BIOGEOCHEMICAL FEATURES OF THE FORMATION OF THE HOLOCENE SEDIMENTS IN LAKE DUKHOVOE AT THE STAGE OF EARLY DIAGENESIS IN EASTERN BAIKALIA
G.A. Leonova1, A.E. Mal’tsev1, S.K. Krivonogov1,2, V.A. Bobrov1, V.N. Melenevskii3, V.A. Bychinskii4, A.A. Bogush1, L.M. Kondrat’eva5, L.V. Miroshnichenko1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
4Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
5Institute for Water and Environmental Problems, Far Eastern Branch of the Russian Academy of Sciences, Khabarovsk, Russia
Keywords: Organic matter, bioproducers, sapropel, mineral matter, diagenesis, microorganisms, pore water transformation, authigenic minerals
Abstract
A 6-meter core of the Holocene sediments in Lake Dukhovoe is studied. The material composition of the core is heterogeneous and has clear bedding. Lacustrine sediments are represented by the upper 293 cm. Each bed of the sediments is subjected to microbiological analysis. A high total number of heterotrophic bacteria is revealed in the upper (0-15 cm) and deeper (110-150 cm) sapropel intervals. Sulfate-reducing bacteria are identified only in Chrysophyceae cysts. The CaO/Fe2O3 ratio shows the degree of “carbonate content” of bottom sediments. It is low in the sapropel of the lake (0.2), which indicates the geochemical specificity (carbonate-free sapropel). The Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr, and Cr concentrations in sapropel are within the average concentrations for the Earth’s crust, shale, and oceanic pelagic clays, while U and Mo exceed them. Phytoplankton is enriched in phosphorus (biogenic element) and chalcophile elements (Zn, Cd, Sn, Sb, Hg, Pb, and Cu), which characterize the pollution of the modern atmosphere of the Baikal region. Diagenetic processes result in the transformation of the pore waters, namely an increase in mineralization as compared to lake water, an increase in the concentrations of biogenic components (HCO3-, NH4+, NO3-, and PO43-) and a decrease in SO42-. Pyrite framboid accumulations are revealed in organomineral sediments below the horizon of 200 cm, and iron phosphates represented by vivianite are identified in sapropel.
|
