in the time-averaged assemblage), or used to estimate the duration of time-averaging in the overall assemblage (maximum range of shell ages)? Unfortunately, damage accrues very quickly apparently within molluscan assemblages (e.g. within the first few hundred years), so that assemblages that accumulate over much longer time scales (hundreds of thousands of years) do not differ significantly in taphonomic grade than those formed over a few thousand years. Comparative analysis of fossil assemblages suggests that other features, such as diagenetic heterogeneity and microstratigraphic complexity within host intervals, may be more useful "clocks" for ranking the time- resolution of assemblages, but these ideas need wider testing. Other uncertainties and directions for investigation are probable differences in the relative degrees and absolute durations of time-averaging (a) among major taxonomic groups, (b) among environments within single embayments, (c) through depositional sequences, owing to shifting rates of sedimentation as well as migrating environments, and (d) over the course of Phanerozoic time, owing to changes in the nature of skeletons produced as well as in the organisms that influence post-mortem preservation. We have testable hypotheses and even preliminary evidence for these larger scale patterns, and they are exciting avenues for future research.

Kowalewski, M., G.A. Goodfriend, and K.W. Flessa, High-resolution estimates of temporal mixing within shell beds: the evils and virtues of time-averaging, Paleobiology, 24 (3), 287-304, 1998.

This study quantifies the fine structure of time-averaging by using large samples of dated shells collected from within individual strata. Time-averaging results in both good and bad news for interpreting bioclastic deposits. Nine samples of shells were collected from four Holocene cheniers on the Colorado Delta (Gulf of California) and 165 shells of the bivalve Chione fluctifraga were dated using C-14-calibrated amino acid racemization (D-alloisoleucine/L-isoleucine). The age range of shells within samples averages 661 years and, in seven out of nine samples, exceeds 500 years. The sample standard deviation ranges from 73 to 294 years and averages 203 years, far exceeding the dating errors (<<100 years) and potential variation in the life span of Chione (<10 years). Time-averaging is homogeneous among strata within cheniers but varies significantly among cheniers. Age-distributions of dated shells indicate that at 50-year resolution, the samples provide a continuous and uniform record for the entire interval. The actual sample completeness (63.6%) is very close to that predicted by simulations of sampling a 100% complete, uniform record (67.3%). The bad news is that, no matter how carefully collected, data from shell beds may not be suitable for studying processes on timescales shorter than 10(2) to 10(3) years; explanations for faunal change that invoke reasoning or models derived from a strictly ecological point of view may rarely be justifiable. Also, notable differences in temporal resolution between the shell beds of seemingly identical origin imply that paleontological patterns (e.g., species diversity) may be affected by cryptic variation in time-averaging. The comparison of our data with time-averaging estimates obtained from other cheniers at coarser sampling resolutions indicates that pooling of samples (analytical time-averaging) can significantly reduce the temporal resolution of paleontological data. The good news is that shell beds can record the optimal type of time-averaging: where paleobiological data are a time- weighted average of the faunal composition from the spectrum of environments that existed during the entire interval of time. Samples from single strata provide a long-term record that is representative of the predominating environments. Within the range of C-14 dating, shell beds can provide a complete, high- resolution record, and thus may offer exceptional insights into the environmental and climatic changes of the last 40 thousand years.

Lueck, K.L.O., and S.W. Snyder, Lateral variations among populations of stained benthic foraminifera in surface sediments of the North Carolina continental shelf (USA), Journal of Foraminiferal Research, 27 (1), 20-41, 1997.

Analyses of stained benthic foraminiferal populations from the 23-Mile Rock area of Onslow Bay, North Carolina continental shelf reveal no vertical partitioning of the sediment into depth-related microhabitats, a finding consistent with that from the Frying Pan Shoals area 40 km to the southwest (Murosky and Snyder, 1994), Because taxa are not segregated by sediment depth, composite populations from the upper 8 cm of the two areas can be compared to assess lateral variation across the middle shelf, Although most of the abundant and persistent taxa occur commonly at both sites, there are differences in taxonomic composition, in terms of both absolute and relative abundances, Populations at the 23-Mile site are approximately four times as large as those at Frying Pan Shoals, Ten taxa, all more abundant and persistent at 23-Mile Rock, account for most of the difference, Reasons for the observed lateral variation cannot be directly related to changes in the depth regime, water mass characteristics, sediment grain size and sorting, or mineralogical composition of the sediment, Foraminiferal abundances and distributions may be related to the chemistry and flow rate of groundwater, variably enriched in nutrients that drive the benthic productivity of Onslow Bay, fluxing through the sediments into the water column, Testing this hypothesis, when data from seepage meters are published, is a promising direction for future research.

Macintyre, I.G., O.H. Pilkey, and R. Stuckenrath, Relict Oysters On United-States Atlantic Continental-Shelf - Reconsideration of Their Usefulness in Understanding Late Quaternary Sea-Level History, Geological Society of America Bulletin, 89 (2), 277-282, 1978.


Mahaney, W.C., Dating Methods, Progress in Physical Geography, 15 (3), 304-309, 1991.


Mallinson, D.J., J.S. Compton, S.W. Snyder, and D.A. Hodell, Strontium Isotopes and Miocene Sequence Stratigraphy Across the Northeast Florida Platform, Journal of Sedimentary Research Section B-Stratigraphy and Global Studies, 64 (3), 392-407, 1994.

A preliminary assessment of Miocene sea-level fluctuations is presented based on the integration of Sr-derived ages and sequence-stratigraphic concepts applied to subsamples of 12 cores that transect the Hawthorn Group on the northeast Florida Platform. The Hawthorn Group section includes phosphorite nodules, peloids, and crusts as well as dolosilt and dolostone nodules and beds formed during early burial diagenesis of organic-rich sediments deposited during periods of intensified and persistent upwelling associated with rising and maximum sea level. The Sr-87/Sr-86 composition of phosphorite and dolomite is used to determine the age of in-place phosphorite crusts and dolostone beds (condensed sections) and reworked phosphorite and dolostone sand and gravel (unconformities and transgressive surfaces). Regional correlation of unconformities and condensed sections provides the basis for a sequence- stratigraphic framework from which the age and relative amplitude of sea-level fluctuations are constructed. Seven depositional sequences are identified from the data. Depositional sequences correspond to local sea-level fluctuations with maximum water depths at approximately 25-24, 21-20, 19-18, 17-15, 14-12, 11-9, and 8-6 Ma. Greatest water depth apparently occurred at 17-15 Ma.

Manighetti, B., and L. Carter, Across-shelf sediment dispersal, Hauraki Gulf, New Zealand, Marine Geology, 160 (3-4), 271-300, 1999.

Side-scan, seismic and surficial sediment data accompanied by current meter records highlight across-shelf sediment transport in Hauraki Gulf, an island-studded embayment off northern New Zealand. Calm weather currents are locally dominated by the tides, with periodic incursions of oceanic water from detached meanders of the East Auckland Current. Under these conditions, bedload transport occurs mainly in three 15-20 km-wide channels, where bathymetric intensification of the flow brings about near-bottom speeds of up to 82 cm s(-1) for Colville Channel and 33-44 cm s(-1) in Jellicoe and Cradock Channels. Surficial sediments are gravelly to muddy sand, winnowed in places, leaving a lag deposit of mainly biogenic carbonate gravel. Modelling results suggest that in Colville Channel, dominant fine to medium sand modes are mobile for 20-60% of the time, with a net eastward movement for fine sand. In Jellicoe and Cradock Channels, the prevailing direction of transport is southwards across the shelf, with sand mobile for up to 33% of the time. Oceanic incursions have the potential to boost flow in the western Gulf, however such incursions are transitory, and there is no measurable expression of oceanic water in the sedimentary record. BI:cause of their association with prolonged periods of calm weather, the incursions are unlikely to accompany storm events, where their cumulative effect might be important for sediment transport. Near-bottom currents resulting from oceanic incursion may reinforce peak tides inside the Gulf by up to 2-4 cm s(-1). Enhancement of prevailing water motions occurs during periods of extreme weather. During cyclone Drena (January 1997), measured flow speeds in Jellicoe Channel reached 48 cm s(-1). Furthermore, the disturbance generated large waves that stirred bottom sediments down to over 100 m water depth. Such events are probably the major agent of sediment redistribution in the Hauraki Gulf. The net effect of storm and calm weather currents is to move sediment across the outer to middle shelf where, in the western and central Gulf it accumulates, and in the eastern Gulf it escapes eastward via Colville Channel. (C) 1999 Elsevier Science B.V. All rights reserved.

Marlow, M.S., A.J. Stevenson, H. Chezar, and R.A. McConnaughey, Tidally generated sea-floor lineations in Bristol Bay, Alaska, USA, Geo-Marine Letters, 19 (4), 219-226, 1999.

Highly reflective linear features occur in water depths of 20- 30 m in northern Bristol Bay (Alaska, USA) and are, in places, over 600 m in length. Their length-to-width ratio is over 100.1. The lineations are usually characterized by large transverse ripples with wavelengths of 1-2 m. The lineations trend about N60 degrees E, and are spaced between 20 and 350 m. Main tidal directions near the lineations are N60 degrees E (flood) and S45 degrees W (ebb), which are parallel to subparallel to the lineations. They suggest that the lineations may be tidally generated. The lineations may be bright sonar reflections from a winnowed lag concentrate of coarse sand.

McBride, R.A., and T.F. Moslow, Origin, Evolution, and Distribution of Shoreface Sand Ridges, Atlantic Inner Shelf, Usa, Marine Geology, 97 (1-2), 57-85, 1991.

A computer mapping system was employed to document the location of 259 shoreface-attached and detached sand ridges in water < 20 m deep and the temporal and spatial distribution of 309 historical and active tidal inlets along the U.S. Atlantic coast (Montauk Point, New York, to Miami Beach, Florida). This database was compiled through the analysis of over 600 historical maps, 50 bathymetric charts, and other published data. A genetic relationship between the location of certain historical and active tidal inlets and shoreface-attached sand ridges is documented. It is inferred that ebb-tidal deltas provided the initial sand source for the development of many shoreface-attached sand ridges. Although shoreface-attached sand ridges appear to have several different modes of formation, a two-step process for the development of most shoreface-attached and detached sand ridges along U.S. Atlantic barrier island and cape coastlines is proposed: (1) sand is deposited as ebb-tidal deltas along the lower shoreface and/or inner continental shelf prior to or during transgression, followed by (2) further transgression, which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes. The best-developed shoreface sand ridge fields along the U.S. Atlantic shelf lie adjacent to shorelines characterized by all of the following: (1) transgression, (2) mixed energy, wave-dominated barrier islands, and (3) laterally migrating tidal inlet systems. Tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport. Ebb-tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface-attached sand ridges. The oblique orientation and linear form of shoreface-attached sand ridges appear to be a function of shoreline transgression, lateral inlet migration, and wave reworking of ebb-tidal delta deposits concentrated along an ebb-tidal delta retreat path. Shelf processes act as modifying agents in the evolution of sand ridges during and after ebb- tidal delta deposition. In general, shoreface-attached sand ridges are poorly developed or absent along eroding headlands, spits, and barrier island shorelines characterized by naturally stabilized tidal inlets. These latter inlets and shoreline types are dominated or influenced by one or all of the following: (1) antecedent topography, (2) higher tidal ranges, (3) larger tidal prisms, (4) lower wave energies, or (5) finer grain sizes. The coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin, evolution, and distribution of shoreface sand ridges in the study area. Modern shoreface-attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during, or immediately before, transgression. Commonly observed vertical and lateral interrelationships of Holocene shoreface-attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models. In addition, the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges.

McKie, T., Geostrophic Versus Friction-Dominated Storm Flow - Paleocurrent Evidence From the Late Permian Brotherton Formation, England, Sedimentary Geology, 93 (1-2), 73-84, 1994.

The Late Permian Brotherton Formation of northeastern England is a 0-75 m thick carbonate sequence which exhibits abundant, erosively amalgamated, hummocky cross-stratification, gutter casts and shallow scour-fills, suggesting deposition in a storm-dominated, platformal shelf setting. The outcrop (ca. 15 m thick) is divisible into three facies associations: a basal transgressive interval, 4-5 m thick (facies association A), which passes upwards into a thinly bedded, argillaceous, condensed section < 1 m thick (facies association B), which in turn rapidly grades upwards into a 8-10 m thick, regressive, highstand succession of hummocky cross-stratified, amalgamated scour-fills (facies association C). The dominance of hummocky cross-stratification in all facies associations would suggest that post-storm deposition (and fairweather reworking) was largely under oscillatory currents. However, the erosional palaeocurrent data indicate that facies associations A and B were deposited following combined oscillatory and geostrophically balanced, shore-parallel flows. In contrast, facies association C was deposited by infilling the scours of friction-dominated, offshore-directed and downwelling, jet-like flows combined with oscillatory wave currents. The dominance of geostrophic or friction-dominated flows in the study area is interpreted to be controlled by relative sea level changes. During transgressive conditions increasing accommodation permitted rotation of the downwelling pressure-driven currents. In the regressive phase, particularly in the accommodation- limited late highstand, bottom friction was important in inhibiting flow rotation. It is suggested that the paucity of evidence for geostrophic flows in the ancient record may in part be attributed to the palaeocurrent indicators in sand- grade substrates being restricted to thin transgressive intervals (or surfaces), whilst in the volumetrically more important regressive deposits, palaeocurrent data are largely contained within facies from the friction-dominated zone.

McNinch, J.E., and J.T. Wells, Sedimentary processes and depositional history of a cape- associated shoal, Cape Lookout, North Carolina, Marine Geology, 158 (1-4), 233-252, 1999.

The sedimentary processes of a cape-associated shoal are an integral component of the sediment budget of the surrounding cuspate foreland shoreline. The manner in which sediment is delivered to a shoal and the fate of this sediment, once delivered, have important implications to shoreline management and yet remain largely unstudied. Modem sedimentary processes and the recent depositional history of Cape Lookout Shoal, a large cape-associated shoal in the mixed-energy environment of the North Carolina continental shelf, were examined in a field- intensive study through high-resolution seismic profiles, hydraulic probes, near-bottom current meters, sediment grab samples, and detailed bathymetric surveys. Our findings indicate that: (1) the sediment budget of the up-drift littoral cell is coupled directly to Cape Lookout Shoal, (2) the sedimentary processes of the shoal remain active down its entire length but at a diminishing level with distance from the shore, and (3) the shoal serves as a long-term sink for littoral-zone sediment and limits sediment exchange between adjacent littoral cells and shelf regions. We present evidence suggesting that the position and morphology of Cape Lookout Shoal are not controlled by underlying erosion-resistant strata and that the shoal appears to have developed in the late Holocene after the shelf was scoured by the transgressing shoreface. (C) 1999 Elsevier Science B.V. All rights reserved.

Mearns, D.L., A.C. Hine, and S.R. Riggs, Comparison of Sonographs Taken Before and After Hurricane Diana, Onslow Bay, North-Carolina, Geology, 16 (3), 267-270, 1988.


Meldahl, K.H., K.W. Flessa, and A.H. Cutler, Time-averaging and postmortem skeletal survival in benthic fossil assemblages: Quantitative comparisons among Holocene environments, Paleobiology, 23 (2), 207-229, 1997.

We used radiocarbon ages on dead Holocene shells of the venerid bivalve Chione spp. to investigate how time-averaging and taphonomy in shallow marine benthic assemblages vary with sedimentary and tectonic setting. We compared shells collected from the sediment surface in five depositional environments from two regions of the Gulf of California, Mexico: Bahia Concepcion, a young faulted rift basin with high rates of terrigenous and carbonate sedimentation; and Bahia la Choya, an intertidal system along a sediment-starved shelf. Frequency distributions of shell ages in all environments form a hollow curve, with a mode at young ages and a long tail toward older ages. This pattern suggests that shells are added to the taphonomically active zone (TAZ) at roughly constant rates (via continuous shell deaths), and removed from the TAZ at random,either through destruction or by achieving final burial. Shell half-lives (the amount of time to remove half the shells from the TAZ) provide a comparative measure of time-averaging. Time-averaging varies with sedimentary and tectonic setting. The lowest amounts of time-averaging (shell half-lives of 90 to 165 years) occur in Bahia Concepcion, where rapid rates of terrigenous sedimentation (on fan-deltas) and carbonate sedimentation (in pocket bays) bury shells rapidly. Time- averaging is higher in the sediment-starved environments of Bahia la Choya (shell half-lives of 285 to 550 years). The highest amounts of time-averaging occur the inner tidal flats of Bahia la Choya (shell half-life of 550 years). Here the conjunction of low sedimentation rates with low rates of shell destruction (due to periodic tidal emergence) permits shells to persist in the TAZ for very long time spans. There is no systematic relationship between a shell's age and its taphonomic condition (taphonomic grade) in any environment, probably because of the complex and random nature of burial- exhumation in the TAZ. Age variance tends to increase with increasing taphonomic alteration: highly altered shells range in age from young to several thousand years old, while less altered shells are mostly young. The correspondence between time-averaging and the taphonomic condition of entire shell assemblages is also weak, but might be resolved with further study. These results provide quantitative data on time- averaging in benthic assemblages as a function of sedimentary and tectonic setting, and suggest some guidelines for facies appropriate for particular studies. Shallow marine rift basins like Bahia Concepcion can potentially contain within-horizon fossil assemblages representing time spans of only a few hundred years-time resolution of ten beyond reach in paleontology. In contrast, sediment-starved shelf habitats like Bahia la Choya are unlikely to yield assemblages with time resolution finer than several thousands of years.

Michener, W.K., E.R. Blood, K.L. Bildstein, M.M. Brinson, and L.R. Gardner, Climate change, hurricanes and tropical storms, and rising sea level in coastal wetlands, Ecological Applications, 7 (3), 770-801, 1997.

Global climate change is expected to affect temperature and precipitation patterns, oceanic and atmospheric circulation, rate of rising sea level, and the frequency, intensity, timing, and distribution of hurricanes and tropical storms. The magnitude of these projected physical changes and their subsequent impacts on coastal wetlands will vary regionally. Coastal wetlands in the southeastern United States have naturally evolved under a regime of rising sea level and specific patterns of hurricane frequency, intensity, and timing. A review of known ecological effects of tropical storms and hurricanes indicates that storm timing, frequency, and intensity can alter coastal wetland hydrology, geomorphology, biotic structure, energetics, and nutrient cycling. Research conducted to examine the impacts of Hurricane Hugo on colonial waterbirds highlights the importance of longterm studies for identifying complex interactions that may otherwise be dismissed as stochastic processes. Rising sea level and even modest changes in the frequency, intensity, timing, and distribution of tropical storms and hurricanes are expected to have substantial impacts on coastal wetland patterns and processes. Persistence of coastal wetlands will be determined by the interactions of climate and anthropogenic effects, especially how humans respond to rising sea level and how further human encroachment on coastal wetlands affects resource exploitation, pollution, and water use. Long-term changes in the frequency, intensity, timing, and distribution of hurricanes and tropical storms will likely affect biotic functions (e.g., community structure, natural selection, extinction rates, and biodiversity) as well as underlying processes such as nutrient cycling and primary and secondary productivity. Reliable predictions of global-change impacts on coastal wetlands will require better understanding of the linkages among terrestrial, aquatic, wetland, atmospheric, oceanic, and human components. Developing this comprehensive understanding of the ecological ramifications of global change will necessitate close coordination among scientists from multiple disciplines and a balanced mixture of appropriate scientific approaches. For example, insights may be gained through the careful design and implementation of broad-scale comparative studies that incorporate salient patterns and processes, including treatment of anthropogenic influences. Well-designed, broad-scale comparative studies could serve as the scientific framework for developing relevant and focused long-term ecological research, monitoring programs, experiments, and modeling studies. Two conceptual models of broad-scale comparative research for assessing ecological responses to climate change are presented: utilizing space-for- time substitution coupled with long-term studies to assess impacts of rising sea level and disturbance on coastal wetlands, and utilizing the moisture-continuum model for assessing the effects of global change and associated shifts in moisture regimes on wetland ecosystems. Increased understanding of climate change will require concerted scientific efforts aimed at facilitating interdisciplinary research, enhancing data and information management, and developing new funding strategies.

Munoz-Perez, J.J., J.M. Gutierrez-Mas, J.M. Parrado, and L. Moreno, Sediment transport velocity by tracer experiment at Regla Beach (Spain), Journal of Waterway Port Coastal and Ocean Engineering-Asce, 125 (6), 332-335, 1999.

Hydrodynamic behavior of the different sand-grain-size fractions, transport paths, and advection speed were studied by two fluorescent tracer experiments at Regla Beach, in Chipiona, SW Spain. Sand tracers, with two different colors, were injected on a cross-shore profile. The coarse- and very-fine- sand fractions were moved seaward and northward from the injection points in the subtidal and intertidal zones. Medium- and fine-grain-size fractions remained longer. The sand advection speed (tracer centroid) was found to be a linear function of the speed of the longshore current, with a mean correlation coefficient of 0.016, similar to that found by previous authors in other beaches.

Murraywallace, C.V., and A.P. Belperio, Identification of Remanie Fossils Using Amino-Acid Racemization, Alcheringa, 18 (3-4), 219-227, 1994.

The extent of racemisation for a range of amino acids for the total acid hydrolysate and free fractions, calibrated against radiocarbon dating, indicates that the foraminifer Marginopora vertebralis, found within ''modern'' tidal flat sediments between Wardang Island and Goose Island, South Australia, is reworked from the underlying Late Pleistocene Glanville Formation. Analyses of amino acids in the total acid hydrolysate and free fractions in conjunction with the determination of absolute concentrations of amino acid residues in fossils, provides an elegant method for assessing the validity of amino acid racemisation dating, and in identifying reworked fossils.

Myrow, P.M., Pot and Gutter Casts From the Chapel-Island Formation, Southeast Newfoundland, Journal of Sedimentary Petrology, 62 (6), 992-1007, 1992.

Member 2 of the Chapel Island Formation of southeast Newfoundland contains a diverse suite of erosional structures known as pot and gutter casts. These are particularly abundant in a lithofacies deposited in a nearshore zone characterized by erosion and sediment bypass during storm emplacement of sands. The steep-to-overhanging walls of both pot and gutter casts imply rapid filling during the same storm events that created these depressions. Erosion is thought to have taken place under strong offshore-directed unidirectional flow (storm surge or other relaxation flow). As with many sandstone tempestites, the initial stages of the storm events were dominated by strong-and in this case highly erosive-unidirectional flow, and the latter stages by oscillatory flow, as evidenced by wave-diagnostic lamination in the sandy infills. Pot casts have geometries and soles indicating vortex flow similar to that which forms potholes in bedrock in glaciated regions. Gutter casts that lead into potholes do so at their edge, a requirement for generating rotary currents within the depression. Pot casts are commonly tilted relative to paleohorizontal, and their direction of plunge is either upcurrent or downcurrent. Variation in geometry of the erosional structures from the Chapel Island Formation, and from erosional structures in general, can be accounted for by the following: substrate type; diagenetic history of substrate; and flow parameters such as pattern of water motion, velocity, and intermittency of flow.

Nittrouer, C.A., and L.D. Wright, Transport of Particles Across Continental Shelves, Reviews of Geophysics, 32 (1), 85-113, 1994.

Transport of particulate material across continental shelves is well demonstrated by the distributions on the seabed and in the water column of geological, chemical, or biological components, whose sources are found farther landward or farther seaward. This paper addresses passive (incapable of swimming) particles and their transport across (not necessarily off) continental shelves during high stands of sea level. Among the general factors that influence across-shelf transport are shelf geometry, latitudinal constraints, and the timescale of interest. Research studies have investigated the physical mechanisms of transport and have made quantitative estimates of mass flux across continental shelves. Important mechanisms include wind-driven flows, internal waves, wave-orbital flows, infragravity phenomena, buoyant plumes, and surf zone processes. Most particulate transport occurs in the portion of the water column closet to the seabed. Therefore physical processes are effective where and when they influence the bottom boundary layer, causing shear stresses sufficient to erode and transport particulate material. Biological and geological processes at the seabed play important roles within the boundary layer. The coupling of hydrodynamic forces from currents and surface gravity waves has a particularly strong influence on across-shelf transport; during storm events, the combined effect can transport particles tens of kilometers seaward. Several important mechanisms can cause bidirectional (seaward and landward) transport, and estimates of the net flux are difficult to obtain. Also, measurements of across-shelf transport are made difficult by the dominance of along-shelf transport. Geological parameters are often the best indicators of net across-shelf transport integrated over time scales longer than a mouth. For example, fluvially discharged particles with distinct composition commonly accumulate in the midshelf region. Across-shelf transport of particulate material has important implications for basic and applied oceanographic research (e.g., dispersal of planktonic larvae and particle- reactive pollutants). Continued research is needed to understand the salient mechanisms and to monitor them over a range of timescales.

Olszewski, T., Taking advantage of time-averaging, Paleobiology, 25 (2), 226-238, 1999.

One of the major obstacles in dealing with any form of data derived from fossils is the effects of Lime-averaging, which are the result of mixing the remains of organisms that did not live contemporaneously. Although this process results in loss of temporal resolution, it also serves to filter out short-term variations. Temporal resolution of a collection depends not only on the range of fossil ages, but also on their frequency distribution. Previous studies of marine molluscs indicate that most shells in an accumulation are relatively young. Such a distribution of shell ages can be fit by an exponential curve (assuming both a constant probability of shell loss and a constant rate of shell addition), which implies that 90% of the shells were added during the last 50% of the time interval represented by the collection. That is to say, differences between two collections can be discerned el en if they overlap 50% in Lime, because the proportion of shells with shared ages is only 10%. Applying the exponential model to previously published data suggests that long-term rates of destruction are controlled by how frequently shells from the taphonomically active zone are re-exposed to rapid destruction. To take advantage of the "noise-filtering" property of time-averaging, samples need to be large enough to catch the full range of environmental variation recorded by an accumulation. A simple probability formula indicates that samples of easily achievable size can give satisfactory time-averaged results depending on the level of confidence and sampling density defined by the researcher.

Pandolfi, J.M., and B.J. Greenstein, Taphonomic alteration of reef corals: Effects of reef environment and coral growth form .1. The Great Barrier Reef, Palaios, 12 (1), 27-42, 1997.

Taphonomic alteration in coral death assemblages showed high variability with respect to reef environment and growth form at Orpheus Island on the Great Barrier Reef Australia. A greater degree of physical and biological alteration occurred in the lower-energy leeward Pioneer Bay site relative to the higher- energy windward Iris Point site. Greater degrees of taphonomic alteration also occurred at 6-7 m than 2-3 m water depth within each site. Clear gradients in the degree of taphonomic alteration of reef corals with reef environment indicate the utility of corals as taphonomic indicators in ancient reef settings. Because greater taphonomic differences between depths occurred at the high wave-energy site relative to the lour wave-energy site, differentiation of fossil reef taphofacies might be greatest in high energy reef settings. Interpretation of ancient reef sedimentary environments may be aided by analysis of taphonomic alteration. of reef corals. Massive corals suffered greater degrees of biological and physical alteration than free-living corals which suffered greater alteration than branching corals. The greater taphonomic alteration in more robust massive coral growth forms from Orpheus Island concurs with other studies that have suggested that bioerosion may be related to overall skeletal area and density, and amount of skeleton not covered by living tissue during the life of the coral. In addition, relative differences in production of coral morphotypes might result in. a greater number of less degraded branching than massive corals. A possible explanation for the two observations that corals in higher wave energy environments are less degraded than those from lower wave energy environments, and that fragile are better preserved than robust coral growth forms, is the differing amount of post-mortem residence time the corals spend in the 'taphonomically active zone'.

Parkinson, R.W., and J.R. White, Late Holocene Erosional Shoreface Retreat Within a Siliciclastic-to-Carbonate Transition Zone, East-Central Florida, Usa, Journal of Sedimentary Research Section B-Stratigraphy and Global Studies, 64 (3), 408-415, 1994.

This study has reconstructed the late Holocene evolution of a section of the North American Atlantic coast barrier-island system in a siliciclastic-to-carbonate transition zone. A transgressive stratigraphy, analogous to that recognized beneath the siliciclastic barriers of the embayed Atlantic and Gulf coasts, was identified in the study area and generated by erosional shoreface retreat of the barrier island during Holocene sea-level rise. Vibracores from the backbarrier revealed the preservation of a thin (< 3.5 m) Holocene sediment succession consisting of muddy skeletal sand overlain by intercalations of clean skeletal sand and muddy skeletal sand capped by fibrous peat. In the foreshore, the fibrous peat is compressed and abruptly overlain by coarse shell hash grading upward into skeletal sand. The entire Holocene section rests unconformably upon a thin (< 0.25 m) quartz sand and featureless, gently seaward-dipping Pleistocene limestone surface. Sedimentologic, paleontologic, stratigraphic, and radiocarbon data suggest that this sequence is transgressive and was generated during erosional shoreface retreat of a wave- dominated, microtidal barrier-island system. The basal, muddy skeletal sand is interpreted to have been deposited in a shallow (3 m) backbarrier lagoon. These sediments were buried during overwash events that transported skeletal sand across the barrier and into the lagoon. Repeated overwash generated a shallowing-upward sequence capped by organic-rich tidal-wetland sediment. Radiocarbon dates suggest that wetland sedimentation started between 1200 and 1960 yr B.P. Landward retreat of the barrier is indicated by the foreshore unconformity (ravinement surface) that now truncates the fibrous peat. The preservation potential of the entire Holocene paralic section is probably low, given the lack of significant antecedent topographic relief and relatively slow rate of sea-level rise. The preservation potential should increase seaward, however, because the older paralic environments would have been subjected to faster sea-level rise.

Parsons-Hubbard, K.M., W.R. Callender, E.N. Powell, C.E. Brett, S.E. Walker, A.L. Raymond, and G.M. Staff, Rates of burial and disturbance of experimentally-deployed molluscs: Implications for preservation potential, Palaios, 14 (4), 337-351, 1999.

Rates of burial and transport of molluscan remains are essentially unknown for deeper continental shelf and slope environments, especially over periods of years. An understanding of the rates of taphonomic loss are critical to paleoecological analyses and to paleoenvironmental studies in general. The post-depositional history of organic remains is highly dependent on the length of time the material remains at or near the sediment/water interface. In order to measure these rates, 100 gastropod and bivalve shells were scattered over a marked area of sea bottom at 21 sites in seven environments of deposition (EOD's) in the Gulf of Mexico and at five EOD's on the Bahamas platform edge. A total of over 2600 shells were deployed. Each site was thoroughly documented with video photography. After one year in the Bahamas and after two years in both the Gulf of Mexico and Bahamas, these sites were re- photographed and videotaped to measure rates of burial and movement of shells. Shell condition (e.g., articulation, encrustation, and color loss) for those shells that remained exposed was also determined. Shells deployed in Gulf of Mexico petroleum seep sites, on the Open continental shelf; and on the continental slope experienced high rates of burial (0.5-3.0 cm) within two years. Shells at these sites generally were not transported or disturbed, and disarticulation rates were lour. ln. the Bahamas, shells on the platform shelf were completely buried within one year. On the steep platform edge from 70 to 300 m, shells on hardground ledges remained exposed, whereas shells in carbonate sands were buried by up to 3.5 cm of sediment. Transport was more common on the steep slopes of the platform edge. Net sedimentation rates for the outer continental shelf and slope of 0.01-0.06 cm yr-l are well below our observed burial rates of (3)1 cm yr-1. Thus, burial rate may be somewhat independent of sedimentation rate due to local reworking of sediments by storms at shallower depths and mechanisms such as deep bottom currents or bioturbation at deeper sites. Therefore, the potential for fossil preservation in offshore areas with low sedimentation rates may be much greater than previously assumed.

Pilkey, O.H., B.W. Blackwelder, H.J. Knebel, and M.W. Ayers, The Georgia Embayment Continental-Shelf - Stratigraphy of a Submergence, Geological Society of America Bulletin, 92 (1), 52-63, 1981.


Pilkey, O.H., R.S. Young, S.R. Riggs, A.W.S. Smith, H.Y. Wu, and W.D. Pilkey, The Concept of Shoreface Profile of Equilibrium - a Critical- Review, Journal of Coastal Research, 9 (1), 255-278, 1993.

The concept of shoreface profile of equilibrium is the basis for most models used to quantitatively describe and predict profile response on beaches. We question the validity of the concept as used in coastal engineering. The equilibrium shoreface profile concept is based on the following assumptions: (1) underlying geology does not play a role in determining the profile shape; (2) shoreface sediment is moved only by the interaction of wave orbitals with the sea floor, unidirectional current flow is not accounted for; (3) them is no significant net movement of sediment seaward of a so called ''closure depth.'' The equilibrium shoreface profile equation implies: (1) offshore bars do not play an important role in shoreface sediment transport; (2) grain size is the only variable determining shoreface profile shape variability; (3) the shoreface transport system is two-dimensional; and (4) all shorefaces in the world can be described by a single equation with sediment grain size as the only variable. To varying degrees, all of these assumptions fail to be met in real world situations in light of well documented oceanographic and geologic phenomena. A fundamental reexamination of the engineering methods of determining nearshore shoreface evolution is needed. As currently practiced such methods are based on poor oceanographic assumptions.

Pilkey, O.H., E.R. Thieler, R.S. Young, and D.M. Bush, Reply to: Houston, J.R., rejoinder to: Pilkey, O.H., Young, R.S., Thieler, E.R., Jacobs, B.S., Katuna, M.P., Lennon, G. and Moeller, M.E., 1996. Reply to Houston, J.R., a discussion of the generalized model for simulating shoreline change (GENESIS). Journal of Costal Research, 12(4), 1044-1050; Ibid., 14(3), 1170-1173, Journal of Coastal Research, 15 (1), 277-279, 1999.


Powell, E.N., and D.J. Davies, When Is an Old Shell Really Old, Journal of Geology, 98 (6), 823-844, 1990.


Powell, E.N., J.A. King, and S. Boyles, Dating Time-Since-Death of Oyster Shells By the Rate of Decomposition of the Organic Matrix, Archaeometry, 33, 51-68, 1991.


Powell, E.N., A Model For Death Assemblage Formation - Can Sediment Shelliness Be Explained, Journal of Marine Research, 50 (2), 229-265, 1992.

A numerical model for carbonate (shell) accumulation in marine sediments is proposed. Sediment shelliness is controlled by carbonate addition, taphonomic loss, carbonate reorganizing processes, and sedimentation rate. Using representative rates of carbonate production, taphonomic loss, and sedimentary carbonate content, the model shows that insufficient carbonate is produced today in many environments to explain sedimentary carbonate content and that most produced carbonate must bc preserved despite a generally high capacity for taphonomic loss. An anthropogenically-produced decrease in carbonate production over thc last approximately 100 vr may explain the former. Representative rates of burial and sedimentation, and a temporal and spatial offset between carbonate production and organic matter decomposition can permit most produced carbonate to be preserved in sediments where taphonomic capacity greatly exceeds the carbonate production rate. The requirement that most carbonate be preserved, despite the observation that most individuals are not, indicates that most adults are preserved and reinforces the finding that biomass is a valuable community attribute for paleoecologic analysis. The requirement that most carbonate be preserved indicates that taphonomic loss must be restricted to the nearsurface in most habitats rather than being distributed throughout the bioturbated zone. The distribution and concentration of carbonate in sediments are partially decoupled from preservational processes because many processes affecting carbonate distribution have little effect on preservation. The time scales of the two differ. Preservational processes usually occur on time scales too short to be recorded as variations in carbonate content with depth. Evidence of preservational processes probably resides solely in the taphonomic signature of shells, hence emphasizing the importance of taphofacies analysis.

Powers, E.R., R.A. Crowson, S.R. Riggs, S.W. Snyder, and A.C. Hine, Chemical Characteristics and Reevaluation of the Phosphate Resource Potential in Onslow Bay, North-Carolina Continental- Shelf, Marine Mining, 9 (1), 1-41, 1990.


Reed, A.J., and J.T. Wells, Sediment distribution patterns offshore of a renourished beach: Atlantic Beach and Fort Macon, North Carolina, Journal of Coastal Research, 16 (1), 88-98, 2000.

Contour plots of sediment characteristics have been used to help delineate the regional distribution of native, renourishment, and relict sediments off a renourished beach on the central North Carolina coast. Shell color, shell polish, and sediment size (sorting) were found to be especially useful indicators of dispersal patterns of renourishment sands, which were characterized by a high percentage of fine-grained sediment and a high percentage of dull, pockmarked shell that was gray-to-black in color. Distribution patterns show that longshore transport of renourishment sediment has been minor and little sand from a recent renourishment project was supplied to the adjacent native beaches. However, possible cross-shore transport was identified in storm layers (shell hash) in offshore sediment cores, and additional evidence was provided by the rippled scour depressions noted in a recent side-scan sonar survey.

Renaud, P.E., S.R. Riggs, W.G. Ambrose, K. Schmid, and S.W. Snyder, Biological-geological interactions: Storm effects on macroalgal communities mediated by sediment characteristics and distribution, Continental Shelf Research, 17 (1), 37-56, 1997.

The North Carolina mid-continental shelf is characterized by a complex sequence of rock substrates, or hardbottoms, which support rich communities of invertebrates and benthic macroalgae. Three hardbottom sites in southern Onslow Bay have been studied over 3 years, including studies of sedimentology and dynamics of the surficial sand bodies and the benthic community structure. Between 1991 and 1993 at two of the sites, there were large differences in sediment characteristics and depth at several of the zones sampled. These differences coincided with considerable variability in the abundance and species composition of the macroalgal community. In sampling zones where there was consistently low sediment coverage, algal biomass was uniformly high. There was only sparse, if any, macroalgal growth where gravelly sand or fine sand covered the hard substrate. Based on hindcasting of bottom currents generated by the March 1993 'storm of the century', it appears that this episodic event cleared fine sand from upper flat hardbottoms, resulting in considerable colonization and growth of macroalgae between the summers of 1992 and 1993. Macroalgae continued to be excluded from areas of gravelly sand, even after storm passage. Furthermore, the storm did not have any significant effects on scarps and ramp areas where sediment cover was already low. Therefore, distribution and characteristics of sediments influenced where the storm was to have biological consequences. Based on the wide areal extent of the upper flat hardbottoms in Onslow Bay, the newly formed macroalgal meadows represent a significant increase in benthic biomass and habitat complexity on a regional scare with potentially important ecological consequences. Copyright (C) 1996 Elsevier Science Ltd

Renaud, P.E., S.R. Riggs, W.G. Ambrose, K. Schmid, and S.W. Snyder, Biological-geological interactions: Storm effects on macroalgal communities mediated by sediment characteristics and distribution, Continental Shelf Research, 17 (1), 37-56, 1997.

The North Carolina mid-continental shelf is characterized by a complex sequence of rock substrates, or hardbottoms, which support rich communities of invertebrates and benthic macroalgae. Three hardbottom sites in southern Onslow Bay have been studied over 3 years, including studies of sedimentology and dynamics of the surficial sand bodies and the benthic community structure. Between 1991 and 1993 at two of the sites, there were large differences in sediment characteristics and depth at several of the zones sampled. These differences coincided with considerable variability in the abundance and species composition of the macroalgal community. In sampling zones where there was consistently low sediment coverage, algal biomass was uniformly high. There was only sparse, if any, macroalgal growth where gravelly sand or fine sand covered the hard substrate. Based on hindcasting of bottom currents generated by the March 1993 'storm of the century', it appears that this episodic event cleared fine sand from upper flat hardbottoms, resulting in considerable colonization and growth of macroalgae between the summers of 1992 and 1993. Macroalgae continued to be excluded from areas of gravelly sand, even after storm passage. Furthermore, the storm did not have any significant effects on scarps and ramp areas where sediment cover was already low. Therefore, distribution and characteristics of sediments influenced where the storm was to have biological consequences. Based on the wide areal extent of the upper flat hardbottoms in Onslow Bay, the newly formed macroalgal meadows represent a significant increase in benthic biomass and habitat complexity on a regional scare with potentially important ecological consequences. Copyright (C) 1996 Elsevier Science Ltd

Riggs, S.R., W.J. Cleary, and S.W. Snyder, Influence of Inherited Geologic Framework On Barrier Shoreface Morphology and Dynamics, Marine Geology, 126 (1-4), 213-234, 1995.

Passive margin coastlines with limited sand supplies, such as much of the U.S. Atlantic margin, are significantly influenced by the geologic framework of older stratigraphic units that occur beneath and seaward of the shoreface. Many U.S. east coast barrier islands are perched barriers in which the underlying, pre-modern sediments determine the morphology of the shoreface and strongly influence modern beach dynamics and composition. Perched barriers consist of varible layers of beach sand on top of older, eroding stratigraphic units with highly variable compositions and geometries. Along many parts of the coastal system, stratigraphically-controlled bathymetric features on the inner shelf modify waves and currents and thereby effect patterns of sediment erosion, transport, and deposition on the adjacent shoreface. It is essential to understand this geologic framework before attempting to model the large-scale behavior of these types of coastal systems. In North Carolina, most shoreline features are controlled by the pre-Holocene stratigraphic framework of the shoreface; the beaches are perched on top of pre-existing Pleistocene, Tertiary, and Cretaceous sediments. The surficial geology of the coastal zone is subdivided into two distinct provinces resulting in different stratigraphic controls of the shoreface. North of Cape Lookout the geological framework consists of a Quaternary sequence that fills a regional depositional basin called the Albemarle Embayment. The coastal zone south of Cape Lookout is dominated by Tertiary and Cretaceous units that crop out across the coastal plain and continental shelf, with very thin Quaternary units only locally preserved. Superimposed upon this regional stratigraphy is an ancient drainage system resulting in a series of fluvial valleys filled with younger coastal sediments separated by large interfluve areas of older stratigraphic units. This results in a coastal system in which the shoreface is either nonheadland or headland dominated, respectively. Headland dominated shorefaces are further divided into subaerial and submarine categories. Nonheadland dominated shorefaces are further divided into those influenced primarily by transgressive or regressive processes, or channel-dominated depositional processes (i.e., inlet migration or stream valley fill). Examples of each of these six types of shorefaces are presented to demonstrate the control that the geologic framework exhibits on shoreface morphologies and processes.

Riggs, S.R., S.W. Snyder, A.C. Hine, and D.L. Mearns, Hardbottom morphology and relationship to the geologic framework: Mid-Atlantic continental shelf, Journal of Sedimentary Research, 66 (4), 830-846, 1996.

High-energy, sediment-starved continental shelves of the mid- Atlantic region have abundant hardbottoms that extend from the shoreface to the shelf edge, Because of the thin and irregularly distributed Holocene sand sheet, shelf morphology is determined mainly by outcropping Tertiary and Pleistocene stratigraphic units, Each unit and combination of units produces different hardbottom morphologies that depend upon the geometry and spatial relationships of the units, lithology and patterns of stratification, and subsequent weathering and erosion. Hardbottoms vary in surface relief from smooth, flat surfaces to scarped surfaces with up to 10 m of relief, The morphology ranges from sloping and stepped erosional ramps to vertical and undercut scarps with associated broad rubble ramps, Hardbottoms associated with each of the different gently dipping Tertiary depositional sequences have distinctive morphologies. Hardbottoms developed on Pleistocene units unconformably overlie the Tertiary sequences as Bat-lying marine carbonates, or cut into them as channel systems backfilled with fluvial and estuarine sediments, Initial dissection of hardbottoms produced highly convoluted surfaces that resulted from subaerial weathering, stream erosion, and karst formation during sea-level lowstands, During subsequent sea-level highstands, these primary morphologies were greatly modified through the interaction of bioerosion and storms. Understanding continental shelf hardbottoms is critical for interpreting the sedimentology and stratigraphy of the Atlantic Coastal Plain and for reconstructing paleoceanographic conditions, for the following reasons, (1) They are an extensive part of the stratigraphic record on shelves that are not actively subsiding and have small volumes of terrigenous input with low sediment accumulation rates, (2) They are important stages in the formation of major stratigraphic unconformities, condensed sections, and sequence boundaries, (3) They support diverse biological communities that produce primary carbonate sediments and are rapidly degraded and modified by bioerosion and physical processes supplying abundant ''new sediment'' to the continental shelf.

Riggs, S.R., W.G. Ambrose, J.W. Cook, and S.W. Snyder, Sediment production on sediment-starved continental margins: The interrelationship between hardbottoms, sedimentological and benthic community processes, and storm dynamics, Journal of Sedimentary Research, 68 (1), 155-168, 1998.

Modern sediment-starved continental shelves represent developing condensed sections analogous to those considered key stratigraphic markers in many stratigraphic models. Condensed sections and their associated hardbottoms on the modern, high energy North Carolina continental margin provide important benthic habitats that are modified on time scales of days to centuries by interrelated sedimentological, biological, and physical processes. Outcropping Upper Cenozoic strata of varying lithologies form distinct hardbottom morphologies that, through differential bioerosion, contribute significant volumes of new sediment to the surficial sand regime of the continental shelf. (1) Vertical and sloped mudstone to muddy sandstone hardbottoms of the Miocene Pungo River Formation are dominated by the endolithic fauna Jouanettia quillingi (bivalve) and Upogebia sp. (shrimp). (2) Vertical and sloped hardbottoms consisting of harder Miocene and Pleistocene limestone are dominated by the endolithic bivalves Lithophaga bisulcata, Gastrochaena stimpsoni, and G. ovata. (3) The highly lithified, flat hardbottoms of Plio-Pleistocene limestone are dominated by the epifloral macroalgal species Dictyopteris hoytii, Zonaria tournefortii, and Sargassum filipendula. These three groups of bioeroders physically and/or chemically degrade their respective lithologies, develop relief on hardbottom surfaces, produce large-scale morphological features on the shelf, and recycle ancient sediment into the modern, surficial sediment system. The rate of sediment production resulting from bioerosion varies from 5.5 kg/m(2)/yr on the vertical and sloped Miocene mudstone hardbottoms, to 0.4 kg/m(2)/yr on vertical and sloped Pleistocene limestone, to 0.03 kg/m(2)/yr on the flat, highly lithified Plio-Pleistocene limestone hardbottoms. Depending on lithology and associated bioerosional processes, bioeroders excavate exposed hardbottom surfaces and develop relief ranging from millimeters to meters, whereas differential rates of bioerosion between different lithologic units results in relief ranging from meters to tens of meters. Recession rates measured on Miocene mudstones at the Chapel site range from 2 to 4 cm per year. For the outcrop exposure, which is 132 m long, this would produce a ten-meter overhang of the overlying Pleistocene Limestone in 250-500 years by removing 13,400 metric tons of eroded sediment (25% fine sand) that would be contributed to the surficial sediments. The overhang would ultimately break off during a storm to produce the next row of the limestone rubble blocks that form a ramp in front of the receding mudstone scarp. These rates of sediment production are rapid enough to bury the hardbottoms producing the sediment. However, surface sediment is generally not accumulating on the shelf; it is present only as thin (0-1 m), highly variable, and ephemeral sand bodies. Major storms modify the abundance and distribution of surface sediment on hardbottom habitats, and routinely export large volumes of these sediments from the shelf system, depositing them as fine- sand clinoforms off the prograding shelf edge. Exposed hardbottom habitats free of sand are dominated by highly diverse communities of endolithic fauna and epilithic fauna and flora, those habitats with 2-6 cm of sand are generally dominated by scattered epilithic fauna with small growths of epilithic flora irregularly distributed on topographic highs, and those habitats with > 6 cm of sand are generally dominated by softbottom benthic communities. Storms modify the distribution of bottom sediments, which either exposes or buries additional hardbottom surfaces and controls the expansion or contraction of hardbottom benthic communities. Thus, the intensity, frequency, and character of individual storms and the seasonal storm pattern determine the amount and location of sand accumulation, which controls the benthic community structure. In turn, the benthic community determines the type, rate, and volume of hardbottom bioerosion and resulting sediment production.

Roberts, R.D., and B.M. Forrest, Minimal impact from long-term dredge spoil disposal at a dispersive site in Tasman Bay, New Zealand, New Zealand Journal of Marine and Freshwater Research, 33 (4), 623-633, 1999.

The effects of dredge spoil disposal on contaminant concentrations and benthic macrofauna were examined at a shallow marine disposal site used for c. 20 years. The site had received c. 50 000 m(3) yr(-1) of maintenance dredgings annually, from the Port of Nelson. Port sediments were contaminated to varying degrees with some trace metals, organochlorine pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. They showed mildly elevated toxicity in laboratory bioassays, and their macrofauna was dominated by small-bodied polychaetes. Despite this, there was very little indication of impact. in the spoil disposal area. The disposal area, spoil spreading zone and control sites were all similar in terms of sediment contaminants, sediment toxicity, neogastropod imposer, and macrofauna. The lack of discernible impact is probably because of the dynamic sedimentary environment in the disposal area, which disperses dumped dredgings and mixes them with ambient sediment.

Sakai, T., and F. Masuda, The relationship between glacio-eustatic parasequences and a third-order sequence in the Kakegawa Group, central Japan, Sedimentary Geology, 122 (1-4), 95-107, 1998.

The Plio-Pleistocene Kakegawa Group, central Japan, consists of a third-order depositional sequence (2.6-1.0 Ma). The northwestern part of the Kakegawa sequence consists of up to 500 m of alluvial, shoreface, shelf, slope and submarine- channel facies. It contains at least sixteen upward-shallowing cycles (parasequences), the deposition of which was affected by high-frequency eustatic sea-level cycles. The lower part of the sequence is characterized by a retrogradational parasequence set, which formed a transgressive systems tract (2.2-1.75 Ma) followed by a progradational parasequence set comprising a highstand systems tract (1.75-1.4 Ma). Subsidence analysis and evaluation of changes in the shelf sedimentation rate estimated from cross-sections, suggest that formation of the third-order sequence was controlled by tectonic subsidence and variation in the sedimentation rate. Rapid subsidence and a high rate of sedimentation during 2.2-2.0 Ma resulted in deposition of the lower part of the transgressive systems tract, characterized by thick backstepping successions. The rate of subsidence decreased in the period 2.0-1.75 Ma. The sedimentation rate also decreased due to a high rate of sediment bypassing. However, subsidence was still the dominant factor, leading to the formation of thin backstepping successions. The 1.75-1.4 Ma progradational succession resulted from a combination of a low rate of subsidence and moderate sedimentation. The progradational units become thicker basinward owing to faster subsidence in the basin center. The maximum flooding surface was formed around 1.75 Ma even though subsidence was slow at this time. (C) 1998 Elsevier Science B.V. All rights reserved.

Schwab, W.C., R.W. Rodriquez, W.W. Danforth, and M.H. Gowen, Sediment distribution on a storm-dominated insular shelf, Luquillo, Puerto Rico, USA, Journal of Coastal Research, 12 (1), 147-159, 1996.

A sea-floor mapping investigation designed to assess the sediment distribution, the movement of the nearshore sand supply, and the fate of sediment eroded from the shoreline was conducted using high-resolution sidescan-sonar, seismic reflection, and sediment sampling techniques on the northern insular shelf of Puerto Rico, off the town of Luquillo. sea- Boor structures and the distribution of sediment texture and composition suggest that regional oceanographic processes result in a net offshore direction for cross-shelf sediment transport on the middle and outer shelf during storms. If these same processes are active on the inner shelf, mapping results indicate that this sediment is not transported seaward of a series of east-west trending Pleistocene-age eolianite ridges that outcrop on the middle shelf. The eolianite ridges may act as natural dams, preventing the removal of sediment from the nearshore area. sand deposits behind the ''dams'' are up to 20 m thick on the shoreward flank of the ridges.

Stauble, D.K., and D.A. Warnke, Bathymetry and Sedimentation of Cape-San-Blas Shoal and Shelf Off St-Joseph-Spit, Florida, Journal of Sedimentary Petrology, 44 (4), 1037-1051, 1974.


Stille, P., S. Riggs, N. Clauer, D. Ames, R. Crowson, and S. Snyder, Sr and Nd Isotopic Analysis of Phosphorite Sedimentation Through One Miocene High-Frequency Depositional Cycle On the North-Carolina Continental-Shelf, Marine Geology, 117 (1-4), 253-273, 1994.

A well-developed seismic-, litho-, and biostratigraphic data base with good models for the formation and deposition of phosphate-rich sediments exist for the Upper Cenozoic sediments on the North Carolina continental margin. This provides a unique opportunity to evaluate the potential of utilizing strontium and neodymium isotopic analyses to help unravel a complex genetic history of phosphate formation and deposition. Thirty one samples from three vibracores in Onslow Bay supplied hand-picked concentrate subsamples of five phosphate grain types and thirty one concentrate subsamples of phosphate peloids for stratigraphic analysis. All subsamples were analyzed for their Sr isotope composition, while only thirteen were analyzed for Nd isotopes. The 31 peloid samples represent three different stratigraphic units and include: (1) Holocene surficial sands with highly variable concentrations and types of reworked phosphate; (2) Pleistocene moldic carbonates with minor concentrations of black peloidal phosphate; and (3) Miocene (mid-Burdigalian), Frying Pan Sequence unit 1 (FPS-1) of the Pungo River Formation with very high concentrations of multiple types of phosphate grains that decrease upsection and change grain types with changing lithofacies. The latter unit represents deposition during one high-frequency sea-level cycle. Stratigraphic analysis utilized one grain type, phosphate peloids, for comparative purposes with the depositional model of Riggs and Mallette (1990). The Sr and Nd data cluster into significant categories that are coincident with these three major stratigraphic units. Sr and Nd isotope compositions of selected phosphate grains from three phosphate- rich depositional sequences are utilized to: (1) date the initial Miocene transgression of unit FPS-1 of the Pungo River Formation; (2) decipher processes of formation and deposition of major phosphate grain types through one Miocene sea-level cycle including the processes of in situ formation versus reworking; (3) develop a Sr and Nd chronostratigraphy for evaluating changing patterns of continental margin sedimentation through high-frequency depositional cycles; (4) determine effects of reworking and weathering on the isotope signals between Miocene, Pleistocene, and Holocene sediments; (5) evaluate the suitability of utilizing Sr and Nd isotopes for detailed chronostratigraphic analysis of phosphorite sedimentation; and (6) refine our understanding of the Upper Cenozoic evolutionary history of North Carolina's continental margin.

Thieler, E.R., A.L. Brill, W.J. Cleary, C.H. Hobbs, and R.A. Gammisch, Geology of the Wrightsville Beach, North-Carolina Shoreface - Implications For the Concept of Shoreface Profile of Equilibrium, Marine Geology, 126 (1-4), 271-287, 1995.

Nearly 300 km of 3.5 kHz subbottom profile and 100 kHz sidescan-sonar data, a suite of over 100 short (similar to 2 m) percussion cores and vibracores have been collected on the shoreface and inner continental shelf off Wrightsville Beach, North Carolina. Sidescan-sonar images were analyzed for acoustic backscatter to delineate the surface sediment distribution. Groundtruth data for the sidescan-sonar interpretations were provided by surface grab samples. Cross- shore sediment transport by combined waves and currents is the predominant sedimentologic signature on this shoreface. The shoreface is dominated by a shore-normal system of rippled scour depressions that begin in 3-4 m water depth and extend to the base of the shoreface about 1 km offshore, at 10 m depth. The depressions are 40-100 m wide, and up to 1 m deep. They are floored by coarse, rippled shell hash and gravel; some are separated by rock-underlain fine sand ridges. On the inner shelf, the bathymetric and sedimentary fabrics become shore- oblique, due to a series of relict ridges with 1-2 m of relief. The ridges are coarse on their landward sides and covered on their seaward flanks by thin veneers of fine sand. Field evidence from the Wrightsville Beach shoreface demonstrates that a shoreface equilibrium profile as defined by Dean (1991) and others does not exist here. For example: (1) the grain size varies widely and inconsistently over the profile; (2) shoreface profile shape is controlled predominantly by underlying geology, including Tertiary limestone outcrops and Oligocene silts; and (3) sediment transport patterns cannot be explained by simple diffusion due to wave energy gradients, and that transport occurs seaward of the assumed engineering ''closure depth'' of 8.5 m. This has several implications for the application of equilibrium profile-based numerical models used to investigate coastal processes and design coastal engineering projects at Wrightsville Beach. The most important practical implication is that a number of assumptions required by existing analytical and numerical models (e.g., Dean, 1991; GENESIS; SBEACH) used for the design of shore protection projects and large-scale coastal modeling over decadal time scales cannot be met.

Thieler, E.R., O.H. Pilkey, R.S. Young, D.M. Bush, and F. Chai, The use of mathematical models to predict beach behavior for US coastal engineering: A critical review, Journal of Coastal Research, 16 (1), 48-70, 2000.

A number of assumed empirical relationships (e.g., the Bruun Rule, the equilibrium shoreface profile, longshore transport rate equation, beach length:durability relationship, and the renourishment factor) and deterministic numerical models leg., GENESIS, SBEACH) have become important tools for investigating coastal processes and for coastal engineering design in the U.S. They are also used as the basis for making public policy decisions, such as the feasibility of nourishing recreational beaches. A review of the foundations of these relationships and models, however, suggests that they are inadequate for the tasks for which they are used. Many of the assumptions used in analytical and numerical models are not valid in the context of modern oceanographic and geologic principles. We believe the models are oversimplifications of complex systems that are poorly understood. There are several reasons for this, including: (1) poor assumptions and important omissions in model formulation; (2) the use of relationships of questionable validity to predict the morphologic response to physical forcing; (3) the lack of hindsighting and objective evaluation of beach behavior predictions for engineering projects; (4) the incorrect use of model calibration and verification as assertions of model veracity; and (5) the fundamental inability to predict coastal evolution quantitatively at the engineering and planning time and space scales our society assumes and demands. It is essential that coastal geologists, beach designers and coastal modelers understand these model limitations. Each important model assumption must be examined in isolation; incorporating them into a model does not improve their validity. It is our belief that the models reviewed here should not be relied on as a design tool until they have been substantially modified and proven in real-world situations. The "solution," however, is not to increase the complexity of a model by increasing the number of variables. What is needed is a thoughtful review of what beach behavior questions should or could be answered by modeling. Viable alternatives to the use of models do exist to predict the behavior of beaches. Three such alternatives to models are discussed far nourished beach design.

Tortora, P., Depositional and erosional coastal processes during the last postglacial sea-level rise: An example from the central Tyrrhenian continental shelf (Italy), Journal of Sedimentary Research, 66 (2), 391-405, 1996.

A transgressive systems tract (TST) deposit on the inner continental shelf of the south Tuscany region (central Tyrrhenian Sea, Italy) formed during the last postglacial sea- level rise. Its small-scale stratigraphy has been detailed using high-resolution seismic profiles, gravity cores, and grab samples. The TST deposit overlies a lowstand unconformity, shows a tabular geometry, and comprises three internal architectures of beach facies: (1) Architecture A, present on the outer sector of the study area, is made up of only a reworked sand sheet; (2) Architecture B, on the middle sector, comprises palustrine (bottom), washover, and the above- mentioned reworked sand sheet; and (3) Architecture C, on the inner sector, represents the absence or scarcity of deposits (reworked sand sheet) over the unconformity. Because the lateral distribution of these vertical successions is not random, but parallel to the coast, each architecture represents an individual sedimentary stage during sea-level rise. However, all architectures were formed via shoreface retreat in response to the landward migration of a beach complex over the unconformity. During this migration the beach system was characterized by a source diastem located in the surf zone and by two sediment dispersal systems, One moved the eroded sand over the flat back-barrier palustrine area by storm washover, while the other transported part of this sand to the lower shoreface, forming a reworked sand sheet above the older and inactive source diastem (ravinement surface). The TST architectures originated from a transgressive succession of beach facies, differentiated according to the intensity of shoreface retreat. Architecture A represents a low preservation potential of the original beach complex, Architecture B relatively high preservation, and Architecture C no preservation. The intensity of erosion and the consequent preservation potential were totally controlled by antecedent topography.

Toscano, M.A., and L.L. York, Quaternary Stratigraphy and Sea-Level History of the United- States Middle Atlantic Coastal-Plain, Quaternary Science Reviews, 11 (3), 301-328, 1992.

Middle-Atlantic, inner continental shelf stratigraphic studies document a regional, Late Pleistocene, fossiliferous mud deposit, from northern New Jersey to Cape Lookout, North Carolina. Seismic reconnaissance and detailed stratigraphic analyses reveal the nature of the mud, termed unit Q2, on the Maryland inner continental shelf. Extensive amino acid relative age determinations (from the single genus Mulinia), combined with additional amino acid analyses from onshore deposits having radiometric dates for calibration, indicate an age range for unit Q2 corresponding to Oxygen Isotope Stage 5. Ostracode assemblages delineate four distinct climatic episodes in unit Q2, enabling correlation of the zones in Q2 to the deep sea isotopic record of climatic fluctuations (substages) in Stage 5. Late Stage 5 is represented, on the Maryland shelf, by the 6 meter-thick mud of unit Q2, deposited in an open-shelf environment at slightly depressed sea levels relative to Substage 5e. Late Stage 5 sea levels (including sea-level minima) can be estimated for the mid-Atlantic Coastal Plain by direct measurement of the altitudes of ostracode zone boundaries offshore, and from peak transgressive facies in correlative deposits onshore. Late Stage 5 sea levels determined from the inner shelf and adjacent nearshore facies on the Atlantic coast comprise the most complete sea-level history for Stage 5 yet proposed. Some recent revisions of glacioeustatic sea-level models advocate slightly higher sea levels during late Stage 5 (Substage 5c in particular) than originally estimated from uplifting reef tracts, and support sea levels higher than estimates from deep-sea isotopic records. The sea-level record from the Maryland inner continental shelf confirms these recent estimates in an area of minimal tectonism, and adds sea-level minima estimates for Substages 5d and 5b. Offshore, a more complete record of Stage 5 is preserved than in onshore deposits, which are limited to peak transgressive facies. Discrepancies in correlation among emerged coastal plain facies therefore become resolvable within the context provided by the shelf stratigraphy.

Van Heteren, S., D.M. Fitzgerald, P.A. McKinlay, and I.V. Buynevich, Radar facies of paraglacial barrier systems: coastal New England, USA, Sedimentology, 45 (1), 181-200, 1998.

Analysis of a large data base of ground-penetrating-radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid- to high-latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment-source areas are characterized by chaotic, parallel, and tangential-oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection-free, and bounding- surface configurations. Back-barrier sediments may yield basin- fill configurations, but generally include abundant signal- attenuating units. The GPR data, calibrated with information from cores, were collected across swash-aligned and drift- aligned barriers in a variety of wave- and tidal-energy settings. Application of a 120-MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0.2 m and 0.7 m. The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt-marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.

vanHeteren, S., and O. vandePlassche, Influence of relative sea-level change and tidal-inlet development on barrier-spit stratigraphy, Sandy Neck, Massachusetts, Journal of Sedimentary Research, 67 (2), 350-363, 1997.

Sandy Neck is a 10-km-long sheltered mesotidal barrier spit along the southeastern New England coast, bordering Cape Cod Bay. Its stratigraphy contains evidence of relative sea-level (RSL) rise and tidal-inlet development, and enables reconstruction of accretion and progradation of this barrier through time. Core, trench, and ground penetrating-radar (GPR) data show that the lower boundary of the uppermost, eolian, facies climbs about 9 m from the proximal to the distal part of the spit, away from the mainland anchor point. This change is thought to be related primarily to a comparable rise in RSL. The same boundary also shows a shallowing trend in a seaward direction, indicating net spit progradation through time. The absence of inlet-channel facies in the stratigraphy of the proximal part of the barrier spit, in contrast to the presence of inlet facies in more distal parts of the spit, indicates that some time elapsed after barrier initiation before an inlet thalweg developed, In its earliest stages, this thalweg was poorly defined, wide, and shallow, but its characteristics changed as the barrier spit lengthened. In the central part of Sandy Neck, the assemblage of inlet channel facies becomes markedly thicker, reflecting thalweg deepening in response to paleotopographic and substrate lithologic factors. The stratigraphy of the distal part of the spit shows the effects of continued, but more gradual, inlet deepening that may be tied directly to increasing barrier length. The process-con trolled stratigraphy presented here differs from current facies models because it accounts for temporal changes in coastal environmental processes and parameters. It suggests a high preservation potential for proximal eolian facies in the spit sequence, underneath a cover of fine-grained and organic back- barrier sediment. Once reliably dated, the new stratigraphic data will help to improve the regional RSL curve for the southern Cape Cod Bay area.

Wehmiller, J.F., L.L. York, D.F. Belknap, and S.W. Snyder, Theoretical Correlations and Lateral Discontinuities in the Quaternary Aminostratigraphic Record of the United-States Atlantic Coastal-Plain, Quaternary Research, 38 (3), 275-291, 1992.


Wehmiller, J.F., L.L. York, and M.L. Bart, Amino-Acid Racemization Geochronology of Reworked Quaternary Mollusks On Us Atlantic Coast Beaches - Implications For Chronostratigraphy, Taphonomy, and Coastal Sediment Transport, Marine Geology, 124 (1-4), 303-337, 1995.

Approximately 200 shells (primarily Mercenaria) from 21 beach sites between New Jersey and Florida have been analyzed for the extent of racemization (epimerization) of their fossilized amino acids. The greatest concentration of sites is in North Carolina, in regions least affected by human modification of natural beach sediment-transport processes. These results can be used to estimate the frequency of age mixing of Pleistocene shell material in Holocene depositional environments. Selected shells have also been dated by C-14 (conventional and/or AMS) to provide direct calibration of the amino acid epimerization ratios. Shell taphonomic characteristics (particularly color) can be qualitatively related to apparent ages. Data for shell fragmentation, combined with amino acid age estimates, provide insights into probable transport distances of reworked shells. Shells with apparent Pleistocene ages have epimerization values equivalent to those seen in onshore exposures of Pleistocene coastal units. Amino acid epimerization measurements are a comparatively rapid and inexpensive chronologic tool for use in taphonomic and sediment-(shell-) transport studies. Paired amino acid-C-14 analyses on single shells provide insights into geochemical alteration of shells and permit modelling of the residence time of shells on beaches. Greater numbers of analyses at each site are needed before statistically valid estimates of age mixing can be obtained, but the apparent distribution of Pleistocene shells on Atlantic coast beaches appears to be related to the distribution of Pleistocene units in the shoreface and inner shelf, and the thickness of Holocene sedimentary cover in specific areas. These observations provide useful criteria for the evaluation of possible age mixing of shells collected at outcrops of Pleistocene units in the Coastal Plain.

Wiberg, P.L., D.E. Drake, and D.A. Cacchione, Sediment Resuspension and Bed Armoring During High Bottom Stress Events On the Northern California Inner Continental- Shelf - Measurements and Predictions, Continental Shelf Research, 14 (10-11), 1191-1219, 1994.

Geoprobe bottom tripods were deployed during the winter of 1990-1991 on the northern California inner continental shelf as part of the STRESS field experiment. Transmissometer measurements of light beam attenuation were made at two levels and current velocity was measured at four levels in the bottom 1.2 m of water. Intervals of high measured bottom wave velocity were generally correlated with times of both high attenuation and high attenuation gradient in the bottom meter of the water column. Measured time series of light attenuation and attenuation gradient are compared to values computed using a modified version of the SMITH [(1977) The sea, Vol. 6, Wiley- Interscience, New York, pp. 539-5771 steady wave-current bottom-boundary-layer model. Size-dependent transmissometer calibrations, which show significantly enhanced attenuation with decreasing grain size, are used to convert calculated suspended sediment concentration to light attenuation. The finest fractions of the bed, which are the most easily suspended and attenuate the most light, dominate the computed attenuation signal although they comprise only about 5-7% of the bed sediment. The calculations indicate that adjusting the value of the coefficient gamma0 in the expression for near-bed sediment concentration cannot in itself give both the correct magnitudes of light attenuation and attenuation gradient. To supply the volumes of fine sediment computed to be in suspension during peak events, even with values of gamma0 as low as 5 x 10(-5), requires suspension of particles from unreasonably large depths in the bed. A limit on the depth of sediment availability is proposed as a correction to suspended sediment calculations. With such a limit, reasonable attenuation values are computed with gamma0 almost-equal-to 0.002. The effects of limiting availability and employing a higher gamma0 are to reduce the volume of the finest sediment in suspension and to increase the suspended volumes of the coarser fractions. As a consequence, the average size and settling velocity of suspended sediment increases as bottom shear stress increases, with accompanying increases in near-bed concentration gradients. Higher concentration gradients produce larger stratification effects, particularly near the top of the wave boundary layer at times when wave shear velocities are high and current shear velocities are low. These are the conditions under which maximum attenuation gradients are observed.

Wiberg, P.L., and C.K. Harris, Ripple Geometry in Wave-Dominated Environments, Journal of Geophysical Research-Oceans, 99 (C1), 775-789, 1994.

The wavelength, height, and steepness of ripples formed under oscillatory flows in flume and field studies are reexamined to construct a simple and accurate method of predicting these ripple properties. Ripples with wavelengths proportional to near-bed wave orbital diameter (orbital ripples), predominant in laboratory experiments, are found to have heights in excess of the thickness of the wave boundary layer. Ripples with wavelengths that are roughly proportional to grain size and nearly independent of orbital diameter (anorbital ripples), which predominate in the field, have heights at least several times smaller than wave boundary layer thickness. Relating wave boundary layer height to the generally more easily estimated wave orbital diameter, a set of expressions are developed for predicting ripple type and geometry based on mean grain size, wave orbital diameter, and estimated anorbital ripple height. This method provides a good characterization of ripple wavelength and steepness for a large set of combined field and flume data.

Wiesner, M.G., B. Haake, and H. Wirth, Organic Facies of Surface Sediments in the North-Sea, Organic Geochemistry, 15 (4), 419-432, 1990.


Willis, A.J., and T.F. Moslow, Stratigraphic Setting of Transgressive Barrier-Island Reservoirs With an Example From the Triassic Halfway Formation, Wembley Field, Alberta, Canada, Aapg Bulletin-American Association of Petroleum Geologists, 78 (5), 775-791, 1994.

Established models for landward barrier-island migration focus primarily on the preservation pattern of transgressive facies in the shoreface, which are typically thin and buried beneath finer grained marine lower shoreface-to-offshore sediments. In contrast, transgressive barrier-island sandstones in the Triassic Halfway Formation of Wembley field in Alberta are preserved interbedded with, and over-lain by, backbarrier and nonmarine sediments. These transgressive barrier sandstones formed from coalescing washover fans during shoreface retreat and were subsequently ''abandoned'' as the shoreline stabilized and resumed progradation. The abandoned transgressive barrier sandstones were subsequently blanketed by backbarrier and nonmarine sediments as the coastline continued to prograde. Abandoned transgressive barrier island sandstones in the Halfway Formation are 2-6 m thick, up to 2 km wide, and form paleocoastline-parallel trends tens of kilometers in length. The trends define the paleolandward limit of transgressive events. The updip pinch-out of these sandstones in backbarrier mudstones forms a stratigraphic trap for hydrocarbons in Wembley field. Top seal is provided by nonmarine mudstones and evaporites which buried the abandoned transgressive barrier island. The sandstone has porosities and permeabilities averaging 11% and 63 md, respectively. By using well logs and cores to correlate individual parasequences in the Halfway Formation to their updip termination, it is possible to define the extent of associated marine flooding events and therefore identify exploration targets for abandoned transgressive barrier-island sandstones.

Woo, H.J., G.F. Oertel, and M.S. Kearney, Distribution of pollen in surface sediments of a barrier-lagoon system, Virginia, USA, Review of Palaeobotany and Palynology, 102 (3-4), 289-303, 1998.

Fine-grained surface sediments of the U.S. middle Atlantic coast contain pollen that are characteristic of the local vegetation. The pollen concentrations and pollen associations in lagoonal sediment appeared to be affected by physical characteristics of the landscape and the dynamic characteristics of the atmosphere and water. Arboreal pollen from the elevated mainland had a greater influence on uniform distribution of pollen in lagoons than arboreal pollen from the low profile barrier islands. The concentration of airborne pollen from the mainland decreased in a seaward direction across the lagoon. The maximum dispersion distance from the mainland was 7-10 km. Non-arboreal plants on the low profile barrier islands of the Virginia coast primarily provided pollen grains to the outer part of the coastal lagoon. The changes in pollen concentration and the relationship between arboreal and non-arboreal pollen documented in this study clearly differentiate into inner, middle and outer lagoon pollen spectra. (C) 1998 Elsevier Science B.V. All rights reserved.

Wood, J.M., and J.C. Hopkins, Traps Associated With Paleovalleys and Interfluves in an Unconformity Bounded Sequence - Lower Cretaceous Glauconitic Member, Southern Alberta, Canada, Aapg Bulletin-American Association of Petroleum Geologists, 76 (6), 904-926, 1992.

The Glauconitic member in Badger, Little Bow, Retlaw, and Turin fields is an unconformity bounded sequence that formed on an ancient coastal plain in response to relative sea level fluctuations. The member consists of valley-fill and inter- valley strata. Valley-fill sandstone bodies are thick elongate pods that formed from inner estuarine bars when sedimentation was laterally confined between valley margins. Inter-valley sandstone bodies are thin discontinuous sheets that accumulated during highstands when outer estuarine embayments covered interfluvial areas adjacent to associated valleys. Numerous oil pools are stratigraphically trapped within quartzose sandstones in valley-fill and inter-valley strata of the Glauconitic member in the study area. Common updip seals for these reservoirs are (1) intra-sequence facies changes from sandstone to shale, and (2) low-permeability lithic sandstones that fill the cross-cutting paleovalleys of a younger sequence. Traps associated with many valley-fill pools are enhanced by differential-compaction anticlines. Several oil pools in the study area are hosted by discrete quartzose sandstone bodies that lie beneath a valley filled with low-permeability lithic sandstone. These quartzose sandstone bodies are interpreted to be remnants of older Glauconitic deposits that escaped erosion when a younger valley incised into, and followed the trend of, one or more older Glauconitic valleys.

York, L.L., and J.F. Wehmiller, Aminostratigraphic Results From Cape Lookout, Nc, and Their Relation to the Preserved Quaternary Marine Record of Se North- Carolina, Sedimentary Geology, 80 (3-4), 279-291, 1992.

Aminostratigraphic data were obtained for Mulinia lateralis samples from closely spaced drillholes on the Cape Lookout, North Carolina barrier islands. Two major aminozones are recognized in the subsurface section based upon D- alloisoleucine/L-isoleucine (A/I) values. These major aminozones can each be subdivided into two additional aminozones based upon direct comparisons with Mulinia A/I data from other North Carolina localities. Correlation of the Cape Lookout Mulinia aminostratigraphy with U-series calibrated A/I data in N.C. indicates that the sampled units represent deposition during the middle to late Pleistocene. The four Cape Lookout aminozones may be assigned to late and early stage 5 (or possibly stages 5 and 7), a portion of the interval during stages 17-19, and at least one interglacial in stages 25-31 of the oxygen isotope record based on correlation to calibrated sites and kinetic model extrapolation. The aminostratigraphic data obtained from the Cape Lookout barrier islands and nearby areas indicate that there are significant differences in the extent of preservation of the Pleistocene sedimentary record to the southwest of Cape Lookout compared with that to the north- northeast. All four of the recognized Cape Lookout aminozones are present in the subsurface section to the north-northeast of Cape Lookout. In contrast, the two late Pleistocene aminozones are almost completely absent in the subsurface of the barrier islands, and in Onslow Bay, to the southwest of Cape Lookout. These aminostratigraphic interpretations are consistent with the incomplete stratigraphic record recognized by previous investigators for the Cape Lookout-Onslow Bay area. The calibrated kinetic model age estimates for the Cape Lookout aminostratigraphic data now permit quantification of these stratigraphic gaps. The detailed aminostratigraphic results from Cape Lookout also have significant consequences for regional aminostratigraphic correlations on the Atlantic Coastal Plain, and provide valuable information with which to test contrasting models proposed for regional correlation within the context of the preserved stratigraphic record.

Young, R.S., O.H. Pilkey, D.M. Bush, and E.R. Thieler, A Discussion of the Generalized-Model For Simulating Shoreline Change (Genesis), Journal of Coastal Research, 11 (3), 875-886, 1995.

The Generalized Model for Simulating Shoreline Change (GENESIS) (HANSON and KRAUS, 1989) is designed to simulate the long-term shoreline changes at coastal engineering sites resulting from spatial and temporal differences in longshore sediment transport. GENESIS is used by the coastal engineering and planning communities for predicting the behavior of shorelines in response to coastal engineering and/or beach replenishment activities that may alter longshore transport. GENESIS is also used by some modelers to develop regional scale sediment budgets. We have evaluated the assumptions behind the GENESIS model in light of well understood nearshore, geologic and oceanographic phenomena In most cases, the assumptions used in the model fail to be met or are so oversimplified that the model's effectiveness as a predictive tool is limited at best. In addition, the GENESIS Technical Reference (HANSON and KRAUS, 1989) makes it clear that adequate data for running the model are seldom, it ever, available. Frequently, averaged values must be used, smoothing over great potential variability in data sets (waves, profile shape, etc.). When predictions are made, it is not possible to quantify the uncertainty in the assumptions or the error in the data, and thus it is not possible to quantify the uncertainty in predicted results. GENESIS does not provide the modeler with statistical answers. The best the modeler can do is to vary the input parameters to produce a range of possible scenarios. There is no way to objectively evaluate which scenario is the most reasonable. As the Technical Reference emphasizes, even with GENESIS the user must still constantly rely on his or her own technical expertise. Ad of this uncertainty makes GENESIS, at best, a qualitative, not quantitative model, and at worst a model that, after a certain amount of assuming and adjusting input parameters, produces a result that the coastal ''expert'' employing its services expected-a way of hacking up one's judgment with what appear to be real numbers. We believe that future modeling efforts need to focus on statistical models where each parameter input into the model is accompanied by probabilities of its accuracy and predictive capabilities, producing probabilistic results.

Zuschin, M., and J. Hohenegger, Subtropical coral-reef associated sedimentary facies characterized by molluscs (Northern bay of Safaga, Red Sea, Egypt), Facies, 38, 229-254, 1998.

The shallow marine subtropical Northern Bay of Safaga is composed of a complex pattern of sedimentary facies that are generally rich in molluscs. Thirteen diver-taken bulk-samples from various sites (reef slopes, sand between coral patches, muddy sand, mud, sandy seagrass, muddy seagrass, mangrove channel) at water depths ranging from shallow subtidal to 40m were investigated with regard to their mollusc fauna > 1mm, which was separated into fragments and whole individuals. Fragments make up more than 88% of the total mollusc remains of the samples, and their proportions correspond to characteristics of the sedimentary facies. The whole individuals were differentiated into 622 taxa. The most common taxon, Rissoina cerithiiformis, represented more than 5% of the total mollusc content in the samples. The main part of the fauna consists of micromolluscs, including both small adults and juveniles. Based on the results of cluster-, correspondence-, and factor analyses the fauna was grouped into several associations, each characterizing a sedimentary facies: (1) "Rhinoclavis sordidula - Corbula erythraeeasis - Pseudominolia nedyma association" characterizes mud. (2) "Microcirce sp. - Leptomyaria sp, association" characterizes muddy sand. (3) "Smaragdia spp. - Perrinia stellata - Anachis exilis - assemblage" characterizes sandy seagrass. (4) "Crenella striatissima - Rastafaria calypso - Cardites akabana - assemblage" characterizes muddy seagrass. (5) "Glycymeris spp. - Parvicardium sueziensis - Diala spp. - assemblage" characterizes sand between coral patches. (6) "Rissoina spp. - Triphoridae - Ostreoidea - assemblage" characterizes reef slopes. (7) "Potamides conicus - Siphonaria sp. 2 - assemblage" characterizes the mangrove. The seagrass fauna is related to those of sand between coral patches and reef slopes with respect to gastropod assemblages, numbers of taxa and diversity indices, and to the muddy sand fauna on the basis of bivalve assemblages and feeding strategies of bi valves. The mangrove assemblage is related to those of sand between coral patches and the reef slope with respect to taxonomic composition and feeding strategies of bivalves, but has a strong relationship to those of the fine-grained sediments when considering diversity indices. Reef slope assemblages are closely related to that of sand between coral patches in all respects, except life habits of bivalves, which distinctly separates the reef slope facies from all others.