Abstract: Identification of Major Distributary-Channel Systems of Desmoinesian (Pennsylvanian) Age in Illinois
James E. Palmer
As early as 1914 a segment of a large distributary channel in western Illinois in rocks of Desmoinesian (Pennsylvanian) age was mapped and described. Subsequently geologists of the Illinois State Geological Survey identified many other areas where large channel sandstones were present at the horizons of the Harrisburg (No. 5) and Herrin (No. 6) Coal Members of the Carbondale Formation. By 1950 it had become clear that the mapped segments of sandstone at the horizon of No. 6 coal were parts of much larger channel systems, which crossed Illinois during Desmoinesian (Pennsylvanian) time. A map of No. 6 Coal reserves of Illinois published in 1950 shows a large number of such segments, some many miles long. Additional work by many geologists provided data on missing links of t e channel systems. The culmination of these efforts over many years was the identification of a complex distributary system at the horizon of the No. 6 Coal. This system is more than 200 mi (320 km) long and extends through much of central and southern Illinois. Low-sulfur coal deposits of Illinois commonly are overlain by a gray shale that is thought to be related in origin to this distributary system. Parts of the distributary system clearly are due to erosion and subsequent filling by coarse and fine clastic sediments. Available evidence suggests that in other areas the distributary channels were contemporaneous with coal swamps. The Illinois Geological Survey is continuing studies to identify additional components of this system and to determine the influence of the system on deposit on of coal beds of Illinois.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC