Sequence Stratigraphic Analysis of the Drip Tank Member of the Straight Cliffs Formation: A New Look at the Leading Non-Marine Models
Schellenbach, William; Lawton, Timothy
The Drip Tank Member of the Straight Cliffs Formation is an amalgamated stacked braided-fluvial deposit exposed in the Kaiparowits Plateau of southern Utah. Measured sections indicate that the Drip Tank Member decreases in thickness from 100 to 30 meters from east to west across the Cordilleran foreland basin. Thickness variability was determined by location within the foreland basin, with the thickest deposits occupying the proximal foredeep and the thinnest deposits occupying the distal foredeep. We evaluated three competing sequence stratigraphic models using sedimentologic and provenance data to assess the proper placement of the sequence boundary and to interpret systems tracts of the Drip Tank Member.
The contact with the underlying John Henry Member is located at a gradational compositional change from feldspathic detritus of the John Henry Member to quartzose detritus of the Drip Tank Member. This compositional change takes place over several channel stories. In contrast, the contact with the overlying feldspathic Wahweap Formation is an abrupt compositional change at a prominent truncation surface where one or more stories of the Drip Tank Member are eroded at several outcrop sections.
A total of eight detrital-zircon samples, two from the John Henry Member, four from the Drip Tank Member, and two from the Wahweap Formation, were collected at two different sections. The uppermost part of the John Henry Member is interpreted as deposits of a northeast-flowing axial fluvial system on the basis of composition, paleocurrent trends, and detrital-zircon provenance. Detrital-zircon data for the John Henry Member imply a dominant source in the Mogollon Highlands to the south of the basin and a subordinate source in Triassic, Jurassic and Cretaceous arc rocks to the southwest. The Drip Tank exhibits east-northeast paleocurrent trends and a dominant thrust belt source. The overlying Wahweap Formation typically exhibits an east-southeast paleocurrent trend with a mixture of both arc-derived grains and thrust belt derived grains.
We propose a model that envisions the displacement of axial fluvial systems in the foredeep by a braided fan system recorded by the Drip Tank Member. The detrital-zircon provenance data suggest mixing of distributive fan and axial fluvial systems, with the John Henry and Drip Tank Members occupying the aggradational systems tract and the overlying Wahweap Formation occupying a younger degradational systems tract.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013