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This story tracks the growth and history of a coastal marine scientist and his efforts to teach coastal dynamics to generations of students and public for over 50 years. It also encapsulates an incredible journey through hundreds of million years, summarizing the story of oceans and their coastal systems that helped to build our North American continent. The journey begins in the Pleistocene glacial world in northern Wisconsin, travels back to the Ordovician beach deposits of the central Mid-West and to the rocky coasts of the northern Appalachian Mountains of New England, and then travels forward to the great Cretaceous Sea in the eastern Rocky Mountain region. However, the core of this story concerns the 200 million year history of the Atlantic Ocean and formation of the southeastern US coastal margin, characterized by continental shelf, barrier island, estuarine, and riverine systems. Human occupation of this region, which began over 10 millennia ago, has recently evolved into a force capable of manipulating and changing the character and processes of modern coastal systems. The story culminates with a discussion of the “perfect conflict” between expanding human populations and the natural dynamic nature of our coasts.

Micropaleontological data provide a strong actualistic basis for detailed interpretations of Quaternary paleoenvironmental change. The 90 m-thick Quaternary record of the Albemarle Embayment in the mid-Atlantic coastal plain of the USA provides an excellent opportunity to use such an approach in a region where the details of Quaternary environmental change are poorly known. The foraminiferal record in nine cores from the northern Outer Banks, east of Albemarle Sound, North Carolina, indicates the deposition of subhorizontal, mostly open-marine early to late Pleistocene units unconformably upon a basement of late Pliocene reduced-oxygen, fine-grained, shelf-basin deposits. Pollen data record several warm–cool fluctuations within the early to mid-Pleistocene deposits. Diatom data indicate that some fresh and brackish-water units occur within the generally open-marine Pleistocene succession. A channel cut by the paleo-Roanoke River during the last glacial sea-level lowstand occurs in the northern part of the study area. Pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest Pleistocene. Overlying silts and muds accumulated under cool climatic, estuarine conditions according to diatom and pollen data. Radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest Pleistocene. The estuarine channel-fill deposits are overlain by Holocene open-marine sands deposited as the rising sea transgressed into the estuary approximately 8.5 to 9.0 kyr BP. Within the barrier island drill cores of this study, fully marine sedimentation occurred throughout the Holocene. However, immediately west of the present barrier island, mid- to late Holocene estuarine deposits underlie the modern Albemarle Sound. The islands that currently form a continuous barrier across the mouth of Albemarle Sound have a complex history of Holocene construction and destruction and large portions of them may be less than 3 kyr old. The barrier island sands overlie open-marine sands of Colington Shoal in the north and to the south overlie fluvial and marine sand filling paleo-Roanoke tributary valleys. The Pleistocene sediments underlying the northern Outer Banks study area are mainly of open inner to mid-shelf origin. If, as is likely, sea level continues to rise, a return to such environmental conditions is likely in the near future.

This study examines the Holocene stratigraphic record and paleoenvironmental evolution of a large estuarine system, at high temporal and spatial resolution, in the context of changing climate, sea level, and hydrodynamics. New data are used to examine two time periods of increased marine influence within Pamlico Sound in northeastern North Carolina interpreted to be the result of extensive barrier island segmentation synchronous with periods of rapid climate change during the late Holocene. The study reveals the controls on the stratigraphic development and the highly dynamic character of the coastal system in response to climate, and sea-level change as it interacts with paleotopography. These findings can be used to inform projections of future environmental changes. Estuarine waters occupied paleovalleys in the Pamlico Sound region as early as ca. 7500 cal BP and Pleistocene interfluves separated the paleovalleys from the Atlantic Ocean until ca. 5500 cal BP, when they were flooded by rising sealevel forming the broad, shallow Pamlico Sound. Initial barrier islands and shoals likely formed sometime between 5500 and 5000 cal BP, providing the geomorphic setting for continued estuarine conditions behind the barriers. At ca. 4000 cal BP, an increase in marine influence and sand content is detected in multiple cores, and is correlated to seismic data within the Pamlico Sound basin. This change is interpreted to be the result of increased segmentation of barrier islands (thus a greater number of inlets, or wider inlets), which is consistent with a rapid transgression seen in other areas of the U.S. east coast. The segmentation may have been partially facilitated by a rapid increase in lagoonal area and tidal prism by overtopping of interfluves. Greater barrier island continuity is evident from 3500 to 1200 cal BP, as indicated by muddy deposits with low brackish estuarine foraminiferal assemblages. At ca. 1200 cal BP, seismic, sedimentological and micropaleontological data suggest an increase in wave and current energy and marine influence throughout southeastern Pamlico Sound. These changes are interpreted to represent extensive segmentation of the barrier islands during the Medieval Climate Anomaly (MCA). Since ca. 500 cal BP, the Pamlico Sound system has returned to a more restricted state, as inlets have closed. Currently only three major inlets segment the Outer Banks, the barrier island system fronting Pamlico Sound, but warming climate and increasing rates of sea-level rise suggest that another episode of barrier island segmentation began about a half century ago and appears that it may extend into the near future.

Barrier islands and associated back-barrier estuaries and lagoons interact via hydrodynamic and sedimentary processes, affecting the evolution of both systems. Understanding coupled dynamic processes between both systems is vital to forecasts of future coastal morphologic and hydrodynamic changes in response to such factors as sea-level rise and storm patterns. The Pamlico Sound and the Outer Banks barrier islands of North Carolina, USA have co-evolved in response to Holocene climate and sea-level change, and autogenic processes. Recent data and models illustrate the dynamic response of this system to minor, but rapid, climate changes occurring throughout the Holocene, including the Medieval Climate Anomaly and Little Ice Age. Periods of extreme barrier segmentation occurred during times of rapid climate change, affecting tidal energy and salinity conditions within the Pamlico Sound. Hydrodynamic models aid in understanding the magnitude of changes, and the impact on barrier morphology. Future changes to coastal systems may be anticipated based upon changes that have occurred in the past.

We produced ∼3000-year long relative sea-level (RSL) histories for two sites in North Carolina (USA) using foraminifera preserved in new and existing cores of dated salt-marsh sediment. At Cedar Island, RSL rose by ∼2.4 m during the past ∼3000 years compared to ∼3.3 m at Roanoke Island. This spatial difference arises primarily from differential GIA that caused late Holocene RSL rise to be 0.1–0.2 mm/yr faster at Roanoke Island than at Cedar Island. However, a non-linear difference in RSL between the two study regions (particularly from ∼0 CE to ∼1250 CE) indicates that additional local- to regional-scale processes drove centennial-scale RSL change in North Carolina. Therefore, the Cedar Island and Roanoke Island records should be considered as independent of one another. Between-site differences on sub-millennial timescales cannot be adequately explained by non-stationary tides, sediment compaction, or local sediment dynamics. We propose that a period of accelerating RSL rise from ∼600 CE to 1100 CE that is present at Roanoke Island (and other sites north of Cape Hatteras at least as far as Connecticut), but absent at Cedar Island (and other sites south of Cape Hatteras at least as far as northeastern Florida) is a local-to regional-scale effect of dynamic ocean and/or atmospheric circulation.

This paper demonstrates a process-based method of graphic logging and stratigraphic interpretation that is based on a new, texturally based classification of clastic sediment which is independent from composition, cementation, and geologic environment. The method integrates facies analysis with sequence stratigraphy because it requires identifying surfaces, compiling vertical changes in texture and attributes between surfaces, and uses these parameters to identify facies units and interpret continuously deposited intervals. Four clastic shelf to shoreface successions from the Atlantic Coastal Plain Province (Cretaceous to Holocene in age) with established chronostratigraphic and sequence stratigraphic frameworks provide examples of the application of this method. For each, graphic logs standardized for texture show the facies and bounding surfaces that define the thickness and hierarchy of event strata (e.g., sequences, beds, bedsets, parasequences, parasequence sets); these are directly compared with gamma-ray log response patterns and the distribution of factors that impact potential permeability. Shelf to shoreface successions were chosen because these facies exhibit the greatest diversity in composition (siliciclastic, carbonate, and glauco-phosphatics), but, in spite of this, exhibit comparable and predictable graphic and gamma-ray response patterns if systematically logged using this method. For the process–response model examined, texture, i.e., principal grain size, controls the amplitude (width) of the graphic log; its shape is constant, and independent from composition. The pattern in the correlated gamma-ray log parallels the log of principal grain size, except that an inverse response is associated with coarser lags; the amplitude of the gamma log is controlled by composition. A proxy for permeability developed from standardized textural fields is applied to two of the examples, to shows how aquifer or reservoir potential is systematically tied to stratigraphic and sedimentologic parameters.

Lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea-level fluctuations. These successions and their timing are often poorly understood. This report defines lithofacies encountered within the north-eastern North Carolina and south-eastern Virginia Quaternary section, interprets their depositional environments, presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and Quaternary evolutionary history of the region. Data were obtained from numerous drill cores and outcrops. Chronology was based on age estimates acquired using optically stimulated luminescence, amino acid racemization, Uranium series and radiocarbon dating techniques. Geomorphic patterns were identified and interpreted using light detection and ranging imagery. Since lithofacies occurrence, distribution and stratigraphic patterns are different on interfluves than in palaeo-valleys, this study focused on interfluves to obtain a record of highstand sea-level cycles with minimal alteration by fluvial processes during subsequent lowstands. Nine primary lithofacies and four diagenetic facies were identified in outcrops and cores. The uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface. Older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle Pleistocene to present. Erosional processes associated with each successive depositional sequence removed portions of older depositional sequences. The stratigraphic record of the most recent sea-level highstands (Marine Isotope Stage 5a and Marine Isotope Stage 3) is best preserved. Glacio-isostatic adjustment has influenced depositional patterns so that deposits associated with late Quaternary sea-level highstands (Marine Isotope Stages 5c, 5a and 3), which did not reach as high as present sea-level according to equatorial eustatic records, are uplifted and emergent within the study area.

Proposed here is a universally applicable, texturally based classification of clastic sediment that is independent from composition, cementation, and geologic environment, is closely allied to process sedimentology, and applies to all compartments in the source-to-sink system. The classification is contingent on defining the term “clastic” so that it is independent from composition or origin and includes any particles or grains that are subject to erosion, transportation, and deposition. Modifications to Folk’s (1980) texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this. The revised ternary diagrams include additional textural fields that better define poorly sorted and coarse-grained deposits, so that all end members (gravel, sand, and mud size fractions) are included in textural codes. Revised textural fields, or classes, are based on a strict adherence to volumetric estimates of percentages of gravel, sand, and mud size grain populations, which by definition must sum to 100%. The new classification ensures that descriptors are applied consistently to all end members in the ternary diagram (gravel, sand, and mud) according to several rules, and that none of the end members are ignored. These modifications provide bases for standardizing vertical displays of texture in graphic logs, lithofacies codes, and their derivatives—hydrofacies. Hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential. Folk’s (1980) ternary diagram for fine-grained clastic sediments (sand, silt, and clay size fractions) is also revised to preserve consistency with the revised diagram for gravel, sand, and mud. Standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences, such as mixed carbonate–siliciclastic ramp settings, and the extreme ends of depositional systems.

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000 yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500 cal yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting.

Nearly 200 km of high-resolution ground penetrating radar (GPR) data were acquired along the Outer Banks barrier island system of North Carolina, USA. GPR data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel, flood-tide delta, overwash, peat and inner shelf. Previously undocumented paleo-inlet channels constitute a significant portion of the shallow geologic framework between Oregon Inlet and Cape Hatteras. GPR data reveal the complex stratigraphy associated with multiple sequences of cut-and-fill within inlet channels. Two types of paleochannels (non-migrating and migrating) were classified based on geometry and fill-patterns. Sediments and foraminifera collected from vibracores were correlated to GPR data to define the regional shallow stratigraphic framework. Channel-fill facies are characterized by clinoform packages, sometimes bounded by erosional surfaces, indicating variable sediment transport directions from the ocean and sound sides. Channels are incised into older flood-tide delta deposits corresponding to older inlet activity when barriers existed further seaward. Flood-tide delta deposits are capped with marsh peat and overwash units. Migrating inlet facies occur under the widest portions of the island, whereas narrow portions of the island are underlain by the non-migrating inlet facies or flood-tide delta/overwash facies. This geologic/geomorphic relationship is attributed to the successional stage of island evolution during transgression, and sediment transport processes associated with the different inlet types. The radar facies, lithofacies, and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record.

Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 20–40 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 45–70 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system.

We have synthesized new and existing relative sea-level (RSL) data to produce a quality-controlled, spatially comprehensive database from the North Carolina coastline. The RSL database consists of 54 sea-level index points that are quantitatively related to an appropriate tide level and assigned an error estimate, and a further 33 limiting dates that confine the maximum and minimum elevations of RSL. The temporal distribution of the index points is very uneven with only five index points older than 4000 cal a BP, but the form of the Holocene sea-level trend is constrained by both terrestrial and marine limiting dates. The data illustrate RSL rapidly rising during the early and mid Holocene from an observed elevation of −35.7 ± 1.1 m MSL at 11062–10576 cal a BP to −4.2 m ± 0.4 m MSL at 4240–3592 cal a BP. We restricted comparisons between observations and predictions from the ICE-5G(VM2) with rotational feedback Glacial Isostatic Adjustment (GIA) model to the Late Holocene RSL (last 4000 cal a BP) because of the wealth of sea-level data during this time interval. The ICE-5G(VM2) model predicts significant spatial variations in RSL across North Carolina, thus we subdivided the observations into two regions. The model forecasts an increase in the rate of sea-level rise in Region 1 (Albemarle, Currituck, Roanoke, Croatan, and northern Pamlico sounds) compared to Region 2 (southern Pamlico, Core and Bogue sounds, and farther south to Wilmington). The observations show Late Holocene sea-level rising at 1.14 ± 0.03 mm year −1 and 0.82 ± 0.02 mm year −1 in Regions 1 and 2, respectively. The ICE-5G(VM2) predictions capture the general temporal trend of the observations, although there is an apparent misfit for index points older than 2000 cal a BP. It is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid-Carolina Platform High or a flaw in the GIA model. A comparison of local tide gauge data with the Late Holocene RSL trends from Regions 1 and 2 support the spatial variation in RSL across North Carolina, and imply an additional increase of mean sea level of greater than 2 mm year −1 during the latter half of the 20th century; this is in general agreement with historical tide gauge and satellite altimetry data.

Coastal areas are among the world's most vulnerable landscapes to impacts related to climate change, including inundation from sea-level rise (SLR), increased exposure to shoreline erosion, and greater frequency and intensity of storms. The status of research on the physical, ecological, and socio-economic effects of vulnerability to SLR and progress toward planning for its consequences varies from region to region worldwide. Here, we synthesize the results of three decades of SLR research and the development of coastal management policies in North Carolina, USA. We identify the major factors responsible for opening new policy ‘windows’ that address SLR, including how stakeholders have developed an increased understanding of the risks, the extent of public dialogue about potential response strategies, and advances in political receptivity to policy change. Research and policy progress in North Carolina continue to provide a model for other regions to help guide and evaluate the development of coastal policies.

A comparison of two sections of the Outer Banks, North Carolina, USA (Pea Island and Avon-Buxton areas), reveals the importance of the interplay between oceanic and estuarine shoreline dynamics to long-term changes in barrier island width. From 1852 to 1998, the northern portion of Pea Island experienced an average net increase in width of 431 m (3 m/y); this area experienced low to moderate rates of oceanic shoreline erosion and high rates of back-barrier land accretion via overwash and formation of flood tidal delta islands. In contrast, between 1852 and 1998, the width of the southern portion of Pea Island and the Avon-Buxton area decreased an average of 515 m (4 m/y) and 594 m (4 m/y), respectively, because of high rates of oceanic shoreline erosion and variable changes in estuarine shoreline accretion and erosion. Net gain or net loss of barrier island width is strongly dependent on the natural depositional processes of overwash and flood tide delta formation. Anthropogenic modifications to ...

A detailed record of late Quaternary sea-level oscillations is preserved within the upper 45 m of deposits along an eight km transect across Croatan Sound, a drowned tributary of the Roanoke/Albemarle drainage system, northeastern North Carolina. Drill-hole and seismic data reveal nine relatively complete sequences filling an antecedent valley comprised of discontinuous middle and early Pleistocene deposits. On interfluves, lithologically similar marine deposits of different sequences occur stacked in vertical succession and separated by ravinement surfaces. Within the paleo-drainage, marine deposits are separated by fluvial and/or estuarine sediments deposited during periods of lowered sea level. Foraminiferal and molluscan fossil assemblages indicate that marine facies were deposited in a shallow-marine embayment with open connection to shelf waters. Each sequence modifies or truncates portions of the preceding sequence or sequences. Sequence boundaries are the product of a combination of fluvial, estuarine, and marine erosional processes. Stratigraphic and age analyses constrain the ages of sequences to late Marine Isotope Stage (MIS) 6 and younger (∼ 140 ka to present), indicating multiple sea-level oscillations during this interval. Elevations of highstand deposits associated with late MIS 5 and MIS 3 imply that sea level was either similar to present during those times, or that the region may have been influenced by glacio-isostatic uplift and subsidence.

A numerical model was used to simulate water levels, currents, waves, suspended sediment and salinity distributions in Pamlico Sound, a large and shallow back-barrier estuary in eastern North Carolina, for four distinct time slices during its geomorphic evolution over the late Holocene. Present-day bathymetry was obtained from a high resolution digital elevation model of Pamlico Sound, and paleobathymetric model grids were created for 500, 1000 and 4000 calibrated years before present (cal yr BP) using age-depth relationships developed from sediment core and time-constrained seismic observations. Hydrodynamic and sediment model results for a one-month simulation at the 0 and 4000 cal yr BP time slices are compared to assess the impacts of varying degrees of barrier island segmentation, long-term changes in basin geomorphology, and sea-level rise on the flow and transport response in Pamlico Sound.

Since the mid 1990s, the Atlantic and Gulf Coast regions have experienced a dramatic increase in the number of hurricane landfalls. In eastern North Carolina alone, eight hurricanes have affected the coast in the past 9 years. These storms have exhibited individualistic hydrologic, nutrient, and sediment loading effects and represent a formidable challenge to nutrient management aimed at reducing eutrophication in the Pamlico Sound and its estuarine tributaries. Different rainfall amounts among hurricanes lead to variable freshwater and nutrient discharge and variable nutrient, organic matter, and sediment enrichment. These enrichments differentially affected physical and chemical properties (salinity, water residence time, transparency, stratification, dissolved oxygen), phytoplankton primary production, and phytoplankton community composition. Contrasting ecological responses were accompanied by changes in nutrient and oxygen cycling, habitat, and higher trophic levels, including different direct effects on fish populations. Floodwaters from the two largest hurricanes, Fran (1996) and Floyd (1999), exerted multi-month to multi-annual effects on hydrology, nutrient loads, productivity, and biotic composition. Relatively low rainfall coastal hurricanes like Isabel (2003) and Ophelia (2005) caused strong vertical mixing and storm surges, but relatively minor hydrologic and nutrient effects. Both hydrologic loading and wind forcing are important drivers and must be integrated with nutrient loading in assessing short-term and long-term ecological effects of these storms. These climatic forcings cannot be managed but should be considered in the development of water quality management strategies for these and other large estuarine ecosystems faced with increasing frequencies and intensities of hurricane activity.

Foraminiferal and sedimentary data, supplemented with geochemical dating and ground-penetrating radar transects, show that the barrier island at Pea Island National Wildlife Refuge just north of Rodanthe, North Carolina, has been dominated by a combination of inlet and overwash processes for at least 1000 years. The stratigraphic record of several vibracores does not preserve every, or even many, overwash events but, instead, is characterized by three to four fining-upward sequences. The last three commence with overwash sand or gravel that is overlain by a variety of finer-grained estuarine, inlet, and marsh deposits. The dynamic nature of this segment of the Outer Banks was muted in the late 1930s by construction of artificial barrier dune ridges, extensive planting of grass and shrubs, and construction of Highway 12 in 1953. Subsequently, the road and barrier dune ridge were rebuilt and relocated several times following storm events.

Ground penetrating radar studies of four representative active back-barrier dunes, combined with radiocarbon and photon-stimulated-luminescence dating techniques and soils analysis, reveal phases of alternating dune activity and stabilization along the North Carolina–Virginia coast. Two smaller dunes represent only the current phase of dune activity. Two larger dunes preserve evidence of three phases of dune development (ca. 740, 1260 and 1810 AD) and intervening phases of soil development. Climate, particularly moisture conditions, played a part in the timing of dune activity and stabilization events. All three dune phases are associated with drier conditions whereas soils formation is associated with humid conditions. Modern (phase 3) dunes are more widespread along the coast and their formation is attributed to a combination of dry conditions, increased storminess associated with the Little Ice Age, and rising sea level. Tidal inlet closing and storm overwash processes likely provided sediment...

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/m2/yr on the vertical and sloped Miocene mudstone hardbottoms, to 0.4 kg/m2/yr on vertical and sloped Pleistocene limestone, to 0.03 kg/m2/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.

The North Carolina mid-continental shelf is characterized by a complex sequence of rock suostrates, 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 scale with potentially important ecological consequences.

The Nd isotopic composition of Atlantic and Tethys seawater, as deduced from marine phosphorites, varied considerably during the past 180 Ma. The early Tethys and Central Atlantic seawater from 180 to 160 Ma ago (Early-Middle Jurassic) had a Nd isotopic signature identical to that of the Pacific (eNd ≈ −6) suggesting that Pacific seawater entered the newly forming Tethys basin. However, with time continental runoff draining into the young basin became more important and led to a decrease in the Nd isotopic composition and, finally, a decoupling from the Pacific Ocean. During the late Early Cretaceous (120-90 Ma ago) Atlantic and Tethys seawater reached continental crust-like Nd isotopic composition values (eNd ≈ −10) which could reflect high weathering rates induced by the warm and humid climate at that time. In the time span between 80 and 50 Ma (Late Cretaceous-Early Tertiary) the Nd isotopic composition of both Tethys and Atlantic seawater strongly increased towards Pacific seawater values. In the case of the Atlantic Ocean, this change has been correlated with the opening of the South Atlantic, which enabled the more radiogenic Pacific seawater to travel westwards around the southern edge of Africa into the South and finally the North Atlantic. In the case of Tethys seawater we have to assume that, during this period, large masses of Pacific seawater entered the Tethys again directly through the Indian-Tethys seaway. The renewed importance of this seaway might be related to the Late Cretaceous-Early Tertiary first-order, global sea level highstand. The most abrupt change towards lower, more crust-like values occurred in the early Miocene (25-17 Ma ago) in the South and North Atlantic, as well as in the Tethys. During this period, the143Nd/144Nd isotope ratios dropped from ≈ 0.5124 (eNd ≈ −4.2) down to ≈ 0.5122 (eNd ≈ −8). This change indicates a diminishing influx of Pacif seawater into the Atlantic and Tethys Oceans and can be correlated with the breakdown of the circum-equatorial circulation patterns of the world oceans, due to plate tectonics. From 20 to 17 Ma ago (Miocene) the Nd isotopic composition of the Atlantic Ocean increased again and reached values as high as 0.5123 (eNd ≈ −6.6), whereas Tethys seawater remained at low values. This decoupling can be correlated with the incipient complete isolation of the Tethys; the Nd isotopic composition was henceforth controlled by the continental runoff from surrounding land masses. The major increase in the Nd isotopic composition observed in the Atlantic can be related to the opening of the Drake Passage and establishment of the circum-Antarctic current system. This allowed Pacific seawater to enter directly the South Atlantic around Antarctica. A renewed drop in the Nd isotopic composition of Atlantic seawater during the late Miocene can be related to the onset of North Atlantic Bottom Water formation and its subsequent upwelling.

Episodic events have been shown to strongly affect structure and function of marine benthic ecosystems. Severe storms can have profound effects on the distribution of marine sediments which could, in turn, influence the development of benthic communities. The rich and diverse epibenthic communities on the United States mid-Atlantic continental shelf owe their existence to the presence of a complex sequence of rocky outcrops. An unusually strong storm struck this shelf system in March 1993. Two of these carbonate platforms had been characterized by moderate sediment cover for at least the previous two years, but bottom water velocities generated by this storm removed considerable amounts of sediment from these upper flat hardbottom habitats. Macroalgal cover on these platforms dramatically increased between 1992 and 1993 with the increased exposure of hard substrate for attachment. The edges of the outcrops (scarps and rubble ramps), which are usually free of sediment, maintained their dense algal cover. Settlement blocks placed in various sub-habitats showed little variation in algal cover among flat hardbottom and scarp areas during both years, indicating that available hard substrate habitat may be the primary limiting factor for algal growth on the North Carolina continental shelf. Since macroalgal meadows provide food and shelter for juvenile fish, the increase in critical habitat following these storms may have implications for recruitment of economically important fish species. Thus, indirect effects of episodic storms, i.e., redistribution of sand bodies leading to algal meadow development over large spatial scales, may have important consequences for benthic community development and persistence in temperate reef systems.

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.

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.

Four phosphate grain types and associated foraminifera were analyzed for their 87Sr/86Sr ratios to test the hypothesis that different authigenic grain types have specific times and processes of formation in response to changing conditions during one sea-level transgression. The samples were collected from one phosphate-rich depositional sequence (FPS-1) of the Miocene Pungo River Formation in Onslow Bay, North Carolina continental shelf. The hand-picked grains were from three cores representing upsection changes from lowstand, to transgressive, and highstand systems tracts. The phosphate grain types carried significantly different strontium isotopic signatures and included the following: peloidal grains (spherical to oval, highly rounded and polished grains with inor inclusions and common coatings), intraclastic grains (irregular-shaped rip-up grains from preexisting crusts and nodules), microsphorite (laminated crusts and bored hardgrounds associated with unconformities and containing common inclusions), and skeletal grains (formed directly by organisms). Four different phosphate skeletal grains were analyzed (brachiopods, vertebrae, teeth, and bone splinters); however, the results were not significantly different and therefore they were all included as one grain type. Analyses of phosphate grain types and associated foraminifera support the interpretation that they formed in response to specific chemical and physical processes and at different times during phosphogenesis, as follows. (1) Peloids cluster tightly and have Sr isotope ages contemporaneous with the associated foraminifera. They are interpreted to represent the time of phosphogenesis and primary sedimentation during early- to mid-stage transgression. (2) Intraclasts are significantly older than other associated phosphate grain types with Sr isotope ages similar to the microsphorites. They are interpreted to have formed as microsphorite on unconformity surfaces during the lowstand, were ripped up from these surfaces during the subsequent transgression, and reworked into the overlying sedi ent sequence. (3) Skeletal grains have quite variable Sr isotope ages, but in general they are younger than the other phosphate grain types. Most skeletal grains are interpreted to be contemporaneous with the peloids and foraminifera. However, their younger ages are interpreted to be in response to secondary geochemical processes associated with (a) recrystallization from carbonate hydroxyapatite to carbonate fluorapatite and (b) subsequent precipitation of apatite in the pore spaces characteristic of porous vertebrate skeletal material. Some skeletal material is older and probably has been reworked from the underlying unconformity surfaces.

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 flat-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 rimary 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.

Clay-size mineral assemblages from lithologically diverse Miocene shelf and upper-slope sediments of the North Carolina continental margin show strong environmental zonation. Three distinct clay-mineral suites are recognized in the Miocene sediments of the Pungo River Formation. (1) A detrital kaolinite suite was deposited proximal to siliciclastic point sources in muddy quartz sand lithofacies. This assemblage reflects intense chemical weathering on the adjacent Coastal Plain and Piedmont Provinces. (2) A detrital illite and smectite suite deposited in phosphatic lithofacies is distinguishable from the clay mineralogy of muddy (distal) terrigenous and biogenic-dominated lithofacies only because illite is more highly crystalline. (3) Lithofacies characterized by authigenic dolomite co tain a clay-mineral suite with palygorskite and sepiolite. These Mg-clay minerals formed authigenically in the upper decimeters of sediment, penecontemporaneously with dolomitization, and in association with diatom dissolution, which provided the silica source for neoformation. Clay-mineral assemblages have not been significantly altered by burial or late-stage diagenesis and therefore appear to be "original signal" depositional indicators of changing environmental conditions through major Miocene fluctuations in sea level. The kaolinite suite is present in a fourth-order cycle immediately preceding the sea-level lowstand. Palygorskite and sepiolite are restricted to organic-rich dolomitic sediments, deposited under highly dysaerobic bottom conditions associated with the highstand and formation of the condensed section.