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ABSTRACT: Controls of Sequence Stratigraphy on Sandstone Body Geometry and Interconnectedness: Example from the Dakota Formation in Kansas

Vincent J. Hamilton

Seaward shifts in facies, evidence of subaerial exposure, and incomplete facies successions allow three sequence-bounding unconformities to be recognized on the eastern margin of the Western Interior basin in western Kansas. The correlative unconformities in Colorado are at the bases of the Cretaceous Plainview Formation, J sandstone, and D Sandstone. In Kansas, the J and D sandstones are amalgamated and comprise the Dakota Formation.

Gamma-ray well logs were used to correlate these sequence boundaries to outcrops in central and southern Kansas. The upward succession of facies in the sequences is from fluvial through shoreface to offshore marine, recording a landward-stepping geometry of progradational events. In a landward direction, toward central Kansas, Dakota Formation strata become increasingly nonmarine and onlap the basal unconformity.

In central Kansas, the formation was deposited almost entirely in fluvial environments with only the upper part deposited by deltas. Sandstones within the Dakota Formation in this area are lense-shaped in cross section and elongated east to west. Individual channel sandstones are about 30 ft thick and up to <fr>1/4</>-mi wide. Large sandstone bodies over 100 ft thick and up to 2 mi wide are an amalgamation of several individual channel sandstones. Channel localization was controlled by east-west-trending faults. Interconnectedness of sandstone bodies is evaluated by constructing cross sections from isopach maps of the sequences and sandstone bodies. Sandstone body connections are located at the intersection of trends. In summary, the development of a regional sequence-stra igraphic framework assists in the interpretation of depositional systems and the evaluation of sandstone body morphology and interconnectedness.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990