Stratigraphic
and Structural Relations in the Permo-Pennsylvanian Cutler Formation of the
Proximal Paradox Basin, Colorado
Moore, Katherine1, G.S.
Soreghan2 (1) OU, Norman, OK (2) University of Oklahoma, Norman, OK
Where exposed immediately adjacent to the
Uncompahgre Plateau (western Colorado), the Pennsylvanian/Permian Cutler Group
consists of coarse-grained detritus that was shed from the Precambrian-cored
Uncompahgre uplift into the proximal Paradox basin during the Ancestral Rocky
Mountains (ARM) orogeny. In the area surrounding Gateway, Colorado, previous mapping
demonstrates that the Cutler Group depositionally onlaps Precambrian basement;
however, well data nearby and seismic data from elsewhere along the
southwestern Uncompahgre front suggests the presence of a large overthrust in
the subsurface. The deposition of >4 km of Cutler Group sediment into the
Paradox basin has been attributed to syndepositional thrusting in the late
Paleozoic. We conducted detailed facies and structural mapping of the Cutler
strata within 2 km of the onlap contact in order to assess the depositional and
structural history of this system. These data confirm that the exposed contact
between the Uncompahgre uplift and the Cutler Group is a depositional onlap
rather than a fault contact. We hypothesize that steepening of dips in a
localized area adjacent to the nonconformity onlap records primary depositional
dips associated with a Gilbert-type lacustrine delta system. This
interpretation is also consistent with the presence of an inferred
syndepositional slump that juxtaposes proximal (subaqueous) boulder
conglomerate atop more distal deltaic facies. The apparent absence of
syndepositional tectonic structures in the Cutler system here implies that
thrusting on the Uncompahgre frontal system had ceased before deposition of the
youngest Cutler strata exposed at the surface, signaling the end of the ARM
orogeny here.