Despite more the 40 years of active debate, consensus interpretations of the late Palaeozoic-early Mesozoic tectonic-related geology of the northern periphery of Gondwana, including central and ...western Turkey, the south Aegean, the southern Balkans and Sicily remain elusive. Recent plate tectonic reconstructions differ drastically for this region. Utilising published information this paper summarises, interprets and discusses a large body of multidisciplinary geological evidence related to the transition from Palaeotethys to Neotethys, mainly during late Carboniferous to early Jurassic time. Key geological information is outlined, discussed, and then used to test alternative plate tectonic models: none are entirely convincing.
During the Carboniferous, the developing Varsican orogen of central Europe passed eastwards into a marine gulf, then into Palaeotethys. Plate convergence and continental collision constructed the Varsican orogen in central Europe by end-early Carboniferous (c. 320 Ma), whereas subduction continued farther east. Variscan continental collision in central and western Europe was followed by late Carboniferous-Permian orogenic collapse, extension/transtension and widespread right-lateral strike-slip displacements that are also likely to have affected the Balkan-Aegean and Anatolian regions.
In the South Aegean, the Balkans (e.g. Albania, Croatia, Bosnia-Herzegovina, Slovenia) and Sicily, Permian-early Triassic basin development, including volcanism, relates to crustal extension/transtension adjacent to the northern margin of Gondwana. Palaeogeography played an important role in Permian-Triassic clastic sediment deposition (e.g. detrital zircons), in addition to plate tectonic setting.
In central and western Turkey, much evidence links the Afyon zone (Anatolides) to adjacent north Gondwana, rather than supporting an origin as an exotic Eurasian terrane that collided with the Tauride continent during latest Triassic time. Evidence from the Eurasian periphery (Bulgaria; N Turkey; Armenia; Georgia; Iran) favours overall northward subduction of Palaeotethys. However, the evidence of upper Carboniferous accretionary complexes in central and western Turkey (Konya Complex, Teke Dere Unit) and the eastern Aegean (Karaburun melange in Turkey; Chios melange in Greece), coupled with upper Carboniferous calc-alkaline granitic magmatism in the Afyon zone, suggests a short-lived southward subduction event along the N margin of Gondwana (i.e. bivergent subduction).
During the Triassic, northward subduction persisted along the Eurasian margin, whereas the opposing North Gondwana margin rifted, associated with late Triassic opening of the both the S Neotethys (=Mesogea) and the N Neotethys (=İzmir-Ankara-Erzincan ocean). Interpretations involving a Triassic relict Palaeotethys, followed by continent-continent collision in the south Aegean (e.g. Crete; Peloponnese) are problematic. Instead, pulsed continental extension appears to have culminated in rifting of ‘Cimmeria' from N Africa (Apulia) during the Triassic and opening of both the S Neotethys to the south and the Pindos ocean to the north (in present co-ordinates).
Regional plate tectonic reconstructions remain disparate because the Africa-Eurasia plate framework is poorly constrained prior to the early Jurassic, evidence is concealed beneath the sea or land, or was lost during later subduction/collision. Large-plate tectonics have limited applicability in relatively narrow oceanic areas involving microcontinents, rifts, small ocean basins and strike-slip displacements. Additional field-based studies of key exposures are a priority.
Investigation of large populations of peteinoid acritarchs recovered from Middle Ordovician strata of the Hälludden and Horns Udde quarry sections (Öland, Sweden) allows for statistical analyses ...based on morphometric measurements. The results indicate the presence of assemblages with a continuous variability of morphotypes, thus a distinction of different peteinoid acritarch taxa in the sections proved to be impossible. This challenges the currently accepted classification based on a differentiation into the three genera Peteinosphaeridium, Cycloposphaeridium and Liliosphaeridium, and a multitude of different species; individual taxa are essentially arbitrary as morphotypes intergrade. Investigations on modern dinoflagellates show that these can develop variable cyst morphologies depending on environmental factors. By analogy, it can be hypothesised that the different morphologies observed among the peteinoid acritarchs from Öland are cysts produced by only very few phytoplanktic organisms (or even a single species) with high morphological variability.
The Early Palaeozoic metamorphic records play a crucial role in determining the geological connection between Hainan Island and the Gondwana supercontinent. Nevertheless, the geochronological data ...for the Early Palaeozoic period is still sparse in Hainan Island. In this study, we conducted an integrated UPb geochronological and geochemical analysis of crystals from six monazite and three titanite samples obtained from the Mesoproterozoic Baoban Complex in the western region of Hainan Island. The mineral morphology and elemental compositions suggest that the examined monazite and titanite crystals exhibit characteristics typical of a metamorphic origin. Monazite and titanite UPb dating show two distinct metamorphic age populations: ca. 453–464 Ma and ca. 430–437 Ma. Our new data, combined with a comprehensive synthesis of metamorphic-magmatic ages from previous studies and other geological observations, offers crucial constraints on the palaeogeographic position and potential timing for the amalgamation of the micro-continents along the fringe of the Gondwana supercontinent. We suggest that Hainan Island was geologically connected to the Gondwana supercontinent during the Early Palaeozoic, a relationship that may have persisted until ca. 430 Ma. By this time, Hainan Island was probably closely linked to the South China and Indochina blocks.
•Monazite and titanite in the Baoban Complex are both metamorphic in origin.•Monazite and titanite record notable metamorphic age population of 430–437 Ma.•Hainan Island had an affinity with the Gondwana supercontinent during the Early Palaeozoic.•Until ca. 430 Ma, Hainan Island remained closely associated with South China and Indochina.
Concurrent gaps in the Late Devonian/Mississippian fossil records of insects and tetrapods (i.e. Romer's Gap) have been attributed to physiological suppression by low atmospheric pO₂ Here, updated ...stable isotope inputs inform a reconstruction of Phanerozoic oxygen levels that contradicts the low oxygen hypothesis (and contradicts the purported role of oxygen in the evolution of gigantic insects during the late Palaeozoic), but reconciles isotope-based calculations with other proxies, like charcoal. Furthermore, statistical analysis demonstrates that the gap between the first Devonian insect and earliest diverse insect assemblages of the Pennsylvanian (Bashkirian Stage) requires no special explanation if insects were neither diverse nor abundant prior to the evolution of wings. Rather than tracking physiological constraint, the fossil record may accurately record the transformative evolutionary impact of insect flight.
The ability to live underground is widespread among continental vertebrates, so understanding the origin and early evolution of fossorial vertebrates and the architecture and function of the burrows ...they excavate is an important component of the history of Life on Earth. However, this topic has not been addressed in a synoptic manner; available information is scattered, hampering our understanding of the overall picture. Here, after a short overview of convergent morphological and behavioural adaptations seen in modern fossorial taxa and the diversity of extant vertebrate burrows, we review the fossil record of inferred vertebrate burrows and fossorial vertebrates from the Devonian to the Triassic. Results highlight a probable Devonian earliest occurrence of fossoriality in continental vertebrates (Dipnoi) and a Carboniferous earliest occurrence of fossoriality in tetrapods (Recumbirostra). During the Devonian–Carboniferous, burrows were probably used primarily for aestivation or temporary shelter and evidence of fossoriality is restricted so far to European and North American localities. During the Permian, fossoriality became geographically widespread and developed in new, distantly-related vertebrate lineages, such as diapsids and synapsids. Additionally, there was a size increase and all the main structural features of sub-vertical and sub-horizontal burrows were acquired, as well as the probable use of burrows as permanent shelters or for breeding. We show that the radiation of fossorial forms and increase in abundance and complexity of burrows are contemporaneous with climatic crises such as the Cisuralian aridification, culminating in the Artinskian Warming Event (AWE), and the end-Guadalupian and end-Permian extinction events. After the end-Permian mass extinction, vertebrate fossoriality became a common and widespread feature of continental environments and in more distal floodplain areas, probably as a consequence of changing fluvial regimes. During the Triassic, fossoriality is recorded in even more groups, such as Procolophonidae and Temnospondyli. The first definite complex burrows used as permanent shelters appeared as early as the Early Triassic, and evidence of shared burrow use by different clades appears, suggesting an emerging role of burrowers as ecosystem engineers.
A timeframe of glacial and nonglacial intervals in the Carboniferous and Permian systems of eastern Australia was published by Fielding et al. (2008a). In this scheme, eight discrete intervals (four ...in the Carboniferous: C1-C4, and four in the Permian: P1-P4) in which indicators of glacial activity and cold climate were preserved alternated with intervals in which no such evidence is preserved. The timeframe has been widely used both to better understand the time-space distribution of glacial events in eastern Australia and as a basis for comparison with late Palaeozoic glacial events in other regions of the world. In the period since publication of that paper, a large inventory of new, radiogenic isotope ages has become available for the late Palaeozoic strata in eastern Australia, and the time ranges of the global stages of the Carboniferous and Permian have also been adjusted in the light of new age data. Accordingly, this paper presents a reappraisal of the Fielding et al. (2008a) timeframe, based on the much-improved chronostratigraphic database. Of the Carboniferous glaciations, only C1 has changed significantly, expanding in time range downward. Of the Permian glaciations, P1 and P2 remain as in the previous evaluation, whereas P3 and P4 become significantly younger in absolute time. Indeed, the close of P4, supported by a large number of high-precision ages, is now estimated to have occurred at 254.5 Ma, only 2.6 m.y. before the end-Permian biotic crisis and extinction event. Carbon isotopic records from Permian marine strata reveal that alternating glacial and nonglacial conditions in eastern Australia corresponded to changes in the global carbon cycle. Palaeoweathering proxies show that the intensity of chemical weathering during the late Palaeozoic in eastern Australia changed in response to climate swings, with nonglacial intervals likely becoming warmer and more humid through the course of the Permian. There are broad coincidences between the timing of glaciations in eastern Australia and those recorded elsewhere on Gondwana, but sufficient differences to support the conclusion that glaciations were not synchronized across the ancient landmass. The eastern Australian record persists in being the best-constrained in time anywhere in the world.
•Time-space framework for late Palaeozoic glaciation in eastern Australia is revised.•C1 to C4 and P1 to P4 glaciations are retained.•P3 and P4 glaciations are younger than previously thought.•Close of P4 is at 254.5 Ma, only 2.6 m.y. before the end-Permian biotic crisis.•Despite some commonality, glaciations across Gondwana were not fully synchronized.
This study presents new zircon LA-ICP-MS U-Pb ages, zircon Hf isotopes, and whole-rock geochemical compositions for Late Palaeozoic-Early Mesozoic intrusive rocks from the Erguna Massif, Northeast ...China. Zircon U-Pb dating results indicate that the intrusive rocks were emplaced during the Late Permian-Middle Triassic (ca. 256-234 Ma) and Late Triassic (ca. 210 Ma) in the western and eastern parts of the Erguna Massif, respectively. The Late Permian gabbros and quartz monzodiorites display enrichment in Rb and K, but are depleted in Nb, Ta, and Ti. Their ε
Hf
(t) values (+5.1 to +9.1 and −0.2 to +3.7, respectively) and one-stage Hf model ages (T
DM1
= 544-704 Ma and 764-889 Ma, respectively) indicate that they might be derived from the reworking of the Neoproterozoic lithospheric mantle that was metasomatised by subduction-related fluids. The Late Permian-Early Middle Triassic quartz monzonites, monzogranites, and syenogranites display variable enrichment of rare earth elements (REEs) and large ion lithophile elements (LILEs). They have ε
Hf
(t) values varying from −5.7 to +2.7 with two-stage Hf model ages (T
DM2
) of 1.09-1.69 Ga, implying that they possibly originated from the Mesoproterozoic continental crust. The Late Triassic syenogranites show geochemical signatures of A2-type granites with various enrichment in LILEs and LREEs and depletion in Nb, Ta, and Ti. Combined with regional geological evidence, we conclude that Late Permian to Late Triassic igneous rocks on both sides of the Mongol-Okhotsk suture belt record an active continental margin environment associated with the ongoing bidirectional subduction of the Mongol-Okhotsk Ocean. The eastern Erguna Massif and Xing'an Massif were likely located in a back-arc setting at least since ca. 216 Ma, with long-term southward subduction of the Mongol-Okhotsk oceanic slab spanning from the Late Permian-Early Jurassic.
Past studies of the end-Permian extinction (EPE), the largest biotic crisis of the Phanerozoic, have not resolved the timing of events in southern high-latitudes. Here we use palynology coupled with ...high-precision CA-ID-TIMS dating of euhedral zircons from continental sequences of the Sydney Basin, Australia, to show that the collapse of the austral Permian Glossopteris flora occurred prior to 252.3 Ma (~370 kyrs before the main marine extinction). Weathering proxies indicate that floristic changes occurred during a brief climate perturbation in a regional alluvial landscape that otherwise experienced insubstantial change in fluvial style, insignificant reorganization of the depositional surface, and no abrupt aridification. Palaeoclimate modelling suggests a moderate shift to warmer summer temperatures and amplified seasonality in temperature across the EPE, and warmer and wetter conditions for all seasons into the Early Triassic. The terrestrial EPE and a succeeding peak in Ni concentration in the Sydney Basin correlate, respectively, to the onset of the primary extrusive and intrusive phases of the Siberian Traps Large Igneous Province.
During the Permian-Triassic transition, dramatic environmental changes occurred, including the segmentation of Pangaea and the beginning of the Alpine orogenic cycle with widespread magmatism and ...tectonic activity. The Permian-Triassic succession deposited in the northern (palaeo-) Gondwana is now exposed in the inner Northern Apennines where it crops out discontinuously in the Middle Tuscan Ridge, a NS-oriented morphotectonic feature mainly formed by blue-schist and green-schist facies metamorphic rocks. In this paper, we describe a previously unreported late Palaeozoic succession exposed in the central part of the Middle Tuscan Ridge: the Montagnola Senese Ridge. This succession provides information concerning the enigmatic late Palaeozoic units exposed in southern Tuscany, and permits the age constraint of continentalization at the Permian-Triassic boundary with associated magmatism. Specifically, by integrating stratigraphic, structural, and petrographic data, we describe a siliciclastic, volcanoclastic-to-carbonate succession which recorded the transition from marine sedimentation to the typical continental, red-beds of the Verrucano tectofacies. Additionally, deformational features, metamorphism and age of the succession are discussed in terms of its tectono-sedimentary evolution and implications for the Palaeozoic-Triassic setting of the central Pangaea sector currently exposed in southern Tuscany. The results allow us to recognize a middle-late Permian pre-Verrucano succession, and to date the transition to continental facies as latest Permian. The microflora permits correlation of the pre-Verrucano succession to the late Palaeozoic units of the inner Northern Apennines, and establishes the diachronous nature of the Verrucano tectofacies exposed in the inner Northern Apennines. Finally, the thermal maturity of the organic matter indicates a maximum temperature of 387 ± 30°C attained during metamorphism.
The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic-early Mesozoic granitoids that are ideal for investigating the ...tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U-Pb geochronological and Lu-Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic-early Mesozoic tectonism in the eastern CAOB. The zircon U-Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219-212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing'an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol-Okhotsk oceanic plate.
PDF
