Journal
GLOBAL BIOGEOCHEMICAL CYCLES
Volume 36, Issue 5, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2021GB007235
Keywords
carbonate mineralogy; Cambrian; calcium isotope; seawater Mg; Ca ratio; marine redox state
Funding
- National Key Research and Development Program of China [2021YFA0718100]
- Fundamental Research Funds for Central Universities [14380125]
- Frontiers Science Center for Critical Earth Material Cycling Fund [DLTD2102]
- Strategic Priority Research Program (B) of the CAS [XDB26000000]
- NSFC [42002002, 41872002]
- program A for Outstanding PhD. Candidate of NJU
- Packard Foundation
- ARC DECRA [DE190100988]
- Australian Research Council [DE190100988] Funding Source: Australian Research Council
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This study used various methods to analyze carbonates from the Ediacaran-Cambrian period, finding evidence of the persistence of an aragonite sea into the Cambrian Age 2, and confirming that the transition from aragonite seas to calcite seas was a prolonged process.
The primary mineralogy of marine carbonates has varied over geological time in concert with the secular evolution of global climate and seawater chemistry. Here, we employed a multi-proxy geochemical and petrographic approach, including measuring the Ca isotope (delta Ca-44) and Sr content of Ediacaran-Cambrian carbonates, to provide new insights into the timing of the transition from a dolomite-aragonite sea to a calcite sea across the Ediacaran-Cambrian transition. We find robust evidence for the persistence of an aragonite sea well into Cambrian Age 2 (and potentially up through Age 4). Together with an updated petrographic compilation of abiotic carbonate precipitates (i.e., ooids and cements), these new delta Ca-44 and Sr data provide further evidence that there was a protracted transition from aragonite seas to calcite seas in the Cambrian. We propose that this transition was mediated, in part, by changes in seawater Mg/Ca ratios potentially regulated by the global marine redox state and extents of authigenic clay precipitation.
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