Pea Island, Oregon Inlet, and Bodie Island, North Carolina, are severely human-modified barrier-island segments that are central to an age-old controversy pitting natural barrier-island dynamics against the economic development of coastal North Carolina. Bodie Island extends for 15 km from the Nags Head–Kitty Hawk urban area to the north shore of Oregon Inlet and is part of Cape Hatteras National Seashore. Pea Island extends 19.3 km from the southern shore of Oregon Inlet to Rodanthe Village and is the Pea Island National Wildlife Refuge. Bodie and Pea Islands evolved as classic inlet- and overwash-dominated (transgressive) simple barrier islands that are now separated by Oregon Inlet. The inlet was opened in 1846 by a hurricane and subsequently migrated 3.95 km past its present location by 1989. With construction of coastal Highway 12 on Bodie and Pea Islands (1952) and the Oregon Inlet bridge (1962–1963), this coastal segment has become a critical link for the Outer Banks economy and eight beach communities that occur from Rodanthe to Ocracoke. The ongoing natural processes have escalated efforts to stabilize these dynamic islands and associated inlet in time and space by utilizing massive rock jetties and revetments, kilometers of sand bags and constructed dune ridges, and extensive beach nourishment projects. As the coastal system responds to ongoing processes of rising sea level and storm dynamics, efforts to engineer fixes are increasing and now constitute a “human hurricane” that pits conventional utilization of the barriers against the natural coastal system dynamics that maintain barrier-island integrity over the long term.

Abstract Previous lithostratigraphic studies of incised, valley-fill systems on the mid-Atlantic coast of the United States indicate a continuous Holocene sea-level rise. Likewise, the lithostratigraphic evaluation of vibracores from Albemarle Sound, North Carolina, can be interpreted as a simple infill history resulting from a continuous Holocene transgression. However, an integrated litho-, high-resolution seismic-, and chronostratigraphic approach suggests that the infill record of Albemarle Sound may be the result of several relative sea-level oscillations during the Holocene. The Holocene section of Albemarle Sound contains at least three depositional sequences (ASDS-1 to ASDS-3), each consisting of lithologically similar successions of depositional environments. Basal sediments from ASDS-1 were deposited in a restricted-estuarine environment behind a continuous barrier island system between 8.1 ka and 5.9 ka. For some interval between 5.9 ka and 5.5 ka sea level dropped (<6 m), producing an extensive erosional surface throughout the middle- and outer-estuarine zone. Deposition resumed as sea level rose to form ASDS-2. Basal sediments of ASDS-2 were deposited in an open-estuarine system between 5.5 ka and 2.9 ka, suggesting that the previous barrier island complex was extensively breached. ASDS-2 is capped with closed-estuarine sediments that date from 2.9 ka to 1.5 ka, suggesting the reformation of a continuous barrier island complex. Another small drop of sea level occurred for some interval between 1.6 ka and 0.4 ka, which truncated ASDS-1 and ASDS-2. This drop was only between 1–2 m based on the absence of basal open-estuarine sediments in the overlying depositional sequence (ASDS-3), suggesting that the barrier island system was preserved and active during this interval. ASDS-3 consists of closed-estuarine sediments that are being deposited during the ongoing sea-level transgression and behind the modern, well developed barrier island system.

Abstract High-resolution seismic data suggest that portions of depositional sequences representing as many as 18 Quaternary sea-level highstands are preserved within 60 m of Quaternary deposits in northeastern North Carolina. Sediments deposited during at least seven of these Quaternary sea-level events have been defined within the upper 33 m in drill holes in Dare County. The complex stratigraphy was resolvable only after integrating detailed lifho-, bio- and aminostratigraphic drillhole data with a high-resolution seismic framework. High-frequency, sea-level cyclicity dominated the depositional patterns of the resulting Quaternary sediment sequences. As high-energy coastal systems moved repeatedly across the low-gradient continental shelf, sediment units that had previously been deposited in coastal and shelf environments were significantly modified. During each glacial episode, fluvial channels extensively dissected previously deposited coastal facies. Subsequent deglaciation and transgression flooded the channels, backfilling them with fluvial and estuarine sediments. The infilled channel facies were then partially truncated by shoreface erosion, which also eroded portions of previously deposited coastal sequences. During sea-level highstands, a new sequence of coastal facies was deposited over the ravinement surface cut into remnants of older and similar Quaternary sequences and the associated channel-fill systems. Thus, the resulting record consists of a series of imbricated coastal deposits of similar, but discontinuous, lithostratigraphic units with irregular geometries that only partially represent interglacial highstand deposition; the depositional sequences are highly punctuated and dominated by unconformity surfaces with extensive incised and backfilled channel deposits.

Abstract The Gulf of Mexico basin is best known for its vast and widespread oil and gas resources. They have been described in the preceding chapter of this volume. The basin, however, also contains important deposits of phosphate, lignite, and sulfur and small deposits of uranium. In addition, salt from several salt domes is produced by underground and solution mining and is used principally as a chemical feedstock for the manufacture of many industrial products. Large volumes of geopressured-geothermal water are also known from the Tertiary sediments of the Gulf of Mexico basin, particularly around its northern margin. It often contains natural gas in solution. This overpressured, gas-bearing hot water may someday be an important source of thermal and kinetic energy; it is now just a gleam in the eye of imaginative energy tacticians. The phosphate deposits of Florida and southeastern Georgia, the Florida Phosphogenic Province, represent about 75 percent of the total domestic phosphate production, and ranged between 34 and 28 percent of the total world production between 1983 and 1987. Important lignite deposits, for the most part of Eocene age, are known from the Gulf of Mexico basin. Two-thirds of the lignite is found in Texas, but it occurs also in parts of northeastern Mexico, Louisiana, Arkansas, Tennessee, Mississippi, and Alabama. Modest resources of Upper Cretaceous bituminous coal are found in northeastern Mexico. Once an important industry, the production of sulfur from the caprocks of some of the many salt domes in the U.S. Gulf Coastal Plain and shallow

ABSTRACT The Miocene Pungo River Formation of the North Carolina continental shelf (Onslow Bay) comprises 18 fourth-order seismic sequences that can be grouped into three larger-scale sections which correlate approximately with third-order coastal onlap events. Fourth-order seismic sequences generally correspond to discrete depositional sequences. Seven regional lithofacies occur within these sequences. Microfossil distributional patterns can best be understood within the context of this seismic and lithologic framework.

Abstract Most early studies of the U.S. Atlantic continental margin were dominated by the concept of 'layer-cake' stratigraphy with disruptions in continuity often explained by 'yo-yo' processes of basin faulting. Recent studies now demonstrate that these two concepts are not totally satisfactory in explaining the stratigraphic patterns of the past 24-million-year history of the Atlantic margin. During the past two decades, increasing sophistication of such tools as high-resolution seismic stratigraphy, biostratigraphic time zonations, and absolute dating techniques have provided a detailed basis for interregional correlations and environmental interpretations of upper Cenozoic lithostratigraphic units. The coastal plain and continental shelf are now recognized as parts of a coherent geologic province on a passive plate margin that have responded as an integral unit to complex sets of rapidly changing environmental conditions. The resulting upper Cenozoic sediment record is characterized by extremely variable lithologies with complex geometries and which are extensively dissected by unconformities.

Abstract The U.S. Atlantic continental margin, which stretches 1,850 km from Georges Bank in the north to the Blake Plateau in the south, encompasses an area of 655,000 km2. The margin comprises several sedimentary basins of different shapes with platforms in between (see Schlee and Klitgord, this volume). The basins appear to have begun their subsidence at about the same time and to have undergone similar rift and postrift phases of development that resulted in a similar sedimentary section (Schlee and Jansa, 1981). Our objectives in this paper are (1) to portray, at selected intervals, the paleogeography of the margin during the Mesozoic and Cenozoic, (2) to discuss the temporal development of the paleoshelf edge, and (3) to outline the major elements of the several different sedimentary regimes that have prevailed (rift, postrift, carbonate-clastic, and authigenic sediment accumulations). The main sources of data are interpretations of multichannel seismic-reflection profiles (Dillon 1982; Dillon and others, 1983a; Grow and others, 1979; Schlee, 1981; Schlee and Fritsch, 1982; Schlee and others, 1985), released drill hole data (Scholle, 1977,1979, 1980; Scholle and Wenkam, 1982; Poag, 1982a, b; Libby-French, 1981, 1984), and Deep Sea Drilling Project (DSDP) data (Hollister and Ewing, 1972; Tucholke and Vogt, 1979; Benson and Sheridan, 1978; Sheridan, and Gradstein, 1983; Van Hinte and Wise, 1987; Poag and Watts, 1987). With few exceptions (Schlee, 1981; Schlee and Fritsch, 1982), published interpretations of offshore basins have been based on a detailed analysis of one or at best a few key profiles (Grow and others, 1979, 1983; Poag, 1982a, b, 1985). Our approach in this chapter is to present interpretations in the form of eight time-slice maps with a brief discussion about data sources, paleogeography, and ties to adjacent areas.

Abstract Most geologic materials may be usable resources in some form and at some time, whether it be for general land fill and aggregate, beach replenishment, construction material, or as a source of metals and fuels. Thus, most natural materials occurring within the Atlantic continental margin are resources, defined as “materials, including those only surmised to exist, that have present or anticipated future value” (U.S.G.S., 1980). Whether a resource becomes a reserve or not (an economically recoverable commodity) depends upon the properties and economic values of that material, which are determined by the following factors: (a) availability, concentration, and occurrence of the material; (b) methods of recovering and processing the commodity; (c) transportation costs of ore and beneficiated products; and (d) environmental setting and costs of permitting and mitigation. Also, the economics of a given mineral resource change dramatically in response to new technological advances, discoveries of new deposits, or as industrial and social demands change through time. An increasingly critical component associated with the economics for development of any mineral commodity, is a good geologic knowledge of the resource base.

Abstract The work presented in this fieldtrip and the associated guidebook was supported by National Science Foundation grants OCE-7908949, OCE-8008326, OCE-8118164, and OCE-8400383 and University of North Carolina Sea Grant College grants from 1982 through 1986. Appreciation is expressed to the following in helping to make this work a success. 1) the many members of the Geology Department at East Carolina University, Greenville, N.C. and the Department of Marine Science at the University of South Florida, St. Petersburg, Florida who supplied help both at sea and in the laboratory; 2) crews of N.S.F. research vessels EASTWARD, ENDEAVOR, COLUMBUS ISELIN and CAPE HATTERAS; 3) Texasgulf Inc., North Carolina Phosphate Corp., International Minerals and Chemical Corp, Agrico Chemical Corp., W.R. Grace and Co., and the North Carolina State University Minerals Research Lab in Asheville, N.C. who supplied professional expertise and analytical capabilities; and 4) the ongoing programs associated with the International Geologic Correlation Program (I.G.C.P.) 156 on Phosphorites sponsored by UNESCO and TUGS. Finally, we would like to acknowledge the Duke/University of North Carolina Oceanographic Consortium who funded the ship time for this field trip and supplied their personnel and facilities.

Abstract The Aurora Phosphate District is located in the general vicinity of Aurora, North Carolina (Fig. 1). It encompasses the area of active mining, and it lies within the Aurora Embayment, a Miocene depocenter bounded to the north and south by paleotopographic highs (Riggs et. al, 1982). The District has been an important producer of phosphate fertilizer products since the opening of the Lee Creek Mine by Texasgulf, Inc. in 1965. With its 1985 purchase of North Carolina Phosphate Corporation, which had planned development of a tract adjacent to the existing Lee Creek Mine, Texasgulf gained control of all known economic phosphate deposits in the Aurora District. In general, economic deposits of phosphate in the North Carolina Coastal Plain occur within 10 miles of Aurora.