ABSTRACT

The Red Fork sandstone was divided into the Upper and Lower Red Forks which are separated by a consistent marker bed. The Red Fork interval thickens markedly across the study area from 250 feet in the northeast to over 1300 feet in the southwest. Most of the thickening is within the Lower Red Fork. A structural contour map of the lowermost Red Fork marker bed shows distinct steepening of dip in a southeast-trend. The Lower Red Fork format thickens abruptly southwestward along this trend. These data are the basis for interpretation of a hinge line during deposition of the Lower Red Fork.

The Lower Red Fork is believed to have been deposited in shelf-to-basin transitional terrain. Sands were located in delta-front, submarine-channel fill and possibly submarine-fan terrain. The lack of marked thickening of the Upper Red Fork indicates an absence of a hinge line. Main gas producing sands are located in the East Clinton Field which is believed to be the site of the maximal progradation of a deltaic complex. Evidence for these interpretations was obtained from cores, basic geometric relationships of stratigraphy, and from the general geologic setting.

Sandstones of the Lower Red Fork are sublithic to lithic arenites; the Upper Red Fork is sublithic arenite. The dominant lithic fraction is detrital mud fragments. The main diagenetic alterations of both the Upper and Lower Red Fork sandstones were destruction of primary porosity by compaction and cementation. Dissolution chiefly of mud fragments has produced well-developed secondary porosity. Clays of the Lower Red Fork mainly are secondary chlorite; clays of the Upper Red Fork mostly are secondary kaolinite.

Present oil and gas production from Red Fork sandstones is most abundant from localities on the paleoshelf.