SYNTHETIC SEISMIC MODELING WITHIN THE BURIED MARATHON COMPLEX, TERRELL AND PECOS COUNTIES, TEXAS

Major outcrops of Ouachita thrust belt facies in Texas are found around Marathon and in the Solitario north of Big Bend Park. However most of this orogeny lies buried along the margin of the Llano province of central Texas. When last seen the Ouachita-Marathon belt is trending eastward into southern Pecos and Terrell Counties. It soon changes to a southeast trend and can only be investigated by wells, seismic, and potential field data.

Industry sponsored research compared reprocessed regional vintage 2D seismic data with modern synthetic seismic modeling of selected structural geometries associated with the buried thrust belt. The Brown-Bassett gas field is an asymmetric northwest-trending anticline in front of the thrust belt in Terrell County. A seismic line shot over this field was compared to synthetic sections generated from a similar structural geometry mapped in Wyoming. The modeling resulted in identifying features on seismic that are comparable to continuous folding and plastic deformation of sedimentary rock in conjunction with basement derived reverse faulting along the northern flank of the field. This information assists greatly in determining the type of traps which may exist along the north flank of the field.

Synthetic structural modeling along the overthrust trend demonstrated that the structural style observed on seismic data is directly linked to interactions between the amount of sedimentation and style of folding and faulting found along the deformation front. Different locations along the deformation front display different amounts of sedimentation. These variations in sedimentation alter the manner and intensity of local tectonic deformation and their respective imaging on reflection seismic data. This work suggested that greater amounts of syntectonic sedimentation within Pecos County when compared to Terrell County. The geometric style of traps varies greatly along the deformation front and is linked to the local amount of syntectonic sedimentation.