Controls on mixed carbonate-siliciclastic slope and basinal depositional architecture




Price, Buddy James

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Deepwater carbonate depositional systems represent historically understudied environments. The Permian Basin provides an advantageous location to re-evaluate these settings due to subsurface data density as well as existing outcrop and subsurface studies providing a framework on which to expand. Regional well log mapping coupled with cores and seismic data highlight a range of carbonate accumulations along the slopes and in the deeper basin indicating a need for updates to current Permian Basin basinal depositional models. Thickness maps and cross sections highlight multiple mounded and elongate carbonate-mud rich accumulations along the western slopes of the Delaware Basin. The mounded nature, lack of platform focused sourcing, and presence of oblique cross-cutting channels suggest these features represent carbonate contourite drifts as opposed to gravity-driven deposits. The drifts extend from the slopes at specific locations corresponding to bathymetric irregularities that likely locally weakened currents, causing deposition. Drift accumulations significantly alter slope geometries but present only one control on slope variation. Additionally, underlying carbonate buildups generates antecedent topography and drives differential compaction which influences platform to basin relief, subsequent slope gradients, and progradation-aggradation ratios. Bottom currents may also locally sweep sediments from toe-of-slope environments, inhibiting progradation. In the deeper basin, mapping highlights previously undocumented calciclastic submarine fans. The fans appear to be point sourced from the platform by antecedent topography, slope reentrants, and regional faults. Some fans extend into the basin over 100km and reach 250m in thickness. The fans range in composition, containing both carbonate debrites and turbidites, and varying volumes of mud-rich siliciclastic turbidites. Runout of gravity flows resulted in concentration of comparatively coarser carbonate material in proximal fan environments and finer siliciclastic mudstone, siltstone, and organic matter in fan fringe environments. This work highlights the first recognition of a carbonate drift system and the expanded interpretation of large-scale calciclastic submarine fans in the Permian Basin. As the Permian Basin represents one of the most heavily studied and geologic data-rich areas in the world, new interpretations of carbonate drift systems and calciclastic submarine fans indicate these systems are likely more common and overlooked in the ancient rock record.


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