Study Of Clay Minerals Research Articles

Application of Nanofibrous Clay Minerals in Water-Based Drilling Fluids: Principles, Methods, and Challenges

Nanofibrous clay minerals, specifically palygorskite (Pal) and sepiolite (Sep), have been becoming a new generation of rheological additives for drilling fluid systems due to their unique nanostructure, high performance, environmentally benign nature, and cost-effectiveness. These nanoclay minerals exhibit excellent colloidal and rheological properties in aqueous systems, even in saline and high-temperature environments. Although Pal and Sep have been employed as auxiliary rheological additives in a few cases to enhance the salt resistance of conventional water-based drilling fluids (WBDFs), these two clay minerals have not yet been used on a large scale due to a lack of understanding of their structures and properties, as well as the control of their performance. This paper presents a comprehensive review of the clay mineralogy, colloidal chemistry, rheological behaviors, and filtration properties of nanofibrous clay minerals in WBDFs, with critical comments. It also discusses the challenges and prospects for further research. This review provides new insights into fundamental and applied studies of nanofibrous clay minerals and helps promote the large-scale application of nanofibrous clay products in drilling fluids.

Study of ZnO nanoparticle-supported clay minerals for electrochemical sensors, photocatalysis, and antioxidant applications

In view of the current study's demonstration of the synthesis of clay-doped ZnO composites, we present a low-cost method for producing clay-metal oxide (clay/ZnO). Utilizing the solution combustion technique, a composite of clay/ZnO was produced utilizing citric acid as both a fuel and a complexing agent. The hexagonal unit cell structure of the created clay/ZnO may be seen using XRD patterns. The ZnO-infused clay was visible in FE-SEM micrographs as homogenous, sphere-shaped ZnO. The possible involvement of clay/ZnO photocatalytic activity in the UV-induced photodegradation of malachite green dye was investigated. The 90% degradation rate shows the composite's outstanding photocatalytic degradation capacity. The resulting substance was electrochemically analyzed using a constructed electrode in 0.1 M KOH electrolyte. It increased its sensor capabilities, which now include chemical and biomolecule sensors, and it excelled in cyclic voltammetry-based redox potential studies. To efficiently evaluate chemically synthesized NPs for electrochemical, sensing, and photocatalytic applications, this study intends to create a solution combustion procedure for the synthesis of clay/ZnO nanocomposite using urea as fuel.

Geochemistry and clay mineral studies of Jurassic sedimentary rocks from the Spiti region, Himachal Pradesh, North India

An attempt is made in the present study to unravel the provenance, paleoweathering and paleoclimatic conditions of the Jurassic (Spiti Formation) black shales and sandstones from the Spiti region, Tethys Himalaya, using multi proxy approach. The sandstones are subarkose in composition and texturally poorly sorted, subrounded to subangular in shape with moderate spheriocity. The range of the chemical index of alteration (CIA) is 55–90, recorded in the black shales strongly suggests moderate to strong chemical weathering conditions in the source area, which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in Jurassic period in the Spiti region. Geochemical studies reveal that shales are enriched in felsic elements (high SiO2, Al2O3, K2O) and depleted in mafic components (Fe2O3 and MgO).The various geochemical discriminant plots and elemental ratios (SiO2/Al2O3, K2O/Al2O3, Al2O3/TiO2, K2O/Na2O, etc.) indicate the rocks to be the product of weathering of felsic rocks. The paleoclimate in the source area seems to be mostly semi-humid. The plot of the samples on the A-CN-K ternary diagram indicates a granitic weathering trend. The X-ray Diffraction studies show that the prominent clay minerals in the Spiti shales are illite, smectite, chlorite, kaolinite and vermiculite along with quartz, muscovite, alkali feldspar, calcite and phosphatic phase.When plotted on the tectonic discrimination diagram, the samples indicate passive margin tectonic setting.

Distinct chemical and stable isotope compositions of smectite formed during steaming of Clearwater Formation oil-sands from Cold Lake, Alberta

Chemical reactions between oil-sands and injected steam or steam condensate during cyclic steam stimulation (CSS), commonly used to mobilize heavy oil and bitumen, result in decomposition of pre-existing minerals and formation of new phases including clay minerals. These changes can reduce reservoir permeability and limit hydrocarbon recovery. In this study, the chemical and stable isotope compositions of berthierine and smectitic clay minerals contained in pre- and post-steam Clearwater Formation oil-sands from Cold Lake, Alberta were analyzed to investigate how these phases were affected by CSS. Berthierine abundance in the injection-zone decreased after steaming whereas the abundance of smectitic clay minerals increased. Pre- and post-steam berthierine exhibited the same range of chemical compositions, while those of pre- and post-steam smectitic clay minerals commonly differed. Some post-steam smectitic clay minerals from the steam injection-zone, in particular, contain significantly more Fe and Si but less Al than pre-steam samples. It is proposed that that berthierine contributed to the formation of new smectitic clay minerals during CCS through partial inheritance of the berthierine 1:1 structure. This inheritance model approximates the unique chemical compositions of the post-steam smectitic clay minerals. The model also helps to explain the incomplete oxygen and hydrogen isotope exchange between injection fluids and smectitic clay minerals formed during CSS.

A study of iron carbonates and clay minerals for understanding the origin of marine ooidal ironstone deposits

A detailed study of cement and matrix of ooidal ironstones of the Bakchar deposit (Western Siberia) was carried out to assess the factors influencing ore-forming processes. This research focusses on a debated issue about iron sources for Phanerozoic ooidal ironstone. Siderite, the main cementing mineral in the ironstones, is of two varieties that differ in morphology, chemical and isotopic composition, and types of fluid inclusions. The first variety of siderite occurs either as veinlet or as anhedral cement, consisting of isotopically light carbon and oxygen (δ13C from −39.5 to −29.7‰ and δ18O from −15.2 to −5.1‰). Fluid inclusions show a relatively high homogenization temperature (170–320 °C) and methane in the gas phase, corresponding to methane-bearing hydrothermal fluids. The second variety of siderite occurs as aggregates of small crystals in the ironstone matrix and is relatively enriched in heavier stable carbon and oxygen isotopes (δ13C from −28.1 to −12.2‰ and δ18O from −28.4 to −2.1‰), suggesting its formation on the seafloor under the combined influence of methane flux and seawater. The zone of the ooidal ironstone most proximal to the most intense ore-mineralization, an area of intense diffusion of metals and methane through marine sediments, is marked by the first variety of siderite, with rare authigenic minerals, a low clay content (kaolinite, chlorite, nontronite) and a high Fe content of the smectites. The authigenic mineral associations reflect the transition from methanic (sulfate-methane transition zone) to ferruginous (iron reduction zone) through sulfidic environment. The intermediate zone is dominated by montmorillonite-illite-saponite-nontronite and the second variety of siderite. The distal zone of the ore deposit is relatively unaltered, and is marked by illite-montmorillonite (illite-smectite), with rare second variety of siderite. The ratio of 1 M phyllosilicates (kaolinite) to the main swelling 2 M phyllosilicates in the clay fraction (K/M mineral index) decreases from the proximal zone of the intense iron-mineralization to the distal zone. The trend of clay mineral changes reflects the decreasing alteration of sediment matrix away from the main iron-rich and/or carbonate-bearing fluid influx. This study shows the expected lateral and vertical variation in authigenic minerals associated with marine Phanerozoic ironstone deposits, related to variable flux of metal- and methane-bearing fluids.

Provenance, Tectonic Setting and Paleoclimate of the Bhuban Formation Exposed in Jampui Hills, Tripura Fold Belt, Tripura, India: Insights from Petrography and Clay Mineralogy

Abstract The sandstones of the Bhuban Formation (Miocene) exposed in the Jampui hills of Tripura Fold Belt, India has been studied for provenance, tectonic setting and paleoclimate using the petrography, heavy mineral assemblage and clay mineral studies. The detrital mode of the sandstones indicate that the sediments consists predominantly of detrital quartz (avg. 92.19%), with subordinate proportions of feldspar (avg. 4.55%) and rock fragments (avg. 3.25%). The provenance discrimination diagrams depict the derivation of the detritus from both plutonic and metamorphic source rocks having affinity to continental block provenance. The plots of QFR and semi quantitative weathering index of the clastics support a moderate degree of paleoweathering in the source area under humid climatic condition. The presence of zircon, tourmaline, rutile, kyanite, epidote, sillimanite and garnet in the Bhuban sandstones is ascribed to the provenance of plutonic and metamorphic rocks. Dominance of zircon in the heavy mineral assemblage and the ZTR index values (75.13% avg.) indicate towards moderate degree of maturity with long distance of transport. The study of the shale samples by XRD and SEM analyses shows the dominance of illite over kaolinite and montmorillonite. The presence of minor amount of montmorillonite may suggest the addition of tuff and volcanic ash in the sediments under alkaline environment.

Peculiar study of clay minerals with special reference to illite and their climatic significance over the past 12 decades

Peculiar study of clay minerals with special reference to illite and their climatic significance over the past 12 decades

Engineering clay minerals to manage the functions of soils

AbstractClay minerals are essential components of soil systems and understanding their role in soil structure and function is critical for soil environmental quality management and sustainable agricultural development. An in-depth study of clay minerals and the development of related materials is essential for a complete understanding and effective management of soil systems. This review is a detailed compilation of relevant studies over the past decade in this area, focusing on an overview of clay minerals and their modified materials and their regulation of soil structure and function. We focus on the direct influence of clay minerals on the physical, chemical and biological properties of soils, such as soil structure, soil fertility, plant growth, soil microbial activity and soil carbon sequestration. Finally, we concluded by summarizing the existing issues with clay mineral materials in soil improvement and by outlining potential future development trends and strategies.

Лессовидные породы на вулканическом конусе Хурай-Хобок в Тункинской впадине

The results of studying the chemical, granulometric and mineral composition of a 2.8-meter sequence of sediment layers exposed on the slope of the cinder cone of the Khurai-Khobok volcano are presented. The lower age limit of sedimentary deposits is determined by the K–Ar dating of 1.57±0.3 Ma for the volcanic cone basalts, which is consistent with the reverse magnetization of the Matuyama Epoch rocks. The lower layers are represented by clayey sands, the middle layers by layered clayey sands, and the upper layers by clayey loess-like rocks. Clay minerals of the layers are identified using X-ray diffraction analysis and scanning electron microscopy. From the results obtained, a conclusion was made about the accumulation of the lower layers in mixed subaqueous and subaerial conditions, the middle ones – in subaqueous conditions, and the upper ones – in conditions of eolian transport of material. The processing of the material was carried out in the joint laboratory of modern research methods in dynamic and engineering geology of ISU and IPC SB RAS. Studies of clay minerals were carried out using a scanning electron microscope (SEM) with an EDS spectrometer at the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences. To determine the mineral composition, samples ground in an agate mortar with alcohol were studied by powder diffraction on a DRON-3.0 X-ray diffractometer. Recording conditions: radiation – СuКα, Ni – filter, V = 30 kV, I = 20 mA, scanning step – 0.05°.

Characteristics of sandstone-type uranium mineralization in the Hangjinqi region of the northeastern Ordos Basin: Clues from clay mineral studies

The uranium deposits in the northeastern Ordos Basin are closely related to clay minerals and coal seam both in space and genesis, and the generation of kaolinite in the Zhiluo Formation is controlled by the coal seam of the Yan'an Formation. Through a systematic analysis, the clay mineral types, assemblage characteristics, and the type of fluid interactions in the uranium bearing rock series were extrapolated by a statistical approach and the drawing of a plain plane figure. By doing this, the constraints of coal seam parameters on uranium mineralization have been identified. The results show that: the dominant clay mineral assemblage in the Zhiluo Formation sandstones is smectite(S) + illite/smectite mixed layer(I/S) + chlorite(C) + kaolinite(Kao), whereas I/S + C + Kao was found in the formations’s mudstones and Kao + I/S + S + C or Kao + I/S + C + S was found in the uranium bearing sandstones. The similarity of authigenic clay minerals in the sandstones and mudstones indicates that, they experienced the same pH and temperature conditions in the early diagenesis, while the difference reflects the change in fluid type and action intensity during the mineralization stage. Since the effect of acid fluid and alkaline fluid on the lower member of the Zhiluo Formation are stronger than that of the upper member, it is speculated that the acidic fluid mainly originated from the coal seam of the Yan'an Formation during diagenesis and the alkaline fluid comes from the deep strata after late Cretaceous era. The reducing fluid produced by the coal seam of the Yan'an Formation enhanced the transformation of clay minerals. Additionally, the parameters such as the thickness of the coal seam, the number of coal layers and the distance between the coal seam and Zhiluo Formation bottom are all interrelated with uranium mineralization. By systematically quantifying the following parameters and uranium mineralization information, it is speculated that, the conditions below were the most reducing medium for the targeted sand body layer, which serves as the most suitable conditions for the precipitation and enrichment of uranium ore: 1) where the shortest distance between coal seam of the Yan'an Formation and Zhiluo Formation bottom interface is less than or equal to 10 m, 2) where the accumulated thickness of the coal seam in the Yan'an Formation ranges between 5 and 10 m, and 3) where the number of coal seam is between 4 and 10 layers. Proposal of the optimum metallogenic parameters of the underlying coal seam is of great significance for enhancing prospecting conditions in coalfield exploration areas and also improving exploration efficiency in the future.

Geochemical characteristics and geological significance of humid climate events in the Middle-Late Triassic (Ladinian-Carnian) of the Ordos Basin, central China

Many Middle-Late Triassic (Ladinian-Carnian) global and local humid climate events that impacted on global palaeontological evolution and mineral distribution have been recorded in the rocks. The lacustrine sedimentary sequence of the Yanchang Formation in the Ordos Basin in the northeastern Tethys region may be an important example of control by global humid climate events. As revealed by an established chronostratigraphic framework and the study of organic carbon isotopes, elemental geochemistry and clay minerals, the Chang 7 Member of the Yanchang Formation was deposited in the Ladinian-Carnian, and the high total organic carbon (TOC) and total nitrogen (TN) contents indicate the high productivity of the ancient lake. The observed elemental ratios (Sr/Cu, Rb/Sr and Al2O3/MgO) and high contents of mixed-layer smectite indicate humid climate events in the Chang 73 and Chang 71 members. The increases in weathering degree, surface temperature and terrigenous clastic material input indicate enhancement of the hydrological cycle driven by a warm-humid climate. The arid-wet transitions, the negative excursions of the studied organic carbon isotope and the temperature fluctuations during the deposition of the Chang 73 and Chang 71 members of the Yanchang Formation are consistent with the Carnian humid event (CHE) and Ladinian-Carnian humid interval (L-CHI). The palaeontological diversity and the development of organic shales, turbidity currents and sandy debris flows in the Chang 7 Member may represent the continental sedimentary responses to coeval global humid climate events. The isochronous eruptions of volcanoes around the Ordos Basin may have intensified the global greenhouse effect and become an important factor driving the multi-stage humid climate events in the Ordos Basin.

Raman microspectroscopic study of reference clay minerals and alteration minerals in volcanic ejecta from the 7 March 2012 phreatic eruption on Ioto Island (Iwo-jima), Izu-Bonin arc, Japan

We used micro-Raman spectroscopy to analyze volcanic ejecta from the 7 March 2012 phreatic eruption at Old Crater (Million Dollar Hole) on Ioto Island, Izu-Bonin arc, Japan, to assess the ability of this technique to identify clay and other alteration minerals in volcanic ejecta. We also analyzed five reference clay minerals (kaolinite, dickite, pyrophyllite, montmorillonite, and saponite) using the same technique. Dickite, montmorillonite, gypsum, pyrite, marcasite, quartz (α-quartz), and anatase were identified by comparison with spectra of the reference materials and published databases. These minerals occur in close spatial association with each other. Marcasite, quartz, and anatase in aliquots of the sample were not observed by a previous powder X-ray diffraction (XRD) study. The presence of dickite, montmorillonite, gypsum, quartz, marcasite, and anatase indicates that these alteration minerals were likely derived from the acidic alteration zone (150–190 °C) below the crater on Ioto Island. Our results demonstrate that Raman microspectroscopy, compared with conventional XRD, is a more sensitive technique for identifying and characterizing alteration minerals present in the volcanic ejecta. However, owing to the strong fluorescence from clay minerals during Raman analysis, the presence of other minerals in the sample may be overlooked. Therefore, the use of the two techniques in combination can be a powerful tool for obtaining a full understanding of mineral phases in volcanic ejecta from phreatic eruptions, thereby providing more accurate information on the hydrothermal conditions below volcanic craters.

Using end-member analysis to determine sediment dispersal and depositional processes on the Heuksan mud belt, southwest Korean shelf

Due to the large volume of the Heuksan mud belt (HMB), the source of the mud and the depositional processes involved have been controversially discussed over the past two decades. To illuminate the issue, an end-member analysis (EMA) was applied to the grain-size data of 74 surficial samples in order to determine the sediment dispersal pattern on the HMB. In addition, a sedimentary facies analysis was carried out to serve an interpretation of depositional processes. Five grain-size end-members (EMs) were identified. Their dominant modes are 1.4 (EM1), 2.4 (EM2), 3.9 (EM3), 5.6 (EM4), and 7.3 ϕ (EΜ5). The EM3 and EM4 are mainly found on the inner shelf, their distribution decreasing from proximal to distal. On the middle shelf, where tidal rhythmites are found, the end-member scores show a mixture of EM4 and EM5, implying that these are good proxies for tidal influence. The distribution of EM4 decreases gradually from proximal to distal, whereas the finest end-member (EM5) increases toward the distal region. It indicates the outcome of progressive size-sorting with distance from the source area. As such, EM4 and EM5 can be interpreted to have been derived from Korean rivers. Previous geochemical and clay mineral studies suggested that sediments were partly supplied from Chinese rivers. The differences between the sedimentological and geochemical results suggest that the sediments may have been redistributed by tidal currents. Consequently, the end-member modeling of grain-size distributions of sediments from the western shelf of Korea has allowed the identification of the main sediment dispersal and depositional mechanisms.

Оценка эффективности методов рентгеноструктурного анализа и дифференциальной сканирующей калориметрии при анализе глинистых минералов

Оценка эффективности методов рентгеноструктурного анализа и дифференциальной сканирующей калориметрии при анализе глинистых минералов

Etude Mineralogique Des Fractions Sableuse Et Argileuse Du Remplissage Du Gisement De Montgaudier, Charente, France

The mineralogical investigation of sand fraction of different sectors of filling of Montgaudier deposit revealed that heavy minerals are mainly composed of amphiboles and disthene in all analyzed samples. The other mineralogical species encountered appear having only a secondary role in the composition of heavy mineral processions. These minerals are: Andalusite, brookite, chlorite, epidote, garnet, pyroxene, rutile, sillimanite and sphene. The opaque minerals are relatively numerous in all the studied samples which they are in different stages of alteration, associated with other minerals presenting a fresh appearance. The light minerals consist mainly of hyaline or translucent quartz grains and milky or opalescent grains. The study of clay minerals generally showed a predominance of kaolinite in all sectors, followed by illite and chlorite. Smectite comes in only fourth place. This cortege is complemented by interstratified smectite-chlorite, which are very poorly represented. The mineralogical study of the deposits at the different parts of the layers filling of the Montgaudier deposit and the sediments in the immediate vicinity permitted to determine the origin of these deposits. Their procession is largely influenced by the geological nature of the Tardoire watershed but also of the mineralogical composition of the surrounding rock in which this cave was.

A dry polishing technique for the petrographic examination of mudrocks

A method of high-quality dry polishing is presented here, in which lubricating agents such as water, isopropyl alcohol, oils and water-based diamond suspensions are eliminated. This method has been developed to avoid various problems that arise through wet-polishing techniques, and to meet the quality requirements for high-resolution microscopy and SEM analysis. The technique has been tested on two epoxy embedded blocks using abrasive silicon carbide papers ranging from 240 (avg. grain size 58.5μm, Struers) to 2500grit (avg. grain size 8μm, Struers), but with different final polishing stages. Both methods show comparable high-quality results, with no optical relief or thermal alteration of embedded organic matter. Such methods could be applied to other rock-types that might be sensitive to the use of any kind of lubricant. The dry-polishing technique enables the high-resolution study of clay minerals and fine-grained sediments using optical and scanning electron microscopy (SEM).

Late Pleistocene–Holocene clay mineral record from the Great Rann of Kachchh basin, Western India: Implications for palaeoenvironments and sediment sources

The present study uses clay mineralogy to delineate a ∼17 ka record of palaeoenvironmental/palaeoclimatic changes in the recently uplifted palaeogulf of Arabian Sea i.e. Great Rann of Kachchh (GRK). Situated on continental margin of Indian subcontinent and flanked by Indus delta, the GRK basin has preserved continuous record of post glacial sedimentation. Clay mineral studies on two long cores (∼60 m and 50 m long) show more abundance of physical weathering products (illite and chlorite) over the chemical weathering products (smectite and kaolinite). We show that the GRK sediments depict multiple sources of sediment input. Dominance of illite-chlorite suggests GRK received sediments dominantly from the Himalayan terrain with minor contribution from adjacent regions. We present the oldest clay mineralogical signature of an interval of intensified monsoon conditions during the late Pleistocene (∼17.7–16.3 cal ka B.P.). Monsoon became stronger before ∼8.4 cal ka B.P., and whereas the mid Holocene weakening of monsoon occurred after ∼7 cal ka B.P. Despite the differences in source region and composition of clay mineral records from the GRK with northeastern and southeastern Arabian Sea, the sedimentation responded to major climatic shifts that have occurred since the LGM.

STUDY OF DEPENDENCE BETWEEN CLAY MINERAL DISTRIBUTION AND SHALE VOLUME IN RESERVOIR ROCKS USING GEOSTATISTICAL AND PETROPHYSICAL METHODS

Identify and obtain a detailed understanding of shale and its clay minerals in three segments; exploration, drilling and reservoir in the oil industry are very important. The study of the formation clay minerals in terms of depth and layers of earth is done through X-ray tests on samples taken from the reservoir which in comparison with logging requires a lot more time and cost and also can't provide continuous results because continuous sampling from the whole well is not possible. NGS (Gamma-ray Spectrometry) log is used to identify formation clay minerals that is an indicator of three radioactive elements thorium, uranium and potassium and the amount of each of these elements and according to amount of each of these elements and their ratio gives a description of clay minerals of each zone. CGR log represents the sum of two elements Thorium and potassium that are present in the shale and uranium has no effect on it. The CGR log is usually used as a shale indicator and it is an essential tool for determining the Shale volume in well logging operation. In this study the relationship between shale volume shown by the CGR log and the type of formation clay mineral was investigated. A very clear relationship between the shale volume and formation clay minerals was observed. In intervals with low shale volume the amount of active clay minerals, especially montmorillonite was higher and in intervals with high shale volume, inactive clay minerals were more. In order to investigate the spatial relation between the logging data, frequency distribution and correlation between logging data was studied. By using logging data and identifying the type of clay minerals in each zone and also the spatial correlation between logging data a suitable program for drilling and exploitation of oil fields in different areas can be proposed.

Clay mineral and grain size studies of sediment provenances and paleoenvironment evolution in the middle Okinawa Trough since 17ka

Okinawa Trough receives a large amount of fluvial sediment transported by complex oceanographic circulations, and is an ideal location for the study of paleoceanography and paleoenvironment changes. However, our knowledge of the sediment provenance and paleoenvironment evolution in the Trough during the past 17 ka is still limited. Based on high-resolution grain size, clay minerals and AMS C-14 data of the Core OKI04, we present new evidences of the provenances and paleoenvironment evolution in the middle Okinawa Trough during the last 17 ka. Our results indicate that clay-sized terrigenous sediment deposited in the middle Okinawa Trough is mainly from those rivers flowing into East China Sea and Yellow Sea (e.g., Yangtze and Yellow Rivers) and Taiwanese Rivers. Their contributions varied greatly in space and time during the past 17 ka. From 16.5 to 13.8 ka, sediment was mainly derived from the Yangtze and Yellow Rivers, with little contribution from Taiwan. From 13.8 to 5.4 ka, the contributions from the Yangtze and Yellow Rivers oscillated multiple times: low in 13.8-11.6 ka, high in 11.6-7.6 ka, and back to low in 7.6-5.4 ka, whereas the pattern of Taiwanese contribution was opposite. After 5.4 ka when the sea level was high and shoreline was far away from the Okinawa Trough, the Yangtze River and eastern Taiwanese Rivers became the main provenances. The contribution from the Yellow River decreased, which is probably because Yellow River mouth was far away from the middle Trough. Sediment grain size data show that two environmentally sensitive populations are 71-7 mu m and 7-0.5 mu m. The variation of the populations' mean grain size and content shows that the strength of Kuroshio Current was weak during 16.5-11.6 ka, and became strong in 11.6-5.4 ka, in which Tsushima Warm Current and Yellow Sea Warm Current formed around 8.5 and 6.5 ka, respectively. The strength of Kuroshio Current decreased in 5.4 ka and increased since 3.2 ka. Based on clay mineralogical analysis, we find that the kaolinite/chlorite could be used as a new effective indicator for the East Asian Winter Monsoon's evolution in the Trough since 17 ka. (C) 2015 Elsevier B.V. All rights reserved.

Triassic-Jurassic Flora of Poland; Floristical Support of Climatic Changes

Abstract Plant macroremains from five boreholes in Poland were studied. Two of them (Huta OP-1 and Studzianna) from the northern margin of the Holy Cross Mountains, yielded several taxa. In the other three boreholes determinable fos-sil plants were sporadic, albeit important. Most of the taxa from the Huta OP-1 and Studzianna boreholes are typi-cal of the European Early Jurassic (Hettangian and Sinemurian). Both localities, although close to one another, show incertae sedis, Desmiophyllum harrisii phytes and conifers (a new species incertae sedis, Desmiophyllum harrisii Barbacka et Pacyna is herein proposed), which would suggest rather wet and warm conditions. This flora is typical of the European Province of the Euro-Sinian Region. In Studzianna the Siberian elements dominate, gymnosperms, mainly Czekanowskiales, which in-dicate a drier and colder environment. The palaeobotanical data correspond to the results of clay mineral studies, in particular the kaolinite/illite ratio in the source formations. The kaolinite content confirms a decrease in temperature and a reduction in rainfall in the late Early Hettangian and the latest Hettangian in the area.