Friday, 14 July 2006

The Holocene Tephra-paleosol Sequences of Kamchatka Peninsula.

Sergey A. Shoba1, Alexander O. Makeev2, Irina O. Alyabina2, Maria S. Marechek3, Alexei A. Sakharov3, and Lalita V. Zaharihina4. (1) Moscow State Univ, Soil Science Dept., Leninskie Gory, Moscow, 119992, Russia, (2) Moscow State Univ, Soil Inst, Leninskie Gori, Moscow, 119992, Russia, (3) Moscow State Univ, Soil Science Faculty, Leninskie Gori, Moscow, 119992, Russia, (4) Science-Research Geotechnological Center of the Far-East Branch of Russian Academy of Sciences, North-East Ave, 30, Petropavlovsk-Kamchatski, Russia

Kamchatka peninsula is characterized by long-distance marker layers of tephra as a result of the largest explosive eruptions during the Holocene. Due to a combination of cold climate and comparatively young age tephra layers are not deeply transformed by weathering. This, together with low bioturbation intensity, results in a sequence of clearly visible horizontal layers, retaining their morphological, chemical and mineralogical identity. These marker layers are interstratified with buried soil profiles, making it possible to study transformation of tephra material within the soil profile under various climatic conditions though the whole Holocene. Soils of Kamchatka, formed on volcanic ashes were studied with consideration of extensive set on radiocarbon dating and constitution of tephra-paleosol sequences. Studied soils have been formed under various bioclimatic conditions, including the main types of vegetation of Central and Western Kamchatka (tundra, taiga, mountain meadows, etc.). The age of present day surfaces in the study area differs from tens of years to 1760 years before present. The vegetation type mostly determines modern features of volcanic soils. These allow using surface organic horizons as diagnostic. Constitution of soil profile is strictly determined by constitution of tephra-paleosol sequence. A set of buried soil horizons within the time span of 8000 years before present was studied. The degree of both physical and chemical weathering increases with tephra age. Tephra marker horizons have been compared within buried soil profiles and adjacent bogs, showing less advanced weathering under the thick layer of peat. The study of constitution and spatial distribution of tephra-paleosol sequences allows determining tephrostratotype as a steady sequence of tephra marker horizons. GIS approach allows to present cartographic images of tephrostratotypes for any given point within the study area, based on combination of marker horizons of 29 largest explosive Holocene eruptions.

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