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

Journal Article · Sun Mar 01 04:00:00 EST 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0271:DFOBCE>2.3.CO;2· OSTI ID:7004169

Murray, R W; Jones, D L ^[1]; Buchholtz ten Brink, M R ^[2]

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1. Univ. of California, Berkeley (United States)
2. Lawrence Livermore National Lab., CA (United States)

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 SiO{sub 2} dissolution, transport, and reprecipitation, suggesting that diagenetic migration of SiO{sub 2} 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 SiO{sub 2} to form entire stratigraphies of bedded chert.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 7004169
• Journal Information: Geology; (United States), Journal Name: Geology; (United States) Vol. 20:3; ISSN GLGYB; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANIMALS
CENOZOIC ERA
CERIUM
CHEMISTRY
CHERT
DIAGENESIS
ELEMENTS
FORAMINIFERA
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
INVERTEBRATES
MESOZOIC ERA
METALS
MICROORGANISMS
MIOCENE EPOCH
ORIGIN
PROTOZOA
RARE EARTHS
ROCKS
SARCODINA
SEDIMENTARY ROCKS
SHALES
STRATIGRAPHY
TERTIARY PERIOD