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Preliminary integrated geologic map databases for the United States:

Delaware, Maryland, New York, Pennsylvania, and Virginia

By: Connie L. Dicken, Suzanne W. Nicholson, John D. Horton, Scott A. Kinney, Gregory Gunther, Michael P. Foose, and Julia A.L. Mueller

Version 1.1

Updated December 2007
Updated August 2008

Choose state Delaware Maryland New York Pennsylvania Virginia

Introduction

The growth in the use of Geographic Information Systems (GIS) has highlighted the need for regional and national digital geologic maps attributed with age and lithology information. Such maps can be conveniently used to generate derivative maps for purposes including mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This Open-File Report is a preliminary version of part of a series of integrated state geologic map databases that cover the entire United States.

The only national-scale digital geologic maps that portray most or all of the United States for the conterminous U.S. are the digital version of the King and Beikman (1974a, b) map at a scale of 1:2,500,000, as digitized by Schruben and others (1994) and the generalized digital version (Reed and Bush, 2004) of the Geologic Map of North America (Reed and others, 2005a, b) compiled at a scale of 1:5,000,000. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis for this product. In a few cases, new digital compilations were prepared (e.g. Ohio, South Carloina, South Dakota) or existing paper maps were digitized (e.g. Kentucky, Texas). Also as part of this series, new regional maps for Alaska and Hawaii are being compiled and ultimately new state maps will be produced.

The digital geologic maps are presented in standardized formats as ARC/INFO export (.e00) files and as ArcView shape (.shp) files. Accompanying these spatial databases are a set of five supplemental attribute tables that relate the map units to detailed lithologic and age information. The maps for the CONUS have been fitted to a common set of state boundaries based on the 1:100,000 topographic map series of the United States Geological Survey (USGS). When the individual state maps are merged, the combined attribute tables can be used directly with the merged maps to make derivative maps. No attempt has been made to reconcile differences in mapped geology across state lines.

Procedures

The various digital geologic maps that form the basis for this product were originally produced in a wide variety of formats. Although most of them are available as ARC/INFO export (.e00) files and/or ArcView shape (.shp)files, the items and formats in the polygon (PATs) and arc (AATs) attribute tables vary dramatically. To unify these disparate maps, it was necessary to create a set of standard formats, and then to convert the state digital geologic maps to conform to these standards. The details of these standards are presented in the documentation of this report. The creation of a unique map unit name, called unit_link, allows the different State maps to be merged. (Database field names are in italics). Unit_link consists of a two-letter State (ST) code, concatenated with the original geologic map unit name, which may be slightly modified to remove special characters for age designations, followed by a semicolon, and an integer that designates geographic regions (or provinces) within the map. For those states where provincial structure is absent, this integer is simply "0". This variable, unit_link, can then be used as a key field to relate the tables that contain age and lithologic information to the spatial database (.dbf).

Compilation of a regional geologic map always requires compromises between the complexity of geologic information for a large region, and the need to keep the compiled map, and its explanation, relatively simple. Similarly, compromises are necessarily made in order to convert the large variety of formats in our source maps into the standard set of formats developed for this series.

Typically, spatial databases were modified from the source in the following general manner: The most recent data was obtained and the arcs and polygons were reattributed in the PAT according to the nomenclature adopted for this series (see documentation in this report and the metadata for individual spatial databases). When this reattribution was complete, the other attributes from the original spatial databases were deleted. Generally, if faults were not an integral part of the spatial database, arcs were retagged to make them so. Additionally, for those states where faults were mapped, fault arcs were extracted and provided as a separate .e00 or shape file (faults_dd, faults_lcc).

A second more detailed set of standardized attribute tables was generated by extracting information from the legends of the source maps and entering it into a set of five tables that record map unit information (STunits), lithologic information (STlith), age information (STage), and references (STref and STref-link). Some existing map legends provided an inadequate level of age or lithologic information. In these cases, we consulted the scientific literature, maps at smaller scales, and, in some cases, the original authors of the compilations or other regional experts. When we used updated information, it was recorded in the STage and STlith tables. Thus, the age and lithology information in these attribute tables may, in some cases, conflict with the information on the legends of the original source maps that may have been compiled decades ago.

In particular, the lithology table (STlith) may be much more extensive than the information in the map legends. Large regional compilations like these State maps often utilize map units that encompass a variety of lithologies. Volcanic rocks are commonly “lumped” extensively, combining tuffs, ash-flow tuffs, flows, and subvolcanic intrusions of a number of compositions, so that individual map units may contain dozens of unique lithologies. Although a dominant (most abundant) lithology has been designated for all map units, users seeking to use this information are advised to be cautious, as many map units simply have no dominant lithology.

Error correction is an ongoing process with most spatial databases. A typical state spatial database consists of tens of thousands of polygons and arcs, and errors introduced during the creation of these spatial databases are inescapable. One common type of error is data coding that does not conform to the original paper map. For example, polygons may be given the wrong map unit, or faults may be called normal faults instead of thrust faults. Some of these errors are unavoidable because, in a few cases, the original paper map cannot be read accurately.

In other cases, newer information is available that can be used to better describe the existing polygons and arcs that are based on decades-old compilations. This type of updating was done where necessary for some of the spatial databases. Any changes to the spatial data are documented (STchanges.txt where ST stands for the two-letter abbreviation for a given state.)

Spatial databases are provided in both Lambert Conformal Conic projection and geographic coordinates (NAD27, decimal degrees).

Projection:	Lambert Conformal Conic
Horizontal datum:	NAD 27
Spheroid:	Clarke, 1866
Standard parallels:	33 degrees North
	45 degrees North
Central meridian:	-100 degrees
Reference Latitude:	0 degrees
Horizontal units:	meters
False easting:	0
False northing:	0

Supplemental attribute tables are provided in Filemaker Pro format (.fp5), in dBase format (.dbf), and comma-separated value (.csv) text.

ArcView files can be viewed with the free viewer, ArcExplorer, which can be downloaded from http://www.esri.com/software/arcexplorer/.

References

King, P.B., and Beikman, H.M., 1974a, Geologic map of the United States: U.S. Geological Survey, scale 1: 2,500,000.

King, P.B., and Beikman, H.M., 1974b, Explanatory text to accompany the geologic map of the United States: U.S. Geological Survey Professional Paper 901, 40 p.

Reed, J.C. and Bush, C.A., 2004, Generalized Geologic Map of the Conterminous United States, U.S. Geological Survey, scale 1:7,500,000. (URL http://pubs.usgs.gov/atlas/geologic/)

Reed, J.C., Jr., Wheeler, J.O., and Tucholke, B.E., 2005a, Geologic map of North America: Geological Survey of America, Decade of North American Geology, 3 sheets, scale 1:5,000,000.

Reed, J.C., Jr., Wheeler, J.O., and Tucholke, B.E., 2005b, Geologic map of North America – Perspectives and explanation: Geological Survey of America, Decade of North American Geology, 28 p.

Schruben, P.G., Arndt, R.E., and Bawiec, W.J., 1994, Geology of the Conterminous United States at 1:2,500,000 Scale — A Digital Representation of the 1974 P.B. King and H.M. Beikman Map, U.S. Geological Survey Digital Data Series 11, release 2. (URL http://pubs.usgs.gov/dds/dds11/)

To download files, right click on the file that you want and either Save target as...(Internet Explorer) or Save link as...(Netscape).

Delaware

The paper geologic map of the State of Delaware was published by the Delaware Geological Survey in 1966 (Spoljaric and Jordan, 1966) at a scale of 1:300,000. This map is currently out of print. The Delaware Geological Survey is undertaking a program of mapping at 1:24,000. For up-to-date information on the progress of this effort, check the home page for the Delaware Geological Survey at http://www.udel.edu/dgs/index.html.

The Water Resources Division of the U.S. Geological Survey digitized the 1966 geologic map of Delaware in the mid-1990’s. Information about products from the Delaware Geological Survey can be found at http://www.udel.edu/dgs/.

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Maryland

The paper geologic map of the State of Maryland was published by the Maryland Geological Survey in 1968 (Cleaves and others, 1968) at a scale of 1:250,000. This map is currently out of print. The Maryland Geological Survey is undertaking a program of mapping at 1:24,000. For up-to-date information on the progress of this effort, check the home page for the Maryland Geological Survey at http://www.mgs.md.gov/.

In 1995 the Water Resources Division of the U.S. Geological Survey digitized the geologic map of Maryland from the 1968 paper map. Information about products from the Maryland Geological Survey can be found at http://www.mgs.md.gov/.

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New York

Updated August 2008

The paper state geologic map of New York was originally published by the New York State Geological Survey in five sheets (Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson; Fisher and others (1970)) at a scale of 1:250,000.

In 1999, a digital version of the 1970 paper bedrock map was created by the New York State Museum. Digital products which are available for NY include surficial materials and bedrock geology (as separate files) from http://www.nysm.nysed.gov/gis/.

Information about products from the New York State Geological Survey can be found at http://www.nysm.nysed.gov/research/geology/.

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Pennsylvania

The paper map was published in 1980 by the Pennsylvania Geological Survey (Berg and other, 1980) at a scale of 1:250,000.

The state map was digitized by the Pennsylvania Geological Survey in 2001 (Miles, et al., 2001) and the spatial data can be freely downloaded from http://www.dcnr.state.pa.us/topogeo/map1/bedmap.aspx.

Additional digital coverages available from the same site include oil and gas data and a state-wide groundwater database. Information about other products from the Pennsylvania Geological Survey can be found at http://www.dcnr.state.pa.us/topogeo/.

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Virginia

The paper bedrock geologic map of Virginia was published in 1993 by the Virginia Division of Mineral Resources in cooperation with the U.S. Geological Survey at a scale of 1:500,000 (Virginia Division of Mineral Resources, 1993).

In 200_ the Virginia Division of Mineral Resources (part of the Virginia Department of Mines, Minerals, and Energy (DMME)), digitized the 1993 state geologic map (Virginia Department of Mines, Minerals, and Energy, 2003) and it is available on-line at https://www.dmme.virginia.gov/commerce/.

In 2005, the digital map was reviewed and updated by the Virginia DMME in cooperation with the USGS. This revised version is the one presented in this publication.

Information about other Virginia Division of Mineral Resources products can be found at http://www.mme.state.va.us/Dmr/home.dmr.html.

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References for maps

Berg, T.M., and others, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, Map 1, scale 1:250,000.

Cleaves, E.T., Edwards, Jonathan, Jr., and Glaser, J.D., 1968, Geologic map of Maryland: Maryland Geological Survey, scale 1:250,000.

Fisher, D. W., Isachsen, Y. W., and Rickard, L. V., 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson: New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250,000.

Miles, C.E., Whitfield, T.G., and others, 2001, Bedrock geologic units of Pennsylvania, scale 1:250,000: Pennsylvania Geological Survey, on-line at http://www.dcnr.state.pa.us/topogeo/gismaps/digital.aspx.

Virginia Department of Mines, Minerals, and Energy, 2003, Digital representation of the 1993 Geologic Map of Virginia: Virginia Department of Mines, Minerals, and Energy, Publication 174, scale 1:500,000, CD-ROM.

Virginia Division of Mineral Resources, 1993, Geologic map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

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