Near surface generation, burial recrystallization, and structural overprinting of carbonate platform dolomites

Hyperspectral analysis of carbonate rocks provides a novel method to recognize not only calcite/dolomite alterations, but also to differentiate dolomite fabrics. Coupled with digital outcrop models, hyperspectral data provide an integrated representation of the geometric and mineralogical characteristics of exposed dolomite geobodies at sub-seismic resolution and over large (seismic-scale) extent. This facilitates the continuous, unbiased, and data-driven assessment of the spatial distribution of dolomites, dolomite types and properties. Here we integrate hyperspectral attributes, geochemical data, fracture analysis, tectonic, and thermal histories to constrain the process and timing of dolomitization and the compositional and textural heterogeneity at cm-scale. Our results suggest that the km-scale strata-bound dolomitized layers of the Arab-D member formed in an overall regressive system tract. near the surface (T ~ 30 °C) by refluxing of slightly evaporated seawater (-1.0 to 0‰ SMOW). With undolomitized shallow transgressive mudstone/wackestone layers forming baffles restricting downward fluid flow, the dolomitization process apparently was repetitive and linked to high frequency cycles with preferential dolomitization of cycle-top grainstone facies. Multiple reflux events during high-frequency cycle deposition led to the alternating dolomite/calcite layering. Thus, a classical one-time-dolomitize-all end-of-sequence reflux system is not indicated. The early-formed metastable dolomites were then recrystallized during burial and finally overprinted by a hot (80 °C or more) deep-seated fluid with a composition of up to 6.5‰ SMOW. This fluid was channeled by a NW-SE oriented regional fracture trend, which originated from a Late Cretaceous plate-wide structural event related to the Alpine I tectonic deformation. As the dolomite fabric was altered, porosity and permeability became enhanced. The temperatures derived from clumped isotope analysis, thermal history, and the Alpine I related fracture conduits consistently suggest a latest Cretaceous origin for the final burial dolomite maturation and textural overprinting.