CARBONATE ASSOCIATED PHOSPHATE (CAP) IN TONIAN EARLY DIAGENETIC DOLOMITES

The Neoproterozoic Era witnessed significant environmental and biological changes including increasing tectonic activity, an increase in surface oxygenation, and biosphere expansion. Continental weathering increases due to tectonic activity enhances the supply of nutrients to the oceans, including phosphorus which is critical for life. Though a limiting nutrient on geologic timescales, phosphorus plays a key role in sustaining oxygenic photosynthesis and regulating the ocean’s redox state. Quantifying phosphate’s incorporation into carbonates as carbonate-associated phosphate (CAP) serves as a proxy to reconstruct phosphate availability throughout the Tonian period if primary CAP can be recovered. CAP signals have been shown to decrease with increasing degrees of alteration, and this work focuses on the impacts of early marine diagenesis on CAP in dolomite. Tonian-aged dolostones from the Coppercap Formation in Northwest Canada have varying CAP values due to early diagenesis with fluid-to-sediment buffering conditions. The mean value of 0.077 mmol/mol is similar to measurements observed in modern-day Bahamian platform carbonates (~0.0785 mmol/mol) and Phanerozoic marine cements and grains (0.052 mmol/mol), yet substantially lower than Neoarchean shallow marine carbonates (0.130 mmol/mol). The mean CAP value in the fluid-buffered regime was 0.068 mmol/mol, similar to the sediment-buffered mean of 0.058 mmol/mol, both less than the sediment-buffered with Tonian seawater and brackish groundwater mean of 0.128 mmol/mol. Fluid-buffered samples track an overall decrease in CAP compared to sediment-buffered samples. Modeling early marine diagenesis for the whole stratigraphic section suggests buffering style influences the extent of CAP alteration. This study analyzes CAP in diagenetic dolomites formed in varying buffering environments to suggest that Tonian shallow marine environments were likely more phosphate-rich than modern marine environments.