Greater Green River Project

The Wyoming State Geological Survey (WSGS) is conducting a resource exploration project in the eastern part of the Greater Green River Basin, in southwestern Wyoming. Like many basins throughout the world, the Greater Green River Basin (GGRB) has been an active source of petroleum for decades. Companies have maintained a continued interest in the area and thousands of wells have been drilled to find oil and gas in the subsurface. Apart from a few active mine, coal, uranium, and other natural resources have been mostly ignored during these production efforts. The Wasatch Formation contains uraniferous coals in this area. The goal of the agency’s current research is to investigate the occurrence of coal and uranium to develop resource assessments and locate potential mining prospects for the future. Using all available resources, including the National Coal Resource Data System (NCRDS), well logs from the Wyoming Oil and Gas Commission, and cores from the core repository of the U.S. Geological Survey, WSGS geologists will document the presence of coal in the GGRB and provide the data to the public via the NCRDS on the WSGS website.

The GGRB is a large foreland basin that along with the other prominent basins of Wyoming was formed during the Laramide orogeny, approximately 65-55 million years ago. The GGRB is subdivided into smaller basins, all separated by Laramide features: Hoback Basin, Green River Basin, Fossil Basin, Washakie Basin, and the Great Divide Basin, which is the focus of WSGS’ current research efforts (Fig. 1). The Great Divide Basin (GDB) is bounded to the east by the Rawlins uplift, north of Rawlins, the Granite Mountains to the north, the Wamsutter Arch to the south, and the Rock Springs uplift to the west. These bounding features are large chunks of granitic basement rock that pushed through the younger sedimentary bedrock, forming the impressive high mountains scattered throughout Wyoming today. Between these peaks are large depressional areas, or basins that buckle down under the pressure of mountain building to create a large bowl-like feature for sediment accumulation.

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The sedimentation story of the GDB is complex and encompasses a geologic history that has provided Wyoming with the largest coal resource in the nation, and possibly the world. Approximately 60 million years ago – a few million years after dinosaurs no longer roamed the Earth – Wyoming was covered in a vast featureless, swampy plains system, landward of the Western Interior Seaway of the Cretaceous period, which resided to the east. This depositional system produced what is considered by many as the most famous and profitable formation of Wyoming, the Fort Union Formation. Large swamp deposits created vast layers of thick coal seams that yield production of 400 million tons of coal per year in the Powder River Basin alone. The GDB area also contains the Fort Union Formation, but industry has never explored this area for its potential coal resources. High peaks surround the basin, but the answer lies beneath the surface of the earth, where much of the coal is located at depths of 10,000 feet. The Laramide Orogeny pushed the Fort Union coals down to 3 miles in places, and was subsequently buried beneath thousands of feet of sediment sourced from gravity and fluvially deposited mountain debris, as well as lake deposits from the massive Lake Gosiute which took advantage of the large depressional space. The majority of the Fort Union coals are technologically not feasible to mine under present conditions, but documenting the surface outcrop occurrence is an important guide to assessing the mineable coal and including that resource in the total amount of Wyoming’s coal resources.