An X-ray and optical study of cuttings from the U. S. Bureau of Reclamation Mesa 6-1 drillhole, Imperial County, California
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Abstract
The Mesa 6-1 drillhole penetrates 8,031 feet of sediments. Cuttings are chiefly siltstones, but with varying amounts of sandstones ranging from very fine sand to very coarse sand size. Color changes in the siltstones constitute the only systematic changes of lithology with depth; these are considered to be the result of variations in oxidation-reduction conditions, not the result of depositional factors. Fragments of igneous and metamorphic rocks occur sporadically in trace amounts. A pebble horizon at least 30 feet thick but of questionable lateral extent is the only distinctive sedimentary horizon.
Montmorillonite was found in siltstone fragments at and above 1,450 feet, but not in siltstone fragments at or below 1,690 feet. Quartz, calcite, microcline, albite, chlorite, and illite are present in whole-rock diffractograms throughout the hole. Dolomite occurs in most samples to a depth of 4,910 feet, and is present intermittently to a depth of 7,697 feet. Pyrite is present intermittently. No zeolites were found. Black, dominantly amorphous grains of native sulfur, which may easily be confused with asphalt, are abundant at one horizon.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | An X-ray and optical study of cuttings from the U. S. Bureau of Reclamation Mesa 6-1 drillhole, Imperial County, California |
| Series title | Open-File Report |
| Series number | 73-72 |
| DOI | 10.3133/ofr7372 |
| Year Published | 1973 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Description | Report: 35 p.; 1 Figure: 92.56 x 14.13 inches |
| Country | United States |
| State | California |
| County | Imperial County |