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Bjorklund, Tom1
(1) University of Houston, Houston, TX

ABSTRACT: Four-Dimensional Analysis of the Whittier Fault, Los Angeles Basin, California: A Model for Oil-Productive, Inverted Half-Grabens Associated with Continental Transform Fault Systems

Analysis of surface geologic maps and data from hundreds of oil wells in the northeastern Los Angeles basin and the application of balanced cross section techniques reveal a three-phase evolution of the Whittier fault.
1. Rotation of the Western Transverse Ranges and the formation of the proto-Whittier normal fault and associated half-graben (ca. 14-10 Ma). During that time, organic-rich shale was deposited in the half-graben and throughout the Los Angeles basin.
2. Transpression along the San Andreas fault and reactivation of the proto-Whittier fault as a basement-involved reverse fault (ca. 8 Ma). Over the next 8 million years, structural uplift continued and turbidite fan-channel systems and pelagic sediments eventually filled the Los Angeles basin. Beginning at ca. 3 Ma, oil generated from the organic-rich shale accumulated in structures along the Whittier fault, which became the oil fields that exist there today.
3. Breakthrough onto the seafloor of the reactivated proto-Whittier fault and formation of the present throughgoing Whittier fault system (ca. 5 Ma). Continued uplift led to subaerial exposure of the hanging wall block and erosion of a possible 3 billion barrel accumulation in the Soquel sandstone on the crest of the block, which could have become the largest oil field in the Los Angeles basin.
Today, oil accumulations along the Whittier fault range in depth from less than 200 meters to 2400 meters and include simple structural closures, faulted noses, combination structural and stratigraphic traps and purely stratigraphic traps, one of which is a large accumulation in a syncline.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.