Precambrian carbonates record secular variations in the style of CaCO3 nucleation and growth, yet the geochemical conditions recorded by some enigmatic textures remain poorly quantified. Here, we performed CaCO3 nucleation experiments in synthetic seawater in order to constrain the mineralization pathways of synsedimentary calcite microspar cement, a prolific component of Proterozoic carbonates. We found that dissolved PO4 above ~12 μmol/L (μM) inhibits the nucleation of aragonite and calcite and permits the formation of an amorphous Ca-Mg carbonate (ACMC) precursor once CaCO3 supersaturation (Ωcal) is ≥ 45. Depending on seawater Mg/Ca, ACMC then rapidly recrystallizes to monohydrocalcite and/or calcite. This precipitation mechanism is consistent with sedimentological, petrographic, and geochemical characteristics of Proterozoic synsedimentary calcite microspar cement, and it suggests that kinetic interactions among common seawater ions may open nontraditional CaCO3 mineralization pathways and sustain high CaCO3 supersaturation.
Research Article|
December 30, 2020
Experimental constraints on nonskeletal CaCO3 precipitation from Proterozoic seawater
Sascha Roest-Ellis;
Sascha Roest-Ellis
1
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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Justin V. Strauss;
Justin V. Strauss
2
Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA
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Nicholas J. Tosca
Nicholas J. Tosca
1
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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Geology (2020)
Article history
received:
18 Jun 2020
rev-recd:
08 Oct 2020
accepted:
15 Nov 2020
first online:
30 Dec 2020
Citation
Sascha Roest-Ellis, Justin V. Strauss, Nicholas J. Tosca; Experimental constraints on nonskeletal CaCO3 precipitation from Proterozoic seawater. Geology doi: https://doi.org/10.1130/G48044.1
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