--> Abstract: Tectonic, Eustatic and Climatic Controls on Sequence Deposition--An Example from the Middle Eocene of Southern California, by M. S. Clark; #90987 (1993).

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CLARK, MICHAEL S., ARCO Oil and Gas Company, Bakersfield, CA

ABSTRACT: Tectonic, Eustatic and Climatic Controls on Sequence Deposition--An Example from the Middle Eocene of Southern California

Middle Eocene strata in the Topatopa Mountains, California contain several 3rd- to 4th-order (5 to 0.1 my duration), unconformity-bounded depositional sequences that formed in response to interrelated tectonic, eustatic, and climatic controls. These sequences were deposited in a tectonically-active basin in which differential subsidence caused migration of the basin depocenters at least every 2 my. Thus, the frequency of tectonic events was similar to that of global eustatic events interpreted in other studies.

A tectonic control during sequence deposition is evidenced by facies relations across some sequence boundaries that indicate switching of depocenters to opposite sides of the basin. Furthermore, some sequence boundaries apparently formed during maximum development of paleohighs; and some boundaries correlate to global highstand, not lowstand, events. The incision of other sequence boundaries by alluvial valleys indicates a eustatic control, whereas the presence of Vail type II sequences indicates combined eustatic and tectonic controls.

Several 3rd- and 4th-order sequences comprise a larger, unconformity-bounded, 2nd-order sequence which represents a 7 my cycle of transgression and regression not associated with global eustatic events. Paleosol and palynomorph analysis indicates that storm wave-dominated facies at the base of the larger sequence were deposited in humid environments; whereas coarser-grained, shoaling wave-dominated facies at the top of the sequence were deposited in arid environments. Thus, the 2nd-order sequence represents a low-frequency cycle of climatic change which contains the integrated, high-frequency responses of 3rd- to 4th-order cycles representing subsidence and sea-level change.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.