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Influence of freshwater flux on 87Sr/86Sr chronostratigraphy in marginal marine environments and dating of vertebrate and invertebrate faunas

Published online by Cambridge University Press:  14 July 2015

J. Daniel Bryant ,
Douglas S. Jones  and
Paul A. Mueller
J. Daniel Bryant
Affiliation:
Department of Vertebrate Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024
Douglas S. Jones
Affiliation:
Lamont-Doherty Earth Observatory and Department of Geological Sciences, Columbia University, Palisades, New York 10964
Paul A. Mueller
Affiliation:
Florida Museum of Natural History, University of Florida, Gainesville 32611, and Department of Geology, University of Florida, Gainesville 32611
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Abstract

87Sr/86Sr chronostratigraphy is an important tool for dating and correlating vertebrate and invertebrate faunas preserved in marginal marine sequences. Freshwater flux in marginal marine environments can influence the 87Sr/86Sr of mollusks and, consequently, Sr-chronostratigraphic interpretations based upon them. To appraise the potential problem we have used a two-component mixing equation to evaluate levels of “measurable effects” (defined as ±5 × 10-5 departure from the marine 87Sr/86Sr ratio) in marginal marine environments. A measurable effect occurs at 12 parts per thousand salinity for a weighted world average river, but can occur at salinity > 34 ppt for rivers draining basins with ancient granitic rocks. Predictions were tested with analyses of mollusks from estuaries in the Mississippi Sound and coastal Florida. Analyses document the largely regular variation in 87Sr/86Sr predicted, but also show that a simple two-component model cannot account for all of the variation. Carbonates formed in restricted marine settings may not record a marine 87Sr/86Sr signal, emphasizing the need to consider freshwater flux for 87Sr/86Sr chronostratigraphy.

Type
Research Article
Information
Journal of Paleontology , Volume 69 , Issue 1 , January 1995 , pp. 1 - 6
Copyright
Copyright © The Paleontological Society 

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