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Geology topics

J. G. Vedder

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

At least 19 recordsLinked to original sources
USGS2009

Basin development along the Late Mesozoic and Cainozoic California Margin: A plate tectonic margin of subduction, oblique subduction and transform tectonics

Along the Californian margin of the North American plate, the configuration and structural stability of late Mesozoic and Cainozoic basins are related to plate kinematics. Three tectonic regimes are recorded; orthogonal high-angle subduction, oblique low-angle subduction, and transform slip. During the first, regionally extensive forearc basins developed; during the second and third, borderland settings formed as a consequence of wrench faulting. In the forearc basins, sedimentological facies constitute regional belts that persist for hundreds of kilometres, with stratigraphic sequences that are 1–15 km thick. Shorelines are relatively straight, shelf facies are broad and well developed, and basin fill is composed of shallow marine, shelf and coalescing submarine-fan facies. Sediment transport in the deeper water facies commonly is parallel to the basin axis. Borderland basins reflect tectonic instability. A principal effect of wrench tectonics is the vertical reciprocation of crustal blocks. Shorelines are generally irregular, and narrow shelves pass abruptly into deep basins. Lithofacies change dramatically along strike, and stratigraphic thicknesses are variable from basin to basin, from tens of metres up to 6 km. Basin-margin facies are marked by unconformities, slump aprons, lithological pinch-outs and submarine canyon channels. Penecontemporaneous slip along the basin-margin faults complicates these lithofacies patterns. Borderland type palaeogeography is most extensively developed in the transform tectonic regime, and therefore the more seaward offshore basins are relatively depleted of terrigenous debris owing to transport barriers.

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USGS1995

Preliminary Geologic Map of the Big Pine Mountain Quadrangle, California

Reconnaissance geologic mapping of the San Rafael Primitive Area (now the San Rafael Wilderness) by Gower and others (1966) and Vedder an others (1967) showed s number of stratigraphic and structural ambiguities. To help resolve some of those problems, additional field work was done on parts of the Big Pine Moutain quadrangle during short intervals in 1981 and 1984, and 1990-1994.

Open-File Report↗
USGS1991

Paleogeographic implications of an erosional remnant of Paleogene rocks southwest of the Sur-Nacimiento Fault Zone, southern Coast Ranges, California

A small tract of heretofore-unrecognized Paleogene rocks lies about 30 km northeast of Santa Maria and 1 km southwest of the Sur-Nacimiento fault zone near upper Pine Creek. This poorly exposed assemblage of rocks is less than 50 m thick, lies unconformably on regionally distributed Upper Cretaceous submarine-fan deposits, and consists of three units: fossiliferous lower Eocene mudstone, Oligocene(?) conglomerate, and basaltic andesite that has a radiometric age of 26.6 ?? 0.5 Ma. Both the sedimentary and igneous constituents in the Paleogene sequence are unlike those of known sequences on either side of the Sur-Nacimiento fault zone. The Paleogene sedimentary rocks near upper Pine Creek presumably are remnants of formerly widespread early Eocene bathyal deposits and locally distributed Oligocene(?) fluvial deposits southwest of the fault zone. The 26.6 Ma basaltic andesite, however, may not have extended much beyond its present outcrops. An episode of Oligocene(?) displacement is required by the contrast in thicknesses, depositional patterns, and paleobathymetry of the juxtaposed rock sequences. -from Authors

Geological Society of America Bulletin↗
USGS1984

Ferrelo fan, California: Depositional system influenced by Eustatic sea level changes

Remnants of an Eocene fan system are preserved onshore at San Diego and in the central part of the southern California borderland. Even though faults and erosion have truncated its margins, geophysical data and exploratory wells indicate that remaining parts of the fan extend beneath an offshore area nearly 400-km long and 40- to 100-km wide. Environments representing fluvial, fan-delta, shelf-channel, overlapping inner- to outer-fan, and basin-plain facies are recognized or inferred. Three progradational cycles onshore and two distinct pulses of sand accumulation offshore are attributable to eustatic low sea-level stands rather than to tectonic uplift or shifts in depositional patterns. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
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.

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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.

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