Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence

Wetland-Dryland Vegetational Dynamics in the Pennsylvanian Ice Age Tropics

“…This seasonality becomes apparent even during the wet phases of glacial-interglacial cycles beginning near the Desmoinesian/Atokan (Bolsovian-Asturian) boundary, revealed by changes from ombrotrophic domed peats to rheotrophic planar peats (Cecil 1990), associated with increases in coal sulfur (Cecil et al 1985;Neuzil et al 2005) and with changes in sandstones, indicating a transition from wet low-seasonality climates to greater seasonality (Bertier et al 2008). The wetland flora also undergoes many compositional and dominance-diversity changes at this same time (Pfefferkorn and Thomson 1982;Phillips and Peppers 1984;Peppers 1996), much more abruptly than the seasonally dry flora.…”

“…However, comparisons at a broader level show consistent differences in quantitative aspects of composition, such as the more common occurrence of the lycopsid Sigillaria or the greater dominance of pteridosperms (King et al 2011;Wagner and Castro 2011) in mineral substrate wetlands than in peat swamps. Some larger-scale patterns, such as the qualitative rise in importance of the marattialean fern clade in wetlands of the late Middle Pennsylvanian (Phillips et al 1974;Pfefferkorn and Thomson 1982;Phillips and Peppers 1984;Peppers 1996;Dimitrova et al 2005;Dimitrova and Cleal 2007) or the decline in wetland cordaitales (Phillips and Peppers 1984;Raymond et al 2010), are detectable in both forms of preservation and appear to occur at approximately the same time in both, despite differences in quantitative aspects (for the rise in tree ferns, cf. Pfef-ferkorn and Thomson 1984or Peppers 1996; the timing is the same even though quantitative expression differs).…”

“…Such restrictions certainly became more severe and the isolation of populations ever greater during the later Middle Pennsylvanian (Desmoinesian) and early Late Pennsylvanian (Missourian), when much evidence indicates increasing aridity in the tropical realm (wets less wet, drys more dry), possibly tied to extensive melting of polar ice Rygel et al 2008). In the midst of this interval, there is a great turnover in the flora, accompanied by the loss of most of the dominant Middle Pennsylvanian lycopsids (Phillips et al 1974;Heckel 1991a), a change in the common tree ferns (Lesnikowska 1989), and many changes in the pteridosperm component of wetlands (Phillips 1981;Phillips and Peppers 1984;DiMichele et al 2006a;Wagner and Á lvarez-Vá zquez 2010). From a life-history viewpoint, perhaps the least likely to produce new species during these periods of habitat contraction and isolation were the arborescent lycopsids.…”

Palaeoecology of Macroneuropteris scheuchzeri, and its implications for resolving the paradox of ‘xeromorphic’ plants in Pennsylvanian wetlands

“…Various lines of evidence -geochemistry (Cecil et al, 1985;Greb et al, 2002), palynology (Eble et al, 2001;Eble, 2002;Eble et al, 2003), plant megafossils (Pfefferkorn and Thomson, 1982;Phillips and Peppers, 1984;Cleal et al, 2009), the distribution of coals (Phillips and Peppers, 1984;Schutter and Heckel, 1985) and paleosols (Schutter and Heckel, 1985;FalconLang et al, 2009;DiMichele et al, 2010;Falcon-Lang and DiMichele, 2010) -indicate that this was a time of much more seasonal climates at all phases of any given glacial-interglacial cycle. Peat swamps appear to have been largely planar, peats (coals) were of higher sulfur content, and vertic paleosols were increasingly common in those rocks between and beneath coals.…”

“…Major compositional and structural changes took place in wetland tropical landscapes across the Desmoinesian-Missourian boundary (Middleto-Late Pennsylvanian: Falcon-Lang et al, 2011a). Considerable evidence (e.g., Phillips and Peppers, 1984;Schutter and Heckel, 1985;Cecil, 1990;Winston, 1990;DiMichele et al, 2001;Fielding et al, 2008aFielding et al, , 2008bHeckel, 2008;Rygel et al, 2009;Bishop et al, 2010) suggests a shift in the climate cycle to increased overall dryness (greater seasonal dryness during both the drier intervals and wetter intervals of glaciogenic cycles) at this time, a change reflecting a period of intensified global warming and ice melting in the south polar regions. Beginning at the time of this major climatic shift, the distributional pattern of this species documents continued ecological confinement to the wettest, swampy environments of the Late Pennsylvanian, particularly those associated with some clastic influx.…”