Sequence Stratigraphy, Diagenesis, and Depositional Facies of an Exposed Megaflap: Pennsylvanian Hermosa Group, Gypsum Valley Salt Wall, Paradox Basin, Colorado

Outcrop exposures mostly of the Pennsylvanian Honaker Trail Formation provide a 2 km strike-oriented view of a megaflap on the southwestern flank of the Gypsum Valley salt wall, Paradox Basin, Colorado that serves as an outcrop analog for megaflaps recently drilled unexpectedly in the Gulf of Mexico and other salt basins worldwide. The near vertical (80–90°) stratal panel comprises a 60 m thick succession of non-evaporite facies of the Pennsylvanian upper Paradox Formation, overlain by a 117 m section of cyclic shallow marine carbonates and siliciclastics of the Honaker Trail Formation. Near vertical upper Paradox and Honaker Trail strata are onlapped by steeply dipping (70°) Permian lower Cutler Formation siliciclastics. Only 156 m of Cutler strata are exposed in an erosional window beneath a second angular unconformity. Above this unconformity, the Cutler and Honaker Trail Formations are onlapped by the Jurassic Entrada Formation to form a large-scale halokinetic growth package referred to here as the “onlap wedge.” The megaflap and onlap wedge were subsequently beveled at a third angular unconformity beneath the overlying Upper Jurassic Summerville and Morrison formations, which form the “overlap wedge.” Laterally, the Honaker trail strata in the megaflap gradually shallow to 50–60° on the southern flank where it is abruptly terminated at radial faults that bound a large graben. Jurassic Summerville and Morrison Formation strata overlap and cover the megaflap on its northern end. The shallow marine facies architecture and diagenesis of the Pennsylvanian carbonates and siliciclastics as well as the laterally concordant behavior of the stratal architecture are interpreted to represent a pre-kinematic roof over an incipient passive diapir. Jurassic aged marine diagenesis overprints Pennsylvanian carbonates during incipient marine transgression of the Summerville Formation