This vector data set contains the rock unit polygons for the surficial geology in the Delaware Coastal Plain covered by DGS Geologic Map No. 16 (Fairmount and Rehoboth Beach quadrangles). The geologic history of the surficial units of the Fairmount and Rehoboth Beach quadrangles is that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology reflects this complex history both onshore, in Rehoboth Bay, and offshore. Erosion during the late Pleistocene sea-level low stand and ongoing deposition offshore and in Rehoboth Bay during the Holocene rise in sea level represent the last of several cycles of erosion and deposition.
To facilitate the GIS community of Delaware and to release the geologic map of the Fairmount and Rehoboth Beach quadrangles with all cartographic elements (including geologic symbology, text, etc.) in a form usable in a GIS, we have released this digital coverage of DGS Geological Map 16. The update of earlier work and mapping of new units is important not only to geologists, but also to hydrologists who wish to understand the distribution of water resources, to engineers who need bedrock information during construction of roads and buildings, to government officials and agencies who are planning for residential and commercial growth, and to citizens who are curious about the bedrock under their homes. Formal names are assigned to all rock units according to the guidelines of the 1983 North American Stratigraphic Code (NACSN, 1983).
This report was prepared to provide a concise description of offshore operations related to exploration for petroleum (oil and natural gas} from the initial geologic and geophysical investigations to production. Petroleum deposits differ in their physical and chemical properties and are associated in the rocks with saline water. The origin of petroleum and its migration through rocks are not well understood. Commercial accumulations are found in certain suitable rocks or geologic structures - stratigraphic and structural traps, respectively. Prospective areas offshore are leased to exploration companies by the federal government. Exploration begins with geological and geophysical investigations that lead to the selection of smaller, promising areas. Detailed studies and drilling are then carried out and, if petroleum is found, various tests are performed to determine the volume of oil or gas or both. If the quantities are large, production facilities are designed and located on the site. The petroleum produced is transported to refining facilities or gas companies onshore by pipelines or tankers. Experience has shown that large, damaging oil spills are very rare. The most common cause of spills is marine transportation. To find new, large petroleum accumulations exploration will have to be expanded into deeper waters and into less hospitable regions.
Since 1992, the Delaware Geological Survey (DGS) has compiled a geologic database known as the Delaware Offshore Geologic Inventory (DOGI) that consists of sediment samples, radiocarbon and amino acid racemization dates, seismic profiles, and vibracores taken from the near-shore and inner continental shelf in state and federal waters. Most of the 366 vibracores are stored at the DGS on-site core and sample repository.
MS5 Map of Exposed and Buried Early Mesozoic Rift Basins/Synrift Rocks of the U.S. Middle Atlantic Continental Margin
A series of elongate rift basins of early Mesozoic age is exposed in eastern North America in a belt extending from Nova Scotia to South Carolina. The Upper Triassic-Lower Jurassic synrift rocks that fill the basins are called the Newark Supergroup comprising continental (fluvial and lacustrine) clastic sedimentary rocks (predominantly colored red) interbedded with basaltic volcanic rocks (Froelich and Olsen, 1985). Similar basins are buried beneath the sediments of the Atlantic Coastal Plain and continental shelf.
MS4 Seismic Stratigraphy Along Three Multichannel Seismic Reflection Profiles off Delaware's Coast (Front and Back Pages)
Three multichannel, common-depth-point (CDP), seismic reflection profiles were run off Delaware's coast for the Delaware Geological Survey. Their purposes were (1) to determine the depth to the unconformity (post-rift unconformity) at the base of the nearshore submerged Coastal Plain sedimentary rocks and (2) to relate onshore with offshore
geology as interpreted from the U. S. Geological Survey's network of regional seismic profiles. In addition, the nearshore profiles reveal considerable detail about the nature of the Neogene lithostratigraphic units and aquifers within them that supply water to the coastal communities of Delaware and Maryland (Miller, 1971; Weigle and Achmad, 1982).
MS2 Structure Contour Map of Pre-Mesozoic Basement, Landward Margin of Baltimore Canyon Trough (North and South Sections)
The structure contour map of pre-Mesozoic basement
indicates the structural complexity of the landward margin of
the Baltimore Canyon trough, especially that shown by the
buried rift basins of probable early Mesozoic age. Information
on depth to basement is important in determining the economic
limit of drilling through overlying rocks in the search for oil
Since 1992, the Delaware Geological Survey (DGS) has compiled a geologic database known as the Delaware Offshore Geologic Inventory (DOGI) that consists of sediment samples, radiocarbon and amino acid racemization dates, seismic profiles, and vibracores taken from the nearshore and inner continental shelf in state and federal waters. Most of the 366 vibracores are stored at the DGS on-site core and sample repository.
Lithologic logs from 268 vibracores taken from the Delaware Atlantic offshore were evaluated for sediment type and compatibility with historical beach sediment textures. A model of sand resource evaluation, known as "stack-unit mapping" (Kempton, 1981) was applied to all of the cores, and each core was labeled by its lithology in vertical sequence. The results are shown in detailed maps of the beach-quality sand resources offshore in state and federal waters. Results show significant quantities (approximately 54 million cubic yards) of excellent beach-quality sand sources within the three-mile state limit offshore Indian River Inlet, and within the Inner Platform and Detached Shoal Field geomorphic regions. In federal waters, sand is found on Fenwick Shoal Field and farther offshore Indian River Inlet on the Outer Platform (approximately 43.6 million cubic yards combined). Most of the beach-quality sand resources are believed to be reworked tidal delta deposits of a former Indian River Inlet during periods of lower sea level. Farther south, the resources are accumulations of recent surficial sands of the inner shelf (Detached Shoal Field and Fenwick Shoal Field) showing that the geomorphic region does influence sediment quality. This study found that paleochannels and bathymetry had no relationship to grain size. Multiple cut and fill episodes contributed to the diversity in grain sizes.
The Delaware Academy of Science has been instrumental in informing Delaware citizens about science and utilization of local resources. Since 1970 the annual meeting of the Delaware Academy of Science has been used as a time for presentation of ongoing research in various areas of science in the Delaware region. The proceedings of these meetings have resulted in publication of transactions of the Delaware Academy of Science. The 1976 annual meeting focused on aspects of the geology of Delaware. Members of the Delaware Geological Survey and the Geology Department at the University of Delaware contributed papers in their specific disciplines. This volume presents an overview of studies of geological features and processes of evolution of the geology of Delaware. Although this collection of papers does not represent an all-inclusive study of the subject, the selections included in this volume highlight past, present, and future trends in the study of Delaware's geology. It is hoped that the combined bibliographies of all the papers will provide a comprehensive view of the literature for further investigation into the geology of Delaware.
The Generalized Geologic Map of Delaware is a brief summary for general use indicating the major types and locations of rocks present throughout the State, and their interrelationships. The map is preliminary as it is a first step in a continuing program of detailed geologic mapping. It is based upon many existing sources of data; additional detail may be found in the references listed.
The nature and occurrence of subsurface resources, whether ground water, minerals, or petroleum, are controlled by the geologic history and framework of any particular area. Several years ago the staff of the Delaware Geological Survey began an informal assessment of the potential resources of southern Delaware and demonstrated the lack of basic data on the deep subsurface in this area. This assessment was later summarized by Benson (1976) with particular emphasis on the possibilities for petroleum occurrence.
This review summarizes the present knowledge of the subsurface geology and resource potential of southern Delaware and outlines the needs for future studies to gain further understanding of these matters. Because of the present interest in exploring for oil and gas beneath the Atlantic Outer Continental Shelf it is most timely that the primary resource considered in this report be the hydrocarbon (petroleum and natural gas) potential of the State. Hydrocarbons occur in commercial quantities only in thick sections of sedimentary rock, therefore, southern Delaware (primarily Sussex County) is the focus of this study because the thickest sedimentary rock section in the State is here. Assessment of the hydrocarbon potential of this area also has bearing on other resources such as groundwater (both fresh water and subsurface brines), underground storage of natural gas, and underground waste disposal.
Population and accompanying water use are expected to increase by 34 percent in southeastern Delaware between 1975 and 2000. To assess the capability of the aquifers in that area to supply the required amount of ground water, a study of those aquifers was started in 1976. Interpretation of geologic sections developed from drilling and geophysical data showed that the confining beds between the Manokin, Ocean City, and Pocomoke aquifers of Neogene age are thin and discontinuous in some parts of the area. Possible fault zones coinciding with deep tectonic features may also contribute to interconnection of these aquifers. Hydrographs of water levels in the aquifers show differential drawdown during periods of heavy pumping, but levels return to a common altitude during unstressed periods. Because of these characteristics, the Manokin, Ocean City, and Pocomoke aquifers are considered to be a single confined aquifer, in most places.
RI36 History of Oil and Gas Exploration in the Mid-Atlantic Region and Delaware's Involvement in the Federal OCS Leasing Program
There has been sporadic exploration for oil and gas in the Mid-Atlantic region for over 50 years. Non-commercial deposits of oil and gas have recently been discovered in the sedimentary rock section of the Outer Continental Shelf (OCS) 80 miles off the New Jersey-Delaware coast. The oil and gas occurs within entrapment structures in ancient rocks deposited and buried in a deep basin called the Baltimore Canyon trough. This trough forms part of the Coastal Plain and continental shelf geologic provinces on the Atlantic Coast.
It is now possible to evaluate some of the earlier assessments and offer tentative conclusions about the hydrocarbon resource potential of the Baltimore Canyon trough, a major northeast-southwest trending sedimentary basin off the Mid-Atlantic coast of the United States. For this purpose the Delaware Geological Survey has examined more than 2,500 miles (4,022 km) of seismic reflection profiles, the results of some offshore magnetic and gravity surveys, the results of the COST B-2 well, and the nonproprietary results through 1978 of exploratory drilling by the petroleum industry on federal leases.