Browsing by Author "Benson, R.N."
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Item Characterization Of The Potomac Aquifer, An Extremely Heterogeneous Fluvial System In The Atlantic Coastal Plain Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2004) McKenna, T.E.; McLaughlin, P.P.; Benson, R.N.Fluvial sands of the subsurface Cretaceous Potomac Formation form a major aquifer system used by a growing population in the northern Coastal Plain of Delaware. The aquifer is extremely heterogeneous on the megascopic scale and connectivity of permeable fluvial units is poorly constrained. The formation is characterized by alluvial plain facies in the updip section where it contains potable water. While over 50 aquifer tests indicate high permeability, the formation is primarily composed of fine-grained silt and clay in overbank and interfluvial facies. Individual fluvial sand bodies are laterally discontinuous and larger-scale sand packages appear to be variable in areal extent resulting in a labyrinth style of heterogeneity. The subsurface distribution of aquifers and aquitards has been interpreted within a new stratigraphic framework based on geophysical logs and on palynological criteria from four cored wells. The strata dip gently to the southeast, with generally sandy fluvial facies at the base of the formation lapping onto a south-dipping basement unconformity. The top of the formation is marked by an erosional unconformity that truncates successively older Potomac strata updip. Younger Cretaceous units overly the formation in its downdip area. In the updip area, the formation crops out or subcrops under Quaternary sands.The fine-grained facies include abundant paleosols that contain siderite nodules and striking mottling that commonly follows ped faces and root traces. These paleosols may serve as regional aquitards. This geologic complexity poses a challenge for determining the magnitudes and directions of ground-water flow within the aquifer that are needed for making informed decisions when managing this resource for water supply and contaminant remediation.Item Geologic And Hydrologic Studies Of The Oligocene - Pleistocene Section Near Lewes, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1990-10) Andres, A.S.; Benson, R.N.; Ramsey, K.W.; Talley, J.H.Borehole Oh25-02, located about 3 miles southwest of Lewes, Delaware, ends at a total depth of 1,337 ft in a mid-Oligocene glauconitic silt unit. It penetrated 317 ft of glauconitic sands and silts between the base of the Calvert Formation at a depth of 1,020 ft and total depth. A hiatus at 1,218 ft separates an outer neritic lower Miocene interval (Globorotalia kugleri Zone) above it from a deep upper bathyal mid-Oligocene (G. opima opima Zone) section below; the lower section is characterized by abundant large uvigerinid benthic foraminiferal species representing the transition from Uvigerina tumeyensis to Tiptonina nodifera. Similar uvigerinid assemblages identify the mid-Oligocene unit in boreholes near Bridgeville and Milford, Delaware; Cape May, New Jersey; and Ocean City, Maryland. Updip from these boreholes, the Calvert Formation, of latest Oligocene-middle Miocene age in Delaware, unconformably overlies middle Eocene glauconitic sands of the Piney Point Formation. The juxtaposition of the downdip mid-Oligocene rocks against the updip middle Eocene rocks can best be explained by a fault between the two regions.Item Geologic Field Trips In Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1977-05) Benson, R.N.; Hahn, W.F.; Jordan, R.R.; Pickett, T.E.; Talley, J.H.; Thompson, A.M.; Woodruff, K.D.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.Item Geological Studies Of Cretaceous And Tertiary Section, Test Well Je32-04, Central Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1985-06) Benson, R.N.; Jordan, R.R.; Spoljaric, NA cored well 1,422 feet (433 meters) deep drilled two miles southeast of Dover is the basis for this integrated study of the lithology and paleontology of the Cretaceous-Tertiary section in central Delaware. The section is subdivided into lithostratigraphic, biostratigraphic, chronostratigraphic, and heavy mineral units. Data and results are presented on a common base in three plates.Item Geology And Paleontology Of The Lower Miocene Pollack Farm Fossil Site Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1998) Benson, R.N.The Pollack Farm Site near Cheswold, Delaware, is named for a borrow pit excavated during highway construction. The excavation exposed a portion of the Cheswold sands of the lower Miocene Calvert Formation. Two sand intervals (Cheswold C-3 and C-4) yielded a diverse assemblage of land and marine vertebrate remains and more than 100 species of mollusks. An isolated occurrence of a sandy silt (the radiolarian bed) stratigraphically between the two macrofossil-bearing units yielded only siliceous microfossils—radiolarians, diatoms, and sponge spicules.Item Geology of South Central Kent County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1986) Benson, R.N.; Pickett, T.E.Item Geology of the Dover Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1983) Pickett, T.E.; Benson, R.N.Item Geology of the Smyrna-Clayton Area, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1977) Pickett, T.E.; Benson, R.N.Item Hydrocarbon Resource Potential Of The Baltimore Canyon Trough(Newark, DE: Delaware Geological Survey, University of Delaware, 1979-01) Benson, R.N.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.Item Internal Stratigraphic Correlation Of The Subsurface Potomac Formation, New Castle County, Delaware, And Adjacent Areas In Maryland And New Jersey(Newark, DE: Delaware Geological Survey, University of Delaware, 2006) Benson, R.N.; McLaughlin, P.P.This report presents a new time-stratigraphic framework for the subsurface Potomac Formation of New Castle County, Delaware, part of adjacent Cecil County, Maryland, and nearby tie-in boreholes in New Jersey. The framework is based on a geophysical well-log correlation datum that approximates the contact between Upper and Lower Cretaceous sediments. This datum is constrained by age determinations based on published and unpublished results of studies of fossil pollen and spores in samples of sediment cores from boreholes in the study area. Geophysical log correlation lines established above and below the datum approximate additional chronostratigraphic surfaces. The time-stratigraphic units thus defined are not correlated parallel to the basement unconformity, as in previous practice, but instead onlap it in an updip direction. In future studies, the sedimentary facies of the Potomac Formation within each time-stratigraphic layer may be mapped and analyzed as genetically related contemporaneous units. This new stratigraphic framework will allow better delineation of the degree of lateral connection between potential aquifer sands, thus enhancing understanding of aquifer architecture.Item Map of Exposed and Buried Early Mesozoic Rift Basins/Synrift Rocks of the U.S. Middle Atlantic Continental Margin(Newark, DE: Delaware Geological Survey, University of Delaware, 1992) Benson, R.N.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.Item Review Of The Subsurface Geology And Resource Potential Of Southern Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1976-04) Benson, R.N.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.Item Seismic Stratigraphy Along Three Multichannel Seismic Reflection Profiles off Delaware's Coast(Newark, DE: Delaware Geological Survey, University of Delaware, 1986) Benson, R.N.; Andres, A.S.; Roberts, J.H.; Woodruff, K.DThree multichannel, common-depth-point (CDP), seismic reflection profiles (Figures 1-3) were run off Delaware's coast (Figure 4) 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 (Figure 5). 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).Item Stratigraphy And Correlation Of The Oligocene To Pleistocene Section At Bethany Beach, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2008) McLaughlin, P.P.; Miller, K.G.; Browning, J.V.; Ramsey, K.W.; Benson, R.N.; Tomlinson, J.L.; Sugarman, P.J.The Bethany Beach borehole (Qj32-27) provides a nearly continuous record of the Oligocene to Pleistocene formations of eastern Sussex County, Delaware. This 1470-ft-deep, continuously cored hole penetrated Oligocene, Miocene, and Pleistocene stratigraphic units that contain important water-bearing intervals. The resulting detailed data on lithology, ages, and environments make this site an important reference section for the subsurface geology of the region.Item Stratigraphy Of The Post-Potomac Cretaceous-Tertiary Rocks Of Central Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1996) Benson, R.N.; Spoljaric, N.This Bulletin presents the subsurface stratigraphy of the post-Potomac Cretaceous and Tertiary rocks of the Atlantic Coastal Plain of central Delaware, between the Chesapeake and Delaware (C & D) Canal and Dover. Geophysical log correlations supported by biostratigraphic and lithologic data from boreholes in Delaware and nearby New Jersey provide the basis for the report. The stratigraphic framework presented here is important for identifying subsurface stratigraphic units penetrated by the numerous boreholes in this part of Delaware, particularly those rock units that serve as aquifers, because such knowledge allows for better prediction at ground-water movement and availability. Also, accurate stratigraphy is a prerequisite for interpreting the geologic history of the rocks and for the construction of maps that depict the structure and thickness of each unit.Item Structure Contour Map of Pre-Mesozoic Basement, Landward Margin of Baltimore Canyon Trough(Newark, DE: Delaware Geological Survey, University of Delaware, 1984) Benson, R.N.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 and gas.