Brown Clay Research Articles

The reconstruction of palaeoenvironment during development of the fourth palaeosol in the southern Loess Plateau of China

The fourth palaeosol (S4) of the Brunhes Epoch (780,000–0years B.P.) at Shuangzhu, Tianjiapo, and Hejiacun in the Guanzhong Plain developed over about 40ka and varies in thickness from 3.6 to 4.0m. It consists of four horizons: the first (uppermost) is a well developed red–brown clay horizon (Bts), the second is a dark yellowish-brown weathering-cracked loess horizon (Cs) with red ferruginous argillans, the third is a yellowish-brown weathering-cracked loess horizon (Cl) without red ferruginous argillans, and the fourth consists of CaCO3 nodules (Ck). The two weathering-cracked loess horizons, which are a major feature differentiating a pedocomplex from a palaeosol, have not been found previously in Chinese palaeosol. The ferruginous clay argillans are composed of montmorillonite–illite with some kaolinite minerals. The pedocomplex suggests that a moist subtropical climate prevailed between 420,000 and 360,000years in the southern parts of the Chinese Loess Plateau. Its profile is Bts–Cs–Cl–Ck–Co. When the pedocomplex was developed, the mean annual temperature and precipitation were about 16°C and 1000mm respectively, about 3°C higher and 400mm more than at present in the Guanzhong Plain. The removal depth of CaCO3 and the weathering-cracked loess layer indicate that the gravitational water reached a depth of at least 3.2m, and the moisture content in S4 would have been sufficient to sustain forest development at that time. In the typical interglacial in which S4 was developed, the Qinling Mountains lost their function as the boundary between the subtropical and temperate zones of China, and water-bearing air masses resulting in rich rainfall could frequently reach the southern Loess Plateau.

Sediment provenance and controls on slip propagation: Lessons learned from the 2011 Tohoku and other great earthquakes of the subducting northwest Pacific plate

The ∼50 m slip of the Tohoku earthquake occurred along a very fine grained red-brown smectitic clay horizon subducting in the Japan Trench. This clay, cored in the plate boundary fault at Integrated Ocean Drilling Program Expedition 345, Site C0019, correlates with similar pelagic clay recovered seaward of the trench at Deep Sea Drilling Project Sites 436 and 1149. Comparable clays occur throughout the northwest Pacific Basin. Backtracking of ocean drilling Sites 436, C0019, and 1149 indicates that they formed during the Early Cretaceous at the Kula-Pacific Ridge. These sites traveled northwestward through the equatorial zone, accumulating siliceous and calcareous oozes until ca. 100–85 Ma. Sites 436, C0019, and 1149 then entered the realm of pelagic clay deposition where they remained until ca. 15 Ma. From ca. 15 Ma to the present, Sites 436, C0019, and 1149 accumulated clays and silty clays with variable amounts of siliceous microfossils and volcanic ash, representing the transition from deep-sea conditions to a continental margin sedimentary environment. The predicted backtracked vertical sequence of sediments fits well with the cores at Sites 436, 1149, and C0019, after accounting for structural complications in the latter. Pelagic clay occurs in numerous boreholes penetrating the relatively smooth ocean floor of the Pacific plate north and northeast of the Tohoku earthquake. Here the widespread pelagic clay apparently fosters tsunami and tsunamigenic earthquakes. Seamounts rising above the normal oceanic crust accumulated sequences of calcareous sediments as their crests remained above the calcite compensation depth for most of their history. A seafloor including pelagic clay and carbonate-covered seamounts occurs south and southeast of the southern extent of the Tohoku earthquake rupture zone. This area has no historic tsunami or tsunamigenic earthquakes along the Japan and Izu-Bonin Trenches with the possible exception of the poorly located Enpo earthquake of A.D. 1677. We believe that the seamounts incoming on the oceanic plate to the south and southeast of the Tohoku rupture zone interfere with long-distance propagation of slip in the pelagic clay, limiting earthquake magnitude, shallow slip, and tsunami generation.

Lithology, fauna and environmental conditions of the Late Pleistocene raised reefal limestone of the Jeddah coastal plain, Saudi Arabia

The upper successions of the raised reefal limestone of Jeddah coastal plain, especially at Obhur area, were investigated through three temporary exposed geologic sections such as south and northeast Obhur and Al Salam Street. Uranium-series age datings of these successions indicated that their topmost parts were mostly deposited during the last interglacial marine isotope stage 5e (MIS 5e). Lithological–faunal analyses and field observations allowed the division of these successions into two distinct layers: white limestone (lower) and brown shell-rich calcareous clay (upper). The lower layer is enriched with in situ coral boulders of Porites sp. and faviids, as well as with the foraminifers Amphistegina sp., indicating deposition near fore reef and reef crest environments. The upper layer is enriched with molluscs, echinoids, branched (and dwarfed faviids) corals, and the foraminifers Elphidium striatopunctatum and Challengerella bradyi, indicating deposition in back reef, lagoonal environments. The boundary between these two layers is very sharp and irregular, suggesting that the transition from the fore reef to lagoonal conditions was very rapid and catastrophe on coral reef ecosystem due likely to sea-level changes accompanied with warming and increased water runoff. The upper surface of the shell-rich calcareous layer seems to be truncated, but its microfossils could indicate that it was deposited when the sea level was higher than the present mean sea level (MSL) by at least 7 m.

Origin of arsenic in Late Pleistocene to Holocene sediments in the Nawalparasi district (Terai, Nepal)

A sedimentological and geochemical study was carried out to explore the origin of arsenic contamination in sediments in Nawalparasi district, in the western Terai of Nepal. The investigation tools include major, trace and rare earth element analyses of core sediments, as well as 14C datings, and O, C isotopic analyses on mollusk shells. The results show that black schists from the Lesser Himalaya highly contributed to the detrital input in Parasi during the Pleistocene–Holocene transition because of focused erosion related to rapid uplift and high rainfall along the Main Central Thrust zone. In addition, aquifer silts, sands, and most of the brown clays underwent a certain degree of chemical weathering and physical reworking, and show possible inputs from the Siwaliks during the Late Holocene. A possible correlation between late Quaternary climate regimes and the concentration of arsenic in sediments is suspected, with arsenic preferentially concentrated during the drier periods of the last 25 kyr BP. The process of arsenic eluviations in sandy and silty sediments can explain the lower arsenic concentrations in sediments during humid periods. During the drier periods, seasonal precipitation was smaller and temperature was lower, leading to wet (less evaporative) soils in swampy environments. This environment favoured the development of aquatic plants and bacteria growing within in the moist land areas, enhancing the strong weathering of initially suspended load particles (micas and clays), which were preferentially deposited in quiet hydraulic environments. These sorting and weathering processes presumably allowed the arsenic to be concentrated in the finest sediment fraction.

Sedimentary signature of Hurricane Isaac in a <i>Taxodium</i> swamp on the western margin of Lake Pontchartrain, Louisiana, USA

Abstract. Compositional and geochemical profiles were established for a 59-cm sediment core extracted from a small pothole pond in a Taxodium (bald cypress) swamp 830 m inland from Lake Pontchartrain in south-eastern Louisiana, USA. The core consists of a top organic unit (peat to clayey peat) from 0–29 cm above a bottom clay unit at 30–59 cm depth. Four distinct zones, marked by gradual changes in organic content and elemental concentrations, occur in the clay unit. These changes probably reflect two cycles of slowly changing water depths. Hurricane Isaac’s signature, a brown clay band at 3–5 cm, is identified based on the stratigraphic and compositional correspondence with the storm’s event layer, documented from nearby sites. Sedimentary and geochemical similarities between this material and clastic bands at 15–19 and 23–25 cm identify those two intervals as potentially representing earlier floods. The Cl/Br ratio presents a potentially useful method for distinguishing fluvial and marine flooding.

Chocolate clays of the Northern Caspian Sea Region (distribution, position and structure)

Chocolate clays are one of the most common facies of Lower Khvalynian sediments of Northern Caspian and Lower and Middle Volga region. After more than a hundred years of research, there are still a number of unresolved issues related to the conditions of its bedding, structure, facial structure and colority. Chocolate clays are confined solely to pre-Khvalynian relief depressions: terraces, paleo down cuttings and junctions of large tributaries at river valleys, and varied in form and origin paleoravines, estuaries, saline-dome depressions (Elton Baskunchak) and ancient deflationary depressions (Kalmykia) at watersheds. Chocolate clay roofing according to the general slope of the surface of the Lower Volga and Northern Caspian gradually decreases from north to south. The highest level of occurrence of clays in the Caspian depression is usually noted at levels +20-25 m. To the north, within the valley of the Volga, clay roof rises to a level35 mand above. There are two types of chocolate clay by the pattern of its distribution: continuous and intermittent (mosaic). Continuous distribution prevails in the Volga River valley and is observed in ancient estuaries and junctions of Volga River’s major tributaries: the Large and Little Irgiz, Large and Little Karaman, Torgun etc. Depending on structure features facies (macrofacies) of chocolate clay are divided into subfacies: monoargillaceous, stratified, sand-clay and silt-clay. The most common monoargillaceous subfacies have total clay composition. It’s massive unstratified or hidden-stratified dark chocolate brown clay with a large block jointing, sometimes interbedded with lighter silt varieties.

Pelagic smectite as an important factor in tsunamigenic slip along the Japan Trench

The very large slip on the shallow portion of the subduction interface during the 2011 Tohoku-oki earthquake (M w 9.0) caused a huge tsunami along the northeast coast of Honshu, Japan. In order to elucidate the mechanics of such tsunamigenic slip, the Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project, JFAST), was carried out one year after the earthquake and succeeded in recovering rocks constituting the active plate boundary fault. Our mineralogical analyses using X-ray diffraction reveal that the shallow portion of the fault zone that caused the earthquake is significantly enriched in smectite compared to the surrounding sediments, which may be intimately linked to the tsunamigenic shallow faulting. For comparison, we also analyzed mineralogical features of incoming sediments just prior to subduction, recovered on the outer rise of the Japan Trench (Site 436, Deep Sea Drilling Project Leg 56), and found a characteristic smectite-rich horizon in the uppermost ∼5 m of the pelagic clay layer. This horizon should be mechanically weak and will become the future plate boundary fault, as observed in the JFAST cores. The smectite-rich deposits are broadly distributed in the northwestern Pacific Ocean, and may therefore potentially enhance conditions for large shallow slip during earthquakes that occur over a broad area of the Japan Trench plate boundary, which would result in large tsunamis for this region.

Geotechnical Properties of Sub- Soils in Escravos Estuary, Western Niger Delta, Nigeria

This study evaluates the sub-soil geotechnical characteristics at the onshore pipeline route at Escravos estuary, Western Niger Delta, Nigeria. Acquisition of soil samples for geotechnical studies was done by conventional boring method using light shell and auger hand rig. Samples were analyzed in the laboratory using standard analytical procedures. The samples explored showed a profile of very soft greenish dark grey and reddish brown clay formation. All samples observed confirmed this lithostratigraphy except for some of the grab samples. The entire formation generally, presents a low amount of organic content, low shear strength and high carbonate content. The unit weight showed an increase with high carbonate content. The samples gave a high amount of moisture content, higher than the liquid limit which indicates that on loading the pipeline route, the weight of the pipeline will dissipate a large amount of the pore water with a resultant increase in settlement. The pipeline should be placed on slippers pad at designated locations on the seabed along the survey route to avoid excessive settlement. This would distribute the anticipated pressure from the pipeline over a greater area and thus reduce the excessive settlement which is the characteristics of the very soft marine clay encountered in this investigation. The dimensions and bearing capacity of such slippers pads can easily be determined.

Structure and lithology of the Japan Trench subduction plate boundary fault

The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ∼7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ∼5–15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

Strength characteristics of Japan Trench borehole samples in the high-slip region of the 2011 Tohoku-Oki earthquake

The 2011 Tohoku-Oki earthquake demonstrated that the shallowest reaches of plate boundary subduction megathrusts can host substantial coseismic slip that generates large and destructive tsunamis, contrary to the common assumption that the frictional properties of unconsolidated clay-rich sediments at depths less than ∼5km should inhibit rupture. We report on laboratory shearing experiments at low sliding velocities (<1mm/s) using borehole samples recovered during IODP Expedition 343 (JFAST), spanning the plate-boundary décollement within the region of large coseismic slip during the Tohoku earthquake. We show that at sub-seismic slip rates the fault is weak (sliding friction μs=0.2–0.26), in contrast to the much stronger wall rocks (μs>∼0.5). The fault is weak due to elevated smectite clay content and is frictionally similar to a pelagic clay layer of similar composition. The higher cohesion of intact wall rock samples coupled with their higher amorphous silica content suggests that the wall rock is stronger due to diagenetic cementation and low clay content. Our measurements also show that the strongly developed in-situ fabric in the fault zone does not contribute to its frictional weakness, but does lead to a near-cohesionless fault zone, which may facilitate rupture propagation by reducing shear strength and surface energy at the tip of the rupture front. We suggest that the shallow rupture and large coseismic slip during the 2011 Tohoku earthquake was facilitated by a weak and cohesionless fault combined with strong wall rocks that drive localized deformation within a narrow zone.

Relationship of Sediment-Biochemistry, Bacterial Morphology, and Activity to Geotechnical Properties in the Central Indian Basin

Distribution of biochemical properties, morphological and functional characteristics of bacteria in the extreme sedimentary environment of the Central Indian Basin (CIB) was examined in relation to geotechnical properties and sediment texture. Interrelationships between these parameters in siliceous northern sediments were compared to southern pelagic clay to understand relationships and to appreciate mining implications. Clay impacted lipids negatively and silt positively in the south. Geotechnical properties had the opposite influence on the distribution of coccoidal and rod forms of bacteria. Rods were affected negatively by water content/porosity and positively by wet bulk density in the north suggesting their preference for deeper niches. Shear strength affected coccoidal distribution negatively in the south. Competition for labile substrates by coccoidal forms in the surface layers could also have restricted the rods to the deeper regions. Principal component analysis (PCA) further strengthened our inference that the distribution of rod forms increased with depth. Enzymatic properties of bacterial isolates also showed that the rods were able to degrade substrates like gelatin and DNA. These observations suggest that they are capable of degrading relatively more recalcitrant compounds in the deeper layers. The minor components, like the rod morphotypes and sand content, could wield a large influence on the variability of other parameters.

Boron isotopes in tourmaline as a tracer of metasomatic processes in the Bamble sector of Southern Norway

The Bamble sector of southern Norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the Sveconorwegian orogeny (~1.06 Ga). The infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of Fe–Ti oxides. Typical secondary mineral assemblages include either scapolite + apatite + amphibole + phlogopite + tourmaline, or albite + epidote + calcite + chlorite + white mica, indicating that the fluids introduced large amounts of Na, Cl, Mg, Ca, K, P, and B to the system. Metasomatic tourmalines associated with different alteration stages as identified by variations in major-element composition and initial 87Sr/86Sr were analyzed for B isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid(s). Measured δ11B values range from −5 to +27 ‰ relative to SRM-951, suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible B source reservoir. The influence of a seawater-derived component is clearly indicated by the heavy B isotope signature of tourmaline related to Al–Mg-rich metapelites. In contrast, negative δ11B values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites. On a regional scale (i.e., several km), δ11B values in tourmaline vary widely, whereas variations within a single outcrop (tens of m) are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses.

Mineral variation of incoming pelagic clay at Japan Trench

Mineral variation of incoming pelagic clay at Japan Trench

Estimating Effect of Vinasse on Sugarcane through Application of Potassium Chloride at Metahara Sugarcane Plantation

A study was conducted at Metahara Sugar Estate in Ethiopia to assess effect of vinasse disposal on sugarcane fields. The experiment was laid out in a randomized complete block design with five replications. To simulate the amount of vinasse to be disposed, three levels of potassium chloride (0, 340, and 580 kg ha-1) were tested on three different soil types (brown clay loam, black non-vertic clay and black vertic clay). Soil analysis result showed that available K in the soil was ranged from 311-547 ppm. Potassium chloride application on cane fields had nonsignificant (P<0.05) effect for cane and sugar yields. Similarly, non-significant (p<0.05) effect was found for juice K2O and leaf nutrient contents (N, P and K%). Therefore, the level of potassium chloride applied at the proposed vinasse disposal rates didn’t affect nutrient uptake, yield, and juice quality in the subsequent crop; thus at Metahara Sugar Plantation, sugarcane fields can be used as disposing site for vinasse. However, long-term effect of vinasse to sugarcane crop and dynamics of K in relation to availability and fixation in the soils of the plantation should be further investigated through vinasse application to sugarcane fields.

Using multivariate analysis and stable isotopes to assess the effects of substrate type on phytobenthos communities

For more than a century, artificial substrates have been employed in phytobenthos studies. In the present study, we compared the phytobenthos community structure in a field experiment over 3 seasons (summer, autumn, and winter) on 3 types of artificial substrates (brick, brown clay tiles, and grey clay tiles) and 3 natural substrates (macrophytes, rocks, and sediment) in a small, temperate system. A combination of multivariate analyses (cluster, multi-response permutation procedure, indicator species [IndVal], and canonical correspondence analysis [CCA]) and stable isotope analysis was used. We identified 96 total phytobenthos taxa. Artificial substrates resulted in different substrate communities, as shown by stable isotope analysis, cluster analysis, and a multi-response permutation procedure, with only those communities growing on grey tiles being similar to natural substrate communities. Overall, artificial substrates exhibited slightly higher species richness compared to natural substrates over the 3 seasons, although there were no significant differences (p> 0.05). Phytobenthos grown on brown tiles, rocks, and bricks showed seasonal variability of the carbon isotope δ13C values using one-way ANOVA (p< 0.05). Phytobenthos community structure did not show great seasonal variation; however, CCA identified water flow, conductivity, ammonium, phosphate, and water depth as important in structuring phytobenthos communities on different substrates. IndVal analysis showed that common phytobenthos taxa were not restricted to a single substrate, but preference was generally high for natural substrate, especially rocks, compared to artificial substrates. Substrate microhabitat type seems to influence the communities within the study areas.

Deposition and weathering of Asian dust in Paleolithic sites, Korea

Paleolithic stone artifacts in Korea typically occur in brown clay–silt (BCS) sequences. The origin and depositional environment of these sequences are important for reconstructing the paleoenvironment as well as for establishing chronologies of artifact-bearing stratigraphic units. We investigated four BCS-bearing sections in foothills and river and marine terraces in Korea by applying quantitative mineralogical, geochemical, microtextural, and K–Ar isotopic methods. In all four sections, the lower units are colluvial and fluvial deposits strongly influenced by diverse local lithology, whereas the upper units are characterized by BCS units. Mineralogical/geochemical compositions, grain sizes, and colors converge into common properties in the upper BCS units in all sections. These common properties are consistent with the eastward trends of increasing weathering degree and grain size fining throughout the loess–paleosol sections of the Chinese Loess Plateau (CLP). K–Ar detrital ages of the sections also converge upward into a narrow range similar to the age ranges of the loess and paleosols in the CLP. The top BCS unit in the Jeongok section, the thickest section, is underlain by an additionally weathered BCS unit, with strong red chroma indicating a change from warm to cold climate. We did not observe any clear evidence of climatic changes in other thinner sections, which may be due to a superposition of cold-stage accumulation and warm-stage deep weathering. The common properties of the BCSs in Korean sections and their relationship to the CLP loess and paleosols indicate widespread deposition of Asian dust and subsequent weathering in the late Quaternary, forming BCS sequences. In this respect, the BCS sequences investigated here are considered to be the additionally weathered equivalents of the CLP loess–paleosol sequences, having been exposed to the high annual precipitation of the Korean Peninsula. Given the wide distribution of BCS sequences at Paleolithic sites throughout the Peninsula, the findings of this study are important for the ongoing debate surrounding the depositional environments of the Paleolithic deposits, and provide a foundation for the establishment of the chronological framework of the Paleolithic artifact-bearing layers and lithic assemblages.

기장산성 집수지의 구조와 변화양상

This paper looked into the structure of and changes in the building process of Gijang mountain fortress and its receiving reservoir by analyzing data from an excavation investigation. The structure of the receiving reservoir may be classified into a flat form, stone sheath, floor facility, wall facility, and entry and exit facility. The flat form of the Gijang mountain fortress and receiving reservoir is round. Concerning the sectional form, the wall was obliquely excavated in the trapezoid. As a stone sheath building method, it was built by undertaking a range work of oblong stone materials in a clockwise direction on a stamped soil floor. Then, it was treated with stamping using double layers of gray clay and yellowish brown clay on the floor and the wall. Also, in a space between the stamped layers on the floor, herbal plants and a straw mat were laid for waterproofing as well as to prevent sinking. As an entry and exit facility, two facilities were confirmed symmetrically in the southeast and in the northwest. It is believed that they were built additionally during rebuilding after the initial construction. The building process was revealed to have been carried out in 8 stages. Given the structure and excavated remains, the building period is estimated to be the early to mid 7th century for the initial building, the later 9th to 11th centuries for the primary rebuilding, and the later 16th to early 17th centuries for the secondary rebuilding.

Mineral Chemistry of Clays Associated with the Jhilmili Intertrappean Bed in the Eastern Deccan Volcanic Province: Palaeoenvironmental Inferences and KTB Transition

Abstract Jhilmili intertrappean bed (~13 m thick) attains its significance with the recent discovery of brackish water ostrocod and planktonic foraminifera fossils (Keller et al. 2009; Khosala et al. 2009). Present XRD data revealed abundance of montmorillonite &amp;gt; montmorillonite/chlorite mixed layer &amp;gt; palygorskite in five physically distinct litho-units namely: (a) lower chocolate brown siltstone with green patches, followed by (b) brick red clayey siltstone, (c) greenish grey clay, (d) yellowish brown clay and (e) uppermost olive grey to dark brown silt layers in the succession-represent higher weathering indices and annual precipitation, reflecting cyclic, but longer spells of weathering. Occurrence of M/C mixed layer with the smectite in Jhilmili area is suggestive of their derivation from the later, whilst montmorillonite to palygorskite transformation is ascribed to the drastic changes in the humid to arid climate, where former served as a source of Al and some of the Si and Mg ions for the later. Jhilmili and Anjar clays represent similar charge occupancies at different sites, but later contains relatively higher amount of palygorskite, formed in the arid environment. Majority of the trace elemental data plots for Jhilmili clays lie within the upper and lower limits of infra (Lametas)-/inter-trappeans clays. The continuous release of Cu throughout the succession (mainly in the palygorskite dominated clays) indicates oxidizing conditions. PAAS normalized REE data plots for these clays show progressive enrichment in the HREE contents in the lower part, but, upper part of the succession is marked by positive cerium anomaly, reflecting oxidizing conditions prevailed at the later stage of the succession. These conditions continued, but, were not conducive to HREE enrichment as evidenced by their depletion in the upper part of the succession. The Ce anomaly observed in the middle part of the succession is similar to that form by continental weathering of the basalt, ascribed to Ce precipitation in the oxic environment, thus suggestive of drastic changes in the oxidizing conditions. Thermodynamic data-sets for Jhilmili clays show I/S mixed layer and celadonite compositions, whereas, Jabalpur infra-/inter-trappean clays correspond to Mg smectites and celadonite end members, thus, representing compositional commonality with those of the other clays derived from the continental weathering of basalt protolith. Jhilmili smectites and smectite-chlorite mixtures show compositional similarity with the dioctahedral and trioctahedral smectites and the smectites formed at 250ºC, having compositions between trioctahedral smectite and chlorite, thus, assigning high temperatures for their formation, where the heat required for the formation of these clays was possibly derived from the hydrothermal fluids, associated with the Deccan volcanism.

Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: δ13C evidence from laminated Ethmodiscus rex mats in tropical West Pacific

Giant marine diatoms, blooming or aggregating within deep chlorophyll maxima under stratified conditions, can generate substantial production and a large export flux of organic carbon from surface waters. However, their role in regulating glacial-interglacial variation in atmospheric pCO2 remains unclear. Here, we report the organic carbon isotopic compositions of Ethmodiscus rex diatoms (δ13CE. rex) and bulk sediments (δ13Corg) from a sediment core in the eastern Philippine Sea dated to ~19.5–31.0kyr B.P. and consisting of (from youngest to oldest) (1) laminated E. rex diatom mats (LDM), (2) diatomaceous clay (DC), and (3) pelagic clay (PC). Our results suggest that δ13CE. rex provides a better record of palaeoceanographic processes during LDM and DC deposition than δ13Corg because of reduced differential vital effects in near-monospecific E. rex fractions. We used the isotopic composition of the coarse E. rex fraction (δ13CE. rex (>154μm)) to calculate the CO2 partial pressure of eastern Philippine Sea surface waters (pCO2-sw) during the Last Glacial Maximum (LGM). Our pCO2-sw records suggest that the eastern Philippine Sea switched from being a strong CO2 source during DC deposition to a weak CO2 sink during LDM deposition. The role of the eastern Philippine Sea as a CO2 sink during the LGM was promoted by elevated primary production and, to a lesser extent, intensified water-column stratification. These observations highlight the potential role of giant marine diatoms in the sequestration of atmospheric CO2 during the LGM and, hence, support changes in biogenic silica fluxes as a potential cause of lower glacial atmospheric CO2. Our findings are consistent with an eolian source of silica, as proposed by the ‘silica hypothesis’ and the ‘silicon-induced alkalinity pump hypothesis’ but not by the ‘silicic acid leakage hypothesis.’

Podział i charakterystyka litofacjalna górnomioceńskich osadów węglonośnych w odkrywce złoża węgla brunatnego Bełchatów

W osadach gornomiocenskich w KWB Belchatow wydzielono 7 jednostek litofacjalnych. Są to utwory facji jeziornej, bagiennej i rzecznej. Wykazują one cykliczny charakter sedymentacji, na podstawie czego w rowie Kleszczowa wyrozniono 3 cyklotemy weglowe. SUBDIVISION AND LITHOFACIES CHARACTERISTICS OF UPPER MIOCENE COAL-BEARING ROCKS FROM THE BELCHATOW BROWN-COAL OPEN-CAST MINE Data gathered in the course of field works in the Belchat6w brown-coal open-cast mine made it possible to compile 6 detailed lithological columns (Fig. 1) of Miocene rocks exposed in exploitation escarpments (western wall, section N -S). Taking into account most characteristic features of the rocks there were differentiated 7 Iithofacies units, denoted with letters A-G: carbonate rocks (A), clayey sapropel coals (B), tuffogemc clays - tonsteins (C), earthy-xylith brown coals (D). clayey brown coals -coally clays (E), gray-brown clays (F), and gray sands (G). Rocks of the above lithofacies belong to the Upper Miocene brown-coal formation which represents an infill of a depressional structure called as the Kleszczow Trough. They represent sedirnents of iacllstrine, swampy, and fluvial facies, and reflect cyclic character of sedimentation, making possible identification of three coal cyc1othems. The cyelicity in sedimentation of Miocene coal-bearing series is explained as mainly due to subsidence (continuous but neither rhythmic nor unifonn subsidence of Kleszcz6w Trough floor in the Cenozoic), compensated by steady accumulation. The recorded coal cyclothems of the Upper Miocene'in the Belchatow brown-coal open-cast mine are developed as follows: - lacustrine carbonate sediments (lithofacies A) or gray· brown clays (lithofacies F); - clayey sapropel coals (lithofacies B) or gray·brown clays (iithofacies F); - earthy·xylith brown coals (lithofacies D) or clayey brown coals (lithofacies E).