USGS Open-File Report 03-230 Date: 17 June 2003 Explanation of data files This directory contains gridded data files for the following depth horizons: 1. NStopo = topography/bathymetry 2. NSLCU = lower Cretaceous unconformity 3. NSshublik = top of Shublik 4. NSbasement = top of pre-Carboniferous basement There are also gridded data files for the following isopachs: 1. NStopo-LCU = Brookian interval 2. NSLCu-Shublik = Beaufortian interval 3. NSshublik-basement = Ellesmerian interval 4. NStopo-basement = total sedimentary section thickness The following data formats are used: *.gxf, *.gxf.gi = Geosoft grid exchange format (see format description below) *.dat, *.dat.gi = ZMAP grid format (see format description below) *.xyz = ASCII xyz point format (see format description below) *.e00 = Arc/Info export format (see format description below) *.tif, *.tfw = Arc Geotiff image format (see format description below) ---------------- Data format descriptions These format descriptions are provided for convenience of the user, but are not exhaustive descriptions of these formats. The user should check with the companies that maintain these formats for more authoritative and complete documentation. 1. Geosoft grid exchange format (Geosoft, Inc., Toronto, Canada) A GXF file is an ASCII file made up of a number of labeled data objects and comments. Each labeled data object has a label line followed by one or more data lines. A label line is identified by a "#" character in the first column followed immediately by an upper-case label. The data associated with that label are found on one or more lines that follow the label. The complete description of this format is available online at: http://www.geosoft.com/support/technote/pdf/gxfr3d9_1.pdf 2. ZMAP grid format (Landmark, Houston, Texas) This is a commonly used format in the seismic processing community. 3. ASCII XYZ point format This is an ASCII format containing one data point per line. The first 8 lines of the file are header records starting with the character "/". The data lines each contain 5 values: X location (in projected meters) of the data point; Y location (projected meters) of the data point, Z depth (meters) of the horizon, LON (degrees, NAD27), and LAT (degrees, NAD 27). The data lines could be read with the following FORTRAN read format, (f11.0,x,f10.0,x,f10.0,x,f11.5,x,f10.5) 4. Arc/Info export format (ESRI, San Diego, California) This format is readable by Arc/Info and Arc GIS programs and contains the full floating point grids. 5. Arc Geotiff (ESRI, San Diego, California) This is an image format readable by many graphic display programs including the ESRI GIS software. The *.tfw file provides georeferencing information to GIS software.