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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG

Abstract


The Geology of Peninsular California; 49th Annual Meeting, 1974
Pages 20-59

The Type Alisitos Formation (Cretaceous, Aptian - Albian) of Baja California and its Bivalve Fauna

Edwin C. Allison

Abstract

The Cretaceous pre-batholithic rocks of the northwestern Peninsular Ranges, predominantly andesitic breccias, tuffs, and interbedded biohermal limestones, are assigned to the Alisitos Formation. The Alisitos Formation is intruded by the 90 to 130 million year old plutons of the Peninsular Ranges batholith.

A stratigraphic thickness of approximately 7500 meters is evident in the type area of the Formation, near the Pacific coast of northern Baja California, south of Canon Santo Tomas. The total thickness is exposed on the southwestern flank of a great north-west-plunging anticline. Fossils occur throughout that section. Eighty-four species of the molluscan class Bivalvia are recorded from 73 fossil localities in the type area of the Alisitos Formation and from 10 other nearby localities. Twenty-nine species are identified with previously described species, 5 of them questionably. Twenty-five species are new. Thirty other species are recognized but not specifically identified. Most of the Alisitos Formation species are identical to, or most closely related to, species in the relatively well-known Tethyan faunas of Europe and other areas adjacent to the Mediterranean Sea. The Bivalvia and other fossil invertebrates suggest a late Aptian-early Albian age for the Formation.


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