Distribution of Elements in Iron-Manganese Formations in Bottom Sediments of Lake Onego (NW Russia) and Small Lakes (Shotozero and Surgubskoe) of Adjacent Territories

Abstract

The morphology and mineralogical and geochemical compositions of the freshwater ferromanganese formations (FMF) of Lake Onego (NW Russia) and small lakes located in its catchment area were studied. The lake waters, bottom sediments and FMF were analyzed by a set of modern methods of geochemistry, mineralogy, and crystal chemistry (powder X-ray diffraction, IR spectroscopy, electron microscopy, ICP–MS analysis, atomic absorption, etc.). A detailed description of the microscopic structure in comparison with the geochemical characteristics of the FMF provides new information on the role of biota in the formation and behavior of individual elements at various stages in the nodule formation process. This study shows the homogeneous composition of microconcretions—only manganese or only ferruginous—in bottom sediments throughout the entire water area of Lake Onego and the rhythmic structures of the nodules, formed by macro- and microlayers with mineralized microbiota. The layers are composed of either crystalline Mn mineral phases (pyrolusite, rhodochrosite) or crystalline Fe mineral phases (siderite, goethite). The separation of Mn and Fe mineral phases in the nodules proceeded during their formation and diagenesis. The examined chemical and mineral compositions, textures, and structures of the nodules are a testament to the hydrogenic source of their ore substance and the formation of FMF is controlled primarily by redox environments at the water–sediment interface.

Structure of Late Pleistocene and Holocene Sediments in the Petrozavodsk Bay, Lake Onego (NW Russia)

“…In addition to these minerals, there are opal (diatoms), Fe-Illite, and Fe-chlorite. [21]. The concentration of rhodochrosite, siderite, and vivianite increases in the zones of gas-saturated Silts (Figure 16).…”

“…According to previous studies conducted by the authors, it was found that the mineral composition of the bottom sediments of lake Onega is formed by minerals (quartz, feldspar, muscovite), which were introduced into the lake from river runoff and aerosols, as well as autigenic minerals. In contrast to wells from other areas of the lake, the mineral phases of Fe and Mn are represented by pyrolusite, vivianite, rhodochrosite, and siderite already in the upper first centimeters of sediments [17,21]. In addition to these minerals, there are opal (diatoms), Fe-Illite, and Fe-chlorite.…”

Multi-Element Imaging of a 1.4 Ga Authigenic Siderite Crystal

“…However, since minor changes in the Eh and pH of the medium lead to great changes in sedimentary Mn/Fe ratios [53], the rims of Mn in the siderite might indicate subtle varying water conditions during the crystal growth, which is different from the modern ferruginous lakes [21].…”

Distribution of Mercury in the Water-Suspended Matter-Bottom Sediments System of the Lake Onego Water Area

“…The geochemical and mineral compositions of the Lake Onego bottom sediments are described in detail in [31][32][33] The authors suggest that the upper part (0-20 cm) of the Holocene bottom sediments can be divided into two stratigraphic types, based on the mineralogical composition and geochemical features. The first type of bottom sediments is characterized by the presence of enriched Fe-Mn layers formed near the water-bottom sediment boundary.…”