6 Exhumation and Topographic Evolution of the Sierra Nevada and Tehachapi Mountains

Wednesday, 12 May 2021
11:00 AM - 12:45 PM
JohnNLouie.com Room

MID-CENOZOIC PALEOSHORELINES, WESTERN TEHACHAPI-EASTERN SAN EMIGDIO MTNS CA

Paper number: 6-7
Program: Theme Sessions
Time: 12:15 PM – 12:20 PM

Authors

Abstract

The late Eocene-early Miocene Tecuya Fm (Tc) is exposed for 30km in an EW cross-section on the southern edge of the San Joaquin Basin. Tc consists of 0.2-1.2km of polymict conglomerate, sandstone, and early Miocene bimodal volcanic rocks (Mv) that were deposited at or near sea level. Tc grades N and W into marine San Emigdio, Pleito, Vedder, and Temblor Fms. New detailed mapping and stratigraphy of Tc, 10 km north of the junction of the San Andreas and Garlock faults, provides a high resolution record of uplift, erosion, and subsidence relative to sea level during the transition to a transform margin.

In the late Eocene, 20-200m of WSW-flowing conglomerate and sandstone rich in exotic orthoquartzite clasts (Tc1) were deposited on a planar erosion surface cut across the early-mid Eocene marine Tejon Fm and pre-Cenozoic crystalline basement. Tc1 grades E to W from braided fluvial to nearshore facies.

In the Oligocene, Tc1 was overlain by ≈800m of exotic polymict conglomerate and locally-derived breccia (Tc2) that were deposited in N-flowing alluvial fans sourced to the S. Paleoshoreline moved N and W.

In the late Oligocene-early Miocene, 20-70 m of locally-derived nearshore conglomeratic sandstone (Tc3) was deposited on a transgressive erosion surface cut across Tc1-2 and basement. Beach, shoreface, and wave-reworked alluvial deposits rim eroded basement highs and Tc1-2 in the footwalls of NW-striking normal faults. Tc is up to 5 times thicker in the hanging walls.

In the far W, wave-reworked Tc3 fanglomerate is overlain by inner shelf deposits. In the E, Tc1-3 and basement are cut by high relief channels and overlain by 40-100m of nonmarine, locally-derived, NNE-flowing, boulder conglomerate and megabreccia (Tc4) with interbedded olivine basalt flows. Overlying basalt, a rhyodacitic vent complex fed by peperitic dikes formed a topographic high.

In the W, subaerial Mv flows are overlain by recycled nearshore conglomeratic sandstone (Tc5) that grades westward to shelf deposits. In the E, Mv contains erosional or fault-related NE-facing paleoscarps that deflected flows. Interbedded, NE-flowing, fluvial conglomerate recycled from eroded Tc is cut by peperitic dikes.

Tc was then tilted 20 degrees to the N and cut by a high relief erosion surface. Overlying Relizian and younger nonmarine conglomerates contain recycled Tc.

Geological Society of America Abstracts with Programs. Vol. 53, No. 4

doi: 10.1130/abs/2021CD-362683

© Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.