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Bedrock Geologic Map of the Delaware Piedmont
(Newark, DE: Delaware Geological Survey, University of Delaware, 2021-06) Schenck, W.S.
The Piedmont rock units in Delaware, and bedrock geologic map of Schenck et al. (2000) are revised in this report based on new rock geochemistry, geochronometric data, petrography, and recent detailed mapping. Major revisions include: • revising the extent of the Christianstead Gneiss and Windy Hills Gneiss • abandoning the Wissahickon Formation as originally mapped in Delaware by Bascom (1902, 1905) and Bascom et al. (1909, 1920, and 1932) and replacing it with the Mt. Cuba Gneiss, a lithodeme of the West Grove Metamorphic Suite (Bosbyshell et al., 2012, 2013, 2014, 2015), and reserving the Wissahickon Schist/Formation for the metasediments on the east side of the Wilmington Complex magmatic arc and referring to them herein as Wissahickon Formation (restricted sense) • extending the Rosemont Shear Zone from Pennsylvania southwest through Delaware to Maryland separating the Mt. Cuba Gneiss and the Wilmington Complex • formally naming and describing two new units in the Wilmington Complex - the Greenville Gabbro and the Thompsons Bridge Gneiss. Additional Notes Plate 1 of OFR54 can also be viewed in a Web Mapping Application. Layers can be turned on and off and manipulated under the "Layers" icon in the upper right hand corner. Cross section is available by clicking on the cross section line. Rock unit descriptions available by clicking on the geologic map. OFR54 Plate 1 (Bedrock Geologic Map of the Delaware Piedmont) Web Mapping Application Plate 1 Summary The vector data set contains the rock unit polygons for the surficial geology for DGS Open File Report 54 - Plate 1. The Piedmont rock units in Delaware, and bedrock geologic map of Schenck et al. (2000) are revised on this map based on new rock geochemistry, geochronometric data, petrography, and recent detailed mapping. Major revisions include: • revising the extent of the Christianstead Gneiss and Windy Hills Gneiss • abandoning the Wissahickon Formation as originally mapped in Delaware by Bascom (1902, 1905) and Bascom et al. (1909, 1920, and 1932) and replacing it with the Mt. Cuba Gneiss, a lithodeme of the West Grove Metamorphic Suite (Bosbyshell et al., 2012, 2013, 2014, 2015), and reserving the Wissahickon Schist/Formation for the metasediments on the east side of the Wilmington Complex magmatic arc and referring to them herein as Wissahickon Formation (restricted sense) • extending the Rosemont Shear Zone from Pennsylvania southwest through Delaware to Maryland separating the Mt. Cuba Gneiss and the Wilmington Complex • formally naming and describing two new units in the Wilmington Complex - the Greenville Gabbro and the Thompsons Bridge Gneiss.
Delaware Geological Survey Petrographic Data Viewer
(Newark, DE: Delaware Geological Survey, University of Delaware, 2021-05) Schenck, W.S.; Wang, L.T.
Petrography is a branch of geoscience focused on the description and classification of rocks, primarily by microscopic study of optical properties of minerals. A thin sliver of rock is cut from a sample, mounted on a glass slide, ground to approximately 30 microns (0.03mm), and viewed under a microscope that uses polarized light. By observing the colors produced as plain polarized light and crossed (90 degrees) polarized light shines through the minerals, petrologists can determine the minerals that comprise the sampled rock. The data and photomicrographs of thin sections within the Delaware Geological Survey (DGS) Petrographic Data Viewer represent the total collection of the Delaware Geological Survey for the Delaware Piedmont and surrounding areas. The data viewer includes slides from DGS research, slides donated by researchers, and slides culled from class reports, master's theses, and Ph.D. dissertations. Within the application, the “Slide Made For” field identifies the original owner of the thin section. The researchers include: John Branca, A.D. Cohen, Bernard Dirska, Gregory S. Ghon, G. Michael Hager, C. Scott Howard, Guy W. Metz, Margaret O. Plank, LeAnn Srogi, Richard F. Ward, and DGS. Existing data/slide descriptions have been included; however, no attempt was made to change the data/descriptions originally prepared by these researchers other than to correct typographical errors. These data appear as they were originally presented unless noted that modifications were made at a later date. Additional Notes The zoom tool allows one to focus on an area of interest. Click on an outcrop (sample) location to open a popup window containing the data for the selected sample(s). The popup window also includes thumbnail photomicrographs of the thin section in both plain polarized light and crossed polarized light. Click the thumbnail to open a full-size image. If interested in specific outcrops or thin sections, use the search tool to query by DGS outcrop ID, lithology, or address. Launch the Delaware Geological Survey Petrographic Data Viewer References Branca, J., 1979, Petrology and structure of the Glenarm Series and associated rocks in the Mill Creek area, Delaware: Newark, Delaware, University of Delaware, unpublished Master's thesis, 84 p. Cohen, A. D., 1964, Petrologic analysis of the gneisses at Windy Hills Bridge, Delaware: Newark, Delaware, University of Delaware, unpublished Geo402 class paper, DGS Sample/thin section record only. Dirska, B., 1990, Petrology and evolution of the plutonic igneous rocks of the Wilmington Complex, northeastern northeastern Delaware and southeastern Pennsylvania: Newark, Delaware, University of Delaware, unpublished Master's thesis, 227 p. Gohn, G.S., John, C.J., Hager, G.M., Niemann, N.L., Grundl, T.J., Bair, P.L., Dempsey, J.M., Ferris, L.A., and Lazzeri, J.J., 1974, Reconnaissance geology of the Mill Creek uplift, northeastern Delaware and southeastern Pennsylvania Piedmont: Newark, Delaware, University of Delaware, unpublished report, 23 p. Hager, G. M., 1976, Petrologic and structural relations of the crystalline rocks in the Hoopes Reservoir area, Delaware: Newark, Delaware, University of Delaware, unpublished Master's thesis, 79 p. Howard, C. S., 1984, Geological and geophysical investigations in the Wilmington Complex/Wissahickon Formation boundary area, Delaware Piedmont: Newark, Delaware, University of Delaware, unpublished Master's thesis, 258 p. Metz, G. W., 1988, The petrology of the cordierite-bearing gneisses near Montchanin, Delaware: Newark, Delaware, University of Delaware, unpublished senior thesis, 44 p. Plank, M. O., 1989,Metamorphism in the Wissahickon Formation of Delaware and adjacent areas of Maryland and Pennsylvania: Newark, Delaware, University of Delaware, unpublished Master's thesis, 111 p. Srogi, L., 1988, The petrogenesis of the igneous and metamorphic rocks in the Wilmington Complex, Pennsylvania-Delaware Piedmont: Philadelphia, Pennsylvania, University of Pennsylvania, unpublished Ph. D. dissertation, 613 p. Ward, R. F., 1958, Petrology and metamorphism of the Wilmington Complex Delaware adjacent Pennsylvania and Maryland: Philadelphia, Pennsylvania, Bryn Mawr College, unpublished Ph. D. dissertation, 103 p.
Kent County Groundwater Monitoring Project: Results of Subsurface Exploration
(Newark, DE: Delaware Geological Survey, University of Delaware, 2019-09) Andres, A.S.; McQuiggan, R.W.; He, C.
This report documents the methods and results derived from subsurface exploration, monitoring well installation, and hydraulic testing conducted during the project "Groundwater and Saline Water Intrusion Monitoring Network Infrastructure Improvements: Kent County, Delaware". This project was focused on the aquifers in Kent County that supply water to wells for domestic, public, irrigation, and commercial uses as well as provide base flow to local streams. From shallowest to deepest, they are the Columbia, Milford, Frederica, Federalsburg, Cheswold, Piney Point, Rancocas, and Mt. Laurel aquifers.
Results of Groundwater Flow Simulations In the East Dover Area, Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 2018-08) He, C.; Andres, A.S.
In 2015, staff of the Water Supply Section of the Delaware Department of Natural Resources and Environmental Control (DNREC) informed the DGS of their concerns about overpumping of the unconfined Columbia aquifer in an area east of Dover (Figure 1). In this area, the City of Dover’s Long Point Road Wellfield (LPRW) and numerous irrigation systems pump water from the shallow Columbia aquifer. Overpumping is a cause for concern because it may 1) increase the risk for saltwater intrusion into the aquifer from saline tidal creeks and marshes and, 2) induce extra drawdown that could reduce the transmissivity of the aquifer and decrease well yields. The potential for overpumping will become more significant when an electric generating station served by the LPRW is expected to increase capacity and requires more water. This report summarizes monitoring and modeling that were conducted to investigate the potential impacts of overpumping. Automated water level and salinity sensors were installed and operated in three monitoring wells, and a digital groundwater flow model was constructed. The model was run in both steady-state and transient modes. As is the case with most models, many assumptions and simplifications had to be made because of data limitations. The model was calibrated to a spatially limited set of data. Consequently, model outputs are meant to inform how the aquifers behave given the assumptions and simplifications and will not represent precise predictions of water pressures in the area represented by the model. Additional data are now being collected in the model domain to refine the accuracy and precision of model results.
Groundwater Monitoring Procedures Part 1: Equipment and Procedures for Manual and Automated Field Measurement of Groundwater Levels in Dedicated Monitoring Wells
(Newark, DE: Delaware Geological Survey, University of Delaware, 2018-08) Andres, A.S.; He, C.; McKenna, T.E.
The Delaware Geological Survey (DGS) has measured, managed, and distributed groundwaterlevel data for several decades using widely accepted procedures and practices, many of which were derived from interactions with staff of the USGS, consulting firms, and other state agencies. Many of the individual methods and procedures have been described in DGS reports, however, written documentation for these tasks have not been assembled in a single published document. The need for such a document has become more apparent with the development of standards for participation in the National Ground-Water Monitoring Network (SOGW, 2009). This document describes methods used by the DGS for routine manual and automated measurement of groundwater levels in dedicated monitoring wells. Alternative methods used for manual measurement of water levels in other types of wells are noted in this document to provide reference for historical measurements but not described in detail. These methods are excerpted and modified from procedures described by federal agencies and national standards organizations (e.g., ASTM, D4750-2007; Drost, 2005; USEPA, 2007). In this document, the term water levels will be used interchangeably with groundwater levels. Please refer to these and other appropriate documents for additional guidance or contact DGS staff with specific questions. Practices pertaining to data processing and management, metadata, and quality assurance procedures for electronic data are rapidly evolving. Additional sections on these topics will be added to this document as time and resources permit.
Database of Quaternary Coastal Geochronologic Information for the Atlantic and Pacific Coasts of North America (additional information for sites in Peru and Chile)
(Newark, DE: Delaware Geological Survey, University of Delaware, 2015-02) Wehmiller, John F.; Pellerito, V.
Open-File Report 50 presents and describes a database of geochronological information for coastal deposits of the US Atlantic and Pacific coasts, as well as for sites from the Pacific coast of South America. This database represents a synthesis of nearly forty years of study conducted by John F. Wehmiller and students in the Department of Geological Sciences, University of Delaware, as well as many collaborating colleagues. The majority of the chronological information in the database is based on amino acid racemization (AAR) data for fossil mollusks obtained from over 1000 collection sites. These chronological data have been used for various mapping, paleoenvironmental, stratigraphic, sea-level, and tectonic studies. In addition to the database itself, 18 on-line supplements containing information related to sample descriptions, sample and collection site photographs, field notes, supporting or related analytical data, and laboratory publications and technical reports are available. Periodic updates and additions will be made where appropriate. The database will be updated regularly to add new data or to complete entries that are currently blank. The instructions provided with the database indicate the date of the latest revision, as well as all revisions after the first release. Some output data from the Amino Acid Racemization Data Base (AARDB) are available at on-line mapping sites or are posted to the NOAA-World Data Center for archival preservation (http://www.ncdc.noaa.gov/paleo/aar.html).
Hydrologeologic Framework Of Southern New Castle County
(Newark, DE: Delaware Geological Survey, University of Delaware, 2008) Dugan, B.L.; Neimeister, M.P.; Andres, A.S.
Southern New Castle County is dependent on ground water for nearly all of its water supply. The area has been undergoing development from predominately agricultural land use to urban/suburban land use (Delaware Water Supply Coordinating Council [WSCC], 2006). With this development comes a need to more accurately predict the availability of ground water to reduce the potential of overusing the resource.
Potential For Ground-Water Recharge In The Coastal Plain Of Northern New Castle County, Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 1983-12) Petty, S.; Miller, W.D.; Lanan, B.A.
This map was constructed primarily to indicate the possibilities for artificial recharge into both the surficial sediments of Quaternary age (exclusive of soils) and the older, immediately underlying sediments. However it can also be used to determine where natural recharge might be entering the ground most readily in those areas relatively free from impermeable cover. The surficial sediments include micaceous sands and gravels in the vicinity of the Fall Line derived from underlying crystalline rocks, Holocene marsh deposits, Delaware River sediments, and the Columbia Formation of Pleistocene age. The Columbia Formation is composed of poorly sorted sands with some gravels, silts and occasional clays. The unit is one of the most important ground-water reservoirs in New Castle County.
Potential For Ground-Water Recharge In The Coastal Plain Of Central New Castle County, Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 1985-05) Petty, S.; Miller, W.D.; Lanan, B.A.
This map indicates the possibilities for artificial recharge into both the surficial sediments of Quaternary age (exclusive of soils) and the older, immediately underlying sediments. However, the map can also be used to determine where natural recharge might be entering the ground most readily in those areas relatively free from impermeable cover. The surficial materials include marsh and Delaware River sediments of Holocene age and older Pleistocene sediments of the Columbia Formation. The Columbia Formation is composed of poorly sorted sands with some gravels, silts, and occasional clays. The unit is one of the most important ground-water reservoirs in New Castle County.
Results Of The Domestic Well Water-Quality Study
(Newark, DE: Delaware Geological Survey, University of Delaware, 2008) Pellerito, V.; Neimeister, M.P.; Wolff, E.; Andres, A.S.
The Delaware Geological Survey conducted a review of existing ground-water quality data collected from shallow (less than 100 feet deep) domestic water-supply wells and small public water-supply wells (serving fewer than 100 residents) to determine the extent to which toxic and carcinogenic compounds are present in the shallow ground water serving domestic water supply wells. These data were generated by several agencies including the Delaware Geological Survey, U.S. Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Division of Public Health Office of Drinking Water, and the Delaware Department of Agriculture Pesticide Management Program.
Digital Watershed And Bay Boundaries For Rehoboth Bay, Indian River Bay, And Indian River
(Newark, DE: Delaware Geological Survey, University of Delaware, 2007) McKenna, T.E.; Andres, A.S.; Lepp, K.P.
Digital watershed and bay polygons for use in geographic information systems were created for Rehoboth Bay, Indian River, and Indian River Bay in southeastern Delaware. Polygons were created using a hierarchical classification scheme and a consistent, documented methodology that enables unambiguous calculations of watershed and bay surface areas within a geographic information system. The watershed boundaries were delineated on 1:24,000-scale topographic maps. The resultant polygons represent the entire watersheds for these water bodies, with four hierarchical levels based on surface area. Bay boundaries were delineated by adding attributes to existing polygons representing water and marsh in U.S. Geological Survey Digital Line Graphs of 1:24,000-scale topographic maps and by dissolving the boundaries between polygons with similar attributes. The hierarchy of bays incorporates three different definitions of the coastline: the boundary between open water and land, a simplified version of that boundary, and the upland-lowland boundary. The polygon layers are supplied in a geodatabase format.
Storm-Water And Baseflow Sampling And Analysis In The Nanticoke River Watershed: Preliminary Report Of Findings 2002-2004
(Newark, DE: Delaware Geological Survey, University of Delaware, 2007) Andres, A.S.; Ullman, W.J.; Savidge, K.B.
This report provides initial research results of a storm-water and baseflow sampling and analysis project conducted by the University of Delaware, College of Marine and Earth Studies and the Delaware Geological Survey. Baseflow samples were collected from four tributary watersheds of the Nanticoke River and one station on the Nanticoke River on 18 occasions from March 2003 to June 2004. Water samples were filtered in the field to separate dissolved nutrients for subsequent analysis, and separate samples were collected and returned to the laboratory for particulate nutrient determinations. On each sampling date, temperature, conductivity, pH, and dissolved oxygen concentrations were determined at each sampling station. The U.S. Geological Survey made stream discharge measurements at each of these sites under a joint-funded agreement with the Delaware Department of Natural Resources and Environmental Control and the Delaware Geological Survey. Together, the nutrient and discharge data were used to determine the total nutrient loads at five stations and unit loads (normalized to watershed area) at two of those stations on a quarterly and annual basis. Problems with watershed delineation and low quality discharge data limit these calculations for some watersheds. At the same five stations, storm water was collected during six storms from March 2003 to June 2004. Storm-water loadings of nutrients in each watershed were calculated from the concentrations of nutrients in water samples collected at fixed time intervals from the beginning of the storm-water discharge period until recession to baseflow. Measured storm loads were used as the basis for estimating loads from unsampled storms. These data provide the Delaware Department of Natural Resources and Environmental Control with a more complete picture of the seasonal dependence of nutrient loading to streams in the Nanticoke River watershed and to Chesapeake Bay receiving waters. These may also be used to establish total maximum daily load goals.
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.
Results Of Trenching Investigations Along The New Castle Railroad Survey-1 Seismic Line, New Castle, Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 2002) McLaughlin, P.P.; Baxter, S.J.; Ramsey, K.W.; McKenna, T.E.; Strohmeier, S.A.
Five trenches were excavated to a depth of 5 to 8 ft along the path of an abandoned railroad grade near the city of New Castle to investigate potential near-surface faults that may be related to earthquake activity in northern Delaware. Seismic reflection profiles along this line suggested the existence of significant faulting in the area, which lies along a postulated fault trend in eastern New Castle County. Subsequent drilling, however, failed to substantiate displacement interpreted for faults in the sedimentary section. Detailed examination of exposures in the trenches also failed to reveal the existence of near surface faults. Together these findings suggest that there has been minimal or no modern near-surface fault activity in this area of New Castle County.
Storm-Water and Base-Flow Sampling and Analysis In the Delaware Inland Bays Preliminary Report of Findings 1998-2000
(Newark, DE: Delaware Geological Survey, University of Delaware, 2002) Ullman, W.J.; Andres, A.S.; Scudlark, J.R.; Savidge, K.B.
This report provides initial research results of a storm-water and base-flow sampling and analysis project conducted by the University of Delaware College of Marine Studies (CMS) and the Delaware Geological Survey (DGS). Base-flow samples were collected from six tributary watersheds of Delaware’s Inland Bays on 29 occasions from October 1998 to May 2000. Water samples were filtered in the field to separate dissolved nutrients for subsequent analysis, and a separate sample was collected and returned to the laboratory for particulate nutrient determinations. On each sampling date, temperature, conductivity, pH, and dissolved oxygen concentrations were determined at each sampling station. Stream discharge measurements at each of these sites were made by the U.S. Geological Survey (USGS) under a joint-funded agreement with the Delaware Department of Natural Resources and Environmental Control (DNREC) and the DGS. Together, the nutrient and discharge data were used to determine the total and unit (normalized to watershed area) nutrient loading from base flow to the Inland Bays from each of these watersheds on a quarterly and annual basis. At the same six stations, storm water was collected during eight storms from May 1999 to April 2000. Storm-water loadings of nutrients from each watershed were calculated from the concentrations of nutrients in water samples collected at fixed time intervals from the beginning of the storm-water discharge period until recession to base flow. These data provide DNREC with a more complete picture of the seasonal dependence of nutrient loading to the Bays from which to establish goals for total maximum daily loads in the Inland Bays watershed.
Catalog Of Earthquakes In Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Baxter, S.J.
The occurrences of earthquakes in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey are well documented by both historical and instrumental records. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677. One of the earliest known events occurred in 1737 and was felt in Philadelphia and surrounding areas. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). The second largest event occurred in the Delaware area in 1973 (magnitude 3.8 and maximum Modified Mercalli Intensity of V-VI). The epicenter for this event was placed in or near the Delaware River. Sixty-nine earthquakes have been documented or suspected in Delaware since 1871.
Beach Sand Textures From The Atlantic Coast Of Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 1999) Ramsey, K.W.
The purpose of this report is to characterize Delaware Atlantic Coast beach sand on the basis of sand texture data in order to identify geologic material suitable for beach nourishment.
Landsat View of Delaware
(Newark, DE: Delaware Geological Survey, University of Delaware, 1979) Spoljaric, N.
In Delaware some linear features recognized on the Landsat image can be related to known faults. Others are interpreted as possible faults; the causes of some lineations are not yet known. Circular features are more difficult to interpret but they are similar to the domal structures and erosional features recognized in the Gulf Coast region, for example. These and the linear features of uncertain origin can be investigated by drilling and geophysical techniques after being localized by clues provided by the satellite images. Detection by satellite images and confirmation by other geologic techniques is an efficient and effective means of geologic investigation.
Preliminary Results Of Seismic And Magnetic Surveys Off Delaware's Coast
(Newark, DE: Delaware Geological Survey, University of Delaware, 1977-07) Woodruff, K.D.
The nature and occurrence of subsurface resources, whether ground water, minerals, or petroleum, are controlled by the geologic history and framework of any particular area. Several years ago the staff of the Delaware Geological Survey began an informal assessment of the potential resources of southern Delaware and demonstrated the lack of basic data on the deep subsurface in this area. This assessment was later summarized by Benson (1976) with particular emphasis on the possibilities for petroleum occurrence.
Regolith Thickness of the Delaware Piedmont
(Newark, DE: Delaware Geological Survey, University of Delaware, 1982) Christopher, M.J.; Woodruff, K.D.
This map shows the total thickness (regolith) of both the loose, transported material and the weathered rock that overlies crystalline rocks of the Delaware Piedmont. Transported material is generally thin and the weathered rock in place (saprolite) usually makes up the bulk of the regolith. Saprolite may vary gradationally from a weathered rock that has retained much of the characteristics of the parent rock to a product mineralogically and texturally different from its source rock.

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