Clastic Rocks of the Basement-Overlying Proterozoic Sedimentary Sequences: Communication 1. Clay Rocks and Main Features of Lithogeochemistry

Minor elements in clay rocks, indicators of the sedimentation environment

Analysis of the bulk chemical composition of fine-grained clastic/clay rocks of a number of objects (Ai, Prikamsk and Trekhgornaya formations, Mukun Group and Ust-Ilya Formation, Starorusskaya and Vasileostrovskaya formations, clay rocks of the Lower Vindhyan and Gwalior, Bhima, Athabasca, Libby Creek groups, etc.), participating in the composition of Proterozoic sedimentary sequences unconformably overlying the crystalline basement, showed that their initial mineral composition was close to the composition of most post-Archean clay rocks. The ratio of Zr, Sc and Th in these rocks suggests that they are composed predominantly of weakly recycled material. The share of erosion products of mafic igneous rocks among the sources of their fine-grained aluminosilicoclastics was relatively small. The features of the bulk chemical composition of such clay rocks give reason to believe that the main suppliers of detrital material for them were rock complexes formed in collisional and/or riftogenic settings.

Analysis of the litho-geochemistry of fine-grained terrigenous rocks (metapelites, shales, and mudstones) of sedimentary megasequences in the Southern Urals, Uchur-Maya area, and the Yenisei Kryazh indicates that Riphean sequences in these regions are dominated by chlorite-hydromica rocks, with montmorillonite and potassic feldspar possibly occurring only in some of the lithostratigraphic units. According to the values of their hydrolysate modulus, most clay rocks from the three Riphean metamorphosed sedimentary sequences are normal or supersialites, with hydrosialites and hydrolysates playing subordinate roles. The most lithochemicaly mature rocks are Riphean clays in the Yenisei Kryazh (Yenisei Range). The median value of their CIA is 72, whereas this index is 70 for fine-grained aluminosilicate rocks from the Uchur-Maya area and 66 for fine-grained terrigenous rocks of the Riphean stratotype. Hence, at ancient water provenance areas from which aluminosilicate clastic material was transported in sedimentation basins in the southwestern (in modern coordinates) periphery of the Siberian Platform, the climate throughout the whole Riphean was predominantly humid. At the same time, the climate at the eastern part of the East European Platform was semiarid-semihumid. The K2O/Al2O3 ratio, which is employed as an indicator of the presence of petro-and lithogenic aluminosilicate clastic component in Riphean sedimentary megasequences, shows various tendencies. According to their Sc, Cr, Ni, Th, and La concentrations and the Th/Sc ratio, the overwhelming majority of Riphean shales and mudstones notably differ from the average Archean mudstone and approach the average values for post-Archean shales. This suggests that mafic Archean rock in the provenance areas did not play any significant role in the origin of Riphean sedimentary megasequences. The Co/Hf and Ce/Cr ratios of the terrigenous rocks of the three Riphean megaseqeunces and their (Gd/Yb)N and Eu/Eu* ratios place these rocks among those containing little (if any) erosion products of primitive Archean rocks. According to various geochemical data, the source of the great majority of fine-grained aluminosilicate clastic rocks in Riphean sediment megasequences in our study areas should have been mature sialic (felsic), with much lower contents of mafic and intermediate rocks as a source of the clastic material. The REE patterns of the Riphean shales and metapelites in the Bashkir Meganticlinorium, Uchur-Maya area, and Yenisei Kryazh show some features that can be regarded as resulting from the presence of mafic material in the ancient provenance areas. This is most clearly seen in the sedimentary sequences of the Uchur-Maya area, where the decrease in the (La/Yb)N ratio up the sequence of the fine-grained terrigenous rocks from 15–16.5 to 5.8–7.1 suggests that mantle mafic volcanics were brought to the upper crust in the earliest Late Riphean in relation to rifting. Analysis of the Sm-Nd systematics of the Riphean fine-grained rocks reveals the predominance of model age values in the range of 2.5–1.7 Ga, which can be interpreted as evidence that the rocks were formed of predominantly Early Proterozoic source material. At the same time, with regard for the significant role of recycling in the genesis of the upper continental crust, it seems to be quite possible that the ancient provenance areas contained Archean complexes strongly recycled in the Early Proterozoic and sediments formed of their material. An additional likely source of material in the Riphean was mafic rocks, whose variable contribution is reflected in a decrease in the model age values. Higher Th and U concentrations in the Riphean rocks of the Yenisei Kryazh compared to those in PAAS indicate that the sources of their material were notably more mature than the sources of fine-grained aluminosilicate clastic material for the sedimentary megaseqeunces in the Southern Urals and Uchur-Maya area.

The Uralian foredeep is a classical marginal structure located on the foreland of the Late Paleozoic Uralian Orogen. It is subdivided into several depressions/sedimentation basins. This paper presents the analysis of the REE and Th distribution in the Middle Carboniferous and Lower Permian clay rocks of the Yuryuzan–Sylva Depression. This structure, like other depressions of the foredeep, is made up of diverse associations of the first sedimentation cycle clastic and clay rocks, which were formed during the orogen erosion. In the (La/Yb)N–Eu/Eu* and (La/Yb)N–Th diagrams, individual and average data points are confined to the field of bottom sediments of mouths of modern rivers draining volcanic provinces. This likely suggests a homogeneous composition of orogen provenance in the Carboniferous and Early Permian.

A new scheme of the stratigraphy and correlation of the Upper Triassic–Middle Jurassic Lozovoe zone of the Crimean Mountains based on spore–pollen data, the mineral composition of clastic and clay rocks, climate and volcanic events, facies and thickness analysis, and a general paleogeographic analysis is described. It is shown that the Lozovsky zone is not a tectonic melange. The complex structural–facies pattern is explained by consedimental tectonics, the presence of at least two olistostrome complexes in the sequence, and subsequent diverse deformations.

Research subject. Clay rocks of the Lower, Middle, and Upper Riphean (respectively, the Burzyan, Yurmatau, and Karatau groups) of the Western slope of the Southern Urals. Changes in their characteristic values of a number of ratios of oxides and some trace elements that are indicators of rock composition in provenances are considered, taking into account the breaks of different duration present in the Riphean stratotype. Methods. Calculation of t he average values of TiO2/Al2O3, Th/Sc, La/Co and (La/Yb)N, typical for shales, fine-grained clay siltstones, and mudstones of the main lithostratigraphic units of the Riphean stratotype (formation and, in some cases, subformation) and analysis of their changes taking into account the hiatuses known in the Riphean stratotype (Pre-Mashak/Pre-Zigalga, Pre- Zilmerdak, Pre-Minyar, Pred-Uk). Results. It was established that throughout the entire Riphean, regardless of breaks in sedimentation, presumably associated with certain transformations in the areas of erosion and sedimentation, a number of lithogeochemical characteristics of fine-grained clastic rocks of the Burzyan, Yurmatau, and Karatau groups (such as TiO2/Al2O3, Th/Sc, La/Co, and, to a significant extent, (La/Yb)N) practically did not experience significant changes. Conclusions. The data obtained give reason to think that there were no fundamental changes in the composition of the sources of fine-grained aluminosiliciclastics for the Riphean sedimentary sequences for more than 1 Ga, and contradict the rather active scenario of tectonic processes at the end of the Early Precambrian and the entire Late Precambrian. Conversely, the data on the values of tNd(DM) and eNd(t) in 37 samples of clay rocks of the Riphean stratotype nevertheless reflect a change in the composition of the rocks of the feeding provinces and, one way or another, fit into the outline of subglobal events established by conventional geological methods in the stratotype area of the Riphean. In accordance with them, in the Ai and Mashak times, an increase in the proportion of juvenile material took place in the areas of erosion. Apparently, the Pre-Zilmerdak hiatus also led to the appearance of a significant proportion of basic igneous rocks among the rocks of the provenances.

Detrital composition and sedimentary provenance of Early Carboniferous Al-bearing rock series in central Guizhou

Research subject. Sandstones and clay rocks of the Lower, Middle, and Upper Riphean (the Kyrpino, Serafimovo, and Abdulino groups, respectively) of the Kamsko-Belsk aulacogen. Changes in the characteristic values of the ratios of a number of oxides and some trace elements that are the indicators of rock composition in paleowatersheds are considered, taking the hiatuses of different nature and duration into account. Methods. An analysis of the average values of K2O/Al2O3 etc., Th/Sc, La/Co and (La/Yb)N, characteristic of sandstones and fine-grained clastic rocks (shales, fine-grained clayey siltstones and mudstones) of the main lithostratigraphic units of the Riphean section, as well as an analysis of their changes given the position below and above the break surface. Results. Throughout the entire Riphean, regardless of breaks in sedimentation associated with certain rearrangements in the recharge and sedimentation areas, the lithogeochemical characteristics of both sandstones and fine-grained clastic rocks (K2O/Al2O3, TiO2/Al2O3, Th/Sc, La/Co, etc.) were found to experience no signi ficant changes. Conclusions. The hiatuses presented in the Riphean section of the Kamsko-Belsk aulacogene were unlikely to have any significant effect on the average values of a number of ratios–indicators of rock composition in paleowatersheds (K2O/Al2O3, SiO2/Al2O3, TiO2/Al2O3, Th/Sc, La/Co, and (La/Yb)N) in sandstones and clay rocks occurring below and above the hiatus surfaces. This suggests that there were no cardinal changes in the composition of rocks in the paleowatersheds surrounding such a large negative structure as the Kamsko-Belsk aulacogene during the Riphean. Similarly, no fundamental changes occurred in the pathways of clastics entering the sedimentation area associated with the named structure.

古元古代北辽河群浪子山组变质沉积岩系主要分布在辽宁省鞍山市、海城市、辽阳市一带，其岩石组合以石英岩、片岩、千枚岩、变粒岩夹大理岩、透闪岩等为主，原岩恢复为砂岩、泥质砂岩、泥岩、泥灰岩等。前人将其置于北辽河群底部。通过对南北辽河群各组进行了详细的地质调查和分析对比工作，依据岩石组合特征和锆石年代学数据，笔者认为浪子山组应与南辽河群盖县组层位相当，故浪子山组不宜置于辽河群底部而应重新厘定为北辽河群顶部。The Paleoproterzoic clastic rocks are widely distributed in the southern portion of Liaoning prov-ince, grouped as the Langzishan Formation of the North Liaohe Group. The Langzishan Formation, previously defined as the bottom of the North Liaohe Group, mainly consists of sandstone, shaly sandstone, clay rock, siltstone interbedded with limestone, and argillaceous limestone. They were metamorphosed to be quartzite, schist, phyllite, marble, and tremolite rocks. Based on detailed field investigation, integrating with zircon U-Pb data, we proposed that the Langzishan Formation is equivalent to the Gaixian Formation (top of the South Liaohe Group). The Langzishan Formation should be grouped into the upper clastic sequence of the North Liaohe Group, but not the bottom as previous consideration.

<p>The Republic of Serbia wishes to evaluate the various options for disposal of radioactive waste and used sources. The evaluation is supposed to be based on international solutions for radioactive waste, the current and future waste inventory of Serbia, and the various possible solutions for final disposal. A high-level assessment of the geological situation in Serbia, as well as an initial screening for suitable host rock material, is inherently included in such an evaluation, and is the aim of the current work.</p><p>Based on available information such as orohydrographical and morphostructural maps, the 1:300.000 geological map, individual but undisclosed 1:100.000 geological mapsheets, the 1:500.000 neo-Alpine tectonic map of Serbia, seismic hazard maps for different return periods, and various scientific publications dealing with the geological and tectonic evolution of Serbia and surroundings, several initial recommendations can be formulated that will support and assist the decision-making process in finding a suitable site (and host rock).</p><p>Roughly, the territory can be divided into two different regions with contrasting tectonic behaviour. South of the Danube, the relief intensity is significant and mountain massives with altitudes up to 2000 m and more are present. The most important morphostructural units include the Dinarides, the Vardar Zone, the Serbo-Macedonian Massif and the Carpatho-Balkanides. This region is characterised by outcropping and subcropping material that underwent significant deformation during various tectonic pulses in the past, resulting in a vast area with rather impermeable meta-sedimentary and metamorphic rocks. Neo-Alpine tectonics from the Oligo-Miocene onwards resulted in significant vertical uplift of the southern massifs, this pattern being interrupted by isolated and closed subsiding depressions. Throughout the region south of the Danube, magmatic rocks of various age, type and composition can be found, which are elsewhere being considered in international solutions for geological disposal. The same is valid for the previously mentioned meta-sedimentary and metamorphic rocks, which include flysch sequences, and several schist and gneiss occurrences.</p><p>North of the Danube, the Pannonian Basin is characterised by significant subsidence, up to several thousand meters since the Oligo-Miocene. The basin is filled with continental clastic deposits, with several prominent clay occurrences of sufficient thickness and depth. Clay rock and (plastic) unlithified clay are often being considered in international solutions for geological waste disposal.</p><p>The neo-Alpine tectonic map indicates the presence of numerous faults: gravitational, reverse and strike-slip. Quite a number of these have shown significant activity in the Pliocene and Quaternary, most notably those that mark the boundary between outcropping massifs and subsiding areas (e.g., between the Carpatho-Balkanides and the marginal part of the Pannonian Basin). Near those faults, historical seismic activity has been recorded with magnitudes up to M = 6.5. Seismic hazard seems to be highest in the central and southern part of the country.</p><p>In summary, this short geological reconnaisance of Serbia suggests that basic geological knowledge is available that will help evaluating the various disposal options, both in terms of host rock material (thickness and depth) and a stable geological environment.</p>

Base on the observation on the core of the Upper Ganchaigou Group of Youshashan Oilfield in Qaidam Basin (N1) and the analysis into the sedimentary background and structure, as well as previous foundings, the Neogene Period in the River Delta can be found as a-shallow lake deposition environment. The Upper Ganchaigou group in the study area is dominated by sandstone, siltstone, clay rock and little carbonate rocks. The sedimentary structures are rich, and it mainly includes: gutter cast (pocket structure), scour surface and truncated structure, hummocky cross-bedding, lapped bedding, wave bedding and so on. By summing up the above characteristic, this area is thought to have the characteristics of storm deposits, and in accordance with the storm sedimentary sequence, a sedimentary model is established.

The purpose of the research. This research aims to study the lithostratigraphy and geologic evolution of the Kurrachine Dolomite Formation in the middle Triassic along the Palmyrian Belt Zone in Syria. Studying this formation in its northern and southern parts has shown that it consists of two lithostratigraphic members, where each of them includes a series of lithological units. The petrographical study of the components of these units shows that they are composed of four distinguished components: dolomitic limestones, clayey limestones, clay and anhydrites, pure or mixed and deposited in repeated harmonic layers, gathered mostly in neutral sedimentary sequences. The relevance of the research. This scientific research can provide information about the sedimentary evolution and stratigraphic succession of the region and its historical development. In addition, it can provide insight into the relationships between different sedimentary layers, and mineral resources available in the basin and their potential for exploitation. This research can also lead to a better understanding of the ancient environment in the region. Research methodology. Data was collected from a range of sources, including geological maps and cross-sections, drill core log data from nine gas wells in the field, field observations, and published research. The study area was divided into different lithostratigraphic units, and the geology of each was studied in detail. Attention was paid to the lithology, hydrocarbon content, structural features and other features of each unit. The data collected was then used to construct a geological history of the region, including its tectonic, sedimentary, and paleogeographic evolution. This information was then used to make inferences about the regional stratigraphic framework, as well as to make predictions about future geological evolution. Results and conclusions. This article focuses on the lithostratigraphy, as well as the geological evolution, of Triassic rocks, specifically the Kurrachine Dolomite Formation in the Northeastern Palmyride Basin of Syria. Laboratory studies were conducted to explore the lithology and sedimentary facies of the formation. Results show that the Kurrachine Dolomite Formation is dominated by deposits of a limited lithological nature. It is limited to calcareous, limestone, dolomitic limestones, dolomite, shale, and clay rocks, with limited intrusions of anhydrite in the upper part. The sedimentary environment of the formation is interpreted as shallow-marine. All analysis reveals that the Kurrachine Dolomite Formation is mainly composed of Middle Triassic deposits. This indicates a change in the sedimentation dynamics in the Palmyride Basin during the Middle Triassic. The results of the study provide a better understanding of the geological evolution of the Palmyride Basin in Syria.

Elastic moduli of clastic rocks with a load-bearing clay framework, such as shale and mudstone differ from other clastic rocks. The small platelets of the clay framework have a large surface area and high reactivity with the saturating fluid. A change in fluid saturation affects the elastic moduli and mechanical strength of the clay framework. Rock physical models of clay borne rocks attempt to account for the fluid sensitivity and, if possible, relate changes in elastic moduli to mechanical strength predicting the stability of shales for instance. Rock physical models proposed so far postulates a continuous matrix medium perturbed by a complex pore-structure. The mineralogy of the clay defines the background medium and the pore-space causes the observable moduli of a specific sample. We argue that a clay framework is closer to a granular assembly of individual grains than a continuous solid frame. As such, the interactions between fluid and solid clay can affect the solid structure itself. Therefore, any background medium assumed comes to depend on both the solid mineralogy and the saturating fluid. We demonstrate the sensitivity of the solid frame to the saturating fluid in compacted clay powders. We normalize elastic moduli measured in compacted clay powders to a load-bearing solid cross-section using the iso-frame model. Comparing the moduli of the solid framework in the dry and brine-saturated states shows that brine saturation does affect the solid structure. Brine saturation decreases the elastic shear modulus of the framework while increasing the elastic bulk modulus. This moduli change is associated with the solid clay and not the pore-space. We interpret the change as water coating of the clay platelets affecting interplatelet contacts.

Flint clay is defined as a sedimentary, microcrystalline to crystalline clay (rock) composed dominantly of kaolin, which breaks with a pronounced conchoidal fracture and resists slaking in water. Additional ceramic (refractory) properties are implied, but not expressed, in the definition. Flint clay first given recognition in the U.S.A., has been observed on all continents; it will probably be found to be more abundant than its occurrences reported to date. It occurs in rocks mainly Carboniferous or Cretaceous in age, and is invariably associated with plant- or coal-bearing measures.The environment of deposition is commonly lowlying paludal, in basins in either clastic silicate rocks or in karstic carbonates. It is inferred that parent illitic and/or kaolinitic clay colloids were transported into the swamps and there under-went further dialysis, alteration, and eventual crystallization in situ, producing a notably homogeneous kaolinite clay possessing interlocking crystallinity. Some occurrences were further desilicated to high-alumina minerals, particularly to diaspore and boehmite.Flint clay is interpreted as being an intermediate member of a so-called flint-clay facies which is a claystone sequence ranging from high-alumina minerals (or potentially so) formed on the highest part, structurally and/or topographically, of the depositional area, and grading down-structure and/or lower in elevation through flint clay to iliite-kaolinite plastic clay and thence to marine illitic shale, all being equivalent stratigraphically. The geochemical reactions are depotassification of parent clay by substitution of K+ by H+, and desilication, especially where high-alumina minerals are formed.

Late Quaternary sediment fluxes from tropical watersheds