Structural, lithotectonic, and rock magnetic studies of decollement folding, Coahuila Marginal Folded Province, northeast Mexico

Variations in rock magnetic parameters provide an objective tool, independent of facies, to correlate between proximal and distal Lower Cretaceous platform carbonates in northeast Mexico. Anhysteretic remanent magnetization (ARM) provides sub-meter scale stratigraphic correlation between inner and middle shelf deposits. Spectral analysis of variations in magnetic mineral concentrations within deposits from the upper Cupido Formation and basinal equivalent San Angel Limestone reveal periodicities in ferrimagnetic mineral concentrations consistent with Milankovitch orbital frequencies. Rock magnetic and SEM/EDX analyses indicate that the ferrimagnetic grains are primary magnetite with grain sizes and shapes consistent with that of far-traveled dust. Variations in the magnetite grain abundance likely reflect regional changes in wind intensity and direction. Inner shelf deposits also record a periodic coarser-grained ferrimagnetic detrital mineral population interpreted to be an orbitally-driven watershed signal such as fluvial runoff. Time-series analysis indicates similar accumulation rates for the inner and middle shelf deposits (8 cm/kyr) suggesting uniform thermal subsidence of the platform, while slower accumulation rates (7 cm/kyr) from outer shelf deposits suggest limited transport of material offshore.; Large-scale stacking patterns of Mesozoic passive margin carbonates at Sierra del Fraile anticlinorium in northeast Mexico play an important role in controlling the distribution of deformation and kinematics during folding. Differences in competency and anisotropy of the ∼4.5 km thick carbonate and clastic units result in predictive patterns of strain history at the regional and outcrop scales. Patterns in mesoscopic deformation features constrain fold kinematics as progressive limb rotation about pinned anticlinal and synclinal hinges, which requires a mobile decollement horizon within the ∼3 km thick section of Minas Viejas evaporites that core the anticlinorium. Distribution and orientation analyses of meso- and microscopic deformation features from all stratigraphic and structural positions allow for the delineation of five regional-scale lithotectonic units. While, mechanical stratification is observed on a variety of scales, the regional-scale stacking patterns of the entire passive margin succession and the meter-scale stacking patterns of individual shallowing-upward carbonate cycles are shown to play the greatest role in influencing deformation kinematics.