FACIES AND SEQUENCE STRATIGRAPHIC ARCHITECTURE OF THE UPPER JURASSIC STUMP AND PREUSS FORMATIONS, LABARGE CREEK, WYOMING, USA

This study investigates the facies and sequence stratigraphic architecture of the Upper Jurassic Preuss and Stump formations which were deposited in the foredeep west of the Sundance Formation. These units are fully exposed at LaBarge Creek, twenty miles west of LaBarge, Wyoming.

The Pruess Formation at LaBarge Creek is a 145 m thick succession of largely maroon, very thinly bedded, silty, very fine-grained sandstone, deposited on tidal flats. The sand flat facies is white, upward-fining sandstone, with large-scale trough cross stratification. The mixed flat facies is a maroon, silty sandstone with halite casts, current ripples, current dunes, vortex ripples, and desiccation cracks. The mud flat facies is maroon mudstone interbedded with very thin beds of silty sandstone. These tidal-flat facies are aggradationally stacked, only weakly developed into parasequences, and interpreted to be in the lowstand systems tract.

The Stump Formation consists of 60 m of medium to very thinly bedded, white, fine-grained sandstone and gray shale, deposited within shoreface and foreshore settings. There are covered intervals between each shoreface that are interpreted as offshore or offshore transition facies due to the presence of grey shale in float. The lower shoreface facies is a thin to medium tabular-bedded white fine-grained sandstone that contains Ophiomorpha. The upper shoreface facies is thin to very thinly bedded white fine-grained sandstone that contains large-scale trough cross stratification and Ophiomorpha. Foreshore facies consists of very thinly bedded, white, fine-grained sandstone with planar laminae and parting lineation. These facies form one retrogradationally stacked offshore unit which passes upwards into three progradationally stacked parasequences, and are interpreted to be in the transgressive and highstand systems tracts.