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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 733

Last Page: 733

Title: Patterns of Shallow-Marine Deposition, Upper Cretaceous of Northern Colorado: ABSTRACT

Author(s): L. W. Kiteley, M. E. Field

Article Type: Meeting abstract

Abstract:

Economically important sandstone bodies encased in marine shales have been described from the Western Interior region of Utah, Colorado, Wyoming, and New Mexico. Our study of a part of an Upper Cretaceous shelf region in northern Colorado shows that the occurrence and distribution of shelf sands were dependent upon a large dynamic sediment system associated with both major and minor transgressive-regressive phases.

Discrete sandstone members of the Mancos and Pierre Shales represent beach, distributary mouth bar, shoreface, and mid-shelf bar deposits. Texture, sorting, bioturbation, thickness, and bed forms of these units are variable, reflecting the variation in rate of deposition and wave energy. Evidence of transgressive reworking is present locally on the caps of some units. Although some sandstone members (e.g., the Hygiene) have been previously correlated over seaward distances exceeding 50 mi (80 km), our detailed examination of cross-bedding patterns and composition indicates deposition in distinctly different shallow-marine environments. Bed forms (medium-scale tabular cross-beds) and lithology of easternmost exposures of the Hygiene are similar to those in modern sand bars on the Unite States Atlantic, Bering Sea, and North Sea continental shelves, suggesting deposition at mid-shelf depths. Sources of sands were to the west; dominant direction of transport, however, was to the south.

Key factors in the Upper Cretaceous were the relation between nearshore depositional environments and mechanisms of sediment transport on the shelf. Nearshore sedimentation rates apparently were high but episodic; shelf areas were broad and shallow resulting in discontinuous seaward progradation of delta-front sheet sands; and minor, local transgressive phases, as well as major phases, had impact on the geometry and stratigraphic associations of discrete marine sand bodies during the Late Cretaceous.

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