Characteristics and paleoenvironmental significance of lacustrine sediments in the El'gygytgyn drill core

Lake El’gygytgyn is a 12 km diameter, 175 m deep lake filling a meteorite impact crater that formed ca. 3.6 million years ago in Chukutko, northeastern Siberia (67°30’ N, 172°05’ E). An international team under the aegis of the Inter Continental Drilling Program (ICDP) drilled three overlapping cores at a site near the center of the lake. The lacustrine sediment fill extends approximately 315 m below the lake floor. Sediment recovery was nearly 100 percent for the uppermost 150 m, but is lower (~63 percent) in the deeper sections of the core. Nonetheless, long (40 m), continuous sections with nearly complete recovery were obtained from the early part of the record. These cores present a unique opportunity to compare sedimentary signatures of glacial/interglacial and Pliocene/Pleistocene environmental conditions in the terrestrial Arctic. The lacustrine sequence has been subdivided into distinct sedimentary facies based on the visual characteristics and color of split core halves, qualitative grain size descriptions, interpretation of radiographs, and microanalysis of thin sections prepared from representative sections of the core. Four fine grained pelagic facies have been differentiated based on the presence or absence and characteristics of fine (<1 mm to 5 mm) laminations. The pelagic sediments are interrupted by distinct graded beds which fine upwards from sand and silt to clay and intervals of disturbed and/or redeposited material likely associated with turbidity flows or mass movements. Deeper sections of the core are also interrupted by poorly sorted, massive deposits containing coarse sand and gravel, the origin of which may challenge prevailing assumptions that the region escaped Quaternary glaciations. Regular variations in the style of pelagic sedimentation likely reflect variations in climate and environmental conditions that have influenced the delivery of fluvial and aeolian sediment to the lake, the length of the ice free season, the temperature and stratification of lake waters, and geochemical and biological conditions within the lake. Continued analysis of the physical, chemical, and biological characteristics of the sediments will help constrain the origin and significance of individual facies.