Age, Stratigraphy, and Correlations of the Late Neogene Purisima Formation, Central California Coast Ranges
Professional Paper
1740
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Abstract
The Purisima Formation is an important upper Miocene and Pliocene stratigraphic unit in central California, cropping out from the coast at Point Reyes north of San Francisco to more extensive exposures in the Santa Cruz Mountains to the south. The fine-grained rocks in the lower parts of the Purisima Formation record a latest Miocene transgressive event, whereas the middle and upper parts of the formation consist of increasingly clastic-rich siltstones and sandstones resulting from uplift of adjacent coastal regions and the Sierra Nevada during Pliocene transgressive and regressive sea-level events. Exposures of the Purisima occur in three different, fault-bounded, structural blocks - the Santa Cruz, Pigeon Point, and Point Reyes tectonic blocks - that complicate correlations and regional age assignments. We summarize and compare published and new biostratigraphic and geochronologic data for various exposures of the Purisima Formation on the basis of mollusks, diatoms, radiometric dating, magnetostratigraphy, tephrochronology, and strontium isotope dating. On the basis of these data, we conclude that the Purisima Formation ranges in age from the latest Miocene (about 7 Ma) to the late Pliocene (about 2.6 Ma).
The Purisima Formation of Santa Cruz County, exposed in the sea cliffs from Santa Cruz to Rio del Mar, is here designated a supplementary reference section because it is the most complete and well studied Purisima section in central California.
Suggested Citation
Powell, C.L., Barron, J.A., Sarna-Wojcicki, A.M., Clark, J., Perry, F.A., Brabb, E.E., and Fleck, R.J., 2007, Age, stratigraphy, and correlations of the late Neogene Purisima Formation, central California coast ranges (Version 1.0): U.S. Geological Survey Professional Paper 1740, 32 p., https://doi.org/10.3133/pp1740.
ISSN: 2330-7102 (online)
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Age, stratigraphy, and correlations of the late Neogene Purisima Formation, central California coast ranges |
| Series title | Professional Paper |
| Series number | 1740 |
| DOI | 10.3133/pp1740 |
| Edition | Version 1.0 |
| Year Published | 2007 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Contributing office(s) | Geology, Minerals, Energy, and Geophysics Science Center, Volcano Science Center, Western Earth Surface Processes |
| Description | 32 p. |
| Country | United States |
| State | California |
| Online Only (Y/N) | Y |