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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 609

Last Page: 609

Title: Miocene Marine to Nonmarine Transition in Southern Coast Ranges of California: ABSTRACT

Author(s): H. E. Clifton

Article Type: Meeting abstract


The southeastern Caliente Range, in the southern Coast Ranges of California, contains a remarkably exposed transition between marine and nonmarine rocks. The transitional sequence consists of depositional facies that contain sedimentary structures comparable to those found at present in coastal environments in Oregon and California. The spatial relations of the facies are consistent with their origin as interpreted from depositional structures. Directional structures and lateral trends within the deposit relate to the local middle Miocene paleogeography as deduced from independent evidence.

Fine-grained ripple-bedded and bioturbated shelf sediment constitutes the seaward-most facies. Medium- to coarse-grained sandstone in which crossbedding dips predominantly seaward defines a facies that resembles deposits produced by laterally migrating longshore bar-rip channel systems. Abundant medium-scale (5-30 cm) trough cross-stratification characterizes a facies similar to that formed in the modern high-energy surf zone. Planar sand and gravel layers that dip gently seaward identify another facies, one with a modern counterpart on the lower foreshore. Heavy-mineral layers 1-10 cm thick that dip gently seaward, where they interfinger with quartzose sand, identify ancient upper foreshore deposits. Other facies include oyster-bearing siltstone (probably a lagoonal deposit) and stru tureless muddy medium-grained sandstone that may represent a vegetated back-beach deposit. Structureless red mudstone, sandstone, and conglomerate of alluvial origin form the most landward facies.

The different facies are repeated cyclically throughout the transitional sequence. Within each cycle the facies lie in an ascending order of increasingly shallow-water deposition. Each cycle represents a progradational episode; the intervening transgressions are indicated by erosional surfaces, in places covered by a thin layer of conglomerate. This cyclic repetition of slow progradation interrupted by rapid submergence may relate to episodic movements on the nearby San Andreas fault.

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Copyright 1997 American Association of Petroleum Geologists