Burial DiaGenesis and Tectonism inferred from paleomagnetism and magnetic fabrics in the Wolfcamp shale, MIdland Basin, TEXAS, USA

An integrated rock magnetic, paleomagnetic, geochemical, and electron microscopy study was performed on three cores penetrating the Wolfcamp Shale interval in the Midland Basin, West Texas. This work presents a temporally constrained diagenetic history of the Wolfcamp Shale, refines our understanding of tectonic influences in the Midland Basin, and postulates an interplay of late diagenetic processes that may contribute to the formation of authigenic magnetite on the surfaces of chlorite/illite. Paleomagnetic results indicate a well constrained, lithofacies independent, Jurassic-aged chemical remanent magnetization carried by SD-PSD magnetite. 1D basin modeling suggests that the Jurassic chemical remanent magnetization occurred within the oil window (100-120 degrees C) during a tectonically quiescent phase. Burial temperatures, electron microscopy, and inorganic geochemistry provide lines of evidence for maturation/migration of hydrocarbons, dissolution of carbonates, and chloritization/illitization. We interpret that the interaction of these processes may have created conditions suitable for the neoformation of magnetite on the surfaces of chlorite/illite. Anisotropy of magnetic susceptibility (AMS) fabrics are carried by paramagnetic clays, and ferroan dolomite is observed in all cores. Geographically corrected data show NE-SW lineations among normal AMS fabrics and streaked inverse AMS fabrics trending NW-SE. Textural observations indicate that authigenic ferroan dolomite formed in undercompacted conditions and likely behaved as passive structural markers. The orientation of AMS fabrics and the relative timing of ferroan dolomite authigenesis suggest that layer-parallel shorting occurred shortly after the deposition of the Wolfcamp Shale and likely corresponds with the timing of Marathon-Ouachita suturing.