Paleoecological analysis of two Early Pennsylvanian mineral-substrate wetlands

The biomass within two Early Pennsylvanian (Langsettian [Westphalian A] equ ivalent) penecontemporaneous swamp communities was sampled quantitatively t o obtain an estimate of the taxonomic contribution to each assemblage. Bloc ks of organic-rich shale were removed from a elastic parting within the Bla ck Creek Coat, and similar to 0.5-m(2) siltstone quadrats were chain-sawed from a elastic swamp community directly above the Bear Creek Coal. Bedding planes were exposed, and the surface areas for each taxon per bedding surfa ce were measured and used as proxies for biomass contribution in each local ity. Biomass over a combined area of 5.47 m(2) was assessed for the Black. Creek Coal parting; biomass covering an area of 9.70 m(2) was evaluated for the assemblage preserved above the Bear Creek coal. In addition to calcula ting standard diversity indices, this data set was analyzed using cluster a nalyses and non-metric multidimensional scaling (NMDS) to differentiate var iations within the general flora. Low species diversity characterizes both floras. Diversity indices for both assemblages are very similar, indicating essentially no difference in asse mblage composition, despite the difference in edaphic conditions. The Bear Creek Coal wetlands show greater variation in species content, while the mi neral-enhanced peat of the Black Creek Coal overlaps this species diversity within a slightly more restricted range of variation. Cluster analysis pro duced 5 stable clusters, whereas three dimensions of the NMDS analysis prov ided the best fit to explain the variation among the samples. The dimension s are interpreted as representing abundance of (1) arborescent lycopsids, ( 2) arborescent and climbing sphenopsids, and (3) pteridosperms. The plant c ommunity preserved within the elastic parting of the Black Creek Coal is co mparable to that of the community found above the Bear Creek Coal. Hence, v egetation that colonized mineral-substrate soils in Early Pennsylvanian coa stal lowlands, whether in peat or non-peat accumulating settings, are very similar. The dominance of pteridosperms in these depositional regimes appea rs to remain stable throughout the Early and Middle Pennsylvanian and port ends community replacements in the Late Westphalian D some 8-10 million yea rs later.