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AAPG Bulletin

Abstract

AAPG Bulletin, V. 93, No. 5 (May 2009), P. 653-681.

Copyright copy2009. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/02180908080

Structural and diagenetic control of fluid migration and cementation along the Moab Previous HitfaultNext Hit, Utah

Peter Eichhubl,1 Nicholas C. Davatzes,2 Stephen P. Becker3

1Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Texas 78758; [email protected]
2Department of Geology, Temple University, Philadelphia, Pennsylvania 19122
3Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Texas 78758

ABSTRACT

The Moab Previous HitfaultNext Hit, a basin-scale normal Previous HitfaultNext Hit that juxtaposes Jurassic eolian sandstone units against Upper Jurassic and Cretaceous shale and sandstone, is locally associated with extensive calcite and lesser quartz cement. We mapped the distribution of Previous HitfaultNext Hit-related diagenetic alteration products relative to the Previous HitfaultNext Hit structure to identify sealing and conductive Previous HitfaultNext Hit segments for fluid flow and to relate Previous HitfaultNext Hit–fluid-flow behavior to the internal architecture of the Previous HitfaultNext Hit zone. Calcite cement occurs as vein and breccia cement along slip surfaces and as discontinuous vein cement and concretions in Previous HitfaultNext Hit damage zones. The cement predominates along Previous HitfaultNext Hit segments that are composed of joints, sheared joints, and breccias that overprint earlier deformation bands. Using the distribution of Previous HitfaultNext Hit-related calcite cement as an indicator of paleofluid migration, we infer that Previous HitfaultNext Hit-parallel fluid flow was focused along Previous HitfaultNext Hit segments that were overprinted by joints and sheared joints. Joint density, and thus Previous HitfaultNext Hit-parallel permeability, is highest at locations of structural complexity such as Previous HitfaultNext Hit intersections, extensional steps, and Previous HitfaultNext Hit-segment terminations. The association of calcite with remnant hydrocarbons suggests that calcite precipitation was mediated by the degradation and microbial oxidation of hydrocarbons. We propose that the discontinuous occurrence of microbially mediated calcite cement may impede, but not completely seal, Previous HitfaultNext Hit-parallel fluid flow. Previous HitFaultNext Hit-perpendicular flow, however, is mostly impeded by the juxtaposition of the sandstone units against shale and by shale entrainment. The Moab Previous HitfaultNext Hit thus exemplifies the complex interaction of Previous HitfaultTop architecture and diagenetic sealing processes in controlling the hydraulic properties of faults in clastic sequences.

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