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The Wichita Group in the Palo Duro basin represents the Wolfcampian-Leonardian transition from carbonate to predominantly evaporite deposition. An interbedded series of dolomitic, anhydritic, and terrigenous clastic lithofacies reflect deposition in inner shelf and evaporitic tidal flat environments. An arid setting and restricted marine circulation over the broad expanse of the basin were conducive to the onset of early diagenesis, which masked much of the Wichita depositional framework.
Petrographic analyses revealed diverse lithofacies in the Wichita Group. Dolomitic lithofacies include (1) pyritic to argillaceous mudstones, (2) organic wackestones, (3) algal-intraclastic wackestones and packstones, (4) skeletal-peloid packstones, (5) coated grain-ooid grainstones, and (6) pisoid grainstones. Nodular-mosaic and massive to laminated anhydrite and terrigenous shales and siltstones complete the sequence. Noncyclic relationships are characterized by rapid vertical change, laminated to thin bedding, and gradational to sharp, commonly erosional contacts.
Wichita subfacies reflect deposition in a complex patchwork mosaic of evaporative supratidal, intertidal, shoal, and subtidal environments rather than a normal shelf to tidal flat transition. Close lateral association of these subenvironments in a low topographic setting yielded rapid facies migration in response to periods of increased terrigenous influx, storm erosion and redeposition, and normal tide and sea-level fluctuations.
Subaerial exposure and hypersaline brines initiated penecontemporaneous sulfate deposition and dolomitization. Two to three stages of dolomite cements were deposited. Primary sulfates provided a source for late poikilitic, blocky, and bladed anhydrite cement. Pseudocubic and bladed anhydrite replacement of dolomudstone is common.
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