Intramontane lacustrine basins in the Siberian Altai: recorders of Cenozoic intracontinental tectonic and climatic events

The Altai Mountains are part of the vast intracontinental Central Asian orogenic system that formed during the Cenozoic as a distal effect of continued indentation of the Indian plate into the Eurasian continent. In the Siberian part of the Altai Mountains there is ample evidence to suggest that the pre-Cenozoic structural fabric of its basement is a controlling factor in the Cenozoic deformation and development of this intracontinental orogen. We give evidence that important Paleozoic fault zones were reactivated during the Cenozoic, particularly the Late Cenozoic and play a key role in the formation, evolution and current morphology of the Siberian Altai Mountains. Some of these faults are still active and recent and historic movements along them have triggered large seismic events. Late Cenozoic reactivation was expressed as pure thrust, oblique thrust to pure strike-slip faulting, resulting in an overall transpressive tectonic regime. In some cases, as for the graben basin of Lake Teletskoye, local, pure extensional stresses are responsible for its formation as we show in this contribution. Various other intramontane, tectonic basins developed. Some of these are very recent structures (the Teletskoye Basin) and are Pleistocene in age or younger, others have a prolonged history and contain a relatively complete Cenozoic sedimentary section, with evidence of Late Mesozoic precursor basins (Chuya Basin, Dzhulukul Basin). Some of these exhibit indications of marine incursions, but the basins are predominantly continental. The development of these basins is clearly associated with the location and Cenozoic reactivation of aforementioned long-lived fault zones in the Altai tectonic assemblage. Many of these basins accommodated fresh water lakes during their evolution and some are still the site of contemporary mountain lakes. Their stratigraphy, as well as the sedimentary architecture and basin morphology is manifestly influenced by and progresses with the stages of (Late) Cenozoic intracontinental mountain building and erosive denudation of the growing mountain ranges. Together with the clastic sedimentary input and the provenance characteristics, the intramontane Altai basin deposits are affected by evolving climatic conditions. These conditions dictate the main mode of erosion and transport, influence the sedimentary facies and supply rate and create the framework for a specific biocoenosis signature found in the fossil record. Our contribution reviews the data obtained over the last years from a selection of intramontane lacustrine basins in the Siberian Altai Mountains. We direct our attention in particular to the Teletskoye basin, the Chuya-Kurai Basin and the Dzhulukul Basin. We combine sedimentologic-stratigraphic data with basin architecture and morphology, and with basement geochronologic-thermochronologic constraints (apatite fission-track, U/Pb and Ar-dating) in order to show the potential of these basins as recorders of Cenozoic tectonic and climatic events in relation with basement features. While for example the data obtained from the Chuya Basin yields a continuous Cenozoic picture of deformation and climatic evolution of the Altai area, data from the Teletskoye Basin zooms in with higher resolution on the Pleistocene to Recent history. In general, all data point towards intensifying tectonic reactivation and mountain building of the Siberian Altai Mountains since the Middle Cenozoic, with clear peak activity in the Pliocene to Recent. This is demonstrated by the molassetype deposits in these basins, and by thermochronologic constraints. This activity is ongoing and structural, (paleo)seismic, geomorphologic and sedimentologic data corroborates this. The lacustrine Altai basins provide a record for a more or less continuous progressive cooling and aridification of the Altai area during the Cenozoic as manifested in the pollen fossil assemblages found in the Altai sediments

A pilot study on the air quality in passive houses with particular attention to radon

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A major stage of convergence in the Issyk-Kul basin (Northern Tien-Shan) at the end of the Neogene

The structural features the northern Tien-Shan mountain belt in Kyrgyzstan, including the Issyk-Kul basin, indicate a complex Cenozoic deformation, associated to the Indian-Eurasian collision. The collision caused deformation to propagate inside the continent, resulting in crustal thickening and mountain growth. The present-day shortening occurs at a rate of about 10-15 mm/yr and is oriented roughly N-S in the southern Tien-Shan and up to 2-6 mm/yr and variably oriented in the northern Tien-Shan. Different rate values and orientation could be related to the presence of a Precambrian microcontinent in the northern Tien-Shan. That microcontinent could affect the formation of the Neogene-Quaternary structure of the Issyk-Kul basin. In the Paleogene, more then 3 km of lacustrine sediments was deposited in the subsiding basin. The onset of uplift of the southern Tien-Shan started in the Neogene, when clastic and proluvial sediments, transported from the rising southern ranges were deposited in the basin. In this stage, the basin was much larger and more elongated than at present. It was probably controlled by ENE trending faults.Starting in the late Neogene, clastic material was deposited in a moderately subsiding basin. This indicates the onset of uplift in the Northern Tien-Shan, reaching a peak at the end of the Pliocene-early Pleistocene. In this period, strong N-S oriented contractions caused rigorous deformations inside the Issyk-Kul Cenozoic deposits. The southern and northern edges of the basin were intensely deformed. They are presently exposed and exhibit two major trends of tectonic lineaments, that correspond to transpressive zones, oriented ENE and NW. Pop-up and transpressive flower structures indicate oblique convergence in these zones.Ramp structures developed at the latitudinal edges of the basin and the thrusting of the basement over the basin is accompanied by late Neogene molasse deposition. E-W striking faults controlled the late Neogene structure of the basin.The deformed Neogene sediments are often unconformably overlain by undeformed Quaternary terraces. The Quaternary tectonics in the uplifted parts of the basin is expressed by reverse reactivation of preexisting faults. The border faults shifted toward the internal parts of the basin which was further narrowing in north-south direction, and the borders of the basin were further uplifted. Within the lake, active deformation has been recorded in its southern part, expressed by upright folding with NE trending axis.A major stage of convergence is consequently evidenced, dating from the end of the Neogene, mainly expressed by transpressive movements along a conjugate set of strikeslip zones. This stage of strong deformation is contrasting with the Quaternary tectonic stage of moderate basin inversion. We investigate the relations between the tectonic history of the Himalaya and of the Tibet plateau, and the deformation stages observed for the Issyk-Kul basin

Stochastic analysis of the effect of heterogeneity and fractures on radionuclide transport in a low-permeability clay layer

Deep low-permeability clay layers are considered as safe environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is a candidate host rock for deep geological disposal. In this study, we analyze the effects of fractures and spatially variable hydraulic conductivity on radionuclide migration through the clay. Fracture geometry and properties are simulated with Monte Carlo simulation. The heterogeneity of hydraulic conductivity is simulated by direct sequential co-simulation using measurements of hydraulic conductivity and four types of secondary variables. The hydraulic conductivity and fracture simulations are used as input for a transport model. Radionuclide fluxes computed with this heterogeneous model are compared with fluxes obtained with a homogeneous model. The output fluxes of the heterogeneous model differ at most 8% from the homogeneous model. The main safety function of the Boom Clay is thus not affected by the fractures and the spatial variability of hydraulic conductivity