The importance of biological factors in the genesis of the unique niobium and rare-earth ores of the Tomtor deposit, in northwestern Yakutia, is indisputable, but the exact conditions under which these ores formed remain poorly understood. The first micropaleontological study of these ores suggested the major role of benthic cyanobacterial mats developing along the sea coast. The goal of this paper was to scrutinize that hypothesis. Reexamination of archival materials found no clear evidence of the development of benthic cyanobacterial mats. Instead, signs of active development of plankton communities and communities of benthic sediments were found. The new data reconstruct the environment of shallow, sun-warmed waters well suited for algal blooms.

The Tatarka bauxite deposit on the territory of the Russian Federation was formed as a result of sedimentation of the products of denudated lateritic weathering crusts of amphibolites in contact-karst depressions. Detailed mineralogical studies of bauxites made it possible to reconstruct reliably the conditions for their formation. As it turned out, the initial rocks and rocks, weathered before, have been denudated due to the close location of the areas of alimentation and accumulation. At the same time, chemical processes have been continued in karst depressions. For the first time, the presence of nanoparticles of amorphous aluminum oxide was revealed in contact-karst bauxites. This specific feature of the form of alumina precipitation is associated with the subsequent cessation of lateritization and their attenuation with depth. The presence of amorphous aluminum monohydrate must be taken into account when choosing a scheme for bauxite enrichment.

The results of a long-term electron microscopic study of Kamchatka geyserites are presented showing biological remains of unique preservation and a wide variety of cyanobacteria silicification types. The data obtained made it possible to consider the geyserites of Kamchatka as a model object for bacterial-paleontological studies.

Modern microbialites formed in soda-saline and soda lakes are of interest as model systems for studying geobiological interactions in the Precambrian, when such geochemical settings were widespread. This work describes the structure and mineral composition of microbialites from the soda-saline Laguna de Los Cisnes (Isla Grande, Tierra del Fuego, Chile), and also characterizes the biodiversity of microorganisms involved in their formation. The microbialites consist mainly of carbonate minerals, of which monohydrocalcite is of particular interest. It was shown that the formation of microbialites occurs under alkaline conditions in the presence of taxonomically and functionally diverse microorganisms and in direct contact with exopolysaccharides produced by the microbial community.

Remains of benthic cyanobacterial communities formed under shallow-water littoral conditions of were found in the Upper Vendian Zavkhan cyano-algo-bacterial association of the upper terrigenous-carbonate section of the Tsagaan-Olom Formation (<632 ± 14 Ma) of the Zavkhan structural-formational zone in Western Mongolia. Filamentous cyanobacteria of the genus Siphonophycus were the main builders of mats. Benthic cyanobacterial communities mark the shallow-water facies of the regressive stage of development of the vast postglacial Vendian–Cambrian Zavkhan paleobasin in Western Mongolia.

The main source of aluminum is bauxite ores and their basic mineral components gibbsite Al(OH)3 and boehmite AlO(OH). Alumina Al2O3 is formed by various methods of decomposition of these components, electrolytically decomposed to pure Al. It has been established that gibbsite is the basic and often the only mineral of aluminum in the Mesozoic and Cenozoic laterite bauxites, representing most of the world’s reserves. Boehmite is formed in laterite-sedimentary bauxites, during lateritization and desilication of albic water-sedimentary continental sediments, as well as the underlying bleached parent rocks. The formation of boehmite is associated with an excess of aluminum generally due to its input from above. Boehmite predominates in the Paleozoic laterites. The formation of aluminum monohydrate is explained by a decrease in the oxidation–reduction potential.

Interesting observations illustrating the process of transformation of some minerals of banded iron formations (BIF) were made while studying the Early Proterozoic jaspilites of the Kursk Magnetic Anomaly (KMA). Examples showing the process of siderite transformation into iron oxides/hydroxides by iron-oxidizing bacteria are given.

Fossilized cyanobacteria(?) represented by trichomes enclosed in common sheaths were detected in early Proterozoic iron banded formations of the Kursk magnetic anomaly (limonite–martite ores of the Lebedinsky mine and iron banded formations of the Korobkovskoye deposit). These fossils morphologically similar to current representatives of the genus Microcoleus were buried in situ.

The Vendian (Ediacaran) beds of the Zavkhan Basin, in the upper part of the Tsagaanolom Formation (<632 ± 14 Ma), yielded a new “Zavkhan” association of algae, microfossils, and problematic organisms, which is established in the series of alternating chert-carbonate shale with phosphorite interbeds. This association is distinct in the predomination of large (250 μm and over) sphaeromorphic microfossils of the genera Tasmanites, Archaeooides, and Leiosphaeridia, whereas acanthomorph acritarchs are represented by rarely found Cavaspina sp. and Tanarium sp. Multicellular algae included fragments of encrusting or foliate thalli with pseudoparenchymatous structure of polygonal cells characteristic of Rhodophyta algae (Thallophycoides sp.), and cordlike thalli of Vendotaenid algae Tyrasotaenia podolica. These layers of siltstone contain imprints of the problematic Vendian macrofossil Beltanelliformis brunsae. In their stratigraphic position, chemostratigraphic data, and fossil assemblage, the “Zavkhan” association can be assigned to the Upper Vendian.

A new species of spheromorphic microfossils of Tasmanites with a characteristically thick cover is established in the Zavkhan association of algae, microfossils, and problematic Upper Vendian organisms from the upper part of the siliciclastic–carbonate section of the Tsagaanolom Formation (632 ± 14 Ma) of the Zavkhan Basin in western Mongolia. Representatives of this genus are widespread in the Phanerozoic beds and their accumulations are recorded in the Domanik facies and near hydrocarbon deposits.

The cyanobacterium Oscillatoria terebriformis was shown to exhibit resistance to high manganese concentrations, remaining viable at 2.5 mM MnCl2 in the medium. Cyanobacterial cells were capable of considerable manganese consumption from the medium. The dynamics of Mn sorption by the cells were the same in all experimental variants, independent of the manganese concentration. Manganese concentration in the biomass peaked after 2–3 days and depended on Mn2+ concentration in the medium and on the amount of biomass introduced. In the case of O. terebriformis, manganese removed from the medium may be subdivided into Mn absorbed by the cell, Mn bound to the cell wall, Mn absorbed by the glycocalix, and chemically precipitated Mn. Of the total 21.25 ± 1.0 mg of consumed manganese, biological absorption and chemical precipitation were responsible for 11.78 ± 0.98 and 9.2 ± 0.8 mg, respectively. In the presence of cyanobacteria, Mn removal from the medium was 2.28 times higher than in the control. This process depended considerably on Mn sorption by exopolysaccharides. At 1.3 mM Mn2+, a lamellar mat was formed with interlayers of manganese carbonate.

Neoproterozoic glaciations are correlated using microfossil, radiometric and chemostratigraphic data that accumulated in recent years [1]. Although tillites and tilloids are widely distributed in Precambrian sequences, only few of them are associated with occurrences of authentic macroscopic fossils [2]. We found problematic discoidal macroscopic fossils in Late Precambrian tillites of Dzabkhan region of Western Mongolia in the course of field study conducted by Precambrian team of the Russian-Mongolian paleontological expedition in 2006–2007. The glacial marine deposits (Maikhanul Fm), discovered in Dzabkhan region in 1990s [3], discordantly overlie the persilicic intrusive bodies of Dzabkhan Fm (732–777 Ma) [4] and are conformably overlayed by the limestones of Tsagaan Oloom Fm. The Maikhanul Fm comprises two relatively thin units of diamictites separated by a section of flysch deposits; total thickness of the formation reaches 220 m. The presence of two diamictite units, cap dolomites, radiometric dates of underlaying volcanics, rock composition, shape and size of intraclasts all suggest correlation of the Maikhanul tillites with Central Australian Neoproterozoic glacial marine deposits. The flysch formed between the two glacial events, and the cap dolomite records the maximum postglacial transgression [5]. There are still uncertainties about the exact age of Mongolian tillites because of the lack of Ediacaran fossils in the overlying strata. They could be of Stirtian age; however, δ13C values from limestones of the overlaying Tsagaan Oloom Fm (+2.8‰) do not exclude of possibility of Varanger age [5]. The Tsagaan Oloom Fm of Dzabkhan structural zone can be correlated with the Doushantuo Fm of South China (600–550 Ma) by the complex of microfossils [6]. Doushantuo Fm overlies diamictites of the Nantuo Fm. Radiometric dates from volcanic tuff beds in cap carbonates of the Doushantuo Fm (635.23 ± 0.57 Ma) are similar to the dates from tuffs in the postglacial Ghaub Fm of Congo [7]. The correlation model of Mongolian and Nantuo tillites was first presented by V.V. Khomentovsky and A.S. Gibsher [3]. Consequently, the age of Maikhanul Fm tillites is not older than Sturtian and not younger than Marinoan.

A laboratory model of a cyano-bacterial mat with mineral layers of carbonates was used to examine the dynamics of the transformation of calcium-magnesium carbonate under the conditions of a soda lake. The activity of various organisms of the cyanobacterial community results in conditions under which the Ca-Mg carbonate precipitate undergoes changes. The crystal lattice of the initial carbonate is restructured; its mineralogical composition changes depending on the conditions of the mat. In magnesium calcites, which are formed under such low-temperature conditions, a rudimentary cation adjustment can occur with the formation of dolomite domains. These experiments confirm the hypothesis that the dolomite found in stromatolites is of a secondary origin and can be formed in the course of transformation of Ca-Mg carbonates under alkaline conditions in an alkaliphilic cyanobacterial community.