Abstract

The central Colorado Plateau, during early and middle Paleozoic time, was dominated by a northwest plunging aulacogen or regional structural downwarp extending southeastward from the Utah portion of the Cordilleran miogeosyncline and terminating toward the craton in the vicinity of the Four Corners. Aulacogens as defined by Hoffman and others (1974) are “long lived deeply subsiding linear troughs that radiate from the interior of a continental platform and deepen outward toward the platform margin where they merge at a high angle into a geosyncline with which their fill is contemporaneous.” Structural downwarping during Pennsylvanian and Permian time continued to dominate the structural pattern with major subsidence localized in the Paradox Basin of southeastern Utah. During the Mesozoic the prior tectonic pattern was strongly repeated with renewed pulses of downwarp in the central Colorado Plateau aulacogen.

In the Early Cretaceous a new mouth of the central Colorado Plateau aulacogen was formed some distance southeast of its earlier position as a result of compressional forces causing the southeast shift of the axis of the Cordilleran miogeosyncline. The axis of the Cordilleran miogeosyncline remained in front of the southeastwardly migrating Sevier thrust belt, a regional northeast-trending compressional fold and thrust fault sequence. The Sevier thrust belt possibly resulted from forces directly or indirectly related to subduction of the Farallon or its predecessor plate as the North America plate migrated northwestward from the Mid Atlantic Ridge.

Intermittent rejuvenation of the central Colorado Plateau aulacogen had an important effect in the generation, entrapment, and preservation of hydrocarbons as well as controlling the pattern of sedimentation throughout Phanerozoic time.

During Laramide time the central Colorado Plateau, which previously has been dominated by the aulacogen, was subjected to major epeirogenic uplift and to clockwise rotation. Significant folds or structures which predominantly had no prior existence were superimposed or overprinted over the entire area, probably as a result of a strongly renewed pulse of plate subduction and collision. Tertiary tectonism saw the continuation of downwarp in restricted areas with a clockwise rotation of the downwarp axes. Tensional stresses during the late Tertiary appear to have been dominant with associated significant igneous activity located in or immediately adjacent to areas undergoing downwarp rather than areas of local uplift.