AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Three-Dimensional Geometry of Platform-Scale Fracture Systems, Guadalupe Mountains, New Mexico, USA
(1) Earth and Environmental Sciences, Wesleyan University, Middletown, CT.
(2) Statoil, Bergen, Norway.
(3) Tengizchevroil, Atyrau, Kazakhstan.
Early-formed fractures play an important role in many carbonate platform hydrocarbon systems. These fractures may be associated with stratigraphic changes and play a critical role in fluid flow associated with karst formation, diagenesis, and hydrocarbon charging, storage, and production. We are mapping a 45 km2 area of the Capitan depositional system near Slaughter Canyon to characterize the occurrence, distribution, and geometry of early platform-scale fractures.
Hunt et al. (2003) first recognized the importance of early faults in the Capitan system. This study and subsequent work identified stratigraphic, structural, and diagenetic changes associated with these structures, but left questions regarding the distribution and along-strike continuity. We have begun to fill these gaps by mapping early faults along a 15 km strike section of the Capitan margin. We map faults and high frequency sequences in 3D using a 1-m resolution, airborne LiDAR and aerial photo based, photorealistic model. Model interpretations are checked and adjusted based on field mapping of key structures and horizons.
Mapping reveals 3-4 margin-parallel fault systems persistent over several kilometers or more along strike. The youngest of these, the Ogle Cave fault system, cuts the exposed Permian section and provides the best opportunity to characterize along-strike continuity and 3D geometry. The fault system is located ~400 meters shelfward of the end-Yates platform margin and is continuous for more than 13 km along strike, bounding a 170-200 m wide graben, down-dropped 20-30 m below the surrounding platform. The fault system consists of 2-3 high angle (~80° dip) normal faults that extend more than 200 m down dip. Fault segments vary in strike by > 25°, paralleling the present day erosional scarp that reflects the Permian platform depositional margin. Faults of this system contain Permian sediment fill in addition to younger fills associated with uplift and karstification of the Guadalupe Mountains.
We interpret the high fault dips, relatively straight segments, and lack of significant rotation or net vertical motion across the Ogle Cave fault system as evidence that the faults formed in response to platform-scale extension rather than slope-rooted failure. The persistence of these early-formed fracture systems confirms that these structures are a common element of Capitan depositional system and are likely to form in other steep-sloped platforms.