Evolution of the Paradox Basin and Controls on Salt Tectonics in an “Immobile” Foreland Basin, Ancestral Rocky Mountains

Bruce Trudgill
Colorado School of Mines, Golden, CO

The Paradox Basin is an asymmetric foreland basin, developed along the southwestern flank of the Uncompahgre basement uplift in SE Utah and SW Colorado, USA. This large petroliferous basin (265km by 190km) formed during the Middle Pennsylvanian-Permian Ancestral Rocky Mountain orogenic event. Uplift and the generation of significant topography along the Uncompahgre thrust front provided the source and slope for deposition of thick alluvial fan sequences in the immediate footwall of the Uncompahgre thrust. These thick, prograding sequences provided the differential load on the underlying salt that triggered salt flow across the northern Paradox Basin. Within the foreland basin, flexure from the foredeep in the northeast to the forebulge in the southwest was accommodated by a series of northwest-southeast trending normal faults that offset the sub-salt units, and localized the position of the salt walls in the basin.

Salt structures in the northern Paradox Basin subsequently evolved into a variety of structural styles. Complex intra-formational unconformities and rapid lateral stratigraphic facies variations indicate that salt structures were active over a least 75my. Analysis of field exposures and sub-surface well and 2D seismic data across the northern part of the basin reveals a complex feedback relationship between crustal shortening, uplift, loading, creation of accommodation space, differential sedimentation and salt movement. Salt flow through time across the northern part of the basin reflects the varying controls on foreland basin geometry and response to sediment depositional systems.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005