No Major Stratigraphic Gap Exists Near the Middle-Upper Pennsylvanian (Desmoinesian-Missourian) Boundary in North America

Abstract

Interregional correlation of the marine zones of major cyclothems between North America and eastern Europe does not support assertions that a major stratigraphic gap exists between the traditional regional Desmoinesian and Missourian stages in North America. Such a gap was previously proposed to explain an abrupt change in megafloral assemblages in the northern Appalachian Basin and by extension across all of North America. Conodont-based correlation from the essentially complete low-shelf Midcontinent succession (distal from the highstand shoreline), through the mid-shelf Illinois Basin, to the high shelf of the Appalachian Basin (proximal to highstand shoreline) demonstrates that all major -400 kyr cyclothem groupings in the Midcontinent are recognizable in the Illinois Basin. In the Appalachian Basin, however, the grouping at the base of the Missourian is represented only by paleosols and localized coal. The immediately preceding grouping was removed very locally by paleovalley incision, as is evident at the 7-11 Mine, Columbiana County, Ohio, from which the original megafloral data were derived. At the few localities where incised paleodrainage exists, there may be a gap of -1000 kyr, but a gap of no more than ~600 kyr occurs elsewhere in the Appalachian Basin at that level and its magnitude progressively decreases westward into the Illinois (-300 kyr) and Midcontinent (<200 kyr) Basins. Thus, while a gap is present near the Desmoinesian-Missourian boundary in North America, it is typically more than an order of magnitude smaller than that originally proposed and is similar to the gaps inferred at sequence boundaries between cyclothems at many horizons in the Pennsylvanian of North America.

Wetland-Dryland Vegetational Dynamics in the Pennsylvanian Ice Age Tropics

“…For example, Elrick et al (2013) report tidal mudflat floras during early interglacial stages, associated with the onset of continental flooding. The dominant plants in these weakly seasonal wetlands are pteridosperms, tree ferns, and the lycopsid tree Sigillaria, suggested to presage major compositional changes that occurred in wetlands at the Middle-Late Pennsylvanian boundary in response to what appears to have been a period of anomalously dry climate (Phillips et al 1974;Falcon-Lang et al 2011a). Similar floras were found preserved in small channels between both Middle and Late Pennsylvanian coal beds in the Illinois Basin.…”

“…Farther east, into the Eastern Interior (Illinois) and Appalachian Basins, marine incursions from the west were progressively less common, and both the number of cycles and the extent of marine influence diminished, resulting in fewer recognizably distinct 100,000-yr cycles. Larger 400,000-yr megacycles, into which the 100,000-yr cycles are grouped, are nearly always recognizable throughout the entire region (Heckel 2008;Belt et al 2011;Falcon-Lang et al 2011a). …”

“…2, 6A). Near the Middle-Late Pennsylvanian boundary, there was a major floristic turnover (Phillips et al 1974;Falcon-Lang et al 2011a), with tree ferns becoming the dominant elements in peat-forming swamps and codominants in many other wetland settings (figs. 2, 6B).…”

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

“…. Distribution and relative abundance of Macroneuropteris scheuchzeri in U.S. stratigraphic successions studied for this analysis, compared with its range in Europe, correlated via global and regional time scales (using Heckel et al, 2007;Davydov et al, 2010;Falcon-Lang et al, 2011a). Pennsylvanian series boundaries are shown at traditional Appalachian levels.…”

“…Pennsylvanian series boundaries are shown at traditional Appalachian levels. Global stage boundary dates follow Peterson (2011), while North American stage boundary date estimations follow Heckel (2008) and Falcon-Lang et al (2011a). Dotted boundary for top of Virgilian shows previous level of Virgilian-Wolfcampian boundary (at base of Admire Group) used in older literature.…”