Evaluation of hypotheses for right-lateral displacement of Neogene strata along the San Andreas Fault between Parkfield and Maricopa, California

Scientific Investigations Report 2017-5125
By: , and 

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Abstract

We used geological field studies and diatom biostratigraphy to test a published hypothesis that Neogene marine siliceous strata in the Maricopa and Parkfield areas, located on opposite sides of the San Andreas Fault, were formerly contiguous and then were displaced by about 80–130 kilometers (km) of right-lateral slip along the fault. In the Maricopa area on the northeast side of the San Andreas Fault, the upper Miocene Bitterwater Creek Shale consists of hard, siliceous shale with dolomitic concretions and turbidite sandstone interbeds. Diatom assemblages indicate that the Bitterwater Creek Shale was deposited about 8.0–6.7 million years before present (Ma) at the same time as the uppermost part of the Monterey Formation in parts of coastal California. In the Parkfield area on the southwest side of the San Andreas Fault, the upper Miocene Pancho Rico Formation consists of soft to indurated mudstone and siltstone and fossiliferous, bioturbated sandstone. Diatom assemblages from the Pancho Rico indicate deposition about 6.7–5.7 Ma (latest Miocene), younger than the Bitterwater Creek Shale and at about the same time as parts of the Sisquoc Formation and Purisima Formation in coastal California. Our results show that the Bitterwater Creek Shale and Pancho Rico Formation are lithologically unlike and of different ages and therefore do not constitute a cross-fault tie that can be used to estimate rightlateral displacement along the San Andreas Fault.

In the Maricopa area northeast of the San Andreas Fault, the Bitterwater Creek Shale overlies conglomeratic fan-delta deposits of the upper Miocene Santa Margarita Formation, which in turn overlie siliceous shale of the Miocene Monterey Formation from which we obtained a diatom assemblage dated at about 10.0–9.3 Ma. Previous investigations noted that the Santa Margarita Formation in the Maricopa area contains granitic and metamorphic clasts derived from sources in the northern Gabilan Range, on the opposite side of the San Andreas Fault, that have moved relatively northwestward by 254 ± 5 km of right-lateral displacement along the fault. Our new diatom ages suggest that Santa Margarita deposition and fault displacement began about 10–8 Ma and imply long-term average slip rates along the San Andreas Fault of about 25–32 millimeters per year (mm/yr), Evaluation of Hypotheses for Right-Lateral Displacement of Neogene Strata Along the San Andreas Fault Between Parkfield and Maricopa, California By Richard G. Stanley, John A. Barron, and Charles L. Powell, II about the same as published estimates of Quaternary average slip rates based on geologic and geodetic studies.

Suggested Citation

Stanley, R.G., Barron, J.A., and Powell, C.L., II, 2017, Evaluation of hypotheses for right-lateral displacement of Neogene strata along the San Andreas Fault between Parkfield and Maricopa, California: U.S. Geological Survey Scientific Investigations Report 2017–5125, 26 p., https://doi.org/10.3133/sir20175125.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Stratigraphy of the Maricopa Area
  • Stratigraphy of the Parkfield Area
  • Comparison of Late Miocene Strata in the Maricopa and Parkfield Areas and Implications for San Andreas Fault Offset
  • Concluding Remarks
  • Acknowledgments
  • References Cited
  • Appendix. Diatom floras from sample localities mentioned in this report and listed in table 1

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Evaluation of hypotheses for right-lateral displacement of Neogene strata along the San Andreas Fault between Parkfield and Maricopa, California
Series title Scientific Investigations Report
Series number 2017-5125
DOI 10.3133/sir20175125
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description Report: v, 26 p.
Country United States
State California
City Maricopa, Parkfield
Other Geospatial San Andreas Fault
Online Only (Y/N) Y
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