Secular Distribution of Biogenic Silica through the Phanerozoic: Comparison of Silica‐Replaced Fossils and Bedded Cherts at the Series Level

Abstract

Abstract The modern marine silica cycle is dominated by silica‐secreting phytoplankton, principally diatoms, but this cycle has evolved considerably during the Phanerozoic. We analyzed the temporal distribution of silica‐replaced fossils and bedded chert to determine the influence of factors such as extinctions and climate change on siliceous facies. Trends in silica replacement of fossils match faunal radiations during the Ordovician and Siluro‐Devonian, with peaks in silica replacement in the Late Ordovician and Middle Devonian corresponding to peaks in the abundance and diversity of siliceous sponges. Sharp drops in the abundance of silica‐replaced fossils and/or bedded cherts coincide with four of the five major mass extinctions. No discernible decrease marks the extinction at the end of the Triassic. We expected peaks in bedded chert deposition during glacial episodes because enhanced ocean circulation should favor more and stronger upwelling. Orogenic episodes, which may trigger continental glaciati...