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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 10. (October)

First Page: 1694

Last Page: 1694

Title: Magnetic Polarity Stratigraphy of Middle Miocene Barstow Formation of Mojave Desert, Southern California: ABSTRACT

Author(s): Bruce J. MacFadden, Michael O. Woodburne

Article Type: Meeting abstract

Abstract:

The Barstow Formation, of medial Miocene age, crops out in a band about 53 mi (85 km) long, from the Mud Hills on the west to West Cronese basin on the east. Because of its excellent exposures, abundant fossils, and important radiometric calibrations, the Barstow Formation is one of the more important rock units to consider when evaluating the geologic evolution of the central Mojave Desert. The stratotype of the Barstow Formation, in the Mud Hills north of Barstow, consists of about 4,265 to 6,560 ft (1,300 to 2,000 m) of highly fossiliferous terrigenous and volcaniclastic sediments that have been folded into a syncline and offset in a right-lateral sense by several northwest-trending faults. The fossil mammals from this formation are central to the concept of the middle Miocene "Barstovian" Land Mammal Age.

During the fall of 1980, about 100 separately oriented hand samples were collected from 32 sites, spaced at stratigraphic intervals of about 49 to 165 ft (15 to 50 m). Analysis of the paleomagnetic characteristics (using the ScT cryogenic magnetometer and associated instruments at the University of Florida) indicates that the principal components of the NRM result from DRM carried by magnetite. In most cases, site polarities can be unambiguously determined after A.F. demagnetization in peak-alternating fields of 250 oe and/or thermal demagnetization at 250°C (482°F). Preliminary results indicate that at least six magnetozones (3 N, 3 R) are represented in the Barstow Formation.

Further work is planned to increase the density of sampling in order to correlate the magnetic polarity stratigraphy of the Barstow Formation to the GMPTS. This study will provide a basis for refined correlation of Holarctic mammalian faunal evolution as well as for an analysis of late Cenozoic tectonic evolution of southern California.

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Copyright 1997 American Association of Petroleum Geologists