Abstract

This paper summarizes the results of a field study of the Simpson Group (Middle Ordovician) in the Salina basin of central Kansas. The Simpson of Scully field is a thin interval of interbedded sandstones and mudstones that is unconformably bounded by the carbonates of the Arbuckle Group and Viola Formation. The lithology and stratification of the Simpson Group indicates that it was deposited in coastal tidal flat and inner shelf environments. Six facies are recognized in the Simpson: A and B, which are composed of mudstones and sandy mudstones deposited on muddy and mixed tidal flats; C, D, and E, which consist of sandstones deposited in tidal creeks of varying size; and F, which consists of transgressive inner shelf sands.

The Simpson of Scully field consists of three sandstone intervals (Facies C, D, E, and F) separated by two intervals of Facies A and B mudstones. The sharp basal contact between the Simpson and the underlying Arbuckle carbonates, the vertical succession of sandstone and mudstone facies in the Simpson, and the lateral extent of these same facies across the field, suggest that the Simpson is a single sequence consisting of a thin basal transgressive system tract overlying a sequence boundary and an upper highstand system tract. Generally, the tidal channel sandstones of the highstand system tract are reservoirs in the Simpson of Scully field. They reach a maximum thickness of 12 ft (3.6 m), and have porosities of 12 to 20% and permeabilities of several hundred millidarcies. The dominant trapping mechanism for these reservoirs is an anticlinal closure.