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Geology topics

J. G. Vedder

Publications and source records attributed to J. G. Vedder.

At least 37 records · Page 2Linked to original sources
USGS1980

A summary report of the regional geology, petroleum potential, environmental geology, and operational considerations in the area of proposed lease sale No. 68, offshore southern California

This report reviews geological, geophysical and technological data that are pertinent to proposed OCS Lease Sale 68. Under consideration are 26,000 mi 2 (67,400 km 2 ) of the California Continental Borderland north of the U.S.-Mexico boundary. The area includes both leased and unleased tracts and lies adjacent to the highly productive coastal basins of southern California. Factors that have contributed to petroleum generation in the onshore basins, such as thickness, burial depth and hydrocarbon content, are less favorable in parts of the offshore region. Nevertheless, regional geologic and geophysical mapping together with data from stratigraphic test wells and bottom samples suggest that source beds, reservoir rocks and traps are present beneath the borderland. Strata of Miocene age are widespread within the area of proposed OCS Lease Sale 68 and contain fair to excellent potential source rocks. Eocene and early Miocene sandstone beds in the Cortes Bank test well and late Miocene and Pliocene rocks in the Point Conception test well have porosities that are within the range of good reservoir rocks. Late middle Miocene through Pliocene sandy turbidites of reservoir quality possibly occur in some outer borderland basins. Additional prospective targets are fractured Miocene shale beds that may be present in the deeper basins and on the down-flank margins of major uplifts. Numerous structural and stratigraphic traps, which formed in response to late Cenozoic wrench tectonics, are distributed throughout the borderland.

California↗
USGS1978

Neogene basin formation in relation to plate tectonic evolution of San Andreas fault system, California

More than 90% of the known petroleum accumulations west of the San Andreas fault in California are in strata deposited in areally restricted Neogene basins that formed during a major tectonic reorganization of western California. These deep, localized Neogene basins replaced broad, regionally persistent Paleogene depositional aprons, although some of the Neogene basins in northern and central California had Paleogene precursors. The evolution of each of the Neogene basins is complex, and aspects of the kinematics of each are unique; nonetheless, all can be considered products of an overall right-lateral shear system associated with a sliding margin between the Pacific and North American lithospheric plates. The sliding margin developed in western California about 29 m.y. ago, when the Pacific plate contacted North America after subduction of the intervening Farallon plate. The initial position of the common boundary between the Pacific and North American plates was along the continental margin. Right slip between the Pacific and North American plates gradually shifted eastward to right-slip faults, such as the San Andreas, located farther inland. This shift seems to be documented by relations in the southern California area. About 300 km of right slip has occurred along the San Andreas fault during the past 10 to 15 m.y., and at least several hundred additional kilometers along associated right-slip faults of the San Andreas system. The Neogene basins in southern California began to develop during the interval in which the boundary between the Pacific and North American plates shifted from the continental edge to the San Andreas fault, apparently because the step-by-step switch to different surfaces of weakness caused local extension and compression within a broad zone of right-lateral shear. A major phase of basin formation appears to have been synchronous with a change in azimuth of relative shear between the Pacific and North American plates to a more westerly direction, resulting in extensional strain. This change in motion initiated basin development in offshore central and northern California and affected the ongoing development of basins as a result of right slip along the San Andreas and related faults in other parts of California.

California↗
USGS1977

Descriptions of pre-Quaternary samples, R/V Ellen B. Scripps, September 1976, Patton Ridge to Blake Knolls, California continental borderland

A sampling cruise under the joint sponsorship of Scripps Institution of Oceanography and the U. S. Geological Survey was completed in early October 1976 as part of the Survey's resource and environmental studies on the California Continental Borderland. J. K. Crouch was Chief Scientist for the cruise aboard R/V ELLEN B. SCRIPPS. Samples were taken entirely by means of dart corers, and navigation for sample sites was done using the LORAC system supported by shipboard radar. Depths were corrected for sound-velocity variations in water (Matthews, 1939). In some instances, recorded depths in the table may not match bathymetric contours on published maps because of imprecise navigation on pre-1940 surveys.

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USGS1974

Preliminary report on the geology of the continental borderland of Southern California

Appraisal of the mineral resource potential and assessment of environmental problems of any specific area require an understanding of the regional geology. The geology of t he coastal zone and offshore islands from Point Conception to the Mexican boundary serves as a frame of reference from which rock units and structures can be extrapolated into submerged parts of the borderland (sheet 1). Such extrapolations should be used with caution, for the tectonic evolution and depositional history of parts of the borderland may not have paralleled those of the mainland. On shore, rocks and structures c an be observed directly with supplemental aid from deep drill holes; but in areas covered by deep water, only indirect techniques such as geophysical methods and shallow coring provide information from which geologic intepretations can be made.

California↗
USGS1973

Age and tectonic implications of some low-grade metamorphic rocks from the Yucatan Channel

Phyllite and marble dredged from the lower part of the continental slope between Cuba and the Yucatan Peninsula seem to support the contention that a pre-early Tertiary metamorphic belt extends from the western Greater Antilles into northern Central America. The minimum K-Ar ages derived from the samples suggest that the metamorphic event was pre-Late Cretaceous, and evaluation of the K-Ar data implies that this metamorphic event is not older than Late Jurassic. Greater antiquity, however, is inferred from structural and stratigraphic relations in British Honduras, where the latest regional metamorphic event was post-Early Permian and pre-Middle Jurassic. Rifting and extension related to plate motions along the British Honduras Quintana Roo margin through Mesozoic and earliest Cenozoic time presumably would preclude extensive regional metamorphism, permitting only limited development of schistose rocks there during that interval. The timing of metamorphic events in western Cuba is uncertain, but a pre-Middle Jurassic episode possibly is reflected in the phyllite and marble terranes of Isla de Pinos and Sierra de Trinidad. Local incipient metamorphism of Early and Middle Jurassic strata in the Sierra de los Organos may have resulted from severe tectonism that began in Late Cretaceous time and diminished in the Eocene.

Yucatan Channel↗
USGS1972

Structural profile of the northwestern Caribbean

A seismic reflection and gravity profile across the continental margin of the Yucatan Peninsula, Yucatan Basin, Cayman Ridge, and Cayman Trough suggests that sediments in the Yucatan Basin consist of a thick succession of beds dominated by turbidites that overlie a thick but irregular sequence of beds, probably dominated by pelagic deposits. The so-called “Carib beds”, present elsewhere in the Caribbean, are not evident in the part of the basin crossed by this profile. The sedimentary section rests on a acoustic basement that probably represents the top of oceanic layer 2. A gravity model indicates that the crust beneath the Yucatan Basin is thin and therefore probably is oceanic in character. The crust thickens southward under the Cayman Ridge but thins again beneath the Cayman Trough. This local thickening is consistent with the suggestion that the Cayman Ridge is a rifted part of the Nicaraguan Rise.

Earth and Planetary Science Letters↗