Sequence stratigraphic and architectural characterization of a Permian carbonate ramp, upper San Andres Formation, Last Chance Canyon, New Mexico
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Characterizing stratal architectures of carbonate outer ramps is an essential part of understanding the depositional processes fundamental to carbonate systems. Accurate representation of the observed facies and stratal geometries requires extrapolation of data into three-dimensions. High resolution digital outcrop models allow the opportunity to interpret and represent outcrop-scale observations in three-dimensions with spatial accuracy. Examination and modeling of Permian (Guadalupian) mixed carbonatesiliciclastic stratigraphy in Last Chance Canyon, Guadalupe Mountains, New Mexico reveals distinct variability in stratal geometries from the ramp crest to distal outer ramp. In numerous places along the ramp profile, the Guadalupian-8 high frequency sequence of the upper San Andres Formation possesses significant mounded geometries that are the result of both constructional and erosional processes. In the fusulinid-rich outer ramp the geometries are the result of bioherm construction, fusulinid mound construction, and erosion by storm waves and currents. In the mud-dominated distal outer ramp the observed geometries are representative of a low-sinuosity carbonate channel-levee complex with grain-rich facies centered in channelized areas. This study chronicles the three-dimensional stratigraphic development of the outer ramp mounds and distal outer ramp channel-levee complex while placing them in a sequence stratigraphic context. Sequence stratigraphic interpretations of the carbonate ramp clinothems suggests that the mounded geometries and channel-levee complex formed during a transgressive sequence. The transgressive nature of the sequence allowed generation of significant quantities of carbonate mud for exportation to the levees and promoted growth of outer ramp mounds into unfilled accommodation. The onset of the subsequent highstand sequence led to siliciclastic sediment bypass into the basin, termination of mounded outer ramp geometries and ultimately resulted in transformation of the carbonate dominated ramp to a mixed carbonate-siliciclastic shelf.