RETHINKING DEPOSITIONAL ENVIRONMENTS OF THE PERMO-TRIASSIC GOOSE EGG/CHUGWATER REDBEDS: PRELIMINARY RESULTS FROM OUTCROPS NEAR RAWLINS, WYOMING
A 104 meter thick section of exposed red beds assigned to the Permo-Triassic Goose Egg and Chugwater Formations 15 miles north of Rawlins, Wyoming was measured with centimeter-scale resolution. The succession is divided into three units, from lowest to highest in the section: (1) 92.3 meters of red alternating siltstone and sandstone; (2) 2.11 meters of carbonate and gypsum typified by an laminae and algal boundstone; and (3) 8.6 meters of brick red, pink, and yellow fine to course sandstone with some conglomerate.
Distinctive features of unit 1 include ripple marks, bioturbation, cross bedding, rip-up clasts, halite casts, cracks, blocky peds, cross-bedding, and rare burrows and root features in stacked successions of fining upward cycles with slightly erosional bases. Unit 2 is typified by flat to upward doming laminations with minor amounts of disturbed bedding. Unit 3 has abundant cross-bedding, some large scale rip-up clasts, bioturbation, and a high degree of lateral discontinuity. Erosional surfaces are common. Based on the observed sediment structures, preliminary interpretations of environment of deposition suggests a paleosol, fluvial, and lacustrine setting.
This study is part of a regional survey to re-examine red beds. Detailed study of Permo-Triassic redbeds and associated evaporites and carbonates will lead to better understanding of Pangaean environments and climates.