Kuril Kamchatka Research Articles

Systematic identification of microplastics in abyssal and hadal sediments of the Kuril Kamchatka trench.

The occurrence of microplastics throughout marine environments worldwide, from pelagic to benthic habitats, has become serious cause for concern. Hadal zones were recently described as the "trash bins of the oceans" and ultimate sink for marine plastic debris. The Kuril region covers a substantial area of the North Pacific Ocean and is characterised by high biological productivity, intense marine traffic through the Kuril straits, and anthropogenic activity. Moreover, strong tidal currents and eddy activity, as well as the influence of Pacific currents, have the potential for long distance transport and retention of microplastics in this area. To verify the hypothesis that the underlying Kuril Kamchatka Trench might accumulate microplastics from the surrounding environments and act as the final sink for high quantities of microplastics, we analysed eight sediment samples collected in the Kuril Kamchatka Trench at a depth range of 5143-8250m during the Kuril Kamchatka Biodiversity Studies II (KuramBio II) expedition in summer 2016. Microplastics were characterised via Micro Fourier Transform Infrared spectroscopy. All samples were analysed in their entirety to avoid inaccuracies due to extrapolations of microplastic concentrations and polymer diversities, which would otherwise be based on commonly applied representative aliquots. The number of microplastic particles detected ranged from 14 to 209kg-1 sediment (dry weight) with a total of 15 different plastic polymers detected. Polypropylene accounted for the largest proportion (33.2%), followed by acrylates/polyurethane/varnish (19%) and oxidized polypropylene (17.4%). By comparing extrapolated sample aliquots with in toto results, it was shown that aliquot-based extrapolations lead to severe under- or overestimations of microplastic concentrations, and an underestimation of polymer diversity.

The Ore and Petroleum Regions of the South Okhotsk Province and Deep Geodynamics

The South Okhotsk Sea province, which includes the Sakhalin, Kunashir, Iturup, Urup islands and surrounding sea areas, comprises numerous occurrences of rare, noble metals and other mineralization, as well as petroleum fields, gas hydrate accumulations, and, locally, active emission of water–hydrocarbon gases. The occurrences and deposits of solid, liquid, and gaseous mineral resources are controlled by hidden deep-seated transform-type fault zones: Nosappu (Tuscarora), Iturup, and Urup. These long-lived extended (over 1000 km) zones are distinguished on the NW Pacific megaplate margin, near the SE flank of the Kuril–Kamchatka trough. Using seismotomographic methods we have established their extension to the west from the seismic focal zone in the oceanic slab subsided into mantle transition zone. In the areas of pull-apart extension, the faults provided active formation of drainage channels for seawater penetration in the lithosphere with subsequent serpentinization of its ultramafic rocks, and for decompressional generation of ascending mantle-derived abiogenic fluid flows. The latter penetrated from the subslab asthenosphere into the suprasubduction mantle wedge and sublithospheric mantle and caused metasomatism. The subsequent migration of the flows led to the generation of the primary magma reservoirs in the lower parts of the continental lithosphere, and intermediate and peripheral chambers in the Earth’s crust. The injection of melts from the chambers in the consolidated crust led to the formation of abyssal and hypabyssal intrusive massifs, arch-dome uplifts, and magmatogenic-ore systems predominantly among the rocks of the pre-Pliocene basement. The concentration of oil and gas accumulations from the mantle-derived abiogenic hydrocarbons bearing mercury, gold, rhenium, and PGE in reservoirs beneath fluid-impermeable beds among Cenozoic sedimentary basins also was related to deep sub- and supraslab fluid flows.

An Analysis of the Generalized Vicinity of a Large Earthquake Using Regional Data: The Kuril–Kamchatka Region

The method for constructing the generalized vicinity of a large earthquake as put forward and implemented in (Rodkin, 2008, 2012, 2020; Rodkin and Tikhonov, 2016) was previously used for analysis of world earthquake catalogs only. The use of this method for the analysis of regional catalogs presupposes a lower magnitude threshold for classification of large events and incorporation of regional seismicity peculiarities. We constructed the generalized vicinity from regional data for the Kuril Islands and Kamchatka. The same seismicity features have been identified as those for the generalized vicinity based on worldwide data; in particular, we identified the effect of earthquake hypocenters getting shallower in the near vicinity of a large earthquake. However, the regional data revealed the unexpected effect of a temporary clustering of large earthquakes, including those cases where they were far from each other. The volumes of higher activity involve considerable parts of the subduction zone far from each other both along the trench and over depth. We have estimated characteristic parameters of these clusters and the fraction of statistically dependent and independent large events. The mutual influence of seismicity at different depths has been discussed.

Peculiarities of Subduction in the Junction of the Kuril–Kamchatka and Aleutian Island Arcs

The peculiarities of the junction between the Kuril–Kamchatka and Aleutian island arcs are studied using different techniques and experimental data. The models of medium structure that were obtained by using surface wave tomography and studies of S-wave anisotropy in the asthenosphere beneath the subduction plate detected an ascending asthenospheric flow of hot material and fluids along the northern boundary of the lithospheric plate. The presence of the ascending asthenospheric flow in the junction zone has been recently confirmed by detailed body-wave seismic tomography. Additional feeding of the Klyuchevskoi volcanic group from the asthenospheric flow explains the great difference in the eruptive activity of these volcanoes in comparison to other volcanoes located in the Eastern volcanic belt of Kamchatka. Comparative study of Quaternary volcanoes lying in the Eastern volcanic belt has revealed a strongly pronounced decreasing productivity from north to the south, i.e., with distance from the end of the subduction plate. This reduction is likely related to a depletion in the invasion of magmatic melts along the subduction plate from the asthenospheric flow in the junction of the Kuril–Kamchatka and Aleutian island arcs.

The Magma Feeding System of the Klyuchevskaya Group of Volcanoes (Kamchatka)

Using observations from a large-scale seismic station network, we built a seismic tomography model of velocity anomalies for longitudinal (P-wave) and transverse (S-wave) seismic waves beneath the Klyuchevskaya group of volcanoes. The observational network (about 150 km) and the number of seismic stations (about 200) made it possible to determine the velocity structure to depths of 150 km. A low-velocity anomaly is observed almost beneath all volcanoes in the Klyuchevskaya group of volcanoes at a depth of 50 km. Beneath the Shiveluch volcano, in the region where the subduction plate discontinues, an anomaly can be detected to depths of 150 km. Most likely, in this zone, there is a channel for the penetration of magmatic melts to the surface along the boundary of the submerging Pacific Plate ending. This is indirectly confirmed by the presence of a mantle plume to a depth of 1000 km, as previously shown by the seismic tomography studies and an anomalous heat flow at the junction of the Kuril–Kamchatka and Aleutian island arcs.

The Contemporary Seismic Deficit in the Kuril–Kamchatka Subduction Zone

Based on an analysis of seismicity for the period of 1900–2018, the seismic potential of the Kuril–Kamchatka subduction zone is estimated, and the geometry of interplate coupling of the North American and Pacific lithospheric plates and the rate of seismic underthrusting of the latter beneath the former are specified. In order to identify areas of modern seismic deficits in the subduction zone, an approach based on the cumulative displacement of interplate earthquakes with Mw ≥ 7.0 is proposed. Together with other methods, such an approach contributes to a more accurate seismic hazard assessment of the region.

Munnopsidae (Crustacea, Isopoda, Asellota) from the Kuril–Kamchatka Trench with a regional and inter-ocean comparison of their biogeographic and richness patterns

The benthos of the Kuril–Kamchatka Trench (KKT) was sampled during the KuramBio II expedition on board the RV Sonne in 2016. Macrobenthos was, for the first time, collected in the KKT hadal zone using an epibenthic sledge. Isopod crustaceans were one of the dominant taxa, and Munnopsidae was the most abundant and diverse asellotan family, comprising 49% of all Isopoda. During the expedition, a total of 67 species of 24 genera from eight subfamilies of Munnopsidae were collected, including 41 species of 15 genera from 18 hadal stations. In general, the taxonomic diversity of the munnopsid fauna in the KKT hadal zone was lower than that of the Northwest Pacific (NWP) abyssal fauna adjacent to the KKT. Two subfamilies, Lipomerinae and Acanthocopinae, were not found in the hadal zone. Most of all collected munnopsid individuals (92%) belonged to the three subfamilies: Eurycopinae (42%; 15 species), Betamorphinae (33%; four species), and Storthyngurinae (17%; two species). The rest of all munnopsid individuals (8%) belonged to the subfamilies Ilyarachninae, Munnopsinae, Syneurycopinae, and to a group of incertae sedis genera. The eight most numerous species representing the three most widely distributed and speciose genera—Eurycope, Betamorpha and Rectisura—encompassed 78% of all munnopsid individuals. The study of the Munnopsidae collected during the four expeditions (SoJaBio in 2010, KuramBio in 2012, SokhoBio in 2015 and KuramBio II in 2016) extended the known diversity of the munnopsid species in the KKT area from 39 described species of 14 genera to 157 species of 36 genera. Most collected species (87%) were new to science. The fauna richness showed a tendency to decrease from the open abyssal towards the hadal zone of the KKT and towards the semi-isolated abyssal Kuril Basin of the Sea of Okhotsk, and especially towards the more isolated abyss of the Sea of Japan. A comparison of the munnopsids from NWP and those from other oceans showed their similar composition with the same dominant subfamilies. The main difference between the abyssal munnopsids from the NWP and from the Atlantic sector of the Southern Ocean was the proportion of the Lipomerinae (2% vs. 16% of munnopsid individuals, respectively). A trend of reduction in the munnopsid diversity from abyssal to hadal depths, similar to that in the KKT, was also revealed in the Puerto-Rico Trench.

Secrets from the deep: Pseudotanaidae (Crustacea: Tanaidacea) diversity from the Kuril–Kamchatka Trench

A combination of morphological and genetic data (subunit I of the cytochrome c oxidase: COX1) was used to study the diversity and distribution of pseudotanaids in the Kuril-Kamchatka Trench and adjacent abyssal plain. Our results uncovered the presence of an undescribed species of Mystriocentrus (M. hollandae) and five new species of Pseudotanais (P. chanelae, P. monroeae, P. curieae, P. szymborskae and P. locueloae). The most abundant species was P. curieae (N = 182), followed by P. monroeae (N = 34), P. szymborskae (N = 31) and P. chanelae (N = 20). The number of individuals sampled was highest in shallower stations, but all four taxa could be found across the studied bathymetric range (4800–5500 m). Pseudotanaid abundance and bottom currents appear to be inversely related, which might be due to lower currents favouring sedimentation and, consequently, successful settlement of tanaids. Results are compared with previous studies on peracarid crustaceans from the Northwestern Pacific.

Short-term earthquake prediction in Kamchatka using low-frequency magnetic fields

This paper is devoted to a method of short-term earthquake (EQ) prediction in Kamchatka, Russia. Properties of low-frequency magnetic fields are the basics of the method, and we used two seismo-electromagnetic phenomena in the EQ prediction: 1. seismo-ionospheric depression in the frequency range of 0.01–0.1 Hz (ULF depression), 2. seismo-atmospheric radiation in the frequency range of 1–30 Hz (ULF/ELF radiation). It is now generally accepted that gas eruption before an EQ causes these ULF/ELF phenomena. We propose a hypothesis that gas emanates from the area in the bottom of Kuril–Kamchatka or Aleutian trenches closest to the epicenter of a forthcoming EQ. The three parameters of an EQ are (i) when (time), (ii) where (position) a next EQ is coming with (iii) how big (magnitude) in the short-term EQ prediction. Position of the source of atmospheric radiation gives an estimate of the epicenter location. Then, we estimate the local magnitude in consequence of its statistical dependence on ULF depression and epicenter distance. Date of a coming EQ is determined by the statistical dependence of delays of EQs relative to the dates of their precursors. The result of application of this method to real magnetic field data is illustrated by official prediction processes during a period of March–May 2016. Limits and possible errors of the method as well as methods to enhance the reliability of the prediction are discussed.

Uniting what belongs together—Reevaluation of the isopod species Macrostylis grandis and M. ovata using ontogenetic, morphological and genetic evidence

Solid taxonomy is the primary basis for many further-reaching studies in biology, such as biogeography. Here we reevaluate the taxonomic status of two species of the isopod crustacean family Macrostylidae Hansen, 1916, Macrostylis grandis Birstein, 1970 and M. ovata Birstein, 1970. Although they differ significantly in size and other morphological characteristics they share, amongst other character states, an oval habitus which makes them stand out from congeners. We test the hypothesis that M. grandis and M. ovata may represent different life stages of a single species. While some of the newly available specimens collected in the northwest Pacific Ocean during the KuramBio I and SokhoBio expeditions could be morphologically identified as either of the two described species, others represented intermediate forms. Based on this new dataset we provide (1) a complemented morphological taxonomic description of M. grandis and (2) reconstruct parts of the postmarsupial development and (3) analyse their genetic distances. Results of all three analyses were used to reevaluate the taxonomic status of both species and provided justification for a transfer of M. ovata into synonymy with M. grandis. The updated biogeography resulting from the new taxonomic status and samples reveals a distribution at abyssal and upper hadal depths across the Kuril Kamchatka Trench with no indication that the trench may represent a barrier for this species.

Biodiversity of echiurans (Echiura) of the Kuril-Kamchatka Trench area

During KuramBio and KuramBioII (Kuril Kamchatka Biodiversity Studies) expeditions of 2012 and 2016 years, 12 sites across the Kuril-Kamchatka abyssal plain and 11 sites along Kuril-Kamchatka Trench area (KKT) were surveyed and sampled and benthic communities were investigated. Samples, which comprised over 300 echiurans from 12 species of 11 genera belonging to the family Bonelliidae and Thalassematidae, were collected. The family Bonelliidae is most common in abyssal and hadal environments in the world ocean with high abundances in all investigated regions, while Thalassematidae is reported first time from the hadal depth. Species identified as representative of the genera Maxmuelleria have been noted first time in Pacific. Previously known echiuran Bonellia pacifica suggested to be Pseudoikedella achaeta. The description of deep-water echiurans from the investigated areas is the second one based on complete specimens with living colouration. The descriptions provide new information on the distribution, abundance, morphology and taxonomic details of the species, which were previously noted from the northwestern Pacific and described from damaged or incomplete specimens. The knowledge of the geographic ranges of these genera are expanded and discussed.

Topographic surface modelling using raster grid datasets by GMT: example of the Kuril–Kamchatka Trench, Pacific Ocean

Abstract The study area is focused on the Kuril–Kamchatka Trench, North Pacific Ocean. This region is geologically complex, notable for the lithosphere activity, tectonic plates subduction and active volcanism. The submarine geomorphology is complicated through terraces, slopes, seamounts and erosional processes. Understanding geomorphic features of such a region requires precise modelling and effective visualization of the high-resolution data sets. Therefore, current research presents a Generic Mapping Tools (GMT) based algorithm proposing a solution for effective data processing and precise mapping: iterative module-based scripting for the automated digitizing and modelling. Methodology consists of the following steps: topographic mapping of the raster grids, marine gravity and geoid; semi-automatic digitizing of the orthogonal cross-section profiles; modelling geomorphic trends of the gradient slopes; computing raster surfaces from the xyz data sets by modules nearneighbor and XYZ2grd. Several types of the cartographic projections were used: oblique Mercator, Mercator cylindrical, conic equal-area Albers, conic equidistant. The cross-section geomorphic profiles in a perpendicular direction across the two selected segments of the trench were automatically digitized. Developed algorithm of the semi-automated digitizing of the profiles enabled to visualize gradients of the slope steepness of the trench. The data were then modelled to show gradient variations in its two segments. The results of the comparative geomorphic analysis of northern and southern transects revealed variations in different parts of the trench. Presented research provided more quantitative insights into the structure and settings of the submarine landforms of the hadal trench that still remains a question for the marine geology. The research demonstrated the effectiveness of the GMT: a variety of modules, approaches and tools that can be used to produce high-quality mapping and graphics. The GMT listings are provided for repeatability.

Long-Term Earthquake Prediction (LTEP) for the Kuril–Kamchatka island arc, June 2019 to May 2024; Properties of Preceding Seismicity from January 2017 to May 2019. The Development and Practical Application of the LTEP Method

This paper is concerned with results from ongoing work using the method of long-term earthquake prediction (LTEP) for the Kuril–Kamchatka island arc based on the seismic gap and seismic cycle patterns. We highlight the most important lines of research in the LTEP method during the preceding decade. A long-term forecast is provided using the basic method for the next 5 years, June 2019 through May 2024, for the most active part of the earthquake-generating zone in the region. The 20 segments of that zone have forecasts for the next 5 years, including the phases of the seismic cycle, the normalized rate of low-magnitude earthquakes (А10), the magnitudes of moderate-size earthquakes that are expected to occur with probabilities of 0.8, 0.5, and 0.15, the maximum expected magnitudes and probabilities of great (М ≥ 7.7) earthquakes. This study continues the well-known work of S.A. Fedotov by examining space–time features of the regional seismic process for the period beginning 2017, including the great Near Islands (Aleutian) earthquake of July 17, 2017, M = 7.7. The results, as obtained here, corroborate a close relationship between the seismic process occurring in the segments that pose the highest earthquake hazard according to the LTEP and the great earthquakes in the region itself and in the adjacent seismic areas, as well as emphasizing a very high earthquake hazard for several areas at the Kuril–Kamchatka island arc; Thus it is necessary to continue and expand the ongoing work in earthquake strengthening and enhancing the level of seismic safety in those areas under the highest hazard, including the administrative center of Kamchatka Krai, the town of Petropavlovsk-Kamchatsky.

Rhenium enrichment in the northwest Pacific arc

Rhenium (Re) is one of the least abundant elements in the silicate Earth. However, independent rhenium sulfide was reported in the Usu and Kudryavy volcanos, namely rheniite (ReS2, 74.5 wt% of Re). This raises questions about the sources of the Kurile–Kamchatka volcanic island arc magmas and geochemical cycling of Re. The oxidation-reduction cycle on the Earth’s surface is the major process that concentrates Re in reduced sediments. The northwest part of the Pacific plate mainly consists of Jurassic to Cretaceous oceanic crust, with abundant organic-rich sediments. During plate subduction, Re is remobilized early due to the devolatilization of organic-rich sediments and then the decomposition of sulfide (e.g., pyrite), and is subsequently added to the mantle wedge at shallow depths, which is usually not sampled by arc magmas unless there is a major change in the subduction regime. Ridge subduction in the northwest Pacific was initially characterized by low angle subduction. When slab rollback started, rhenium-enriched components were involved in arc magmas, and further concentrated in volcanic vents because of the volatility of Re, forming rheniite.

Color and chemical composition of bottom sediments from the Kuril Basin (Sea of Okhotsk) and the Kuril–Kamchatka Trench area (Northwest Pacific)

The colorimetric method of analysis was first used to study the distribution of the color characteristics (spaces RGB and HSL) in sediment cores from the Kuril Basin of the Sea of Okhotsk and the nearby Kuril-Kamchatka Trench area of the Northwest Pacific. The statistic processing of these and in addition obtained geochemical and grain-size data made it possible to establish the controlling factors and significant relations. The most stable direct correlation is demonstrated by the characteristics of R–Mn–Mo (fine-grained oxidized sediments enriched in hydroxides of iron and manganese and related with them microelements) and H–L–SiO2 (coarse-fragmental part of sediments involving the grains of rock-forming minerals and sometimes a significant admixture of the diatom frustules). Usually, saturation S and phosphorus content gravitate to the first group of parameters, and the additive primary blue color B tends to the second group. Informative are some relations of the color characteristics, for example, the additive primary red color R and green color G (the boundary of the oxidized and reduced sediments). The admixture of the volcanogenic (pyroclastic) material can be reflected in the shift and disruption of the described relations.The results obtained show the regional conditions of sedimentation with the participation of the terrigenous, biogenic, and volcanogenic material and subsequent diagenetic redistribution of the matter. The revealed regularities together with other characteristics of the matter composition can be used for the detailed description of the sediment cores of the regions with the similar settings of sedimentation.

Deepest known gastropod fauna: Species composition and distribution in the Kuril–Kamchatka Trench

The joint German–Russian expedition KuramBio II in 2016 provided a significant opportunity to reinvestigate the species composition and distribution of the abyssal and hadal gastropod fauna in the Kuril–Kamchatka Trench, which was sampled previously only by the Russian research vessel (R/V) Vityaz in the 1940–1960s. During the cruise of the German R/V Sonne, benthic animals were collected using an Agassiz trawl, an epibentic sledge, a multiple corer and a giant box corer. A total catch of 592 live specimens of non-heterobranch gastropods were classified into 86 species and 22 families of the subclasses Neomphaliones, Vetigastropoda, and Caenogastropoda. The abundance, richness and phylogenetic diversity were lower in the hadal zone than in the abyssal zone. Seven hadal stations (6,442–9,584 m) yielded a total of 101 specimens belonging to 22 species in 11 families, whereas catches from four abyssal stations on the landward and seaward slopes (5,102–6,221 m) included 491 specimens and 70 species in 21 families. The abundance, richness and diversity for the hadal zone are, however, particularly high in comparison with other oceanic trenches, due, presumably, to high primary production in the surface layer of the subarctic Northwest Pacific. The uniqueness of species composition increased with depth; sixteen out of the 22 species from the hadal stations (72.7%) were found exclusively in this depth zone. Two unnamed species of Neomphalidae and Sahlingia from 9,577 to 9,584 m represent the world’s deepest records for Neomphaliones and Vetigastropoda and suggest the as yet unidentified presence of the world-deepest cold-seep habitats in the Kuril–Kamchatka Trench.

The MW = 7.8 Earthquake of July 17, 2017 near the Commander Islands: Tectonic Position and Geodynamic Setting

The tectonic position and overall geodynamic setting, as well as the seismological characteristics and peculiarities of the aftershock process, are considered for the source of the strongest Near Island Aleutian earthquake of July 17, 2017, М W = 7.8, on the Commander Islands. It is shown that in contrast to the eastern segments of the Aleutian island arc, the subduction of the Pacific lithospheric plate beneath the Commander block is not observed. The analysis has shown that, according to the distribution of the aftershock epicenters in the form of a linear elongated narrow zone with a length of about 400 km, the seismic source occupied almost entire northern slope of the Commander Island rise and spread in the Bering fault zone. It spanned the whole of this seismogenic zone up to the transverse structure west of the Near Islands (Attu islands). The focal mechanism solutions and the pattern of displacements in the sources of the main shock, as well as the strongest foreshocks and aftershocks, suggest that the slip in the source was an almost pure right-lateral shear. The aftershock process of the earthquake on July 17 developed quite feebly for an earthquake of this magnitude. Besides, it has two specific features distinguishing it from the aftershock processes of most of the Kuril-Kamchatka earthquakes: (1) a low release of the cumulative scalar seismic moment (M 0cum aft ), which, according to different estimates, made up from 0.75 to 1.0% of the main-event seismic moment (M 0me ); and (2) a very slow growth of the deficit in the release of seismic moment (M 0 ). At the same time, the duration of the quasi-stationary phase of the M 0cum release in the aftershocks, which is estimated at approximately half-a-year and which took a considerable span of the total length of the aftershock process from this earthquake, appears to be untypically long. These features of the aftershock process of the Near Island Aleutian earthquake of July 17, 2017 distinguish it from the aftershock processes peculiar to most of the strong Kuril–Kamchatka earthquakes. Overall, its source can be considered as a transform one between the two Benioff zones, the Aleutian and Kuril–Kamchatka ones, rather than as a subduction source characteristic of the last two zones.

Sedimentary evidence of prehistoric distant‐source tsunamis in the Hawaiian Islands

AbstractOver the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low‐lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north‐eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon‐based age models date sand beds from three sites to ca 700 to 500 cal yr bp, which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands.

New Radiolaria Species from the Cenozoic Deposits on the Island Slope of the Kuril–Kamchatka Trench

Descriptions of four new radiolarian species from the material collected from the Cenozoic deposits of the submarine Vityaz Ridge (the island slope of the Kuril–Kamchatka Trench) are provided in the article. The descriptions of the new species Amphistylus gladiusiacus sp. nov. and Thecosphaerella tochilinae sp. nov. from the Upper Eocene–Lower Oligocene deposits are based on the criteria established for the class of spherical porous Sphaerellaria: the number of skeletal shells, the shape of the cortical shell, and the development of the system of spines and axopodial complex. The new species Stylotrochus bipedius sp. nov. and S. tripedius sp. nov. from the Lower Pleistocene are considered among stauraxon radiolarians of the class Stauraxonaria due to the discoid geometric shape of their skeleton. The history of changes in the systematic position of the family Spongodiscidae is reviewed, and a proposal is made to restore the name of the order Discoidea Haeckel, 1862.

New Data Relating to the Age, Material Composition, and Geological Structure of the Central Kamchatka Depression (CKD). Part 1. Rock Classification. Age, Petrology, and Isotope Geochemistry

This paper presents new data on the age and isotope geochemistry for plateau effusive rocks sampled from the Central Kamchatka Depression and Nikolka Volcano. We have compared these materials with data on rocks sampled in the Klyuchevskaya Group of Volcanoes, as well as from Shiveluch, Kharchinsky, Zarechnyi, Nachikinsky, and Bakening volcanoes, and from an “NEB-adakite” Pliocene shield volcano in the interfluve between the Ozernaya Kamchatka and the Pravaya Kamchatka rivers. We show that the relatively “advanced,” in the sense of evolution, (mostly alkaline) compositions of rocks sampled from Nachikinsky, Bakening, and Nikolka volcanoes, as well as from the Pliocene shield edifice, have isotope characteristics that are significantly different from those for the Klyuchevskaya Group of Volcanoes. This type of rock is typical of the CKD as a rifting structure. The rocks in the Klyuchevskaya Group of Volcanoes are not typomorphic for this structure and reflect the phase of ordinary orogenic volcanism that has involved a much larger area. The Miocene plateau effusive rocks are only different from the rocks of this group in having a slightly higher potassium alkalinity. Rocks of the rifting type can be recognized, not only by their higher alkalinity, but also by a definite relationship among microcomponents: Ti/V > 0.004, Nb/Y > 0.28, Dy/Yb > 2.00, La/Yb > 6.5, Sm/Yb > 2.4, Lu/Hf < 0.08. Along with the isotope characteristics, these relationships suggest the existence of a common deep-seated asthenospheric mantle reservoir for the parent melts. The area of junction between the Kuril–Kamchatka and the Commander-Islands–Aleutian island arc system is marked by a higher fluid enrichment (the cerium REE group) in melts for rocks of some volcanoes, viz., Shiveluch, Kharchinskii, and Zarechnyi.