Acoustic-reflection profiles, Scripps Utility Boat, August 1973, San Diego Bay, California
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Geology topics
Publications and source records attributed to George William Moore.
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Introduction As part of a cooperative marine research program designated the International Decade of Ocean Exploration (IDOE), the United States Geological Survey is participating in an investigation of the geologic framework and resource potential of continental margins and small ocean basins in the Gulf of Mexico, Caribbean Sea, and west African continental shelf areas. These studies are funded through the National Science Foundation. Acoustic-reflection profiles of Leg 1, described in this report concern mainly a 200 X 250 kilometer project area in the Bay of Campeche in the southwestern part of the Gulf of Mexico. The cruise leg began at Corpus Christi, Texas, and ended at Veracruz, Mexico. Other geophysical records collected during the cruise include magnetometry, gravimetry, and bathymetry. Visiting scientists from the Institute of Geophysics of the National University of Mexico, the Oceanographic Commission of the Mexican Navy, and the Mexican Institute of Petroleum joined the research vessel UNITEDGEO I throughout the cruise in the Bay of Campeche. The cruise offered an excellent opportunity for scientific interchange between investigators from Mexico and the United States and permitted collaboration in the instrumentation, operational techniques, and interpretation of acoustic-reflection records aboard the research vessel.
Analyses of 82 samples collected from the surface of the continental shelf between the Oregon-California border and Eureka, Calif., indicate that the background gold content on this shelf is about 0.1 ppb (part per billion). Four anomalous tracts, which range in extent from 10 to 30 square kilometers, have gold values above 10 ppb, and the richest sample contains 300 ppb. The anomalous areas seem to lack a close correlation with water depth, but they are related to areas underlain by soft Cenozoic strata that contain small quantities of dispersed gold originally derived from lodes in the Klarnath Mountains. This relationship suggests that the offshore gold accumulations are lag concentrates produced from the Cenozoic deposits by wave erosion during the postglacial rise in sea level. Gold contents at the surface are too low for economic recovery, and drilling will be required to determine whether the anomalous areas are underlain by higher grade material.
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The uranium mineral uranocircite, a barium uranyl phosphate, occurs in a channel sandstone in the Chadron formation of Oligocene age in the White River badlands, Pennington County, S. Dak. A vertical section of the basal l-foot of the channel contains 0.25 percent uranium. Small amounts of metatyuyamunite (?) occur in the upper part of a freshwater limestone bed in the Chadron formation, and carnotite occurs in chalcedony veins in the overlying Brule formation, also of Oligocene age. The source of the uranium is thought to have been volcanic ash in the Brule formation and the overlying rocks of Miocene age. Downward moving ground water may have leached this uranium and deposited it in the rocks below.
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