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Strontium Isotope Ages of the Marine Merced Formation, near San Francisco, California

  • B. Lynn Ingram (a1) and James C. Ingle (a2)
Abstract

The strontium isotopic compositions of foraminifers ( Elphidiella hannaiwere determined to refine the age of coastal sediments of the Merced Formation and to evaluate the relation between transgressive–regressive cycles and Pleistocene glacio-eustatic sea-level fluctuations. Relatively good age resolution (± 0.1 myr) is possible in the upper part of the section. The Sr isotope ages provide strong supporting evidence for the fission track ages of an ash layer at the top of the formation (0.45 myr), as well as recent age estimates for the mammoth fossil of ∼0.45 myr. Sr isotope ages in the upper part of the section also confirm that marine/nonmarine cyclic sedimentation in the Merced Formation is controlled by glacial–interglacial cycles. Good age resolution for the lower part of the section is not possible, due to little variation of the87Sr/86Sr ratio in global sea water between 2.4 and 4.3 myr. The age of the base of the formation is constrained only between 2.4 and 4.8 myr. Sediment accumulation rates in the upper portion of the Merced Formation (between 0 and 720 m) are significantly higher than those calculated for the basal portion (between 720 and 1670 m). The change in accumulation rate may be due to increased continental weathering rates and/or increased tectonic subsidence beginning about 0.8 myr ago.

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Addicott W.O. (1969). Late Pliocene molluscs from San Francisco Peninsula, California, and their paleogeographic significance. California Academy of Science Proceedings 37, 5793.
Capo R.C., and DePaolo D.J. (1990). Seawater strontium isotopic variations from 2.5 million years ago to the present. Science 249, 5155.
Clifton H.E., and Hunter R.E. (1987). The Merced Formation and related beds—A mile-thick succession of late Cenozoic coastal and shelf deposits in the seacliffs southwest of San Francisco, California. Geological Society of America Centennial Field Guide—Cordilleran Section 257262.
Clifton H.E., Hunter R.E., and Gardner J.V. (1988). Analysis of eustatic, tectonic and sedimentologic influences on trangressive and regressive cycles in the late Cenozoic Merced Formation, San Francisco, California. New Perspectives in Basin Analysis Springer-Verlag, New York.p. 109–128
DePaolo D.J. (1986). Detailed record of the Neogene Sr isotopic evolution of seawater from DSDP Site 590B. Geology 14, 103106.
Hall N.T. (1965). Petrology of the Type Merced Group, San Francisco Peninsula, California..
Hall N.T. (1966). Fleishacker Zoo to Mussel Rock (Merced Formation)—A Plio-Pleistocene nature walk. California Division of Mines and Geology Mineral Information Service 19, S22S25.
Ingram B.L., and Sloan D. (1992). Strontium isotopic composition of estuarine sediments as paleosalinity-paleoclimate indicator. Science 255, 6872.
Ingram B.L., and DePaolo D.J. (1993). A 4,300-yr record of salinity and paleo-streamflow in San Francisco Bay, California. Earth and Planetary Science Letters 119, 103119.
Lawson A.C. (1893). The past-Pliocene diastrophism of the coast of southern California. University of California Publications, Department of Geology, Bulletin 1, 115160.
Lucas S.G. (1996). The Thornton Beach mammoth: Consistency of numerical age and morphology. Quaternary Research 45, 332333.
Madden C.T. (1980). Earliest isotopically dated Mammuthus . Quaternary Research 13, 147150.
Meyer C.E., Sarna-Wojcicki A.M., Hillhouse J.W., Woodward M.J., Slate J.L., and Sorg D.H. (1991). Fission-track age (400,000 yr) of the Rockland tephra, based on inclusion of zircon grains lacking fission tracks. Quaternary Research 35, 367382.
Poore R.Z. (1981). Temporal and spatial distribution of ice-rafted mineral grains in Pliocene sediments of the North Atlantic: Implications for late Cenozoic climatic history.Warme J.E., Douglas R.G., Winterer E.L. The Deep Sea Drilling Project: A Decade of Progress. Society for Economic Paleontology and Mineralogy, 505515.
Sarna-Wojcicki A.M., Meyer C.E., Bowman H.R., Hall N.T., Russell P.C., Woodward M.J., and Slate J.L. (1985). Correlations of the Rockland ash bed, a 400,000-year-old stratigraphic marker in northern California and western Nevada, and implications for middle Pleistocene paleogeography of central California. Quaternary Geology 23, 236257.
Sarna-Wojcicki A.M., Meyer C.E., Hillhouse J.W., Hall N.T., and Curtis G.H. (1996). Age of the Thornton Beach, California, mammoth fossil updated. Quaternary Research 45, 327331.
Sarna-Wojcicki A.M., Lajoie C.E., Meyer C.E., Adam D.P., and Rieck H.J. (1991). Tephrochronologic Correlation of upper Neogene Sediments along the Pacific Margin, Conterminous United States. Geological Society of America, Boulder.
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Quaternary Research
  • ISSN: 0033-5894
  • EISSN: 1096-0287
  • URL: /core/journals/quaternary-research
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