Stratigraphic Analysis of Key Beds in Cyclothems in the Staunton Formation (Middle Pennsylvanian) in the Clinton Area, West-Central Indiana

Abstract

ABSTRACT During a coal resources study in the Clinton area, covering 260 square miles, the author found that six unnamed and little understood coal beds that lie within an average vertical interval of 62 ft in the Staunton Formation (middle Pennsylvanian) were difficult to identify and correlate. A study of these beds was made, using data from numerous outcrops and coal test holes. These six coals resemble one another in physical appearance and spore content, but each occurs in a separate cyclothem. The cyclothems are designated informally A through F in ascending order. The key beds, nearly identical lithologically in each cyclothem, vary in thickness and are discontinuous in geographic distribution. A table and six histograms summarize the results of the stratigraphic analysis of continuity and thickness of key beds (underclay-limestone, underclay, coal, carbonaceous black shale, and marine limestone) and of the intervals between the Seelyville Coal Member (III), which marks the top of the Staunton, and each of the six unnamed coals. Limestone is absent in cyclothems A and F; the two types of limestones gradually increase in distribution from cyclothem E through cyclothem B; the five key beds coexist with most frequency in cyclothem B; cyclothem D contains the most widespread underclay, coal, and black shale; coal is the most common key-bed lithology. Coal D is the most common key-bed unit and yet is found in only 70 percent of the stragitraphic sections. More than half of the key beds occur in 50 percent or fewer of the stratigraphic sections. These facts indicate the high degree of discontinuity of lithologic units that caused the difficulty in identification and correlation. Tentative correlation of the six unnamed coal beds in the Clinton area is made from generalized geologic columns in other areas, which are published, in large part. All six coals are correlated from Dubois County, and from Fountain, Warren, and northern Vermillion Counties; five are correlated from the Brazil Quadrangles, Clay County: four from Spencer County; and three from near Oakland City, Gibson County.