--> Abstract: Neogene Tectonics and Sedimentation Along the Western Margin of the Salton Trough, California, by D. R. Kerr; #90958 (1995).

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Abstract: Neogene Tectonics and Sedimentation Along the Western Margin of the Salton Trough, California

Dennis R. Kerr

Neogene sedimentary and volcanic rocks exposed along the western margin of the Salton Trough record 2 distinct phases of tectonic activity. The tectonic history is revealed through the mapping (7.5^prime-quadrangle scale) of depositional facies and systems, maximum clast size trends, and variations in paleocurrent patterns. Paleontologic data, and paleomagnetic and geophysical surveys are also compiled to supplement the author's own work.

The early to middle Miocene phase records regional extension producing northeast trending (present orientation disregarding rotation) half-graben basins. Broad, shallow braided fluvial systems drained the back-tipped bursts. Narrower, deeper braided fluvial systems drained the basin axial region. Faulted margins were the site of deposition of alluvial fans, which were mostly debris-flow dominated with lesser fluvial dominated, and the site of local emplacement of rock avalanche breccias. Alkalic and tholeiitic basalt volcanism (22 to 14 M.a.) was not confined to the faulted margins. Stratigraphic relations and clast compositions clearly demonstrate that the continental sedimentary rocks are in part coeval with the volcanic effusions.

The early Pliocene to present phase records regional transtension with local transpression as the Gulf of California opened. The earliest record is exposed in the Split Mountain area where the topographic gradient was reversed probably as a result of the juxtaposition of a former half-horst against a former half-graben basin along the incipient San Jacinto fault zone. Across most of the western margin the early to middle Miocene section is separated from younger rocks by an unconformity. Highly irregular, steep basin margin settings included fan-delta, rock avalanche/debris flow, and localized evaporite sedimentation. The principal basin fill, however, came from the Colorado River ultimately depositing a tide-dominated deltaic section of some 4.0 km thick.

Although the regional pattern of tectonism is transtensional, the present-day local pattern is transpressional. This is expressed in the realignment of fold axes. These patterns may have resulted from at least 35° of clockwise rotation since the late Pleistocene.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California