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The increasing need for phosphorus and rare earth elements (REEs) has initiated the studies of new mineral deposits and new complex processing technologies. Estonian phosphate rock (EPR) resources, which are not in use, are estimated to be more than 3 billion metric tons or 800 million tons of P2O5. The experiments of dissolution of three different EPR samples in hydrochloric acid were carried out with the aim of studying the impact of the chemical and mineralogical composition of EPR on the leaching process. The leaching of P, Ca, Mg, and consumption of H+ ions depend on HCl concentration and dosage. The solubility of fluorine and REEs are also influenced by CaF2 and REEs-phosphates precipitation. Fe solubility depends on the mineralogical composition of EPR but also on particle size, acid dosage, pH, and phosphorus content in the solution. The dissolution of pyrite is much lower than the solubility of carbonate apatite. Dolomite dissolution depends on the acid dosage and the fractional composition of EPR. Dolomite dissolution also rests lower than that of apatite. For all the samples studied, the best regression models that describe P, Mg, and Ca solubility and the optimum concentration of HCl for phosphorus dissolution were found using mathematical modeling.

This paper is a methodological development, where optical microscopy, X-ray diffractometry (XRD) and microanalysis under a scanning electron microscope (SEM) were used for comparative determination of heavy minerals in Quaternary sandy sediments in the Lemme outcrop, southwestern Estonia, and for evaluation of possible provenance rocks. For comparison, samples from Devonian drill cores were analysed. Heavy minerals in the Lemme coastal deposits mostly originated from the till of the last glaciation, which contained clasts and fines from rocks of the Svecofennian Domain of the Fennoscandian (Baltic) Shield. Garnets were the dominating minerals in the Lemme samples, whereas the crystal lattice parameter of the main component was 11.535 Å. The Devonian garnets were different, with the lattice parameter of the main component being 11.610 Å. Amphiboles, ilmenite and magnetite were also important minerals in the Lemme samples, but scarce in the Devonian samples. A detailed study of magnetite revealed a Ti content of 0.3%, which is consistent with the lattice parameter 8.397 Å. The hematite content of the Lemme samples was about twice as high as that of magnetite. The Ti content of hematite grains was higher in the surface (about 5%) than in the middle section (1.6%). The XRD analysis showed that titanium in hematite grains was probably fine crystalline rutile. In the Devonian samples, the main opaque mineral was pseudorutile.

Graptolite–argillites (black shales) are studied as potential source of different metals. In the processing technologies of graptolite–argillites, a preceding thermal treatment is often applied. In this study, the thermal behavior of Estonian graptolite–argillite (GA) samples from Toolse, Sillamäe and Pakri areas were studied using a Setaram Labsys Evo 1600 thermoanalyzer coupled with the Pfeiffer OmniStar Mass Spectrometer. The products of thermal treatment were studied by XRD, FTIR, and SEM analytical methods. The experiments were carried out under non-isothermal conditions of up to 1200 °C at different heating rates in the atmosphere containing 79% Ar and 21% O2. The differential isoconversional Friedman method was applied for calculating the kinetic parameters. All studied GA samples are characterized with high content of orthoclase (between 38.0 and 57.3%) and quartz (between 23.8 and 35.5%), and with lower content of muscovite, jarosite, pyrite, etc. The content of organic carbon in GA samples studied varied between 7.3 and 14.2%. The results indicated that, up to 200 °C, the emission of hygroscopic and physically bound water takes place. Between 200 °C and 500–550 °C, this is followed by thermo-oxidative decomposition of organic matter. The first step of thermo-oxidation of pyrite with the emission of water, carbon and sulphur dioxide, nitrogen oxides, and different hydrocarbon fragments indicated the complicated composition of organic matter. At higher temperatures, between 550 °C and 900 °C, the transformations continued by dehydroxylation processes in clay minerals, and the decomposition of jarosite and carbonates took place. At temperatures above 1000–1050 °C, a slow increase in the emission of sulphur dioxide followed, indicating the beginning of the second step of thermo-oxidative decomposition of pyrite, which was not completed for temperatures of up to 1000 °C. Kinetic calculations prove the complicated mechanism of thermal decomposition of GA samples: for Pakri GA samples, it occurs in two steps, and for Silllamäe and Toolse GA samples, it occurs in three steps. Preliminary tests for the estimation of the influence of pre-roasting of GA samples on the solubility of different elements contained in GA at the following leaching in sulphuric acid is based on Toolse GA sample.

The chemical composition of the clay fraction separated from the carbonate rock of the north-eastern Baltoscandian Basin was analysed and interpreted. Increased contents of Rb, Zr, Nb, Ti and their Al 2 O 3 -normalised ratios were detected at several stratigraphical levels in the geological sections of the Middle Ordovician–Upper Llandovery. In the weathering areas, Rb, Zr, Nb, Ti and Al are sensitive to moist conditions in the clay-forming process. In the sedimentary basin, the contents of these elements in clay are preserved and allow to infer past climates. Humid events occurred in the Dapingian, Sandbian, early Katian and Hirnantian (Ordovician) and in the Middle and Late Llandovery (Silurian). Juxtaposition with the sea-level curve shows correlation of five humid climate intervals with eustatic transgressions, suggesting global causes for these climatic changes. The warm and humid events, lasting one to two million years, occurred as climaxes between ice ages. An exceptional humid event within the Hirnantian glacial time occurs during mid-Hirnantian transgression, i.e . at a time of relative warming, as well.

In order to check the immobility and mobility of elements during conversion of acidic volcanic glass to bentonites in normal marine environments, we studied the composition of three altered volcanic ash layers from the Palaeozoic of the Baltoscandian Region, correlated through different facies. Regular changes in element concentrations in accordance with loss and gain of material during the transformation of volcanic ash indicate that Al, Nb, Ti, Zr, Sn, Pt, Ta, Hf and Th were generally immobile and can be used for the interpretation of source magma and correlation of ash layers. Cd behaves similarly with immobile elements and this can be explained with preservation only of the immobile portion of Cd that is fixed in phenocrysts. In bentonites in shales during the formation of kaolinite, the data indicate small-scale mobility of Al and Cd. In lime muds where K-feldspar forms from volcanic ash, Ta, Hf and Th reveal some small scale mobility. These slightly mobile elements must be used with caution for interpretation of thin ash layers with thicknesses of

The late Llandovery (Silurian) – early Lochkovian (Devonian) climate of the tropical zone is tracked considering orogenesis, global glaciation events, and cratonic drift. Mineral and chemical compositions of clay fractions of Canadian (the Franklinian Basin) and Estonian (the Baltoscandian Basin) sedimentary rocks from different sides of the emerging Caledonides were studied, using clay as an index of climatic conditions of the provenance area. Illite is the main clay mineral, with addition of orthoclase, muscovite, and chlorite in both regions. Authigenic chert is present in some Canadian sections. The similarity of clay minerals and elemental composition in the two regions suggest common chemical weathering conditions. Nevertheless, the Al/Ti ratio of the 13C of marine carbonates is recorded at some stratigraphical levels, suggesting a link between humid climatic episodes in mainland and waning of glaciers at the South Pole.

Twenty-six samples from two major altered volcanic ash beds, Kinnekulle and BII Bentonite of the Kuressaare core section (K-3), Saaremaa Island, were explored to record the geochemical and mineralogical heterogeneity of beds. Signs of ash transport fractionation, redeposition of volcanic ash and diagenetic redistribution of material are described and interpreted. In authigenic mineralogy of the Kinnekulle Bentonite illite–smectite dominates with addition of K-feldspar at the margins. The BII Bentonite is composed of chlorite–smectite and illite–smectite. The stability of phenocryst compositions, including that of sanidine and biotite, indicates that both bentonites originate from a single eruption. The observed rather stable pyroclastic sanidine compositions in the cross section of bentonites confirm the reliability of sanidine-based fingerprinting of altered volcanic ash beds. Trace element distribution in bentonites and host rocks indicates that Zr, Ga, Rb, Nb, Ti and Th stayed largely immobile during volcanic ash alteration and reflect primary ash composition. However, some redistribution of Nb and Ti as well as Y has probably occurred near the contacts of bentonite with the host rock. More scattered grain size distribution and immobile element patterns of the Kinnekulle Bentonite support the idea that the primary ash bed had a heterogeneous composition and it was one of the biggest bentonites of the Phanerozoic and most likely records an extended volcanic event. Significant geochemical variations, including a high S content, near the upper and lower contacts of the Kinnekulle Bentonite and elevated Ca and P in host rocks of both bentonites suggest that the studied large ash-falls caused notable perturbations in shallow marine and early post-sedimentary environment.

Altered volcanic ash interbeds (bentonites) in the upper Katian of Baltoscandia indicate significant volcanic activity in neighbouring tectonically active areas. Katian bentonites in the East Baltic can be reliably correlated using sanidine phenocryst composition. Ratios of immobile trace elements TiO2, Nb, Zr and Th to Al2O3enable extension of the correlations to Scandinavia, where late diagenetic alterations could have caused recrystallization of sanidine phenocrysts. At least seven volcanic eruptions were recognized in Baltoscandian sections. Several bentonites found in deep-sea sediments are absent in shallow-sea sediments, indicating extensive breaks in sedimentation and erosion during late Katian and Hirnantian times. The areal distribution pattern of Katian bentonites in Baltoscandia indicates a volcanic source from the north or northwest (present-day orientation) from the margins of the Iapetus Palaeo-Ocean. Signatures of ultra-high-pressure metamorphism in the Seve Nappe (Central Sweden) and intrusions in the Helgeland Nappe Complex in Central Norway have been proposed as potential sources of the magmas that generated the volcanic ashes deposited in the East Baltic in Katian times. Geochemical similarities between Baltoscandian and Dob's Linn bentonites from southern Scotland suggest a common volcanic source in Katian times.

Integrated correlation of bentonites (altered volcanic ashes) and graptolite biozonation is presented. Detailed study of two Lithuanian drill core sections extended previous knowledge of the occurrence and composition of bentonites to the south. Identification of graptolite species allowed bentonites to be assigned their proper stratigraphical position. Silurian bentonites in Lithuania are mostly characterized by wide and very wide XRD 20 1 reflections of the main component of sanidine phenocrysts. Only fourteen of the 69 samples studied contained sanidine with a sharp reflection, which gave the best correlation potential. In the Lithuanian sections one bentonite was found in the Rhuddanian, five bentonites were recognized in the Aeronian, 17 bentonites in the Telychian, 26 in the Sheinwoodian, 10 in the Homerian and six in the Ludlow. All bentonites found in Lithuania are characterized by the main component of sanidine. A large number of Lithuanian bentonites are not known in Latvia and Estonia, indicating that volcanic ashes reached the East Baltic area from two source regions - the Central European and Norwegian Caledonides.

Nowadays carbon isotopes and bentonites have become new authorities in stratigraphy besides traditional biostratigraphy. Three positive carbon isotope excursions have been identified in the Upper Silurian of Podolia: the mid-Ludfordian excursion, the late Přidoli excursion at the Trubchyn/Dzvenygorod junction and the SIDE at the Silurian–Devonian boundary. Fourteen bentonite beds are known from this upper Ludlow–Přidoli interval. Some of these are better studied and are helpful for correlation of sections. Using the stage slices as a framework, we show that the Přidoli can be subdivided into “natural” stage rank units based on the integrated bio-, litho- and chemostratigraphy.

This article presents a dataset of geochemical analyses from Silurian altered volcanic ash beds (bentonites) characterising 132 eruptions and preserved in sedimentary sections of the East Baltic area. TiO2, Nb, Zr, Th, Y, Ce, Cr and V ratios with Al2O3 are used for identifying correlations between ash beds from Scandinavian sections. Some correlated ash beds are illustrated by schematic maps of areal distribution indicating volcanic sources from directions of both Iapetus and Rheic palaeo-ocean margins.

The Upper Devonian Plavinas Regional Stage in southern Estonia and northern Latvia is represented by dolostones containing interlayers of dolomitic marlstones and limestones. Petrographic, cathodoluminescence, electron microprobe and isotope techniques were used to investigate diagenetic evolution of dolostones. The rock succession has been affected by multiple dia­genetic events. Based on petrographic and geochemical data, six dolomite textures were identified. The crystal size (5–1200 μm) and morphology of dolomites are variable. Commonly, dolomites are close to the stoichiometric composition, with low iron and manganese content. Their stable isotope composition (δ13C, δ18O) differs greatly from that of dolomite precipitated from Frasnian seawater. Dolomitization is more pronounced in the lower part of the studied sequence, in the Snetnaya Gora Formation and Lower Pskov unit where carbonates are completely dolomitized, whereas upwards in the section the dolomite content decreases. Voids and pores of the Lower Pskov unit are mainly open, but partly or completely occluded in the Upper Pskov unit. Void-filling dolomite has slightly and void-filling calcite notably depleted stable isotope signatures. Major dedolomitization and calcite-filling processes took place during the final uplift and emergence of the northern part of the Baltic basin, connected with the migration of karst-related meteoric waters into previously dolomitized horizons within carbonate rocks.

This paper reports on the geochemistry of the mid-Silurian Grotlingbo Bentonite, a ca. 0.1–0.4-m-thick and regionally important bentonite bed in Sweden and the East Baltic area. A series of eight samples, spaced by 5 cm, were taken from the Hunninge-1 drillcore in Gotland, Sweden, and were analysed in order to establish the vertical element composition and variation in the bentonite. The results show that the Gotlingbo Bentonite originates from one source magma and from one single eruption. The lowermost 0.1–0.15 m of the bentonite (compacted) was deposited from air-transport fall-out, whereas the upper portions have been reworked in a shallow-marine environment and re-deposited. Vertical differences in Ti and Zr within the Grotlingbo Bentonite mean that regional correlation of the bed may need several samples at each locality to be reliable.

In the Fennoscandian Shield the fluctuations in arid–humid climate conditions are inferred from the Al2O3/TiO2 ratio of the clay fraction of Estonian carbonate rocks of the Baltoscandian sedimentary Basin. The Late Ordovician climate of the Fennoscandian Shield was mainly semi-humid with several humid pulses in the Sandbian, mid-Katian and Hirnantian. The post-Hirnantian climate was fluctuating between humid and arid until stable humid conditions were established in the Middle and early Late Llandovery. Starting from the latest Llandovery, the climate turned semi-arid and arid. The Ordovician–Silurian long-term trend toward aridity was caused by the equator-ward drift of the Baltica plate. Shorter-term fluctuations of Al2O3/TiO2 reflect climate changes of the global extent.

The distribution of altered volcanic ash layers (K-bentonites) and Telychian chitinozoans in four East Baltic drill core sections are compared. This information is integrated with graptolite and conodont biozonations to give a precise correlation chart using four different stratigraphical tools: K-bentonite-based chemostratigraphy; chitinozoan biostratigraphy; graptolite biostratigraphy; and, conodont biostratigraphy. Thickness variations in the K-bentonites suggest that the source of the volcanic ash was to the west and northwest.

In the central part of the Mid-Ordovician–Early Silurian Baltic Basin, two different transport pathways of terrigenous material can be recognized. Kaolinite indicates the south-to-north sediment influx, and Cr the western and northern sources. A pathway from the Ukrainian Shield in the South was active in the Floian–Darriwilian (Ordovician) and in the Llandovery (Silurian). The influx from the western source was active in the Sandbyan, and influx from the northern side occurred in the Katyan. The sediment transport was carried out by water flows, which turned into rapid currents from time to time. These currents, coming from the ocean surface waters, were oxygenated facilitating red facies formation in the central Baltic Basin. Currents on the shelf were linked to the adjacent oceanic currents, which changed in course with the drift of Baltica from temperate to subtropical latitudes.

The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history of Martian iron hydroxide concretions.

Seven Wenlock bentonite beds from four drill cores in Lithuania with sufficient thickness for sampling were analysed by XRD and XRF. The sanidine composition of bentonites combined with graptolite biozonation of the host rock were used for correlations. Two of the studied bentonite samples at the antennularius/flexilis biozone boundary can be confidently correlated between two Lithuanian sections. Four of the studied bentonites can be correlated with lower or higher probability with earlier studied bentonites in Estonia and Sweden. Identification of the Grotlingbo Bentonite in the Vidukle-61 drill core, and descriptions of other east Baltic sections enables composition of it thickness map of the Grotlingbo Bentonite. The thickness pattern with two axes, and the layered composition of the Grotlingbo Bentonite, indicate a change of the wind direction during a long lasting eruption. Hypothetical location of the volcanic source in the Silurian was within the zone of the Baltica-Laurentia collision. (Less)

The mineral composition of altered volcanic ash beds, bentonites, deposited in marine environments is typically characterized by smectite or illite–smectite type clay minerals. Silurian bentonites from an unmetamorphosed normal marine sedimentary sequence in the eastern Baltic Palaeobasin, however, show a complex and varied mineral composition with illite–smectite, K-feldspar and kaolinite as the dominant authigenic phases. The whole-rock XRD study of 52 bentonite beds from two drill-cores — Ruhnu and Ohesaare, southwestern Estonia, reveals a range of compositions varying between different beds as well as laterally within a single bed. The observed variations are found to reflect the bentonite development and diversification during initial stages of volcanic ash transformation and diagenesis that was probably overprinted by a later K-metasomatic event.

Changes in mineralogy, geochemistry and grain size in a deep shelf succession from the Ordovician Baltic Basin are used to determine shifts in marine current direction and sea-level fluctuations. The analyses show a long-term, relatively stable interval in the Arenig–Llanvirn followed by shorter periods of perturbations and rearrangements in the early Caradoc. The Arenig deposits of the Aizpute-41 core have a high 2–10 µm terrigenous component. During the Llanvirn the proportion of this size fraction diminished. The grain size change was accompanied by mineralogical changes. In the early Caradoc the kaolinite disappeared, the muscovite content decreased, and quartz and albite increased. This and several geochemical indicators point to an input of considerable part of sediment from different sources than in the Arenig–Llanvirn. Two currents, a southwesterly for the Arenig and a westerly for the early Caradoc, are proposed. A red facies belt in the deep shelf marks the pathway of the Arenig–Llanvirn current. Smaller shifts in SiO2/Al2O3 ratio in the Aizpute-41 section are interpreted as reflecting transgressions and regressions corresponding to regional stage boundaries.

In the Telychian section of Estonia and Latvia K-bentonites from 45 volcanic eruptions were discovered. The thickness of K-bentonite interbeds varies from a few millimetres to 20 cm. The sodium component concentration in sanidine phenocrysts measured by XRD ranges from 20 to 48 mol% and was used for establishing correlations. The Ti, Zr, Nb, Th and Sr concentrations and ratios show temporal trends indicating fractional crystallization in magma chambers. The analysis of biotite phenocrysts revealed magnesium and iron rich biotites in bentonites. Synthesis of these geochemical data enabled a classification of bentonites into seven geochemical types, which probably originate from seven different volcanic sources. Isopach schemes indicate ash transport from the west and north-west directions.

Thirty suspected altered volcanic ash (bentonite) samples from the Nassumaa-825 and Orissaare-859 sections were analysed by the X-ray fluorescence method. Twenty of these samples revealed chemical signs of pure volcanogenic material, one was of mixed terrigenous-volcanogenic origin, and nine were classified as terrigenous claystones. Twenty of the bentonites were correlated, with variable confidence, with bentonites from earlier studied sections; one sample represents a formerly unknown eruption. New and earlier published bentonite correlations were used for tracing the diachronous nature of the Rumba-Velise formations boundary and for composing new isopach schemes of six Telychian bentonites.

Silurian bentonites from Sweden and the eastern Baltic are correlated using XRD analysis of sanidine composition. Identifying the same bentonite in different sections has constrained correlations between the conodont, graptolite and chitinozoan zonations. Three bentonites correlate the Cyrtograptus murchisoni Zone with the upper part of the Pterospathodus amorphognathoides Zone and both the Lower and the Upper Pseudooneotodus bicornis conodont biozones at their type locality. Thus the base of the Llandovery–Wenlock boundary stratotype can be correlated with a level in the upper part of the Cyrtograptus murchisoni graptolite Biozone. Identifying the Y Bentonite (Gotland, Sweden) in eastern Baltic drill-cores shows that the base of the Eisenackitina lagena chitinozoan Biozone is close to the base of the K. patula conodont Biozone, which is coeval with an upper part of the C. rigidus graptolite Zone. Sanidine data from the Grotlingbo Bentonite fit well with previous correlations. Some bentonites from Gotland with distinct sanidine compositions and bulk geochemistries have not yet been identified elsewhere.

The composition of altered volcanic ash of the Late Ordovician Kinnekulle bed was studied in geological sections of the Baltic Paleobasin. The composition of altered ash varies with paleosea depth from northern Estonia to Lithuania. The ash bed in shallow shelf limestones contains an association of illite-smectite (I-S) and K-feldspar, with the K2O content ranging from 7.5 to 15.3%. The limestone in the transition zone between shallow- and deep-shelf environments contains I-S-dominated ash with K2O content from 6.0 to 7.5%. In the deep-shelf marlstone and shale, the volcanic ash bed consists of I-S and kaolinite with a K2O content ranging from 4.1 to 6.0%. This shows that authigenic silicates from volcanic ash were formed during the early sedimentary-diagenetic processes. The composition of the altered volcanic ash can be used as a paleoenvironmental indicator showing the pH of the seawater or porewater in sediments as well as the sedimentation rate.

The Baltic Ordovician–Silurian sedimentary succession embodies numerous altered volcanic ash beds that are illite–smectite dominated. Only a few beds rich in chlorite–smectite are known from the Upper Ordovician Pirgu Stage of Estonia. Mixed-layer chlorite–smectite occurs commonly in low-grade metamorphic and hydrothermal environments. However, chloritic K-bentonites of the Pirgu Stage have never been buried deeply and lack signs of metamorphic overprinting. In order to understand the origin of chloritization, three distinct beds were sampled in 14 drillcores from Estonia and Latvia and analysed by means of XRD and SEM. The principal authigenic assemblage of the bulk samples consists of chlorite–smectite (corrensite) together with illite–smectite and K-feldspar. The actual mineral composition of K-bentonites though varies from sample to sample. The clay mineral assemblages range from virtually pure chlorite–smectite to illite–smectite dominated assemblages with minor or no chlorite–smectite. The proportion of chlorite–smectite in K-bentonites shows systematic lateral variations: the share of chloritic phases is highest in the shallower-water part of the palaeobasin and decreases towards the deeper part of the basin. Such regular lateral variations suggest a possible link between chloritization and the configuration of ancient palaeobasin. The present study suggests that the chloritization of primary felsic ashes occurred during early diagenesis and that it was caused by an influx of Mg-rich water probably from a marine sabkha-type environment.

A whole-pattern fitting of X-ray diffraction (XRD) patterns, including lattice-parameter and size–strain analysis, was elaborated and applied to a sample set of extant and fossil vertebrate tooth apatite. Recent and subfossil human tooth enamel and dentine, extant and fossil shark tooth enameloid, sarcopterygian and coelacanth tooth enamels were studied. As comparative materials, a modern coelacanth fish scale and a pharyngeal tooth of bony fish were used. It was found that the enamel apatite of human milk teeth had lattice parameter valuesa≃ 9.4 Å andc≃ 6.88 Å, which are close to the corresponding values of subfossil human teeth. The apatite of fossilized vertebrate teeth always has a loweralattice parameter (about 9.37 Å), while the lattice parametercappears to be more stable, being around 6.88 Å. The strain appears to be correlated with the lattice direction, being around ten times higher in the [hk0] direction. During fossilization, the strain diminished in the [00l] direction, but was random in the perpendicular [hk0] direction. The enamel tissues of vertebrates are built of two discrete crystallite series. About one-third of the human milk tooth enamel is composed of larger crystallites with dimensions of about 400 × 500 Å, and two-thirds of smaller crystallites with dimensions of about 50 × 150 Å. The latter range of dimensions is also characteristic for the crystallites forming the mineral part of human dentine and fish scales. Shark tooth enameloid is also built of two distinct series of apatite crystallites of different sizes and shapes. The larger crystallites (amounting to ∼15% of all crystallites) have approximate dimensions of 500 × 1000 Å, while the smaller ones are 400 × 500 Å. Both series are distinguishable in XRD patterns of modern, Jurassic and Devonian shark enamel.

Samples of Recent–Miocene fish and marine mammal bones from the bottom of the Atlantic and Pacific oceans and Miocene Maikop deposits (Transcaspian region) are studied by the X-ray diffraction (XRD) technique combined with the chemical and energy-dispersive (EDX) analyses. Changes of lattice parameters and chemical composition of bioapatite during the fossilization and diagenesis suggest that the development of skeletal apatite proceeds from the dahllite- type hydroxyapatite to the francolite-type carbonate-fluorapatite. It is assumed that a jump-type transition from dahllite to francolite during the initial fossilization reflects the replacement of biogeochemical reactions in living organisms, which are subject to nonlinear laws of nonequilibrium thermodynamics, by physicochemical processes according to the linear equilibrium thermodynamics.

The occurrence of black shale in deep shelf environments, chertification in shoreward carbonate facies, barite occurrences, positive δ 13 C excursions in carbonate sections and enhanced micritic limestone accumulation give evidence of a primary bioproductivity rise suggesting upwelling in the Aeronian of the East Baltic. The end-Rhuddanian onset of the rise in primary bioproductivity corresponds to the beginning of black shale formation on the deep shelf and micritic limestone formation on the shallower shelf. The bioproductivity maximum was in the mid-Aeronian, judging from the highest values of δ 13 C. Upwelling ceased and primary productivity decreased at the end of Aeronian.

A collection of subfossil specimens of Discinisca tenuis from Luderlitz, Namibia was studied by means of the X-ray diffraction (XRD) technique. Using the whole-pattern fitting procedure refined by the authors, the unit cell dimensions, crystallite dimensions, and number of strains were detected. Post-mortality alterations in shell apatite are related to mineral component content ranging from 69 to 82% in subfossil shells, as compared to 68% in shells of living species. It has been established that the lattice parameter a decreases from 9.380 to 9.370 A, while parameter c is less involved during the decomposition of organic matter. The post-mortality alteration is assumed to proceed by the subsequent recrystallization of shell apatite. Consequently, primarily elongated hexagonal prisms (150 × 370 A) turn to smaller ones (120 × 260 A), and the number of strains tends to increase.

Environmentally friendly product, calcium-silica-aluminum hydrate, was synthesized from oil shale fly ash, which is rendered so far partly as an industrial waste. Reaction conditions were: temperature 130 and 160°C, NaOH concentrations 1, 3, 5 and 8M and synthesis time 24h. Optimal conditions were found to be 5M at 130°C at given parameter range. Original and activated ash samples were characterized by XRD, XRF, SEM, EFTEM, (29)Si MAS-NMR, BET and TGA. Semi-quantitative XRD and MAS-NMR showed that mainly tobermorites and katoite are formed during alkaline hydrothermal treatment. Physical adsorption of CO(2) on the surface of the original and activated ash samples was measured with thermo-gravimetric analysis. TGA showed that the physical adsorption of CO(2) on the oil shale fly ash sample increases from 0.06 to 3-4 mass% after alkaline hydrothermal activation with NaOH. The activated product has a potential to be used in industrial processes for physical adsorption of CO(2) emissions.

The article deals with grain size distribution of the insoluble residue of Upper Ordovician carbonate rocks of the Baltoscandian Basin in the West Latvian Aizpute-41 core. Great fluctuations in mean grain size in the sections of the Pirgu (uppermost Katian) and Porkuni (Hirnantian) stages are considered as indications of eustatic sea level fluctuations, pointing to the glaciation in the Hirnantian and its prelude in Pirgu time. An alternative cause of grain size fluctuations might be the up-and-down tectonic movements. Nevertheless, the synchronicity of cessation of fluctuations with the end of the Hirnantian glaciation supports the glaciation-related reasons.

This paper describes vertical fine-scale geochemical heterogeneity of Estonian graptolite argillite (GA). GA samples from Pakri and Saka out- crop sections were collected at 20 cm intervals for chemical analysis of major and trace elements, including rare earth elements. The study indicates GA enrichment in U, V, Mo and Pb with respect to the average black shales and thus confirms the formerly reported data on GA geochemistry in general. However, the content of enriched elements and other trace metals was recorded to vary greatly across the sequences suggesting that trace metal distribution in GA is notably more heterogeneous than previously assumed. The origin of the observed complex distribution of trace elements was likely controlled by the interplay of different primary metal supply-sequestration factors/processes, such as synsedimentary redox-driven sequestration of redox sensitive elements, the provenance of clastic input, the post- sedimentary redistribution, etc.

Partly dissolved prismatic quartz crystals have been found in an Upper Ordovician volcanic ash bed of the Vasagård section on Bornholm, Denmark. Similar crystals occur also in a volcanic ash in the Adze Formation of the Aizpute core, Latvia. Although biostratigraphic data are insufficient for the correlation of these findings, the abundant occurrence of this rare form of quartz at Vasagård indicates that it can be reliably used as a correlation criterion in future studies. Partly dissolved prismatic quartz crystals were most likely formed during hydrothermal processes in the volcanic source area.