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Cretaceous "D" Sandstone Delta, Denver Basin, Colorado: Ancient Previous HitAnalogNext Hit for Shallow Water Bayfill Sequences

WILSON, KEVIN M., Bryn Mawr College, Bryn Mawr, PA

The "D" Sandstone is a relatively thin subsurface unit laid down during the Cenomanian regression within the Western Interior Seaway. Hydrocarbon reservoirs have been documented in a variety of facies, including barrier island, bay mouth bar, distributary channel, and valley fill sequences. Three or more major delta lobes may be inferred from subsurface mapping of the western portion of the facies wedge. Twelve cores from one of these lobes were carefully examined with the intent of establishing core/log calibrations for a large area. Facies identified in these cores include shoreface, baymouth bar, interdistributary bayfill, rivermouth bar, splay, delta plain, distributary channel, alluvial channel, and transgressive/delta abandonment sand. In spite of this complexity, no "D" section exceeded 40 ft in thickness.

Application of the core/log calibrations to regional mapping provides new insights into the nature of "D" delta progradation. Results suggest that the "D" Sandstone may serve as an ancient Previous HitanalogTop for shallow water bayfill systems such as the present-day Atchafalaya, Guadalupe, and Colorado river deltas of the Gulf Coast. Implications for hydrocarbon exploration include: (1) small-scale fluvial-deltaic systems may be understood using deterministic models in spite of rapid facies changes; (2) such models may be useful in understanding a number of ancient deltaic sequences in mature basins in the U.S.; and (3) these models may be used successfully to search for untapped reserves in mature basins.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)