Volgian–Early Berriasian Marginal Filter in the West Siberian Marine Basin and Its Influence on Sediment Distribution

Lithology and Mineral Resources - The West Siberian marine basin of the Volgian–initial Berriasian ages is described. It is shown that a marginal filter (according to A.P. Lisitsyn)...     

Secular variation of the geomagnetic field over the past 4000 years recorded in the lavas and pyroclastics of the Northern Group of Kamchatka volcanoes: New data

New paleomagnetic determinations satisfying the up-to-date methodical and instrumental standards of paleomagnetic studies are obtained from the lava flows and volcanic ash of the Northern Group of Kamchatka volcanoes. In the past 4000 years, 12 stratigraphic levels with tephrostratigraphic ages are explored. The obtained directions of the geomagnetic field fill a gap in the data on the secular variation for northeastern Asia and can be used for developing global models. Besides, a promising outlook for the use of the variations of the geomagnetic field for the regional correlation of volcanic events is demonstrated.     

Tephrochronological dating of paleoearthquakes in active volcanic arcs: A case of the Eastern Volcanic Front on the Kamchatka Peninsula (northwest Pacific)

Investigation of active faults is crucial for the seismic hazard assessment and, in the case of volcanic belts, it provides a deeper understanding of the interactions between volcanism and tectonic faulting. In this study, we report the results of the first paleoseismological and tephrochronological investigation undertaken on Holocene faulting in Kamchatka's volcanic belts. The studied trenches and additional excavations are located along the axial fault zone of the Eastern Volcanic Front, where the earlier dated tephra layers provide a robust age control of the faulting events. Electron microprobe analysis of glass from 22 tephra samples permitted correlations among the disparate tephra profiles for constructing a summary tephra sequence. The latter, together with published geochronological data, allowed the construction of a Bayesian age model. Detailed examination of the tephra layers deformed by faulting allowed us to reconstruct and date six faulting events with the offsets of 1 to 20 cm indicating paleoearthquakes with magnitudes of M_w < 5.4. Holocene crustal seismicity of the Eastern Volcanic Front manifests temporal clustering rather than a uniform flux of events. However, no correlation between dated seismic events and the largest Holocene eruptions of proximal volcanoes was observed.     

Identification of Icelandic tephras from the last two millennia in the White Sea region (Vodoprovodnoe peat bog,northwestern Russia)

The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.     

Active tectonics and geomorphology of the Kamchatsky Bay coast in Kamchatka

Kamchatsky Bay is the northernmost bay at the Pacific Kamchatka coast. It is located at the junction between the Kamchatka segment of the Pacific subduction zone and the dextral transform fault of the western Aleutians. The combination of the subduction and collision processes in this region results in the unique set of tectonic controls influencing its geological and geomorphological evolution. The Kamchatka River estuarine area is located on the northern coast of Kamchatsky Bay. The modern Kamchatka River valley, its estuary, and an aggradation marine terrace some 30 km long and up to 5 km wide were formed in this area during the Holocene. A vast area in the rear part of the terrace and in the Stolbovskaya lowlands is now occupied by the peats deposited directly above lacustrine-lagoonal and fluvial facies. These aggradational landforms record traces of tsunamis and vertical coseismic deformations associated with great subduction earthquakes, as well as strike-slip and thrust faulting associated with the collision. The results indicate that the average recurrence interval for major tsunamis in the Kamchatsky Bay is 300 years. The recurrence interval on individual fault zones associated with the collision between the western Aleutian and Kamchatka arcs is a few thousand years for earthquakes of magnitude between 7 and 7.5. For the entire region, the recurrence interval for major crustal earthquakes associated with motions along faults may be equal to a few hundred years, which is comparable with that for subduction-zone earthquakes.     

Organic Carbon Distribution in the Bazhenov Horizon Rocks of the Western Siberian Megabasin

The distribution of organic carbon in the Bazhenov horizon rocks of the western Siberian sedimentary basin is investigated. The organic carbon concentration in rocks is estimated by the results of core analyses (4094 core analyses) and by the calculations of the core-log data correlations (48 500 measurements) according to the data of radiation and electrical loggings. The average content of organic carbon in the rocks of the Bazhenov and Tutleim (lower subformation) formation is 7.7%. The map of organic carbon concentrations in the sedimentary rocks of the basin is constructed. In the basin, C_org is distributed asymmetrically. The region of maximum C_org concentrations occupies the southwestern part of the internal area of the sedimentary basin. Silicites and biogene silica-enriched mixtites are enriched with organic matter most of all.     

The caldera-forming eruption of Ksudach volcano about cal. A.D. 240: the greatest explosive event of our era in Kamchatka, Russia

The largest Plinian eruption of our era and the latest caldera-forming eruption in the Kuril-Kamchatka region occurred about cal. A.D. 240 from the Ksudach volcano. This catastrophic explosive eruption was similar in type and characteristics to the 1883 Krakatau event. The volume of material ejected was 18–19 km³ (8 km³ DRE), including 15 km³ of tephra fall and 3–4 km³ of pyroclastic flows. The estimated height of eruptive column is 22–30 km. A collapse caldera resulting from this eruption was 4 × 6.5 km in size with a cavity volume of 6.5–7 km³. Tephra fall was deposited to the north of the volcano and reached more than 1000 km. Pyroclastic flows accompanied by ash-cloud pyroclastic surges extended out to 20 km. The eruption was initially phreatomagmatic and then became rhythmic, with each pulse evolving from pumice falls to pyroclastic flows. Erupted products were dominantly rhyodacite throughout the eruption. During the post-caldera stage, when the Shtyubel cone started to form within the caldera, basaltic-andesite and andesite magma began to effuse. The trigger for the eruption may have been an intrusion of mafic magma into the rhyodacite reservoir. The eruption had substantial environmental impact and may have produced a large acidity peak in the Greenland ice sheet.     

Ages of calderas,large explosive craters and active volcanoes in the Kuril-Kamchatka region,Russia

The ages of most of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region have been determined by extensive geological, geomorphological, tephrochronological and isotopic geochronological studies, including more than 600 ¹⁴C dates. Eight Krakatoa-type and three Hawaiian-type calderas and no less than three large explosive craters formed here during the Holocene. Most of the Late Pleistocene Krakatoa-type calderas were established around 30 000–40 000 years ago. The active volcanoes are geologically very young, with maximum ages of about 40 000–50 000 years. The overwhelming majority of recently active volcanic cones originated at the very end of the Late Pleistocene or in the Holocene. These studies show that all Holocene stratovolcanoes in Kamchatka were emplaced in the Holocene only in the Eastern volcanic belt. Periods of synchronous, intensified Holocene volcanic activity occurred within the time intervals of 7500–7800 and 1300–1800 ¹⁴C years BP.     

Spectral and structural properties of carbon nanoparticles synthesized in natural and anthropogenic processes

In this contribution, we considered the character of carbon nanoparticle formation in the cosmos and during volcanic eruptions of a certain type and compared it with existing methods of synthesis in nanotechnology. Using the methods of electron diffraction and Raman spectroscopy, we investigated nanodiamond samples synthesized by hydrodynamic cavitation in various hydrocarbon liquids. Different forms of nanometer-sized carbon were distinguished, including complex fullerenes, nanodiamonds, and a face-centered cubic (fcc) carbon phase. The synthesized nanodiamonds were doped with silicon, their photoluminescence spectra were analyzed, and application of the results for geochemistry and cosmochemistry were discussed.