Subsurface Geology of the Area Between Wrangle Hill and Delaware City, Delaware

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Author(s)Jengo, J.W.
Author(s)McLaughlin, P.P.
Author(s)Ramsey, K.W.
Date Accessioned2013-04-04T12:13:04Z
Date Available2013-04-04T12:13:04Z
Publication Date2013-03
DescriptionThis report includes 4 plates and 4 appendices as separate files.en_US
AbstractThe geology and hydrology of the area between Wrangle Hill and Delaware City, Delaware, have been the focus of numerous studies since the 1950s because of the importance of the local groundwater supply and the potential environmental impact of industrial activity. In this report, 490 boreholes from six decades of drilling provide dense coverage, allowing detailed characterization of the subsurface geologic framework that controls groundwater occurrence and flow. The region contains a lower section of tabular Cretaceous strata (Potomac, Merchantville, Englishtown, Marshalltown,and Mount Laurel Formations in ascending order) and a more stratigraphically complex upper section of Pleistocene-to-modern units (Columbia, Lynch Heights, and Scotts Corners Formations, latest Pleistocene and Holocene surficial sediments and estuarine deposits). The lowermost Potomac Formation is a mosaic of alluvial facies and includes fluvial channel sands that function as confined aquifer beds; however, the distribution of aquifer-quality sand within the formation is extremely heterogeneous. The Merchantville Formation serves as the most significant confining layer. The Columbia Formation is predominantly sand and functions as an unconfined aquifer over much of the study area. To delineate the distribution and character of the subsurface formations, densely spaced structural-stratigraphic cross sections were constructed and structural contour maps were created for the top of the Potomac Formation and base of the Columbia Formation. The Cretaceous formations form a series of relatively parallel strata that dip gently (0.4 degrees) to the southeast. These formations are progressively truncated to the north by more flatly dipping Quaternary sediments, except in a narrow north-south oriented belt on the east side of the study area where the deeply incised Reybold paleochannel eroded into the Potomac Formation. The Reybold paleochannel is one of the most significant geological features in the study area. It is a relatively narrow sandfilled trough defined by deep incision at the base of the Columbia Formation. It reaches depths of more than 110 ft below sea level with a width as narrow as 1,500 ft. It is interpreted to be the result of scour by the sudden release of powerful floodwaters from the north associated with one or more Pleistocene deglaciations. Where the Reybold paleochannel cuts through the Merchantville confining layer, a potential pathway exists for hydrological communication between Columbia and Potomac aquifer sands. East of the paleochannel, multiple cut-and-fill units within the Pleistocene to Holocene section create a complex geologic framework. The Lynch Heights and Scotts Corners Formations were deposited along the paleo-Delaware River in the late Pleistocene and are commonly eroded into the older Pleistocene Columbia Formation. They are associated with scarps and terraces that represent several generations of sea-level-driven Pleistocene cut-and-fill. They, in turn, have been locally eroded and covered by Holocene marsh and swamp deposits. The Lynch Heights and Scotts Corners Formations include sands that are unconfined aquifers but complicated geometries and short-distance facies changes make their configuration more complex than that of the Columbia Formation.en_US
URLhttp://udspace.udel.edu/handle/19716/12521
Languageen_USen_US
PublisherNewark, DE: Delaware Geological Survey, University of Delawareen_US
Part of SeriesReport of Investigations;78
Keywordsaquiferen_US
KeywordsColumbia aquiferen_US
KeywordsColumbia Formationen_US
KeywordsCretaceous Perioden_US
Keywordscross-sectionsen_US
KeywordsDelawareen_US
KeywordsDelaware Bay Groupen_US
KeywordsDelaware Cityen_US
KeywordsEnglishtown Formationen_US
Keywordsenvironmental monitoringen_US
Keywordsgeologyen_US
Keywordsgroundwateren_US
Keywordshydrogeologyen_US
KeywordsLynch Heights Formationen_US
KeywordsMagothy Formationen_US
KeywordsMarshalltown Formationen_US
KeywordsMerchantville Formationen_US
KeywordsMount Laurel Formationen_US
KeywordsNew Castle Countyen_US
KeywordsPotomac aquiferen_US
KeywordsPotomac Formationen_US
KeywordsScotts Corners Formationen_US
Keywordsstratigraphyen_US
Keywordssubsurfaceen_US
Keywordsunconfined aquiferen_US
KeywordsWrangle Hillen_US
TitleSubsurface Geology of the Area Between Wrangle Hill and Delaware City, Delawareen_US
TypeTechnical Reporten_US
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