POLLOCK, STONNIE L., and TIMOTHY F. LAWTON
New Mexico State University, Las Cruces, NM

Abstract: Transverse and Axial River Systems of the Wahweap Formation, Cordilleran Foreland Basin, Southern Utah

In the southern part of the Cordilleran foreland basin, Upper Cretaceous fluvial strata of the Wahweap Formation record two major river systems with different headwater regions. Exposed along the flanks of the southern High Plateaus and Kaiparowits Plateau of southern Utah, the Wahweap consists of four informal members with an aggregate maximum thickness of 460 m. The lower three members were deposited by north- and northeast-flowing meandering rivers that transported feldspar-rich lithic detritus along the foredeep axis from a basement source in the Mogollon highlands. The uppermost capping sandstone member was deposited by east- and southeast-flowing, transverse braided rivers that transported quartz-lithic detritus from uplifted Paleozoic and Mesozoic sedimentary rocks of the Sevier orogenic belt. The Wahweap overlies the Santonian Straight Cliffs Formation and underlies the middle-late Campanian Kaiparowits Formation.

Thickness trends of the Wahweap and stratigraphically adjacent units indicate that the foreland basin was structurally partitioned following Wahweap deposition. The capping sandstone member thins downdip from 150 m in the northwest part of the Kaiparowits Plateau to 30 m in the southeast part. In the updip direction, it is absent beneath the Eocene Claron Formation west of the Paunsaugunt fault. We infer that the Paunsaugunt fault, most recently with Neogene normal offset, is an inverted Campanian thrust fault. Uplift along a thrust-tip anticline resulted in erosion of much of the Wahweap from the present Paunsaugunt Plateau.

Eastward propagation of the Sevier thrust system segmented the Santonian foredeep, forming a wedge-top basin west of the Paunsaugunt Plateau and a Campanian foredeep occupied by the Kaiparowits Formation to the east.

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