Structural Evolution of Paradox Basin, Four Corners Area

Ernest Szabo

The Paradox and Eagle basins, on either side of the Uncompahgre axis, formed during Early Pennsylvanian time, had similar development and contain similar lithofacies. Uplift along the Uncompahgre axis during Late Pennsylvanian time ruptured the larger, subsident Paradox area into basin segments. Structural evolution of this region, from incipient basin to ruptured basin stage, is explained adequately by a centripetal hypothesis of basin evolution. A centripetal hypothesis makes mathematical analysis possible, because the geometric properties of the earth can be used in an analysis of subsidence. The earth is a spherical solid of fixed volume and finite size, and a point on the sphere also is a point on a great circle. Subsidence involves vertical translation of a point fr m the arc toward the position of the subtending chord.

An oval sag developed in the Paradox region during Early Pennsylvanian time. The sagging followed point-centered loss of subcrustal support, and subsidence was accelerated by vertical movement along arcuate, down-to-the-basin-type, contemporaneous faults. A midbasin arch, the Uncompahgre, was generated by lateral compression generated by subsidence from the arc. Contemporaneous peripheral uplift resulted in basin-limiting positive elements--the Zuni, Kaibab, Uinta, and Front Range uplifts. The peripheral uplifts were faulted and eroded.

Basin expansion, a relief mechanism, stopped by the end of the time of Desert Creek deposition. Lateral compression exceeded the elastic limit of the crust during late Desmoinesian time, and caused the rupture of the midbasin arch. The resulting asymmetrical uplift bisected the Paradox region into two half-basins. Crustal failure was followed by basin collapse during Late Pennsylvanian time.

AAPG Search and Discovery Article #91051©2012 AAPG Rocky Mountain Section Meeting, Albuquerque, New Mexico, 23-26 February 1969