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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2009. 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
fault
, 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; peter.eichhubl@beg.utexas.edu
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 fault
, a basin-scale normal
fault
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
fault
-related diagenetic alteration products relative to the
fault
structure to identify sealing and conductive
fault
segments for fluid flow and to relate
fault
–fluid-flow behavior to the internal architecture of the
fault
zone. Calcite cement occurs as vein and breccia cement along slip surfaces and as discontinuous vein cement and concretions in
fault
damage zones. The cement predominates along
fault
segments that are composed of joints, sheared joints, and breccias that overprint earlier deformation bands. Using the distribution of
fault
-related calcite cement as an indicator of paleofluid migration, we infer that
fault
-parallel fluid flow was focused along
fault
segments that were overprinted by joints and sheared joints. Joint density, and thus
fault
-parallel permeability, is highest at locations of structural complexity such as
fault
intersections, extensional steps, and
fault
-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
,
fault
-parallel fluid flow.
Fault
-perpendicular flow, however, is mostly impeded by the juxtaposition of the sandstone units against shale and by shale entrainment. The Moab
fault
thus exemplifies the complex interaction of
fault
architecture and diagenetic sealing processes in controlling the hydraulic properties of faults in clastic sequences.
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