Cathodoluminescence and Fluid-Inclusion Study of Upper Smackover Cements, Boyd Hill Field, Miller County, Arkansas

Leonard M. Young, Oliver R. Boyd, Shirley A. Bingham

Earlier work on Smackover cements has been confined primarily to the transitional and southern diagenetic zones. Although located in the northern zone, the study area also exhibits features associated more with the other zones, including overpacking of allochems, bladed rather than fine equant rim cements, coarse mosaic and poikilotopic calcspar in addition to fine-grained calcite cements.

Bladed scalenohedral rim cements (64°-114°C) are nonluminescent; these may have stabilized in highly oxidizing pore waters. Fine-grained calcite cements (79°-104°C) show bright luminescence and may have formed from mildly reducing pore waters. Nonferroan calcspar cements (83°-110°C) show cathodoluminescence (CL) zoning, dull in the center and surrounded by a nonluminescent and then alternating bright and dull zones. Echinoderm grains (75°-102°C) show dull luminescence; their overgrowths show bright to nonluminescent zoning. Replacive dolomites (77°-89°C) vary in CL; some are dull or zoned dull to bright, but others are nonluminescent or zoned bright to nonluminescent. Thus at least two episodes of dolomitization occurred. Replacive anh drite occurs as two generations--a fabric-selective phase (76°-99°C) and cross-cutting phase (84°-100°C).

These data indicate that Smackover diagenesis at Boyd Hill field was characterized by changes in redox potential, composition, salinity, and temperature of pore waters. Previous studies suggest that fluid-inclusion temperatures of some Smackover cements may be suspect because of stepwise reequilibration during higher temperature events. We tend to agree with this hypothesis, although the lowest values of the overlapping ranges may come close to some original temperatures.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.