Wells Creek Dolomite: geospatial geologic structural datasets in Tennessee

The Wells Creek Dolomite is the lowest unit of the Stones River Group. The Wells Creek consists of cherty limestone that underlies the Murfreesboro Limestone of the Stones River Group of Middle Ordovician age, and directly overlies the Knox Group of early Ordovician and late Cambrian age. The unit ranges in thickness from less than 1.52 meters (5 feet) in the eastern part of the Central Basin to approximately 54.86 meters (180 feet) in Stewart County. The depth of the Wells Creek generally ranges from 121.92 meters to 457.2 meters (from 400 to 1500 feet) below land surface (Smith, 1959). 
The Wells Creek Dolomite does not yield water but it can be easily recognized when drilling wells and it overlies the Knox Group, a deep aquifer in middle Tennessee and a significant source of groundwater for some areas. For this data release, the raster interpolated for the top of the Knox Group in Middle Tennessee (ra_knx_tp.tif) was also used to represent the altitude of the bottom of the Wells Creek Dolomite (See process steps for more details).
An isopach map of the thickness of the Wells Creek Dolomite in Middle Tennessee was prepared as a part of a cooperative groundwater study by the Tennessee Division of Geology and the U.S. Geological Survey (USGS) (Smith, 1959). The 43 x 71 cm map covers parts of Middle Tennessee, from Camden east to Crossville, and from the Kentucky border to the Alabama border. The map scale is approximately 1:600,000. Contour intervals are 5 feet (east of the 100-foot isopach) and 10 feet (west of the 100-foot isopach), which show the thickness of the Wells Creek Dolomite. The associated data are altitude values from a study of cuttings in 120 wells between the western boundary of the Cumberland Plateau and the Tennessee River (Smith, 1959). Prior to the current work, the Wells Creek Dolomite isopach map (Smith, 1959) existed in limited quantities, mainly restricted to the Nashville, TN offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS). 
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 thickness of the Wells Creek Dolomite using the data from the isopach map (Smith, 1959), altitude of the bottom of the Wells Creek Dolomite by using the data for the top of the Knox Group (Newcome, 1954), altitude of the top of the Wells Creek Dolomite using the bottom of the Wells Creek Dolomite added to the thickness of the Wells Creek Dolomite (Smith, 1959), and depth from land surface to the top and bottom of the Wells Creek (USGS, 2012). 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. Raster 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
"p_" = extent polygons 
"ra_" = altitude raster
"rd_" = depth from land surface raster
"rt_" = thickness raster
The datasets included on this child item page are as follows:
wllscr_metadata.xml - metadata file
wllscr_alldata.zip:
GRI/
i_wllscr.tif - thickness contour map for the Wells Creek Dolomite (Smith, 1959)
polygon/
p_wllscr_ext.shp - study area extent for the Wells Creek Dolomite
rasters/
ra_wllscr_btm.tif - altitude raster for the bottom of the Wells Creek Dolomite (same dataset as ra_knx_tp.tif [Newcome, 1954; Smith, 1959]) (NAVD 88) (meters)
ra_wllscr_tp.tif - altitude raster for the top of the Wells Creek Dolomite (NAVD 88) (meters)
rd_wllscr_btm.tif - depth from land surface raster of the bottom of the Wells Creek Dolomite (same dataset as ra_knx_tp.tif [Newcome, 1954; Smith, 1959]) (meters)
rd_wllscr_tp.tif - depth from land surface raster of the top of the Wells Creek Dolomite (meters)
rt_wllscr.tif - thickness raster for the Wells Creek Dolomite (meters)
vectors/
c_wllscr.shp - thickness contours for the Wells Creek Dolomite
po_wllscr.shp - point data for the thickness of Wells Creek Dolomite
References: 
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.
Smith, Ollie, Jr., 1959, Isopach Map of the Wells Creek Dolomite in Middle Tennessee: Tennessee Division of Water Resources, one 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, maps-and-atlases, stratigraphic-thickness, structure-contours, tennessee, usgs-6723bf26d34e4f57573e8cf4, wells-creek, wells-creek-dolomite
Organization: Department of the Interior