A. R. Geptner

Glauconite from lower cretaceous marine terrigenous rocks of England: A concept of biochemogenic origin

Detailed mineralogical characteristics of various forms of glauconite occurrence in Lower Cretaceous marine terrigenous rocks of the White Island (Binnel Bay, southern England) are discussed. It has been shown that glauconite was formedin situ due to the transformation of fine-dispersed and sandy-silty terrigenous materials. The influence of bacterial activity on glauconite formation is supported by the study of dissolution zones on quartz and feldspar grains, which revealed biomorphic structures akin to fossilized bacteria.

Glauconite at Different Stages of Lithogenesis in Lower Cambrian Rocks of Western Lithuania

It is shown that glauconite was mainly formed under diagenetic conditions in terrigenous–clayey rocks (Rausven Unit) of the Lower Cambrian Virbalis Formation in western Lithuania. This was preceded by bioturbation at some levels of geological column and local short-term reworking at other levels. Different forms of glauconite and its interrelation with ambient minerals in diagenesis and epigenesis are considered. A two-phase micaceous (glauconite–illite) composition of globules has been revealed and crystallochemical characteristics of each phase is presented.

Exothermic and endothermic soils of Iceland

This paper is based on the results of the study of soils and soil-forming rocks on five key sites in Iceland, including the coastal plain (the Hvammur key site), piedmont plain (the Hveragerði key site), the Holocene lava plateau (the Reykjanes key site), and the zone of modern hydrothermal activity in the north of the rift zone of Iceland (the Theistareykir and Námafjall key sites). The studied soils are subdivided by us into the groups of exothermic and endothermic soils. Exothermic soils are the soils that develop from the congealed volcanic deposits. These soils are specified by the homogeneous dark gray color and sandy texture. Their mineral components are weakly transformed. Exothermic soils developed under good drainage conditions have the low content of organic matter (about 1.5% Corg). The soil reaction is neutral within the entire profile. Under impeded drainage conditions, the organic carbon content in the exothermic soils reaches its maximum of about 7%, and the soil reaction varies from acid to neutral values. Endothermic soils are the soils that are subjected at present or were subjected in the past to the high-temperature hydrothermal metamorphism. They have mottled color patterns with sharp color contrast in the soil profile; their texture is loamy or clayey. These soils are rich in secondary minerals with a predominance of smectite; kaolinite, pyrite, anatase, gypsum, and other secondary minerals can also be found in them. The properties of endothermic soils are largely controlled by the provincial features of the hydrothermal activity, including the chemical composition of hydrothermal water, the soil temperature, the duration of hydrothermal activity, etc.

Polycyclic Aromatic Hydrocarbons in Holocene Sediments and Tephra of Iceland (Composition and Distribution Features)

This work considers results of the study of Holocene cover sediments of Iceland largely composed of wind-transported palagonitized hyaloclastite particles and coeval horizons of acid and basic tephra. It is established that polyciclic aromatic hydrocarbons (PAH) are released from the basaltic glass in natural environments only in the case of intense physicochemical alteration and destruction of its structure. This process does not influence the composition of polycyclic aromatic hydrocarbons and their quantitative proportions. No new polyclic aromatic hydrocarbons formed during several thousands of years of the Holocene section accumulation. Hydrocarbons are transferred from fixed the state in basaltic glass into the free state in palagonites practically without any changes. Polyciclic aromatic hydrocarbons were mainly redeposited by winds, derived together with palagonite from weathered hyaloclastites, and precipitated from atmosphere with tephra during eruptions.

Freshwater stromatolites with the cone-in-cone structure from the Neogene lacustrine sediments of Vietnam

Morphological features of the columnar-stratiform stromatolites, which resemble the cone-in-cone structure, from Neogene lacustrine sediments of northern Vietnam are analyzed. Their structural-textural peculiarities and interrelations with the host terrigenous sediments of a stromatolitic buildup are discussed. It is shown that stages of the growth of columns are recorded in the succession of vertically oriented carbonate plates, which form stromatolites, and in the serrate surface protrusions of the plates at their contacts with host sediments. It is established that replacement of the columnar stromatolites by the stratiform varieties in the section can be related to variations in the intensity of terrigenous material influx to the sedimentation basin. Stratiform stromatolites were formed during relatively slow accumulation of sedimentary material. Appearance of the columnar varieties is attributed to intensification of sedimentation.

Glauconite from Paleogene volcano-terrigenous rocks in Western Kamchatka

It is shown that glauconite-bearing interbeds are widespread in the layer-by-layer studied sections on the Sea of Okhotsk coast (Mainach section) and Kheisliveem River valley (Kavran section), the volcanoterrigenous rocks of the Kovachin, Amanin, and Gakkhin formations of the Paleogene in western Kamchatka (Upper Eocene-Lower Oligocene boundary beds). Detailed mineralogical and structural-crystallochemical characteristics of glauconite from the Amanin Formation are presented. It is suggested that such glauconite should not be used for geochronological purposes.Some specific features of glauconite formation, particularly, the preservation of specific morphological forms at high accumulation rates of volcano-terrigenous rocks, are discussed. Possibility of the formation of glauconite with the active influence of bacterial metabolism is considered.

Hydrothermally altered clayey sediments in the rift zone of Iceland (influence of microbiota on accumulation of minor elements)

Results of the first detailed study of mineral and chemical compositions in the rift zone of Iceland near the town of Hveragerði are presented. The major clayey components represented by dioctahedral smectites (mainly, montmorillonite with variable Fe contents) are associated with the subordinate kaolinite. The geological setting, timing, and composition of metasomatic clay minerals and their synthesized counterparts precipitated from solution in the course of interaction of hot groundwaters with basaltic volcanics and sedimentary clayey rocks are considered. Based on textural-structural features and (or) compositions, the sediments are divided into three types: (1) massive unsorted sediments with abundant fine-grained sand to silt-sized clay pellets, (2) horizontally laminated clayey sediments, and (3) organogenic sediments. The massive unsorted sediments enclose remnants of microorganisms replaced by smectite, while laminated clayey sediments host a siliceous layer with abundant mineralized remains of filamentous microorganisms. Clayey rocks of hydrothermally altered hyaloclastites and sediments related to their redeposition are similar in the composition of petrogenic elements. However, they differ notably from each other in the contents of some minor elements (Au, As, Se, Sb, and Hg). Increase in the share of minor elements in sediments is explained by the active influence of bacteria and fungi on their accumulation. The data obtained shed light on some specific features in the composition of clayey rocks, which can be used for mud cure of arthritis and rheumatism in the Health and Rehabilitation Clinic of the Nature Health Association of Iceland, Hveragerði.

Abiogenic and Biochemogenic Alteration of Basaltic Glass under Low-Temperature Conditions

The material for investigations was obtained in Iceland in the area of active volcanism and tectonics in the recent rift zone under cold-temperate and humid climate and glacial conditions. The presence of abundant remnants of microbiota differently mineralized by palagonite was established in weathering zone on the surface of basaltic glass fragments situated at the top of hyaloclastites devoid of terrestrial vegetation. This gives conclusive evidence for the biochemogenic nature of palagonization in basaltic glass under these conditions. Among a number of possible reasons of the origination of palagonite, the most interesting is the relation of microbiological processes to the influx of gaseous hydrocarbons from the depth. This mechanism needs further investigations.

Siderite microconcretions in the glauconite-bearing clayey-silty rocks of the Khaipakh Formation (Middle Riphean, Olenek Uplift)

Siderite microconcretions in the glauconite-bearing clayey-silty rock member of the lower sub-formation of the Khaipakh Formation (Middle Riphean, Olenek Uplift) are scrutinized for the first time. In two Khorbusuonka River sections located with a spacing of 12 km, the microconcretions occur as lenses and interlayers. Together with glauconitites, they serve as a distinct marker horizon of this stratigraphic interval. Their structures, morphologies, diffraction characteristics, chemical compositions, and isotope data are considered. They were examined comprehensively with modern investigation methods (X-ray diffraction, scanning electron microscopy with the application of local microprobe analysis, and others). Structural-morphological types of microconcretions are identified. Calculation of the chemical composition of carbonates based on numerous microprobe analyses made it possible to reveal different degrees of mineral heterogeneity in each type in terms of the distribution of macro- and microlevel isomorphous trace-elements and to refine the character of their secondary alterations at different stages of lithogenesis. The results of oxygen and hydrogen isotopic studies are presented for algal dolomites and limestones from the Middle and Lower Riphean sections in the Olenek Uplift (Debengda, Arymass, and Kyutingda formations). They demonstrated that siderites are similar to limestones and dolomites in terms of the oxygen isotopic composition (δ18O = 17.6–24.8, δ18Oav = 20.0 ± 2.4‰), but are marked by low δ13C values (from −6.3 to −12.0‰ (δ13Cav = −8.6 ± 2.1‰), suggesting the formation of microconcretions during early diagenesis. Siderite microconcretions were formed in the clayey-silty sediment slightly after glauconite, whose grains could serve as crystallization centers and (or) be entrapped during the growth of separate microcrystals. The role of catalyzers during the formation of both glauconite and siderite was played by bacterial communities, whose poorly preserved remnants have been detected not only in the studied member of the lower Khaipakh subformation, but also above and below the section. Separate types of microconcretion could be formed during the replacement of oncolites by siderite.

Fossilized filamentous microbiota in volcanosedimentary deposits in iceland

The mineralization of bacterial organic matter in the groundwater of Iceland is discussed. Structural relationships between secondary minerals in cavities within a Pleistocene basaltic sill and the general sequence of their precipitation allowed us to recognize five stages of the secondary mineral formation. Two stages of layer silicate formation separated by a stage of zeolite and apophyllite formation were pointed out. The composition and structure of clay minerals formed at different stages as a result of the interaction between groundwater and basalt with an active participation of bacteria have been investigated. Clay minerals of the second stage are similar in composition and microstructure to biomorphic structures previously studied in Miocene plateau basalts. The last stage of mineralization is related to the fossilization of filamentous microbiota residing in open cavities and covering all older secondary minerals