DGS Geologic Map Series
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- ItemGeologic Map of the Elkton, Saint Georges, and Delaware City Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-05) Tomlinson, J.L.; Ramsey, K.W.Geologic mapping was conducted at 1:12,000 with a 1-ft contour basemap. In some instances, stratigraphic boundaries drawn at topographic breaks reflect detailed mapping using LiDAR data. Elevations of stratigraphic contacts along stream valleys are projected from subsurface data. Except for a few erosional bluffs, these contacts are covered by colluvium. This map supersedes this portion of Geology of the Chesapeake and Delaware Canal Area, Delaware: Delaware Geological Survey Geologic Map Series No. 1 (Pickett, 1970) and Geologic Map of New Castle County, Delaware: Delaware Geological Survey Geologic Map Series No. 13 (Ramsey, 2005). The geological history of the surficial units of the Elkton, Saint Georges, and Delaware City Quadrangles is the result of erosion of the Potomac Formation and younger Cretaceous and Cenozoic units by glacial dam burst events during the early Pleistocene. These periods of erosion were followed by stream incision and fluvial and estuarine deposition associated with multiple sea-level fluctuations during the middle to late Pleistocene. Periglacial activity that followed produced Carolina Bay deposits, alluvium along stream valley slopes, and freeze-thaw features on the land surface.
- ItemGeologic Map of the Cecilton and Middletown Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2020-09) Tomlinson, J.L.; Ramsey, K.W.Mapping was conducted using field maps at a scale of 1:12,000 with 2-ft contours. Stratigraphic boundaries drawn at topographic breaks reflect detailed mapping using contours not shown on this map. Most stratigraphic units mapped in stream valleys are projected from subsurface data. Except for a few erosional bluffs, these units are covered by colluvium. This map supersedes Geology of the Middletown-Odessa Area, Delaware: Delaware Geological Survey Geologic Map Series No. 2 (Pickett and Spoljaric, 1971). The geology of the map area reflects a complex history with a cut and fill geometry where the Pleistocene-aged deposits incised into older units. The Tertiary deposits were modified by erosion and deposition of the Columbia Formation during the early Pleistocene and again by the Lynch Heights and Scotts Corners Formations as a result of sea-level fluctuations during the middle to late Pleistocene. The geology is further complicated by periglacial activity that produced Carolina Bay deposits in the map area, which modified the land surface.
- ItemGeologic Map of Offshore Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2020-02) Mattheus, C.R.; Ramsey, K.W.; Tomlinson, J.L.Delineation of map units is based on sediment-core descriptions (e.g., texture, color, and composition) from 469 locations and seafloor morphology, which was assessed from a seamless NOAA/USGS topo-bathymetric model (Pendleton et al., 2014). The latter was integrated with high-resolution ‘chirper’ seismic reflection data, collected in 2013 by the Delaware Division of Natural Resources and Environmental Conservation (DNREC) and in 2015 as part of the 2015-2017 Bureau of Ocean Energy Management (BOEM) Atlantic Sand Assessment Project (ASAP), using sweep frequency pulses of 2-12 kHz and 0.7-12 kHz, respectively. Stratigraphic mapping based on these data allowed seafloor composition to be inferred across areas of limited core coverage (e.g., Federal waters, beyond 3 miles from shore) and facilitated the delineation of unit boundaries based on subsurface trends and seafloor geomorphology. A minimum surface-unit thickness of 1 ft served as the cut-off for geologic mapping of the seafloor, given the vertical resolution constraints of geophysical data. If surficial sediments were <1 ft thick, the underlying unit was mapped. Unit names and descriptions conform to those established in prior subsurface work along the Delaware barrier shoreline by Ramsey (1999), a synthesis of the Delaware coastal plain geology (Ramsey, 2010), and a previous map which included portions of the offshore surface geology (Ramsey and Tomlinson, 2012).
- ItemGeologic Map of the Millington, Clayton and Smyrna Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2018-04) Ramsey, K.W.; Tomlinson, J.L.The geological history of the surficial units of the Clayton, Smyrna, and the Delaware portion of the Millington Quadrangles are the result of deposition of the Beaverdam Formation and its modification by erosion and deposition of the Columbia Formation during the early Pleistocene. These units were then modified by the Lynch Heights and Scotts Corners Formations as a result of sea-level fluctuations during the middle to late Pleistocene. The geology is further complicated by periglacial activity that produced Carolina Bay deposits in the map area, which modified the land surface. This map supersedes Geologic Map of New Castle County, Delaware (Ramsey, 2005) and Geology of the Geologic Map of Kent County, Delaware (Ramsey, 2007).
- ItemGeologic Map of the Seaford West and Seaford East Quadrangles, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2015-08) Tomlinson, J.L.; Ramsey, K.W.; Andres, A.S.The geological history of the surficial units of the Seaford East Quadrangle and the Delaware portion of the Seaford West Quadrangle was the result 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 by the cut and fill geometry of the middle and late Pleistocene deposits incised into the Beaverdam Formation. The geology is further complicated by periglacial activity that produced dune deposits and the Carolina Bays in the map area, which modified the land surface.