--> Tectonic Controls on Alluvial Systems in a Distal Foreland Sefting: The Cloverly/Lakota Formations (Cretaceous) in Wyoming and South Dakota, by J. N. Way, P. J. O'Malley, and L. J. Suttner; #90986 (1994).

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Abstract: Tectonic Controls on Alluvial Systems in a Distal Foreland Sefting: The Cloverly/Lakota Formations (Cretaceous) in Wyoming and South Dakota

J. Nathan Way, Patrick J. O'Malley, Lee J. Suttner

Integrated surface and subsurface stratigraphic/sedimentologic analysis of the nonmarine Lower Cretaceous rocks along the eastern distal margin of the Rocky Mountain foreland basin suggests that progressive west to east activation, first of intraforeland and then cratonic-margill structures, primarily controlled the location of Early Cretaceous trunk rivers.

During deposition of the Cloverly and middle Lakota Formations, trunk rivers flowed N to NE along reactivated basement faults. Changes in sand-body thickness along previously documented N and NE trending lineaments and occurrence of local intraformational angular-unconformities provide evidence of syndepositional movement of these structures. Reactivation of these faults occurred first in west-central Wyoming about 144 Ma and then farther east, about 130-134 Ma, controlling a migration of rivers to the east. This migration culminated by the start of the Albian (113 Ma) with a change in provenance and a reversal and increase in gradient. This is indicated by a 90.180° change in direction of paleocurrents and increase in grain size from the middle to upper Lakota Formation in the a ea of the present northern Black Hills. Presumably these changes were caused by uplift of the Transcontinental Arch in northern Nebraska where cobbles of Sioux Quartzite and/or Deadwood Formation sandstone common in the upper Lakota Formation were most logically sourced.

Assuming that both the intraforeland and cratonic-margin structural movement were induced by stress associated with fold-thrust belt tectonics along the west edge of the foreland in Wyoming, Idaho and Utah, a "stress-wave" may have been transmitted nearly 900 km inboard over approximately 30 million years in order to account for the progressive eastward activation of basement structures that controlled early Cretaceous nonmarine sedimentation.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994