Recently discovered overthrusting northeast of Llano uplift along extension of San Marcos platform: new exploration frontier in central Texas
TJB Resources recently completed gravity, magnetotelluric, and seismic geophysical surveys in San Saba and Mills Counties north of the Llano uplift, west of the Ouachita Disturbed belt. Significant results show overthrusting has occurred 60-70 mi west of the Ouachita Disturbed belt. Earliest thrusting could have occurred in the Silurian-Devonian from south or southeast. Faulting reoccurs during Pennsylvanian Ouachita thrusting and again in the Late Cretaceous. The primitive Llano uplift buttressed the allochthonous rocks moving north and west. Magnetotelluric and gravity data indicate the Llano uplift is a separate and distinct isolated remnant or terrain, with numerous igneous intrusions reaching to great depths. Associated with this thrusting is a major tectonic northwest-southeast lineament located parallel to the termination of the Cretaceous rocks, outcropping on the western edge of Mills and Lampasas Counties. This lineament is documented by east-west seismic lines displaying a 0.3-sec displacement and farther southwest a 1.1-sec displacement. Paleozoic fossils were found near the surface trace of the northwest-southwest lineament as observed on the east-west seismic line. This area was previously mapped as Cretaceous. Surface inspection found Paleozoic rocks containing crinoids, spirifers, and rugose corals, with beds dipping to 45/sup 0/, contrasted with the N2/sup 0/ regional dip surrounding the lineament area. Well-log correlations from Marble Falls to Ellenberger range from 350 to 600 ft from east to west near the Llano uplift. The 60 to 70-mi frontal edge of the thrusting provides potential hydrocarbon traps along a north to northeast trend from central Texas to Oklahoma.
- OSTI ID:
- 5160974
- Report Number(s):
- CONF-860624-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:5; Conference: American Association of Petroleum Geologists annual meeting, Atlanta, GA, USA, 15 Jun 1986
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PETROLEUM DEPOSITS
EXPLORATION
TEXAS
CRETACEOUS PERIOD
DEVONIAN PERIOD
FOSSILS
SEISMIC SURVEYS
SILURIAN PERIOD
WELL LOGGING
FEDERAL REGION VI
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOPHYSICAL SURVEYS
MESOZOIC ERA
MINERAL RESOURCES
NORTH AMERICA
PALEOZOIC ERA
RESOURCES
SURVEYS
USA
020200* - Petroleum- Reserves
Geology
& Exploration