Provenance and stratigraphy of the Eocene Tejon Formation, Western Tehachapi Mountains, San Emigdio Mountains, and Southern San Joaquin Basin, California

The Eocene Tejon Formation of the western Tehachapi and San Emigdio Mountains of California provides a unique east-west-trending outcrop belt of otherwise deeply buried strata that underlie the San Joaquin basin to the north. Its stratigraphy and framework mineralogy have been used to define offsets along the San Andreas fault, a major Neogene plate-boundary transform fault that has translated coastal California northward more than 300 km by right slip. The Tejon Formation was deposited directly on crystalline basement rocks as a result of an eastward transgression of at least 45 km from the early to the late middle Eocene, followed by a major regression in the late middle Eocene, The basal Uvas Conglomerate Member consists entirely of coarse-grained transgressive-system-tract (TST) deposits characterized by abundant current-formed sedimentary structures. It is overlain by offshore marine shales of the Liveoak Shale Member, which consist of lower TST deposits overlain by highstand-system-tract (HST) deposits. The overlying regressive Metralla Sandstone Member consists mostly of highly bioturbated fine-grained shallow-marine HST sandstones with local thin-bedded turbidites present in some western exposures. The quartzofeldspathic sandstones (grand mean Qm51 +/- 12F42 +/- 12Lt7 +/- 4) of the Tejon Formation suggest a provenance consisting of plutonic, metamorphic, and volcanic rocks such as those present in the basement of the San Emigdio and Techachapi Mountains, northwestern Mojave Desert, and southern Sierra Nevada. Petrologic parameters, however, suggest variable contributions from these source areas through time. Three distinctive petrofacies coincide with the three principal lithostratigraphic subdivisions. The shallow-marine TST sandstones from the Uvas Conglomerate Member are more quartzose than those of the HST Metralla Sandstone Member, possibly because higher-energy deposition preferentially preserved quartz. Thin-bedded turbidites in the western exposures of the Metralla Sandstone, in contrast, have more abundant feldspar and volcanic lithic fragments than the Uvas and Liveoak members. The composition of the Tejon Formation suggests derivation from a basement uplift provenance, with progressive upsection changes from Qm60 F33 Lt8 (Uvas) to Qm46 F44 Lt10 (Liveoak) and Qm 43 F52 Lt5 (Metralla). The composition and provenance of the Tejon Formation is different from that of the coeval Butane Sandstone and Point of Rocks Sandstone, submarine-fan deposits to the north and west. (C) 2000 Elsevier Science B.V. All rights reserved.