USGS Home
Contact USGS
Search USGS

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5167

Back to Table of Contents

Appendix A. Development of Database

Stratigraphic information interpreted from geophysical and lithologic logs was entered into a Microsoft Excel™ spreadsheet. The spreadsheet was set up with Excel’s AutoFilter capability, which allowed data in each field to be easily queried, sorted, or filtered. The spreadsheet can be imported into Microsoft Access™. Stratigraphic data were entered into 14 individual fields. A field list with a brief description of each field is given in table A1.

Data flags were used if information was irrelevant or unavailable. An -888 flag was entered if no data were available. A -999 flag was used if an entry was irrelevant; for example, -999 was entered under the Thickness_Geophys field for all basalt units, because geophysical logs were not used to quantify basalt thicknesses.

Locations of each well (Albers coordinates) and elevations to the top of the wells were obtained from a USGS-INL shapefile of borings on the INL. The depth of the well log was entered as the deepest log recording from either lithologic or geophysical logs. For lithologies logged by USGS personnel, a flag value of 2 was entered in the Source_Flag field, and for coreholes logged by non-USGS personnel, a 1 was entered. The general lithology (sediment or basalt) of each identified unit was entered under the StratUnit_type field.

Sediment interbeds were generally represented by higher natural-gamma signatures. A sedimentary interbed was interpreted to exist only where the width and height of natural-gamma spikes were distinct from background (basalt) levels. Boundaries between sediment and basalt were interpreted at the midpoints of the top and bottom shoulders of the natural-gamma interbed signal.

A relative confidence flag (high, medium, or low) was entered under the Confidence_Composite_unit field to qualify the degree of confidence with which a composite unit assignment was made. The degree of confidence was qualitatively based (high, medium, or low) on the proximity of coreholes to boreholes with established composite unit stratigraphy and on how well composite units could be correlated between these and the new coreholes. Where confidence was low, an alternative composite unit designation was entered under the Alt_Comp_Unit field to record the next most likely designation.

The depth to the base of each sedimentary or basalt unit (in feet below top of well), regardless of lithology, was entered under the DepthBase field. For holes with lithologic logs, the thickness of sedimentary interbeds interpreted only from lithologic logs was entered under the Thickness_Lith field. Only logged sediment thicknesses were considered. Missing intervals in lithologic logs due to poor core recovery did not contribute to this thickness, although in some cases, sediment likely existed but was not recovered. Sediment interbed thickness interpreted only from natural-gamma logs was entered under the Thickness_Geophys field. If no natural-gamma spike was observed corresponding to an interbed recognized in a lithologic log, a thickness value of 0 was entered to record the failure of the geophysical log to detect the interbed. For holes with only geophysical logs, it was not possible to identify sedimentary interbeds that were not recorded by natural-gamma logs. In this situation, some fraction of interbeds presumably were not recorded. For holes with both lithologic and natural-gamma logs, the most likely interbed thickness was determined using lithologic and natural-gamma logs and entered under Thickness_Inferred. This represents the best quality thickness data available on the basis of both lithologic logs and natural-gamma signatures of interbeds. The relative confidence in the inferred thickness was entered under the Confidence_Thickness field. The degree of confidence (high, medium or low) was based on the explicitness of the base and top of interbeds as recorded by lithologic logs, geophysical logs, or both.

Table A1. List of fields under which data were entered in the database with a brief description of each field.

Back to Table of Contents