Abstract

Post-Paleozoic History Of The West Texas Basin And Its Margins: Llano Arch, Glass Mountains Homocline, Salt Basin And More

Thomas E. Ewing
Frontera Exploration Consultants, San Antonio TX 78259

The present margins of the West Texas Basin are mostly defined by pre-Cretaceous erosion. On the east, the Llano Arch is marked by low-angle beveling of Permian and Pennsylvanian strata in North Texas that culminates in the exposed Llano Uplift. On the south, the Glass Mountains Homocline is a sharper feature with dips of 5 degrees northward into the basin below Cretaceous strata. Both features lie northwest of the late Triassic to middle Jurassic rifting that ultimately formed the Gulf of Mexico; they are inferred to represent a rift shoulder unconformity caused by crustal heating on the flanks of the main rift zone. On the southwest, the NW-trending Hueco Arch truncates Paleozoic strata beneath mid-Cretaceous in far West Texas; it extends northwest into the Burro Arch of southwestern New Mexico. This uplift may be younger than the previous (early Cretaceous) and related to rifting and subsidence of the Bisbee and Chihuahua troughs to the southwest.

After deposition of Cretaceous marine strata, the southern and western margins were deformed by Laramide (early Paleogene) uplift and faulting including the Carta Valley Fault Zone, the Marathon Dome, and various features in Trans-Pecos Texas.

The entire area was uplifted and tilted to its present elevation during Neogene time. Large-scale extensional faulting in the west formed the Salt Basin and Tularosa Valley, Basin and Range features that are related to the Rio Grande Rift.

The effect of these episodes of uplift is a ‘freezing in’ of oil generated in Paleozoic strata. Lack of subsidence keeps substantial zones out of the gas window and helps to preserve liquid hydrocarbons. Large-scale uplift, however (as in the Kerr Basin) may raise strata in the gas window and cause depressuring and loss of reserves.

AAPG Search and Discovery Article #90164©2013 AAPG Southwest Section Meeting, Fredericksburg, Texas, April 6-10, 2013