Provenance of Middle Tertiary sandstones of the San Emigdio and Tehachapi Mountains, southern California
- Univ. of Rochester, NY (United States). Geosciences Dept.
Petrographic analysis of 78 medium to coarse-grained sandstones collected from complete depositional sequences of early Eocene to early miocene age exposed in the San Emigdio and Tehachapi Ranges reveal moderately sorted, subangular arkoses and lithic arkoses. Framework sand-sized grains are primarily detrital quartz, potassium feldspar, plagioclase and lithic fragments. Lithic fragments consist of: (a) Volcanic/meta-volcanic types, (Lv); (b) low/high grade metamorphic types, (Lm); and, (c) sedimentary/meta-sedimentary types, (Ls). Gazzi-Dickinson point-counts of 450 framework grains per slide yield the following modal averages: Tejon Fm-Uvas Member: %QFL = 62, 34, 4; Metralla Member: %QFL = 43, 50, 7; San Emigdio Fm-Basal Member: %QFL = 49, 38, 13; Upper Sandstone Member: %QFL = 59, 34, 7; Tecuya Fm: %QFL = 62, 28, 10; Pleito: %QFL = 43, 49, 8; and, Temblor Fm: %QFL = 47, 46, 6. Modal data plotted on provenance discrimination diagrams indicate a continental block-uplifted basement provenance and a dissected arc provenance suggesting Sierran and Mojavian block sources. To determine the extent that depostional processes control sandstone composition, QFL averages and standard deviations were calculated for samples grouped by facies. Modal averages were distinct between facies: Fluvial, %QFL = 40, 47, 13; eolian, %QFL = 80, 16, 4; beach, %QFL = 75, 13, 12; surf zone-longshore trough, %QFL = 51, 41, 8; shelf, %QFL = 41, 46, 13. In general eolian and beach sandstones are more mature than fluvial, surf zone and shelf sandstones. Climate during deposition of the sandstones was not a dominant factor controlling sandstone composition. However, sandstone deposition during the tropical conditions of the Eocene produced predominantly quartose sandstones. Sandstones deposited after the Eocene/Oligocene climatic deterioration produced predominantly feldspar-rich sandstones.
- OSTI ID:
- 5809170
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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