Lower Eocene Fluvial-to-Lacustrine Strata of the Greater Green River Basin: Relative

Timing of Tectonic and Climatic Change in the Generation of Stratigraphic Cycles

By

Jeff P. Crabaugh

University of Wyoming, Laramie, WY

Lower Eocene fluvial-to-lacustrine strata preserved in the greater Green River Basin (GGRB) provide an unparalleled field laboratory in which to study the interplay between tectonic and climatic change during the generation of a hierarchy of stratigraphic cycles. In the southeastern to southern part of the GGRB, the Cathedral Bluffs Tongue of the Wasatch Formation, together with the Tipton Shale Member, the Wilkins Peak Member, and the lower LaClede Bed of the Laney Member of the Green River Formation, represent a third-order stratigraphic cycle. The Cathedral Bluffs Tongue of the Wasatch Formation forms the alluvial core, or clastic wedge, of this cycle that records the interplay of tectonic and climatic change spanning the latter half of the early Eocene; a 3.0 m.y. interval from 52 to 49 Ma.

Recently published data on radiometric and paleomagnetic dating of lower Eocene strata in the GGRB, as well as improvements in the temporal resolution of the Global Cenozoic Time Scale, allow correlation of global paleoclimate records and the GGRB cycle stratigraphy. Hyperthermal pulses of climatic warming are recorded at 52.3 and 49.0 Ma (Thomas and Zachos, 2000). These intervals of abrupt warming coincide with the upper and lower boundaries of the third-order stratigraphic cycle, represented by maximum flooding intervals in the LaClede Bed of the Laney Member (above) and the Tipton Shale Member (below). Cross-cutting stratigraphic relationships present at the basin margin provide evidence that the Uinta Uplift was active during middle Cathedral Bluffs deposition (~51.5 to 50.5 Ma), a time of relative climate cooling.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming