THE BLUE CREEK COAL MIRE: A POLAROID PICTURE IN TIME

The Early Pennsylvanian (Langsettian) Blue Creek mire preserved by tidalites in the Mary Lee coal cycle, Black Warrior basin, consists of both standing, erect canopy and subcanopy trees, and the ultimate forest litter horizon, including lianas, within 10 cm of the coal-clastic interface. Forest-litter burial is estimated to have been less than one year; burial of standing vegetation on the order of decades. Exploitation in the Cedrum mine, Walker County, AL, over a 5-month period allowed for biomass analysis of the mire in 17 sites over an area of approximately 0.44 km². Presence/absence data were acquired for variously sized quadrats of ripped roof shale at 2-3 stratigraphic horizons within the bed, resulting in a raw data set consisting of 46 form taxa. Lycopsid, calamitean, and pteridopserm data were transformed into a biological data set in which photosynthetic, reproductive, and subterranean form taxa were apportioned in relation to trunk/stem taxa. Raw data for pteridophyte and sphenophyllalean taxa were considered equivalent to biological data. Data were analyzed using ternary diagrams, ANOVA on ranks, cluster analysis (Spearman rank order coefficient), Nonmetric MultiDimensional Scaling, and plotted spatially following Kriging. Three communities can be identified based upon synusial relationships of canopy, understory, and groundcover/liana taxa – those with >60% canopy, 50-60% canopy, and <50% canopy – and these are spatially partitioned across the mire. Within these, sites with 50-60% canopy may be either groundcover/liana poor or rich, with identifiable transitional sampling sites. When systematic data are clustered, five associations have been identified, again spatially assembled within parts of the mire. The vegetational mosaic is complex across the mire, with coexisting taxa that often are believed to be indicative of specific edaphic conditions. In general, lepidodendrids coexisted with an understory of neuralethopterids, whereas Lepidophlois and sigillarians coexisted with higher proportions of groundcover/lianas. NMDS results identify similar patterns. Hence, major lycopsid groups had wider ecophysiological tolerances than previously recognized.