The earliest Phanerozoic carbonate hardground (Cambrian Stage 5, Series 3): Implications to the paleoseawater chemistry and early adaptation of hardground fauna

摘要: Abstract Carbonate hardgrounds are lithified seafloors formed by synsedimentary cementation of carbonate sediments, which dominantly occur during the period calcite seas. The earliest typical Phanerozoic hardground known until now was reported from Furongian USA, suggested to indicate onset early Paleozoic sea period. In this study, we report and middle parts Cambrian Series 3 (Stage 5 Drumian) North China Platform, predate previously hardgrounds. surfaces developed on oolitic grainstone, oncolitic wackestone, microbialite (thrombolite dendrolite), sharply truncate underlying deposits. radial fibrous cements between grains below that marine cementation. EPMA analysis reveals typically consist low-Mg calcite. sometimes encrusted microbialites coated hematite, suggesting long exposure open seawater after formation surface. addition, detailed review sedimentological studies deposits throughout world there may be several other these times, could have been overlooked. abundant occurrence in suggests general paleoseawater chemistry suitable induce calcite, implying would changed aragonite seas or even earlier Metazoan encrustors macroborers possibly not adapted newly appeared substrate condition yet, latest 3.