A.V. Ershov

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution

Abstract During its Riphean to Palaeozoic evolution, the East European Craton was affected by rift phases during Early, Middle and Late Riphean, early Vendian, early Palaeozoic, Early Devonian and Middle-Late Devonian times and again at the transition from the Carboniferous to the Permian and the Permian to the Triassic. These main rifting cycles were separated by phases of intraplate compressional tectonics at the transition from the Early to the Middle Riphean, the Middle to the Late Riphean, the Late Riphean to the Vendian, during the mid-Early Cambrian, at the transition from the Cambrian to the Ordovician, the Silurian to the Early Devonian, the Early to the Middle Devonian, the Carboniferous to Permian and the Triassic to the Jurassic. Main rift cycles are dynamically related to the separation of continental terranes from the margins of the East European Craton and the opening of Atlantic-type palaeo-oceans and/or back-arc basins. Phases of intraplate compression, causing inversion of extensional basins, coincide with the development of collisional belts along the margins of the East European Craton. The origin and evolution of sedimentary basins on the East European Craton was governed by repeatedly changing regional stress fields. Periods of stress field changes coincide with changes in the drift direction, velocity and rotation of the East European plate and its interaction with adjacent plates. Intraplate magmatism was controlled by changes in stress fields and by mantle hot-spot activity. Geodynamically speaking, different types of magmatism occurred simultaneously.

The Black Sea basin: tectonic history and Neogene–Quaternary rapid subsidence modelling

Abstract The Black Sea basin originated as a back-arc basin during Cretaceous times. Continental rifting took place during the Aptian to Albian with large-scale crustal thinning and separation occurring since the Cenomanian, mainly along a former Albian volcanic arc. Both western and eastern Black Sea basins opened almost simultaneously during Cenomanian to Coniacian times. However, during the Santonian to Palaeocene, the Black Sea region was affected by compressional deformation. Apart from a tensional event that took place in eastern part of the region during the Eocene, deepening of the basin has been induced by compressional deformation from latest Eocene to recent times. Kinematic and dynamic modelling of the subsidence history of the Black Sea basin shows that downward bending of the lithosphere beneath the basin due to compressional deformation could be the cause of this rapid additional subsidence.

Northern Caucasus basin: thermal history and synthesis of subsidence models

Abstract Burial histories of the eastern, central and western parts of the Northern Caucasus basin are reconstructed on the basis of well data and seismic sections. Subsidence began in the Early Triassic after the Late Carboniferous–Permian orogeny. Triassic sediments were mainly removed during Late Triassic–Early Jurassic uplift and erosion. Platform cover began to form in the Middle Jurassic and Albian sediments covered the whole territory of the basin. Thermal modelling shows that Jurassic–Eocene subsidence was mainly controlled by Late Triassic–Early Jurassic intrusive warming. This heating event induced thermal uplift of the whole territory followed by exponentially decelerating subsidence due to cooling of the lithosphere. In the southern areas adjacent to Great Caucasus, subsidence was also affected by Caucasian extensional and compressional events. In the Oligocene–Early Miocene, the eastern and the central basins underwent rapid long wavelength subsidence (Maikopian subsidence). The geodynamic cause of this subsidence is probably associated with the mantle flow appearance after cessation of the Tethyan subduction, due to reequilibration of subducted slab. While in the Late Miocene–Quaternary times, the eastern and the western basins underwent foreland-type asymmetrical subsidence due to loading of the Great Caucasus orogen; the central basin was uplifted. According to flexural modelling, the main component of orogen loading was the lithospheric root load; delamination of the latter under the Central Caucasus caused rapid uplift of the orogen and adjacent basin.

geological history of Western Caucasus and adjacent foredeeps based on analysis of the regional balanced section

Using seismic evidence and other geological data, a balanced section has been built for the Tuapse foredeep-Western Caucasus-Western Kuban foredeep tectonic system. This section enabled us to restore the history of the region, from the Callovian time. It was suggested that, in the Callovian-Eocene, the western Caucasian basin existed in the form of a rift. The principal phase of rift inversion occurred in the Oligocene-Miocene, and in the Pliocene-Quaternary, it evolved into the orogeny phase. The extent of the Caucasus compression within the section area was more than 30 km.

Effective middle surface of lithosphere

Representation of the lithosphere by an equivalent elastic plate is a common method in Earth sciences, when the mechanical behaviour of the lithosphere is investigated. The equivalent plate is determined by two parameters: thickness and configuration of the middle surface, named as effective elastic thickness (EET) and effective middle surface (EMS) of the lithosphere. EET is related to the flexural deformation of the lithosphere to vertical loading while EMS controls the lithosphere’s response to lateral force variations. EET has been well investigated, whereas EMS remains ‘in the shadow’ in geophysics. The present paper proposes a mathematical formulation for the EMS allowing to calculate it theoretically, from a stress‐strain distribution. The equilibrium equation of the equivalent elastic plate is derived from the general rheologically independent equilibrium equation for the lithosphere. It contains a member proportional to the EMS curvature, which describes pre-existing flexure of the equivalent elastic plate. It must be included in flexural calculations with non-zero in-plane forces, because it is an integral part of the equilibrium. EMS (like EET) depends on the lithosphere’s structure, constitution and thermal state. Contrasting with EET, bending and mechanical layering do not substantially affect EMS. Temperature exerts the strongest influence on EMS: change in thermal regime may shift EMS vertically by 50 km. Possible deflection of EMS, due to variations of other parameters, is usually lower than 10 km. Tectonically, EMS reveals through stress-induced vertical movements. Their amplitude may be detectable even under the action of moderate intraplate force. The most pronounced effect of EMS variation is expected at continental rifts and orogens.

Late Palaeozoic and Mesozoic evolution of the Amu Darya Basin (Turkmenistan, Uzbekistan)

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.