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Structural Controls on the Development of Eocene Lake Gosiute and Lake Uinta, Southwest Wyoming, Northwest Colorado, and Eastern Utah

Ronald Johnson
U.S. Geological Survey

This study examines the relations between tectonism and the development of Eocene Lake Gosiute, which occupied the Greater Green River Basin in southwest Wyoming and northwest Colorado, and Eocene Lake Uinta, which occupied both the Uinta Basin of northeast Utah and the Piceance Basin of western Colorado. About 52-53 Ma, both lakes began to form as relatively small, externally drained, fresh-water lakes, then evolved into much larger internally drained saline lakes. This unusual evolution could have been the result of: 1) movement on surrounding uplifts that elevated spill points until external drainage was lost, or 2) regional sagging that led to drainage reversals and ultimate loss of external drainage. The first implies that lake elevations were above sea level, whereas the latter implies lake elevations below sea level. Evolution of brines in the lakes, however, appears to be inconsistent with invasion of sea water. Interestingly, as Lakes Uinta and Gosiute formed they transgressed across comparatively minor structural arches that, based on isopach maps, had been active prior to transgression but became largely inactive during saline lake deposition. Uplift on these arches resumed sometime after the lakes were filled in. The progressive infilling of the lakes by volcaniclastic debris from the Absaroka volcanic field also may have been partially controlled by structural activity. Infilling began about 49-50 Ma in the northern Green River Basin and progressed southward, filling in Lake Gosiute and then the Piceance Basin part of Lake Uinta. Lake Uinta persisted in the Uinta Basin until about 43-44 Ma. Subsidence patterns largely mimic this infilling pattern, with subsidence diminishing first in the northern Green River Basin and last in the Uinta Basin.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013