Woods Hole Coastal and Marine Science Center


Abstracts


The North Carolina Coastal Geology Cooperative-a Model of Federal, State, and Academic Cooperation
Hoffman, C W
bill.hoffman@ncmail.net
N.C. Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States
Thieler, E R
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
Riggs, S R
East Carolina Univ., Dept. of Geology, Greenville, NC 27858 United States
Schwab, W C
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States


In June 1999, The U.S. and N.C. Geological Surveys hosted a meeting of coastal geologists and engineers to identify coastal geological issues of greatest importance to North Carolina and to explore the possibility of initiating a cooperative research program to address these issues. Several factors came together to allow a coordinated program to develop: keen state interest in coastal hazards following several significant hurricanes, interest on the part of the USGS in combining work in North Carolina with a similar program in South Carolina, and recognition of the strong knowledge base that existed within the coastal scientific community in N.C. The meeting resulted in a strong consensus for comprehensive study of the entire coastal system and for initiating work in the northern coastal region (the Quaternary section east of the Suffolk Scarp, focusing on the barrier-island and estuarine system). Among the most important issues to be addressed by the data and knowledge developed from this program are: coastal and estuarine shoreline erosion (controls on erosion rates, sediment transport, response of wetlands to sea level rise); sand resources (location, quality, and quantity of offshore, estuarine, or onshore sand); storm impacts (barrier island/inlet migration, estuarine water movement, relative stability of barrier island segments); sea level change (history and potential impacts); water resources (surface and groundwater); habitat (ability to sustain uses, trends, threats). The cooperative will provide a strong science foundation for management of the N.C. coastal zone. Endorsements, support, and cooperation have come from the N.C. Coastal Resources Commission, several state and federal resource agencies, and local government units who all have an interest in information the program is producing. Supplemental federal appropriations have resulted from such support and the National Park Service has provided partnership funding. Additional partnership opportunities exist and are being pursued with the Army Corps of Engineers (two feasibility studies are active in the project area), the N.C. Outer Banks Task Force, and U.S. Minerals Management Service.

OS52F-05
Neogene Seismic Stratigraphic Framework and Fill History of the Northeastern Albemarle Embayment, North Carolina
* Mallinson, D J
mallinsond@mail.ecu.edu
East Carolina University, Department of Geology, Greenville, NC 27858 United States
Riggs, S R
riggss@mail.ecu.edu
East Carolina University, Department of Geology, Greenville, NC 27858 United States
Thieler, R
rthieler@usgs.gov
United States Geological Survey, Coastal and Marine Geology Program 384 Woods Hole Road, Woods Hole, MA 02543 United States
Culver, S J
culvers@mail.ecu.edu
East Carolina University, Department of Geology, Greenville, NC 27858 United States
Corbett, D R
East Carolina University, Department of Geology, Greenville, NC 27858 United States
Hoffman, C W
bill.hoffman@ncmail.net
North Carolina Geological Survey, Coastal Plain Office 1620 Mail Service Center, Raleigh, NC 27699 United States
Wehmiller, J
jwehm@udel.edu
University of Delaware, Department of Geology, Newark, DE 19716 United States
Foster, D S
dfoster@usgs.gov
United States Geological Survey, Coastal and Marine Geology Program 384 Woods Hole Road, Woods Hole, MA 02543 United States


Seismic and chirp sonar surveys were conducted in the eastern Albemarle Sound and adjacent tributaries and the inner continental shelf to define the geologic framework and evolution of the North Carolina coastal system. Surveys were utilized to target paleofluvial channels for drilling and core recovery for the assessment of sea level and climate change during the Quaternary. Lithostratigraphic and chronostratigraphic data are derived from eight drill sites on the Outer Banks, and the Mobil #1 well in the eastern Albemarle Sound. Within the study area, parallel-bedded, gently dipping Miocene beds occur at 100 to >180 mbsl, and are overlain by a southward-thickening Pliocene unit characterized by steeply inclined southward-prograding beds. The Quaternary section unconformably overlies the Pliocene unit, and consists of at least five depositional sequences exhibiting numerous incised channel-fill facies. The Quaternary section is 55 to 60 meters thick. Shallow stratigraphy (0-50 mbsl) is dominated by complex fill-stratigraphy within the incised paleo-Roanoke River valley. Radiocarbon and amino acid racemization (AAR) dates indicate that the valley-fill is late Pleistocene to Holocene in age. At least 6 distinct valley-fill units are identified in the seismic data based upon reflection geometry. Cores reveal a 3 to 6 meter thick basal fluvial channel lag that is overlain by a 15-meter thick unit of interbedded freshwater muds and sands. Organic materials within the freshwater deposits have ages of 13-11 cal. ka, and are overlain by several units comprised of shallow marine sediments. Shallow marine sediments within the valley are silty, fine- to medium-grained sands containing abundant neritic forams, suggesting that this area was an open embayment during much of the Holocene. Seismic data reveal that initial infilling occurred from the north and west during the late Pleistocene and early Holocene. Later infilling occurred from the east and is characterized by a large shoal body (Colington Island and Shoals; radiocarbon dated to 8.6 cal. ka) and adjacent inlet fill. Establishment of a continuous barrier island system resulted in the deposition of a final phase of fill characterized by estuarine organic-rich muds.
URL: http://core.ecu.edu/geology/RIGGS/ECU_USGS/Chirp.html

OS52F-08
Linking Geologic Framework to Nearshore Processes and Shoreline Change: Results from the Outer Banks of North Carolina
* McNinch, J E
mcninch@vims.edu
Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062 United States
Miselis, J L
jmiselis@vims.edu
Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062 United States
Schupp, C A
cschupp@vims.edu
Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062 United States


Within the coastal geology community, a consensus appears to have developed that the geologic framework of the inner-shelf plays an important role in shoreline change. It has yet to be determined, however, whether geology exerts a first-order control on shoreline dynamics and, if so, across what time and spatial scales. Furthermore, principal mechanisms that may link underlying geology and shoreline behavior remain poorly understood and untested. To this end, an extensive survey of the seafloor surface and shallow sub-bottom utilizing an interferometric swath bathymetry sonar system and a chirp sub-bottom profiler mounted on an amphibious vessel was conducted across the surf zone of the Outer Banks of North Carolina. Recent findings from a small region near Duck, North Carolina suggest a connection between partial exposure of pre-modern, non-sandy substrates in the surf zone and bar morphodynamics leading to the repeated occurrence of shoreline hotspots. Support from the US Geological Survey, US Army Corps of Engineers, and the Army Research Office has expanded this work to include a 40 km length of surf zone extending from Duck to Nags Head, North Carolina. Preliminary results from the larger survey are consistent with earlier findings at Duck which show: 1) an underlying ravinement surface with very irregular relief across the surf zone; 2) a thin cover of modern sand, ranging from 0 to a maximum of 2.5 m thick, with a surface morphology that does not necessarily mirror the underlying topography; 3) the presence of large transverse bars located beside exposures of non-sandy substrate; and 4) a spatial correlation between hotspots and regions with exposed non-sandy substrates and transverse bars in the surf zone. Future work will examine shoreline behavior and bar morphodynamics associated with the geologic framework of the nearshore over event and seasonal time scales. These observations will be designed to provide insight into the processes responsible for hotspot formation and to identify key geologic variables that could be incorporated into, and ultimately, improve shoreline evolution models.


Geophysical Surveys of the Northern North Carolina Inner Continental Shelf Show Geologic Framework, Modern Sediment Distribution and Sediment Transport Patterns
* Thieler, E R
rthieler@usgs.gov
USGS, 384 Woods Hole Rd., Woods Hole, MA 02543-1598 United States
Foster, D S
dfoster@usgs.gov
USGS, 384 Woods Hole Rd., Woods Hole, MA 02543-1598 United States
Hammar-Klose, E S
ehammark@usgs.gov
USGS, 384 Woods Hole Rd., Woods Hole, MA 02543-1598 United States
Roberts, C S
csroberts@usgs.gov
USGS, 384 Woods Hole Rd., Woods Hole, MA 02543-1598 United States
Polloni, C F
cpolloni@usgs.gov
USGS, 384 Woods Hole Rd., Woods Hole, MA 02543-1598 United States

We have recently mapped the inner continental shelf off the northern Outer Banks of North Carolina using sidescan sonar, interferometric swath bathymetry, and high-resolution CHIRP and boomer subbottom profiling systems. The study area is approximately 170 km long by 11 km wide, extending from False Cape, VA to Cape Hatteras, NC, in water depths ranging from 7 m (mid-shoreface) to 34 m (inner shelf). Late Pleistocene stratigraphic units provide the basic, shallow geologic framework of this region. Regional to local-scale variations in the geometry and lithology of these units dictate the character of sediments on the sea floor as shown by sidescan sonar imagery. For example, areas of high acoustic backscatter typically correspond to coarse-grained, fluvial and marine sediments representing several Pleistocene units that crop out on the sea floor. The distribution of Recent sediment (above the Holocene ravinement surface) on the shoreface and inner shelf suggests that sediment availability is controlled by the underlying geologic framework, which influences the geomorphology of the overall barrier island system. For example, sediment-rich coastal segments have wide, accretionary barriers dominated by beach ridges; sediment-starved coastal segments have narrow, washover-dominated barriers. The large shoal complexes in the study area, False Cape, Platt, Wimble and Kinnakeet, are composed of both underlying indurated sediments and mobile sand bodies. Historical bathymetric comparisons indicate that large volumes of sediment in these complexes are moving hundreds of meters in tens of years. Sediment transport patterns inferred from the analysis of modern bedforms suggest that the inherited paleo-topography of the present sea floor may exert a primary influence on near-bottom currents and thus sediment transport pathways. When viewed in a larger context with other studies of this area, it appears that inner shelf geology and the regional coastal sediment budget are coupled in complex but understandable ways over time scales ranging from storm events to millennia.

OS71B-0278
The Relationship Between Shoreline Change and Surf Zone Sand Thickness
* Miselis, J L
jmiselis@vims.edu
Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062-1346 United States
McNinch, J E
mcninch@vims.edu
Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062-1346 United States


There is a lack of information concerning surf zone geologic processes and their relationship to shoreline behavior despite the consensus that the two are intimately linked. Variations in sand thickness over a highly irregular migration surface close to the shoreline may influence wave dynamics and sediment transport and thus may be connected to hotspot formation. A nearshore survey, spanning 40km from north of the USACE-FRF pier in Duck, NC to just north of Oregon Inlet, was conducted using an interferometric swath bathymetry system and a chirp sub-bottom profiler. The study was conducted within 1km of the shore (in the surf zone) to investigate the processes that may be responsible for the behavior of shoreline hotspots in the area. The topmost reflector and the seafloor of the seismic profile were digitized and the depth difference between them was calculated. Though no ground truths were done in the survey area, cores collected from just north of the site suggest that the topmost reflector is a pre-modern ravinement surface (cohesive muds with layers of sand and gravel) upon which the Holocene sands migrate. An isopach map was generated and shows that the layer of sand above the first sub-bottom reflector is very thin and in some places, exposed. There are many variables that may influence hotspot behavior, including bar position and wave conditions, however, the purpose of this study is to determine if there is a spatial correlation between a thin or absent (exposed reflector) nearshore sand layer and the presence of a shoreline hotspot. In an area associated with a hotspot approximately 14km south of the USACE-FRF pier in Duck, the maximum thickness of Holocene sands was less than 2.5m. The average thickness was less than 1m (0.705m). Thicknesses that were less than 0.2m were classified as areas where the reflector was exposed and accounted for 5 percent of those calculated. It seems the thin layer of sand may represent a deficient nearshore sand source, which may perpetuate erosion in the area. Also, the interaction of waves with both a sand-starved nearshore and exposed reflectors may cause variations in sediment transport, which may be linked to hotspot formation. Research was conducted with the support of the USGS, USACE, and ARO.

OS71B-0280
Evaluating the Persistence of Shoreline Change Hotspots, Northern North Carolina
* List, J H
jlist@usgs.gov
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02536 United States
Farris, A S
afarris@usgs.gov
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02536 United States
Sullivan, C
csullivan@usgs.gov
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02536 United States

Shoreline change hotspots are sections of coast that exhibit significantly higher rates of erosion than adjacent areas. Although hotspots may occur at a wide range of spatial and temporal scales, we consider two distinct types of hotspots that have been observed on high-energy coasts away from the influence of coastal structures: 1. hotspots related to individual storms, with an alongshore spatial scale of 2-5 km and the characteristic of being almost completely reversed by accretion within 1-2 weeks of calm conditions following the storm, and referred to here as short-term reversible hotspots, and 2. hotspots related to the long-term trend of shoreline change on a time scale of decades, with a similar spatial scale as short-term hotspots but not readily reversible during fair weather, and referred to here as long-term hotspots. Here we evaluate these hotspot types with respect to their persistence, i.e., the degree to which hotspot locations remain fixed through time. Relevant to this session, hotspots that are spatially fixed and/or recurring are more consistent with hypotheses relating hotspot formation to geologic framework controls than hotspots with variable or moving locations. Observations consist of a recently-completed three-year time series of monthly shoreline position measurements along 130 km of North Carolina's Outer Banks using SWASH, a ground-based system for surveying regional shoreline position as the mean high water datum's intersection with the beach foreshore. We identify short-term reversible hotspots through the comparison of pre-, mid-, and post-storm shoreline surveys. The pre- to mid-storm comparison typically exhibits 2-5 km wide regions of significant shoreline erosion (10-20 m) alternating with areas of little change. The mid- to post-storm accretion appears as a mirror image of the erosion pattern, almost completely reversing the storm erosion. We identify long-term hotspots through a comparison between our three-year SWASH time series and a three-year series of beach profiles surveyed by the U.S. Army Corps of Engineers in the 1970's. We find the mean shoreline position for each series through time-averaging, greatly reducing the variance due to short-term reversible hotspots and other sources of shoreline position variability. We then find shoreline change as the difference between the two series' mean shorelines, with shoreline change significance estimated with a standard t-test. Observations show that short-term reversible hotspots have both fixed and changing locations. Some hotspots repeatedly occur at fixed locations through multiple storms, while others occur only once, with the hotspot/coldspot pattern completely reorganized from one storm to the next. At a broader spatial scale (10's of km), there are zones where hotspots typically occur (with or without fixed locations for individual hotspots), while in other zones we have never observed hotspots during our three years of observations. Long-term hotspots also have both fixed and non-fixed characteristics, although the paucity of data relevant to this temporal scale make conclusions difficult. However, a preliminary comparison between our long-term change results (found as described above), and shoreline change results previously published by the State of North Carolina for a 50-year period ending in 1992, suggests that while the overall patterns of shoreline change (hotspots and coldspots) have remained the same, there is also some evidence for the along-coast migration of several of the most significant erosional hotspots.

OS71B-0282
Sedimentologic and Stratigraphic Aspects of Late Quaternary (<14 cal. ka?) Valley Fill (Paleo-Roanoke River) Beneath the Barrier Islands of the Outer Banks, North Carolina, USA
* Farrell, K M
Kathleen.Farrell@ncmail.net
North Carolina Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699-1620 United States
Brooks, R W
Bob.Brooks@ncmail.net
North Carolina Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699-1620 United States

Provided here is a preliminary interpretation of the late Pleistocene (<14 cal. ka) facies succession that infilled the paleo-Roanoke River valley, and its transition into the overlying barrier island complex beneath the Outer Banks of North Carolina. Previous work (e.g. Riggs and others, 1992) reported that the Albemarle Embayment of eastern N.C. is underlain by a series of Pleistocene paleovalley complexes and provided hypotheses to test regarding valley distribution, sea level changes, and the ages of facies and sequences generated in response to coastal evolution. This report provides stratigraphic and sedimentologic criteria to support collaborative interpretations of eight cores acquired by a coastal geology cooperative research program on the Outer Banks to test these hypotheses. In cores OBX-02, 03, and 05, the late Quaternary (<14 cal. ka) fill is about 41 m thick. Here it erosionally overlies a bioturbated marine shelf deposit (OBX-2, 3, 5) that Wehmiller (personal communication) correlated (at OBX-05, depth -41 m) with the early/middle Pleistocene aminozone, AZ-4 (see Riggs and others, 1992). Above this, the late Quaternary fill (in cores OBX-02, 03, 05, 06) includes a succession of four facies units: 1) a basal sandy gravel (<6 m), 2) a dark gray complexly interbedded mud and gravel (<9 m), 3) bioturbated muddy sand (<15 m), and 4) an upward fining sand, with a basal gravel (<15 m). (Dimensional aspects of these units remain undefined until integration with GPR and seismic profiles). Six radiocarbon dates (from Thieler, personal communication) on samples from unit 2 (OBX-05: from -32.3, -33.6 and -35 m; OBX-02: from -27.7, -33.0, and -33.0 m) fall within the range 10 to 14 cal. ka. These were deposited during the Younger Dryas (Mallinson and others, Thieler, personal communications). Stratigraphic relations suggest that unit 1, although not dated, was deposited at the onset of this phase of global cooling. Unit 1, interpreted as fluvial thalweg and channel bar deposits, fines upward into unit 2. Unit 2 includes deltaic like features such as laminations, wavy, flaser and lenticular bedding, coarse lags with gravel, detrital organics, chaotic bedding, and slump blocks. It was deposited subaqueously with no evidence of subaerial exposure in a non-marine setting. The interbedding of high-energy lags and suspension deposits in unit 2 suggests that periods of intense flooding alternated with standing water deposition. Units 3 and 4 are Holocene. Unit 3 appears to either coarsen upward from a basal interbedded zone with unit 2 (OBX-02, 05), or is a sharp-based upward fining unit (OBX-03). It has common {it Ophiomorpha} and {it Thalassinoides} burrows (OBX-02, 03, 05, 06), traces of parallel laminations (OBX-02, 03, 06), and zones of mud intraclasts (OBX-05 only). Unit 3 formed as accretionary shoreface deposits that laterally infilled the embayment during the Holocene transgression. The contact at the base of unit 3 is a significant flooding surface. Unit 4 represents a complex of inlet, shoreface and regressive beach ridge deposits.

OS71B-0284
Quaternary Sea-level Fluctuations and Environmental Change Indicated by Foraminiferal Assemblages, Outer Banks, North Carolina
Culver, S J
culvers@mail.ecu.edu
East Carolina University, Department of Geology East Carolina University , Greenville, NC 27858 United States
* Riggs, S R
riggss@mail.ecu.edu
East Carolina University, Department of Geology East Carolina University , Greenville, NC 27858 United States
Thieler, R E
rthieler@usgs.gov
US Geological Survey , US Geological Survey 384 Woods Hole Road, Woods Hole, MA 02543 United States
Wehmiller, J F
jwehm@udel.edu
University of Delaware, Department of Geology University of Delaware, Newark, DE 19716 United States
Snyder, S W
snyders@mail.ecu.edu
East Carolina University, Department of Geology East Carolina University , Greenville, NC 27858 United States
Mallinson, D A
mallinsond@mail.ecu.edu
East Carolina University, Department of Geology East Carolina University , Greenville, NC 27858 United States
Bratton, J
jbratton@usgs.gov
US Geological Survey , US Geological Survey 384 Woods Hole Road, Woods Hole, MA 02543 United States


A 155-ft. drillcore at the site of a former inlet penetrates several Quaternary depositional sequences previously recognized in seismic records and shorter cores. Several foraminiferal assemblages from the early Pleistocene to the Recent reflect changing environmental conditions that correspond to several high frequency sea-level fluctuations previously described for this region. At the base of the core, low energy, low oxygen, open embayment mud, containing a high diversity fauna dominated by {it Elphidium excavatum} and buliminids (Assemblage 6), and of probable early to mid-Pleistocene age, is overlain at 128 ft by inner to mid shelf, high energy sand containing a high diversity assemblage dominated by {it E. excavatum}, {it Epistominella} sp. and the epifaunal taxon {it Cibicides refulgens} (Assemblage 5). New amino acid racemization (AAR) data suggest a mid-Pleistocene age (ca. 500 to 600 ka) for Assemblage 5. A sparsely fossiliferous, shallow inner shelf sand, containing a low diversity fauna (Assemblage 1) dominated by {it E. excavatum}, follows at 114 ft, and is overlain at 104 ft by a barren, probably non-marine, carbon-14 dead, muddy unit. A moderate diversity, inner shelf fauna, dominated by {it E. excavatum} and {it Ammonia parkinsoniana} (Assemblage 3) characterizes overlying sand (at 95 ft) that is probably of mid-Pleistocene age (530 to 330 ka based on previously published AAR data). Assemblage 2, again dominated by {it E. excavatum}, but containing several miliolid taxa indicative of normal salinities, occurs at 68 ft in the overlying muddy sand and is of similar probable mid-Pleistocene age (carbon-14 dead at 64 ft; new AAR data from 65 ft indicate350 to 420 ka). Assemblage 1 is a high dominance ({it E. excavatum}), low diversity, low abundance fauna occurring in sand that comprises the top 55 feet of the core. This unit represents the shoreface and inlet sands of the modern (late Holocene) barrier island, although correlations with nearby cores suggest that the lower 20 ft of this sequence may represent an earlier, late Pleistocene (78 to 51 ka based on previously published AAR data) barrier island complex.

OS71B-0286
Utilizing GIS for a Regional Aminostratigraphic Database
* Pellerito, V
vpelleri@udel.edu
University of Delaware Department of Geology, 101 Penny Hall , Newark, DE 19716 United States
Wehmiller, J F
jwehm@udel.edu
University of Delaware Department of Geology, 101 Penny Hall , Newark, DE 19716 United States


Several laboratories have obtained Aminostratigraphic data from Atlantic Coastal Plain sites over the past two decades, occasionally with conflicting results or interpretations. The University of Delaware Aminostratigraphy Lab (UDAL) has obtained amino acid racemization (AAR) data for over 1000 collection sites in the region, with particular emphasis on North and South Carolina. AAR data are used to delineate stratigraphic units, whether by calibration with independent methods, such as radiocarbon or U-series, or as a relative dating tool. Outcrop, subsurface, beach, core, and inner shelf grab samples are included in this collection. Recently, several cores were collected along the barrier island system of the northern Outer Banks, NC. Both AAR and radiocarbon analyses are available from these more recent cores and are compared with existing data for surface and subsurface samples from the region. Because of the need to amass geochronologic information for ongoing studies of the geologic framework of the Carolina Coastal Plain, a regional AAR/radiocarbon/U-series database is being compiled. Ultimately, data from all published references and currently unpublished (UDAL) data will be included in this database; the first stage is focused on sites in North Carolina. The database presents AAR analyses via a Relational Database Management System (RDBMS) and exhibits the data on a geographic information system (GIS). An RDBMS allows for querying among data sets so that comparison and evaluation of all available data may be conducted. Results from different labs, or the same lab over a period of several years, from multiple genera or from "similar" sites can be compared in a systematic manner, once all data are included in the database. Accessibility of the AAR database via web-mapping software is crucial to allow broad inquiry and augmentation of the database by interested coastal managers and regulatory agencies with the goal of better understanding coastal processes along the Carolinas.

Process-Response, Time-Slice Geomorphic and Ecologic Mapping of Core Banks, Cape Lookout National Seashore (CLNS), NC
White, R M
whitermw@yahoo.com
East Carolina University, CRM, Ragsdale Building, Greenville, NC 27858
* Riggs, S R
riggss@mail.ecu.edu
East Carolina Univerrsity, Geology, Graham Building, Greenville, NC 27858 United States
Mallinson, D A
mallinsond@mail.ecu.edu
East Carolina Univerrsity, Geology, Graham Building, Greenville, NC 27858 United States
Ames, D
amesd@mail.ecu.edu
East Carolina Univerrsity, Geology, Graham Building, Greenville, NC 27858 United States

The Core Banks barrier islands are relatively unaltered by human development. However, major geomorphic and ecologic changes have occurred in their character and dynamics since it became part of CLNS in 1966. To understand this evolutionary change, it is imperative to evaluate the barrier's recent history and develop a set of four-dimensional, process-response maps. The goal is to determine the causative processes and define the detailed responses operating within this dynamic and complex coastal system. Sixty four of the original 77 USACE survey transects established in 1960-62 along Core Banks were located and resurveyed to define vertical and horizontal changes through time. These transects were occupied by Godfrey et al. in 1972-74 for ecological mapping of Core Banks. Type localities were established along Core Banks for detailed time slice analysis using aerial photography. These were mapped at 1:2000 scale on 1998 DOQQ's and ground-truthed with cross-barrier geomorphic, ecological, and elevation survey transects. Using these data sets, the geomorphic and ecologic mapping was extrapolated backwards through time utilizing georeferenced aerial photographic time slices back to 1940. The time-slice interpretations are integrated with GPR surveys and pre-existing drill data of Heron et al. Shallow vibracores provide samples for stratigraphic analysis and age dating. The process-response geologic maps of undeveloped Core Banks are being compared to those of the highly modified Cape Hatteras National Seashore barrier system to the north to aid in future short- and long-term management of this coastal resource.

OS52F-04 INVITED
Role of Geologic Framework, Paleotopography, Sediment Supply, and Human Modification in the Evolutionary Development of the Northeastern North Carolina Barrier Island System
* Riggs, S R
riggss@mail.ecu.edu
Geology Dept., East Carolina University, Greenville, NC 27858 United States
Thieler, E R
rthieler@usgs.gov
U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
Mallinson, D A
mallinsond@mail.ecu.edu
Geology Dept., East Carolina University, Greenville, NC 27858 United States
Culver, S J
culvers@mail.ecu.edu
Geology Dept., East Carolina University, Greenville, NC 27858 United States
Corbett, D R
corbettd@mail.ecu.edu
Geology Dept., East Carolina University, Greenville, NC 27858 United States
Hoffman, C W
bill.hoffman@ncmail.net
N.C. Geological Survey, 4100-A Reedy Creek Rd., Raleigh, NC 27607 United States

The NE North Carolina coastal system contains an exceptionally thick and well preserved Quaternary stratigraphic record that is the focus of a five-year Cooperative Coastal Geology Program between the USGS, several academic institutions, and state agencies. The major goal is to map this Quaternary section on the inner continental shelf, Outer Banks barrier islands, Albemarle-Pamlico estuarine system, and adjacent land areas. The program objectives are to define the geologic framework, develop the detailed evolutionary history, and understand the ongoing process dynamics driving this large, complex, and rapidly changing, high-energy coastal system. Preliminary data synthesis demonstrates that the major controls dictating the present health and future evolution of this coastal system include the following. 1) The regional late Pleistocene morphology constitutes the underlying geologic framework that the Holocene system has inherited. 2) The controlling paleotopography is a series of lowstand drainage basins consisting of trunk and tributary streams and associated interstream divides that are being drowned. 3) Three major sediment sources dictate the highly variable sand resources available to specific barrier segments and include riverine channel and deltaic deposits associated with lowstand trunk streams, the large cross-shelf cape shoal sand deposits, and sand-rich units occurring within the adjacent shoreface and inner-self strata. 4) Wherever large sand supplies have historically been available, the barrier segments occur as complex islands with large sand volumes producing high and wide barriers, whereas barrier segments without adequate sand supplies are sediment starved and occur as simple overwash barriers. 5) Human modification of the barrier islands over the past seven decades represents a major force that has significantly changed the barrier island dynamics and evolution. 6) The Albemarle Embayment appears to have a slightly higher rate of sea-level rise than adjacent regions due to a slow rate of regional subsidence. Consequently, if the ongoing pattern of storm activity and sea-level rise either continues or increases during the next few decades to centuries, several simple overwash barrier segments on the Outer Banks, that are currently disintegrating, will ultimately collapse into Pamlico Sound. These barrier segments will likely back-step across the open marine Pamlico Embayment and reform on the landward side. A few sand-rich complex barrier segments will persist as isolated, but perched and eroding islands for some longer period of time. In contrast, simple overwash barrier segments that have received minimal human modification and are associated with narrow and shallow back-barrier sounds, appear to be maintaining themselves in their upward and landward migration in response to ongoing storms and sea-level rise.

OS52F-06
A Preliminary Evaluation of ohe Sediment Dynamics in the Albemarle Estuarine System, North Carolina
* Corbett, D R
corbettd@mail.ecu.edu
East Carolina University, Department of Geology Graham Bldg, Greenville, NC 27858 United States
Mallinson, D
mallinsond@mail.ecu.edu
East Carolina University, Department of Geology Graham Bldg, Greenville, NC 27858 United States
Letrick, E
EML1107@mail.ecu.edu
East Carolina University, Department of Geology Graham Bldg, Greenville, NC 27858 United States
Vance, D
djv1213@mail.ecu.edu
East Carolina University, Department of Geology Graham Bldg, Greenville, NC 27858 United States

The Albemarle estuarine system (AES) drainage basin covers an area of approximately 45,500 km^{2} within Virginia and North Carolina, and is comprised of the Roanoke River Basin, Chowan River Basin, and Albemarle Sound Basin. The AES, a product of rising sea level (eg. drowned-river estuarine system), covers approximately 2,340 km^{2} and includes several major and minor embayed (lateral) tributaries. As earlier studies have pointed out, the estuarine system is the settling basin for sediments, organic matter, and anthropogenic waste from these three major drainage basins. The most abundant sediment within the AES, forming the benthic habitat for nearly 70% of the estuarine system, is a chemically active organic-rich mud (ORM). This sediment type has been shown to be important to the water quality, contaminant characteristics, and potentially the ecosystem dynamics. During the summer of 2001, several short cores (~ 50 cm) were collected in the AES, and downcore measurements for radiochemical tracers (^{210}Pb, ^{137}Cs) and organic matter signatures (13C, ^{15}N, C:N, LOI) were conducted. These organic matter signatures have been used to elucidate potential temporal changes in fluxes and cycles of organic matter in the AES. Pb-210 analyses indicate temporal and spatial variations in sediment deposition rates (0.05 - 0.50 cm/yr). Sedimentation rate variations are potentially associated with dam construction on the Roanoke River and increased estuarine shoreline erosion along many banks of the Albemarle Sound. Sediment deposition varies spatially in the AES and is highest near its western limit relative to the rest of the estuary. d13C and d ^{15}N concentrations from cores collected in the AES range from -21.7 to -28.3 permil and 0.4 to 4.6 permil, respectively. The variation signatures indicate typical mixing between terrestrial and marine end members, as well as potential influences associated with increased agriculture over the last century.


Are There Connections Between Erosional Hot Spots and Alongshore Sediment Transport Along the North Carolina Outer Banks?
* Ashton, A
andrew.ashton@duke.edu
Duke University, Division of Earth and Ocean Sciences Nicholas School of the Environment and Earth Sciences Center for Nonlinear and Complex Studies PO Box 90227, Durham, NC 27708 United States
List, J H
U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA 02543-1548 United States
Murray, A
abmurray@duke.edu
Duke University, Division of Earth and Ocean Sciences Nicholas School of the Environment and Earth Sciences Center for Nonlinear and Complex Studies PO Box 90227, Durham, NC 27708 United States
Farris, A S
U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA 02543-1548 United States

Recent, high-definition measurements taken along the northern North Carolina Outer Banks reveal that the shoreline moves in a surprisingly alongshore-heterogeneous way over time scales ranging from storms to decades. SWASH is a shoreline measuring system developed by the USGS that utilizes Global Positioning System measurements to determine the location of the shoreline (List and Farris, Coastal Sediments, 1999). Surveys taken before and after storms, as well as at monthly intervals, have documented zones of accentuated erosion or deposition, or `hot spots'. We classify hot spots into three general categories: 1) Short-term Reversible Hot Spots, consisting of alongshore non-uniform patterns of storm erosion that are erased during post-storm accretion; 2) Medium-term Hotspots, occurring over hundreds of meters and persisting for months while often shifting in the alongshore direction; and 3) Long-term Hotspots, which can be couplets of shoreline erosion and accretion occurring over decadal time scales. Recent research (Ashton, et al., Nature, 2001) has indicated that when waves approach at an angle greater than the one that maximizes alongshore sediment transport (approximately 45 degrees in deep water, which we call `high-angle' waves), any plan view perturbations on a nearly straight coastline will grow. This growth involves erosion in seaward-concave shoreline segments and accretion in convex areas. (Similarly, low-angle waves produce accretion where the shoreline is concave, and vice versa.) Simple numerical simulations using wave distributions weighted towards high angle waves show shoreline features that migrate in the direction of net sediment transport. Hot spots are likely to be influenced by many factors, including variations in shoreface lithology, off-shore bathymetry that concentrates wave energy, the configuration of alongshore bars, and variations in cross-shore sediment transport. However, evidence that hotspots migrate, occur in different locations at different times, and can range across many scales suggests that they may be partly related to variations in alongshore sediment transport due to changes in shoreline orientation. If alongshore transport is related to hot spot behavior, shoreline curvature will correlate with shoreline change. Preliminary analyses of field measurements indicate a surprisingly high correlation between shoreline curvature and the local rate of shoreline change. Simplified numerical simulations reveal information about what combinations of shoreline orientation, wave climate, and shoreline perturbations will produce migrating zones of erosion and accretion over the monthly to annual time scales of medium-term hot spots. For long-term (decadal) hot spots, we have performed numerical simulations based on the measured northern Outer Banks shoreline and wave climates. The goal is not to quantitatively predict rates of shoreline change, but to compare model predictions of general regions of long-term erosion and accretion to the observations. Initial tests of these predictions are encouraging. The dominantly low-angle wave climate of the northern Outer Banks should result in long-term coastline smoothing. This shoreline contains subtle undulations occurring over many scales, verifying that controls or processes other than gradients in alongshore sediment flux affect coastline shape. However, we have preliminarily identified links between erosional hot spots and alongshore sediment transport.

OS71B-0277
Quaternary Seismic Stratigraphic Framework of the Northern North Carolina Inner Continental Shelf
Foster, D S
dfoster@usgs.gov
US Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
* Thieler, E R
rthieler@usgs.gov
US Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
Capone, M K
mcapone@usgs.gov
US Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States
Denny, J F
jdenny@usgs.gov
US Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02543 United States

The U.S. Geological Survey has recently collected high-resolution Boomer and CHIRP seismic-reflection profiles along the inner continental shelf of North Carolina between False Cape, VA and Cape Hatteras, NC. The two systems were used concurrently on a dense survey grid with shore parallel lines spaced about 300 m apart. Tie lines were run perpendicular to shore and were spaced about 4 km apart. The survey area covers the inner shelf from about the 7-m isobath to 11 km offshore. Boreholes were drilled on the barrier islands to provide ground truth and correlate the seismic stratigraphy mapped on the shelf and in the backbarrier estuary. Seismic interpretations on the inner shelf are being verified with vibracore data. At least five transgressive unconformities are observed as planar reflections that dip to the southeast. The seismic sequences bounded by these unconformities also thicken slightly to the southeast. As a result, the Quaternary stratigraphic section is more compressed in the northern part of the study area. The deepest unconformity is believed to be the top of the Yorktown Formation (Pliocene) and is recognized as a distinct angular unconformity on Boomer profiles in the northern part of the study area. Three shallower unconformities have been identified on the Boomer profiles, which can be related to discrete Pleistocene sea-level fluctuations using amino acid racemization chronologies. In addition to these surfaces, the Holocene transgressive unconformity is best identified on the Chirp profiles. However, for much of the study area there is no definitive seismic reflection where we believe the unconformity should be located, based on lithologic contacts in vibracores. In some areas, there is a strong seismic reflection that correlates to the base of a mud unit that is most likely pre-Holocene back-barrier lagoon deposits. Accurate mapping of Recent marine sands requires integrating Chirp data with vibracores. There are several areas of fluvial cut and fill that partially remove older Pleistocene units and truncate some of the transgressive unconformities. The paleo-Roanoke River valley complex is the most extensive seen on the seismic profiles. The relative ages of smaller fluvial channel complexes to the north and south cannot be linked with the main Roanoke channel complex based on the geophysical data alone. Radiocarbon ages from onshore boreholes indicate the channel complex was cut during at least two late Pleistocene lowstands.

OS71B-0279
Relationship of Hotspots to the Distribution of Surficial Surf-Zone Sediments along the Outer Banks of North Carolina
* Schupp, C A
cschupp@vims.edu
Virginia Institute of Marine Science, Route 1208 Greate Road, Gloucester Point, VA 23062 United States
McNinch, J E
mcninch@vims.edu
Virginia Institute of Marine Science, Route 1208 Greate Road, Gloucester Point, VA 23062 United States
List, J H
jlist@usgs.gov
U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02536 United States
Farris, A S
afarris@usgs.gov
U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02536 United States


The formation and behavior of hotspots, or sections of the beach that exhibit markedly higher shoreline change rates than adjacent regions, are poorly understood. Several hotspots have been identified on the Outer Banks, a developed barrier island in North Carolina. To better understand hotspot dynamics and the potential relationship to the geologic framework in which they occur, the surf zone between Duck and Bodie Island was surveyed in June 2002 as part of a research effort supported by the U.S. Geological Survey and U.S. Army Corps of Engineers. Swath bathymetry, sidescan sonar, and chirp seismic were used to characterize a region 40 km long and1 km wide. Hotspot locations were pinpointed using standard deviation values for shoreline position as determined by monthly SWASH buggy surveys of the mean high water contour between October 1999 and September 2002. Observational data and sidescan images were mapped to delineate regions of surficial sediment distributions, and regions of interest were ground-truthed via grab samples or visual inspection. General kilometer-scale correlation between acoustic backscatter and high shoreline standard deviation is evident. Acoustic returns are uniform in a region of Duck where standard deviation is low, but backscatter is patchy around the Kitty Hawk hotspot, where standard deviation is higher. Based on ground-truthing of an area further north, these patches are believed to be an older ravinement surface of fine sediment. More detailed analyses of the correlation between acoustic data, standard deviation, and hotspot locations will be presented. Future work will include integration of seismic, bathymetric, and sidescan data to better understand the links between sub-bottom geology, temporal changes in surficial sediments, surf-zone sediment budgets, and short-term changes in shoreline position and morphology.

OS71B-0281
Acquisition, Processing, and Archiving of High-Quality Core Data, North Carolina Outer Banks
* Brooks, R W
bob.brooks@ncmail.net
North Carolina Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States
Hoffman, C W
bill.hoffman@ncmail.net
North Carolina Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States
Farrell, K M
kathleen.farrell@ncmail.net
North Carolina Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States


Rotosonic drilling technology was used to recover approximately 350 m of core (10 cm diameter) at eight different locations on the Outer Banks of North Carolina as part of a coastal geology cooperative research program. A combination of vibration and rotation of the drill pipe and casing is used to advance the hole. Water is used to wash out the casing, but is not circulated and no cuttings are brought to the surface. This leaves the site relatively undisturbed, so working in municipal areas is not a problem. Drill costs averaged about 140/m. Coring runs are 3.3 m (10 ft) long, with each run recovering two 1.65 m (5 ft.) long polycarbonate tubes containing the core sample. In the laboratory, tubes are cut lengthwise with a circular saw and then split by pulling piano wire through the sediment. One half-core is used for sampling; the other half is used to create a detailed visual log and digital image, and is retained as an archive sample. The drilling recovered high-quality lithologic samples in unconsolidated sediments with recovery rates of over 90 percent in most holes. This allowed for thorough, detailed description and stratigraphic analysis, and closely controlled sampling for age dating and geochemical studies. High-resolution (2048 x 1536 pixel) digital images (TIFF format) of the cores are taken in a controlled setting. Lighting, camera settings, and core positioning are carefully monitored to ensure consistency. A tape measure is included in the frame to provide depth reference information in each image. Approximately 36cm of the core is imaged at a time (9 Mb file). To construct composited core images, each 36 cm-long segment is digitally stitched together using a software program written specifically for piecing together panoramic photographs. This process yields a high-resolution (TIFF format; 36 Mb) image showing the full 1.65 m (5 ft.) core tube. The composite image is then saved in JPEG format to reduce the file size to just over 4.5 Mb without unduly compromising the image quality. Lower-resolution images can be easily made for Internet distribution.

OS71B-0283
Aminostratigraphy of Subsurface Units, Eastern Albemarle Sound and Northern Outer Banks, North Carolina
* Wehmiller, J F
jwehm@udele.edu
Department of Geology, 101 Penny Hall University of Delaware, Newark, DE 19716 United States
Thieler, E R
US Geological Survey, 348 Woods Hole Road, Woods Hole, MA 02543 United States
York, L L
U. S. National Park Service Southeast Regional Office, 100 Alababa St., S.W., Atlanta, GA 30303 United States
Pellerito, V
Department of Geology, 101 Penny Hall University of Delaware, Newark, DE 19716 United States


The Quaternary geochronology of subsurface and emergent units on the US Atlantic Coastal Plain aids the understanding of the geologic framework that affects Holocene coastal processes. Amino acid racemization (AAR) and radiocarbon results for mollusk samples from a variety of sampling sites along the NC coastal plain contribute to this chronologic framework. Recent drilling on the northern Outer Banks has yielded AAR/14C results that are compared with existing data for samples from nearby inner shelf or beach sites, or from subsurface sampling in mainland Dare County (Riggs and others, 1992). AAR data serve to delineate stratigraphic units; suitably calibrated, AAR data can be used to estimate ages for units with no independent radiometric data. New AAR data from two holes, OBX-5 and OBX-8 (north and central portions of cross-section D-D' of Riggs et al., 1992), identify three pre-Holocene aminozones. The oldest one (OBX-5, 135' depth) corresponds to an early/middle Pleistocene aminozone (AZ-4) seen in other subsurface sections in the region (Riggs et al., 1992). Based on AAR, AZ-4 is approximately 2/3 the age of the James City Formation, a mapped early Pleistocene unit exposed in central NC. Two younger aminozones are seen in superposition in OBX-8, at 65' and 114'. These aminozones have D/L values that are slightly greater than those seen in AZ-2 and AZ-3, interpreted as late and late/middle Pleistocene (Riggs et al., 1992), respectively. Infinite or near-infinite 14C dates at depths between 65' and 104' in OBX-8 confirm the Pleistocene age assignment based on AAR. Radiocarbon and AAR constrain the boundary between the early Holocene and AZ-4 (early/middle Pleistocene) in OBX-5 to an interval between ca. 110' and 135' depth; intervening late Pleistocene strata may be present but are not identified based on chronologic data. Paired 14C/AAR analysis of reworked/transported beach or shelf shell in the region supports the relative ages seen in the OBX holes and correlates these reworked samples with their source units exposed on the inner shelf or shoreface.
URL: http://www.geology.udel.edu/wehmiller/shells.html


Ground-Water Salinity and Isotope Stratigraphy of North Carolina's Outer Banks
* Bratton, J F
jbratton@usgs.gov
USGS, 384 Woods Hole Road, Woods Hole, MA 02543-1598 United States
Thieler, E R
USGS, 384 Woods Hole Road, Woods Hole, MA 02543-1598 United States
Hoffman, C W
NC Geological Survey, Coastal Plain Office 1620 Mail Service Center, Raleigh, NC 27699-1612 United States
Brooks, R W
NC Geological Survey, Coastal Plain Office 1620 Mail Service Center, Raleigh, NC 27699-1612 United States

As part of a larger investigation of the geologic framework of the North Carolina coast, ground-water and sediment samples were collected and analyzed for salinity and d13C of total organic carbon (TOC). Salinity was measured on samples from eight borings (depths up to 56 m), located between Kitty Hawk and Nags Head, to determine the thickness of the barrier island's fresh-water lens, and to examine stratigraphic control on freshwater-saltwater boundaries. d13C was measured to establish the origin of organic matter (OM) preserved in the sediments. Results indicate that ground-water salinity is strongly correlated with stratigraphy based on core descriptions and downhole gamma logs. The subsurface fresh-water lens is 3-30 m thick across the study region (20 km). The thickness of the fresh-saline transition at depth is also highly variable (<2 m to 15 m). At three of four deep coring locations (>38 m), a zone of fresher water exists beneath an intermediate saline zone. The maximum salinity of water in the saline zone is typically around 27 ppt, but in one location a brine (45 ppt) is present. Based on preliminary d13C-TOC data, most OM in the cores appears to be derived from mixed terrestrial (d13C approx -26 permil VPDB) and marine (d13C approx -20 permil) sources. Two cores show a clear trend from more terrestrial OM at depth toward more marine OM with a component of salt-marsh material (d13C approx -13 to -15 permil) near the surface. Sharp upcore transitions from terrestrial to mixed, or mixed to salt-marsh OM may indicate either unconformities, marine incursions associated with rapid sea-level rise events, or opening of inlets. Such transitions are present in one core at a depth of 20 m (^{14}C age = 23.7 cal ka), and in two other cores at 33 to 36 m (10.6 cal ka). The study showed that filled paleo-valleys and paleo-tidal inlets under the modern barrier are serving as conduits for both salt-water migration and sub-estuarine transport of fresh water from the mainland. Channel fills contain OM from a variety of distinct coastal paleoenvironments.
URL: http://woodshole.er.usgs.gov/project-pages/northcarolina/index.htm

OS71B-0287 INVITED
Digital Geomorphic Mapping of Cape Hatteras National Seashore, North Carolina Using Remotely Sensed Data
* Hoffman, C W
bill.hoffman@ncmail.net
N.C. Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States
Farrell, K M
N.C. Geological Survey, Coastal Plain Office, 1620 MSC, Raleigh, NC 27699 United States


Several digital databases have become available in the last several years that permit high-resolution mapping of the geomorphology of the North Carolina Coastal Plain. Cape Hatteras National Seashore was mapped using such databases in support of the geological resource inventory program of the National Park Service. The primary digital data layers used are 1998 color infrared orthophotos (1:12,000 scale) and high-resolution topographic data generated from a recent LIDAR survey (available as bare earth points and as 20- and 50-foot DEM's). Additional digital photography (1998 black and white) at higher resolution was applied in limited areas. National Wetlands Inventory maps, a refined wetlands map series by the N.C. Division of Coastal Management, and soils maps (all in digital form) were also used. Cape Hatteras National Seashore encompasses approximately 130 km of the N.C. Outer Banks barrier island system. This system includes barrier island segments with well-developed beach ridge complexes as well as segments dominated by overwash processes. Two tidal inlets (Oregon and Ocracoke) presently occur within the study area, however several former inlets are known from historical records. Thus, a wide variety of subaerial and submarine geologic environments are present within the project area. These environments are characterized by landforms that are mappable via heads-up digitizing using Geographic Information System (GIS) software. Map units include salt marsh, overwash fan, flats, dunes, dune ridge, beach ridge, beach, tidal delta, among others. The map produced by analysis of these data sources in GIS results in a significant improvement over existing maps and provides a digital database for use as a resource management tool. Refinement of the mapping by field ground truth and integration with ongoing research by the northeastern N.C. coastal geology cooperative will further improve the maps.

OS71B-0289
Shoreline Erosion in the Albemarle-Pamlico Estuarine System, Northeastern North Carolina
* Murphy, M A
ma_murphy00@hotmail.com
Geology Dept., East Carolina University, Greenville, NC 27858 United States
Riggs, S R
riggss@mail.ecu.edu
Geology Dept., East Carolina University, Greenville, NC 27858 United States


Computer analysis of aerial photographic series demonstrates that the estuarine shorelines within the North Carolina Albemarle-Pamlico coastal system are eroding at 2-3 times greater rates than previous studies reported. Specific rates and amounts of shoreline recession vary tremendously depending upon local variables including: 1) shoreline type, geometry, and composition; 2) geographic location, size, and shape of associated estuary; 3) frequency, intensity, and fetch of storms; 4) type and abundance of associated vegetation; and locally 5) boat wakes. Organic or wetland shorelines (marsh and swamp forest) comprise approximately 62% of the estuarine margins in NE NC, whereas sediment banks (low, high, and bluff) constitute about 38%. The goals of this study were to determine the rates of recession for different shoreline types and the role of local variables in the erosion process. Shorelines were mapped using high precision GPS mapping techniques, digital orthographic quarter quadrangles, and other georeferenced aerial photographs from the early 1950's to 2001. Shoreline change was then calculated for 20 estuarine study sites. Field mapping of each site provided data on shoreline characteristics and erosional processes. Data synthesis suggests mean annual shoreline erosion rates are significantly different for shoreline types as follows: 1) marshes = 7.4 ft/yr (range 2.7-17.0 ft/yr), low sediment banks = 5.0 ft/yr (range 1.0-12.0 ft/yr), bluff sediment banks = 5.0 ft/yr (range = 3.9-6.0 ft/yr), swamp forests = 3.0 ft/yr (range = 1.7-4.0 ft/yr), high sediment banks = 2.8 ft/yr (range = 2.7-2.9 ft/yr). Modified shorelines continue to erode, however at lower mean annual rates that range from 0.9-2.7 ft/yr. Locally, specific marsh shorelines have eroded at rates up to 100 ft/yr during particularly stormy periods. Thus, about 1166 acres of land are lost each year along the 1593 miles of mapped estuarine shoreline in NE NC. If these erosion rates are representative of all 3,000 miles of NE NC's estuarine shorelines, if sea level continues to rise, and if the storm pattern persists at present levels, NC will experience significant loss of both wetlands and uplands at the estuarine water-land interface.

The Late Holocene Stratigraphy of an Inlet-Dominated Barrier Island, Pea Island, North Carolina.
Smith, C G
cgs0818@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
Ames, D
amesd@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
* Corbett, D R
corbettd@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
Culver, S
culvers@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
Mallinson, D
mallinsond@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
Riggs, S R
riggss@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States
Vance, D
djv1213@mail.ecu.edu
Department of Geology, East Carolina University, Room 101, Graham Building, Greenville, NC 27858 United States


Sedimentological, foraminiferal, geochemical, and geophysical data sets as well as aerial photographs have been used to investigate the natural processes (inlet dynamics, ocean/estuarine washover, and sea-level change) responsible for the late Holocene units preserved in the barrier island subsurface at Pea Island National Wildlife Refuge. Historic nautical charts indicate that three inlets characterized Pea Island between early European exploration (1590) and the late 19th century; aerial photographs show New Inlet open in 1932 and 1940. Vibracores (up to 5.5 m) collected along three transects across Pea Island extend our knowledge of the geological evolution of this region to pre-historic times. The section in the longest core (PI01S6) consists of four fining-upwards depositional sequences. The basal unit of each sequence is a bedded, medium to fine, clean quartz sand with increasing concentrations of organic matter (3-4 % detrital and 5-7 % {it in situ Spartina alterniflora} roots) or irregular mud clasts (2-5 cm) to spherical mud balls (1-2 cm) up core. The clean sand units have so far proven to be barren of foraminifera except for a shelly unit at ca. 220 cm below MSL. The foraminiferal assemblage in this unit is of open shelf character ({it Elphidium excavatum}, {it Hanzawaia strattoni}, and {it Buccella inusitata}). A ^{14}C age on a disarticulated {it Chione cancellata} valve from this unit is cal. 930pm60 BP. The sand grades into a gray, tight mud in the first two sequences and into an inter-laminated mud and in situ peat in the third sequence. The peat contains leaf fragments and rhizomes of the marsh plants {it Juncus roemarianus}, {it Spartina cynosuroides}, and/or {it Phragmites} spp. The peat and muddy sand units contain marsh foraminifera ({it Trochammina} spp., {it Miliammina fusca}, {it Arenoparrella mexicana}), which are also found in modern marsh deposits. A peat sample from the third fining upward sequence (the only one to grade into a true peat) has a ^{14}C age of cal. 395pm35 BP, cal. 295pm35 BP, or cal 180pm40 BP. The four fining-upwards sequences have sharp erosional basal contacts. These deposits appear to reflect back-barrier processes including sequential deposition of flood-tide delta sands and/or sound sands adjacent to marshes. The shelly sands, containing open shelf foraminiferal assemblages, represent oceanic overwash, inlet deposits, or open embayment sands deposited behind a laterally extensive breach in the barrier island. The sequences are capped by the deposits of modern environments that include algal flats, tidal creeks, high and low marshes, back-barrier berms, overwash fans, and aeolian dunes. Several of the modern environments became covered with marsh vegetation after the construction of barrier dune ridges in the late 1930?s.



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