ПОЗДНЕМЕЛОВЫЕ–КАЙНОЗОЙСКИЕ ОТЛОЖЕНИЯ БАЙКАЛЬСКОЙ РИФТОВОЙ ВПАДИНЫ В СВЯЗИ C МЕНЯЮЩИМИСЯ ПРИРОДНЫМИ ОБСТАНОВКАМИ

The late Cretaceous-Cenozoic sediments of fossil soils and weathering crusts of the Baikal rift have been subject to long-term studies. Based on our research results, it is possible to distinguish the following litho-stratigraphic complexes which are related to particular stages of the rift development: the late Cretaceous–early Oligocene (crypto-rift Arheo-baikalian), the late Oligocene–early Pliocene (ecto-rift early orogenic Pra-baikalian), and the late Pliocene-Quaternary (ecto-rift late orogenic Pra-baikalian – Baikalian) complexes. Changes of weathering modes (Cretaceous-quarter), soil formation (Miocene-quarter) and differences of precipitation by vertical and lateral stratigraphy are analysed with regard to specific features of climate, tectonics and facial conditions of sedimentation. Tectonic phases are defined in the Cenozoic period of the Pribaikalie.Подведены итоги многолетних исследований позднемеловых–кайнозойских отложений, палеопочв и кор выветривания Байкальского рифта. Они расчленены на позднемеловой–раннеолигоценовый (крипторифтовый – Археобайкальский), позднеолигоценовый–раннеплиоценовый (экторифтовый раннеорогенный – Прабайкальский) и позднеплиоценовый–четвертичный (экторифтовый позднеорогенный Палеобайкальский – Байкальский) литостратиграфические комплексы, связанные с отдельными этапами геологического развития рифта. Прослежены изменения характера выветривания (мел–квартер), почвообразования (миоцен–квартер) и различия осадков по стратиграфической вертикали и латерали, определяемые особенностями климата, тектоники и фациальных условий осадконакопления. Выявлены тектонические фазы в кайнозое Прибайкалья – Тункинская (27–25 млн), Северобайкальская (10 млн), Ольхонская (4–3 млн), Приморская (1.2–0.8 млн), Тыйская (0.15–0.12 млн лет)

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

<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^-1. 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_org, Si_bio and N_tot 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^-1). 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_bio, C_organd N_tot and occur at approximate recurrence rates of 300 years. </p

LATE CREATACEOUS-CENOZOIC SEDIMENTS OF THE BAIKAL RIFT BASIN AND CHANGING NATURAL CONDITIONS

The late Cretaceous-Cenozoic sediments of fossil soils and weathering crusts of the Baikal rift have been subject to long-term studies. Based on our research results, it is possible to distinguish the following litho-stratigraphic complexes which are related to particular stages of the rift development: the late Cretaceous–early Oligocene (crypto-rift Arheo-baikalian), the late Oligocene–early Pliocene (ecto-rift early orogenic Pra-baikalian), and the late Pliocene-Quaternary (ecto-rift late orogenic Pra-baikalian – Baikalian) complexes. Changes of weathering modes (Cretaceous-quarter), soil formation (Miocene-quarter) and differences of precipitation by vertical and lateral stratigraphy are analysed with regard to specific features of climate, tectonics and facial conditions of sedimentation. Tectonic phases are defined in the Cenozoic period of the Pribaikalie

Extracting paleo-weathering signals from authigenic phases in lake sediments: A case-study of Lake Baikal

Authigenic phases in lake sediments hold the potential to record changes in the isotope compositions of past lake water, potentially yielding valuable information on secular changes in continental weathering patterns and rates, including over past glacial cycles. Here, different leaching approaches are investigated with the aim of extracting Sr, Nd, Pb, and Be hosted in authigenic Fe-Mn (oxy)hydroxide sediment phases for precise isotope measurements. Elemental Al/Mn, Ca/Mn, and P/Mn ratios obtained via a mild reductive leach agree well with the composition of marine authigenic Fe-Mn phases. For core top sediments, leached Sr isotope compositions obtained with this leach agree well with the composition of lake water. The Be and Nd isotope compositions of core top leachates are consistent with the spatial variability observed in the water column. Due to high concentrations in Fe-Mn phases, leachate compositions are dominated by authigenic Be, Sr, Nd, and Pb, even in cases when as much as 40% of leached phases (by mass) are non-authigenic. These lines of evidence suggest that the mild reductive leach successfully extracts the modern lake isotope composition from modern sediments in terms of the isotope systems investigated. We further show that the leaching method is also reliable for older sediments (<340 ka): leached paleo-Sr isotope compositions are consistent between the current and previous interglacial periods, as well as for glacial periods. This suggests that reconstructed water isotope compositions are not affected by early diagenetic processes, instead reflecting environmental factors around the lake that determine the composition of weathering fluxes. Although more difficult to assess for Be, Nd, and Pb due to the heterogeneity of modern lake water, the data we present indicate the overall robustness of the leaching approach. These promising results open up lakes as archives for paleo-weathering reconstructions. Given that marine reconstructions face some important limitations (e.g., integration of basin-wide changes in weathering processes, long residence times for Sr, etc.Fe), lake records provide an avenue to improve our understanding of changes in regional weathering processes over glacial-interglacial timescales. The mild reductive leach used here may also be useful for meteoric Be studies in marine shelf settings, to prevent leaching of terrestrial sedimentary Fe-Mn oxy(hydroxide) phases.ISSN:0009-2541ISSN:1872-683

Correction: Diatom evidence of 20th century ecosystem change in Lake Baikal, Siberia.

[This corrects the article DOI: 10.1371/journal.pone.0208765.]

Lake Baikal diatom assemblage data from sediment cores covering the last 200 years

Lake Baikal has been experiencing limnological changes from recent atmospheric warming since the 1950s, with rising lake water temperatures, reduced ice cover duration and reduced lake surface-water mixing due to stronger thermal stratification. This study uses lake sediment cores to reconstruct recent changes (c. past 20 years) in Lake Baikal's pelagic diatom communities relative to previous 20th century diatom assemblage records collected in 1993 and 1994 at the same locations in the lake. Recent changes documented within the core-top diatom records agree with predictions of diatom responses to warming at Lake Baikal. Sediments in the south basin of the lake exhibit clear temporal changes, with the most rapid occurring in the 1990's with shifts towards higher abundances of the cosmopolitan Synedra acus and a decline in endemic species, mainly Cyclotella minuta and Stephanodiscus meyerii and to a lesser extent Aulacoseira baicalensis and Aulacoseira skvortzowii. The north basin, in contrast, shows no evidence of recent diatom response to lake warming despite marked declines in north basin ice cover in recent decades. This study also shows no diatom-inferred evidence of eutrophication from deep water sediments. However, due to the localised impacts seen in areas of Lake Baikal's shoreline from nutrient pollution derived from inadequate sewage treatment, urgent action is vital to prevent anthropogenic pollution extending into the open waters

Diatom evidence of 20th century ecosystem change in Lake Baikal, Siberia.

Lake Baikal has been experiencing limnological changes from recent atmospheric warming since the 1950s, with rising lake water temperatures, reduced ice cover duration and reduced lake surface-water mixing due to stronger thermal stratification. This study uses lake sediment cores to reconstruct recent changes (c. past 20 years) in Lake Baikal's pelagic diatom communities relative to previous 20th century diatom assemblage records collected in 1993 and 1994 at the same locations in the lake. Recent changes documented within the core-top diatom records agree with predictions of diatom responses to warming at Lake Baikal. Sediments in the south basin of the lake exhibit clear temporal changes, with the most rapid occurring in the 1990's with shifts towards higher abundances of the cosmopolitan Synedra acus and a decline in endemic species, mainly Cyclotella minuta and Stephanodiscus meyerii and to a lesser extent Aulacoseira baicalensis and Aulacoseira skvortzowii. The north basin, in contrast, shows no evidence of recent diatom response to lake warming despite marked declines in north basin ice cover in recent decades. This study also shows no diatom-inferred evidence of eutrophication from deep water sediments. However, due to the localised impacts seen in areas of Lake Baikal's shoreline from nutrient pollution derived from inadequate sewage treatment, urgent action is vital to prevent anthropogenic pollution extending into the open waters