The Lake Krasnoe obsidian source in Chukotka (Northeastern Siberia): geological and geochemical frameworks for provenance studies in Beringia

摘要

Basic data on the geology and geochemistry of obsidian from the Lake Krasnoe source in Chukotka (Northeastern Siberia) are reported for the first time. The data are based on 2009 fieldwork and analytical studies of igneous rock samples. The lake shore and surrounding parts of the Rarytkin Range were thoroughly examined. Two geochemical types of rhyolitic obsidian were recognized for the first time: (1) metaluminous obsidian related to the fine-grained crystalline rocks and (2) peralkaline obsidian corresponding to ignimbrite ash-flows or lapilli-tuffs composition. Both types are related to the final phase of acidic volcanism in the Western Kamchatkan-Koryak Volcanic Belt. Based on the results obtained, we conclude that accumulation of obsidian pebbles in the lake's modern beach deposits is related to silicic melts that erupted during the late Eocene-early Oligocene in the form of extrusive domes or pyroclastic flows, which are now either covered by Quaternary sediments or located below the water level. The Lake Krasnoe obsidian was intensively used by the ancient populations of Chukotka as a raw material for making stone tools. It was also occasionally transported to Alaska across the Bering Strait in later prehistory. The distances between source and utilization sites are up to 700-1100 km. Geochemical data for Lake Krasnoe obsidian, based on neutron activation analysis and X-ray fluorescence that are presented here, can now be used for provenance studies in the Northeastern Siberia and adjacent regions of northern North America.