Holocene and Late Glacial sedimentation near steep slopes in southern Lake Baikal

Abstract

<p>We here present new data on sedimentation at and near the steep north-slopes of southern Lake Baikal. Short sediment cores were taken at 550 m and at 1366 m water depth, within 3600 m offshore Cape Ivanovskii at the station of the <em>Baikal Deep Underwater NEUTRINO</em> <em>Telescope</em>. The sediments within 3600 m off the northern coast of Southern Lake Baikal are dominated by pelagic deposition. Our data reveal surprisingly little influence from terrigenous material from adjacent coastal areas, tributaries and their catchment. At the shallow-water site (at 550 m water depth, 700 m off shore) just 27 cm thick homogenous sediments have accumulated during the Holocene on top of Pleistocene deposits resulting in Holocene sedimentation rates of 0.003 cm a<sup>-1</sup>. The very low rates are caused by long-term persistent winnowing of fine particles caused by week contour currents along the slope. The uppermost sediments are oxidized down to 22 cm. Very low concentrations of C<sub>org</sub>, Si<sub>bio</sub> and N<sub>tot</sub> in Pleistocene sediments increase dramatically within the Holocene. The heavy mineral fraction of the shallow-water sediments contains up to 33.6 % olivine and up to 2.4 % spinel. These rare minerals originate from white marbles of the nearby coastal outcrop <em>Belaya Vyemka</em> of the Early Precambrian <em>Sharyzalgaiskaya</em> <em>Series</em>. At the deep-water site (at 1366 m water depth, 3600 m off shore) Holocene sedimentation rates are 10-times higher (0.036 cm a<sup>-1</sup>). Sediment oxidation occurs just within the uppermost 2 cm. Of the two rare type minerals of the <em>Sharyzalgaiskaya</em> <em>Series</em> spinel does not occur at all and olivine is represented by very diminished concentrations. This indicates insignificant influx of terrestrial material from the nearby shore to the deep-water site . Distal turbidites of far-off sources are intercalated to pelagic sediments at the deep-water site. Breakdown events of deltas at the SE- and S-coast of the basin are suggested to be responsible for the formation of the turbidites. They contain terrestrial (deltaic) material, low amounts of biological material (diatoms, spiculae, chrysophyte cysts), low concentrations of Si<sub>bio</sub>, C<sub>org </sub>and N<sub>tot</sub> and occur at approximate recurrence rates of 300 years. </p>