L. A. Ganzey

Late Pleistocene-Holocene coastal development of islands off Vietnam

Abstract Relief and deposits of Vietnam shelf islands (Tkhanlam, Kaoptyaotyai, Koto, Kaotkhaotyai, Dongkho, Fongwong, Timatao Re, Che, Mung, Tyam, Kondao, Baikan, Fukuok, Tkhotyu, Tkhom) were studied. In the Late Pleistocene-Holocene these areas were the islands during transgressions, when the continent was submerged. The islands were connected to the continent during regressions. Coastal relief and deposits indicate the mark of Riss-Wurm and some Middle-Late Holocene transgressions and regressions. Transgressions were recorded in 10, 4–6, 3–4, 2.5–3, 1.5–2 m terraces, elevated benches and elevated coral reefs. Deposits of transgressive phases of Middle-Late Holocene with sea level rises from 0.5 to 3 m were dated: 5060–6800, 3357–4100, 2170–2435, 900–1200 years B.P. Regressions were accompanied by intensive eolian activities, downslope processes and erosional downcut of river valleys.

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.

Marine terraces of Western Sakhalin Island

Abstract Biostratigraphical and sedimentological studies of deposits of terraces with heights of 2–3, 3–4, 4–6, 8–10, 12–15, 20–30, 35–40, 60–80 and 100–120 m on Western Sakhalin Island have shown that they were all marine in origin. The upper complex of terraces (Q I –Q II ) formed during a period of slow tectonic uplift ( − in this area to 120 m above modern sea level. The lower complex of terraces (Q III –Q IV ) may have formed in response to sea level oscillations without any influence of tectonic uplift.

THE DEVELOPMENT OF LANDSCAPES OF THE SHKOTOVO PLATEAU OF SIKHOTE-ALIN IN THE LATE HOLOCENE

New data in the development of the basalt plateau landscapes under multidirectional changes of climate in the late Holocene is presented. Objects for paleolandscape reconstructions were lacustrinemarsh deposits of the Larchenkov marsh. The marsh arose on the site of a paleolake that has passed several stages of development. The greatest depth and area of the lake had about 3220–4000 14 С years BP in the conditions of warming and increasing moisture. At the fi nal stage of its existence, there have been periods of flooding and the shallowing with general tendency to active bogging. At the top of the sections of peat bogs, the volcanic ash B-Tm of Baitoushan volcano (the eruption 969 AD) was found. Stages in the development of landscapes were highlighted and the borders of their reconstructions were defined. Natural landscape-forming factors with the analysis of change rates of the biotic components were analyzed. Conclusions on stability of geosystems are made, and the contribution of global and regional paleoclimatic events is estimated. In forest vegetation of the plateau, the share of broadleaf species has increased during warming periods, the share of the Korean pine and dark coniferous, primarily spruce, has increased in the cold periods. In forest vegetation of the plateau, the share of broadleaf species has been increasing during warming periods, the share of the Korean pine and dark coniferous, primarily spruce, has been increasing in the cold periods. The expansion of dark coniferous forests had occurred in climatic conditions similar to modern – about 2550 14 С years BP; coniferous-deciduous forests had retreated to the edge of the plateau. The larch ( Larix komarovii ) had existed framing the paleolake during the all studied period and is a relic of the Last Glacial Maximum. The formation of modern landscapes with identifying their ages was analyzed.

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�

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.

Deposits of the 1983 and 1993 tsunamis on the coast of Primorye

Deposits of the two strongest tsunamis of the 20th century have been found on the eastern coast of Primorye. The tsunamis had epicenters in the Sea of Japan west of the coast of Hokkaido. The distribution and preservation of deposits in bays of different geomorphological structure have been analyzed. The best defined sedimentary covers occur in the upper part of sections in low-lying areas of bay shores, where the wave runup was more than 3 m. The best preserved deposits have been observed in bays attributed to loworder streams. Variations of the structural composition of tsunami deposits formed by traction processes associated with the tsunamis have been analyzed depending on distance from the shoreline; the sources of material have been identified. Tsunami waves transported sand not only from beaches, ancient storm ridges, and terraces, but also from the underwater coastal slope; waves also grabbed material from estuarine lagoons and lakes located in the shore inundation zone. Deposits include marine diatoms with dominant sublittoral planktonic and benthic species, which suggests that the material was transported from a depth no more than 15 m. Deep-sea species of diatoms and their fragments have been encountered. Among freshwater diatoms are species with different ecological identities, indicating erosion and redeposition of material transported from various sources.

Deposits of the Tohoku Tsunami (March 11, 2011) in the southern Kuril Islands: Composition and fossils

The deposits of the Tohoku Tsunami were studied on the Kunashir, Shikotan, Zelenyi, Yurii, and Tanfil’ev islands. They were sampled immediately after this event from ice, half a year later, and one and a half years later. The sampling was accompanied by measurements of the runup heights and the description of the innudation zones. Sand and mud covers were recorded only in closed bays that were covered by ice. The tsunami waves broke the ice cover to provoke bottom erosion and peatland destruction in low coastal areas even under insignificant runup. The investigations included the analysis of the grain-size distribution in the deposits and the taxonomic composition of the microfossils, including benthic foraminifers, diatoms, and pollen assemblages. The marine diatom assemblages are dominated by sublittoral benthic forms accompanied by subordinate sublittoral planktonic, neritic, and oceanic species. The palynospectra include pollen and spores of the local island vegetation, allochthonous pollen transported by the tsunami wave and wind from adjacent areas, and taxa reworked from the upper Holocene deposits eroded by the tsunami. The examined sections have been revisited to estimate the degree of preservation of the tsunamigenic deposits.

Response of Landscapes of the Sikhote-Alin Western Slopes to the Middle–Late Holocene Climatic Changes

The response of landscape biotic components of the western slope of the Sikhote-Alin Mountains (Bikin River middle flow) to the Middle–Late Holocene climate changes is discussed. The paleoreconstruction object was the Krasny Yar mari, which developed under the control of multidirectional short-term climatic changes. The last millennium was marked by particularly rapid and frequent changes in the local landscapes. The closely spaced orographic barrier strongly affected the development of biotic components and changes in the swamp hydrological regime. The moisture dynamics within the river catchment considerably controlled the development and change of the peat-forming plants. Several stages of the mari development were reconstructed; each began from the accumulation of eutrophic peat. It was followed by the transitional eutrophic–mesotrophic stage, with a higher role of atmospheric supply. The larch forests appeared in this part of the valley within the Atlantic–Subboreal cooling period. Korean pine developed in the forest vegetation in the low mountain relief at the beginning of the Subboreal and became one of the leading trees ~2.6–2.3 ka BP. The lower role of the Korean pine and birch forest expansion in the first half of the Subatlantic could be related to the fires. The broadleaf–Korean pine forests became widespread in the Medieval Warm Period. Local swamp landscapes changed dramatically in the Little Ice Age, while the slope vegetation was not subject to any major changes. The landscapes were also affected by the fires, which became more frequent. The derivative communities with birch appeared on the mari. Moreover, this part of the valley was occasionally subject to heavy flooding.

Environmental changes recorded in deposits of the Izyubrinye Salontsi Lake, Sikhote-Alin

Paleoecological changes during the development of Lake Izyubrinye Solontsi from the Solontsovskie (Shanduyskie) Lakes located in the midlands of the Eastern Sikhote-Alin have been reconstructed. Lake formation is related to landslides on the paleovolcano slopes. A complex study of the peat-bog section (botanical, diatom, spore-pollen, and radiocarbon analysis) allows reconstructing paleoenvironmental changes with high resolution. A considerable variability of lake and swamp environments highly responsive to climate changes in the late Holocene has been revealed. Peat accumulation began about 400014С BP. The main peat-forming plants were Sphagnum mosses and herbs, except for the period 2330‒1530 14C BP (2360‒1480 cal. BP), when a swamp overgrown by larch forests and predominantly woody peat accumulated. Forest ecosystems on the lake coasts were quite stable. The role of fir and broadleaved species increased in the composition of dark coniferous forests with Korean pine during the warm phases and the role of birch, in the cold phases; secondary forests occupied the low slopes during the last 1000 years. The age of paleofires has been determined.