Unraveling the Geologic History of the Greater Green River Basin in Wyoming



10/2 (Tuesday), Unraveling the Geologic History of the Greater Green River Basin in Wyoming, Presented by Ranie Lynds,Wyoming State Geological Survey

How did Wyoming’s dramatic scenery, consisting of high mountains with intervening deep basins form? The answer to this question has been debated for over a century, and geologists are still working to provide answers. Wyoming State Geological Survey geologist Ranie Lynds will explore and explain some of the recent data that shed additional light on the formation of the scenery we see and love across Wyoming.

During the Late Cretaceous, Wyoming was part of an epicontinental seaway that extended from Canada to Mexico, otherwise known as the Western Interior Seaway (WIS). The WIS was a low spot in the North American continent that formed from mountain building and crustal loading of the Wyoming fold-and-thrust belt to the west, an event generally known as the Sevier orogeny. At some point in the Late Cretaceous, the western interior foreland basin was segmented into a series of intermontane basins by basement-cored uplifts that are today’s mountain ranges in an event known as the Laramide orogeny. The timing of the Laramide orogeny, and its impacts on the east-flowing drainage systems from the Sevier hinterland, has been the subject of research and argument for more than a century.

This talk will address new age data obtained from zircons preserved in outcrop samples collected from Wyoming’s Great Divide and Hanna basins. Although zircon is a mineral that forms during crystallization of magma, it is commonly found in sedimentary strata derived from magmatic-sourced igneous rocks. This dataset suggests at least two episodes of Laramide deformation in the Late Cretaceous through Paleocene strata, beginning at about 79 million years ago.

Constraining the timing of evolution of the Rocky Mountain region is key to understanding how and why continents deform. Some of the most prolific hydrocarbon-bearing formations were deposited during this time, and the ability to predict reservoir facies and distribution is important to Wyoming’s economy. Video