Woods Hole 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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