Abstract

In Late Pennsylvanian and Early Permian time, the Palo Duro basin was part of a relatively deep seaway that extended northward from the Midland basin into the Mid-Continent. Deep central basinal areas were surrounded by massive, carbonate shelf margins and shallow shelf terrain.

In the southeastern Palo Duro basin, high-constructive, elongate delta systems were present and deposited quartzose sand derived from eastern sources (Wichita Mountains). Late Pennsylvanian and early Wolfcampian delta-front sandstones (>200 ft thick) occur on the basinward side of the shelf margin, suggesting that deltas prograded beyond the shelf margin and into deep water. Later, as terrigenous sediment supply was sharply reduced, the shelf margin prograded basinward over deep-water delta facies. During middle Wolfcamplan time, clastic input was increased and high-constructive deltas once again prograded into the southeastern Palo Duro basin. However, progradation was not as extensive as earlier episodes and most delta-front sands were deposited in shallow shelf environments. Consequently, shallow-water conditions precluded formation of thick delta-front sequences in shelf environments.

Upper Pennsylvanian-Lower Permian deltaic sandstones in the southeastern Palo Duro basin are subarkoses. Porosity ranges from 0 to 13% and averages 4.8%. Both primary and secondary (leached feldspars) porosities are present. Cementation began with clay coats, followed by quartz overgrowths. Fe-rich dolomite replaced margins of framework grains and filled most remaining pores. Timing of feldspar leaching and kaolinits cement is presently unknown.