Development of the Northwestern Gulf of Mexico Continental Shelf and Coastal Zone as a Result of the Late Pleistocene-Holocene Sea Level Rise

The Northwestern Gulf of Mexico shelf, from western Atchafalaya Bay to the mouth of the Rio Grande, is comprised of four physiographic zones: 1) the western Louisiana shelf, 2) the Colorado-Brazos delta complex, 3) the South Texas intra-deltaic ramp and 4) the Rio Grande Delta. Over the past four decades, there have been thousands of kilometers of high resolution seismic data collected across these regions. From these data, a high resolution sedimentary framework was constructed. The sediment regimes of the last Pleistocene-Holocene sea level rise are clearly defined within these records.

The central and inner submerged shelves from Atchafalaya Bay to the southern edge of the Colorado-Brazos complex and the Rio Grande delta are devoid of significant Pleistocene-Holocene deposits, save cross shelf valley fill. However, on the upper shelf break and the inner and central South Texas shelf up to 50 meters of sediment have accumulated during the Late Pleistocene-Holocene sea level rise. The framework of the south Texas shelf, define by seismic stratigraphy, revels that there have been two sedimentary processes which have dominated to the formation of this part of the shelf: sand transport whose variation can be tied world wide climate variation and clay transport delivered to the shelf during annual seasonal change. Each of process has lead to the construction of unique sedimentary facies clearly defined in the seismic profiles. Coupling these sedimentary facies to the recently published sea level curve by Balsillie and Donoghue paints a clear picture of the interplay of these end-member processes to the development of the South Texas Shelf. The seismic-stratigraphy and sea level curve also explains the formation of the shelf edge reefs along the South Texas, forming during the lower sea level of the Younger Dryas.