Other
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.120..409k&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 120, no. 3-4, p. 409-430
Other
33
Carbon Isotopes, Geochronology, Paleoclimatology, Sea Water, Strontium Isotopes, Tectonics, Erosion, Glaciology, Hydrothermal Systems, Marine Environments, Neodymium, Planetary Evolution
Scientific paper
New Sr and C isotopic data, both obtained on the same samples of marine carbonates, provide a relatively detailed record of isotopic variation in seawater through the latest Proterozoic and allow, for the first time, direct correlation of these isotopic changes in the Vendian (about 540-610 Ma). The strong isotope variations determined in this study record significant environmental and tectonic changes. Together with a fairly poorly constrained Nd isotopic record, the Sr and C isotopic records can be used to constrain rates of erosion, hydrothermal alteration and organic C burial. Further, comparison of these records with those of the Cenozoic permit investigation of the general relationship between global tectonics and continental glaciation. In particular, results of this study show a very large change in the Sr-87/Sr-86 or marine carbonates from low pre-Vendian (greater than 610 Ma) values (about 0.7066) to high Middle Cambrian values (about 0.7090). This change is greater in magnitude than the significant increase in seawater Sr-87/Sr-86 through the Cenozoic. Both changes are attributed to high erosion rates associated with continent-continent collisions (Pan-African and Himalayan-Tibetan). In the latest Proterozoic these high erosion rates, probably coupled with high organic productivity and anoxic bottom-water conditions, contributed to a significant increase in the burial rate of organic C. Ice ages mark both the Neoproterozoic and Cenozoic, but different stratigraphic relationships between the Sr isotopic increase and continental glaciation indicate that uplift-driven models proposed to explain Cenozoic climatic change cannot account for the latest Proterozoic ice ages.
Jacobsen Stein B.
Kaufman Alan J.
Knoll Andrew H.
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