Alluvial-fan and lacustrine fan-delta sedimentation in west-central California during the Middle Tertiary transition from subduction to transform tectonics
- Univ. of Rochester, NY (United States). Dept. of Geological Science
- 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--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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