PALEOECOLOGICAL PATTERNS AT THE COAL-ROOF SHALE TRANSITION

The transition from a peat-forming to a clastic environment can represent several different scenarios. It has been hypothesized that the roof-shale floras differ in composition from coal-ball floras and palynofloras of the coal, but also that plant material found within roof-shale assemblages directly reflect the plants that grew on the underlying peat and that the spatial variation in species diversity and quantity of plant material represents heterogeneity of the original peat swamp community. This polarity of opinions needs further investigations at many different sites in order to establish a more natural picture of the deposition and burial of peat and the formation of clastic swamps of the Carboniferous.

The project in SW Indiana provides a more extensive Late Pennsylvanian peat-forest data set collected throughout the coal and roof-shale flora. The Lower Block coal in the Illinois basin is well exposed in surface mines and well studied in other respects. This solid foundation of knowledge enabled the pursuit of more specialized questions. The Lower Block coal seam is located at the base of the Brazil Formation, Racoon Creek Group, in south-west Indiana and is Bolsovian (Westphalian C) in age. In addition to coal palynoflora, there is an extensive roof-shale flora above the Lower Block coal containing lycopsids, sphenopsids, ferns, pteridosperms, and cordaites. These conditions provided the opportunity to examine quantitatively the paleoecology and compare it to the previously studied Langsettian (Westphalian A) Blue Creek coal assemblage from the Black Warrior basin in Alabama. The comparison gives insight into the differences of changing forest structures during two times with slightly different climate and two places in different geotectonic settings.