Petrophysical characterization of the lacustrine sediment succession drilled in Lake El'gygytgyn, Far East Russian Arctic

Abstract

Seismic profiles of Far East Russian Lake El'gygytgyn, formed by a meteorite impact some 3.6 million years ago, show a stratified sediment succession that can be separated into subunits Ia and Ib at approximately 167 m below lake floor (=~3.17 Ma). The upper (Ia) is well-stratified, while the lower is acoustically more massive and discontinuous. The sediments are intercalated with frequent mass movement deposits mainly in the proximal areas, while the distal region is almost free of such deposits at least in the upper part. In spring 2009, a long core drilled in the lake center within the framework of the International Continental Scientific Drilling Program (ICDP) penetrated the entire lacustrine sediment succession down to ~320 m below lake floor and about 200 m farther into the meteorite-impact-related bedrock. Downhole logging data down to 390 m below lake floor show that the bedrock and the lacustrine part differ significantly in their petrophysical characteristics. The contact between the bedrock and the lacustrine sediments is not abrupt, but rather transitional with a variable mixture of impact-altered bedrock clasts in a lacustrine matrix. Physical and chemical proxies measured on the cores can be used to divide the lacustrine part into five different statistical clusters. These can be plotted in a redox-condition vs. input-type diagram, with total organic carbon content and magnetic susceptibility values indicating anoxic or oxic conditions and with the Si / Ti ratio representing more clastic or more biogenic input. Plotting the clusters in this diagram allows identifying clusters that represent glacial phases (cluster I), super interglacials (cluster II), and interglacial phases (clusters III and IV)

Magnetostratigraphy of sediments from Lake El'gygytgyn ICDP Site 5011-1: paleomagnetic age constraints for the longest paleoclimate record from the continental Arctic

“…The lake has one outlet, the Enmyvaam River, which has cut its way through the crater rim in the southeast and drains into the Bering Sea. Based on the interpretation of refraction-and reflection-seismic data, the layered sediment infill was estimated to have a thickness of 320 to 340 m (Gebhardt et al, 2006(Gebhardt et al, , 2013. This was confirmed by the ICDP drilling, intersecting the transition zone from sediments to impact breccia at a depth of around 316 m. Currently, the lake is oligotrophic and monomictic, and the water column becomes thermally stratified under the ice cover, which persists from October to mid-July.…”

Mass movement deposits in the 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic

“…Subsequently the elemental composition was measured and radiographs were obtained on the core halves with an ITRAX core scanner (Cox Analytics) in resolutions of 2 mm and 200 µm, respectively, and gamma-ray density measurements were performed at Alfred Wegener Institute in Bremerhaven, Germany, with an MSCL core logger (Geotek Ltd.). For a more detailed description of the drilling operations and core processing, see Melles et al (2011Melles et al ( , 2012, Francke et al (2013), Gebhardt et al (2013) or Wennrich et al (2013b).…”

“…Below 314.4 m cd a breccia comprised of partly layered sand and a downwards-increasing percentage and diameter of lithic clasts reflects the transition zone between lake sediment and impact rocks. The clasts include shocked rocks and impact rocks to a depth of 318 m cd Gebhardt et al, 2013). The transition zone likely represents the wash-out of sediments and rocks within the crater shortly after the impact.…”

“…Occasional thin brecciated intervals, possibly caused by dewatering or short-term desiccation events, are characteristic . Facies E represents the phase after the impact, initial lake filling and the first lacustrine deposition Gebhardt et al, 2013;Brigham-Grette et al, 2013). Over the course of the lake history, sedimentation rates have significantly decreased.…”

“…It can be divided into four major facies, which sensitively reflect different climate conditions Brigham-Grette et al, 2013;Gebhardt et al, 2013). During colder climate stages of the Quaternary, under perennial lake ice, dark gray, finely laminated silt and clay are deposited (facies A).…”