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Open accessJournal ArticleDOI: 10.7203/SJP.20.1.20544

Dicranophyllum glabrum (Dawson) Stopes, an unusual element of lower Westphalian floras in Atlantic Canada

02 Mar 2021-Vol. 20, Iss: 1, pp 7-13
Abstract: Rare but well preserved repeatedly dichotomised leaves, apparently in a single plane, are identified with Dicranophyllum, an unusual gymnosperm attributed to a special order, the Dicranophyllales. The specimens recorded here from the “Fern Ledges” at Saint John, New Brunswick are from lower Westphalian (Langsettian) strata, which is a low horizon for this genus, which is best known from the Stephanian and Lower Permian. Comparison is made with various species described from the Carboniferous in Europe.

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Topics: Carboniferous (52%), Westphalian sovereignty (51%), Permian (50%)
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Journal ArticleDOI: 10.1016/J.COAL.2010.01.007
Abstract: Wetland floras narrowly define perceptions of Pennsylvanian tropical ecosystems, the so-called Coal Age. Such wetlands reflect humid to perhumid climate, leading to characterizations of Pennsylvanian tropics as everwet, swampy. These views are biased by the high preservation potential of wetlands. Sedimentation patterns, paleosols, and fossil floras indicate the presence of vegetation tolerant of subhumid to dry–subhumid, perhaps semi-arid climate in basins between peat formation times. Understanding the significance of this seasonally-dry vegetation has suffered from conceptual and terminological confusion. A clearer view has emerged as models for framing the data have improved. Basinal floras typical of seasonally-dry conditions, relatively low soil moisture regimes, are well documented but mainly from isolated deposits. Some of the earliest, dominated by primitive pteridosperms (“Flozfern” floras), occur in clastic rocks between European Early Pennsylvanian coal beds. Later Early Pennsylvanian, fern–cordaitalean vegetation, different from coal floras, is preserved in marine goniatite bullions. Conifers are first suggested by late Mississippian Potoniesporites pollen. About the same time, in North America, broadleaf foliage, Lesleya and Megalopteris occur in basin-margin settings, on drought-prone limestone substrates. The best known, xeromorphic floras found between coal beds appear in the Middle through Late Pennsylvanian, containing conifers, cordaitaleans, and pteridosperms. The Middle Pennsylvanian appearances of this flora are mainly allochthonous, though parautochthonous occurrences have been reported. Parautochthonous assemblages are mostly Late Pennsylvanian. The conifer flora became dominant in western and central Pangaean equatorial lowlands in earliest Permian. Location of the humid–perhumid wetland flora during periods of relative dryness, though rarely discussed, is as, or more, perplexing than the spatial location of seasonally-dry floras through time — wetland plants had few migratory options and possibly survived in small refugia, within and outside of basins. Coupled oscillations in climate, sea level, and vegetation were driven most likely by glacial–interglacial fluctuations, perhaps controlled by orbital cyclicity.

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Topics: Pennsylvanian (62%), Carboniferous (53%), Goniatite (51%) ... show more

121 Citations


Journal ArticleDOI: 10.1016/J.REVPALBO.2013.09.006
Abstract: The distribution and community ecology of Early Pennsylvanian (middle Bashkirian, Langsettian) vegetation on a seasonally dry fluvial megafan is reconstructed from plant assemblages in the Tynemouth Creek Formation of New Brunswick, Canada. The principal motif of the redbed-dominated succession consists of degraded interfluve surfaces overlain by coarsening-upward aggradational sequences, a pattern that expresses the approach of an active channel system over a part of the megafan where landscape stasis prevailed. Accrual under a (dry) subhumid tropical climate, typified by a protracted dry season and a short wet season with torrential rainfall, resulted in Vertisol-like paleosols, episodic discharge and sedimentation, shallow channels incised into partially indurated interfluve strata, and scattered ‘waterhole’ deposits. Plant fossils, including many upright stumps, are preferentially preserved above paleosol-mantled interfluve surfaces, recording the inundation of a vegetated landscape. Quantitative analysis of 41 census-sampled megafloral assemblages collected in facies context indicates that a cordaitalean-rich flora dominated the dryland ecosystem. Less common was a wetland flora typical of tropical lowlands at coeval localities, comprising medullosalean pteridosperms and calamitaleans with rare ferns and lycopsids. ‘Enigmatic dryland’ plants, taxa of ambiguous affinity including Megalopteris, Pseudadiantites, and Palaeopteridium, were rare but surprisingly diverse. The taphonomic and sedimentologic context of fossiliferous horizons indicates that low-diversity, old-growth stands of gigantic cordaitaleans blanketed distal interfluves and inactive parts of the megafan, environs marked by limited deposition and extended paleosol development. Small patches of the pteridosperm-dominated wetland flora were interspersed within the dense cordaitalean forest, restricted to landforms that acted as waterholes during the dry season, such as perennial lakes, stagnant ponds, and seasonally active interfluve channels. In contrast, cordaitaleans and wetland plants formed mixed communities in disturbance-prone proximal interfluves and fluvial tracts, where more flooding and sedimentation resulted in less moisture-stressed conditions and a wider range of habitable landforms. Dense calamitalean groves persisted alongside fluvial channels, and an array of wetland plants occupied seasonally active abandoned channels that retained water throughout the year (waterholes). Rare ‘enigmatic dryland’ species were more prevalent in flood-prone fluvial tracts, and were dispersed within cordaitalean-dominated and wetland communities rather than forming discrete, compositionally unique patches. Although frequently characterized as ‘extrabasinal’ or ‘upland’ elements, this study confirms that these unusual plants occupied Pennsylvanian tropical lowlands during episodes of climatic drying.

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Topics: Pennsylvanian (52%), Fluvial (51%), Vegetation (50%)

66 Citations


Journal ArticleDOI: 10.1016/J.PALAEO.2005.09.005
Howard J. Falcon-Lang1Institutions (1)
Abstract: The vegetation ecology of Pennsylvanian upland/dryland regions is poorly known, despite its evolutionary significance. Here, fossil plant assemblages are described from well-drained alluvial fan/piedmont deposits in the uppermost Boss Point and Tynemouth Creek formations (late Yeadonian–Langsettian), southern New Brunswick. Beds record the northward building of a large alluvial fan complex over alluvial plain deposits in response to near-continuous sourceland uplift. Proximal alluvial fan environments, characterized by sheetfloods and braided streams, were dominated by large cordaitalean trees, medullosan pteridosperms, ferns, and calamiteans. Distal alluvial fan environments, where braided stream and levee/splay sedimentation predominated, were covered by similar vegetation, together with lycopsids in localized poorly drained depressions. Calamitean thickets were particularly widespread in rapidly aggrading settings on the distal fan. Well-drained alluvial plains beyond the fan toe were characterized by axial braided rivers containing cordaitalean trunks transported from proximal settings. Piedmont vegetation is otherwise poorly resolved. All studied plant assemblages are of low- to medium-diversity, and dominated by the remains of a single group, cordaitalean seed plants. Such dominance-diversity characteristics, together with the presence of charcoal, the product of wildfire, imply that Pennsylvanian upland/dryland vegetation experienced water-stress and that the seed habit was integral to successful colonization.

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Topics: Alluvial fan (63%), Alluvial plain (60%), Pennsylvanian (54%) ... show more

47 Citations


Journal ArticleDOI: 10.1016/J.PALAEO.2010.03.037
Abstract: article The spatial heterogeneity and community ecology is reconstructed for Late Pennsylvanian (Stephanian B sensu lato) vegetation preserved in La Magdalena Coalfield, northwestern Spain. The ≈1500 m thick basin- fill accumulated rapidly along the margin of the Variscan Mountains, and the principal sedimentary facies comprise the deposits of large braided streams that dissected extensive wetlands containing large lakes. Quadrat analysis of 93 mostly (par)autochthonous megafloral assemblages indicates that pteridosperms and ferns dominated communities, with three taxa (Pecopteris spp., Callipteridium pteridium, and Neuropteris ovata) accounting for ≈58% of all plant remains. Sphenopsids and lycopsids were less common but widespread, and cordaitaleans were rare. At the local scale, laterally exposed bedding planes reveal that communities comprised a complex and heterogeneous mosaic of species. At the landscape scale, ecological gradients are evident from multivariate analyses of quadrats in a facies context. Pteridosperms dominated marginal wetlands adjacent to steep basin margins. A greater proportion of ferns occurred in or adjacent to

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Topics: Pennsylvanian (53%), Pecopteris (53%), Neuropteris (53%)

42 Citations


Journal ArticleDOI: 10.1144/0016-76492006-189
Abstract: The Pennsylvanian Lancaster Formation (‘Fern Ledges’) of Saint John, New Brunswick, Canada contains a world-famous fossil biota. Largely unstudied since the works of Hartt, Dawson, Matthew, and Stopes in the mid-nineteenth to early twentieth century, we present new data concerning biostratigraphy, taxonomy, palaeoenvironments, and palaeoecology. Megafloral assemblages suggest a mid- to late Langsettian age for the succession, making it approximately coeval with the classic Joggins Formation of nearby Nova Scotia. Facies analysis suggests deposition on a tectonically influenced coastal plain whose braided channels drained into a shallow brackish gulf. Most of the historical fossil collections are derived from flooding surfaces formed by abrupt subsidence events along the coastline. Three communities are recognized. Phoronids, crustaceans, and xiphosurans lived in brackish coastal waters. A lowland community of gastropods, insects, arachnids, and myriapods inhabited coastal forests. Coastal vegetation was dominated by shrubby cordaitaleans and pteridosperms whereas ferns, sphenopsids, and lycopsids were rare. An upland or dryland community, discernible from allochthonous assemblages, comprised forests of giant cordaitaleans, archaic pteridosperms, and plants of uncertain affinity.

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Topics: Coastal plain (53%), Pennsylvanian (52%), Carboniferous (50%)

25 Citations


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