Academic literature on the topic 'Cimmerian blocs'

Abstract Eastern Myanmar is an indispensable part of the Cimmerian Continent with Gondwana provenance. Fusulinids from Eastern Myanmar remain poorly known despite their biochronological and paleogeographical significance. This paper describes Rugososchwagerina (Xiaoxinzhaiella) subrotunda sp. nov. and Chusenella quasidouvillei of Murgabian age (Middle Permian) from the Thitsipin Formation at the Pindaya in the Shan Plateau, Eastern Myanmar. Taxonomic analysis of this new collection and of Rugososchwagerina (s.l.) in the literature leads us to suppress Xiaoxinzhaiella Shi, Yang & Jin, 2005 as a subgenus of RugososchwagerinaMiklukho-Maklay, 1959. This subgenus is diagnosed with much tighter coiling and reduced septal folding in juvenarium as well as relatively smaller test diameter throughout the ontogeny, compared with Rugososchwagerina (s.s.) which is typified by R. yabeiSkinner & Wilde, 1966. Furthermore, our comprehensive review reveals that the known occurrences of R. (Xiaoxinzhaiella) are strictly confined within blocks that previously constituted the Cimmerian Continent during the Permian period, and they were even more widespread than Rugososchwagerina (s.s.) among these blocks. Therefore, the previous understanding that Rugososchwagerina (s.l.) is characteristic for the Middle Permian Cimmerian region can be refined. We propose that R. (Xiaoxinzhaiella) is more appropriate as the truly endemic foraminiferal index signifying Cimmerian affinity.

Numerous granitic intrusions occur along the southern margin of the Tajik Block and the Band-e-Bayan Zone in the Ghor Province of Central Afghanistan. Previously, they used to be linked to the Cimmerian igneous episodes of Triassic and Cretaceous ages. However, the new U-Pb dating has revealed that these granite intrusions occurred during the Eocene within a narrow time span of 41–36 Ma. They are related to the number of local depressions filled with the volcanic-sedimentary sequence of the same age. These data indicate an intense short-termed magmatic event that affected the region in the Palaeogene. The magmatism might be related to the India-Eurasia collision, which started approximately at the same time. It is likely to have induced the horizontal displacement of crustal blocks westwards along the Hari Rod fault.

AbstractThe Garedu Red Bed Formation (GRBF) of the northern Tabas Block (Central-East Iranian Microcontinent, CEIM) is a lithologically variable, up to 500-m-thick, predominantly continental unit. It rests gradually or unconformably on marine limestones of the Esfandiar Subgroup (Callovian–Oxfordian) and is assigned to the Kimmeridgian–Tithonian. In the lower part, it consists of pebble- to boulder-sized conglomerates/breccias composed of limestone clasts intercalated with calcareous sandstones, litho-/bioclastic rudstones and lacustrine carbonates. Up-section, sharp-based pebbly sandstones and red silt-/fine-grained sandstones of braided river origin predominate. Palaeocurrent data suggest a principal sediment transport from west to east and a lateral interfingering of the GRBF with marine greenish marls of the Korond Formation at the eastern margin of the Tabas Block. Westwards, the GRBF grades into the playa deposits of the Magu Gypsum Formation. Red colours and common calcretes suggest arid to semi-arid climatic conditions. The onset of Garedu Red Bed deposition indicates a major geodynamic change with the onset of compressive tectonics of the Late Cimmerian Tectonic Event (LCTE), being strongest at the eastern margin of the northern Tabas Block. When traced southwards, the same tectonic event is expressed by extension, indicating a shift in tectonic style along the boundary fault between the Tabas and Lut blocks. The complex Upper Jurassic facies distribution as well as the spatio-temporal changes in tectonic regime along the block-bounding faults are explained by the onset of counterclockwise vertical-axis rotation of the CEIM in the Kimmeridgian. The block boundaries accommodated the rotation by right-lateral strike slip, transpressional in today’s northern and transtensional in today’s southern segments of the block-bounding faults. Rotation occurred within bracketing transcurrent faults and continued into the Early Cretaceous, finally resulting in the opening of narrow oceanic basins encircling the CEIM. Palaeogeographically, the GRBF is part of a suite of red bed formations not only present on the CEIM, but also along the Sanandaj-Sirjan Zone (NW Iran), in northeastern Iran and beyond, indicating inter-regional tectonic instability, uplift and erosion under (semi-)arid climatic conditions across the Jurassic–Cretaceous boundary. Thus, even if our geodynamic model successfully explains Late Jurassic tectonic rotations, fault motions and facies distribution for the CEIM, the basic cause of the LCTE still remains enigmatic.

A density model was built along the Bs05-22 profile, which made it possible to identify individual blocks with different crustal parameters. The consolidated crust of the East European Platform (EEP) has a “key” structure. The southern boundary of the EEP is clearly fractured and falls to the south at an angle of about 83° The South Ukrainian monocline (SUM) covers not only the basement of the EEP but also the northern part of the Scythian Plate (SP). The central part of SP block overlapped by the SUM is characterized by the maximum capacity of the folded-metamorphic base. The axial part of the Karkinit Trough (KT) has a structure typical for riftogens. The rift is practically one-sided with a width of 6.5 km. The southern slope of the KT developed as a result of the falling of the surface by the mechanism of the planj-principle. The border between the Karkinit Trough and the Kalamitsky rise (KR) is clearly defined by the Sulinsko-Tarkhankutsk fault. The core of the KR is a sufficiently massive body of lenticular shape with a density corresponding to the Taurian series of the Mountainous Crimea. There is a narrow transition zone between KT and Edge step (ES). The southern edge of the Scythian plate is a 25,0 km wide transition zone to West-Black Sea depression (WBSD). Modeling established the extension of the “granodiorite” layer into the WBSD for 100 km. The crust thickness within the EEP is 44,0 km, on the Scythian plate under SUM is average 43.5 km, 37,0 km within KT and 33,0 km under ES, in the West Black Sea basin 28,7 km under the foot of the Upper Cretaceous continental slope and 21,5 km at the southern edge of the profile. In the model chosen, the density of tectonic faults in the EEP is 0,06 and in the SP — 0,14 per 1,0 km. Vertical shifts of crystalline crust blocks at SP reach 5,5 km, which is almost three times higher than at the southern flank of the EEP. The most of disjunctions are vertical and have transcrust stretch. The structure of the Earth’s crust obtained as a result of modeling allowed us to draw some conclusions about the Meso-Cenozoic evolution of the studied region in the profile section. At the southern edge of the EEP in the Late Cimmerian tectogenesis epoch there has been a revitalization, in the Alpine phase this structure was generally passive. Activity of the Cimmerian epoch was observed throughout the Scythian plate: within the Kalmitsky rise from the early phase, and in the Karkinit Trough and on the Edge step from the late Cimmerian phase. The periods of activation on the KT and KR are traced up to the Sawa phase, and on the ES — to the Walach phase of the Alpine tectogenesis inclusive.

The study provides a deeper understanding of the early Mesozoic paleogeogeographic spatial-temporal relationship by studying the two Adria-Europe intervening basement blocks. The Drina-Ivanjica and Pelagonian crustal fragments play important role in the internal early Alpine oceanic constitution further controlling the late Jurassic emplacement of Tethyan Dinaric-Hellenic ophiolites. The proposed paleogeographic reassessment is driven by the new paleocontinental inheritance data associated with the Variscan – pre-Variscan basement terranes. The recently published data suggest an Avalonian-type inheritance of the Pelagonian basement block which indicates a different pre-Variscan plate-tectonic journey, including separate spatial arrangement during Variscan amalgamation. In turn, Cadomian-type basement inheritance has been documented within the sliced Adria microplate. Thus, the Avalonian inheritance place the Pelagonian block away from the Apulia/Adria (Dinarides). In the investigated context of Paleozoic-Mesozoic paleogeographic transition, the Pelagonian block may represent a segment of the Cimmerian ribbon continent or southernmost segment of the Variscan Europe. With regards the nearby Adria microplate, a Triassic-Jurassic oceanic opening led to the decoupling (spreading away from the main Adria microplate) of the Drina-Ivanjica block. The rifting is in line with the simultaneous yet opposite or westward-directed drift of the Pelagonides. The breakup of south European Variscan configuration eventually result in the spatial alignment of the two basement fragments referred to as the “Drina–Pelagonide continental splinter”. By linking the paleogeographic pre-Jurassic–Jurassic relationship between these continental units, the two landlocked Neotethyan Vardar s.l. basins are extrapolated, “Dinaric Tethys” / Inner Dinaric-(Mirdita-Pindos) and the main Vardar Ocean (Western Vardar Zone).

This paper reports a diversified fusuline fauna from the Middle Permian (Guadalupian) Xilanta Formation in the Gyanyima area, Burang County, southwestern Tibet, China. Nine genera, Lantschichites, Kahlerina, Nankinella, Yangchienia, Chusenella, Verbeekina, Armenina, Paraverbeekina and Neoschwagerina are recognized.Anew species Yangchienia gyanyimaensis n. sp. is established. This fauna indicates a Midian age in terms of the coexistence of Kahlerina, Lantschichites and Neoschwagerina. Paleobiogeographically, the fauna closely resembles that from the Lasaila exotic limestone block of Tibet, both resemble the fusuline assemblages known from the western Cimmerian continents in the Western Tethys Province. However, the absence of Afghanella and Sumatrina in the fauna suggests that the Gyanyima limestone block as well as the Lasaila exotic limestone block, the Batain plain of Oman and the Salt Range of Pakistan, were affected by relatively cool water during the Middle Permian.

ABSTRACT This paper is a review of the geology of the widely distributed Mesozoic rocks of Afghanistan. The country is a mosaic of structural blocks in a variety of geodynamic settings that were juxtaposed during the evolution of the Tethyan Ocean; the Mesozoic sedimentary, volcanic, and plutonic rocks therefore differ greatly from one block to another. Because of the adverse security situation, fieldwork has not been possible since the late 1970s and the data used in this review are therefore relatively old but are the best available. Interest in the geology of Afghanistan remains strong due to its position between the mountain chains of the Middle East and the collisional ranges of the Pamirs and Himalayas. A special feature of Tethyan geodynamics is the presence of Cimmerian (latest Triassic to earliest Cretaceous) continental blocks, microcontinents, or terranes located between the Eurasian and Indian landmasses. They are fragments of Gondwana inserted between the Paleo- and Neo-Tethys during the Mesozoic. This complex part of the Tethyan realm is well exposed in Afghanistan where the effects of the Indo-Eurasian collision were less intense than in regions of frontal collision, such as the Pamir and Himalayan ranges. It is for this reason that Afghanistan is of particular geodynamic interest and a key region in the understanding of the genesis and evolution of the Tethyan system during the Mesozoic.

AbstractTwelve rugose coral species belonging to seven genera are described and discussed based on 70 thin sections of 32 specimens collected from the Anarak section, northeast of Nain, Esfahan Province, Yazd Block, central Iran. These species include two new colonial rugose coral species,Antheria fedorowskiiandAntheria robusta, and five previously named species of colonial rugose corals,Antheria lanceolataandStreptophyllidium scitulum, and solitary rugose corals,Arctophyllum jiangsiense,Caninophyllumcf.somtaiense, andPseudotimania delicata. Five species are left in open nomenclature:Antheriasp.,Arctophyllumsp.,Caninophyllumsp.,Nephelophyllumsp., andYakovleviellasp. These Iranian corals are associated with the fusulinidsRauserites(several species) andUltradaixina bosbytauensis, indicating a latest Carboniferous age (Gzhelian age). All the described genera and named species belong to the families Aulophyllidae, Bothrophyllidae, Cyathopsidae, and Kepingophyllidae, among which the family Kepingophyllidae has been previously documented only from China and Indochina. They are typical representatives of the Cathaysian rugose fauna, which was widely developed around the South China and Indochina blocks near the paleoequator and was absent from the Gondwanan and Cimmerian continents in high latitudes during the Late Pennsylvanian. Hence, the occurrence of the Cathaysian fauna from central Iran in the latest Carboniferous suggests that it may have had a close biogeographical connection with China and Indochina, which further implies its latitudinal position intermediate between the Gondwanan continent and South China and Indochina blocks during this time.UUID:http://zoobank.org/5257d2bb-1346-4dee-8f3e-f4b1b33ba5a9

A density modeling of the north-western shelf of the Black Sea along 31°20’ E was carried out. According to its results, a complex block structure of the area is determined, which is closely connected with the history of its development. Signs of Baikal tectonic activation of the southern edge of the pre-Riphean Eastern European platform, as well as the adjacent part of the Scythian plate have been revealed. Areas formed during the Hercynian and Cimmerian epochs of tectogenesis have been identified within the Scythian plate. At the base of the Karkinit Trough, two areas of reduced crust resulting from riftogenesis with varying degrees of intensity of basification have been established. Two ancient volcanos of ryolite composition were found on the basement surface on the northern slope of the Kalamit swell. It is highly probable that the Gamburtsev uplift is an eastern extension of the Gubkin swell. According to the structure and value of the calculated densities, it is established that the Gamburtsev uplift is a «blind» mud volcano, which was formed during the second stage of the late Cimmerian cycle and was active throughout the Cretaceous period. A detailed analysis of the deep structure and fault tectonics of the local structures of the sedimentary cover in the intersection of the profile and the area of gas seeps was carried out. It was found that the Flangova, Partizanska and Hamburtseva structures are more promising for hydrocarbon accumulation. The hydrocarbon potential of the Ushakov structure (H-41) is questionable, because structurally and tectonically it is analogous to the Delphin structure, which was deemed unproductive based on drilling results. The area of gas seeps was found to be confined to a mantle fault, which separates two blocks with distinctly different structures and Meso-Cenozoic evolution of the Earth’s crust. It is proposed to conduct a detailed seismic survey in this area in order to identify local structures in the sedimentary cover, promising for hydrocarbons.

La tectonique des plaques relie le mouvement des plaques tectoniques rigides à la surface de la terre et la convection du manteau. Bien que les panaches mantelliques puissent interagir avec les plaques en érodant mécaniquement leur base et en augmentant leur potentiel gravitationnel, ils ne fournissent pas de forces suffisantes pour rompre une plaque continentale en l'absence d’un forçage cinématique ou de mécanismes d'affaiblissement, e.g. injection de dykes magmatiques. La convection du manteau peut également exercer un frottement basal visqueux pouvant entrainer les plaques, ou résister à leur mouvement. Néanmoins la limite lithosphère asthénosphère étant une zone mécaniquement faible, le lien principal entre le mouvement des plaques et la convection du manteau est la subduction des panneaux de lithosphère océanique. Ceux-ci sont assez résistant pour transmettre les forces depuis la terre profonde jusqu'à la surface en participant à la fois au mouvement des plaques à la surface et à la convection du manteau. Cette thèse étudie la relation entre la dynamique de la subduction et la rupture des continents. Alors qu'il est reconnu depuis longtemps que la subduction peut conduire à la rupture continentale dans la plaque supérieure grâce à l'affaiblissement par la percolation des fluides et la convection à petite échelle, très peu d'études se concentrent sur la dynamique de la rupture continentale de la plaque inférieure en réponse à la traction des panneaux plongeant. Ce mécanisme a été proposé pour la fragmentation du Gondwana durant le Permien et pour l'ouverture de la mer de Chine méridionale à l'Oligocène. Dans les deux cas, la rupture continentale de la plaque inférieure doit se produire en absence de dorsale medio-océanique, sinon la subduction des plaques serait accommodée par l'accrétion à leur niveau. J'ai mis en place une série de simulations numérique 2D de plaques sans dorsale en subduction pour étudier par le biais d'une étude paramétrique quand et où la plaque continentale se rompt en fonction du mouvement relatif des plaques. Étant donné l'importance des forces de volumes produite par le panneau plongeant, un soin particulier a été donné à la prise en compte de l'effet des changements de minéralogie sur la densité dans les simulations. Les simulations présentent quatre modes de rupture continentale : en plaque supérieure, en plaque inférieure, sur les deux plaques ou absente. L'étude montre que l'augmentation marquée de la densité du panneau plongeant liée à la transition de phase de 410 km, en plus de l'énergie potentielle gravitationnelle de la lithosphère continentale, peut provoquer un rifting continental dans la plaque inférieure de la subduction si le continent n’est pas cisaillé à sa base. Le modèle de "slab-drag" apparaît comme un mécanisme viable de rupture continentale en plaque inférieure. Par ailleurs, les simulations démontrent également qu'il existe un décalage temporel important entre la subduction de la dorsale et la rupture continentale (c'est-à-dire le temps nécessaire pour que le panneau plongeant atteigne la discontinuité de 410 km). Ces conditions limitantes (mouvement relatifs et écart temporel) font de son potentiel enregistrement géologique une contrainte importante sur les reconstructions paléogéograhiques du mouvement des plaques et en particulier des blocs Cimmérien au Permien. En m'appuyant sur les résultats de cette première série de simulations et sur la littérature abondante qui documente l'ouverture de la mer de Chine méridionale, j'ai mené une deuxième étude adaptée au contexte géodynamique régional. Cela me permet de proposer un nouveau modèle conceptuel qui combine l'inversion de la dorsale, la rupture continentale liée à la traction des panneaux plongeant et l'inversion de la subduction pour réconcilier les données géologiques et géophysiques de cette région. La fin de ce manuscrit discute les limites de mes résultats et apporte des pistes de remédiation
Plate tectonics relates the movement of rigid plates at the Earth's surface to mantle convection. Although upwelling flows such as mantle plumes can interact with plates by mechanically eroding their bases and increasing their gravitational potential, they do not provide sufficient forces to break up a continental plate in the absence of far field extensional forces or other weakening mechanisms such as the injection of magma dykes. Mantle convection can also exert viscous friction at the base of tectonic plates, which can drive, or resist, plate motion. Nevertheless, the Lithosphere Asthenosphere Boundary is among the mechanically weakest regions of the mantle, therefore, the main link between plate motion and mantle convection in terms of driving force is the subduction of oceanic lithosphere slab. These subducting slabs indeed drive both plate motion at the surface and mantle convection and are strong enough to transmit forces from the deep earth to the surface. This thesis therefore studies the relationship between subduction dynamics and continental breakup. While it has long been recognized that subduction can lead to continental breakup in the upper plate through weakening by fluid percolation and small-scale convection, very few studies focus on the dynamics of continental breakup in the lower plate in response to slab pull force. This mechanism has been proposed for the breakup of Gondwana during the Permian and for the opening of the South China Sea in the Oligocene. In both cases, continental breakup of the lower plate must occur after the mid-ocean ridge has ceased activity or when subduction becomes normal to the ridge, otherwise oceanic plate subduction would be accommodated by accretion at the mid-oceanic ridge. I set up a series of 2D numerical simulations of subducting ridge-free plates to study by means of a parametric approach when and where the continental plate breaks up as a function of the relative motion of the plates. Given the importance of the volume forces produced by the sinking slab, special care was taken to take into account the effect of mineralogical changes on density in the simulations. The simulations present four modes of continental breakup: upper plate, lower plate, both plates, or absent. Focusing on lower plate continental lithosphere breakup, the parametric study shows that the sharp increase in density of the sinking slab related to the 410 km phase transition, in addition to the gravitational potential energy of the continental lithosphere, can cause continental rifting in the lower subducting plate. However, simulations also show that this mechanism requires the lower plate to move at the same speed as the underlying mantle (i.e. no significant horizontal basal shear on the continent). The slab-drag model appears to be a viable mechanism for continental breakup of the lower plate and the conditions limiting this process in terms of timing and relative motion make its potential geological record an important constraint on the dynamics of the system. Furthermore, the simulations also demonstrate that there is a significant time lag between ridge subduction and continental breakup (i.e. the time required for the plunging panel to reach the 410 km discontinuity). These last two points provide new constraints on paleogeographic reconstructions of Permian Cimmerian blocks motion. Based on the results of this first set of simulations and the extensive literature documenting the opening of the South China Sea, I conducted a second study adapted to the regional geodynamic context. This allows me to propose a new conceptual model that combines ridge inversion, continental breakup related to slab pull and subduction reversal to reconcile the geological and geophysical data of this region. The end of this manuscript discusses the limitations of my results and provides suggestions for remediation