Glacioeustatic transgressive reflux: Stratiform dolomite in Pennsylvanian bioherms of the western Orogrande basin, New Mexico

Upper Paleozoic (Pennsylvanian) algal bioherms of the western Orogrande bas in consist of multiple high frequency sequences with stratiform dolomitizat ion that preferentially affects peritidal facies and strata proximal to seq uence boundaries. Field, petrographic, and geochemical analyses reveal two replacive dolomite phases, and several dolomite cements. The facies-selecti ve (FS) replacive phase affects peritidal facies, and consists of micritic to finely crystalline, fabric-preserving dolomite with high Sr and Na conce ntrations and low to moderate Fe and Mn. The non facies-selective (NFS) pha se affects facies proximal to sequence boundaries, and consists of finely t o medium crystalline dolomite that is both fabric selective and commonly fa bric-destructive. This phase has moderate to locally elevated Sr and Na con centrations, and moderate to high Fe and Mn. Dolomite cements line and occl ude pores and molds, and consist of medium to coarsely crystalline rhombs w ith moderate Sr and Mn, low Na, and high Fe, Stable oxygen isotope values f or bulk dolostones exhibit a wide range and include relatively low values, suggesting precipitation and recrystallization over a wide range of conditi ons. FS dolomitization occurred penecontemporaneously with peritidal deposition at glacioeustatic fall to lowstand, NFS dolomitization oc curred early post depositionally, by reflux of mesosaline to hypersaline brines during early- middle stages of each glacioeustatic transgression, Virgilian lowstand gyps um deposits of the southwestern Orogrande provided the Mg source for the tr ansgressive brines. Dolomite cements precipitated largely under reducing co nditions of the burial environment, Early dolomite in the western Orogrande basin and its absence in the easter n Orogrande basin reflects local and regional physiographic asymmetry. The western shelf was of low relief, with an archipelago of high-relief mounds, which favored fall-stage peritidal conditions with local restriction in th e mounded region. In contrast, the eastern shelf was of high relief and rel atively elevated, which precluded tidal-flat development and allowed marine inundation only at late transgressive to highstand stages, by nearly norma l marine waters, Development of both peritidal (penecontemporaneous) and tr ansgressive reflux (early postdepositional) dolomitization was therefore re stricted largely to the western Orogrande basin.