Perriwinkle and Perriwinkle North Fields, Martin County, Texas: A Cisco-Canyon Lowstand Reef Complex

Abstract

During the middle-early through early-middle deposition of sediments in Canyon field, a series of glacio-eustatically controlled sea level lowstands resulted in carbonate buildups seaward of the Horseshoe Atoll in Martin County, Texas. The resulting reef tracts consist of algal-bryozoan boundstones, clean forereef talus conglomerates, and other high-energy shelf carbonates. The reef complex was chemically eroded into a tower karst terrain during subsequent sea level lowstands and associated subaerial exposure. The highly sculptured paleotopography was mechanically eroded during the onset of a sea level highstand, filling lows with locally derived conglomerates. In addition, highstand basinal foreshelf conglomerates from the atoll were deposited. These conglomerates contain at least one reservoir-size upper Strawn high-energy shelf allochthon. A transgressive-regressive shelf margin reef tract was deposited seaward of the now exhumed Canyon paleokarst surface during a lowstand that occurred early in Cisco deposition. The tract consists of an algal-bryozoan boundstone, associated forereef talus conglomerates, immediate backreef grainstones and packstones, and erosional foreshelf detritus. Although subaerially exposed, the Cisco reef tract is not as highly solutioned as the Canyon tract, resulting in a lower relief paleotopographic surface. During subsequent sea level highstands, both the Cisco and Canyon reef tracts were buried under lower Cisco basinal foreshelfmore » conglomeraters, masking the stratigraphic intricacies of the paleobathymetric surface and obscuring the relationship of time correlative reservoirs within the shelf-edge complex.« less