Potentially economic, low-permeability (tight), gas-bearing sandstone reservoirs in the Uinta, Piceance Creek, and greater Green River basins are found in predominantly nonmarine rocks of Late Cretaceous, Paleocene, and Eocene ages. Accurate subsurface correlations are essential to the estimation of reserves and to the understanding of the nature of reservoirs; but, in the absence of paleontologic data, the nonmarine rocks historically have proven to be difficult to correlate with geophysical logs. Pollen, spores, and other plant micro-fossils recovered from surface exposures and from boreholes have provided data on the age of the rocks and have facilitated accurate biostratigraphic correlation of surface and subsurface sections.

The rocks generally represent sediments deposited in lacustrine, alluvial-fan, braided- and meandering-stream, delta-plain, lagoonal, and littoral-marine environments. The nature of source, reservoir, and trapping units in these rocks is commonly, in part, a function of the depositional environment of the units. Palynologic data in combination with sedimentological, petrographic, mineralogic, geochemical, and other paleontologic data, all derived from the same samples, have been used to refine interpretations of lithofacies and to determine the paleoclimate, paleoecology, and paleoenvironment

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at several key reference sections in the study area.

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