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AAPG Bulletin

Abstract


Volume: 44 (1960)

Issue: 8. (August)

First Page: 1371

Last Page: 1413

Title: Pennsylvanian Paleotectonics of Colorado Plateau

Author(s): Richard W. Fetzner (2)

Abstract:

During the Pennsylvanian interval of time, the Colorado Plateau area underwent the most active period of tectonic activity of the Paleozoic era. Pennsylvanian paleotectonic relationships have been reconstructed from stratigraphic and lithologic data acquired from 264 control points. This was accomplished through the use of isopach maps, lithologic ratio maps, vertical sandstone distribution maps, field evidence, and paleontological data.

Pennsylvanian tectonic elements of the Colorado Plateau area defined a northwest-trending parageosynclinal seaway. Greatest subsidence occurred in the north where the Paradox Salt basin formed as an asymmetrical half graben. On the south, depositional centers formed in the Pennsylvanian San Juan and Lucero basins. The seaway opened northwest onto the rapidly subsiding Oquirrh shelf, northeast into the northern Colorado trough, west into the Cordilleran geosyncline, southeast into the southern Colorado trough, and south and southwest into the Pedregosa basin and the Sonoran geosyncline. The seaway was bounded to the northwest by the Emery uplift, to the northeast and east by the Uncompahgre and San Luis uplifts, and to the west and southwest by the Kaibab-Zuni uplift. The Defiance upli t, a structural subsidiary of the Kaibab-Zuni lineament, projected north into the southern Paradox basin, where it strongly affected depositional patterns during Pennsylvanian time.

Throughout most of Pennsylvanian time, the Emery uplift was a low, partly submerged, structural arch. A southeastern spur of tectonism, probably archipelagic in nature, affected depositional patterns from Desmoines to Wolfcamp time in the northwestern Paradox basin. Earliest and greatest Uncompahgre tectonism occurred in its southern part. Here it became a clastic source area in Atoka time, remained orogenically positive into the Permian, and during this time interval shed a tremendous coarse clastic delta to the southwest. The northwestern Uncompahgre responded to uplift later in the Pennsylvanian, but probably permitted marine access between the Eagle and Paradox evaporite basins during Desmoines time. Consequently, Paradox evaporites may be the composite product of two evaporite ba ins. The San Luis uplift, which was slightly positive in pre-Pennsylvanian time, did not respond to sharp uplift until late Pennsylvanian time. The Penasco uplift underwent early and late Pennsylvanian tectonism, but impressed only minor influence on the regional lithofacies. Although the Kaibab-Zuni uplift existed as a nearly continuous structural lineament during most of the Pennsylvanian, greatest and earliest tectonism occurred in the eastern, or Zuni segment. The Defiance uplift was probably positive in the Mississippian, and underwent successive tectonic pulses during Atoka-early Desmoines, late Desmoines, and late Pennsylvanian-early Permian times. Major hydrocarbon production in the Four Corners area displays close relationship to this tectonic element geographically and geologic lly.

Because of sedimentary and tectonic barriers, a thick sequence of evaporites was deposited within the Paradox Salt basin. The Emery and Uncompahgre uplifts created restriction on the northwest, north, and east, and the Kaibab-Zuni uplift provided restriction on the southwest. The combination of a clastic barrier projecting into the Four Corners area from the northeast and the Defiance uplift projecting into the Four Corners area from the southwest formed nearly continous physical restriction across the southern Paradox basin and provided conditions necessary for cyclical evaporite deposition within the basin.

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