Decker overburden

Title: Decker overburden
Abstract:: This ArcView shapefile contains a representation of thickness of overburden above the Anderson-Canyon coal zone in the Decker coalfield, Powder River Basin, Montana. This theme was created specifically for the National Coal Resources Assessment in the Northern Rocky Mountains and Great Plains Region.
Supplemental_Information:: The overburden thickness map theme represents a digital polygon coverage of the overburden isopach (thickness) map for the Anderson-Canyon coal zone. The overburden isopach map represents the thickness of rock overlying the top of the Anderson-Canyon coal zone. The extent of the overburden isopach map is constrained by the boundaries of the Crow and Northern Cheyenne Indian Reservations, the Montana state line, and the outcrop (or clinker contact) of the Anderson coal bed, which defines the top of the Anderson-Canyon coal zone. A caveat to Anderson-Canyon coal zone overburden relates to the area lying between the outcrops (or clinker contacts) of the Anderson and Canyon (or lower Canyon) coal beds, which define the top and base of the zone, respectively. Here the coal zone is exposed, and the area technically falls within a category of no overburden. For this reason, this area is defined as "exposed coal zone" in the overburden thickness coverage. In addition, because rocks (including coal beds) in the Anderson-Canyon coal zone may extend from tens to hundreds of feet stratigraphically below the top of the coal zone (Anderson coal bed), the overburden as depicted in the coverage represents a minimum overburden thickness. The overburden interpretations were derived by first developing a grid representing the top of the Anderson-Canyon coal zone (including faults) using a commercial gridding and contouring software package (EarthVision; Dynamic Graphics, Inc.). This grid, which was calculated using a grid spacing of 200 x 200 meters, was then subtracted from a composite Digital Elevation Model (DEM) grid of topographic elevation for the entire coal field, resulting in a grid of thickness values that could then be contoured as overburden thickness isopachs. Multiple 2 arc-second DEMs with a resolution of approximately 60 meters were merged using the 'mosaic' command in ARC/INFO to create the composite DEM grid used in the overburden calculations. The overburden isopach map was then converted to a contour output file in EarthVision, and subsequently converted into a digital polygon coverage by using a combination of programs ('ISMARC' and 'CONVERT-ISM.AML') furnished to the U.S. Geological Survey by the Illinois State Geological Survey. This overburden isopach coverage was then generalized using a weed tolerance of 30 meters to reduce file size. The generalized cover was then converted to a shapefile for incorporation as a theme in the ARCVIEW project. The overburden thickness categories included in the theme (for example, 0 - 100 ft, 100 - 200 ft, etc.) are consistent with overburden thickness categories used in the tabulation of total coal resources.

Range of values
Minimum:	0.0000
Maximum:	983205.0000

Range of values

Minimum:

0.0000

Maximum:

983205.0000

Data format:	Geographic features and attributes in format Shapefile (version 1.0)
Network links:	<http://energy.cr.usgs.gov/coal/nca/rockiesgis.htm>
Media you can order:	CD-ROM (2 disc set) (format ISO 9660)

Data format:

Geographic features and attributes in format Shapefile (version 1.0)

Network links:

<http://energy.cr.usgs.gov/coal/nca/rockiesgis.htm>

Media you can order:

CD-ROM (2 disc set) (format ISO 9660)

Decker overburden

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