TECTONICS, MAGMATISM, AND SEDIMENTATION OF THE FIRST 17 MA OF THE LATE CRETACEOUS IN THE SOUTH-CENTRAL REGION: AN OVERVIEW

The first 17 Ma of the Late Cretaceous was an important episode of magmatic, tectonic, and sedimentation activity in the south-central USA and NE Mexico. The Cenomanian (100-93.9 Ma) and Turonian (93.9 – 89. 8 Ma) (C-T time) witnessed alkalic igneous activity in Kansas, the Ouachitas of Arkansas, around the Reelfoot Rift in Mississippi and Arkansas, and perhaps associated with the Eagleford in S. Texas. Mantle unrest (reflected by tectonic movements and alkalic volcanism) migrated south into Louisiana, Mississippi, and S. Texas from C-T into Coniacian and Santonian time (89.8 – 83.6 Ma). Stranded fragments of Gondwana (Sabine and Monroe uplifts) and some adjacent parts of Laurentia (San Marcos Arch, Ouachitas) were uplifted, resulting in tilting, erosion, and development of extensive unconformities, including that separating the Comanchean and Gulfian Series of Texas. These tectonic movements resulted in a large river – perhaps the proto-Mississippi river - debouching in NE Texas during Cenomanian time to produce the Woodbine delta. The Sabinas and Burgos basins in NE Mexico adjacent to S. Texas may also have been formed by Late Cretaceous reactivation of the Jurassic Borderlands Rift System. Much tectono-magmatic activity occurred about the same time as a major global episode of oceanic anoxia (OAE II ~93.9 Ma), which developed in response to increased magma flux to ocean basins, especially associated with the Caribbean Large Igneous Province. Anoxia in Gulf of Mexico basin (GoM) may have been particularly intense because of proximity to the Caribbean LIP, relative isolation of the GoM from the world ocean, and because of volcanism around the GoM itself. C-T time in the south-central region witnessed deposition of the Eagleford and Tuscaloosa Marine shales in the US and equivalent Agua Nueva Formation in the Burgos Basin and Boquillas/Eagle Ford in the Sabinas Basin, which are important hydrocarbon source rocks. C-T tectonic and magmatic activity was important for hydrocarbon evolution. For example, uplift of the San Marcos Arch isolated carbonate-rich Eagleford basin in S. Texas from clay-rich Eagleford in NE Texas, and igneous activity may have played a role in hydrocarbon maturation. Understanding what happened C-T time in the south-central US requires combined efforts of academic and industrial geoscientists.