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Summary Information for Field Activity 1974-014-FA

Area of Operations: south Texas outer continental shelf, Texas, United States, Gulf of Mexico, North America, North Atlantic

Dates: November 11, 1974 to November 25, 1974

Chief scientist: Gerry Shideler

Objectives: The overall objective of the program is to acquire the necessary geological, chemical, and biological baseline data for an environmental assessment of the South Texas Outer Continental Shelf. The data acquisition phase of the program is to be completed prior to leasing of the area for energy-resource development. The geological phase of this program is concerned primarily with determining the nature of sea floor sediments and substrate, as well as the nature of suspended sediment within the water column.

Type of Activity: Sampling; Seismic profiling; Photography;

Information to be derived: Samples and chemical analysis; Bathymetric maps; Morphology;

Summary: The 3.5 kHz seismic reflection profiles suggest some possible hydrocarbon seeps associated with faulting near the edge of the continental shelf. Ferro-manganese encrusted reef rock was obtained in 98 meters of water in the southeastern corner of the North Padre Island Area. A cursory inspection of XBT records suggests that the inner shelf waters are generally homogeneous, or else exhibit slightly increasing temperature gradients. This may possibly be attributed to pronounced mixing associated with the high wind velocities and sea state conditions experienced during the cruise. In contrast, the middle and outer shelf waters exhibit increasingly higher degrees of thermal stratification with increasing water depth. Relatively warm surface water masses generally overlie colder deeper masses, with well-defined thermoclines. There is also some indication of a relatively warm intermediate-depth layer at some of the deeper stations. The bottom sediments throughout most of the Texas OCS area that was sampled during BLM Leg Bravo consist of grayish-olive or olive-brown mud. Sand was found to be a minor constituent, and gravel detritus was not observed in any significant quantity. Water samples: 49 (3 at each of 13 stations plus 10 for quality control); XBTs: 44 stations; Bottom photographs: 19 stations; Smith-MacIntyre grab samples: 71 stations (6 subsamples at each); Gravity cores: 26 stations; Box cores: 39 stations; Samples for organic analyses: 34 stations; Benthic faunal collections: 110 (from grabs and box cores); Drift bottle casts: 24 stations; Seismic reflection profiles (3.5 kHz) and bathymetry: all stations.

Contact: Gerry Shideler ()

InfoBank: uses the identifier K-B-74-GM. Visit this site for more information.

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Publications resulting from these data

Flores, R. M., and Shideler, G. L.,1978, Factors controlling heavy-mineral variations on the South Texas outer continental shelf, Gulf of Mexico: Journal of Sedimentary Research, v. 48, no. 1: p. 269-280. (Also available at

Shideler, Gerald L., and Flores, Romeo M.,1976, Maps showing distribution of heavy minerals on the south Texas outer continental shelf: U.S. Geological Survey Miscellaneous Field Studies Map 841, 1 sheet. (Available as a PDF version)

Shideler, Gerald L.,1988, Heavy-mineral placer potential map of the U.S. continental shelf, western and northern Gulf of Mexico: U.S. Geological Survey Miscellaneous Field Studies Map 2037, 1 sheet. (Available as a PDF version)

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