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  • Print publication year: 1996
  • Online publication date: July 2010

7 - Magnetostratigraphy of the upper middle Eocene Coldwater Sandstone, central Ventura County, California



A magnetostratigraphic study was undertaken to improve the age control of the middle Eocene Coldwater Sandstone in southern California. The results show that, although magnetic overprinting is common in Coldwater rocks, most samples yield a stable characteristic remanence that passes reversal and fold tests and shows a clockwise rotation of about 100° ± 17° (consistent with other pre-Miocene units in the western Transverse Ranges). Magnetic stratigraphy and refined chronostratigraphy of the late Uintan and Duchesnean mammals found within redbeds of the Coldwater show that the upper Cozy Dell Shale-Coldwater Sandstone-Sespe Formation succession in central Ventura County spans Chrons C19r-C18n (approximately 39.5-42.5 Ma). These data do not corroborate the sequence stratigraphic interpretations of Campion et al. (1994) or Clark (1994). We suggest that local tectonic forces may have been more important than eustatic sea level fluctuations in causing sequence boundaries in the Coldwater and Sespe formations.


The Transverse Ranges of southern California (Fig. 1) contain an important succession of strata that records a complex history of transgressions and regressions during the Eocene. In the upper Sespe Creek area of central Ventura County, over 4,800 m of Eocene strata were deposited, and some of these formations are even thicker to the east or west. The Eocene succession starts with the lower Eocene deep-water Juncal Shale, overlain by the middle Eocene shallow- to deep-marine Matilija Sandstone, and then by the deep-water Cozy Dell Shale (Kerr and Schenk, 1928; Page et al., 1951; Vedder, 1972; Dibblee, 1966, 1982; Jestes, 1963; Ingle, 1980; Campion et al., 1994).

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The Terrestrial Eocene-Oligocene Transition in North America
  • Online ISBN: 9780511665431
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