From Outcrop to Numerical Modeling of Dolomitizing Fluids, Permian San Andres Fm, Guadalupe Mountains and Algerita Escarpment

Outcrop data are used to constrain a numerical model of brine circulation during the deposition of the Permian San Andres Formation. We hypothesize that high-salinity fluids were present in restricted parts of the platform; this is documented by the presence of evaporite-rich peritidal deposits. Such fluids circulated through the platform in response to density and hydraulic gradients and caused early dolomitization. Platform geometry, relative position of the shoreline, depositional environments, distribution of hydraulic properties and lithologies, and timing of events are constrained from sequence-stratigraphic and sedimentologic studies on San Andres outcrops along the Guadalupe Mountains, Brokeoff Mountains and Algerita Escarpment Subsurface data was also examined to support outcrop observations. The result is a complex pattern of brine circulation that evolves over time. The source of dolomitizing fluids migrates across the platform top in response to relative sea-level fluctuations and feeds brine plumes within the underlying sediments. The plumes also migrate, grow, and shrink in response to such fluctuations. Dolomitization is most likely to occur in areas of high-flow rates of high-salinity fluids. We show by numerical simulations that this mechanism is sufficiently efficient to be capable of dolomitizing the San Andres Formation. Preliminary reactive transport modeling provides further insight on the diagenetic processes taking place along flow paths in this system. It is especially useful in exploring chemical controls as dolomitization progresses over time and space, such as kinetic rates, porosity/permeability feedbacks etc.