Characterization and Geological Implications of Precambrian Calcite-hosted Phosphate


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Authors
Richardson, Jocelyn 
Roest-Ellis, Sascha 
Phillips, Brian 
Strauss, Justin 
Webb, Samuel 
Abstract

Constraints on marine phosphate availability and cycling directly inform our understanding of long-term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and are susceptible to post-depositional modification. Well-preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro-X-ray Fluorescence mapping, X-ray absorption and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, herringbone calcite and microspar, are qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite-hosted phosphate, which is pervasive at low concentrations in herringbone calcite and microspar. This study provides evidence that ancient, well-preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time.

Description
Keywords
Precambrian, phosphorus, synchrotron-XRF, NMR spectroscopy, XANES spectroscopy, carbonate
Journal Title
Geophysical Research Letters
Conference Name
Journal ISSN
0094-8276
1944-8007
Volume Title
Publisher
Wiley
Sponsorship
Leverhulme Trust (PLP‐2015‐286)
National Geographic Society (CP‐129R‐17)
Leverhulme Trust Grant PLP-2015-286