Alluvial-fan and lacustrine fan-delta sedimentation in west-central California during the Middle Tertiary transition from subduction to transform tectonics

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6137206

Cole, R B ^[1]; Stanley, R G ^[2]

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1. Univ. of Rochester, NY (United States). Dept. of Geological Science
2. Geological Survey, Menlo Park, CA (United States)

The Plush Ranch (PR) Formation was deposited in one of several sedimentary basins in west-central California. The PR consists of more than 1,800 m of nonmarine sedimentary rocks and interbedded basaltic volcanic rocks that together record a complicated history of synsedimentary faulting, volcanism, and deposition in alluvial-fan, fan-delta, and lacustrine depositional settings. The sedimentological analysis indicates that both the northern and southern margins of the PR basin apparently were controlled ENE-trending normal faults, but that the two margins are characterized from each other by distinctive depositional facies, provenance, and sediment transport directions. The northern basin margin is recorded by sandstone-dominated braidplain deposits, with interbedded lenses of boulder-rich breccia derived by landsliding from a nearby granitic provenance. The southern basin margin is represented by matrix- and clast-supported boulder- to pebble-conglomerate with interbedded trough-crossbedded sandstones; these represent debris-flow and stream-flow alluvial-fan deposits. The alluvial-fan deposits grade northward into lacustrine fan-delta facies and provide an excellent detailed record of interfingering between alluvial-fan and lacustrine fan-delta deposits on a bed-by-bed scale. Basalt are interbedded with turbidite sandstones and evaporite/carbonate-rich intervals, but not with alluvial-fan deposits. The analysis of the sedimentary record of the PR Formation permits documentation of detailed facies relations that are useful in understanding alluvial-fan and fan-delta transitions in fault-bounded lacustrine basins. In addition, results support the conclusion of earlier workers that the Big Pine fault was a down-to-the-north, normal-slip fault along the southern margin of the PR basin during late Oligocene-early Miocene time, and then became a predominantly left-slip fault during the Quaternary.

• OSTI ID: 6137206
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
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GEOLOGIC STRUCTURES
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NORTH AMERICA
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SEDIMENTARY ROCKS
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VOLCANIC ROCKS
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