Geochemical data from Ordovician and Silurian mafic rocks in the Wilmington Complex in Delaware, the James Run Formation in Cecil County, Maryland, and the Wissahickon Formation in Delaware and Pennsylvania were collected in conjunction with preparation of a new geologic map of the Delaware-Pennsylvania Piedmont. Although concentrations of most elements may have been disrupted by metamorphism, the more stable high field strength elements, including the rare earth elements (REE), are consistent within mapped lithodemic units and are compared to modern basaltic magmas from relatively well known tectonomagmatic environments.
Our results are similar to those for other Appalachian mafic rocks and suggest a suprasubduction zone tectonic setting for the Wilmington Complex and the James Run Formation in Cecil County, Maryland. Thus, the rocks of the Wilmington Complex plus the James Run Formation in Cecil County may be stages in a continuum that records the temporal magmatic evolution of an arc complex.
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
Ground water comprises nearly all of the water supply in Kent County, Delaware. The confined aquifers of the area are an important part of this resource base. The aim of this study is to provide an up-to-date geologic framework for the confined aquifers of Kent County, with a focus on their stratigraphy and correlation. Seven confined aquifers are used for water supply in Kent County. All occur at progressively greater depths south-southeastward, paralleling the overall dip of the sedimentary section that underlies the state. The two geologically oldest, the Mount Laurel and Rancocas aquifers, are normally reached by drilling only in the northern part of the county. The Mount Laurel aquifer is an Upper Cretaceous marine shelf deposit composed of clean quartz sands that are commonly glauconitic. It occurs at around 300 ft below sea level in the Smyrna Clayton area and is typically just less than 100 ft thick. Southward, toward Dover, it passes into fine-grained facies that do not yield significant ground water. The Rancocas aquifer is a Paleocene to Eocene marine unit of shelf deposits consisting of glauconite-rich sands with shells and hard layers. It occurs as high as 100 ft below sea level in northwestern Kent County and deepens southeastward, rapidly changing facies to finer-grained, nonaquifer lithologies in the same direction.
This publication formally establishes the Old College Formation, a lithostratigraphic unit located along the Fall Zone of Delaware. It is named for sediments encountered in numerous drill holes on, and adjacent to, the Old College campus of the University of Delaware in Newark, Delaware. The Old College Formation consists of micaceous, brown to reddish-brown, fine to coarse sand with scattered gravelly sand overlain by sandy silt beds. The Old College Formation has a distinctive suite of abundant heavy minerals including sillimanite, staurolite, and magnetite. Provenance of the sand is local, derived from erosion of Piedmont rocks along and just to the west of the Fall Zone. The unit is the result of alluvial fan deposition on a pediment-like surface extending from the Fall Zone to the adjacent Coastal Plain. The Old College Formation is a surficial unit that overlies Piedmont saprolite, the Cretaceous Potomac Formation, and the Pleistocene Columbia Formation. No fossil data are available for the unit. Stratigraphic and geomorphic positions indicate that it ranges from 500,000 to 1,000,000 years old; slightly younger than the Columbia Formation.
The Cypress Swamp of Sussex County, Delaware, is underlain by a body of late Pleistocene- to Holocene-age unconsolidated sediments. They form a mappable geologic unit herein named the Cypress Swamp Formation. Deposits of the formation can be found outside the current boundaries of the Cypress Swamp and record the erosion and redistribution of older Pleistocene coastal and Pliocene sedimentary units.
RI61 The Occurrence and Distribution of Several Agricultural Pesticides in Delaware’s Shallow Ground Water
In June 1996, the U. S. Environmental Protection Agency (USEPA) proposed a regulation to require individual states to develop Pesticide Management Plans (PMPs) to protect their ground-water resources from pesticide contamination. The USEPA designated the predominantly agricultural pesticides atrazine, alachlor, cyanazine, metolachlor, and simazine as the first five that would require a PMP.
This report accompanies a new map that revises the original bedrock geologic maps of the Delaware Piedmont compiled by Woodruff and Thompson and published by the Delaware Geological Survey (DGS) in 1972 and 1975. Combined detailed mapping, petrography, geochemistry, and U-Pb geochronology have allowed us to redefine two rock units and formally recognize eleven new units. A section of the Pennsylvania Piedmont is included on the new map to show the entire extent of the Mill Creek Nappe and the Arden Plutonic Supersuite.
The stream-gaging network in Delaware is a major component of many types of hydrologic investigations. To ensure that the network is adequate for meeting multiple data needs by a variety of users, it must represent the range of hydrologic conditions and land-use types found in Delaware, and include enough stations to account for hydrologic variability. This report describes the current stream-gaging network in Delaware and provides an evaluation of its representativeness for the State.
The Setters Formation, identified on the southeast side of Pleasant Hill valley in well Cb13-16, contains the prograde mineral assemblages (1) microcline, biotite, and sillimanite +/- garnet, and (2) microcline, biotite, sillimanite, and muscovite +/- garnet. These pelitic assemblages allow us to infer peak metamorphic conditions between 620° and 680°C and 4 to 6 kilobars pressure, if PH20/Pfluid is > 0.5. There is some evidence in the drill cuttings to indicate that partial melting accompanied the formation of sillimanite, thus constraining peak temperature to > 640°C.
Investigation of the Neogene and Quaternary geology of the Milford and Mispillion River quadrangles has identified six formations: the Calvert, Choptank, and St. Marys formations of the Chesapeake Group, the Columbia Formation, and the Lynch Heights and Scotts Comers formations of the Delaware Bay Group. Stream, swamp, marsh, shoreline, and estuarine and bay deposits of Holocene age are also recognized. The Calvert, Choptank, and St. Marys formations were deposited in inner shelf marine environments during the early to late Miocene. The Columbia Formation is of fluvial origin and was deposited during the middle Pleistocene prior to the erosion and deposition associated with the formation of the Lynch Heights Formation. The Lynch Heights Formation is of fluvial and estuarine origin and is of middle Pleistocene age. The Scotts Corners Formation was deposited in tidal, nearshore, and estuarine environments and is of late Pleistocene age. The Scotts Corners Formation and the Lynch Heights Formation are each interpreted to have been deposited during more than one cycle of sea-level rise and fall. Latest Pleistocene and Holocene deposition has occurred over the last 11,000 years.
Radiocarbon dates from 231 geologic samples from the offshore, coastal, and upland regions of Delaware have been compiled along with their corresponding locations and other supporting data. These data now form the Delaware Geological Survey Radiocarbon Database.
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.
This map shows the total thickness (regolith) of both the loose, transported material and the weathered rock that overlies crystalline rocks of the Delaware Piedmont. Transported material is generally thin and the weathered rock in place (saprolite) usually makes up the bulk of the regolith. Saprolite may vary gradationally from a weathered rock that has retained much of the characteristics of the parent rock to a product mineralogically and texturally different from its source rock.
The information contained in this Guidebook was compiled on the occasion of the Annual Meeting of the Association of American State Geologists held in Delaware in June 1977. The Delaware Geological Survey is pleased to have been selected to host this national meeting. The field trip logs were designed to familiarize geologists from across the United States with basic features of Delaware's geology and resources. We have also sought to identify some points of historical and cultural interest that may help the visitor become familiar with our State. Experience has shown that field guides retain their usefulness beyond the event that they initially served. They may assist classes, other groups, and individuals seeking additional information about their physical environment. Therefore, this Guidebook has been published as an Open File Report for public distribution. All users of this information are urged to exercise caution, especially at rock faces and along waterways, and to obtain specific permission for visits from landowners where necessary.
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.
OFR4 Papers Presented by Staff Members of the Delaware Geological Survey at the Baltimore Meeting of the Northeastern Section of the Geological Society of America, March, 1974
This report is a compilation of four papers presented by DGS staff members at the Baltimore Meeting of the Northeastern Section of the Geological Society of America, March, 1974.
OFR38 Data Report on Rock Cores from Red Mill Road, Harmony Road, Prices Corner, and Newport, Delaware
The Delaware Piedmont is underlain by metamorphosed sedimentary and igneous rocks of Middle Proterozoic to Paleozoic age. The rocks have been studied for many years, but because of poor exposure, high-grade metamorphism, and intense deformation, it has been difficult to identify units, understand their stratigraphic relationships to one another, and determine their origin and history; however, northern Delaware occupies a critical position in the central Appalachian Piedmont, and understanding its geology is key to understanding the geology of this region.