Synsedimentary Deformation of the Upper Permian Capitan Reef Carbonate Platform, New Mexico

DW Hunt¹, E. Kosa², AJ Simo³, and L. Piccoli^4
1 Norsk Hydro Research Centre, Sandsli, Norway
² Shell UK, Ltd, Aberdeen, United Kingdom
³ Wisconsin-Madison, Wisconsin
⁴ Dept. of Geology & Geophysics, Madison,

The basinward thickening and steepening of the ‘fall-in' beds, back reef strata equivalent to the Upper Permian Capitan Reef, has long proven the subject of debate. Recent integrated structural and stratigraphic studies, show that these back reef strata are cut by syndepositional dip slip faults in the outer 5-6 km of the platform. The fault systems are known to extend 33 km along strike parallel to the platform margin and have displacement of up to 30 m. Most tip-out upward within the platform succession and localized the development of penetrative karst systems. Here the architecture of the faults and their impact on back reef sedimentation, stratal geometries and correlation is illustrated using field and GPR data.

Most of the syndepositional faults are steep, with dips more than 80°, and a normal and/or reverse sense of movement. Four different morphologies represent the relationships between the upper tips of the faults and the platform top (or free surface) during deposition; (I) faults that broke the platform top, (II) buried faults that tipped-out upwards below a growth monocline, (III) buried faults that tipped upward into a fault splay and a growth monocline and (IV) buried fault tips with no expression at the free surface. The distribution, thickness, geometries and changes in facies of growth strata allow for precise reconstruction of the timing and rates of fault growth.

Understanding the role of syndepositional faulting adds a new and dynamic variable to the evolving picture of the Capitan depositional system.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005