Kh. A. Arslanov

Deposits of historical and paleotsunamis on the coast of eastern Primorye

Deposits left by tsunamis from earthquakes in the Sea of Japan floor were identified for the first time on the coast of eastern Primorye. Data are presented on the definite coastal zones from Plastun Bay to Peschanaya Bay, Ol’ga Bay, and from Valentin Bay to Proselochnaya Bay. Historical and Late Holocene paleotsunamis, the traces of which were found in the sections, were presumably the larger scale events than known tsunamis of the 20th century. The grain-size composition of the tsunamigenic deposits was analyzed, their similarity with and difference from the other coastal-marine facies were established, and the source areas of the material were determined. The age of the events, the height of the wave runups, and the length of the flood zones on the coastal areas with different geomorphology were determined. The obtained data may serve as the first step for compiling a geological record of tsunamis for the northwestern Sea of Japan.

Manifestation of holocene tsunamis on the Lesser Kuril Ridge

The data on the paleotsunami manifestations on some islands of the Lesser Kuril Ridge are presented. The sedimentation features during the different-intensity tsunamis are analyzed and the timing of the most significant events and their recurrence in the middle-late Holocene were determined.

The white sea level change and glacioisostatic land uplift during the Holocene near the Settlement of Kuzema, North Karelia Region

This paper contains lithostratigraphic and chronometric (radiocarbon dating) data on one of the regions on the Karelian coast of the White Sea obtained in the course of investigation of sedimentary sections from recent lake basins, which were separated at different times from the sea due to uplift of the glacioisostatic crust of the Earth. They were used as a basis for stratigraphic subdivision of marine and fresh water sediments and for reconstruction of the White Sea coast level change during the Late Pleistocene-Holocene near the Settlement of Kuzema, Karelia.

New Data on the Ladoga Transgression, the Neva River Formation, and Agricultural Development of Northwestern Russia

The geological history of Lake Ladoga, its connection with the Baltic basin, the formation of the Neva River, and the development of the whole region by people have been studied by Russian and Finnish scholars for a long time. Investigations carried out over the last fifteen years [1‐4] have made it possible to obtain new data on the problem; nevertheless, many problems still remain to be solved. To fill the existing gaps as well as to reveal the effect of hydrological changes on the early human settlements, international complex studies were carried out within an INTAS project and a project of the Russian Foundation for Basic Research. As subjects of investigation there were chosen peat bogs and lakes located in the central part of the Karelian Isthmus, in the region of the Vetokalio Rapids, the lowest area of the Ladoga‐Baltic watershed (the absolute height is 15.4 m above sea level) situated near the settlement of Veshcheevo, Vyborg raion, Leningrad oblast. Moreover, sections in the Neva River valley and in the southern part of the Ladoga region at the Volkhov and Oyat’ rivers (Fig. 1) were also studied. In the region of Veshcheevo (Karelian Isthmus), deposits of the Nizhneosinovskoe bog and Lamskoe and Makarovskoe lakes located west and east of the Vetokalio Rapids respectively were studied (Fig. 2). The section of the Nizhneosinovskoe bog located 23 m above sea level (masl) exposed the sequence of lacustrine and mire lake‐bog deposits reflecting early stages of the existence of the so-called Hejnijoki Strait: a Baltic Ice lake (BIL), the Yoldia Sea, the later stage of which was dated at 9580 ± 100 years (9200‐8600 cal BC, LY-5306), and Ancylus Lake. Judging from the data obtained, the level of the Yoldia Sea in the central part of the Karelian Isthmus (25 masl) was reached 9400 ± 130 years (9150‐8250 cal BC, LU-5309). Overlying deposits comprise the diatom assemblage characteristic of the Ancylus freshwater lake. Between 8250 and 7100 cal BC, following the regressive lowering of the Ancylus Lake level, the basin in Nizhnesinovskoe peatbog area became isolated, existed for some time as a small lake and consequently became transformed into a bog. The study of bottom deposits of Makarovskoe (11.4 masl), Lamskoe (14.5 masl), and Uzlovoe (13.0 masl) lakes revealed final episodes of the existence of the Hejnijoki Strait. Deposits represented by lake mud were formed under conditions of shallowwater, slightly running-water, and stagnant lakes. The disappearance of “Ladoga elements” from the diatom flora and a change of the sedimentary environment from the strong-flow (sandy deposits), to slow-flow and stagnant ones (organogenic deposits) perceptible after 1980 cal BC, are indicative of isolation of lakes in the course of recession of the Lake Ladoga water level.

Chronology of Tsunamis Documented in Sections of the Coastal Lowlands in East Primorye

One of the fields in the study of how catastrophic events are manifested is investigation of sediments produced by historical and paleotsunamis. This infor� mation allows researchers to define the age, scale, and frequency of these events in the past. These studies are especially topical for the coasts of the Russian Far East where chronicles have provided almost no evidence and instrumental observations have been carried out only since the second half of the 20th century (1, 2). The longterm works on studying paleotsunamis have been being carried out in the Kuril-Kamchatka Region (3-5), but there are no data on the sediments of the historical and paleotsunamis for the continental coast of the Sea of Japan until the recent time. The Primorye is located in the rare seismoactive zones of Russia, and although most earthquakes in this region are deep focus ones, some strong shallow earthquakes of 5-7 in magnitude have been reported (6). Large tsu� namis in the region are related to the earthquakes whose epicenters are clustered along the narrow band of the shelf and submarine slope of the island of Japan, stretching to Moneron Island (2). Four large tsunamis were reported here during the 20th century: in 1907, 1940, 1983, and 1993; the effects of the last two events were investigated on the coasts of Primorye immedi� ately after the tsunami struck (1, 7, 8). The effects of these tsunamis on the natural and economic objects located in the coastal zone were also assessed, and the zonation of coasts in terms of tsunami hazard was car�

Development of lacustrine-boggy sedimentary environments in the ancient Rasshua Island caldera (Central Kuril Islands) in the Holocene

The evolution stages of the lacustrine-boggy sedimentary environments and the role of the climatic and volcanic factors were reconstructed on the basis of complex stratigraphic (botanical, palynological, and diatom analyses and tephrostratigraphy) and radiocarbon studies of the peat lands on Rasshua Island during the middle-late Holocene. The stages of the landscape evolution and the time of their reorganization were determined.

The first uranium-thorium dating of the Middle Neopleistocene peat in West Siberia

For a sample from the roof of peat (0–2 cm) located in a reference section for the Middle Neopleistocene in West Siberia near the village of Krivosheino, we obtained an exorbitant value of 14C date ≥53.9 ka B.P. (LU-6024). In the peat proper, the 230Th/U dates obtained by the isochronous method are 195.2 ± 10.8/9.1 ka B.P. for the L/L model and 204.1 ± 17/13 ka B.P. for the TSD model. The palynospectra of the peat characterize, from the bottom up, birch forests with fir and spruce participation; then spruce forests with fir; next spruce-cedar forests, similar to the middle taiga subzone. In the clay, the following palynospectra have been examined: forb-gramineous grasslands and light forests with spruce and Betula fruticosa. In the upper part of clays, the palynospectra reflect the evolution of swampy, birch, light forests with spruce participation. The conclusion is made that the studied part of the section formed at the end of the Samarovo Ice Age and in the last third of the Taz Ice Age. The break in sedimentation related to the erosion contact covers a part of the Samarovo Ice Age and the first two-thirds of the Taz Ice Age.

Chronology of Hydrothermal Activity Within the Yubileynoye Ore Field (Mid-Atlantic Ridge, 20°08′ N)

This paper reports on the integrated geochronological and geochemical methods used in studying the ore deposits and metalliferous sediments of the Yubileinoye field. This study gives the opportunity to carry out cross dating of hydrothermal deposits, including the 230Th/U dating of sulfides, the 230Th, 14C dating, and foraminiferal analysis of the sediments, and, on this basis, to reconstruct hydrothermal activity over time. It was established that the ores started forming about 100 000–123 000 years ago and were renewed 4–5 times with a frequency of 10–20 ka. As a result, the complex of pyrite-marcasite, chalcopyrite and sphalerite ores and the associated metal-bearing and ore-bearing sediments with consistent geochemical specialization were formed. The integrated geochronological and geochemical studies of the ores and sediments allow us to obtain detailed data on evolution of the hydrothermal ore-formation not only in the certain areas but also for the entire Mid-Atlantic Ridge.

The problem of past megatsunami reconstructions on the southern Kurils

Tsunamis are reconstructed on the basis of distribution of tsunamigenic sediments in coastal lowland sections. Reflections of anomalous tsunamis are recorded in detail in the lacustrine–boggy sections of the Lesser Kuril Ridge, while only fragments of these sediments have been found on the islands of the Greater Kuril Ridge. The distribution and composition of the sediments left by recent large-scale tsunamis (locally documented 1994 and 1894 Shikotan tsunamis and transoceanic 2011 Tohoku tsunami) are analyzed for the purpose of understanding deposition features during large and megatsunamis. Interregional correlation of the events during the last ~2.5 kyr is carried out with estimation of their scales. It is established that large events took place in the 17th and 18th centuries and approximately at 1.0, 1.4–1.6, 1.7–1.8, and 2.0–2.1 ka ago. New data on large tsunami chronology since the Middle Holocene are presented. A unique natural peatland section with abundant tsunamigenic sand layers is studied on the Pacific side of Zelenyi Island (Rudnya Bay), where deposition continued through the entire Holocene. The largest tsunamis which happened on the South Kuril Islands during the last ~7.5 kyr and can be classed as megatsunamis are revealed.

The origin and evolution of relict larch stands on Shikotan Island (Lesser Kuril Ridge) in the Holocene

Palynological and geochronological data have been used to ascertain the time history of a unique natural-territorial complex — the relict larch stands that have persisted in the southeastern part of Shikotan Island since the Late Pleistocene. The study revealed the development stages of landscapes. Factors favoring vegetation conservation in the refugium are discussed.