Abstract

In Middle Early through Early Middle Canyon time, a series of glacio-eustatically controlled sea level lowstands resulted in carbonate buildups seaward of the Horseshoe Atoll in Martin County, Texas. Areal distribution of carbonate sedimentation was largely controlled by contemporaneous tectonism. 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 in lows with locally derived conglomerates. In addition, highstand basinal foreshelf conglomerates from the Atoll were deposited. At least one reservoir size Late Strawn age high energy shelf allochthon was also deposited.

During an Early Early Cisco lowstand, a transgressive-regressive shelf margin reef tract was deposited seaward of the then exhumed Canyon age paleokarst surface. 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 age reef tract is not as highly dissolutioned as the Canyon age tract, resulting in a lower relief paleotopographic surface. During subsequent sea level highstands, both the Cisco and Canyon age reef tracts were buried under Early Cisco age basinal foreshelf conglomerates, masking the stratigraphic intricacies of the paleogeomorphic surface and obscuring the relationship of time correlative reservoirs within the shelf edge complex.