GEOLOGIC MAP OF THE CECILTON AND MIDDLETOWN QUADRANGLES, DELAWARE

Funded by an award from the U.S. Geological Survey’s STATEMAP program, the Delaware Geological Survey (DGS) mapped the Middletown Quadrangle and the Delaware portion of the Cecilton Quadrangle (scale 1:24,000). The map area includes the south central portion of New Castle County and is adjacent to Cecil County, Maryland. The primary mapping goals were to identify the surficial geologic units, to identify the geologic units which subcrop beneath those units (including a major regional aquifer), and to understand the relationship between underlying geology and the overprint of Carolina Bays which occur at the land surface. Twenty-nine split spoon borings were obtained, totaling over 700 ft of new core in the Coastal Plain. Sixty-seven locations were hand augered for a total of 415 linear feet of sampling. To supplement the newly collected data, historic well and soil boring records and previous mapping efforts were utilized. Geologic contacts were constructed in ESRI’s ArcMap™ and Adobe Illustrator™ CS5 was used for the map layout and cartography.

The geologic map is comprised of eleven surficial lithostratigraphic units and two anthropomorphic units. Five additional lithostratigraphic units that occur only in the subsurface are included on the cross section. The geology of the map area reflects a complex history with cut and fill geometry of the Pleistocene deposits incised into Miocene and older units. The older units were modified by erosion and deposition of the Columbia Formation during the early Pleistocene and again by the Lynch Heights and Scotts Corners Formation 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.