6 D5. Sediments, Soils, and Stratigraphy (Posters)

Wednesday, 15 May 2019
9:00 AM - 6:00 PM
Exhibit Hall B

FIELD EVIDENCE FOR PALEOGEOGRAPHY AND PROVENANCE OF OLIGOCENE-EARLY MIOCENE POLYMICT NON-MARINE CONGLOMERATES, SAN EMIGDIO AND TEHACHAPI MTNS AND OFFSET EQUIVALENTS IN THE GABILAN RANGE, CA

Paper number: 6-6
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Tecuya Fm. is a 0.2-1.2km thick sequence of Oligocene-early Miocene non-marine coarse clastic rocks (Ttc) and 21-25Ma bimodal volcanic rocks (Tv) exposed in a 30km EW-trending outcrop belt, 10km north of the junction of the San Andreas and Garlock faults. Coarse-clastic rocks can be divided into three informal members 1) lower (Ttcl ); 2) middle (Ttcpm); and 3) upper (Ttcu) that are respectively pre-, syn-, and post-Tv.

Based on detailed mapping and sedimentology, Ttcl conglomerates contain 3 statistically distinct compositional assemblages that, from N to S, contain >50%, 1) orthoquartzite (Ttcoq,), 2) siliceous-felsic metavolcanic rock (Ttcmv), or 3) mixed carbonate rocks (Ttcc) that are areally restricted to 3 separate coarsening-upward, alluvial fan-braided river systems with sources to the west and south. Resedimented late Paleocene Goler Fm. and/or late Cretaceous-early Miocene Witnet Fm. are possible sources, but Ttcmv assemblages are unique and a regional petrographic survey of quartzites found no source for supermature Ttcoq orthoquartzites.

Ttcpm overlies a regional high-relief erosion surface with local angular discordance. It is thickest adjacent to high angle faults interpreted to be early Miocene domino-style, extensional faults. Composition is >50% local plutonic and metamorphic rocks with paleocurrents that flowed NE in the east and NW in the west.

Ttcu overlies a second high-relief erosion surface cut into Tv and contains up to 5% Tv clasts, 5 distinct conglomerate assemblages, and NE flowing paleocurrents. Ttcpm and Ttcu grade to the west and up section into marine sandstone of the Temblor Fm. The poorly exposed mid-Miocene Nameless Conglomerate overlies all Oligocene-early Miocene rocks with angular discordance. Oligocene redbeds in the Gabilan Range contain similar assemblages and stratigraphic relationships. Detailed paleogeographic reconstruction of Oligo-Miocene alluvial fans may identify additional provenance relationships and piercing points that will be useful in evaluating complex fault kinematics at the Big Bend.

Geological Society of America Abstracts with Programs. Vol. 51, No. 4

doi: 10.1130/abs/2019CD-329446

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