--> Abstract: Constraints for Determining the Southern Extent of Overthrusted Platformal Strata in the Ouachita Orogenic Belt, Oklahoma, USA, by C. A. Ferguson; #91012 (1992).

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ABSTRACT: Constraints for Determining the Southern Extent of Overthrusted Platformal Strata in the Ouachita Orogenic Belt, Oklahoma, USA

FERGUSON, CHARLES A., University of Calgary, Alberta, Canada

Exploration programs for extending gas reserves south of the Arkoma basin into deeper and more complex areas of the Ouachita orogen should consider an interpretation, proposed herein, that the overthrusted carbonate platform is not as extensive as it is popularly thought to be.

Evidence for location of the platform's south-facing shelf margin is present in the allochthon of the north-vergent Ouachita fold-thrust belt. The allochthon is divided into two sequences by the Ti Valley fault (TVF), a major thrust that runs parallel to and less than 10 km hindward of the frontal thrust. The southern sequence, or Ouachita facies, consists of a deep marine equivalent of the autochthonous platform overlain by a southward-thickening (1 to 8 km) wedge of flysch that contains conspicuous shelf-derived olistostromes. The northern sequences of the allochthon, or Arkoma facies, is dominated by a thick flysch unit that buried the platform during initial stages of thrusting. The Arkoma-Ouachita facies transition (essentially the TVF) therefore represents an allochthonous trace of the buried shelf margin.

A balanced cross-section of the northern Ouachita Mountains was used to palinspastically restore the Arkoma-Ouachita facies transition and therefore locate the buried position of the shelf margin. This technique places the margin about 25 km south of the frontal thrust, which corresponds to about 60% tectonic shortening. This is 70 km farther north than many other estimates.

A metamorphosed carbonate platformal sequence, structurally buried beneath the southern Ouachita Mountains, is widely interpreted as a southern continuation of the platform that underlies the Arkoma basin. If this were true, it would require unaccountably large amounts of shortening (over 90%) in the frontal Ouachitas. The metamorphosed platform is herein interpreted as part of a terrane exotic to North America. Large areas of the central Ouachita Mountains may not be underlain by platformal rocks of any kind.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)