Skip to main content
U.S. flag

An official website of the United States government

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

December 31, 1992

Theories concerning the formation of bedded chert traditionally have emphasized either depositional or diagenetic processes. 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 distributions between Franciscan and Claremont bedded chert=shale closely match chemical fractionations recorded by Monterey Formation and Deep Sea Drilling Project-sampled cherts formed by diagenetic SiO2 dissolution, transport, and reprecipitation, suggesting that diagenetic migration of SiO2 from proto-shale to proto-chert is also largely responsible for chert-shale couplets. Identical Ce anomalies (Ce/Ce*) found in immediately adjacent chert-shale layers indicate that turbidites or other transport mechanisms are not responsible for the alternating beds. Neither the chemistry of the chert-shale couplet nor the overall stratigraphy of the sequences is consistent with couplet formation being caused by productivity fluctuations. Chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic SiO2 to form entire stratigraphies of bedded chert.

Publication Year 1992
Title Diagenetic formation of bedded chert: Evidence from chemistry of the chert-shale couplet
DOI 10.1130/0091-7613(1992)020<0271:DFOBCE>2.3.CO;2
Authors Richard L. Murray, David L. Jones, Marilyn R. Buchholtz ten Brink
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Index ID 70196627
Record Source USGS Publications Warehouse
USGS Organization Woods Hole Coastal and Marine Science Center