Dryland vegetation from the Middle Pennsylvanian of Indiana (Illinois Basin): the dryland biome in glacioeustatic, paleobiogeographic, and paleoecologic context

Abstract

A macrofloral assemblage dominated by elements of the Euramerican dryland biome is described from the Brazil Formation in Clay County, Indiana (Illinois Basin). Fossils were recovered from a thin heterolithic unit between a shallow-marine bed and the paleosol beneath the Minshall Coal, a Middle Pennsylvanian succession deposited near the Atokan-Desmoinesian and Bolsovian-Asturian boundaries. Sedimentological indicators imply accumulation under a seasonal climate, including interbedded siltstone and sandstone deposited during flashfloods, intraclasts eroded from local sources, and charcoal produced by wildfires. The macrofloral assemblage is consistent with a dryland setting, being dominated by large, coriaceous gymnosperm leaves with mesic to xeric traits, includingCordaitesspp. indet.,Lesleyasp. indet., andTaeniopterissp. cf.T. multinervia. Sphenopsids and ferns typical of the wetland biome are rare. In contrast, the microfloral assemblage is dominated by fern spores, with lesser lycopsid spores and cordaitalean pollen. The succession indicates that the dryland biome predominated during late regression, prior to the onset of perhumid conditions that resulted in peat accumulation at late lowstand. However, the abundance of palynomorphs from wetland vegetation implies gradual fragmentation of the prevailing dryland flora and replacement by the wetland biome in the transition to glacial maximum. The taphonomic and paleobiogeographic context confirms that floras adapted to seasonal moisture deficit periodically dispersed into tropical lowlands, rather than being transported from ‘extrabasinal’ or ‘upland’ environments. The precocious occurrence ofTaeniopteris, more typical of Late Pennsylvanian and Permian floras, may be the earliest record of the fossil-genus, and exemplifies the association of derived plant taxa with dryland habitats. The predominance of broad-leaved gymnosperms with mesic to xeric characters suggests that dryland communities contained more slow-growing and long-lived plants than contemporaneous wetland floras.

Dynamic Carboniferous tropical forests: new views of plant function and potential for physiological forcing of climate

“…At the 10 5 yr timescale, there is an oscillatory pattern throughout the Pennsylvanian of relatively wetter flora characteristics of swamp habitats and those floras of seasonally dry habitats, rich with woody cordaitaleans and a variety of other taxa. This oscillation is most easily observed in coal‐bearing deposits throughout North American and European basins (Falcon‐Lang, ; Plotnick et al ., ; Falcon‐Lang & DiMichele, ; DiMichele, ; Bashforth et al ., ). In these settings and at this timescale, sea level minima (suggesting maximum accumulation of high‐latitude ice sheets) coincide with expanded tropical everwet floras near the equator, whereas maximum flooding intervals (times of maximum deglaciation) and subsequent falling stages of sea level (early glacials) are notable for the expansion of summer‐wet or seasonally dry forests (DiMichele et al ., ; Horton et al ., ; Cecil et al ., ).…”

“…Moreover, many of these plants had large biogeographic ranges across major latitudinal regions and paleoclimate zones within those regions, probably related to their wind‐ and water‐dispersal and pollination mechanisms (e.g. Wagner & Lyons, ; Tidwell & Ash, ; Moore et al ., ; Bashforth et al ., ,b). Exceptions reside mainly in the pteridosperms, where large pollen and seed sizes suggest animal mediation, resulting in somewhat more restricted geographic ranges and shorter temporal ranges/higher species turnover (Raymond & Costanza, ).…”

A new Late Pennsylvanian floral assemblage from the Douro Basin, Portugal

“…Culmitzschia frondosa var. zeilleri Florin, Culmitzschia parvifolia Florin, Dicranophyllum gallicum Grand'Eury and Dicranophyllum lusitanicum (Heer) Lima) that occur commonly in DCB strata (e.g., Correia et al, ) have not been described in Montes da Costa outcrops, but other dryland elements such as cordaitopsids (e.g., Bashforth et al, ; Cleal et al, ; Opluštil et al, ) were found in this region (Table ). They are essentially composed of remains of trunks and foliage of Cordaites .…”

“…The more common (shared) taxa are composed of wetland species, belonging to the orders Equisetales and Marattiales. Other wetland floras like lycopsids (e.g., Bashforth et al, ; Cleal et al, ; Greb et al, ; Opluštil et al, ; Wagner, ) are very poorly represented in the Douro Basin.…”

“…The study of palaeofloras has played an important role in understanding the evolution of plant communities and their ecosystems. In this sense, the study of Carboniferous–Permian floras contributes to the understanding of global‐scale continental palaeogeographic and palaeoclimatic changes, and to infer their palaeoenvironments and palaeoecologies, in the late Palaeozoic time (e.g., Bashforth, DiMichele, Eble, & Nelson, ; Bashforth, Opluštil, Drábková, Gibling, & Falcon‐Lang, ; Bashforth & Zodrow, ; Cleal, Opluštil, Thomas, & Tenchov, ; DiMichele, Bashforth, Eble, & Nelson, ; DiMichele, Cecil, Montañez, & Falcon‐Lang, ; DiMichele, Chaney, Kerp, & Lucas, ; DiMichele, Pfefferkorn, & Gastaldo, ; Falcon‐Lang, ; Falcon‐Lang & DiMichele, ; Hilton & Cleal, ; Opluštil, Šimůnek, Zajíc, & Mencl, ; Wagner, ).…”