Abstract The geological evolution of Central Asia commenced with the evolution of a complex Precambrian–Palaeozoic orogen. Cimmerian blocks were then accreted to the southern margin during the Mesozoic, leading to tectonic reactivation of older structures and discrete episodes of basin formation. The Indian and Arabian blocks collided with Asia during the Cenozoic, leading to renewed structural reactivation, intracontinental deformation and basin development. This complex evolution resulted in the present-day setting of an elongated Tien Shan range flanked by large Mesozoic–Cenozoic sedimentary basins with smaller intramontane basins distributed within the range. The aim of this volume is to present multidisciplinary results and reviews from research groups in Europe and Central Asia that focus on the western part of the Tien Shan and some of the large sedimentary basins in that area. These works elucidate the Late Palaeozoic–Cenozoic tectono-sedimentary evolution of the area. Emphasis is placed on the collision of terranes and/or continents and the ensuing fault reactivation; the impact of changes in climate on the sedimentation is also examined. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license .

Abstract The Amu Darya Basin (ADB) has been studied primarily for its important hydrocarbon reserves and to a lesser extent for its geodynamic evolution. The ADB is located on the SE portion of the Turan Platform, between the sutures of the Turkestan and Palaeo-Tethys oceans, which closed during the Late Palaeozoic and Early Mesozoic, respectively. Blocks and island arcs accreted to Eurasia during the Palaeozoic form a poorly defined, heterogeneous basement underlying the ADB. They played an important role in shaping its composite structure into variously orientated sub-basins and highs. In this paper, depth–structure and isopach maps, and regional cross-sections, are analysed to unravel the location and origin of the main structural elements and to characterize the subsidence evolution of the ADB. The main tectonic events leading to the formation and evolution of the ADB took place: (1) in the Late Palaeozoic–Early Triassic (back-arc, rollback and extension/strike-slip); (2) from the Middle Triassic to the Triassic–Jurassic boundary (Eo-Cimmerian collision of Gondwana-derived continental blocks with Eurasia); and (3) during the Early–Middle Jurassic (post-collision extensional event). The last part of this evolution reflects shortening and flexure due to Cenozoic collisions to the south. Palaeotectonic maps are used to relate these events to the geodynamics of the Tethyan domain.

Abstract The Bukhara-Khiva region forms the northern margin of the Mesozoic Amu-Darya Basin. We reconstructed several cross-sections across this margin from subsurface data. The objectives included examining the structure of the Bukhara and Chardzhou steps and determining the tectonic–sedimentary evolution of the basin during the Jurassic. Subsequent to the Cimmerian collision in the Middle Triassic, an extensional event controlled the deposition of the Early–Middle Jurassic siliciclastic succession in the Bukhara-Khiva region. The main Late Palaeozoic inherited structures were reactivated as normal faults during this period. Continental coarse-grained siliciclastic sediments are mainly confined to the basal Lower Jurassic section, probably Pliensbachian–Toarcian in age, whereas marine siliciclastic sediments occur in the early Late Bajocian. In the Early–Middle Jurassic the Bukhara and Chardzhou steps were predominantly sourced by areas of relief, the remains of Late Palaeozoic orogens located to the north. The rate of extension significantly declined during the Middle Callovian–Kimmeridgian period. Deposition of the overlying Lower Cretaceous continental red-coloured clastic sediments was related to the interaction of basin subsidence, a fall in eustatic sea-level and sediment supply. Subsequent marine transgression in the Late Barremian, partially related to broad thermal subsidence in the Amu-Darya Basin, resulted in the deposition of an extensive Late Cretaceous clay–marl succession.

Abstract Based on 11 sections, the palaeoenvironments and depositional history of the NW Afghan–Tajik Basin in southern Uzbekistan have been reconstructed for the time interval of the Early Jurassic–Early Callovian. The earliest sediments, resting on Palaeozoic basement rocks, date from the Early Jurassic Period. Up to the end of the Early Bajocian time, more than 500 m of non-marine sediments accumulated as a result of extensional tectonics inducing active subsidence. In the Late Bajocian time interval, transgression led to the establishment of siliciclastic ramps that were influenced by storm processes. After a condensed unit in the Middle Bathonian, sedimentation resumed in an outer carbonate ramp–basinal setting as the subsidence rate outpaced the diminished siliciclastic sediment supply. The change from siliciclastic to carbonate sedimentation in the Middle Jurassic Period is thought to be multifactorial, reflecting levelling of relief in the hinterland, the subsidence moving to a thermally more quiet stage and a change from humid to arid climatic conditions. These features are also observed in the area of present-day Iran. Similarly, the timing of the transgression coincides with that in eastern and northern Iran, stressing the regional significance of this event.

Abstract The Greater Caucasus is Europe's highest mountain belt and results from the inversion of the Greater Caucasus back-arc-type basin due to the collision of Arabia and Eurasia. The orogenic processes that led to the present mountain chain started in the Early Cenozoic, accelerated during the Plio-Pleistocene, and are still active as shown from present GPS studies and earthquake distribution. The Greater Caucasus is a doubly verging fold-and-thrust belt, with a pro- and a retro wedge actively propagating into the foreland sedimentary basin of the Kura to the south and the Terek to the north, respectively. Based on tectonic geomorphology – active and abandoned thrust fronts – the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning. The central part of the mountain range – defined by the Main Caucasus Thrust to the south and backthrusts to the north – forms a triangular-shape zone showing the highest uplift and fastest rates, and is due to thrusting over a steep tectonic ramp system at depth. The meridional orogenic in front of the Greater Caucasus in Azerbaijan lies at the foothills of the Lesser Caucasus, to the south of the Kura foreland basin.

Abstract The structurally and stratigraphically complex area of northern and central Iran holds the key to understanding the plate tectonic evolution of the South Caspian–Central Iran area. The closure of the Palaeotethys, the opening of the Neotethys, the rise and demise of the Cimmerian mountain chain, as well as the onset of Neotethys subduction and large-scale Neotethyan back-arc rifting all predated the formation of the more than 20 km-thick fill of the South Caspian Basin. This volume brings together work by specialists in different disciplines of the geosciences (tectonics, geophysics, sedimentology, stratigraphy, palaeontology, basin modelling and geodynamics) in order to elucidate the complex Late Palaeozoic–Cenozoic geodynamic history of the Iran area and the birth of the South Caspian Basin.

Abstract A combination of fieldwork, basin analysis and modelling techniques has been used to try and understand the role, as well as the timing, of the subsidence–uplift mechanisms that have affected the Azerbaijan region of the South Caspian Basin (SCB) from Mesozoic to Recent. Key outcrops have been studied in the eastern Greater Caucasus, and the region has been divided into several major tectonic zones that are diagnostic of different former sedimentary realms representing a complete traverse from a passive margin setting to slope and distal basin environments. Subsequent deformation has caused folds and thrusts that generally trend from NW–SE to WNW–ESE. Offshore data has been analysed to provide insights into the regional structural and stratigraphic evolution of the SCB to the east of Azerbaijan. Several structural trends and subsidence patterns have been identified within the study area. In addition, burial history modelling suggests that there are at least three main components of subsidence, including a relatively short-lived basin-wide event at 6 Ma that is characterized by a rapid increase in the rate of subsidence. Numerical modelling that includes structural, thermal, isostatic and surface processes has been applied to the SCB. Models that reconcile the observed amount of fault-controlled deformation with the magnitude of overall thinning of the crust generate a comparable amount of subsidence to that observed in the basin. In addition, model results support the tectonic scenario that SCB crust has a density that is compatible with an oceanic composition and is being under-thrust beneath the central Caspian region.

Abstract The Precaspian and South Caspian basins are two superdeep basins whose modeling has been undertaken in the frame of the international Peritethys Program that was sponsored by 13 companies or institutions. The Precaspian Basin is situated to the north of the Caspian Sea mainly on land and has been trapped at the border of the east European Platform with the closure of the Urals Ocean during the Carboniferous. It is also influenced by the repercussions of Tethys closure during the Cenozoic, with the Caucasus compression to the southwest. The Precaspian Basin contains about 20 km (12 mi) of clastic and carbonate sediments deposited since a time perhaps as old as the Riphean. It comprises a 4-km (2.5-mi) salt layer of Kungurian age (Lower Permian). Salt movements produce numerous salt structures that prevent a precise analysis of the post-salt subsidence. The basement of the central Precaspian depression (central part of the Precaspian Basin) is characterized by a thin crust (around 10 km [6 mi]) where a low-velocity layer is absent. Its origin is still controversial; it could be either thinned continental or oceanic crust. At the base of the crust, a 8–10-km (4.9–6-mi) layer of velocity 8–8.1km/s (4.9–5mi/s) is recognized by seismic and gravity observations: anomalously high velocities at the base of the crust coincide in place with intense gravitational maxima. Analysis of some peculiarities of the structure, gravitational field, and composition of the crust leads us to suppose that this layer may be interpreted as eclogite. The problem remains on the way of implementation of full analysis.

Abstract The Greater Caucasus (GC) fold-and-thrust belt lies on the southern deformed edge of the Scythian Platform (SP) and results from the Cenozoic structural inversion of a deep marine Mesozoic basin in response to the northward displacement of the Transcaucasus (lying south of the GC) subsequent to the Arabia-Eurasia collision. A review of existing and newly acquired data has allowed a reconstruction of the GC history through the Mesozoic and Cenozoic eras. In Permo(?)-Triassic times, rifting developed along at least the northern part of the belt. Structural inversion of the basin occurred during the Late Triassic corresponding to the Eo-Cimmerian orogeny, documented SE of the GC and probably linked to the accretion of what are now Iranian terranes along the continental margin. Renewed development of extensional basin formation in the area of the present-day GC began in Sinemurian-Pliensbachian times with rift activity encompassing the Mid-Jurassic. Rifting led to extreme thinning of the underlying continental crust by the Aalenian and concomitant extrusion of mid-ocean ridge basalt lavas. A Bathonian unconformity is observed on both sides of the basin and may either correspond to the end of active rifting and the onset of post-rift basin development or be the record of collision further south along the former Mesozoic active margin. The post-rift phase began with deposition of Late Jurassic platform-type sediments onto the margins and a flysch-like unit in its deeper part, which has transgressed the basin during the Cretaceous and Early Cenozoic. An initial phase of shortening occurred in the Late Eocene under a NE-SW compressional stress regime. A second shortening event that began in the Mid-Miocene (Sarmatian), accompanied by significant uplift of the belt, continues at present. It is related to the final collision of Arabia with Eurasia and led to the development of the present-day south-vergent GC fold-and-thrust belt. Some north-vergent retro-thrusts are present in the western GC and a few more in the eastern GC, where a fan-shaped belt can be observed. The mechanisms responsible for the large-scale structure of the belt remain a matter of debate because the deep crustal structure of the GC is not well known. Some (mainly Russian) geoscientists have argued that the GC is an inverted basin squeezed between deep (near)-vertical faults representing the boundaries between the GC and the SP to the north and the GC and the Transcaucasus to the south. Another model, supported in part by the distribution of earthquake hypocentres, proposes the existence of south-vergent thrusts flattening at depth, along which the Transcaucasus plunges beneath the GC and the SP. In this model, a thick-skinned mode of deformation prevailed in the central part of the GC whereas the western and eastern parts display the attributes of thin-skinned fold-and-thrust belts, although, in general, the two styles of deformation coexist along the belt. The present-day high elevation observed only in the central part of the belt would have resulted from the delamination of a lithospheric root.

Abstract The southern part of the Eastern European continental landmass consists mainly of a thick platform of Vendian and younger sediments overlying Precambrian basement, referred to as the East European and Scythian platforms (EEP and SP). Some specific geological features, such as the Late Devonian Pripyat–Dniepr–Donets rift basin, the Karpinsky Swell, the Permo(?)-Triassic troughs of the SP, and the deformed belt running from Dobrogea to Crimea and the Greater Caucasus, in which rocks as old as Palaeozoic crop out, form a record of the geodynamic processes affecting this part of the European lithosphere. Hard constraints on the Palaeozoic history of the SP are very sparse. The conventional view has been that the SP is a Late Palaeozoic orogenic belt. However, it is shown that the few available data are also consistent with an alternative interpretation in which it is the thinned margin of the Precambrian continent, reworked by Late Palaeozoic–Early Mesozoic rifting events. The geodynamic setting of the margin is classically reported as one of active convergence throughout the Late Palaeozoic and Early Mesozoic, with subduction of the Palaeotethys Ocean beneath Europe. Actually, there are no direct observations constraining the polarity of Palaeotethys subduction in this area although indirect evidence is not inconsistent with the conventional model. In such a case, the sedimentary–tectonic record of the SP suggests that convergence during the Permo-Triassic(?) and certainly during the Early and Mid-Jurassic was oblique. An Eo-Cimmerian (Late Triassic–Early Jurassic) event is widespread and implies a tectonic compressional regime with systematic inversion of most sedimentary basins. There is also a widespread unconformity at the end of the Mid-Jurassic and in the Late Jurassic. These can be interpreted as indicators of compressional tectonics; however, nowhere is there evidence of intense shortening or other orogenic processes. A revised tectonic model is proposed for the area but, given the degree of uncertainty characterizing the geology of this area, it is best considered as a basis for further discussion.