ABSTRACT: Progradation of the Mesaverde Group, Bighorn Basin, Wyoming-Sequence Stratigraphy Forced by Sevier Thrusting

KLUG, BERND, Geologisches Institut, Universitat Bonn, Germany

This study used facies analysis of numerous outcrops and well logs to delineate the three-dimensional sequence evolution of the Mesaverde Group on a regional scale. In the study area, the Mesaverde records two major regressions of the western interior shoreline interrupted by eastward transgression of the Claggett sea. In cross section, more than 300 m of alluvial strata in the west grade into wave-dominated, deltaic and nondeltaic shoreline sandstones and eventually into storm-dominated offshore mudstones in the eastern Bighorn basin. These facies transitions can be resolved into complex patterns of parasequence stacking.

The (earlier) Telegraph Creek-Eagle regression comprises alternating slowly/rapidly prograding parasequence sets that constitute

fourth-order sequences, and include field evidence for the 80-Ma sequence boundary. It likely corresponded to a phase of moderate basin subsidence and of possible eustatic fall under moderate clastic supply. The subsequent Claggett transgression is marked by a conspicuous ravinement surface overlain by backstepping parasequences, which might document increased subsidence due to the onset of activity along the Absaroka thrust system. The (later) Parkman-Judith River regression caused an initial rapid basinward shift of the shoreline, followed by shoreline aggradation, and then dramatic progradation that culminated in the easily recognizable Teapot sequence boundary. Yet, this offlap presumably occurred during a time of global sea level rise and thus is inferred to have been the product of mainly two processes: (1) decreasing foreland basin subsidence as thrusting terminated, and (2) a pulse of detrital influx due to retarded arrival of sediment eroded from the thrust-rejuvenated relief in the Sevier belt.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)