* Denotes speaker other than senior author.
FRITSCHE, A. EUGENE, MARY S. STECHESON*, JESSE F. HOLT, ARTURO
A. OROZCO, MARK O. KRUGER, and SHERIEF A. MANSOUR
Department of Geological Sciences, California State University, Northridge, CA
Abstract: Medial Eocene Paleogeography of Southwestern California
Palinspastic restoration of the area of the western Transverse Ranges to their pre-rotated medial Eocene position parallel to the southern coast of California allows for integration of middle Eocene stratigraphy of the Transverse Ranges with middle Eocene stratigraphy of coastal southern California west of the Peninsular Ranges. This stratigraphic integration provides a more complete picture of medial Eocene paleogeography than has heretofore been possible. On this palinspastic restoration, the area that today contains the northern Channel Islands is oriented in a north-south direction and is west of coastal southern California; farther west, also oriented north-south, is the area of today's Santa Ynez Range, and today's Santa Monica Mountains are north of the present-day Santa Ana Mountains.
In the vicinity of present-day San Diego, the medial Eocene Ballenas river system flowed westward into a coastal braided delta, lagoons, and tidal flats. A similar river system, the Las Palmas, existed in the vicinity of present-day northern Baja California. These coastal deposits were cut by submarine canyons which fed into submarine fans. Middle fan deposits existed at the rotated, medial Eocene location of the northern Channel Islands region, and outer fan deposits accumulated in the vicinity of the Santa Ynez Range. A third westward-flowing, braided river and delta system existed in the Santa Ana-Santa Monica Mountains area. This delta merged progressively west-ward into wave-dominated shoreface, shelf, and slope deposits.
The fact that the middle Eocene stratigraphy of the Transverse Ranges and coastal southern California mesh so well in producing a simple paleogeographic interpretation is evidence that the rotational model for the tectonic evolution of southwestern California is valid.
AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California