T. A. Grebennikova

Sedimentation Particularities during the Tsunami of December 26, 2004, in Northern Indonesia: Simelue Island and the Medan Coast of Sumatra Island

Sediments deposited during the tsunami of December 26, 2004, in coastal areas that differ in their structure and orientation relative to the tsunami front are studied with defining of the factors controlling particular features of the sedimentation under different wave intensities. The lithology of tsunami-related deposits and data on various fossils (diatoms, foraminifers, and mollusks) are analyzed. It is established that the tsunami resulted in the accumulation of sediments of various composition, which is explained by the features of the transformation of the wave as well as by the structure of the underwater coastal slope, the flooded zone, and the provenance. Variably oriented coseismic motions are one of the factors influencing the sedimentation patterns. The paleotsunami deposits discovered are compared with their recent counterparts.

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.

The peat bog of Ketoi Island: The Middle-Upper Holocene reference section of the Central Kuriles

The results of the complex study of a Holocene peat bog in the southern part of Ketoi Island, which is proposed to serve as a reference section for the Central Kuriles, are discussed. The peat bog’s stratigraphy is based on botanic, palynological, and diatom data, 16 radiocarbon age determinations, and the composition of the volcanic ashes. The peat accumulation initiated approximately 6500 years ago. The successive changes of the island’s vegetation are traced through the Middle-Late Holocene with defining of the phases of its development and dating the paleolandscape transformations related to the climatic oscillations and volcanic eruptions.

Stratigraphy of peat bog in the Gorobets River valley and development of natural environments of Shikotan Island (Lesser Kurile Ridge) in the Holocene

The stratigraphic subdivision of peat in the Gorobets River valley, the largest river on Shikotan Island, is conducted based on the study of palynological and diatom assemblages, tephrostratigraphy, and radiocarbon dating. The study object is one of the oldest peats in the South Kurile region and reflects the development of natural environments beginning from the early Holocene. Nine phases are distinguished in the development of vegetation on Shikotan Island. The changes in vegetable communities were determined by climatic fluctuations during the Holocene. Their ages, the factors responsible for the appearance and extinction of particular coniferous, small-, and broad-leaved taxa, and changes in their landscape-forming role during different periods of the Holocene, as well as specific features in the formation of the present-day vegetation on the Lesser Kurile Ridge representing a separate floral area, are established. In addition to the climatic and sea-level fluctuations, the development of the island landscapes was determined to a significant extent by its topography, size, and isolation.

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.

Tsunami deposits of the Shikotan earthquake of 1994

This paper describes the results of the grain-size and mineralogical studies of the deposits of the tsunami of 1994 on Shikotan, Tanfil’ev, and Kunashir islands. The studies were carried out within the portions of the coast with different configurations, geomorphologic structures, lithodynamical environments, and character of the tsunami manifestation. The composition of the tsunami deposits is shown to be controlled mainly by erosion-accumulative processes during the tsunami events and is in many respects inherited from the matter sources. The tsunami deposits contain marine diatom species, whose richest assemblages were found within the areas where the material from the underwater coastal slope was redeposited. The data concerning the deposits of earlier historical tsunamis encountered in the same cross sections are discussed too. Their examination points to a similar development of the erosional-accumulative processes during tsunami events with the same intensity and an entrainment of the matter from the same sources.

Natural-environment dynamics within the Amur basin during the Neoglacial

We examine the natural-environment development dynamics within the Amur basin during the Neoglacial. The study revealed the opposing directedness in climate humidity changes for different parts of the basin. In the maritime and inland parts, a cooling was accompanied by an increase and decrease in humidity, respectively. It is established that a cooling in the maritime part of the basin led to a shift of the boundaries of vegetation zones, an enhancement in waterlogging of bog systems, and to a change of biogeocenoses. In the inland part of the basin, an enhancement in aridization was conducive to a retrogression of the lakes’ level, and to an intensification of aeolian processes.

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.

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.

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�