Field Trip Information

SJGS Field Trip – April 15th 2015


Geologic Evolution of the Southwestern Sierra Nevada-­San Joaquin Basin Transition-­An Excursion to Some Critical Exposures
Jason Saleeby and Zorka Saleeby  Division of Geological and Planetary Sciences,  California Institute of Technology, Pasadena CA 91125


The goal of this one day field trip is to bring to light a number of critical relationships that we have discovered in regard to the Neogene-­Quaternary history of the eastern San Joaquin Basin by the tracking of relationships into the Basin margin that we have discovered during multi‐decadal structure mapping and petrologic­‐geochemical studies of the southern Sierra Nevada‐Tehachapi Mountains basement uplift. In published papers and in manuscripts that are in preparation we show that the Neogene-­lower Quaternary section of the Basin margin extended nonconformably eastwards across recently re-­exhumed Sierran basement for a considerable distance, and that strata of the Basin margin were in continuity with strata of a significant Miocene basin (termed the Walker graben) that covered most of the southern Sierra Nevada until medial Pliocene time. Neogene basin development, reorganization of principal depocenters, and partial exhumation phases are recognized to have been forced by three distinct tectonic regimes: 1) Early and Middle Miocene opening of the Pacific-­Farallon slab window; 2) Late Miocene initiation of the eastern Sierra escarpment system, and derivative westward tilting of the Sierra‐Great Valley basement surface; and 3) Late Pliocene‐Quaternary delamination of mantle lithosphere from beneath the southern Sierra and Great Valley region. Some of the specific features that we will focus on in the field include: 1) the Neogene‐Quaternary southern Sierra fault system, which consists of numerous topographically and bathymetrically significant high‐angle normal and transfer faults that cut across the entire southern Sierra, and extended as growth structures into the eastern San Joaquin Basin; 2) Early and Middle Miocene chronostratigraphic markers that extend from the Walker graben into the eastern San Joaquin Basin; 3) evidence for Early to Middle Miocene rapid normal fault growth along eastern Basin exposures; 4) multiple phases of profound sediment re-­‐dispersal from the Walker graben into the southern San Joaquin Basin, and then from uplifts along part of the Basin margin into the Maricopa and Tulare sub-­basins; and 5) the development of the lower Kern River gorge and the Kern gorge fault scarp.

Field Trip limited to the first 25 people.

COST: $175

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