4 Late Cretaceous–Paleogene Tectonism from the Southwestern Cordillera to the Rocky Mountains

Wednesday, 12 May 2021
8:30 AM - 11:10 AM
Mackay School of Earth Sciences & Engineering Room

THE GOLER FORMATION: EOCENE FLUVIAL DEPOSITS AND PALEOGEOGRAPHY AT THE SOUTHERN END OF THE SIERRA NEVADA

Paper number: 4-1
Program: Theme Sessions
Time: 8:30 AM – 8:50 AM

Authors

Abstract

The Goler Formation in the El Paso Mountains, near Ridgecrest, California, represents Paleocene-Eocene deposition at the southeastern termination of the Sierra Nevada Mountains. Building on the pioneering work of Cox (1982 UCR PhD thesis), we re-evaluate 1254m from the central part of the basin and reconstruct paleo-environments and basin geometry. New data include detailed geologic interpretations of 8 outcrops and 5 new paleocurrent sites (imbricated clasts, epsilon cross-beds, channel margins, n=64) from the central part of the exposed strata. We define five lithofacies; coarse-grained sandstone with crossbeds (Sc), gravelly siltstone (Fm), pebble-cobble conglomerate (Gcm), pebbly coarse-grained sandstone (Gcm-Sc), and a fine-grained sandstone with laminations (Sh), which we group into three map units (3c, 4a, and 4b following Cox, 1982). Unit 3c is 175m thick and is unconformable on, or locally faulted against the El Paso Mountains basement. It is dominated by 0.5-2.0 m-thick Sc and Gcm beds within Fm, contains west-directed paleocurrent indicators, and is interpreted as distal fan deposition sourced from the east (Cox, 1982). Unit 4a (175-629m) is dominated by Fm strata with occasional, 0.5-2.0 m-thick discontinuous beds of Sc. We interpret this interval to represent primarily floodplain strata adjacent to a meandering fluvial system. Unit 4b extends from 629m to 1254m and consists of 10-20 m-thick sections of discontinuous Sc and Gcm interpreted as meandering channel complexes. The base of this unit is identified by a 40m thick section of Sc and Gcm. 10-20 m-thick sections of Fm are common and contain petrified wood, calcareous and laminated beds, and imply overbank and lacustrine floodplain deposition. Paleocurrent directions are 036 and 354 degrees (n=23, 13) suggesting a north flowing meandering river system. Overall, we interpret the Goler Formation to represent an NNE flowing axial river system (units 4a, 4b) fed by transverse fans (i.e. unit 3c) from the valley edges. In total, we speculate the Goler Formation strata represents eastward migration of the depocenter within a north-northeast trending river valley related to progressive extension above an east-dipping detachment.

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

doi: 10.1130/abs/2021CD-363250

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