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Boron during meteoric diagenesis and its potential implications for Marinoan snowball Earth delta (super 11) B-pH excursions

Joseph A. Stewart, Marcus Gutjahr, Fay Pearce, Peter K. Swart and Gavin L. Foster
Boron during meteoric diagenesis and its potential implications for Marinoan snowball Earth delta (super 11) B-pH excursions
Geology (Boulder) (July 2015) 43 (7): 627-630

Abstract

Large negative carbon (delta (super 13) C) and boron (delta (super 11) B) isotope excursions (both >6 ppm) within the widely distributed Neoproterozoic carbonates associated with the Marinoan "snowball Earth" event are interpreted to represent considerable perturbations of the carbon cycle and the accompanying reduction in global ocean pH. Yet this interpretation is predicated on these isotopic signals being primary in origin. Recent studies of Pleistocene carbonate platform sediments from the Great Bahama Bank (western Atlantic Ocean; Clino core, drilled by the Bahamas Drilling Project) and elsewhere demonstrate that delta (super 13) C excursions of similar magnitude and global distribution to the snowball Earth excursions are formed following eustatic sea-level fall and exposure of shelf carbonates to meteoric diagenesis. Here we present delta (super 11) B and trace element data (B/Ca, Na/Ca, Mg/Ca, and Sr/Ca) from the same Clino core carbonate sediments in order to explore the influence of this diagenetic process on the boron system. We find that within the interval of meteoric diagenesis the delta (super 11) B of bulk carbonate is reduced by approximately 6 ppm in conjunction with a drop in the B/Ca ratio of 90%. Our results clearly demonstrate that the boron system is impacted by meteoric diagenesis, implying that a rigorous assessment of the diagenetic history of all ancient carbonates is required to ensure any paleoceanographic interpretation based on delta (super 11) B and/or B/Ca are robust.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 7
Title: Boron during meteoric diagenesis and its potential implications for Marinoan snowball Earth delta (super 11) B-pH excursions
Affiliation: University of Southampton, National Oceanography Centre, Southampton, United Kingdom
Pages: 627-630
Published: 201507
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 32
Accession Number: 2015-093517
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2015218
Illustration Description: illus. incl. sketch map
N22°00'00" - N26°00'00", W79°19'60" - W76°00'00"
Secondary Affiliation: Helmholtz Centre for Ocean Research Kiel, DEU, GermanyUniversity of Miami, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201540
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