How to join the society:
The San Joaquin Geological Society has no formal dues, and our activities are open to anyone interested in geology.
FEBRUARY 10th DINNER MEETING ABSTRACT
Vertical Field Methods in Geology
Dr. Michael S. Clark
Petroleum Geologist, Aera Energy, Bakersfield, CA
Yosemite Valley is an amazing granite gorge located on the western slope of the Sierra Nevada Mountains of California. Cretaceous-age plutonic rocks up to 114 MA in age were emplaced during several intrusive events, with subsequent ice age glaciations that over the last 30 MA have excavated a one-mile by seven-mile u-shaped valley with sheer granite walls displaying up to 3,000 feet of vertical relief. Although these incredible exposures provide unique opportunities for geologic study, the magnitude of relief also makes large areas of the valley inaccessible to the average geologist. However, pioneering ascents of the largest rock walls beginning in the late 1950s and continuing up to the present demonstrate that the techniques exist to analyze and interpret these outcrops in detail. This talk explores how these field methods may be successfully applied to studying vertical rock walls, whether they are in Yosemite or elsewhere.
Michael S. Clark is a petroleum geologist, currently working at Aera Energy. He has an A.S. degree in Biology from Cabrillo Junior College in Aptos, California (1973), a B.S. degree in Earth Sciences from the University of California at Santa Cruz (1975), an M.S. degree in Geology from the University of California at Davis (1979), and a Ph.D. in Geology from the Colorado School of Mines (1991). Dr. Clark has worked as an exploration geologist for Amoco Production Company in Denver, a research geologist for Exxon Research in Houston, and for Elf Aquitaine in Pau, France, a senior geologist for ARCO Western Energy in Bakersfield, CA and a staff geologist for Chevron in Bakersfield. His research interests include sequence stratigraphy, process sedimentology, and organic geochemistry, and he has published several professional articles on various aspects of the Cretaceous and Tertiary of California.
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.