Diagenetic formation of bedded chert: evidence from chemistry of the chert-shale couplet

Abstract

Major and rare earth element data from Franciscan assemblage (Mesozoic) and Claremont Formation (Miocene) bedded chert sequences, along with physical observations such as the presence of rare and highly corroded radiolarians in shale interbeds, are most consistent with a dominantly diagenetic origin of chert-shale couplets and are incompatible with many depositional theories. Chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic SiO 2 to form entire stratigraphies of bedded chert. -from Authors