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Seafloor-precipitated carbonate fans in the Neoproterozoic Rainstorm Member, Johnnie Formation, Death Valley Region, USA

Pruss, Sara Brady and Corsetti, Frank A. and Fischer, Woodward W. (2008) Seafloor-precipitated carbonate fans in the Neoproterozoic Rainstorm Member, Johnnie Formation, Death Valley Region, USA. Sedimentary Geology, 207 (1-4). pp. 34-40. ISSN 0037-0738.

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Cm-sized carbonate seafloor fans occur in the Neoproterozoic Rainstorm Member of the Johnnie Formation, Death Valley, USA. The fans formed in a mixed carbonate-clastic succession near storm wave base at the base of parasequences on a storm-dominated ramp. Petrographic observations indicate that the fans were originally precipitated as aragonite and later inverted to calcite during diagenesis. Although not directly dated, the Rainstorm Member preserves a large magnitude negative carbon isotopic anomaly (down to −11‰ PDB) tentatively correlated to the largest known carbon isotope excursion found in many stratigraphic successions around the world between 585 Ma and 550 Ma. Thus, the age distribution of seafloor aragonite fans in Neoproterozoic strata appears more widespread than previously thought, occurring in strata significantly younger than the last widespread Neoproterozoic glaciation. Rainstorm Member carbonate fans and oolitic units (representing time-correlative shallower environments) record similar carbon isotope ratios during the negative carbon isotopic anomaly. The carbon isotopic homogeneity displayed between fans and other carbonate sediments implies that waters across the shelf were well-mixed rather than stratified during the late Neoproterozoic isotopic anomaly. In addition, the similarity of carbon isotope ratios shared among fans along a stratigraphic horizon (on a m- to cm-scales) suggests that the local source of alkalinity required for fan growth was derived from a well-mixed reservoir, likely seawater, rather than local diagenetic fluids. Increased alkalinity and the presence of inhibitors to carbonate nucleation (perhaps Fe2+ under anoxic conditions) likely fostered precipitation of aragonite crystal fans on the seafloor.

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Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2008 Elsevier. Received 6 March 2007; revised 26 February 2008; accepted 13 March 2008. Available online 1 April 2008. The authors would like to thank C. Summa for her helpful comments regarding this research and Dan Schrag's laboratory at Harvard University for stable isotope analysis. S. Pruss would like to thank K. Hankins, D. DeSwert, and M. Fraiser for help in the field. Helpful comments and discussion by P. Marenco, M. Clapham, N. Lorentz, J. Bartley, I. Montañez, M. Vogel, A. Knoll, and N. James on a previous version of this manuscript were greatly appreciated.
Subject Keywords:Aragonite; Precipitates; Ediacaran; Carbon cycle
Issue or Number:1-4
Record Number:CaltechAUTHORS:PRUsg08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12179
Deposited By: Archive Administrator
Deposited On:28 Oct 2008 16:44
Last Modified:03 Oct 2019 00:26

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