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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 57 (1973)

Issue: 4. (April)

First Page: 781

Last Page: 781

Title: Foraminiferal and Nannoplankton Biostratigraphy, Paleoecology, and Basinal Reconstruction, Anita Formation, Western Santa Ynez Mountains, California: ABSTRACT

Author(s): James M. Gibson

Article Type: Meeting abstract


The Anita Formation crops out along the crest of the Santa Ynez Mountains, California, from Santa Ynez Peak westward to Point Conception. Planktonic and benthonic foraminiferal faunas and calcareous nannoplankton floras were studied from 6 measured sections between Arroyo el Bulito and Santa Ynez Peak. In general, Anita Formation strata are assigned to the time interval from early Paleocene to early middle Eocene on the basis of prevailing planktonic correlations. Also from planktonic evidence, reported Ynezian benthonic foraminiferal assemblages appear to be early Paleocene to late Paleocene in age; Bulitian assemblages are of late Paleocene age; Penutian assemblages are late Paleocene in some sections and early Eocene in others; Ulatisian assemblages are late Paleocene o early middle Eocene. The time-transgressive nature of the benthonic provincial stages is apparent; the stages become geologically younger toward the basin margins as well as stratigraphically higher. Furthermore, strata mapped as Anita Formation by Dibblee have been found to be of late Cretaceous age in several areas.

Lithologically, the Anita Formation can be split into three gross members, which can be mapped throughout the Western Santa Ynez Range. The unit is divisible into the following stratigraphic units, all of which are typed in the upper Arroyo el Bulito area: Gato siltstone (upper member); Augustin mudstone (middle member); and Bulito siltstone (lower member).

The Anita Formation is thickest south of the present Santa Ynez fault system, whereas northward, telescoped sections occur, and the Anita gradually disappears. This relation suggests that the Santa Ynez fault may have been a prominent structural feature in early Paleogene time. Eastward the Anita wedges into "Matilija" type clastics, which were shed from the nearby San Marcos high. Southward the Anita disappears under the Santa Barbara Channel.

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Copyright 1997 American Association of Petroleum Geologists