Multiple scales of mechanical stratification and décollement fold kinematics, Sierra Madre Oriental foreland, northeast Mexico

Abstract

Regional- to outcrop-scale stratigraphic relationships within Mesozoic shallow marine carbonates and clastics at Sierra del Fraile anticlinorium in northeast Mexico play an important role in controlling the deformation distribution, strain history and kinematics during folding. Structural analyses of meso- and microscopic deformation features from all stratigraphic and structural positions within the anticlinorium allow for the delineation of five regional-scale lithotectonic units. Kilometer- to decameter-scale stacking patterns of the preorogenic succession and the meter-scale stacking patterns of individual shallowing-upward carbonate cycles are shown to influence deformation kinematics in predictable ways. Mesoscopic faults and cleavage patterns along with penetrative strain from anisotropy of magnetic susceptibility (AMS) fabrics constrain fold kinematics as progressive limb rotation about pinned anticlinal and synclinal hinges with constant limb length and a mobile basal décollement horizon within the evaporites of the Minas Viejas Formation that core the anticlinorium. AMS fabrics are shown to be a useful proxy for nascent penetrative strain orientations in sedimentary rocks. Macroscopic differences in strain suggest strong lithologic facies control responding to differences in bed thickness, grain size and carbonate content. At the regional scale, variation in deformation between the lithotectonic units identifies décollement horizons coincident with lithotectonic boundaries in the Minas Viejas, upper Taraises, and Parras Formations.