Good-bye to the Upper Cretaceous Seaway – Models for Lewis,
Fox Hills, and Lance Strata in the Greater Green River and Wind River Basins
Mike Hendricks, Hendricks and Associates, Inc, 6950 South Holly Circle, Suite 101,
Centennial, CO
80112, phone: 303-843-9890, [email protected]
Rapid filling of Rocky
Mountain basins occurred
near the end of the Upper Cretaceous (Maestrichtian).
Depositional environments associated with this final regression include shelf,
slope, and turbidite-basin deposits of the Lewis Formation,
shoreface deposits of the Fox Hills Formation, and
coastal plain and fluvial plain deposits of the Lance Formation. This talk will
emphasize the Fox Hills and Lance strata and their reservoir potential.
The Fox Hills was deposited in near shore and shoreface
environments. Mesotidal deposits occur along the
western edge of the Great Divide and Washakie basins and deltaic deposits are
common in the central and eastern portions of these basins. Reservoir potential
exists in shoreface environments where lobes of sand
are encased in shale or pinch out into shale. Slope channels, related to low
stand or bypassed distributary channels, are also
potential reservoirs.
Lance deposits in the Jonah area and throughout the Wind River Basin
are fluvial plain sediments that were deposited in single to multi-story,
braided channels and low to highly sinuous meandering channels. A west to east
depositional change from fluvial plain to coastal plain environments occurs in
the Lower Lance across the Rock Springs Uplift. Productive channel sandstones
within the coastal plain are locally interbedded with
coals. East of the Rock Springs Uplift, intertonguing
of Fox Hills shoreface environments occurs within
coastal plain deposits. Potential reservoirs exist in these marginal marine and
marine sandstones.
In the Wind River Basin, Lower Meeteetse
coastal plain strata are time equivalent to the Lower Lance in the Great Divide
and Washakie basins, but channels systems are poorly developed and only
marginally productive.