--> Abstract: Cambrian Rifting And Subsequent Structures In Eastern Texas, by W. A. Thomas and G. R. Keller; #90928 (1999).

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THOMAS, WILLIAM A.1 and KELLER, G. RANDY2
1University of Kentucky, Lexington, KY
2University of Texas at El Paso, El Paso, TX

Abstract: Cambrian Rifting and Subsequent Structures in Eastern Texas

The margin of Precambrian continental crust (Laurentia) in eastern Texas was originally framed by a Cambrian rift (Ouachita rift). An early stage of Mesozoic rifting that led to opening of the Gulf of Mexico followed approximately the same rift outline. The Cambrian rift ends northward at the Alabama-Oklahoma transform fault, outlining the Ouachita embayment in Precambrian crust. Crustal structure models show an abrupt boundary between continental crust and transitional to oceanic crust along the transform. Adjacent to the Cambrian continental margin (Ouachita rift) in eastern Texas, the post-rift thermal subsidence history of the Texas promontory of Laurentia is consistent with an upper-plate setting in a simple-shear low-angle detachment model for continental rifting. Such a setting has specific implications for crustal structure which can be tested by models based on a compilation of geological and geophysical data. Although available data outline the general structure of the rifted margin, more specialized geophysical surveys are needed to confirm structures of sub-regional scale. Important outstanding questions include (1) the magnitude of rift-stage faults; (2) possible fault reactivation that might have affected Cambrian-Ordovician passive-margin carbonate deposition; (3) possible reactivation or inversion of rift-stage faults during the late Paleozoic Ouachita orogeny, both beneath the Ouachita allochthon and in the Fort Worth basin and Llano uplift of the Ouachita foreland; (4) and reactivation or reuse of Cambrian rift-stage faults during Mesozoic extension. Cambrian rift-stage structures in basement (upper crust) rocks probably controlled subsequent compressional and extensional structures and related sedimentary accumulations. Resolution of the history of these structures has important implications for exploration targets throughout the Paleozoic and lower Mesozoic stratigraphy of eastern Texas.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas