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Provenance, paleogeography, and paleotectonic implications of the mid-Cenozoic Sespe Formation, coastal southern California, USA

By
Raymond V. Ingersoll
Raymond V. Ingersoll
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095-1567, USA
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Claire D. Spafford
Claire D. Spafford
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095-1567, USA
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Carl E. Jacobson
Carl E. Jacobson
Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, Iowa 50011-3212, USA
Department of Earth and Space Sciences, West Chester University of Pennsylvania, West Chester, Pennsylvania 19383, USA
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Marty Grove
Marty Grove
Department of Geological and Environmental Sciences, Stanford University, Green Earth Sciences, Room 225, Stanford, California 94305-2115, USA
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Jeffrey L. Howard
Jeffrey L. Howard
Department of Geology, 0224 Old Main, Wayne State University, Detroit, Michigan 48202, USA
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Jeremy Hourigan
Jeremy Hourigan
Department of Earth and Planetary Sciences, 552 Red Hill Road, University of California, Santa Cruz, California 95064-1077, USA
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Jane Pedrick
Jane Pedrick
Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, Iowa 50011-3212, USA
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Publication history
05 February 201805 October 2018

ABSTRACT

The upper Middle Eocene to Lower Miocene Sespe Formation is the youngest part of an ~7-km-thick Cretaceous–Paleogene forearc stratigraphic sequence in coastal southern California. Whereas Upper Cretaceous through Middle Eocene strata of southern California record a transition from local (i.e., continental-margin batholith) to extraregional (i.e., cratonal) provenance resulting from Laramide deformation (75–35 Ma), the Sespe Formation records the reversal of this process and the re-establishment of local sediment sources by Middle Miocene time.

In contrast to underlying dominantly marine strata, the Sespe Formation primarily consists of alluvial/fluvial and deltaic sandstone and conglomerate, which represent terminal filling of the forearc basin. Prior to Middle Miocene dissection and clockwise rotation, the Sespe basin trended north-south adjacent to the west side of the Peninsular Ranges. The integration of paleocurrent, accessory-mineral, conglomerate, sandstone, and detrital zircon data tightly constrains provenance. Sespe sandstone deposited in the Late Eocene was supplied by two major rivers (one eroding the Sonoran Desert, to the east, and one eroding the Mojave Desert, Colorado River trough area, and Transition Zone, to the north), as well as smaller local drainages.

As the Farallon slab rolled back toward the coast during the Oligocene, the drainage divide also migrated southwestward. During deposition of the upper Sespe Formation, extraregional sources diminished, while the Peninsular Ranges provided increasing detritus from the east and the Franciscan Complex provided increasing detritus from the west (prerotation). As the overall flux of detritus to the Sespe basin decreased and deposition slowed, nonmarine environments were replaced by marine environments, in which the Miocene Vaqueros Formation was deposited.

The provenance and paleogeographic information presented herein provides new insights regarding the unique paleotectonic setting of the Sespe forearc from the Late Eocene through earliest Miocene. Nonmarine sedimentation of the Sespe Formation initiated soon after cessation of coastal flat-slab subduction of the Laramide orogeny and terminated as the drainage divide migrated coastward. Competing models for movement along the Nacimiento fault system during the Laramide orogeny (sinistral slip versus reverse slip to emplace the Salinian terrane against the Nacimiento terrane) share the fact that the Peninsular Ranges forearc basin was not disrupted, as it lay south and southwest of the Nacimiento fault system. The northern edge of the Peninsular Ranges batholith formed a natural conduit for the fluvial system that deposited the Sespe Formation.

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Contents

GSA Special Papers

Tectonics, Sedimentary Basins, and Provenance: A Celebration of the Career of William R. Dickinson

Geological Society of America
Volume
540
ISBN electronic:
9780813795409

GeoRef

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