West-central Indiana Research Articles

Sedimentologic and Reservoir Characteristics of Abandoned Delta Distributary: ABSTRACT

An abandoned delta distributary of the Bethel-Sample Formations, a very small part of the Michigan River system that supplied sand and mud to and across the Illinois basin during the Late Mississippian, has been delineated for 15 mi in west-central Indiana by outcrop mapping and shallow drilling. This elongate sandstone body has sharp and relatively straight boundaries, averages 2 mi in width, and has a maximum thickness of 145 ft. Along its axis of maximum thickness the sandstone body fills a shallow channel cut in the underlying thick limestone sequence. Cross-bedding and ripple marks constitute its two principal facies and form as many as five fining-upward cycles. The ripple-bedded facies is very fine grained and much less permeable than the generally coarser grained cross-bedded facies. Cross-bedding dips uniformly southeast except in the very basal part of the sandstone body where the orientation is northwest--considered to be the product of up-channel tidal currents that introduced sparingly glauconitic marine sand into the shallow channel prior to deposition of the flu ially derived sand. Decementation by groundwater percolating downward into the underlying carbonate has greatly increased the permeability of the sandstone body. The cross-bedded facies has an average permeability of 400 md except within 20-30 ft of the base where permeability values in excess of 2,000 md occur. Intra-sandstone-body channeling plus the distribution of the low permeability ripple-bedded facies modify permeability. Comparable buried reservoirs should occur where an ancient distributary system is truncated by an unconformity with 100-200 ft or more of relief. Permeability will be enhanced greatly in such reservoirs if they are underlain by limestone and if the limestone-sandstone contact was above stream level during the development of the unconformity. End_of_Article - Last_Page 532------------

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

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.

Notes on Some Salamanders of West Central Indiana

Notes on Some Salamanders of West Central Indiana