Abstract
Abstract. This paper focuses on the characterization and genesis of mass movement deposits (MMDs) in the Quaternary and Pliocene sediments of Lake El'gygytgyn, Far East Russian Arctic. Three partly overlapping holes were drilled into the 320 m long sediment record at International Continental Scientific Drilling Program (ICDP) Site 5011-1 in the lake basin, recovering 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, 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 that deforms frontal sediments, 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 composite sediment record 230 mass movement events are identified, comprising 33% of the sediment length. Turbidites contribute 93% of the number of Quaternary MMDs, but only 35% of their thickness. In the Pliocene sediments between 123 and 320 m, 181 additional mass movement deposits are identified, which constitute ~33% of the recovered sediments. The mean recurrence interval for MMDs is 11 and 5 ka in the Quaternary and Pliocene, respectively.
Highlights
Detailed investigation of these cores, as well as another 16 m long core from the lake center (Lz1024), revealed that the acoustically transparent seismic unit consists of a basal debris flow deposit, which is directly overlain by a grain-flow deposit of wider distribution and further by a deposit settled from a suspension cloud that presumably covers wide areas of the lake floor
We present the correlation of the movement deposits (MMDs) between the drill cores and pilot core Lz1024 (Juschus et al, 2009), as well as a chronological catalogue of the Quaternary and mid- to late Pliocene MMDs in Lake El’gygytgyn
We suppose that the formation of MMDs in Lake El’gygytgyn is associated with an initial sediment failure on the upper lake slope that advances towards the lake basin
Summary
Lake El’gygytgyn (67◦30 N, 172◦5 E), formed after a meteorite impact 3.58 ± 0.04 Ma ago (Layer, 2000), is situated in the Far East Russian Arctic, 100 km north of the Arctic Circle (Fig. 1a). During snow-free summers, gravel bars at the shoreline of several inlet streams today form lagoons, which trap fine-grained sediment, and hinder suspension flow into the lake (Nolan and Brigham-Grette, 2007). Pelagic sedimentation in Lake El’gygytgyn is fine grained (Francke et al, 2013) It can be divided into four major facies, which sensitively reflect different climate conditions (Melles et al, 2011, 2012; Brigham-Grette et al, 2013; Gebhardt et al, 2013). During the first ca. 300 ka after the impact, the average sedimentation rate accounted for 44.5 cm ka−1, and dropped to 15 and 4.7 cm ka−1 during the remaining Pliocene and the Quaternary, respectively (Haltia and Nowaczyk, 2013; Nowaczyk et al, 2013)
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