Mathematics – Logic
Scientific paper
Aug 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983gecoa..47.1487s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 47, Issue 8, pp.1487-1499
Mathematics
Logic
10
Scientific paper
Isotopic and mineralogic data from an 8500-m thick section of the Great Valley sequence, northern California, indicate that changes in the 18 O values of authigenic minerals resulted from the conversion of smectite to a 10 Å clay-mineral as temperature increased with burial in the Jurassic- Cretaceous outer-arc basin. The clay-mineral assemblage in mudstone is characterized by a proportional increase of the 10 Å clay-mineral with increasing stratigraphic depth, and by a depletion in the 18 O value of the mixed-layer smectite/10 Å clay-mineral with descending stratigraphic position from +21.9 to + 15.5%. SMOW. Modeling of the oxygen isotopic data from authigenic phases, based on equilibrium fractionation during clay-mineral diagenesis, indicates that 18 O values of calcite in mudstones and of calcite cements in sandstone precipitated along a temperature gradient of about 25°C/km during maximum burial to about 6-7 km. D values of the mixed-layer smectite/10 Å clay-mineral range between -69 to -44%. SMOW. Using temperatures calculated from the oxygen isotopic data, the deuterium and oxygen isotopic data indicate that the smectite underwent late-stage dehydration and probably buffered the composition of formation waters from sea water values to isotopic compositions of 18 O +8%. SMOW and D -25%. SMOW. The 13 C values of calcite from mudstone and sandstone imply that crystallization of authigenic calcite was linked to organic diagenesis during which dissolved HCO t- 3 was continuously enriched in 13 C as temperature increased with burial. At the base of the sequence and immediately overlying the ophiolitic basement rocks, several hundred meters of strata were altered by more oxygen-depleted ( 18 O +4 to +5%.) hydrothermal fluids emanating from the ophiolitic rocks, probably at maximum burial depth.
Land Lynton S.
Suchecki Robert K.
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