Abstract

The relative abundance of phosphorite as a function of age was estimated for the southeastern United States using 87Sr/86Sr derived ages. The Sr-derived ages define seven phosphogenic episodes on the northeast Florida platform. Phosphorus burial rate estimates for the southeastern United States margin range from 2 to 12 × 109 mol ṁ P ṁ yr−1, and phosphorus accumulation rates range from 1 to 3 µmol ṁ cm−2 ṁ yr−1, similar to modern phosphogenic margins. The estimated amount of organic carbon burial ranges from 1 to 12 × 1016 mol C; sufficient to shift the ocean δ13C by 0.1‰ to 0.6‰. On long time scales (>1 m.y.) phosphogenesis in the southeastern United States corresponds to increased organic carbon burial (positive δ13C shifts) and rising sea level (negative δ18O shifts). On shorter time scales (<1 m.y.), the correlation of phosphogenesis to positive δ13C and δ18O shifts suggests a different relation between phosphogenesis, organic carbon burial, eustasy, and climate transitions during the Miocene.

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