This vector data set contains the rock unit polygons for the surficial geology in the Delaware Coastal Plain covered by DGS Geologic Map Series No. 17 (Harbeson quadrangle). The complex geologic history of the surficial units of the Harbeson Quadrangle 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 is further complicated by periglacial activity that produced dune deposits and Carolina Bays scattered throughout the map area.

The complex geologic history of the surficial units of the Harbeson Quadrangle is one of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology is further complicated by periglacial activity that produced dune deposits and Carolina Bays scattered throughout the map area.

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).

Rising and highstands of sea level during the middle to late Pleistocene deposited swamp to nearshore sediments along the margins of an ancestral Delaware Bay, Atlantic coastline, and tributaries to an ancestral Chesapeake Bay. These deposits are divided into three lithostratigraphic groups: the Delaware Bay Group, the Assawoman Bay Group (named herein), and the Nanticoke River Group (named herein). The Delaware Bay Group, mapped along the margins of Delaware Bay, is subdivided into the Lynch Heights Formation and the Scotts Corners Formation. The Assawoman Bay Group, recognized inland of Delaware’s Atlantic Coast, is subdivided into the Omar Formation, the Ironshire Formation, and the Sinepuxent Formation. The Nanticoke River Group, found along the margins of the Nanticoke River and its tributaries, is subdivided into the Turtle Branch Formation (named herein) and the Kent Island Formation.

Delaware Bay Group deposits consist of bay-margin coarse sand and gravel that fine upward to silt and silty sand. Beds of organic-rich mud were deposited in tidal marshes. Near the present Atlantic Coast, the Delaware Bay Group includes organic-rich muds and shelly muds deposited in lagoonal environments.

Assawoman Bay Group deposits range from very fine, silty sands to silty clays with shells deposited in back-barrier lagoons, to fine to coarse, well-sorted sands deposited in barriers and spits.

Nanticoke River Group deposits consist of coarse sand and gravel that fine upward to silty clays. Oyster shells are found associated with the clays in the Turtle Branch Formation. Organic-rich clayey silts were deposited in swamps and estuaries. Well-sorted fine sands to gravelly sands were deposited on beaches and tidal flats on the flanks of the ancestral Nanticoke River and its tributaries.

The Lynch Heights, Omar, and Turtle Branch Formations are age-equivalent units associated with highstands of sea level,which occurred at approximately 400,000 and 325,000 yrs B.P. (MIS 11 and 9, respectively). The Scotts Corners, Ironshire, Sinepuxent, and Kent Island Formations are age-equivalent units associated with highstands of sea level, which occurred between 120,000 and 80,000 yrs B.P. (MIS 5e and 5a, respectively).

This vector data set contains the rock unit polygons for the surficial geology in the Delaware Coastal Plain covered by DGS Geologic Map No. 15 (Geologic Map of the Georgetown Quadrangle, Delaware). The geologic history of the surficial geologic units of the Georgetown Quadrangle is primarily that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition of younger stratigraphic units. The age of the Beaverdam Formation is uncertain due to the lack of age-definitive fossils within the unit but is thought to be between late Pliocene to early Pleistocene in age. Refer to Ramsey, 2010 (DGS Report of Investigations No. 76) for details regarding the stratigraphic units.

To facilitate the GIS community of Delaware and to release the geologic map of the Georgetown Quadrangle 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 15. 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).

The geologic history of the surficial geologic units of the Georgetown Quadrangle is primarily that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition of younger stratigraphic units. The age of the Beaverdam Formation is uncertain due to the lack of age-definitive fossils within the unit. Stratigraphic relationships in Delaware indicate that it is no older than late Miocene and no younger than early Pleistocene. Regional correlations based on similarities of depositional style, stratigraphic position, and sediment textures suggest that it is likely late Pliocene in age; correlative with the Bacons Castle Formation of Virginia (Ramsey, 1992, 2010).

This map shows the surficial geology of Kent County, Delaware at a scale of 1:100,000. Maps at this scale are useful for viewing the general geologic framework on a county-wide basis, determining the geology of watersheds, and recognizing the relationship of geology to regional or county-wide environmental or land-use issues. This map, when combined with the subsurface geologic information, provides a basis for locating water supplies, mapping ground-water recharge areas, and protecting ground and surface water. Geologic maps are also used to identify geologic hazards, such as flood-prone areas, to identify sand and gravel resources, and to support state, county, and local land-use and planning decisions.

This data set contains the rock unit polygons for the surficial geology in ESRI shapefile format for DGS Geologic Map No. 14 (Geologic Map of Kent County, Delaware). This map shows the surficial geology of Kent County, Delaware, at a scale of 1:100,000.