Detailed measured sections, cross sections, and paleogeographic reconstructions of the upper cretaceous and lower tertiary nonmarine interval, Wind River Basin, Wyoming: Chapter 10 in Petroleum systems and geologic assessment of oil and gas resources i

Detailed measured sections and regional stratigraphic
cross sections are used to reconstruct facies maps and
interpret paleogeographic settings for the interval from the
base of Upper Cretaceous Mesaverde Formation to top of
lower member of the Paleocene Fort Union Formation in
the Wind River Basin, Wyoming. The Mesaverde Formation
spans the time during which the Upper Cretaceous seaway
retreated eastward out of central Wyoming in Campanian time
and the initial stages of the Lewis transgression in earliest
Maastrichtian time. This retreat stalled for a considerable
period of time during deposition of the lower part of the
Mesaverde, creating a thick buildup of marginal marine
sandstones and coaly coastal plain deposits across the western
part of the basin.
The Lewis sea transgressed into the northeast part of
Wind River Basin, beginning in early Maastrichtian time
during deposition of the Teapot Sandstone Member of the
Mesaverde Formation. The Meeteetse Formation, which
overlies the Teapot, was deposited in a poorly-drained coastal
plain setting southwest of the Lewis seaway. The Lewis
seaway, at maximum transgression, covered much of the
northeast half of the Wind River Basin area but was clearly
deflected around the present site of the Wind River Range,
southwest of the basin, providing the first direct evidence of
Laramide uplift on that range.
Uplift of the Wind River Range continued during
deposition of the overlying Maastrichtian Lance Formation.
The Granite Mountains south of the basin also became a
positive feature during this time. A rapidly subsiding trough
during the Maastrichtian time formed near the presentday trough of the Wind River Basin in which more than
6,000 feet of Lance was deposited. The development of this
trough appears to have begun before the adjacent Owl Creek
Mountains to the north started to rise; however, a muddy
facies in the upper part of Lance in the deep subsurface, just to
the south, might be interpreted to indicate that the Cretaceous
Cody Shale was being eroded off a rising Owl Creek
Mountains in latest Cretaceous time.
The Paleocene Fort Union Formation unconformably
overlies older units but with only slight angular discordance
around much of the margins of the Wind River Basin. Pre-Fort Union erosion was most pronounced toward the Wind
River Range to the southwest, where the Fort Union ultimately
overlies strata as old as the upper part of the Cretaceous Cody
Shale. The unconformity appears to die out toward the basin
center. Coal-forming mires developed throughout the western
part of the basin near the beginning of the Paleocene. River
systems entering the basin from the Wind River Range to the
southwest and the Granite Mountains to the south produced
areas of sandy fluvial deposition along mountain fronts. A
major river system appears to have entered the basin from
about the same spot along the Wind River Range throughout
much of the Paleocene, probably because it became incised
and could not migrate laterally. The muddy floodplain
facies that developed along the deep basin trough during
latest Cretaceous time, expanded during the early part of the
Paleocene. Coal-forming mires that characterize part of the
lower Fort Union Formation reached maximum extent near
the beginning of the late Paleocene and just prior to the initial
transgression of Lake Waltman.
From the time of initial flooding, Lake Waltman
expanded rapidly, drowning the coal-forming mires in
the central part of the basin and spreading to near basin
margins. Outcrop studies along the south margin of the basin
document that once maximum transgression was reached, the
lake was rapidly pushed basinward and replaced by fluvial
environments.