New Chronological,Paleontological, and Geochemical Data on the Formation of Glacier-Dammed Lakes in the Kurai Depression (Southeastern Russian Altai) at the End of the Late Pleistocene

Doklady Earth Sciences - One of the debated problems in Pleistocene paleogeography of the Altai region is the extent and time of existence of the last glacier-dammed lakes. For the first time...     

Radiocarbon chronology of Holocene glacial and climatic events in southeastern Altai (Central Asia)

The geomorphological studies and radiocarbon dating of moraine complexes and the tree line within the North Chuya Ridge, along with active slope processes, soil formation, and peat formation in southeastern Gorny Altai, constrain the age of the main glacial and climatic events in this area at 7 ka to the first half of the 19th century. It is for the first time in the history of Altai studies that 57 absolute dates were obtained for glaciation in a vast but climatically and neotectonically homogeneous area. The new data refute the conventional idea that the Holocene glaciation in this mountain land comprised eight stages of the gradual retreat of the Late Würm (Sartan) glaciation. Also, they evidence that glaciation in the upper parts of the troughs retreated almost completely no later than 7 ka and valley glaciers in southeastern Altai were activated many times in the second half of the Holocene. Data are given on the morphology and age of three moraine generations reflected in the topography. A combination of temperature minima and humidity maxima led to a catastrophically rapid and the largest (up to 5–6 km) ice advance at the Akkem Stage (4.9–4.2 ka). In addition to the radiocarbon data, the time limits of the Historical stage (2.3–1.7 ka) were defined more precisely using dendrochronological and archaeological data from Scythian burials of Pazyryk culture in SE Altai. The moraines closest to the present-day glaciers formed at the Aktru Stage (late 13th–middle 19th century). During warm interglacials, the glaciers waned considerably or retreated completely and the zone of recent glaciation was reforested. As a result of progressive aridization in the Holocene, the glaciers in southeastern Altai waned at each successive stage, and their mass balance was not positive during the greatest temperature minimum of the last millennium (middle 19th century).     

The First Data on Late Pleistocene Ostracods from the Kurai Depression (Gornyi Altai)

Doklady Earth Sciences - In the sections of Late Pleistocene deposits of the Kurai Depression of Gornyi Altai studied, an ostracod assemblage, including Leucocythere sp. 1, L. sp. 2, Leucocythere...     

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.     

Connection of the Late Paleolithic archaeological sites of the Chuya depression with geological evidence of existence of the Late Pleistocene ice-dammed lakes

The complexity of the age dating of the Pleistocene ice-dammed paleolakes in the Altai Mountains is a reason why geologists consider the Early Paleolithic archaeological sites as an independent age marker for dating geological objects. However, in order to use these sites for paleogeographic reconstructions, their locations, the character of stratification, and the age of stone artifacts need to be comprehensively studied. We investigate 20 Late Paleolithic archaeological sites discovered in the Chuya depression of the Russian Altai (Altai Mountains) with the aim of their possible use for reconstructions of the period of development of the Kurai–Chuya glacio-limnosystem in the Late Neopleistocene. The results of our investigation show that it is improper to use the Paleolithic archaeological sites for the dating of the existence period and the draining time of ice-dammed lakes of the Chuya Depression in the modern period of their study owing to a lack of quantitative age estimates, a wide age range of possible existence of these sites, possible redeposition of the majority of artifacts, and their surface occurrence. It is established that all stratified sites where cultural layers are expected to be dated in the future lie above the uppermost and well-expressed paleolake level (2100 m a.s.l.). Accordingly, there are no grounds to determine the existence time of shallower paleolakes. Since the whole stone material collected below the level of 2100 m a.s.l. is represented by surface finds, it is problematic to use these artifacts for absolute geochronology. The Late Paleolithic Bigdon and Chechketerek sites are of great interest for paleogeographic reconstructions of ice-dammed lakes. The use of iceberg rafting products as cores is evidence that these sites appeared after the draining of a paleolake (2000 m a.s.l.). At this time, the location of these archaeological sites on the slope of the Chuya Depression allows one to assume the existence of a large lake as deep as 250 m synchronously with the above paleolake or later. The location of the lowermost archaeological sites is evidence that a paleolake could have existed at an altitude below 1770 m a.s.l. in the Late Neopleistocene–Early Holocene. The absolute geochronology of the archaeological sites (cultural layers in multilayered sites, split surfaces on dropstones, etc.) can be useful for further reconstructions of the existence time, depths, and a number of ice-dammed lakes in the Kurai–Chuya system of depressions.     

Assessing the rate of seismogravitational denudation of the relief of southeastern Altai: The Chagan-Uzun R. Basin

This paper considers the influence of earthquake-induced slope processes on relief changes. We used the parameters of Holocene maximum earthquake-induced landslides resulting from past great earthquakes in order to use these data for the Chagan-Uzun R. basin for deriving the rate of Holocene seismogravitational denudation for the highest southeastern part of the Russian Altai, which shows the highest seismic activity. It is shown that the influence of moderate earthquakes on this relief is negligibly small compared with that of larger earthquakes, while the landslides due to aftershocks provide a significant contribution in seismic regions where the aftershock process does not obey the Bath-Omori laws. Our numerical estimate for the rate of seismogravitational denudation obtained by statistical methods was corroborated by measuring the volumes of Holocene seismogravitational movements using the method of detailed profiling. It is shown that the volume of an earthquake-induced landslide is largely controlled by the size of the associated earthquake and by climate.