Abstract: Late Cretaceous Depositional Environments, Northern Santa Ana Mountains, Southern California

Frederick A. Sundberg, John D. Cooper

The Upper Cretaceous (Turonian-Campanian) sedimentary rocks of the northern Santa Ana Mountains, southern California, are represented by five major lithofacies. Sedimentologic features, stratigraphic relations, and macroinvertebrate assemblages suggest that the lithofacies were deposited in a paralic setting that included shallow-marine shelf, marine-shoreface, and terrestrial paleoenvironments. The lithofacies are named after the formal lithostratigraphic units of which they compose a major part.

The Trabuco lithofacies is a red, poorly sorted, basal conglomerate that accumulated as alluvial fans, some of which prograded seaward to form fan-delta systems. The Baker Canyon lithofacies consists of conglomeratic fan-delta deposits and delta-fringe sandstones that contain the intertidal Crassostrea and Trigonarca-Flaventia molluscan assemblages. The Holz lithofacies of gray mudstone and siltstone includes part of the Holz Shale Member of the Ladd Canyon Formation. Benthic molluscan faunas include the Inoperna-Glycimeris and Eriphyla-Parallelodon assemblages, characteristic of a shallow-marine, bay-type paleoenvironment, and the Pseudoperna-Amuletum and Inoceramus-Acila assemblages, suggestive of restricted lagoonal conditions. Sandstone and conglomerate lenses in the Holz shale re resent fan-delta tongues and lobes that prograded across the bay and lagoonal mudstones, and record the intercalation of Baker Canyon and Holz lithofacies. The conglomeratic Shulz lithofacies includes fan-delta and other shallow-marine shoreface deposits. This Upper Cretaceous section is topped by the fossiliferous mudstones and sandstones that comprise the open-marine, shallow-shelf Pleasants lithofacies.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California