GCAGS Abstract-Salt tectonic controls on facies and sequence

Salt tectonic controls on facies and sequence stratigraphy of the Triassic Chinle
Formation, Gypsum Valley salt wall, Co
Stratigraphic correlation of the Chinle formation with its contact against the
Gypsum Valley salt wall illustrates how tectonism and onlap can influence the
distribution of potential reservoir facies. In Gypsum Valley, a salt wall in the Paradox
basin of southwestern Colorado, the Triassic Chinle formation interacted with passively
rising salt during deposition. Gypsum Valley is a dissolution valley with a breached salt
core that exposes a salt shoulder formed by the Chinle formation in 3-dimensions. Along
the northeast margin of the diapir, the Chinle formation thins onto the diapir and thickens
into the adjacent minibasin. The description of the facies of the Chinle Formation is
important for mapping the distribution of fluvial channels and environmental changes
with respect to the Gypsum Valley salt wall.
In northern Gypsum Valley, 3-dimensional exposures of the Chinle formation
extend from the exposed contact with the diapir to approximately 0.7 Km away.
Measured sections show complex thinning of strata and internal angular unconformities
with proximity to the salt wall. The Chinle formation thickens from 60m to 210 m within
600 m of the diapir. The sections include ledge-forming channel-fill sandstones
separated by slope-forming, finer-grained silty sandstones. Immediately adjacent to the
salt contact abundant conglomerates contain caprock clasts forming potential reservoir
analogs. The caprock conglomerates grade laterally into sandstone and siltstone beds.
Further from the diapir new channels appear in the lower part of the silty shale intervals
no longer containing caprock conglomerates. Three facies associations were defined from
the sections so far. 1.) Thin conglomeratic lenses forming basal channel lags. Near the
diapir the clasts are predominately composed of carbonate and caprock clasts eroded
from the diapir. 2.) Fine to medium grained trough cross-beds, and 3.) Horizontally
laminated medium sandstone. Individual channels are approximately 0.5 – 1.0 m thick
and extend roughly 2.0 m in outcrop.