Demir Altiner

Origin and assembly of the Tethyside orogenic collage at the expense of Gondwana Land

Abstract The Tethysides are a superorogenic complex flanking the Eurasian continent to the south and consisting of the Cimmerides and Alpides, products of Palaeo- and Neo-Tethys respectively. We here review their evolution, mainly on the basis of new maps showing the distribution of sutures, magmatic rocks, certain palaeobiogeographically and palaeoclimatologically significant taxa and facies, and fragments of Pan-African (900–450 Ma) orogenic system forming the basement of many Tethyside blocks. These are supplemented by palaeomagnetic data reported in the literature. A fundamental tenet of this paper is that major sutures which contain ophiolite fragments, represent tectonic sections between continental blocks where oceanic crust has been subducted. Palaeo-Tethys came into existence largely in late Carboniferous time. Coevally, it began to be consumed by both internal and peripheral subduction zones, which continued into the Permian; some of these had been inherited from pre-Tethyan times. In the later Permian, rifting subparallel with the northern margin of Gondwana Land began between the Zagros and Malaysia, separating a Cimmerian continent from N. Gondwana Land, and thus heralding the opening of Neo-Tethys and other smaller oceans that were back-arc basins of Palaeo-Tethys. This rifting possibly also extended farther west into Crete and mainland Greece. However, the North China block, Yangtze block, Huanan block, the eastern moity of the Qangtang block (North Tibet), and Annamia, all originally pieces of the end-Proterozoic-early Palaeozoic Gondwana Land, had already separated from it in pre-late Carboniferous times, possibly during the Devonian. All of these blocks, and the Cimmerian continent, were characterized by Cathaysian floral elements in late Palaeozoic time. Palaeomagnetic and palaeontological data showing the original Gondwana Land affinity of these continental blocks are supplemented by correlating late Proterozoic-early Palaeozoic Pan-African sutures, orogenic belts, and sedimentary basin fragments across Tethyside sutures. Late Permian foraminiferal provinces are related to this palaeogeographical interpretation. By Triassic times, most Cimmeride subduction zones were already in existence. The Cimmerian Continent accelerated its separation from Gondwana Land and—locally in the late Permian—began disintegrating internally along the Waser/Rushan-Pshart/Banggong Co-Nu Jiang/Mandalay ocean. By late Triassic time all of the Chinese blocks—except Lhasa-and Annamia had collided with each other and with Laurasia. The resulting enormous orogenic collage had a ‘soft cushion’ between itself and Laurasia, in the form of the enormous accretionary complex of the Songpan-Ganzi. This connection enabled Laurasian land vertebrates to reach south-east Asia by late Triassic time. In late Triassic to middle Jurassic times, most major Cimmeride collisions were completed. Widespread aridity in Central Asia occurred in late Jurassic time, probably in the rain shadow of the newly formed Cimmeride mountain wall. Neo-Tethyan subduction systems formed along the S. margin of the Cimmerides or within Neo-Tethyan oceanic lithosphere during the Jurassic. Most, if not all, were north- or east-dipping. They continued the northerly migration of the Tethyside blocks. Evolution of the Tethysides influenced the distribution of marine and terrestrial organisms, and affected sea-level changes and patterns of atmospheric circulation during much of the Mesozoic and Cainozoic. It is likely to have reflected the surface expression of a persistent trend in the large-scale convective circulation in the mantle, that continuously transported material northward into the Tethyan domain.

Erosional truncation of uppermost Permian shallow-marine carbonates and implications for Permian-Triassic boundary events

On shallow-marine carbonate buildups in south China, Turkey, and Japan, uppermost Permian skeletal limestones are truncated by an erosional surface that exhibits as much as 10 cm of topography, including overhanging relief. Sedimentary facies, microfabrics, carbon isotopes, and cements together suggest that erosion occurred in a submarine setting. Moreover, biostratigraphic data from south China demonstrate that the surface postdates the uppermost Permian sequence boundary at the global stratotype section and truncates strata within the youngest known Permian conodont zone. The occurrences of similar truncation surfaces at the mass-extinction horizon on carbonate platforms across the global tropics, each overlain by microbial buildups, and their association with a large negative excursion in δ 13 C further suggest a causal link between erosion of shallow-marine carbonates and mass extinction. Previously proposed to account for marine extinctions, the hypothesis of rapid carbon release from sedimentary reservoirs or the deep ocean can also explain the petrographic observations. Rapid, unbuffered carbon release would cause submarine carbonate dissolution, accounting for erosion of uppermost Permian skeletal carbonates, and would be followed by a pulse of high carbonate saturation, explaining the precipitation of microbial limestones containing upwardgrowing carbonate crystal fans. Models for other carbon-release events suggest that at least 5 × 10 18 g of carbon, released in <100 k.y., would be required. Of previously hypothesized Permian-Triassic boundary scenarios, thermogenic methane production from heating of coals during Siberian Traps emplacement best accounts for petrographic characteristics and depositional environment of the truncation surface and overlying microbial limestone, as well as an associated carbon isotope excursion and physiologically selective extinction in the marine realm.

Cretaceous and Triassic subduction-accretion, high-pressure–low-temperature metamorphism, and continental growth in the Central Pontides, Turkey

Biostratigraphic, isotopic, and petrologic data from the Central Pontides document major southward growth of the Eurasian continental crust by subduction-accretion during the Cretaceous and Triassic Periods. A major part of the accreted material is represented by a crustal slice, 75 km long and up to 11 km thick, consisting of metabasite, metaophiolite, and mica schist that represent underplated Tethyan oceanic crustal and mantle rocks. They were metamorphosed at 490 degrees C and 17 kbar in mid-Cretaceous time (ca. 105 Ma). The syn-subduction exhumation occurred in a thrust sheet bounded by a greenschist facies shear zone with a normal sense of movement at the top and a thrust fault at the base. A flexural Foreland basin developed in front of the south-vergent high-pressure-low-temperature (HP-LT) metamorphic thrust sheet; the biostratigraphy of the foreland basin constrains the exhumation of the HP-LT rocks to the lbronian-Coniacian, similar to 20 m.y. after the HP-LT metamorphism, and similar to 25 m.y. before the terminal Paleocene continental collision. The Cretaceous subduction-accretion complex is tectonically overlain in the north by oceanic crustal rocks accreted to the southern margin of Eurasia during the latest Triassic-earliest Jurassic. The Triassic subduction-accretion complex is made up of metavolcanic rocks of ensimatic arc origin and has undergone a high pressure, greenschist facies metamorphism with growth of sodic amphibole. Most of the Central Pontides consists of accreted Phanerozoic oceanic crustal material, and hence is comparable to regions such as the Klamath Mountains in the northwestern United States or to the Altaids in Central Asia.

Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: implications for tempo and mode of biotic recovery from the end-Permian mass extinction

Abstract Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems.

Marine anoxia and delayed Earth system recovery after the end-Permian extinction

Significance The end-Permian mass extinction not only decimated taxonomic diversity but also disrupted the functioning of global ecosystems and the stability of biogeochemical cycles. Explaining the 5-million-year delay between the mass extinction and Earth system recovery remains a fundamental challenge in both the Earth and biological sciences. We use coupled records of uranium concentrations and isotopic compositions to constrain global marine redox conditions across the end-Permian extinction horizon and through the subsequent 17 million years of Earth system recovery. Our finding that the trajectory of biological and biogeochemical recovery corresponds to variations in an ocean characterized by extensive, shallow marine anoxia provides, to our knowledge, the first unified explanation for these observations. Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and 238U/235U isotopic compositions (δ238U) of Upper Permian−Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ238U across the end-Permian extinction horizon, from ∼3 ppm and −0.15‰ to ∼0.3 ppm and −0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans—characterized by prolonged shallow anoxia that may have impinged onto continental shelves—global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe.

Late Permian Foraminiferal Biofacies Belts in Turkey: Palaeogeographic and Tectonic Implications

Abstract Upper Permian marine carbonates are distinguished in two contrasting biofacies belts in Turkey. The Southern Biofacies Belt, represented by low-energy inner platform deposits of the Tauride Belt and the Arabian Platform, is rich in algae and smaller foraminifera but poor in fusulines. The Kubergandian and Murgabian stages are missing, although the rest of the Upper Permian consists of monotonous, shallow-marine carbonate deposits. The extremely tectonised and fragmented Northern Biofacies Belt includes the Upper Permian of the Karakaya Orogen and outer platform or platform margin deposits of the Tauride Belt. These deposits are rich in parachomata-bearing fusulines comprising Cancellina, Verbeekina, Afghanella, Sumatrina, Neoschwagerina and Yabeina. The reconstructed biostratigraphic scheme indicates that all Upper Permian stages (Kubergandian-Dorashamian) are present. The lateral continuity of the two biofacies belts is detected by the presence of tongues of he Northern Biofacies Belt pinching out in the Southern Biofacies Belt. Upper Permian blocks in the Karakaya Orogen display similar palaeontologic and biofacies characteristics, with the outer platform or platform margin deposits of the Taurides constituting the northernmost extension of the carbonate platform. This platform was probably facing a basin or a trough to the north. The lack of any transgressive Upper Permian deposits resting unconformably on the pre-Permian basement of the Sakarya Continent strongly suggests that such a basin was located between the Late Permian carbonate platform in the south and the basement rocks of the future Sakarya Continent in the north.

CYCLIC SEDIMENTATION ACROSS THE PERMIAN – TRIASSIC BOUNDARY (CENTRAL TAURIDES, TURKEY)

The best preserved Permian-Triassic boundary beds in Turkey are found in the Hadim region of the central Taurides. The succession is exposed in one of the allochthonous units of the Tauride Belt, the Aladag Unit, whose stratigraphy includes beds ranging from the Devonian to the Cretaceous systems. In the Aladag Unit, the Permian-Triassic boundary beds are entirely composed of carbonates. The Permian portion of these beds belongs to the Paradagmarita Zone, whereas the lowermost Triassic contains the Lower Griesbachian marker Rectocornuspira kalhori . The uppermost Permian carbonates, composed of meter-scale upward shallowing subtidal cycles, are characterized by oolitic limestones of regressive character at the top and are overlain sharply by Lower Triassic stromatolites. Cyclic Upper Permian carbonates are interpreted as highstand sytems tract deposits of the last third-order sequence of the Permian System. The Permian-Triassic boundary is an unconformity corresponding to both erosional and non-depositional hiatuses. The gap at the Permian-Triassic boundary partially corresponds to the shelf-margin systems tract and partly to the transgressive systems tract of the overlying third-order sequence. Stromatolites are interpreted as transgressive systems tract deposits. Special issue International Conference on Paleozoic Foraminifera, Paleoforams 2001 Edited by Demir Altiner (Guest Editor)

MIDDLE JURASSIC-LOWER CRETACEOUS BIOSTRATIGRAPHY IN THE CENTRAL PONTIDES (TURKEY): REMARKS ON PALEOGEOGRAPHY AND TECTONIC EVOLUTION

The deposition of Jurassic-Lower Cretaceous carbonates in the Pontides was controlled mainly by the evolution of an Atlantic-type continental margin in the Tethys. The study of several stratigraphic sections from allochthonous slices and blocks of the North Anatolian Ophiolitic Melange provided insight into the Middle Jurassic-Early Cretaceous paleogeographic evolution of the Central Pontide Belt. The Callovian-Aptian successions span the Globuligerina gr. oxfordiana, Clypeina jurassica (equivalent of the Tubiphytes morronensis zone), Protopeneroplis ultragranulata (with the Haplophragmoides joukowskyi subzone), Montsalevia salevensis , Hedbergella delrioensis - Hedbergella planispira - Leupoldina - Globigerinelloides and Globigerinelloides algerianus biozones. Two major stratigraphic gaps corresponding to the pre-Callovian and Hauterivian-Early Aptian ages are recognised within the successions. Lithostratigraphic and biostratigraphic studies indicate strong similarities in the evolution of the successions in the Amasya region (Central Pontides) and Biga-Bursa-Bilecik (BBB ) Platform (North-western Anatolia).

Within- And Among-Genus Components Of Size Evolution During Mass Extinction, Recovery, And Background Intervals: A Case Study Of Late Permian Through Late Triassic Foraminifera

Abstract One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within- and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within- and among-genus components. We find that size reduction following the end-Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within-lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within- and among-lineage processes rather than from large but offsetting effects of within- and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms.

Triassic limestone, turbidites and serpentinite–the Cimmeride orogeny in the Central Pontides

The basement of the Central Pontides, and by implication that of Crimea, consists of pre-Permian low-grade metaclastic rocks intruded by latest Permian – Early Carboniferous (305–290 Ma) granitoids. Further up in the stratigraphic sequence are Triassic limestones, which are now preserved as olistoliths in the deformed Upper Triassic turbidites. New conodont and foraminifera data indicate an Anisian to Carnian (Middle to Late Triassic) age for these hemi-pelagic Hallstatt-type limestones. The siliciclastic turbidites surrounding the Triassic limestone contain the Norian (Late Triassic) bivalve Monotis salinaria ; the same species is also found in the Tauric series in Crimea. The Upper Triassic flysch in the Central Pontides is locally underlain by basaltic pillow lavas and includes kilometre-size tectonic slices of serpentinite. Both the flysch and the serpentinite are cut by an undeformed acidic intrusion with an Ar–Ar biotite age of 162 ± 4 Ma (Callovian–Oxfordian). This indicates that the serpentinite was emplaced into the turbidites before Middle Jurassic time, most probably during latest Triassic or Early Jurassic time, and that the deformation of the Triassic sequence pre-dates the Middle Jurassic. Regional geological data from the circum-Black Sea region, including widespread Upper Triassic flysch, Upper Triassic eclogites and blueschists of oceanic crustal affinity, and apparent absence of a ‘Cimmerian continent’ between the Cretaceous and Triassic accretionary complexes indicate that the latest Triassic Cimmeride orogeny was accretionary rather than collisional and is probably related to the collision and accretion of an oceanic plateau to the southern active margin of Laurasia.