Journal
CHEMICAL GEOLOGY
Volume 513, Issue -, Pages 200-225Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2019.02.030
Keywords
Gross primary production; Marine sulfate; Proterozoic; Precambrian; Sulfate; Triple oxygen; Oxygen isotopes; Sulfur isotopes; Multiple sulfur; Isotope geochemistry; Evaporite; Gypsum; Barite; Atmospheric oxygen; Primary production; Primary productivity; Evolution of life; Biosphere
Categories
Funding
- NSERC-CREATE CATP
- NSERC PGS-D fellowship
- McGill McGregor Fellowship
- McGill Mobility and GREAT programs
- Canadian Polar Continental Shelf Program
- Northern Science Training Program
- Mineralogical Association of Canada Foundation
- Agouron Geobiology Post-doctoral Fellowship Program
- FQNRT through the GEOTOP Research Center
- NSERC Discovery program
- CAS [XDB18010104]
- NSERC [RGPIN-316500]
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The Proterozoic Eon spans Earth's middle age during which many important transitions occurred. These transitions include the oxygenation of the atmosphere, emergence of eukaryotic organisms and growth of continents. Since the sulfur and oxygen cycles are intricately linked to most surface biogeochemical processes, these transitions should be recorded in changes to the isotopic composition of marine and terrestrial sulfate minerals. Here we present oxygen (Delta O-17, delta O-18) and sulfur (Delta S-33, delta S-34) isotope records of Proterozoic sulfate from currently available data together with new measurements of 313 samples from 33 different formations bearing Earth's earliest unambiguous evaporites at 2.4 Ga through to Ediacaran aged deposits. This record depicts distinct intervals with respect to the expression of sulfate isotopes that are not completely captured by established intervals in the geologic timescale. The most salient pattern is the muted Delta O-17 signatures across the GOE, late Proterozoic and Ediacaran with values that are only slightly more negative than modern marine sulfate, contrasting with highly negative values across the mid-Proterozoic and Cryogenian. We combine these results with estimates of atmospheric composition to produce a gross primary production (GPP) curve for the Proterozoic. Through these results we argue that changes in GPP across Earth history likely help account for many of the changes in the Proterozoic Earth surface environment such as rising atmospheric oxygen, large fluctuations in the size of the marine sulfate reservoir and variations in the isotopic composition of sedimentary sulfate.
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