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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 9. (September)

First Page: 1428

Last Page: 1428

Title: Previous HitMagnetotelluricNext Hit Soundings in Ouachita Thrust Belt of Central Texas: ABSTRACT

Author(s): J. G. Muncey, W. J. Ehni

Article Type: Meeting abstract


A 25-station, 84-line-mi, remote referenced Previous HitmagnetotelluricNext Hit (Previous HitMTNext Hit) traverse across a portion of central Texas has been recorded and analyzed. Among the geologic and geophysical elements crossed are the Ouachita foreland, the frontal and interior zones, and the rimming gravity maximum.

Previous HitMTNext Hit signatures of the allochthonous Ouachita facies have been established with the aid of well control and are correlated along the traverse. Both conductive foreland facies and the underlying resistive Precambrian can be traced beneath the resistive frontal thrust zone, but become indeterminate along the central part of the traverse, owing to abrupt thinning of the Precambrian resistor. Well control suggests that this resistive basement is correlative with the Grenville-age granitic basement of the nearby Llano uplift. A thick conductive interval of metasedimentary(?) basement material underlies Paleozoic rocks along the central portion of the traverse. This conductive basement appears to dip steeply beneath the Llano-type resistive basement and subcrops on the foreland flank of a bas ment antiform coincident with the rimming gravity maximum.

Still another resistive basement interval appears deep within the basement near the central portion of the traverse, and shallows abruptly to the southeast to form the core of the basement antiform coincident with the rimming gravity maximum. Stratigraphic relationships within the Precambrian basement suggest that the resistive basement, which cores the basement antiform, may be older than the conductive metasedimentary(?) and resistive Llano-type basement, and that the basement beneath the Ouachita trend is of North American affinity at least as far south and east as the rimming gravity maximum.

The Previous HitMTTop signature of the subthrust foreland facies is truncated on the crest of the basement antiform coincident with the rimming gravity maximum. The geometry of the truncation suggests that the frontal thrust zone may have detached from the age-equivalent foreland facies near the present crest of the basement uplift, and that the distance between the foreland facies truncation and the foreland facies-frontal thrust zone boundary may serve as a crude minimum estimate of frontal thrust zone translation (about 60 mi).

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