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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Thermal maturity estimates from vitrinite reflectance and clay mineralogy point to significant differences between the Newark Supergroup basins in their thermal structure and/or their original depth of burial. The Richmond and Taylorsville basins are relatively immature, with mean vitrinite reflectance values in the range of 0.6 to 1.1%. The clay mineral assemblages are dominated by early diagenetic smectite and mixed-layer clays. Likewise, organics in the Hartford basin have mean vitrinite reflectances between 0.7 and 1.1%. In contrast, the Culpeper, Gettysburg, and Newark basins are thermally more mature. Although a wide range of vitrinite reflectance values is observed in each of the basins, the majority of the mean reflectances are 1.5-3.0%. Well-crystallized illite a d chlorite constitute the fine-grained clay fractions.
In general, the lowest degrees of thermal maturity are associated with rocks that either are stratigraphically and structurally highest in the basins or form the updip taper of the half grabens. However, systematic correlations are not observed between stratigraphic/structural position within a basin and the degree of thermal maturity. This may be attributed to a thermal "homogenization" of the basins by circulating hydrothermal fluids. The basins with the highest thermal maturities are those with large volumes of diabase intrusions and that had presumed higher geothermal gradients.
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