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Effects of Paleozoic Tectonics on Structural and Stratigraphic Developments in Southeastern Colorado

Luca Rigo, William H. Kanes

The low-lying but tectonically active Paleozoic Front Range and Apishapa-Sierra Grande uplift controlled the structural and stratigraphic development of southeastern Colorado. By middle Mississippian time, two transgressive, shallow, marine limestone sequences were deposited in this region. Latest Mississippian uplift of the Front Range led to gentle southwestward dip of the basin with concomitant development of an antiform--the Las Animas arch--on the east flank. Subsequent basement cooling and faulting led to karstification of exposed limestones on horst blocks. This topography played a significant role in the distribution of later regressive sediments.

Periodic uplift, faulting, and possible eustatic sea level changes during the Pennsylvanian were responsible for facies variations within the basin. The faulting led to development of a large trough, extending from the Front Range to the Hugoton embayment, and continuing development of the Las Animas arch. Basin sediments are characterized by marine-shelf shaly limestones, becoming more sandy and shaly near the basin margins. Reefs developed along the Las Animas arch, with associated bioclastics on the arch flank.

Tectonic stability in the area during the Permian allowed the seas to transgress the Apishapa-Sierra Grande uplift, with a thick sedimentary wedge deposited on the flanks. The final regressive sequence developed in response to the Laramide orogeny, when the configuration of the Las Animas arch and other prominent structural features was delineated. Extensive drilling since 1953 has given us better insights into the interrelationship of stratigraphy and tectonism, and indicates there are still significant hydrocarbons to be found.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.