MULTIPLE SCALES OF LITHOTECTONIC STRATIFICATION IN THE SIERRA MADRE ORIENTAL FORELAND, MEXICO

Deformation characteristics of cyclical platform sediments within the Coahuila Marginal Folded Province define lithotectonic units and provide insight into regional-grain scale deformation patterns in the orogenic foreland. The doubly plunging Sierra del Fraile anticlinorium comprises thick (> 3km) Jurassic evaporites overlain by 3.8 km of mixed Mesozoic strata of varying competency. Distribution and geometry of structures define the following lithotectonic units; the lowermost, unit 1, consists of the incompetent, isotropic evaporites of the Minas Viejas Fm., concordant in anticline Garcia and diapiric in anticline Chico; it is the décollement throughout the Sierra Madre Oriental. Area balanced cross sections establish salt flow from synclines to anticlines, supporting structural relief. AMS, cleavage and faulting within 1.3 km of shale and limestone in the Zuloaga, La Casita and lower two-thirds of the Taraises Fm., record limb rotation about a pinned hinge in unit 2. Variable carbonate content and thin bedding generates incompetence and anisotropy. Undeformed 1.2 km thick platform carbonates of the Cupido and Aurora Fms., and the intervening 0.03 km of thinly bedded La Pena shales, define unit 3, the dominant fold member. Unit 4, like 2, is stratigraphically mixed, incompetent and anisotropic. Fault-slip, cleavage, and AMS data in 0.5 km thick Cuesta del Cura and Indidura Fms. also record limb shear towards a fixed hinge. Finally, pervasive cleavage and ubiquitous bed parallel slip in the 0.7 km thick Parras shales characterizes incompetent, isotropic unit 5. Identification of deformation patterns in cyclical platform facies based on composition and stratigraphic packaging allows for the predictability of reservoir properties and fold kinematics throughout the foreland.