Anna Agatova

Pleistocene glaciations of the SE Altai, Russia, based on geomorphological data and absolute dating of glacial deposits in Chagan reference section

Abstract Geomorphological evidence of at least two Pleistocene glacial epochsis noted within the Chagan-Uzun river basin, SE Altai. A review and analysis of all available absolute dates for reference Chagan section is presented. The highest correlation amongst all TL dates is observed for the lens of glacio-lacustrine sediments – the most suitable among glacial deposits for luminescence dating, and indicates its possible Middle Pleistocene age. IRSL dates obtained from feldspar indicate a Middle Pleistocene age of moraines already in the upper part of the section. The small number of obtained IRSL dates does not allow making geochronological reconstructions of the Pleistocene glaciations, but gives the possibility for further experiments with different variation of OSL (IRSL) techniques. Strong low temperature peak in TL signal and strong response to IR stimulation are specific regional quartz features, which could be explained by combination of short transportation distance and low number of depositional cycles for mineral grains. Available radiocarbon dates of carbonate concretions from this section are not related to the age of moraine sedimentation and most likely indicate the period of the Chagan river incision into the ancient glacial deposits. This study has shown that TL method is not valid for dating glacial sediments and TL dates cannot be utilized as chronostratigraphic markers. Generally, the Chagan section could hardly serve as a reference section for the Altai stratigraphy; available depositional correlation schemes for the Russian Altai and Siberia which are based on several TL dates obtained in the last century needs to be improved.

Using Dendrochronological Analysis for Dating Earthquake-Triggered Landslides (By the Example of SE Altai, Russia)

Paleoseismogeological investigations of the high mountain, seismically active southeastern part of the Russian Altai reveal a previously unknown complex of earthquake induced landslides. Using dendrochronological analysis of the wood penetrating injuries of trees (both dead and living ones) caused by seismically induced rockfalls allowed establishing the date of previously unknown strong medieval earthquake. This date was also confirmed by radiocarbon dating of seismically cut fossil soil overlapped by undistorted one. The specified recurrence interval of strong (М > 7) earthquakes for the SE Altai (about 400 years during the last 3,000 years) argues the high regional seismicity.

A new aspect of application of dendrochronological analysis for dating strong earthquakes of the past: A case study of the Altai Mountains

One of the main problems in seismic zoning and dis� tinguishing the territories of high seismic activity is defini� tion of the Mmax value and the recurrence period for strong events leading to large deformations in relief and affecting the economic activity. Relative to the recurrence period of strong earthquakes, the duration of instrumental observa� tions is very small; therefore, calculation of this parameter implies application of historical and archaeological data, as well as definition of the age for paleoseismodislocations found in the studied territory. The present work proposes a new method of dating the seismic events by means of the dendroseismological method and gives the first results of dendrochronological analysis to determine the age and recurrence period of strong earthquakes during the Holocene in the seismoactive Southeastern Altai Moun� tains (figure).

Extreme climatic events in the Altai Republic according to dendrochronological data

The results of dating of extreme climatic events by damage to the anatomical structure and missing tree rings of the Siberian larch in the upper forest boundary of the Altai Republic are given. An analysis of the spatial distribution of the revealed dates over seven plots (Kokcy, Chind, Ak-ha, Jelo, Tute, Tara, and Sukor) allowed us to distinguish the extreme events on interregional (1700, 1783, 1788, 1812, 1814, 1884), regional (1724, 1775, 1784, 1835, 1840, 1847, 1850, 1852, 1854, 1869, 1871, 1910, 1917, 1927, 1938, 1958, 1961), and local (1702, 1736, 1751, 1785, 1842, 1843, 1874, 1885, 1886, 1919, 2007, and 2009) scales. It was shown that the events of an interregional scale correspond with the dates of major volcanic eruptions (Grimsvotn, Lakagigar, Etna, Awu, Tambora, Soufriere St. Vinsent, Mayon, and Krakatau volcanos) and extreme climatic events, crop failures, lean years, etc., registered in historical sources.

Recurrence interval of strong earthquakes in the se Altai, Russia revealed by tree-ring analysis and radiocarbon dating

Abstract This paper presents the results of paleoseismogeological investigations including tree-ring analysis and radiocarbon dating in pleistoseist zone of the 2003 Chuya earthquake, SE Altai, Russia. Twenty-five radiocarbon dates of previously unknown evidences of prehistoric earthquakes along the fault bounders of the Chagan-Uzun massif, North Chuya and South Chuya ranges are reported. Perspectives of applying dendroseismological approach within the high mountainous seismically active southeastern part of Russian Altai are demonstrated. In addition to estimating the germination ages of trees growing on the bare surfaces of seismically triggered landslides, analysis of wood penetrating injuries in the individual tree ring series was applied for dating paleorock-falls. Analysis of distribution patterns of tree-ring anomalies and injured trees suggests a criterion of recognizing seismic origin of past rock-falls. Dendrochronologically obtained dates of abrupt intensifications of rock-falls can be considered as supposed dates of past earthquakes, which should be verified by alternative proxy data. Obtained results argue for the high regional seismicity in the second half of the Holocene. Strong earthquakes occurred here AD 1532, and 600–700, 1300–1500, 2400–2700, 3400–3700, 3800–4200 cal BP. This data clarifies the chronology of seismic events within the SE Altai. The specified recurrence interval of strong earthquakes is about 400 years during the last 4000 years.

Discovery of Upper Oligocene–Lower Miocene brown coal deposits (Kosh-Agach formation) in the Dzhazator River valley (Southeastern Russian Altai): Neotectonic and paleogeographical aspects

Results of complex paleontological and geochemical analysis are reported for a new locality of the Upper Oligocene–Lower Miocene Kosh-Agach carbonaceous formation in the Dzhazator River valley. This find specifies the scales of lacustrine–marsh sedimentation at the end of the Paleogene and beginning of the Neogene, as well as the character and amplitude of post-Neogene neotectonic movements in the southeastern highest mountain part of Russian Altai. Systematic rejuvenation of the radiocarbon age of the sequences studied, which has been established for the first time in Altai, is related to influx of young carbon during the subsequent complex geological history. This fact is of great importance for deciphering the chronology of Pleistocene glacial–dammed lakes in the intermontane basins of Altai and Tuva, the erosion zone of which spanned exhumed Tertiary deposits.

Influence of aftershock process on the rate of seismic gravity denudation (Example of the Chuya earthquake in 2003)

Slope processes induced by seismicity in mountainous regions along with water and ice activity play an important role in transporting matter on the Earth’s surface. Stresses of mountainous rocks, seismic accelerations, and vibrations during earthquakes change radically the stability of rock grounds and slope sediments triggering enormous collapses, landslides, and formation of avalanche cones of anomalously large size. In the overwhelming majority of cases, the greatest volume of material is transported as a result of the main shock with the maximum amplitude. At the same time, the aftershock process, which takes place during almost all strong earthquakes, can also lead to seismic gravity transport of material on the slopes. However, the influence of the aftershock process on topography transformation has been studied extremely poorly. In the Altai region, such investigations have not been carried out at all. In this work, we deduce a relation that allows us to estimate the contribution of the aftershock process to seismic gravity denudation from the example of the aftershocks of the Chuya earthquake of 2003, which occurred in the southeastern part of the Gornyi Altai. The rate of topography denudation caused by slope processes induced by seismicity can be calculated from the following relation: