Multidisciplinary study of a key section on the Laptev Sea Coast (Bykovsky Peninsula, east Lena Delta) in 1998-2001 provides the most complete record of Middle and Late Weichselian environments in the East Siberian Arctic. The 40-m high Mamontovy Khayata cliff is a typical Ice Complex section built of icy silts with a network of large syngenetic polygonal ice wedges, and is richly fossiliferous. In combination with pollen, plant macrofossil and mammal fossils, a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka. The large number of radiocarbon dates from the section, together with an extensive 14 C database on mammal bones, allows chronological correlation of the various proxies. The Bykovsky record shows how climate change, and the Last Glacial Maximum in particular, affected terrestrial organisms such as insects and large grazing mammals. Both during the presumed ''Karginsky Interstadial'' (MIS 3) and the Sartanian Glacial (MIS 2), the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats: the tundra-steppe type. This biome was supported by a constantly very continental climate, caused by low sea level and enormous extension of shelf land. Variations within the broad pattern were caused mainly by fluctuations in summer temperature, related to global trends but overprinted by the effect of continentality. No major changes in humidity were observed nor were advances of modern-type forest or forest-tundra recorded, suggesting a major revision of the ''Karginsky Interstadial'' paradigm. The changing subtypes of the tundra-steppe environment were persistently favourable for mammalian grazers, which inhabited the shelf lowlands throughout the studied period. Mammal population numbers were lowered during the LGM, especially toward its end, and then flourished in a short, but impressive peak in the latest Weichselian, just before the collapse of the tundra-steppe biome. Throughout MIS 3 and MIS 2, the climate remained very favourable for the aggradation of permafrost. No events of regional permafrost degradation were observed in the continuous Bykovsky sequence until the very end of the Pleistocene. r

correlation of certain stratigraphic levels in various deposiDetailed tephrochronological studies in Kamchatka Peninsula, tional successions. Their ages being determined, they beRussia, permitted documentation of 24 Holocene key-marker come excellent time markers and can be used in geochronotephra layers related to the largest explosive eruptions from 11 logical investigations. Tephra (volcanic ash) horizons are volcanic centers. Each layer was traced for tens to hundreds of among the best marker beds of this kind. C yr B.P.) SH 2 (É1000 yr B.P.) and SH 3 (É1400 yr B.P.) from is a few tens of centimeters thick in areas distant from the Shiveluch volcano; KZ (É7500 yr B.P.) from Kizimen volcano; active volcanoes and increases up to several meters at their KRM (É7900 yr B.P.) from Karymsky caldera; KHG (É7000 yr foot. This cover provides a continuous record of the explo-B.P.) from Khangar volcano; AV 1 (É3500 yr B.P.), AV 2 (É4000 sive eruptions during the Holocene, while earlier ash layers yr B.P.), AV 4 (É5500 yr B.P.), and AV 5 (É5600 yr B.P.) from in Kamchatka were almost everywhere destroyed during Avachinsky volcano; OP (É1500 yr B.P.) from the Baraniy Amfi-Late Pleistocene glaciation and occur as isolated beds. stratigraphic value and 9 important local marker ash layers.from Shtyubel cone in Ksudach volcanic massif; and KO (É7700 yr B.P.) from the Kuril Lake-Iliinsky caldera. Tephra layers SH 5 Identification of tephra sources was possible due to prelimi-(É2600 yr B.P.) from Shiveluch volcano, AV 3 (É4500 yr B.P.) nary studies that included detailed mapping of the Holocene from Avachinsky volcano, OP tr (É4600 yr B.P.) from Opala vol-eruptive centers (Melekestsev et al., 1974) and investigations cano, KS 3 (É6100 yr B.P.) and KS 4 (É8800 yr B.P.) from Ksudach of geochemical types and petrology of Late Cenozoic volcacalderas, KSht 1 (É1100 yr B.P.) from Shtyubel cone, and ZLT nic rocks (Volynets, 1994). These data allowed us to identify

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The ages of most of calderas,