Northern Pangea Research Articles

First report of Early Permian Tasmanite oil shales in northern Pangea with global implications

During the Late Paleozoic Ice Age (LPIA; particularly early Permian), organic material of the alga Tasmanites was extensively deposited in sediments of southern Gondwana, which formed the Tasmanite oil shales that have only been identified in Tasmania, Australia. It remains unclear whether other analogous geological records exist worldwide that formed at the same time, and the origin is enigmatic. This paper reports the first discovery of Tasmanite oil shales in northern Pangea, specifically in the Lucaogou Formation of the Junggar Basin, China, deposited during the Artinskian (ca. 290 Ma). The organic petrological features of Tasmanites are clearly visible, including thick-walled disks with tubes and radially arranged channels. These shales have markedly elevated C28/C29 steranes and tricyclic terpanes/hopanes ratios. Based on inorganic geochemical data, the salinity of the paleo-lake during deposition of the Tasmanite oil shale interval decreased abruptly from saline to brackish–freshwater. In addition, the pH changed from alkaline to nearly neutral, while the redox environment changed from anoxic to suboxic. Enhanced continental chemical weathering and the change in salinity of the paleo-lake occurred at the same time as global warming and large-scale glacier melting during the Artinskian, which promoted the habitat of the low-salinity tolerant Tasmanites. Our results provide new geological evidence for another occurrence of early Permian Tasmanite oil shales, indicating that Tasmanites flourishs and the associated oil shales may have been widely deposited at the end of the LPIA. The flourishment of Tasmanites archives biotic–environmental co-evolution.

A detailed stratigraphic and taphonomic reassessment of the late Paleozoic fossil flora from Promontory Butte, Arizona

A late Paleozoic, likely early Late Pennsylvanian (Missourian/early Virgilian), flora from Promontory Butte, Arizona, USA is the westernmost assemblage of this age yet described from northern Pangea. The palynological species pool is similar to that typical of more central parts of the supercontinent; in contrast, the macroflora differs by facies, reflective of original habitat differentiation. The flora is preserved in a succession that includes sandstone, siltstone, shale, and conglomerate in an upward-fining series of beds. A break between the siltstone and shale is marked by an organic-shale bed, previously described as a coal, and its underclay/paleosol. This stratigraphic unit is interpreted as an active channel fill terminating in a lake. A detailed bed-by-bed facies analysis of the macroflora, focusing on the relationship between sedimentological features and fossil-plant composition reveals that the wetland floral elements are concentrated in the upper, fine-grained beds of the fill, including the organic shale and overlying mudrock, whereas the drought-tolerant, xeromorphic plants are concentrated in siltstones and sandy siltstones below the organic-shale/underclay couplet. Palynology, in contrast, suggests a uniform flora throughout the interval, indicating that macrofloral changes within the channel-fill sequence reflect microhabitat differences resulting from local changes in soil moisture conditions rather than climate change. The palynoflora is dominated by tree ferns and compositionally suggests a Missourian (Kasimovian) age, possibly early Virgilian; rare lycospore grains, characteristic of the Middle Pennsylvanian, are likely reworked from older sediments. Earlier collecting at this site did not sort the fossils by microstratigraphy and facies types, combining all floral levels into one assemblage that indicated possible co-occurrence of wetland plants and plants tolerant of seasonal moisture stress. Furthermore, a Pennsylvanian-Permian boundary age was inferred due to the abundance of xeromorphic, drought-tolerant taxa. In light of this investigation, a late Missourian age is inferred as most likely.

Paleo-environmental conditions and organic carbon accumulation during glacial events: New insights from saline lacustrine basins

Organic carbon accumulation was common during glacial events, but previous studies have focused primarily on marine facies and few have investigated lacustrine facies. This study investigates the sedimentation and organic matter accumulation during the Late Paleozoic Ice Age (LPIA; Late Carboniferous–Early Permian) in the Junggar Basin of China, which was located in a mid-latitude region of Northern Pangea at the time. Organic-rich hydrocarbon source rocks in three sags were examined. Our findings indicate that the Fengcheng Formation (ca. 300 Ma) in the Mahu Sag was deposited in a saline (carbonate content = 40.8 ± 18.4 wt%), sub-oxic–anoxic (total S/Fe [TS/Fe] = 0.5 ± 0.3), and highly alkaline (δ15N = 19.6‰ ± 2.6‰) lacustrine environment. The Lucaogou Formation (ca. 290 Ma) in the Jimusaer Sag was deposited in a freshwater–saline (carbonate content = 28.9 ± 15.6 wt%), oxic–anoxic (TS/Fe = 0.4 ± 0.8), and circum-neutral–highly alkaline (δ15N = 10.7‰ ± 3.2‰) lacustrine setting. The Lucaogou Formation in the Fukang Sag was deposited in a freshwater–saline water (carbonate content = 11.5 ± 4.3 wt%), oxic–sub-oxic (TS/Fe = 0.1 ± 0.1), and relatively neutral pH (δ15N = 7.0‰ ± 0.9‰) lacustrine environment. The source rocks in these three sags represent a completely evolutionary sequence of a saline lacustrine basin, as the saline degrees follow the order of the Lucaogou Formation in the Fukang Sag < the Lucaogou Formation in the Jimusaer Sag < the Fengcheng Formation in the Mahu Sag. The co-evolution of depositional environment, particularly pH, and source rock quality is shown as the abundance of organic matter and hydrocarbon-generating potential first increasing and then decreasing with increasing pH, as the type of organic matter first became increasingly oil prone and then remained unchanged. This reflects the interplay between the bio-precursors, paleo-environment, and organic C accumulation. This may be a common feature of saline lacustrine basins throughout geological time worldwide, such as the Eocene Piceance Basin in USA (the Green River Formation), the Cretaceous Campos Basin in Brazil (the Itapema and Barra Velha formations), and the Eocene saline lacustrine basins in China (e.g., the Shahejie, Qianjiang, and Xiaganchaigou formations). During glacial periods, it is common for lacustrine basins to undergo salinization, which ultimately leads to such basins being ideal for fossil energy exploration. The accumulation of organic carbon drove and responded to the glacial period by sequestrating atmospheric CO2, and was thus an important part of the global carbon cycle that requires further research.

Revision of the Late Triassic metoposaurid “Metoposaurus” bakeri (Amphibia: Temnospondyli) from Texas, USA and a phylogenetic analysis of the Metoposauridae

Metoposaurids are a clade of large-bodied temnospondyls commonly found in non-marine Late Triassic deposits across northern Pangea. Three taxa are known from North America: Anaschisma browni, Apachesaurus gregorii, and “Metoposaurus” bakeri. While the osteology of most metoposaurids has been recently revised, that of a few taxa, including “Metoposaurus” bakeri remains poorly characterized. This taxon was formally described in 1931 as “Buettneria bakeri,” and its taxonomy has remained in flux ever since then. “Metoposaurus” bakeri is the earliest appearing metoposaurid in North America (Carnian of Texas), and Metoposaurus has frequently been utilized as an index taxon of the Otischalkian estimated holochron (‘land vertebrate faunachron’) and for biostratigraphic correlations with other geographic regions. The taxonomy of this species is therefore relevant for both taxonomic experts and biostratigraphers. Here we redescribe all material from the type locality of “M.” bakeri, the Elkins Place bone bed, and perform a phylogenetic analysis using a revised matrix assembled from several previous studies. Anatomical comparisons and phylogenetic analyses do not support placement in either Metoposaurus, a taxon otherwise only found in Europe, or Anaschisma, the only other large-bodied taxon from North America. Therefore, we erect a new genus, Buettnererpeton gen. nov., to accommodate this species. Metoposaurus is consequently absent from North America, and this genus cannot be used in global biostratigraphy. Phylogenetic analyses provide evidence that the phylogeny of the Metoposauridae remains extremely labile, with drastic differences in topological resolution and structure being linked to just a handful of characters and scores. Metoposaurids’ morphological conservatism and the increased recognition of intraspecific variation thus continue to be major confounds to elucidating the evolutionary history of this clade.

Astronomical constraints on the development of alkaline lake during the Carboniferous-Permian Period in North Pangea

Astronomical forcing associated with Earth's orbital and inclination exerts a major control on climate as recorded in the sedimentary rocks. Alkaline lake deposits in the second member (F 2 ) of the Fengcheng Formation provided a unique geological record to explore the paleoclimatic conditions during the Late Paleozoic Ice Age (LPIA) in northern Pangea. In this study, we utilize high-resolution downhole logs (GR, DEN and CAL) to conduct a comprehensive cyclostratigraphic analysis of the Fengcheng Formation. Time series analysis reveals evidences for 405-kyr long eccentricity cycles in logs series, which is also confirmed by objective statistical approaches by modeling of optimal sedimentation rates. Tuning of these downhole logging datasets to the interpreted 405-kyr eccentricity obtained a ~ 5.0-Myr-long astronomical time scale (ATS). Afterwards, by anchoring the U-Pb age at the first member (F 1 ) and second member (F 2 ) boundary, obtaining an absolute age framework for the Fengcheng Formation that extends from 297.0 to 301.98 Ma. Under the high-precision time framework, we performed sedimentary noise model to reconstruct the lake-level changes in terrestrial Junggar Basin. Notablely, modeling of the tuned CAL series reveals high-frequency lake-level changes at 10 5 –10 6 kyr orbital time scale (i.e., ~1.2 Ma, ~450 kyr, ~180 kyr, ~116 kyr). These high-frequency lake-level variations were possibly teleconnected with the high-latitude ice sheets periodic waxing and waning and/or low latitude monsoonal circulation. Moreover, the development of rhythmic evaporite-containing mudstone in the F 2 was tightly linked to the basin's hydrological cycles, which was ultimately paced by the astronomical forcing. Finally, we propose a simplified model for illustrating the formation of the rhythmic evaporite layers and emphasize that the favorable paleotectonic, paleogeographic and paleoclimatic conditions were necessary for development of the alkaline lake. • Comprehensive cyclostratigraphic analysis of the Fengcheng Formation • Reconstruct the lake-level changes by using DYNOT simulation approach. • A novel alkaline development model associated with orbital forcing was firstly proposed.

Triassic turtles from Pangea: The legacy from South America

The Triassic is a key period in turtle evolution for three main reasons: First, the oldest fully shelled body-fossil records of the clade Testudinata come from Late Triassic (Norian) rocks. Second, tracks attributed putatively to turtles (Chelonipus isp.) are reported from the Early Triassic of North America and from the Middle and Late Triassic of Europe. Third, the undisputed sister taxon (Odontochelys semitestacea from the Carnian of China) and some putative successive sister group taxa were found in Middle and Late Triassic rocks (e.g., Pappochelys rosinae from the Ladinian of Germany, Eorhynchochelys yuantouzhuensis from the Carnian of China). These three facts highlight the importance of the Triassic for the origin and early evolution of turtles. Regarding the oldest records of the clade Testudinata, the majority of the body-fossil record are known from Northern Pangea (6 species distributed in central Europe, North America, Greenland, and Thailand). In Southern Pangea, the testudinatan record in the Triassic is restricted to Palaeochersis talampayensis and Waluchelys cavitesta from Argentina. Although the southern Pangean record of basal testudinatans is less diverse than the northern record, it brings valuable information for understanding the first steps in turtle evolution. In this contribution we: 1, present new information about the oldest turtles, mainly new evidence provided by the South American and European records; 2, critically summarize and discuss the putative ichnological record of turtles during the Triassic, a topic usually left aside; 3, discuss new perspectives on the origin and early evolution of the turtle shell based on recent discoveries in Triassic turtles and putative stem-testudinatans.

Global warming leads to Early Triassic nutrient stress across northern Pangea

Abstract The largest extinction in Earth history, in the latest Permian, was followed throughout most of the Early Triassic by a prolonged period of ecologic recovery. What factors delayed biotic recovery are still under debate and partly revolve around impacts of global warming on primary marine productivity. We examined N isotope records from the Festningen section on Spitsbergen, Arctic Norway, to examine changes in nutrient availability through the Early to Middle Triassic along the northern margin of Pangea. Our results show progressive decline in N availability throughout the Griesbachian, leading to severe nutrient limitations through the remainder of the Early Triassic, until returning to a highly productive continental margin in Middle Triassic time. These results are consistent with other studies from northern and western Pangea and thus show regional nutrient limitations occurred in what should have been the main zone of marine primary productivity. Such nutrient limitation likely stressed primary production and consequently contributed to prolonged marine recovery. We suggest this was driven by high ocean temperatures depressing the marine nutricline.

Mud‐rich delta‐scale compound clinoforms in the Triassic shelf of northern Pangea (Havert Formation, south‐western Barents Sea)

AbstractIn recent years it has become clear that many shallow‐marine heterolithic and mudstone‐dominated successions are deposited as mud belts forming part of subaqueous deltas that are related to major fluvial sources either upstream or along shore. Here the Havert Formation is presented as an ancient example of this kind of system. The Havert Formation in the south‐western Barents Sea represents shelf margin clinoforms consisting predominantly of heterolithic deposits. Sediments were mainly derived from the east (Ural Mountains), but a smaller system prograded northward from Fennoscandia. The Havert Formation holds a lot of interest due to: (i) its stratigraphic position, directly above the Permo–Triassic boundary and contemporaneous to the emplacement of the Siberian Traps; (ii) the fact that it represents the first siliciclastic input in the south‐western Barents Sea and it shows interaction between Uralian‐derived and Fennoscandian‐derived sediments; and (iii) its hydrocarbon potential. This study is focused on a detailed sedimentological analysis of cored intervals of the (Ural‐derived) Havert Formation, in combination with seismic interpretation, well‐log correlations and palynological analysis of the Havert and overlying Klappmyss formations. The cored intervals belong to the shelf environment of the Havert shelf‐margin clinoforms (300 to 500 m thick). This sedimentological analysis distinguishes six facies associations, spanning from tidally‐influenced channels at the shoreline to mud‐rich subaqueous platform and foresets of the subaqueous delta. Seismic lines and well‐log correlations show the larger‐scale evolution of the Ural‐derived Havert Formation, characterized by episodes of low‐accommodation and high‐accommodation. The palynological analyses provide the first detailed study of the Havert Formation in the Nordkapp Basin, revising its depositional age in the region as Induan to early Olenekian (Smithian). Furthermore, they strengthen the environmental interpretation; palynofacies present on the shelf record flora of tidally‐influenced coastal plains, whereas the palynofacies in the deep‐water slope contain only amorphous organic matter.

Flora of the Kazanian–Urzhumian boundary in the middle Permian of the Russian Platform

Rich fossil plant localities in the upper Guadalupian and the lowermost Lopingian of the Russian Platform are confined to several discrete “levels” or “horizons” divided by intervals that are almost devoid of plant remains. One such “horizon” is located at the boundary between the Upper Kazanian and the Urzhumian of the regional stratigraphic scale. Numerous localities of this level can be grouped into two geographical clusters, the northern one being confined to the Kama River Basin, and the southern one to the Orenburg Region and Southern Bashkortostan. Regarding the southern localities, three floras that are seemingly successive in time can be distinguished. Against a common background of articulates (Paracalamites and Equisetites), the lowermost flora is characterized by the dominance of leaves of Rufloria (Cordaitanthales) with very rare conifers. Conifers (Quadrocladus, Sashinia, Dvinostrobus) and leaves of Phylladoderma (Peltaspermales) are the most abundant elements of the middle assemblage, whereas Rufloria leaves are very seldom found together with the peltasperm Ginkgophyllum and the conifer-like Steirophyllum. The uppermost flora is dominated by Odontopteridium and Ustyugia, two closely related genera of peltasperms, whereas cordaitaleans are totally absent. Comparison with the northern localities, which can be linked to the type sections of the Upper Kazanian and the Urzhumian, enables the dating of these assemblages in terms of the regional stratigraphic scale. All three floras prove to be confined to the uppermost Kazanian, and only the youngest one could also occur in the lowermost Urzhumian. As the stratigraphic ranges of all observed plant taxa exceed the total stratigraphic interval under study, the sequence of the floras seems to be caused by ecological (most likely climatic) factors rather than the actual evolution of plants. In particular, the observed gradual elimination of cordaitaleans confirms the general view on the extinction of this group on the Russian Platform. The southwestern boundary of the occurrence of cordaitaleans on the Russian Platform stretched from the southwest to the northeast, approximately parallel to the palaeolatitudes reconstructed on the basis of palaeomagnetic data. During the Guadalupian it moved to the northeast, which is to the north considering the position of the North Pole of that time. Cordaitaleans were the main peat-forming plants in the Late Palaeozoic of northern Pangea (in the Kuznetsk, Tunguska and Pechora Basins). So their retreat to the north was most likely a consequence and a reflection of the warming and drying of the climate.

Depositional history of a condensed shallow marine reservoir succession: stratigraphy and detrital zircon geochronology of the Jurassic Stø Formation, Barents Sea

The Early to Middle Jurassic Stø Formation (Toarcian to Bajocian) was deposited in a relatively shallow (10 s of meter deep) epicontinental sea in northern Pangea and represents one of the most prolific reservoir intervals in the Barents Sea basin. It comprises a condensed, predominantly shallow marine succession characterized by long hiatuses and erosional reworking with several horizons of extraformational pebble grade conglomerate. Six distinct facies associations describe sedimentological environments ranging from transgressive, tidal, fluvial and regressive shoreface. Deposits are interpreted and correlated within three sequence stratigraphic units (SI to SIII) which reflect variations in relative sea-level during an overall transgression of the basin. Interpreted depositional systems show subtle variations in petrographic character, but provenance analyses reveal different sedimentary sources. Thirteen core samples distributed geographically and stratigraphically were analysed for detrital zircon U-Pb geochronology. Data show that the Southwestern Barents Sea Basin (SWBSB) was dominated by mixing of reworked material and coarse grained sediment supply from extrabasinal source areas including a Caledonian provenance in the southwest and a Fennoscandian provenance to the southeast. Intra-basinal erosion of underlying strata with Triassic zircon grains dominate in northern parts of the basin. Supplementary material : Supporting information relating to the analysis of different dataset and the interpretations presented in the paper are available at https://doi.org/10.6084/m9.figshare.c.3841282 .

Evidence for Late Triassic provenance areas and Early Jurassic sediment supply turnover in the Barents Sea Basin of northern Pangea

We used detrital zircon fractions from the Late Triassic to Early Jurassic sedimentary succession in the Norwegian Barents Sea to constrain the role of eastern provenance areas in the basin infill history of the Northern Pangea Boreal basin. Geochronological data from sedimentary rocks in this succession reveal detrital zircon ages that are very close to the biostratigraphically defined maximum depositional age of the two lowermost intervals: The Norian to Rhaetian Fruholmen Formation show U-Pb minimum ages of 208.3 ± 4.2 Ma (discordant by -0.58) and 213.8 ± 5 Ma (discordant by 0.8), and the Rhaetian to Sinemurian Tubaen Formation is 200.6 ± 4.9 Ma (discordant by -3.99) at its minimum. These are the youngest ages thus far documented in the Norwegian Barents Sea, and they demonstrate that a provenance area was magmatically active while, or shortly before, these formations were being deposited. Such protolith ages have not been documented close to the study area, but based on the regional tectonic setting and paleogeography, we argue that the Novaya Zemlya protrusion of the northern Uralian orogen was the most likely provenance area in the region. The Sinemurian to Pliensbachian Nordmela Formation samples yielded, with an exception of a single detrital zircon age of 211 ± 4.3 Ma, a consistent 240–237 Ma minimum detrital zircon age, which suggests that either the magmatic activity or the sediment supply had come to an end by Sinemurian times. This turnover can be explained by a change in the hinterland drainage pattern. This study documents that eastern provenance areas were actively supplying sediments into the Norwegian Barents Sea Basin later than previously assumed, and our data offer age constraints for tectonic activity in the basin and its hinterland inferred from the changes in sediment supply to the basin.

Nearshore euxinia in the photic zone of an ancient sea: Part II – The bigger picture and implications for understanding ocean anoxia

Biomarker, palaeontological and isotopic evidence suggests that the Late Permian carbonate seas, i.e. the Northern (NPB) and Southern (SPB) Permian basins of northern Pangea, were characterized by significant spatial and temporal variations in the palaeowater-column redox state. This is particularly the case with regard to the deposition of the Lopingian Zechstein cycle 2 carbonate rocks. A shelf to basin reconstruction of environmental conditions was achieved by analysing nearly 400 core samples from 49 wells. This allowed an evaluation of the spatial variations in facies and broad oceanographic conditions at the basin scale. Specifically, in the lower slope and shallow-basin facies of the northern margin of the SPB (present-day northern Poland and eastern Germany), highly variable concentrations of the green sulphur bacterial biomarkers chlorobactane and isorenieratane (and their likely degradation products, C15 to C31 2,3,6-aryl isoprenoids, indicative of photic zone euxinia) and homohopane indices (indicative of anoxia), combined with the presence of a benthic fauna and bioturbation, indicate a variable but occasionally anoxic/euxinic water column. Locally in lagoonal facies in the northern and southern margin of the SPB, euxinic conditions also developed but these were likely associated with localised conditions or benthic production in association with microbialites. The presence of gammacerane in the eastern SPB (south-eastern Germany and eastern Poland) suggests elevated salinities there, compatible with the restricted configuration of the basin. However, a lack of these signatures in basinal settings of the eastern SPB indicates that strongly reducing conditions were restricted to the lower slope and shallow-basin locations and restricted lagoons, and were not developed in the basin centre. Moreover, this anoxia/euxinia in marginal settings is restricted to the north-eastern part of the SPB. The south-eastern part of the SPB (SE Poland), in contrast, is devoid of evidence for PZE. The southern margin of the SPB is also characterized by generally oxic-suboxic conditions, with local anoxia limited to more restricted embayments, and elevated salinities limited to restricted oxic-anoxic lagoons. In the western SPB (NE England and adjacent offshore) and the NPB (Outer Moray Firth, offshore Scotland) the water columns were oxic-suboxic. Overall, it appears that high but episodic primary bioproductivity of organic matter was concentrated on (or even limited to) the lower slopes of the SPB's north-eastern margin and the restricted lagoons and shallow basin of its southern margin, leading to the formation of source rocks for petroleum in these areas. In addition, the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large and more widespread quantities of organic matter; in fact TOC contents exhibit a poor correlation with ecological and anoxia indicators. Crucially, this work confirms that the strong evidence for PZE observed in shelf and lower slope/shallow-basin facies of the north-eastern SPB need not be associated with widespread, basin-scale anoxia; this conclusion has implications for organic matter burial, carbon cycling and biotic crises during other times in Earth history.

Tectonic evolution of Western Tethys from Jurassic to present day: coupling geological and geophysical data with seismic tomography models

ABSTRACTThe geodynamic evolution of the Western Tethys is characterized by multiple phases of rifting, seafloor spreading, subduction, and collisional events. Regional reconstructions are highly dependent on the kinematic history of the major plates bounding the Atlantic and Tethyan tectonic domains, as well as small micro-plates resulted from the fragmentation of northern Gondwanaland. The complexity of tectonic events in this area leads to major discrepancies between competing models about the timing, location, and polarity of subduction zones, for both the Cenozoic evolution and earlier phases. We focus on unravelling the Mesozoic evolution of the Western Tethys. We first reassessed kinematic models for the Early Jurassic–Late Cretaceous opening of the central, north central, and north Atlantic and used these as boundary conditions on the kinematic reconstructions of the Tethyan realm. We combined reconstructions of rifting and early seafloor spreading in northern Pangea that incorporate quantitative estimates of continental extension, and suggest a transtensional motion of Iberia relative to Europe in Early Cretaceous time to fit within the refined plate configuration of Central North Atlantic. We combined this regional framework with a recently published model for the motion of smaller blocks within the Western Tethys; from this model, we created synthetic isochrons for extinct oceanic basins and built evolving topological plate boundaries based on the new rigid plate model to derive a self-consistent and time-dependant model for the last 200 million years. We then examined the consistency of subduction history implied by the kinematic reconstructions, by comparing reconstructed plate boundary configurations to mantle velocity structure imaged by a range of seismic tomography models. Our results show that a satisfactory match can be made between Cenozoic subduction events in the Western Tethys region and observed shallow tomographic high-velocity material. However, the match is less clear for older subducted material. Correlations between surface reconstructions and deep Earth structure suggest that mid-deep mantle seismic features under present day Northeast-Central and Northwest Africa-Arabia may correspond with the Mesozoic subduction systems in the Vardar Ocean, Alpine Tethys, and Western Neotethys, respectively. These correlations support a model with intra-oceanic subduction of the Vardar Ocean from Middle Jurassic to Early Cretaceous, and mid-Early Cretaceous initiation of oceanic subduction in the Ligurian-Piemont Ocean. The results from the plate-tomography comparison suggest the existence of oceanic subduction in the Alpine Tethys Oceans in late early Cretaceous time. We investigated the uncertainties in the tectonic model in terms of absolute and relative plate motion and surface velocities and showed that choice of absolute reference frame can partially account for the lateral offset between the Vardar subduction zone and associated slab material in deep mantle; additional mismatches may be attributable to the limitations of our methodology, such as the assumption that slabs sink vertically.

Climatic impact on the reef biota in the Cisuralian and Guadalupian (Permian), East European Platform

Abstract As important components of extinct as well as modern reefs, the measurement of changes in the composition of reef biota is crucial in order to evaluate the influence of extrinsic factors on the marine communities. The dramatic abiotic changes in the eastern and northern Pangea was mirrored by a gradual transition from a photozoan to a heterozoan association and the appearance of cool- (temperate-) water carbonates both in reef and carbonate ramp environments. Analyses of large skeletal and microbiotic components as well as microfacies succession were used for detailed explanation of reef structure, especially for lesser-known heterozoan skeletal mounds. The youngest skeletal mounds are recognized in the Roadian. The stable isotope data demonstrated a negative oxygen shift between latest Sakmarian and late early Artinskian coinciding with the end of P2 glaciation. The multiplicative nature of the event included the series of successive changes of extrinsic factors such as ice melting in interglacial episodes, eustatic ocean level rise, change of oceanic circulation and decrease of water temperature. The late Artinskian and subsequent Kungurian climatic impacts in the Northern Hemisphere were irreversible for the photozoan biota and prevented its further development. Roadian (Guadalupian) bryonoderm extended skeletal mounds developed in rather warm-water environments.

Triassic river systems and the paleo-Pacific margin of northwestern Pangea

Detrital zircon U–Pb ages from Triassic strata exposed in the circum-Arctic, analyzed by LA-ICP-MS and SHRIMP-RG, are compared at the regional scale to better understand the paleogeography of northern Pangea and help restore rift opening of the Arctic. Data sets are compared based on their zircon age distributions, cumulative age probability plots, and the K–S test. Three major source regions are characterized. These fed clastic material to transcontinental river systems that transported material from the highlands of northwestern Pangea to its once continuous paleo-Pacific continental margin. The paleo-Lena River System was fed from sources in the Baikalian and Altay-Sayan mountainous regions of Siberia. Zircon populations are characterized by a limited number of Precambrian zircons (~1.8–2.0Ga with fewer ~2.5–3.0Ga), lack of 0.9–1.8Ga zircons, and a dominant 480–500Ma and 290–300Ma age population. The paleo-Taimyr River System was sourced from the Uralian orogenic belt region and deposited along a rifted portion of the Siberia–Baltica margin beginning in the Permo–Triassic. Precambrian zircon populations are similar to those of the paleo-Lena system, and samples closest to Siberia have similar populations in the 480–500Ma and 290–300Ma age ranges. Chukotka, Wrangel Island and Lisburne Hills, Alaska, have sparse ages between 900 and 1800Ma, Ordovician ages are younger (~440–450Ma), and, along with abundant ~300Ma ages, they contain ~250–260Ma and lesser ~215–235Ma zircons, interpreted as derived from silicic volcanic centers associated with Permo–Triassic to Triassic continental flood basalt provinces in Siberia, Taimyr and Kara Sea region. The trans-Laurentian River System was likely fed by rift-related uplift along the proto North Atlantic/Arctic margin and delivered sediment to the Cordilleran margin of Pangea. These samples have no significant upper Paleozoic zircons and have a much broader age range of Precambrian zircons.

The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation.

BackgroundArchosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains.Methodology/Principal FindingsWe redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Röt Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation.Conclusions/SignificanceComprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs.

CARBONIFEROUS NON‐MARINE SOURCE ROCKS FROM SPITSBERGEN AND BJØRNØYA: COMPARISON WITH THE WESTERN ARCTIC

In this paper, we demonstrate that Carboniferous coaly and lacustrine strata have significant liquid hydrocarbon potential in an area extending from the Norwegian Barents Sea in the east to the Canadian Arctic in the west. Organic geochemical analyses were conducted on seven coals and coaly shales from the islands of Spitsbergen (Svalbard archipelago) and Bjørnøya (Norwegian Barents Sea). The results were interpreted in the context of published data from the two areas, and of time‐equivalent non‐marine successions on the Finnmark Platform (Norwegian Barents Sea), East Greenland, and the Sverdrup Basin (Canadian Arctic). In each of these areas, a warm and humid climate, together with the onset of rifting on the northern Pangea margin, facilitated the deposition and preservation of organic‐rich non‐marine sediments on a regional scale. All of the sediments have an elevated content of liptinitic macerals, dominated by alginite or sporinite. In the studied areas, the prolific younger source rocks which may be common in adjacent regions are often immature or absent. The identification of Carboniferous terrestrial strata with source rock potential may therefore enhance the petroleum potential of the studied regions.

Recent volcanism in relation to plate interaction and deep-level geodynamics

The spatial distribution of recent (under 2 Ma) volcanism has been studied in relation to mantle hotspots and the evolution of the present-day supercontinent which we named Northern Pangea. Recent volcanism is observed in Eurasia, North and South America, Africa, Greenland, the Arctic, and the Atlantic, Indian, and Pacific Oceans. Several types of volcanism are distinguished: mid-ocean ridge (MOR) volcanism; subduction volcanism of island arcs and active continental margins (IA + ACM); continental collision (CC) volcanism; intraplate (IP) volcanism related to mantle hotspots, continental rifts, and transcontinental belts. Continental volcanism is obviously related to the evolution of Northern Pangea, which comprises Eurasia, North and South America, India, Australia, and Africa. The supercontinent is large, with predominant continental crust. The geodynamic setting and recent volcanism of Northern Pangea are determined by two opposite processes. On one hand, subduction from the Pacific Ocean, India, the Arabian Peninsula, and Africa consolidates the supercontinent. On the other hand, the spreading of oceanic plates from the Atlantic splits Northern Pangea, changes its shape as compared with Wegener’s Pangea, and causes the Atlantic geodynamics to spread to the Arctic. The long-lasting steady subduction beneath Eurasia and North America favored intense IA + ACM volcanism. Also, it caused cold lithosphere to accumulate in the deep mantle in northern Northern Pangea and replace the hot deep mantle, which was pressed to the supercontinental margins. Later on, this mantle rose as plumes (IP mafic magma sources), which were the ascending currents of global mantle convection and minor convection systems at convergent plate boundaries. Wegener’s Pangea broke up because of the African superplume, which occupied consecutively the Central Atlantic, the South Atlantic, and the Indian Ocean and expanded toward the Arctic. Intraplate plume magmatism in Eurasia and North America was accompanied by surface collisional or subduction magmatism. In the Atlantic, Arctic, Indian, and Pacific Oceans, deep-level plume magmatism (high-alkali mafic rocks) was accompanied by surface spreading magmatism (tholeiitic basalts).

Evidence for a western extension of the Angaran phytogeographic province in the Early Permian

Abstract A newly described Early Permian fossil plant assemblage in the Mt. Dall conglomerate in the Farewell terrane (Alaska Range, USA) is analyzed from a paleobiogeographic perspective. These data constitute the youngest paleontological dataset yet discovered in this terrane, represent the terrane's only predominantly terrestrial fossil assemblage, and are the only plant macrofossil remains of Early Permian age within a > 1500 km radius today. A suite of multivariate statistical analyses comparing the Mt. Dall paleoflora to similar age (Asselian–Artinskian) collections from the Angaran, Euramerican, and Cathaysian Permian phytogeographic provinces reveals that the Mt. Dall paleoflora has a paleobiogeographic affinity with Sub-Angaran plant fossil assemblages collected from Mongolia and the Primorye region of southeastern Russia. The paleoflora has dual importance in the construction and testing of hypotheses for which there are geographically and temporally few controls. First, these data may be used in association with other faunal and floral remains to test models of the assembly of Alaska, which seek, in part, an understanding of the paleogeographic and lithological origins of accreted terranes. That the Mt. Dall paleoflora indicates mixed Eurasia–North America paleobiogeographic affinity among individual taxa and plots in multivariate space with mid-latitude assemblages on northern Pangea may suggest deposition in that latitudinal belt. Second, contrary to the well-sampled fossil plant-bearing Permo-Carboniferous of the paleotropics and the northeastern temperate Pangean regions (Angaraland), terrestrial biome structure and vegetation type of northwestern Pangea are poorly known. This lack of understanding is due to the paucity of paleofloral collections from this region in this time period and the paleogeographic uncertainty of their position along the ancient active margin of Laurentia. The Mt. Dall paleoflora's phytogeographic affinity to paleobotanical collections from the northeastern Pangea therefore suggests that the Angaran province extended meridionally westward in the Early Permian into what is now northern North America.

Permian climate development in the northern peri-Tethys area — The Lodève basin, French Massif Central, compared in a European and global context

The Lodève basin, which contains an exceptional long and nearly uninterrupted profile of Early to Late Permian continental red beds, is well correlated to the other European Permocarboniferous basins. Together they cover the time span from the Late Pennsylvanian to the Permian–Triassic boundary. Although these basins were placed within the equatorial belt for the whole Permian, several climatic changes are recorded in the sediments. Terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree. Therefore, small scale climatic variations of the Milankovitch band are hardly discernable and if so, they could not be correlated between different basins. Indeed, larger scale climatic shifts could be identified. It is shown, that the shift from the Carboniferous icehouse to the Mesozoic warmhouse was a multi-stage process. This global warming resulted in a general aridisation of northern Pangea, indicated by outspreading playa and sabkha red beds, aeolianites and evaporites. Several short phases of increased humidity interrupted this trend, indicated by wet red beds, lake sediments and coal deposits. In central and southern Europe, these wet periods are traceable within the Late Stephanian/Lower Rotliegend (Gzhelian/Asselian), topmost Lower Rotliegend (Asselian/Sakmarian), Upper Rotliegend I (late Artinskian/early Kungurian) and Upper Rotliegend II/Zechstein (Wuchiapingian). The aridisation of the northern Pangea which accelerated near the Sakmarian/Artinskian transition is attributed to a reorganisation of the major ocean currents. Cold water currents along the western flank of the Pangea, indicated by the Permian chert event, blocks moisture transport from West onto the continent. During Roadian and Wordian the onset of an additional cold water current along the Cimmerian continents, blocks moisture transport from the East. Both phenomena together are responsible for the maximum of aridity at the Early to Middle Permian transition. Additionally, the equatorial climate has been affected by an increasing seasonality within the Late Pennsylvanian and Permian, caused by the wide shifting of the Zone of Inter-tropical Convergence (ITC) over the equator. Based on a new reconstruction of the Pangean assembly in this paper, climatic changes in the Permian are interpreted and causes of the arid-humid-arid shifts are examined . Phases of higher humidity are often related to events of global impact, like the waxing and waning of the Gondwanan glaciation, obtained in the South African Karoo Basin (Dwyka Group). But also regional events had strong climatic influence. The Zechstein transgression in the Northern and Southern Permian Basin as well as the Bellerophon transgression of the Southern Alps caused the wet phase in the Wuchiapingian.