Asking the pikas politely…
ABSTRACT Few if any accumulations of petroleum classified as being of stratigraphic origin are totally independent of structural control. In a consideration of the stratigraphic potential of a basin, therefore, it is prerequisite that due consideration be given to at least the principal structural deformations that have occurred within the basin during and since the deposition of the most prospective formations. Scrutiny of thickness variations in the sediments the Piceance Creek basin reveals that the basic tectonic framework controlling the present configuration of the basin was in evidence at least as early as the oldest Cretaceous sediments represented in the basin. Stronger border components, such as the Uncompahgre arch, the White River uplift, and possibly the Douglas Creek arch are identifiable as positive structural elements during earlier periods, and were periodically active in influencing the nature of deposition within the Piceance Creek basin from Cretaceous through Eocene time. With the exception of a few features deep within the basin, where data is not available or is inconclusive, thickness variations within the Mancos shale section indicate either early or continued phases in the structural development of all of the principal components forming the tectonic framework of the present basin. The Danforth Hills anticline on the northeastern side of the basin is revealed as an active positive area during Mancos time. The Douglas Creek arch is clearly defined by a relatively thin Mancos shale section. Thickness variations of the later Cretaceous sediments (Mesaverde) indicate continued structural development of the basin similar to Mancos time, though of a greater magnitude. The end of Cretaceous time in the Piceance Creek basin is marked by broad uplift and local folding, followed by a period of erosion. Flank structures of the basin were extensively eroded and peneplaned before being covered by later sediments. Basal members of the overlying Paleocene sediments usually contain conglomerates of a diversified origin. Paleocene sediments in the basin are similar to the Mesaverde section. They range in thickness from a few feet on the edge of the basin to more than 3,000 feet in the deep basin, and indicate active structural growth of the basin during this period. Growth of the basin continued to be active during Wasatch time. Thickness variations of this section indicate that structural deformation was mainly on a broad basis; previously prominent local features within the basin had only slight influence on the thickness of the Wasatch sediments. Continued growth of the basin is clearly evident in the thickness variations of the Green River sediments. In contrast to the Wasatch period, however, the local structural features within the basin were again active and are expressed in thickness and facies changes. The present great structural relief of the Piceance Creek basin is mainly the result of tectonic activity following the deposition of the Green River sediments, the last consolidated sediments found in the basin. The most favorable stratigraphic-type reservoirs within the present economic reach of the drill in the Piceance Creek basin are of Cretaceous and later age. The nearly constant structural deformation of these sediments since their deposition along established patterns has maintained favorable conditions for the accumulation of petroleum in stratigraphic-type traps on the flanks of the basin. Significant deposits of gas and some oil have been found in stratigraphic traps in widely scattered areas of the basin. Some accumulations appear to have had strong local structural influence; others can have been influenced only by broad structural movements. Apparent economic productive potentials have been measured from nearly all Cretaceous and post-Cretaceous formational units represented in the basin.
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