Knox Group: geospatial geologic structural datasets in Tennessee

The Knox Dolomite is currently recognized as the Knox Group. The Mascot Dolomite, the upper unit of the Knox Group, is dolomite and dolomitic limestone of Lower-Ordovician-age that occurs in the subsurface of most of Tennessee. This data release will focus on Middle Tennessee, where the only outcrop of the Knox Group is in the Wells Creek basin in Stewart and Houston counties (Bradley, 1986; Wilson and Stearns, 1968). The top of the Knox Dolomite is an erosional surface that is useful as a structural datum because of the importance of the Knox Group for oil and gas resources, zinc mineralization, and domestic drinking water supplies. Since the upper approximately 30 meters of the Knox Group is paleokarst, groundwater is generally under confined conditions (Bradley, 1986; Wilson and Stearns, 1968). This upper portion of the Knox is often low-yielding and variable in water quality. However, it can be a reliable aquifer in specific areas - mostly in the Central Basin.
A structure contour map on the Knox Group in Middle Tennessee was prepared by Newcome (1954) as a part of a cooperative program of groundwater investigations by the U.S. Geological Survey and the Tennessee Division of Geology at Nashville, Tennessee. Prior to this work, this paper map existed in limited quantities, mainly restricted to the Nashville offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). The map measuring 46 x 64 cm, with an approximate scale of 1:500,000 was prepared with well elevation data, determined by aneroid barometer or from topographic quadrangle maps (Newcome, 1954). Structure contours were drawn on top of Knox Group at 100 feet intervals.
The work for this project consisted of (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) interpolating raster surfaces for the top altitude of the Knox Group and depth from land surface to the top of the unit. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. Vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88).
Dataset types can be identified by the following naming convention:
i_ = georeferenced map images (GRI)
po_ = points
c_ = contours and closed depressions
f_= faults and other structural features
p_ = extent polygon(s)
ra_ = altitude raster
rd_ = depth from land surface raster
rt_ = thickness raster
The datasets included on this child item page are as follows:
knx_metadata.xml - metadata file
knx_alldata.zip:
GRI/
i_knx_tp.tif - structure contour map on the top of the Knox Group (Newcome, 1954)
i_knx_outcrop.tif - map of the Wells Creek Disturbance (Wilson and Stearns, 1968)
polygons/
"p_knx_ext" - extent polygon for the Knox Group 
"p_knx_outcrop" - extent polygon the Wells Creek Structure - Knox Group outcrop
rasters/
ra_knx_tp.tif - altitude raster for the top of the Knox Group (NAVD 88) (meters)
rd_knx_tp.tif - depth from land surface raster of the top of Knox Group (meters)
vectors/
c_knx_tp.shp - structure contours for the top of the Knox Group (NGVD 29) (feet)
c_knx_tp_modified.shp - modified structure contours for the top of the Knox Group (hachures removed from closed basins). This vector used to interpolate raster for the top of the Knox Group (NGVD 29) (feet)
po_knx_tp.shp - point data for the altitude of top of the Knox Group (NGVD 29) (feet)
References:
Bradley, M. W., 1986, Preliminary Evaluation of the Knox Group in Tennessee for Receiving Injected Wastes, U.S. Geological Survey, Environmental Protection Agency, Water-resources investigations report, Volume 85-4304, 20 p.
Clark, B.R., Barlow, P.M., Peterson, S.M., Hughes, J.D., Reeves, H.W., Vigor, R.J., 2018, National-Scale Grid to Support Regional Groundwater Availability Studies and a National Hydrogeologic Framework, U.S. Geological Survey, ScienceBase data release, doi:10.5066/F7P84B24.
Newcome, R. Jr., 1954, Structure contour map on top of the Knox Dolomite in Middle Tennessee, Tennessee Division of Geology, Ground-Water Investigations Preliminary Chart 5, 1 sheet.
Wilson, C.W. and Stearns, R.G., 1968 Geology of the Wells Creek Structure, Tennessee: Tennessee Division of Geology, Bulletin 68, 248 p.

Tags: contouring, earth-structure, elevation, geographic-information-systems, geology, geoscientificinformation, geospatial-datasets, inlandwaters, knox-aquifer, knox-group, maps-and-atlases, natural-resource-exploration, stratigraphic-thickness, structure-contours, tennessee, usgs-6723c588d34e4f57573e8dd1, water-resources
Organization: Department of the Interior