Recognizing Decoupled Controls on Accommodation and Sediment Supply, and the Importance of Axial Drainages in Foreland Basins: Adventures in Stratigraphic Correlation From the Cretaceous Straight Cliffs Formation of the Kaiparowits Plateau, Southern Utah

Abstract

Recent studies summarized here revisit the Straight Cliffs Formation of the Kaiparowits Plateau more than 20 years after first-order studies that resulted in widely cited sequence stratigraphic models. Key findings based on detailed studies from fluvial, paralic, and marine deposits across the plateau emphasize the importance and implications of drainage systems that were oriented sub-parallel to the main Sevier fold-thrust belt. Provenance and paleocurrent data point to major sediment sources to the south (Mogollon Highlands) and southwest (the Cordilleran Magmatic Arc), with Sevier sources most prominent in marine sections showing evidence for longshore drift from the north. Temporal provenance trends indicate pulses of increased sediment input from Sevier sources that are likely linked to specific thrust events to the west. Stratigraphic correlations are typically drawn from west to east in this basin, across generally “proximal to distal” facies belts. However, this view implies a direct correlation between sediment supply and flexural subsidence, which is dangerously misleading when interpreting stratigraphic architecture in terms of accommodation versus sediment supply. As previously interpreted, there is evidence across the plateau for base level shift(s) in the lower John Henry Member. However, new work suggests the main basinward shift in facies and subaerial unconformity formed higher in the section than previously thought, and this event is expressed as north-trending valley system with dramatic thickening trends (>2-3x compacted thickening over 15 km) in the northern Kaiparowits Plateau. The valleys align with the central plateau which is dominated by tidal, lagoonal, and estuarine facies in the middle John Henry Member, suggesting transgressive flooding of a vast area from the north. Following the major transgressive interval of the middle John Henry Member, fluvial systems across the plateau signal progradation of a distributive fluvial system, and possibly largely autogenic signals. The upper John Henry Member section is transitional into the Drip Tank Member, with an associated sequence boundary that, again, likely occurs higher in the section than previously thought. A broadly analogous interpretation applies to another widely-distributed ‘fluvial sand/gravel sheet,’ the Calico Bed, which underlies the John Henry Member with a major unconformity and transgressive ravinement surface interpreted here at the top rather than base of the unit.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016