A significant paleobotanical shift is defined along

A significant paleobotanical shift is defined along the Mississippian-Pennsylvanian boundary by
the dissappearance of the Namurian A index flora, and the first occurrence of more diverse plant
species adapted to a swamp habitat (Pfefferkorn and Gillespie, 1981; Wagner, 1982; Jennings,
1986). Plant fossils in the lowermost Pennsylvanian units in the Appalachians (Fig. 3.2) suggest
a correlation with the Namurian B strata of Europe (Kosanke, 1984; Pfefferkorn and Gillespie,
1982). The major Mississippian-Pennsylvanian (mid-Carboniferous) vegetational change is
seemingly tied to a global climatic change (from semiarid to wet conditions) within the
paleoequatorial belt (Gastaldo et al., 1996).
Figure 3.3- Paleogeographic reconstruction for Late Mississippian (Mid-Carboniferous) time
redrawn from Cleal and Thomas (1996) after Scotese (1986). The central Appalachian
Basin occupied a near-equatorial (5-10 degrees south) paleolatitude during the early stages
of Alleghenian orogenesis.
LITHOLOGIC INDICATORS OF PALEOCLIMATE
Vertic and Calcic Paleosols
Vertically stacked paleosols constitute a significant proportion (50% or more) of the
terrestrial redbeds in the Hinton and Bluestone formations (Fig. 3.2). These red beds are
interpreted to represent fluvial channel and floodplain deposits upon a low-relief coastal plain
(Miller and Eriksson, in review). The red vertisols are characterized by thick (up to 2 m), clay-
rich B horizons with well-developed angular-blocky pedogenic fabrics and slickensides. Root
traces are locally present as downward branching, gray-green reduction haloes. Isolated
carbonate nodules up to 3 cm in diameter are locally developed. In rare cases, coalesced
carbonate nodules occur as discontinuous horizons within the soil profile.

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The vertisols and calcic vertisols are suggestive of seasonally dry climatic conditions in
the Appalachian Basin during much of the Late Mississippian (Cecil, 1989; Cecil, 1990).
Modern vertisols develop in strongly seasonal climates (4 to 8 dry months per year) in areas
where the water table is low (Ahmad, 1983; Gibling and Bird, 1994). Geochemical analysis of
equivalent paleosols from the Pennington Formation in Tennessesse has shown that the Late
Mississippian climate in the Appalachian region was hot, and markedly seasonal with yearly
precipitation similar to that in present-day south Texas (Caudill et al., 1996).
Lacustrine Limestones
Laterally continuous carbonate units up to 1 meter in thickness are interbedded with the
vertisols. Ostracodes and bivalves are sparsely distributed within these units, which, in thin
section, are comprised of dense micrite with a weakly laminar or peloidal fabric. These
carbonates commonly show evidence of pedogenic disruption and grade upward into vertisols
(cf. Tandon and Gibling, 1997).
The bedded carbonates are interpreted as lacustrine limestones that developed as a result
of episodic inundation of the coastal floodplain. The lack of root traces and close association
with vertisols suggests that the lacustrine carbonates developed under seasonal climatic