Anastasia V. Arzhannikova

Transpressional tectonics and stream terraces of the Gobi‐Altay, Mongolia

We studied the patterns, rates and evolution of fluvial terraces and fault system during the building process of an intracontinental transpressional mountain in the Gobi-Altay (Mongolia). By analyzing incisions and offsets of fluvial terraces and alluvial fans, we show that the massif has grown by outward migration of thrust faults through time. On the northern flank, the present bounding thrust fault began its activity ~600 ka ago, while a more internal sub-parallel fault was still active until ~200-100 ka. Vertical offset of an alluvial fan abandoned ~100 ka ago allows an estimate of 0.1 mm/yr Upper Pleistocene - Holocene uplift rate. The morphology of the catchment-piedmont system strongly suggests a periodical formation of the alluvial surfaces, controlled by the climatic pulses, at the beginning of the wet interglacial periods. The abandonment of the alluvial terraces lags by several thousand years the abandonment of the alluvial fans, showing a diachronous incision propagating upstream. The incision rate deduced from the different elevations of straths exceeds of one order of magnitude the rock uplift rate. This excess is mostly due to ongoing drainage network growth at the core of the massif, and incision due to alluvial apron entrenchment near the outlet. This implies that fluvial response is mainly controlled by drainage growth, interaction with piedmont and cyclic climatic variations, rather than by rock uplift.

Earthquake Geology of the Bulnay Fault (Mongolia)

The Bulnay earthquake of 23 July 1905 (Mw 8.3–8.5), in north‐central Mongolia, is one of the world’s largest recorded intracontinental earthquakes and one of four great earthquakes that occurred in the region during the twentieth century. The 375 km long surface rupture of the left‐lateral, strike‐slip, N095°E‐trending Bulnay fault associated with this earthquake is remarkable for its pronounced expression across the landscape and for the size of features produced by previous earthquakes. Our field observations suggest that in many areas the width and geometry of the rupture zone is the result of repeated earthquakes; however, in those areas where it is possible to determine that the geomorphic features are the result of the 1905 surface rupture alone, the size of the features produced by this single earthquake are singular in comparison to most other historical strike‐slip surface ruptures worldwide. Along the 80 km stretch, between 97.18° E and 98.33° E, the fault zone is characterized by several meters width and the mean left‐lateral 1905 offset is 8.9±0.6  m with two measured cumulative offsets that are twice the 1905 slip. These observations suggest that the displacement produced during the penultimate event was similar to the 1905 slip. Morphotectonic analyses carried out at three sites along the eastern part of the Bulnay fault allow us to estimate a mean horizontal slip rate of 3.1±1.7  mm/yr over the Late Pleistocene–Holocene period. In parallel, paleoseismological investigations show evidence for two earthquakes prior to the 1905 event, with recurrence intervals of ∼2700–4000  yrs.

Catastrophic flooding, palaeolakes, and late Quaternary drainage reorganization in northern Eurasia

ABSTRACT We review the long history of Russian scientific study of the major late Quaternary palaeodrainages and palaeolakes in northern Eurasia to provide overviews of (1) past research efforts (mainly published in the Russian language) and (2) recent studies that include contributions from those outside of the former Soviet Union region. There are two major groups of catastrophic flooding phenomena and related palaeodrainage and palaeolake systems in this region: (1) those involving large-scale lowland basins and (2) those involving upland intermontane basins. Many of these palaeodrainages and palaeolakes were active during the late Quaternary, though the available age data are inconclusive in regard to more exact timing and synchronicity. These palaeodrainages and palaeolakes in the late Quaternary are strongly linked with climatic change, most notably to ice age. For the megalakes in large-scale basins, spillover events probably occurred because of impoundment by the late Pleistocene Arctic ice sheets. In some cases, gradual transgressions of the megalakes caused by varying climatic conditions could also have contributed to the spillovers. Some of these spillover events may have been catastrophic. Ice-dammed lakes formed when drainage into intermontane basins was impounded by late Pleistocene alpine-type glaciers. The collapses of the glacier dams caused downstream catastrophic flooding, producing a characteristic suite of flood-related landforms. In the Azas Plateau volcanic field, there is evidence for Icelandic-type subglacial flooding.

Catastrophic outburst and tsunami flooding of Lake Baikal: U–Pb detrital zircon provenance study of the Palaeo-Manzurka megaflood sediments

ABSTRACT Lake Baikal, the largest freshwater reservoir on Earth (~600 × 30 km in size and up to 1.6 km in depth), has more than 300 contributing rivers but only one N-trending outflow – River Angara. In the Pliocene or Pleistocene, another N-trending outflow operated through the Palaeo-Manzurka to Lena. Provenance analysis using U–Pb dating of detrital zircons from the Palaeo-Manzurka sediments demonstrates that the dominant source of the zircons was the lake deposits, while the contribution of zircons from local bedrocks was limited to about 8% only. Looking for an explanation of this, we propose a hypothesis that formation of the Palaeo-Manzurka sediments took place in association with a catastrophic mega-landslide (~15 × 3 km) into the lake and the resulting mega-tsunami flooding.

The Neogene de-greening of Central Asia

There remains substantial debate concerning the relative roles of tectonics and global climate in driving the evolution of climate in Central Asia. Today, interior Asia—including the Taklamakan, Gobi, and Ordos Deserts—is exceptionally arid and is surrounded by distinct rainfall boundaries, such as those generated by the Asian monsoon systems to the east and south and those generated by high topography to the north and west. Determining how and why these boundaries have varied over the Neogene is hindered by the lack of a single proxy that can be broadly applied through space and time. We construct isoscapes of pedogenic carbonate δ 13 C (δ 13 C c ) over the Neogene in Asia by combining a compilation of 2236 published measurements with new data from three localities in northern Central Asia. Pedogenic carbonate δ 13 C records local aridity—excepting localities impacted by C 4 grasslands and during large changes in atmospheric p CO 2 —through variations in soil respiration, depth of carbonate formation, and the effect of water stress on plant δ 13 C. Together, these effects reflect changes in both primary productivity and mean annual precipitation. Throughout the Neogene, we find consistent and exceptionally high δ 13 C c in interior Asia with a ring of lower δ 13 C c that demarcates higher precipitation. This persistent ring of lower δ 13 C c corresponds in the south and east with the influence of the Asian monsoon systems; in the west and north, it reflects both orographic rainfall due to uplift of the Tian Shan and to moisture delivery by the mid-latitude westerlies. Finally, δ 13 C c and, hence, aridity increases regionally in the latest Neogene, reflecting the effects of Northern Hemisphere glaciation and cooling. This widespread “de-greening” would have increased regional albedo and modified basin-scale water balances, resulting in greater dust fluxes due to reduced vegetative cover and precipitation.

Morphotectonic Analysis of Pliocene-Quaternary Deformations in the Southeast of the Eastern Sayan

The paper is concerned with the kinematics of the major faults, their pattern, and the time of occurrence of compression and extension deformations in the southeast of the Eastern Sayan. The geometry of the mountain ranges and the kinematics of the major faults exhibit northeast-oriented compression responsible for the current processes of relief formation, which corresponds to the direction of the vector of deformations associated with the Indo-Asian collision. The results obtained thus far may be indicative of the remote influence of collision on the orogenic activity and transpressional deformations in the Eastern Sayan since the end of the Miocene. Morphotectonic analysis has shown that the areas of Quaternary extension-related deformations in the Eastern Sayan are not a response to active rifting in the Baikal Rift Zone. The position and geometry of the subsided blocks and magma ruptures point to the fact that they form locally as extension structural elements near the strike-slip faults. The strike-slip and thrust faults are widespread and play the leading role in the development of the southeastern part of the Eastern Sayan.

Characterizing the Present‐Day Activity of the Tunka and Sayan Faults Within Their Relay Zone (Western Baikal Rift System, Russia)

The Sayan and Tunka faults are located at the boundary between the northernmost mountain belt of Central Asia (the Sayan-Baikal ranges) and the Siberian platform. These prominent crustal structures were involved in the opening of the southern Baikal rift system since the beginning of the Cenozoic and define large-scale sharp morphotectonic features. Despite low instrumental seismic activity, Late Pleistocene-Holocene morphotectonic features along the two faults indicate that the faults are active and have the capacity to produce strong earthquakes. A careful mapping of the most recent trace of activity, within the southeastern parts of the two faults where they merge within a relay zone, demonstrates that they correspond now to left-lateral-reverse faults, suggesting a recent inversion of their vertical component. We also show that the two faults are now structurally connected via a young surface rupture and that no obvious post-Last Glacial Maximum ruptures are observed along the central part of the Sayan Fault beyond its junction zone with the Tunka fault. This suggests that the left-lateral strike-slip deformation is transferred from the eastern Sayan fault to the Tunka fault. A detailed morphotectonic study along the southeastern Sayan fault allows estimating a left-lateral slip rate between 1.3 (min) and 3.9 mm/year (max). Finally, a critical review of Russian paleoseismic data, combined with our paleoseismological investigations, allows us to propose that the mean recurrence time along the two faults is on the order of 4 kyr and that they may have either ruptured together or during seismic clusters.

Source Provenance and Paleogeographic Conditions during Deposition of Jurassic Continental Sediments in the Southern Part of the Siberian Platform (Implication of Sm–Nd and U–Pb Data)

The first Sm–Nd isotopic data and U–Pb (LA–ICP–MS) detrital zircon ages from sandstones of the Prisayan and Kuda Formations (the Irkutsk Basin, southern part of the Siberian Platform) have been obtained. They demonstrate that during accumulation of the sediments in the Irkutsk Basin, the contribution of local erosion sources decreased over time, while input from the Paleo–Transbaikalia sources increased. The change in provenance areas was triggered by tectonic rebuilding in Paleo–Transbaikalia caused by the closure of the Mongol–Okhotsk Ocean.

Data for:Catastrophic events in the Quaternary outflow history of Lake Baikal

File with original data for U-Pb dating of detrital zircons by laser ablation inductively coupled plasma mass spectrometry