Alluvial Fans, Loess Plains, Lakes, and Distributive Fluvial Systems: Depositional Systems of the Permian-Triassic Red Beds and Evaporites of Wyoming (USA)

Abstract

Willow Hill Elemental Concentration Data 2. Bulk semi-quantitative XRD Data 3. Automated Mineralogy Data from Red Peak Formation 4and evaporites of Pangea. This study will resolve conflicts between previously proposed models for red bed formation and the previously proposed depositional environments of the red beds, carbonate, and gypsum of the Permo-Triassic of Wyoming. It will also contribute to an understanding of the Permian-Triassic environments, climate, and paleogeography. SCIENTIFIC AND SOCIAL IMPORTANCESedimentologists study the deep-time rock record to address important questions about the evolution of life, guide exploration for natural resources, and understand the range of environments on Earth and other rocky planets. This dissertation reconstructs depositional environments using details of sedimentary features, geochemistry, and fossils. The Permian and Triassic Periods have proven particularly important to study as an analog for a warming climate. However, the rocks of the Permo-Triassic has been difficult for geologists to understand because they vary widely from modern analogs. The Earth at the end of the Permian was widely different from modern experience, yet the uniformitarian-approach is still valid. Detailed sedimentological studies, like this one, are required to understand geological processes and their consequences during a global warming event, such as that at the end of the Permian.The Permian-Triassic mass extinctions, extreme environments, and global warming is a Phanerozoic endmember for aridity, heat, and surface water chemistry. Red beds and evaporites are common Permian and Triassic rock types. However, outcrops of red beds and evaporites are difficult to study, and well-preserved cores are rare. This study will elucidate some of the physical, chemical, and biological processes during extremely arid environmental conditions. As modern global atmospheric CO 2 increases, the rate of climate change is expected to increase (Solomon et al., 2007). The rapid and sustained increase in CO 2 and its impact on earth systems is not a no-analog situation in human experience; however, the Permo-Triassic rocks record continental environments that have undergone this type of global climate change. The specific physical processes, geochemical products, and biological interactions with the environment may provide insight into the Earth's future.This study also contextualizes the Goose Egg and Red Peak's highly arid environments within the context of the wider Permian-Triassic ecological system. These rocks are located adjacent to three extreme depositional systems identified as widespread at the time: (1) loess-dominated rocks, (2) acid saline systems, and (3) open marine systems with unusual chemistry. Wyoming's understudied rocks may hold the key to delineating the extent of extreme environments on the supercontinent and help constrain sediment transportation, habitability, and geochemical cycling within these systems.Understanding the relationships between the marine rocks of western Wyoming...

Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

“…Rocks of the Chugwater Group are well-exposed around the flanks of Laramide uplifts in north-central Wyoming. Descriptions of the Chugwater note its distinctive red colour, fine grain size, reptile trackways, the presence of gypsum, and its assumed lateral continuity and consistent thickness F I G U R E 1 Stratigraphic nomenclature of the Chugwater Group and its four formations, modified after Knapp (2020).…”

“…The Red Peak Formation is the lowest formation of the Chugwater Group, considered to be approximately 170 m thick, and composed of red beds and bedded gypsum (Maughn, 1972; Figure 1). While the Chugwater Group and its distinctive bright-red colour are well-known to geologists familiar with Wyoming, the interpreted depositional environments remain contentious (Branson, 1915;Cavaroc & Flores, 1917;High & Picard, 1969;Picard, 1967;Irmen & Vondra, 2000;Lovelace & Lovelace, 2012;Knapp et al, 2015Knapp et al, , 2016Knapp, 2020). The bedded gypsum of the Chugwater Group has not yet been described in sedimentological detail; ancient bedded gypsum, in general, is understudied.…”

“…Stratigraphic nomenclature of the Chugwater Group and its four formations, modified after Knapp (2020). …”

“…Sedimentological observations of the Chugwater Group have focussed on the siliciclastics. Field and petrographic studies by Knapp (2020) interpreted the red bed siliciclastics of the Red Peak Formation as episodic sheet flood deposits on alluvial plains that underwent pedogenesis. The abundance of palaeosols strongly suggests a continental origin for this sequence of Permo‐Triassic red beds and bedded gypsums.…”