Exploring the basin fill history of the Green River Formation
in the Piceance Creek and the Uinta Basins
Yuval Bartov, Colorado Energy
Research Institute, Colorado School on Mines, Golden, CO 80401, phone:
303-2733841, [email protected] and Dag Nummedal, Colorado Energy Research Institute, Colorado
School of Mines, Golden, CO 80401.
The Green River lakes occupied the Uinta, Piceance
and Great Green River Basins
during the Early to Middle Eocene time. These foreland basins were initiated
during the late Cretaceous and early Cenozoic Laramide
Orogeny. The Green River Formation in the Piceance
Creek Basin
contains over 2000 ft of lacustrine deposits composed
of alternating, kerogen-rich mudstones, carbonates
and sandstones and forms the world's larges oil shale reserve of about 1
trillion BOE. In this study we used outcrops, cores and over 100 well-logs to
identify the major sequences across the Piceance Creek
Basin and into the Uinta Basin,
in order to quantify the various controlling factors of the basins' fill. The
sections that we analyzed are composed of numerous high frequency sequences
manifested by distinctive flooding surfaces. These prominent surfaces have a
relatively conformable flat-lying stacking thus indicate small incision between
sequence boundaries that are probably tied to high frequency low amplitude lake
level changes. The sections also indicate an important sedimentary source from
the Douglas Arch that divides the two basins, and a sedimentary fill that keeps
pace with the spatially variable basin subsidence. The chronostratigraphic
correlation also points to an in-phase relationship between the two lakes not
only during the Mahogany Ledge time but throughout the entire Parachute Creek
Member. The correlated signals in the gamma-ray logs between the two basins
indicate either a physical connection between the two lakes with an over-filled
condition or a similar response to climate changes in closed under-filled
conditions. At the time this abstract is written we cannot differentiate
between the two possibilities.