Article

A fossil forest from Italy reveals that wetland conifers thrived in early Permian peri-Tethyan Pangea

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Abstract

In-situ fossil forests are valuable biogenic archives for the structure and setting of paleocommunities and the ecology of their organisms. Here, we present the first trees preserved in growth position in their embedding strata from the Kungurian (lower Permian) Athesian Volcanic Group, Northern Italy—one of the most extensive volcanic successions of post-Variscan Euramerica. We reconstruct the structure, rise and demise, and paleoecology of the forest based on high-resolution documentation of facies architectures and petrography, and the paleontological and taphonomic characters of the fossil content. Generally, the fossiliferous strata record a volcanotectonically controlled base-level rise in a limnic, possibly endorheic wetland basin from a low-relief volcanic landscape. The forest, preserved as calcified stem bases with roots, grew during a short interval of lake-level stasis on a small deltaic sheetflood fan. The forest comprised trees less than 5 m tall with tabular root systems adapted to the waterlogged substrate, and was buried and destroyed by mass flows following rapid submergence. These mass-flow deposits yield parautochthonous woody debris providing anatomical evidence of conifers as the major arborescent plants of the fossil forest. Our results not only elucidate the root architecture of Paleozoic conifers, but also document the ecomorphological plasticity of these plants and substantiate the presence of coniferopsids in wetlands around the Carboniferous/Permian boundary. Further, the evidence of lake perenniality in the studied succession is among the youngest known from the Permian of Europe, pointing to the highly differentiated late-icehouse impacts on continental environments in the Euramerican tropics.

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... One of the reference areas for the study of terrestrial ecosystems at low latitudes during the Cisuralian is located in the Southern Alps in northern Italy. The Athesian Volcanic Group (AG) formed by the explosive activity of a megacaldera during 289-274 Ma (e.g., Schaltegger and Brack, 2007;Visonà et al., 2007;Marocchi et al., 2008;Morelli et al., 2012) is one of the most extensive volcanic successions of post-Variscan Euramerica (e.g., Trümper et al., 2023) which preserve fossiliferous sedimentary rocks intercalated in the radiometrically dated volcanic units. The palynological studies carried out in this area focused on the qualitative study (sporomorphs taxa presence/absence) of few siliclastic sedimentary successions of the late Kungurian from the Tregiovo Doubinger, 1991, 1992;Barth and Mohr, 1994;Neri et al., 1999;Pittau in Cassinis et al., 2000) and Guncina (Hartkopf-Fröder et al., 2001) formations. ...
... The palynological studies carried out in this area focused on the qualitative study (sporomorphs taxa presence/absence) of few siliclastic sedimentary successions of the late Kungurian from the Tregiovo Doubinger, 1991, 1992;Barth and Mohr, 1994;Neri et al., 1999;Pittau in Cassinis et al., 2000) and Guncina (Hartkopf-Fröder et al., 2001) formations. Multidisciplinary studies of lithofacies, ichnofossils, plant macro-and microfossil assemblages, highlight the potential of these successions to reconstruct the complex tropical landscapes of the Kungurian and local, regional and global changes in vegetation, environment and climate (e.g., Marchetti et al., 2015;Forte et al., 2018Forte et al., , 2023Vallé et al., 2023;Trümper et al., 2023). Marchetti et al. (2022) reviewed the different fossil assemblages (ichnofossils, macroflora and microflora) from the mid-late Cisuralian continental basins in northern Italy (Orobic Basin, Collio Basin and the AG) updating their stratigraphic context and compared them with other Euramerican basins to investigate biota changes during this interval. ...
... 2,3). These sedimentary successions are subordinate in thickness compared to those of the volcanic rocks and form repeated interlayers of different alluvial and lacustrine facies mostly of local extension, marking periods of volcanic quiescence or reduced activity (Giannotti, 1963;Cassinis and Neri, 1992;Fels and Paul-Koch, 1985;Barth and Mohr, 1994;Aspmair and Krainer, 1998;Krainer and Spötl, 1998;Avanzini et al., 2007Avanzini et al., , 2010Avanzini et al., , 2012Marocchi et al., 2008;Bargossi et al., 2010;Forte et al., 2018;Trümper et al., 2023). Most epiclastic units are age-constrained by U/Pb radiometric dating obtained from under-and overlying volcanic units (Marocchi et al., 2008;Morelli et al., 2012) and are well-known for their abundant plant macro-and microfossils as well as vertebrate and invertebrate remains and vertebrate traces (e.g., Doubinger, 1991, 1992;Cassinis and Neri, 1992;Barth and Mohr, 1994;Neri et al., 1999;Visscher et al., 2001;Avanzini et al., 2008Avanzini et al., , 2011Forte et al., 2017;Marchetti et al., 2017;Forte et al., 2018Forte et al., , 2023. ...
Article
We used a combined approach (lithofacies and palynology) and multivariate analyses to reconstruct the different depositional environments and changes in the plant communities throughout the middle to late Kungurian in the tropical Pangea. The late Palaeozoic terrestrial biotas underwent changes under the pressure of a general aridification trend and a warming event that changed biota composition favouring drought-tolerant taxa during the Artinskian. Few studies integrate the different terrestrial ecosystem components to reconstruct palaeoenvironments and climate changes throughout the Cisuralian (early Permian). We analysed several sedimentary successions of different stratigraphic positions intercalated in well-dated volcanic units of the megacaldera of the Athesian Volcanic Group (Southern Alps, northern Italy). The obtained palynofacies and quantitative sporomorph records with an exceptional high resolution (~10 Ma) evidence a palaeoenvironmental/climatic change in the plant communities from the middle to the late Kungurian. The late Kungurian shows a higher diversity in the plant communities with a dominance of seed ferns and a higher relative abundance of xeromorphic-hygromorphic sporomorph taxa. This suggests the presences of more stable and putatively more humid environmental conditions in respect to the middle Kungurian. Furthermore, a direct comparison between lithofacies and all primary components of the palynofacies assemblages permits to characterize lacustrine and alluvial depositional environments since these studies are underrepresented for terrestrial environments.
... The latter authors recently discussed whether the Cisuralian representatives of the genus Sphenopteris from the Athesian Volcanic District can indeed be assigned to the order Lyginopteridales. It must be admitted that so far no typical reproductive organs have been described from the Kungurian of the Southern Alps, but Trümper et al. (2023) discuss wood remains from the Kungurian succession of Sinich that support the presence of pteridosperms, more specifically Lyginorachis. Morover, a lyginopterid pollen organ has been described from the Lopingian of the Dead Sea (Zavialova et al., 2021). ...
... Sphenopterids are preserved by small leaf fragments, and could be representatives of the order Lyginopteridales. The presence of woody fragments belonging also to this order in the nearby Sinich/Singo outcrop (Trümper et al., 2023), supports this assignment. Peltaspermales are documented in the Gorl section both by sporomorphs (Falcisporites, Vesicaspora, Vittatina, Strotersporites, Costapollenites) and small plant remains and cuticles (Germaropteris cf. ...
... Sphenopteris sp.) and ginkgophytes (Sphenobaiera sp.) as well as delicate bifurcating leaves. Perhaps some of the conifers could be more hygophytic elements than previously thought (see Trümper et al., 2023) but most of the elements are typical of xerophytic environments such as representatives of the Peltaspermales (Germaropteris cf. martinsii,?Peltaspermum sp., cf. ...
... 11 • 10′58.39"E, Fig. 1) the sedimentary succession is represented by a 22 m thick intercalation within the rhyodacitic lava flows of the Monte Luco Formation (Bargossi et al., 2011;Trümper et al., 2023). This succession is famous for its sandstone horizon with in situ fossil stems and a dark gray, carbonaceous shale yielding abundant and well-preserved plant fossils and sporomorphs (e. g., Aspmair and Krainer, 1998;Fritz and Krainer, 2006;Forte et al., 2023;Trümper et al., 2023;Vallé et al., 2024). ...
... Fig. 1) the sedimentary succession is represented by a 22 m thick intercalation within the rhyodacitic lava flows of the Monte Luco Formation (Bargossi et al., 2011;Trümper et al., 2023). This succession is famous for its sandstone horizon with in situ fossil stems and a dark gray, carbonaceous shale yielding abundant and well-preserved plant fossils and sporomorphs (e. g., Aspmair and Krainer, 1998;Fritz and Krainer, 2006;Forte et al., 2023;Trümper et al., 2023;Vallé et al., 2024). The depositional environment has been interpreted as a low-energy alluvial setting with persistence of shallow lakes occasionally affected by higher-energy clastic inputs. ...
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‘Mycterosaurus’ smithae, from the Cisuralian (early Permian) of Colorado, was first described in 1965 as a second species of the genus Mycterosaurus. While the type species of this genus, M. longiceps, has been shown by multiple cladistic analyses to belong to the basal synapsid family Varanopidae, ‘M.’ smithae has been largely ignored since its original description. Additional preparation and synchrotron scanning has revealed new significant information that supports the assignment of this species to a new genus: Vaughnictis gen. nov. Vaughnictis lacks many of the characteristics of mycterosaurines and varanopids in general: it lacks the slender femur, the linguo-labially compressed and strongly recurved teeth, and the lateral boss on the postorbital characteristic of this family. Instead, it possesses coronoid teeth, a large supratemporal, and a large pineal foramen positioned midway along the length of the parietal, features that support its assignment to Eothyrididae. Moreover, the postcranium shares many characters with the eothyridid Oedaleops. An expanded version of a recently published phylogenetic analysis of pelycosaurian-grade synapsids positions Vaughnictis as the sister taxon of Eothyris within the clade Eothyrididae. The addition of data on the postcranium of eothyridids and the inclusion of the recently-described basal caseid Eocasea confirms the recently-disputed position of caseasaurs as the most basal synapsids. As the parsimony analysis produced low support values and a lack of resolution due to missing data, additional analyses were undertaken using Bayesian and Implied Weights methods, which produced better resolution and relationships with higher support values. While the results are similar, alternative positions for the enigmatic Moscovian age (Carboniferous) synapsid Echinerpeton are suggested by Bayesian analysis; the parsimony analysis found it to be an ophiacodontid, while the Bayesian and Implied Weights analysis found it to be the sister to the Sphenacomorpha.
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Chert and silicified wood from the Permian through Cretaceous of Antarctica contain abundant information on fungal diversity and plant–fungal interactions. The chert deposits represent a particularly interesting setting for the study of plant–fungal interactions because they preserve remains of distinctive high latitude forest ecosystems with polar light regimes that underwent a profound climate change from icehouse to greenhouse conditions. Moreover, some of the cherts and wood show the predominance of extinct groups of seed plants (e.g. Glossopteridales, Corystospermales). Over the past 30 years, documentation of fossil fungi from Antarctica has shifted from a by-product of plant descriptive studies to a focused research effort. This paper critically reviews the published record of fungi and fungal associations and interactions in the late Palaeozoic and Mesozoic cherts and silicified wood from Antarctica; certain fungal palynomorphs and fungal remains associated with adpression fossils and cuticles are also considered. Evidence of mutualistic (mycorrhizal), parasitic and saprotrophic fungi associated with plant roots, stems, leaves and reproductive organs is presented, together with fungi occurring within the peat matrix and animal–fungus interactions. Special attention is paid to the morphology of the fungi, their systematic position and features that can be used to infer fungal nutritional modes.
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Fossil stromatolites enclosing structurally preserved land plant remains have rarely been documented and studied in detail. Permineralized woody Tylodendron sp. conifer axes (slender stems, branches) from a lacustrine sedimentary sequence in the lower Permian fossil Lagerstätte of Manebach (Thuringian-Forest Basin, central Germany) are frequently surrounded by stromatolites that consist of successive, usually asymmetrical microbial layers. The stromatolites show various growth forms ranging from laminar to palisadic. They developed in stagnant water from microbial overgrowth dominated by slender, unbranched sessile cyanobacterial filaments aligned vertically into tufts or turf-like stands. Interspersed among the filaments were other filamentous and coccoid microorganisms. Preservation of the Tylodendron axes can be exquisite and sometimes even includes extraxylary tissues containing remains of fungi, suggesting that stromatolite formation began soon after the axes had entered the water and were perhaps even conducive to their preservation. Structurally similar fossil microbialitic structures from elsewhere likewise demonstrate that they were effective in preserving plant morphology. The Manebach stromatolites and the plant remains they contain contribute to a more accurate understanding of the complex biological processes in late Paleozoic lake ecosystems.
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The sedimentary succession of the Sinich/Sinigo Basin is one of the oldest sedimentary intercalations of the Cisuralian (lower Permian) Athesian Volcanic Group of the Bozen/Bolzano area. The plant remains that were deposited in its alluvial and lacustrine sediments are middle Kungurian in age and are characterized by a wide variety of preservation types. The nearly 600 specimens from Sinich/Sinigo include permineralized stems, compressions/impressions and casts/molds, which belong to various plant groups, such as putative lycopsids, sphenophytes, ferns, seed ferns, cordaitaleans and conifers. Strata of the Sinich/Sinigo Basin yield one of the richest and best-documented Kungurian plant assemblages of eastern paleoequatorial Pangea. The conifers are represented by both walchian and more derived voltzian Voltziales, forming the earliest co-occurrence of these two groups in eastern Pangea. The three-dimensional preservation mode revealed xeromorphic features in more than one conifer species, such as the presence of fleshy and "deciduous" leaves in both walchian and voltzian conifers. These morphological features were probably more common during the early Permian, being an adaptation to aridity. The comparison of the Sinich/Sinigo collection with other Kungurian plant assemblages strengthens the assumption of more widespread semi-arid to arid conditions in the middle-late Kungurian of the Southern Alps, whereas the strata and the presence of hygrophytic elements indicate that increased rainfall and flooding events could have occasionally occurred.
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The Pennsylvanian–Permian Maroon Formation of northwest Colorado is an up to 4,600 m thick succession of mainly siliciclastic continental red-beds deposited in equatorial intermontane basins of the Ancestral Rocky Mountains. Sedimentary surfaces of fluvio-lacustrine to eolian siltstones and fine-grained sandstones from various stratigraphic levels within the Maroon Formation preserve cm-sized straight to gently curved sediment-filled acicular structures referred to five morphological groups: single, branched, stellate, rosette, and bunched. Depositional environment, shape, and size of the structures are most similar to ice crystal marks that result from freezing of water-saturated fine-grained substrate at the sediment-air interface. They differ from other syngenetically produced crystals and crystal pseudomorphs in sedimentary rocks mainly by crystal shape and environmental conditions. The potential ice crystal marks of the Maroon Formation are notable for the fidelity and morphological diversity of the crystal casts and could be a key for the understanding of similar but hitherto often only called enigmatic structures of the sedimentary rock record. The ice crystal mark occurrences in the Maroon Formation suggest that night frost affected lower elevation equatorial areas during the climax of the Late Paleozoic Ice Age and may stimulate research on evolutionary adaptations of early terrestrial biota to overcome significant air temperature fluctuations.
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Arthropleura is a genus of giant myriapods that ranged from the early Carboniferous to Early Permian, with some individuals attaining lengths >2 m. Although most of the known fossils of the genus are disarticulated and occur primarily in late Carboniferous (Pennsylvanian) strata, we report here partially articulated Arthropleura remains from the early Carboniferous Stainmore Formation (Serpukhovian; Pendleian) in the Northumberland Basin of northern England. This 76 × 36 cm specimen represents part of an exuvium and is notable because only two comparably articulated giant Arthropleura fossils are previously known. It represents one of the largest known arthropod fossils and the largest arthropleurid recovered to date, the earliest (Mississippian) body fossil evidence for gigantism in Arthropleura , and the first instance of a giant arthropleurid body fossil within the same regional sedimentary succession as the large arthropod trackway Diplichnites cuithensis . The remains represent 12–14 anterior Arthropleura tergites in the form of a partially sand-filled dorsal exoskeleton. The original organism is estimated to have been 55 cm in width and up to 2.63 m in length, weighing c. 50 kg. The specimen is preserved partially in three dimensions within fine sandstone and has been moderately deformed by synsedimentary tectonics. Despite imperfect preservation, the specimen corroborates the hypothesis that Arthropleura had a tough, sclerotized exoskeleton. Sedimentological evidence for a lower delta plain depositional environment supports the contention that Arthropleura preferentially occupied open woody habitats, rather than swampy environments, and that it shared such habitats with tetrapods. When viewed in the context of all the other global evidence for Arthropleura, the specimen contributes to a dataset that shows the genus had an equatorially restricted palaeogeographical range, achieved gigantism prior to late Paleozoic peaks in atmospheric oxygen, and was relatively unaffected by climatic events in the late Carboniferous, prior to its extinction in the early Permian. Supplementary material: Images of 3D mesh model of Arthropleura are available at https://doi.org/10.6084/m9.figshare.c.5715450
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For the biostratigraphy of mixed continental-marine and purely continental sections in the palaeotropical belt of Euramerica, 9 insect and 8 conchostracan zones are newly defined or improved. These zones encompass the time interval from the Early Pennsylvanian (middle Bashkirian) up into the early Permian (early Asselian) of the Euramercian biotic province. They are linked as much as possible to the marine Standard Global Chronostrigraphic Scale by common occurrences of insects and/or conchostracans with conodonts in mixed marine-continental sections as well as by the thus far available and reliable radioisotopic ages of associated volcanic rocks. This insect and conchostracan zonation is an alternative tool to the well-established macro-plant biostratigraphy of the Pennsylvanian. In contrast to the latter, only single specimens of insects or conchostracans, even if more rare than plant remains, allow biostratigraphic dating with a similar high temporal resolution.
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Fossil forests provide some of the most fascinating and compelling records of the geological past. If rapidly preserved in-situ, they yield multifaceted knowledge about the environment and habitat structure, diversity of organisms and their varied interrelationships. Further, fossil forests shed light on palaeoclimatic conditions and taphonomic pathways. Although discovered almost 300 years ago, only during the last decade, the Chemnitz Fossil Forest, central-east Germany, has been recognised as a complex fossil lagerstätte represented by outstanding fossil assemblages preserved by pyroclastics. The fossil biota was buried as a T0 thanatocoenosis resulting from instantaneous entombment by the Zeisigwald Tuff (Leukersdorf Formation, Chemnitz Basin). The eruptions constitute some of the last events of post-Variscan felsic volcanism in Central Europe and resulted in ash falls, pyroclastic surges, and flows, which ultimately covered and preserved the ecosystem. Based on magmatic zircons, the tuff yielded an age of 291 ± 2 Ma (late Sakmarian/early Artinskian). Fine-crystalline alpha-quartz, chalcedony, moganite, and particularly fluorite, which is restricted to plant fossils, pumice lapilli and vitreous matrix constituents, effected wood-petrifaction. Organic remains in fossil wood are restricted to scattered anthracite particles. Cathodoluminescence uncovered site-specific multiphase silicification including rapid precipitation under oxygen-deficiency in a low-temperature (<250°C) hydrothermal environment. Attention is focused on two excavations in Chemnitz that recovered abundant new data and opened a unique window into a low-latitude 'wet spot' ecosystem. This spatially restricted habitat sheltered a dense hygrophilous arborescent vegetation of seed plants and cryptogams but also epiphytes and climbers. The biota also includes a diverse fauna of vertebrates, arthropods and gastropods, several of them documented for the first time from the Permian. Chemnitz reflects a relatively youthful, but already well-established forest bionetwork with a remarkably well-developed trophic pyramid. Highlighted by many trees, still standing upright in their places of growth and rooted in the palaeosol, the Chemnitz Fossil Forest represents the most complete Permian forest biome/ecosystem recorded to date. To illustrate the environmental settings more precisely, palaeontological, pedological and geochemical indicators of deep-time palaeoclimate have been tested. The ecosystem developed on a palaeosol of low maturity, even though it received annual precipitation of ca. 800–1100 mm. Although the habitat was affected by environmental disturbances and seasonality, conservative hygrophilous forms dominated the multi-aged vegetation. Growth features of woody trees provided excellent natural data archives and afforded reliable information, e.g., severe droughts and lightning strikes recorded as event rings and wound responses in affected trees. Tree-ring sequences were analysed to ascertain both annual growth rates and mean sensitivity, and to correlate growth increments between the trees. The tree-ring data provided insights into the fourth dimension (time), enabling appraisal of the stages of forest growth. The results yield a high-resolution palaeoenvironmental signal for eight decades during the early Permian and permit the recognition of fossil deadwood for the first time. Surprisingly, the woody trees, medullosan seed ferns, cordaitaleans, and calamitaleans revealed nearly 11-year cyclicity in tree-ring formation despite exhibiting different physiological reactions. The 11-year sunspot cycle, usually affecting atmospheric circulation patterns, was recorded in the trees and demonstrates how abiotic factors affect plant growth. Finally, multidisciplinary research achieved conclusions comparable to analyse modern ecosystems. The Chemnitz Fossil Forest significantly contributes to understanding the controls of palaeoclimate, palaeoenvironment, and palaeoecological dynamics on a confined wet-forest habitat of sub-tropical Northern Hemisphere Pangaea.
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Silicified wood is one of the most frequent and insightful records of ancient life since the Devonian. Although cellular anatomy is often preserved in great detail, alterations of organic matter occur during fossilization modifying tissue properties. Due to taphonomic pathways, plant tissues experience multiple changes, which may cause a tissue-volume reduction, including desiccation, microbial decay, charcoalification, coalification and mineralization. Case studies from different geological ages, fossilization backgrounds and paleogeographical positions provide evidence of widely distributed but still underestimated shrinkage phenomena in fossil woods. Samples from seven Paleozoic to Cenozoic localities representing several geologic settings are analyzed to understand putative shrinkage reasons. Volume reduction is more widespread in fossilized wood than commonly thought. Accordingly, quantitative data on cellular anatomy may be misleading, and cell size and shape modifications affect morphometric purposes, like the interpretation and identification of fossil species. Differences in preservation demonstrate the profound effects of microbial degradation, such as lacking tracheid secondary walls and decayed tissue constituents. Differential shrinkage of silicified wood and their encrustation by stromatolites help quantify volume loss during fossilization. They provide graphically measurable, one- and two-dimensional parameters to assess percental volume loss. Our approach reveals essential shrinkage-related alterations independent of paleoenvironment, plant material and host rock. Tissue contraction varies considerably: Unexpectedly, variability even occurs in wood from the same fossil site, the same strata and reflecting the same taphonomy. The results demonstrate that shrinkage needs to be taken into account in comparisons of morphometric data obtained from fossil and modern woods, irrespective of their particular provenance.
Article
We evaluate the influences of elevation and climate on the spatio-temporal distribution of wetland and dryland biomes during the Pennsylvanian and early Permian in tropical Pangea. The longstanding ‘‘upland model” places drought-tolerant vegetation in elevated habitats, where slope and drainage created moisture-limited substrates under a humid climate that simultaneously promoted peat accumulation in contemporaneous lowlands. Upland plants were periodically transported to, and buried in, lowlands. Rare preservation of dryland vegetation thus reflects its general absence in basins, and taphonomic vagaries of long-distance transport. The alternative ‘‘climate model” proposes that drought-tolerant plants dominated tropical habitats when climate was seasonally dry, with wetland vegetation reduced to scattered refugia. Environmental changes attending glacial-interglacial cycles caused alternating wetter-drier conditions, and the relative abundance of wetland versus dryland biomes in basinal lowlands thus varied with climatic oscillations. The paucity of drought-tolerant plants reflects a preservational megabias against habitats with seasonal moisture deficits. The environmental signal of ‘‘mixed” plant-fossil assemblages, comprising taxa characteristic of both wetland and dryland biomes, may help resolve these debates. We review key Pennsylvanian and lower Permian mixed assemblages from tropical Euramerican Pangea, and interpret their original habitats and climatic contexts based on multidisciplinary lines of evidence, including sedimentology, taphonomy, physiology, and paleoecology. Evaluations also consider patterns of vegetational distribution and taphonomy in modern tropical environments. We suggest that even a cursory view of current tropical plant distribution exposes flaws in the upland model. Where tropical climate is sufficiently humid to support peat swamps, slopes and elevated habitats do not host drought-tolerant vegetation, but are occupied by plants similar to those in lowland settings. This occurs because equable, high precipitation strongly dampens water-table variation across entire landscapes. Furthermore, taphonomic studies indicate that most plant-fossil assemblages record vegetation living near the burial site. Fossil floras thus reflect environmental conditions near their growth site, excluding an upland origin for most occurrences of drought-tolerant taxa. Conversely, the climate model is consistent with modern tropical vegetational distribution and soundly explains late Paleozoic floristic patterns. When Pangean tropical lowlands experienced seasonally dry conditions, plants tolerant of moisture deficits dominated most habitats, whereas wetland vegetation was restricted to wetter sites with greater preservation potential. This occurred because topographic variations are magnified under seasonal precipitation regimes, creating a complex habitat mosaic with wetland patches in a landscape subject to seasonal drought. Accordingly, we propose that a macrofloral assemblage with even rare drought-tolerant taxa indicates seasonality in the broader landscape. At larger spatio-temporal scales, disagreement also persists about whether tectonic uplift or long-term climatic drying was the primary driver of changes in late Paleozoic floristic patterns and areal extent of tropical peat swamps. We argue that tectonic activity alone cannot explain the drastic reduction in peat swamps or coincident changes in dominance-diversity of wetland vegetation. Rates of plant dispersal and evolution far outpace that of mountain building, and peat-forming wetlands persisted in elevated habitats well into the Late Pennsylvanian. Therefore, progressive late Paleozoic aridification was the most probable driver of changing floral patterns and the distribution of wetland and dryland biomes in tropical Pangea.
Article
The medullosans represent a diverse group of pteridosperms that was widely distributed in forested landscapes of the late Paleozoic. These plants became widely known from the extensive tropical lowland basins of Euramerica, where they grew as slender plants with large fronds and fern-like foliage. Besides, there also exist medullosans of Late Pennsylvanian–early Permian intramontane basins of Central Europe, which have been out of research focus for more than a century. They had bigger stems with larger amounts of secondary xylem and a modified organization of the vascular system. We provide an overview on taxonomy, anatomy and paleoecology of these medullosans from the most important fossil localities, encompassing Chemnitz (Germany), the type locality for most taxa, Autun (France), Nová Paka (Czech Republic) and others. Late Pennsylvanian–early Permian medullosans of intramontane basins were thriving under seasonally-dry paleoclimate on wet clastic soils showing proximity to the groundwater level. In forested landscapes, they occurred mostly sub-ordinated as part of the forest understorey. The plants' architecture and taphonomical inferences point to a (semi-)self-supporting growth habit of most of the taxa presented here. Plant architectural and anatomical peculiarities suggest a high water-conducting potential of these plants, raising questions on their ecological role in early Permian habitats. Anatomical differences with tropical relatives of Carboniferous age might reflect an evolutionary process that was driven by environmental changes during the late Paleozoic. The unusual arrangement of their stem tissues addresses the question of their role in seed plant evolution, e.g., their potential relationship with cycads.
Article
The Late Mississippian and Pennsylvanian have been referred to as the Coal Age due to enormous paleotropical peat accumulations (coal beds). Numerous fossil floras have been collected from these coals, and their associated seat-earth paleosols and roof-shales, over more than two centuries, leading to the inference of vast swampy wetlands covering the Pangean tropics during the Pennsylvanian. In contrast, the Permian tropics are characterized as more arid, with sparser and more heterogeneous vegetation than inferred for the Pennsylvanian. In the tropics, the Pennsylvanian to Permian transition has been described as a changeover from a pteridophytedominated “Paleophytic flora”, to a seed-plant dominated “Mesophytic flora. This view notwithstanding, floras dominated by xeromorphic seed plants also are well known from the Pennsylvanian tropics. Some authors have characterized these plants as being occupants of uplands, subsequently transported into basinal-lowland, preservational environments. In this model, uplands are well drained, causing areas of drought under otherwise everwet climates. In this paper, we present an alternative interpretation: that the apparent transition in Pennsylvanian-Permian tropical vegetation reflects two types of taphonomic megabias. First is a preservational megabias, strongly favoring the vegetation of humid climates over that of seasonally dry climates. Accordingly, tropical-plant preservational potential fluctuated in concert with Late Paleozoic Ice Age glacial-interglacial oscillations, and contemporaneous sea-level and climatic changes. Second is an analytical megabias, strongly favoring the discovery and collection of the wetland biome from Pennsylvanian strata, overlooking the less frequently and more poorly preserved drought-tolerant biome. By Permian times, vast wetlands, and their fossil record, had largely disappeared from central Pangea (although continuing in Cathaysia), making drought-tolerant vegetation more “visible” to searchers, without changing its preservational circumstances. We demonstrate that the upland model is untenable, being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record.
Article
An early Permian tuff bed between Coal 7 and Coal 6 of the Wuda Coalfield in Inner Mongolia bears T 0 peat-forming vegetation preserved in situ. Documentation of the fossil record uncovered in an area of about 80 m 2 shows 14 morphotaxa representing 11 whole-plant species with a wide variety of growth forms. The uncovered phytocoenosis is interpreted as a forest dominated by cordaites as the tallest trees, the remains of which covered over 50% of the excavated area. Marattialean tree ferns represent the lower canopy that was not taller than about 3 m. This storey fills gaps between cordaites and covers over 20% of the area. A rare element of lower canopy taxa was the cycadophyte genus Pterophyllum represented by a single plant. Poorly developed herbaceous groundcover includes Sphenophyllum oblongifolium, and four small fern species mostly with sphenopteroid type of foliage. Although members of the herbaceous layer covered only 7% of the excavated area, it was the most diverse storey of the peat-forming forest. Considering the small area excavated, along with the higher diversity known from the same tuff bed in the adjacent, former opencast mine, it appears that species richness in the forest was comparable to some of the less diverse Westphalian peat-forming floras in Euramerica.
Article
Hyperalkaline waters display unusually high productivity, which makes them prime targets in the search for life elsewhere in the solar system. However, the formation mechanisms of alkaline waters are not well understood, because the response of biogeochemical proxies to these conditions is poorly constrained. To address this issue, we assessed the influence of hydrothermal fluids on the salinity and pH of alkaline lakes based on a case study of an early Permian paleo-alkaline lake (~290 Ma; Fengcheng Formation) in the Mahu Sag, northwestern Junggar Basin, China. Multiple proxies indicate that hydrothermal fluids in the central salt rock and marginal tuff–mudstone areas of the Fengcheng Formation were affected by deep and shallow hydrothermal fluids, respectively. A small part of the transitional area was affected by hydrothermal fluids with a hybrid nature. The hydrothermal fluid activity gradually weakened up-section in all areas while salinity (inferred from carbon and oxygen isotopes) increased and pH (inferred from nitrogen isotopes and mineralogy) decreased from hyperalkaline (>9.25) to moderately alkaline conditions. These trends suggest that hyperalkalinity was largely driven by hydrothermal processes. In contrast, evaporation, which dominated towards the end of the lake's lifetime, maintained an elevated pH but did evidently not have a similarly strong effect as hydrothermal fluids. Our data suggest that hydrothermal activity and evaporation in closed lacustrine basins have the potential to create extreme conditions for the formation of alkaline lakes. The evolution of salinity and pH may not necessarily be synchronized.
Article
Cores from the middle Eocene sediments, Dongying Depression of the southern Bohai Bay Basin in east China yield various kinds of sedimentary deformation structures. They include microfolds, load casts, flame structures, ball-and-pillow structures, load-casted ripples, pinch-and-swell structures, boudinage structures, sand dikes, microfaults and cataclastic breccias. Besides, gravity flows including turbidites and debris-flows also occur in the study area. The deformation layers can be divided into plastic deformation and brittle deformation. These develop in the succession composed mainly of dark finely laminated and massive mudstone interbedded with thin sandstones and carbonate rocks that accumulated in a low-energy semi-deep to deep lacustrine environment in a tectonically active setting. Considering the facies attributes in the study area, intrinsically possible trigger mechanisms such as rapid sediment loading and storm currents are absent. Thus, the sedimentary deformation features should be induced by seismic activities, the same with gravity flows. These seismites are interpreted to have originated from earthquakes with magnitudes exceeding M 5.6. Basin-controlling fault in the north border of Dongying Depression give rise to the occurrence of seismites. The increasing occurrence frequency of seismites from Es4u to Es3l is correspond with the increase of activity velocity of basin-controlling fault. Compared with the seismites developed in other fault depressions in Bohai Bay Basin, seismites developed in Dongying Depression have relatively smaller scale and are dominant by microfault layers, relatively more cohesive sediments and greater distance between seismites and active faults result in the occurence of these features.
Article
With more than 1,100,000 described species, the insects are the most diverse clade of extant animals, far before all other groups. Nevertheless, they undergo a drastic decrease of their populations, due to the sixth extinction of human origin. Thus it is important to define when and how they became so diverse and if they were impacted by the major crises of biodiversity in the deep past to estimate the importance of the current one. Insects are generally among the best preserved terrestrial fossil organisms, much more complete than the vertebrates. They are also much more frequent. Thousands can be found in Konservat-Lagerstätten since the Carboniferous. They are preserved either in lacustrine sediments as compression fossils, or embedded in amber (fossil resins) (Fig. 1). The Hexapoda (or six-legged arthropods, viz., wingless Collembola, Diplura, Protura ; wingless and winged Insecta) are among the oldest known terrestrial organisms, with first records dated from the Middle Devonian of Rhynie in Scotland. Recent molecular phylogenetic dating suggests that they appeared during the Silurian or even the Ordovician, with the first terrestrial plants. The Devonian hexapodan record is very scarce and disappointing, with less than six described fossils, all wingless [1]. The early Carboniferous one is even worse, without any fossil insects. But at the very end of this period and during the late Carboniferous, the insect diversity exploded, with a ‘sudden appearance’ of winged insects with very diverse feeding resources, e.g., carnivorous, plant suckers, leaf eaters, detritivorous, gall-makers, etc. The wingless clades remained a minority and the high diversification of the Carboniferous Hexapoda clearly concerned the winged forms. Wings and flight were probably the first crucial structures and function that allowed the first burst of diversification of the insects. Flight allows them to escape predators, find new resources, sexual partners, and travel to new environments. The most popular fossil insects are the Paleozoic ‘giant’ dragonflies Meganeuridae. These flying insects with very large wingspans (ca. 70 cm wide) had large bodies but comparable to those of some extant beetles. In fact, the unique really giant Carboniferous terrestrial arthropod was Arthropleura, a myriapod that was more than 1 m long. It is supposed that the great increase of oxygen proportion in the air during the Late Carboniferous favored the gigantism among the terrestrial arthropods, due to their breathing via trachea. The question is in fact more complex, because the winged insects knew a unique situation during the late Paleozoic, as they had no flying vertebrates as predators. As they were the only flying animals, they probably knew a phenomenon of parallel increases of sizes of predators (the Meganeuridae) and preys, the Palaeodictyoptera that also became larger and larger [2]. At the end of the middle Permian, both clades are very diverse, with still very large taxa, while the oxygen proportion began to decrease. The first gliding ‘lizard-like’ vertebrates are also recorded at the same time, and certainly began to predate these giant insects, which became rarer during the late Permian and no longer existed in the Triassic. The late Carboniferous was also the time of the oldest known holometabolous insects, with complete metamorphosis (wasps, beetles, scorpionflies), and of the oldest bugs (Hemiptera). These were discovered very recently because they were very small insects [3]. They are now the most diverse animal clades, with the ‘big five’ (Hemiptera, Hymenoptera, Diptera, Lepidoptera, and Coleoptera). But during all the Paleozoic, these insects were clearly very few. Holometaboly in itself was not ‘sufficient’ to cause their diversification and each of these orders ‘separately’ diversified during the last 220 Ma. The exact impact on the insects of the most important Permian–Triassic crisis of diversity remains difficult to estimate because there are very few latest Permian and earliest Triassic outcrops with insects. Thus if we know that the Triassic entomofaunas are very different from the Permian ones, we cannot establish that the great changes that occurred between the two periods happened during this crisis or before, during the late Permian or even at the end of the middle Permian. Nevertheless, the Palaeodictyoptera and the Meganisoptera are no longer present in the Triassic, while all the Triassic entomofaunas are clearly ‘dominated’ by the beetles and other Holometabola. Beetles were still minority during all the Permian in the fossil record. The ‘true’ flies (Diptera) and crown group of Hymenoptera are also dated from the Middle Triassic. At the end of this period, all the extant orders were present, except, maybe the parasite groups such as fleas (Siphonaptera), whose oldest fossils are middle Jurassic. The ‘modern’ entomofauna is thus much older than the extant mammal orders. During the Jurassic, the insects continued their diversification, with the first parasitoid wasps (there is no record of parasitoid insects before). The Cretaceous was the second crucial period for the insect (especially the Holometabola) diversification, with the oldest eusocial taxa (termites, wasps, bees, ants). The Albian–Cenomanian (ca. 100 Ma.) was the time of replacement of the gymnosperms by the angiosperms in all the terrestrial biotas, and the time of appearance of nearly all the extant insect families (even some extant genera have this age). It is also an important time of extinctions of several older Jurassic clades, replaced by extant taxa. Only the insects that adapted to the new environments related to flowering plants could diversify. The modern insect–plant relationships were established during the late Cretaceous. The recent new studies of the extraordinarily rich and diverse entomofauna of the ‘mid’ Cretaceous Burmese amber allowed one to discover that the Cretaceous insect world was as complex, rich and diverse as the extant one. The Cretaceous–Cenozoic (K–T) crisis had clearly a very weak impact on insect diversity, at least at the family level [4]. In fact, there were more extinctions and appearances of new families during the Paleocene–early Eocene than during the K–T crisis. These were periods of global warming followed by global cooling. The entomofaunas suffered the successive periods of cooling of the Oligocene, Miocene, and the Pliocene–Pleistocene glaciations, causing the extinctions of numerous widespread families that survived in small areas (the Australian mastotermitid termites or the Tasmanian hairy cicadid Tettigarctidae are the most spectacular examples). The deep past history of insects is unique, with bursts of diversification ca. 330 Ma, 220 Ma, and 100 Ma ago. The causes of the first one remain poorly known, those of the second one are probably linked to the renewal of the ecosystems during the early Triassic, and the third one to the great floristic change. At least the K–T crisis did not affect much insect diversity. Thus the current crisis of biodiversity that begins to greatly affect the insect biomass, is extremely alarming. It may be more important than the K–T one.
Article
Nonmarine biostratigraphic/biochronologic schemes have been created for all or parts of the late Carboniferous–Middle Triassic using palynomorphs, megafossil plants, conchostracans, blattoid insects, tetrapod footprints and tetrapod body fossils, and these provide varied temporal resolution. Cross correlation of the nonmarine biochronologies to the Standard Global Chronostratigraphic Scale has been achieved in some parts of the late Carboniferous–Middle Triassic in locations where nonmarine and marine strata are intercalated, the nonmarine strata produce biochronologically significant fossils and the marine strata yield fusulinids, conodonts and/or ammonoids. Other cross correlations have been aided by magnetostratigraphy, chemostratigraphy and a growing database of radioisotopic ages. A synthetic nonmarine biochronology for the late Carboniferous–Middle Triassic based on all available nonmarine index fossils, integrated with the Standard Global Chronostratigraphic Scale, is presented here. The focus is on the nonmarine biostratigraphy/biochronology of blattoid insects, conchostracans, branchiosaurid amphibians, tetrapod footprints and tetrapod body fossils within the biochronological framework of land-vertebrate faunachrons. Correlation to the Standard Global Chronostratigraphic Scale presented here is divided into seven time intervals: Pennsylvanian, Carboniferous–Permian boundary, Cisuralian, Guadalupian, Lopingian, Permian–Triassic boundary and Early to Middle Triassic. The insects, conchostracans and branchiosaurs provide robust nonmarine correlations in the Pennsylvanian–Cisuralian, and the footprints and tetrapod body fossils provide robust correlations of varied precision within the entire Pennsylvanian–Middle Triassic. Radioisotopic ages are currently the strongest basis for cross correlation of the nonmarine biostratigraphy/biochronology to the Standard Global Chronostratigraphic Scale, particularly for the Pennsylvanian–Cisuralian. Chemostratigraphy and magnetostratigraphy thus far provide only limited links of nomarine and marine chronologies. Improvements in the nonmarine-marine correlations of late Paleozoic–Triassic Pangea require better alpha taxonomy and stratigraphic precision for the nonmarine fossil record integrated with more reliable radioisotopic ages and more extensive chemostratigraphic and magnetostratigraphic datasets.
Article
Debris flows occurring in well-vegetated alpine areas usually contain a range of sizes of woody debris. Large woody debris (LWD), which has a retaining effect on further transportation of debris downstream, is mainly distributed in upstream reaches, and the amount of small woody debris (SWD) deriving from LWD increases dramatically midstream and downstream. The Dongyuege (DYG) bouldery debris flow with a sandy-matrix took place in a wildwood area, causing 96 deaths and its clay-sized fraction does not contain typical clay minerals. However, its total travel distance and runout distance in a low-gradient reach (between 2° and 5°) upstream of the depositional fan apex reached 11 km and 3.3 km, respectively. The abundant SWD in the DYG debris flow might have played a crucial role in slurrying, persistence, and the long runout over the low gradient. To understand why this debris flow extended so far, slurrying experiments, pore water escape experiments, and excess pore pressure experiments were performed. Crude debris (CD) collected from the DYG debris flow deposit was used throughout the experiments, the tested materials of which are separated into CD-containing SWD with a maximum grain size (MGS = 2 mm), purified debris (PD) without SWD with a MGS of 2 mm, and SWD < 2 mm in diameter. In the five slurrying experiments with PD-SWD-water mixtures, as the SWD content was elevated from 0.0 to 2.0 wt%, the current velocity of escaping pore water decreased uniformly from 17.2 to 0.9 mm/s. When the SWD content was 1.0 wt% or greater, the mixtures can be considered as one-phase flows of viscous fluids. The six pairs of pore water escape experiments based on the slurries remolded with CD and PD, respectively showed that the time needed for pore water to escape from the CD slurries was much greater than those from their PD counterparts. Also, measured was the dissipation rate of the relative excess pore pressure of CD and PD slurries of various densities and volumes, which showed that most of the rates of the PD-slurries were always greater than CD-slurries. Overall, the results show that SWD has a strong influence on the slurrying of the DYG debris without typical clay minerals found in other debris flows, and SWD helps to sustain the high excess pore pressure in the interior of the debris flow mass which resulted in the extended travel distance over such a low gradient. SWD favors the formation and stability of one-phase water-debris mixtures because of its large specific surface area and low density, which makes it able to absorb fine particles and able to be suspended in slurry flows over long timescales. In well-vegetated mountainous areas, SWD should be taken into account in the assessment of debris-flow hazards.
Article
Four substantial tetrapod extinctions have been identified during the Permian, but only one of these is an apparent mass extinction. Analyses of global compilations of the family-level diversity of Permian tetrapods have been confounded by incorrect and compiled correlations. Instead, analyzing diversity patterns at the genus level in “best sections” identifies only one apparent mass extinction of Permian tetrapods. Much evolutionary turnover took place among tetrapods during the latter part of the early Permian and had been identified as a single mass extinction at the Artinskian-Kungurian boundary. However, the only stratigraphically dense tetrapod record of the late early Permian, from the southwestern USA, indicates a succession of extinctions spread out from Redtankian through Littlecrontonian (Kungurian) time, not a single mass extinction. Olson's gap remains a hiatus in the global record of Permian tetrapods equivalent to part of the Kungurian-Roadian. Across the gap, eupelycosaur-dominated assemblages were replaced by therapsid-dominated assemblages, but the claim that this is associated with a mass extinction (“Olson's extinction”) has been based on compressing all of the extinctions of the Redtankian-Littlecrotonian and Olson's gap into one event. Recognition of Olson's gap does not preclude the possibility of an extinction at the early-middle Permian boundary (“Olson's extinction”). However, the gap in the tetrapod fossil record makes it impossible to establish the magnitude, precise timing and structure of the extinctions that took place across Olson's gap.
Article
A major global change, the transition from an icehouse to a greenhouse world, took place during the Permian. In the equatorial Euramerican floral realm this resulted in stepwise changes from sub-humid climates in the early Cisuralian to semi-arid/arid climate by the late Cisuralian. During the same time interval we see a change from spore plant-dominated lowland floras, to increasingly drought-tolerant floras dominated by conifers and other seed plants. A recently discovered Kungurian (late Cisuralian) flora from the “Le Fraine” section near the village of Tregiovo (Trento Province, NE-Italy), is characterized by several types of conifers, callipterids, sphenopterids, and sphenopsids. The conifer fossils included both vegetative and reproductive organs. Five different ovuliferous dwarf shoot types were found, ranging from forms with many sterile free scales and interspersed sporophylls, that typically resemble late Pennsylvanian and early Permian walchian conifers, to stalked forms with largely fused sterile scales and sporophylls, comparable to early and late Permian voltzian conifers. One of the voltzian-type dwarf shoots belongs to the genus Dolomitia, extending the range of this genus back to the late Cisuralian. Another form strongly resembles those of the voltzian conifer Pseudovoltzia. The other three dwarf shoot types show a wide morphological variation, but cannot be assigned to any known genus due to the imperfect preservation. In western Euramerica, the transition from walchian- to voltzian-conifer-dominated floras took place during the late Cisuralian. This study shows that this change occurred across the entire equatorial Euramerican realm. The well-dated Tregiovo flora is one of the very few late Cisuralian floras of Euramerica. As such, this flora documents an important step in the evolution of Permian terrestrial biotas.
Article
Modern-day periodic climate pattern variations related to solar activity are well known. High-resolution records such as varves, ice cores, and tree-ring sequences are commonly used for reconstructing climatic variations in the younger geological history. For the first time we apply dendrochronological methods to Paleozoic trees in order to recognize annual variations. Large woody tree trunks from the early Permian Fossil Forest of Chemnitz, southeast Germany, show a regular cyclicity in tree-ring formation. The mean ring curve reveals a 10.62 yr cyclicity, the duration of which is almost identical to the modern 11 yr solar cycle. Therefore, we speculate and further discuss that, like today, sunspot activity caused fluctuations of cosmic radiation input to the atmosphere, affecting cloud formation and annual rates of precipitation, which are reflected in the tree-ring archive. This is the earliest record of sunspot cyclicity and simultaneously demonstrates its long-term stable periodicity for at least 300 m.y.
Article
Abstract The Variscides of Europe and N-Africa are the result of the convergence of the plates of Gondwana and Laurussia in the Paleozoic. This orogen is characterized by the juxtaposition of blocks of continental crust that are little affected by the Variscan orogeny. These low strain domains principally consist of Neoproterozoic/Cambrian Cadomian basement overlain by volcano-sedimentary successions of an extended peri-Gondwana shelf. These Cadomian blocks are separated by high strain zones containing the record of subduction-related processes. Traditionally the high strain zones are interpreted as sutures between one or more postulated lithospheric microplates sandwiched between the two major plates. Paleobio-geographic constraints in combination with geochemical and isotopic fingerprints of the protoliths, however, imply that the Variscides are the result of the exclusive interaction of the two plates of Gondwana and Laurussia. Here we explain the Variscan orogen in a two plate scenario, reasoning that the complexity of the Variscan orogen (multitude of high-grade metamorphic belts, compositional diversity of coeval magmatism, and arrangement of foreland basins) is the result of the distribution of crustal domains of contrasting rheological properties. Post-Cadomian rifting along the Cadomian–Avalonian belt, which culminated in the opening of the Rheic Ocean, resulted in vast coeval intracontinental extension and the formation of extended peri-Gondwana shelf areas, namely the Avalonian shelf and the Armorican Spur to the north and south of the evolving Rheic Ocean, respectively. Both shelf areas affected by heterogeneous extension consist of stable continental blocks separated by zones of thinner continental crust. During Variscan collisional tectonics the continental blocks behave as unsubductable crust, whereas the thinner continental crust was subductable and came to constitute the high strain domains of the orogen. The variable interplay between both crustal types in space and time is seen as the principal cause for the observed sequence of orogenic processes. The first collisional contact along the convergent Gondwana–Laurussia plate boundary occurred between Brittany and the Midland microcraton causing the early Devonian deformation along the Anglo-Brabant Fold Belt. This process is coeval with the initiation of continental subduction along the Armorican Spur of the Gondwana plate and the formation of back arc and transtensional basins to both sides of the Armorican Spur (e.g., Lizard, Rheno-Hercynian, Careón, Sleza) on the Laurussia plate. As further subduction along this collision zone is blocked, the plate boundary zone between the Gondwana and Laurentia plates is reorganized, leading to a flip of the subduction polarity and a subduction zone jump outboard of the already accreted blocks. The following Devonian–Early Carboniferous subduction accretion process is responsible for the juxtaposition of additional Cadomian blocks against Laurussia and a second suite of high-pressure rocks. The final collision between Gondwana and Laurussia is marked by an intracontinental subduction event affecting the entire internal zone of the orogen. Subduction stopped at 340 Ma and the following isothermal exhumation of the deeply subducted continental crust is primarily responsible for Late Variscan high-temperature metamorphism and cogenetic voluminous granitic magmatism. During this final transpressional stage the irregular shape of the Variscan orogen was established by the highly oblique motion of the decoupled lithospheric blocks (e.g. Iberia and Saxo-Thuringia). Rapid overfilling of synorogenic marine basins in the foreland and subsequent folding of these deposits along vast external fold and thrust belts finally shaped the Variscides, feigning a relatively simple architecture. In terms of plate tectonics, the model places the opening of the Paleotethys in the Devonian with a rotational axis of the spreading center just east of the Variscan orogen. The movement of Gondwana relative to Laurussia follows small circle paths about this axis from 370 to 300 Ma. As a consequence of the incomplete closure of the Rheic Ocean after the termination of the Variscan orogeny, Gondwana decoupled from the European Variscides along the dextral Gibraltar Fault Zone. The relative motion between Gondwana and Laurussia after 300 Ma is associated with a shift of the rotational axis to a position close to the Oslo Rift, and is related to the opening of the Neotethys and the evolution of the Central European Extensional Province. The Permian convergence of Gondwana and Laurussia led to the final Permian collisional tectonics along the Mauritanides/Alleghanides. The assembly of the “Wegenerian” Pangea is complete by the end of the Paleozoic.