Mass movement deposits in the 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic: classification, distribution and preliminary interpretation

This paper focuses on the characterization and genesis of mass movement deposits (MMD) in the Quaternary and Pliocene sediments of Lake El'gygytgyn, Far East Russian Arctic. The 320 m long sediment record was drilled by three partly overlapping holes at ICDP Site 5011-1 in the lake basin, representing the Quaternary almost completely, and the Pliocene down to 3.6 Ma with 52% recovery. Mass movement deposits were investigated in all three cores, based on macroscopical core descriptions, radiographic images, and high-resolution magnetic susceptibility and gamma-ray density. Five different types of MMDs were identified: turbidites, grain flow deposits, debrites, slumps and slides. These are formed by transitional mass movement processes, and thus, can be co-generic. An initial slope failure is thought to transform into a debris flow, deforms frontal sediments and partly disintegrates and dilutes into a turbidity flow. Turbidites are by far the most frequent MMD type in the lake center. They occur throughout the record in all pelagic sedimentary facies, but they are thinner in facies formed during cold climate conditions. All other MMDs, by contrast, incise exclusively the pelagic facies deposited during warm climates. In the 123 m thick Quaternary sediment record 238 mass movement events are identified, comprising 37% of the sediment length. Turbidites contribute 92% of the number of Quaternary MMDs, but only 32% of their thickness. In the Pliocene sediments between 123 and 320 m, additional 185 mass movement deposits are identified, which constitute 32% of the recovered sediments. The mean recurrence rate for MMDs is 11 ka and 5 ka in the Quaternary and Pliocene, respectively.