Geochemical Signatures of Karlad Lake Sediments,North Kerala: Source Area Weathering and Provenance

In the present study, the lake floor sediments of the Karlad lake, located at higher elevation in Wayanad region of north Kerala, were analyzed for textural characteristics, organic matter, calcium carbonate, major oxides and trace elements. This study was carried out to infer the chemical composition, provenance and intensity of chemical weathering of the source rocks in the lake catchment area. Textural studies signify that lake floor sediments are predominantly as clays (38.75%) followed by sand (36.36%) and silt (25.19%) fractions. The C/N ratio of the lake sediments signify that the sediments are both autochthonous and allochthonous in origin. The major oxides average content reveals the order of abundance as follows; SiO₂ > Al₂O₃ > Fe₂O₃ > TiO₂ > MgO > CaO > K₂O > P₂O₅ > Na₂O > MnO. Moreover, the various weathering indices such as Chemical Index of Alteration (CIAAvg. 93.5%), PlagioclaseIndex of Alteration (PIA- Avg. 95.6%) and Chemical Index of Weathering (CIW- Avg. 95.76%) suggest an intense chemical weathering of the source area. The A-CN-K diagram is also corroborating the same. Various provenance discrimination diagrams reveal that the sediments are derived from the mafic source rocks.     

Geochemical characteristics of modern river sediments in Myanmar and Thailand: Implications for provenance and weathering

The elemental composition of organic matter and the major and trace element compositions of stream sediments from Myanmar (Ayeyarwady and Sittaung rivers) and Thailand (Mekong and Chao Phraya rivers, and their tributaries) were determined to examine their distributions, provenance, and chemical weathering processes. Higher total organic carbon (TOC) and total nitrogen (TN) contents in the finer grained sediments indicate hydrodynamic energy may control their distributions. TOC/TN ratios indicate inputs of both aquatic macrophyte and higher vascular plant material to the river sediments. The major element abundances of the sediments are characterized by predominance of SiO₂ in coarser fractions and a marked negative correlation with Al₂O₃, representing primary grain size primarily control on SiO₂ content. Marked depletion of most labile elements (Na₂O, CaO, K₂O, Ba and Sr) relative to UCC (upper continental crust), indicate destruction of feldspar during chemical weathering in the source area or during transport. However, enrichment of some high field strength elements (Zr, Th, Ce and Y) relative to UCC and higher Zr/Sc ratios indicate moderate concentration of resistant heavy minerals in finer-grained samples. Discriminant diagrams and immobile trace element characteristics indicate that the Mekong, and Chao Phraya river sediments were largely derived from felsic sources with compositions close to typical rhyolite, dacite/granodiorite, UCC, I- and S-type granites. Relative enrichment of ferromagnesian elements (e.g. MgO, Cr, Ni) and high Cr/V and low Y/Ni ratios in Ayeyarwady and Sittaung sediments indicate the presence of a mafic or ultramafic component in their sources. The ICV (Index of Compositional Variability), CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), α^Al, Rb/Sr and K₂O/Rb ratios indicate that the Ayeyarwady and Sittaung sediments record low to moderate degrees of chemical weathering in their source, compared to moderate to intense chemical weathering in the Mekong and Chao Phraya river basins. These results are compatible with existing major ion data for river waters collected at the same locations.     

Weathering and anthropogenic influences on the water and sediment chemistry of Wular Lake,Kashmir Himalaya

This paper presents a study on the Wular Lake which is the largest fresh water tectonic lake of Kashmir Valley, India. One hundred and ninety-six (196) water samples and hundred (100) sediment samples (n = 296) have been collected to assess the weathering and Anthropogenic impact on water and sediment chemistry of the lake. The results showed a significant seasonal variability in average concentration of major ions being highest in summer and spring and lower in winter and autumn seasons. The study revealed that lake water is alkaline in nature characterised by medium total dissolved solids and electrical conductivity. The concentration of the major ion towards the lake central showed a decreasing trend from the shore line. The order of major cations and anions was Ca²⁺ > Mg²⁺ > Na⁺ > K⁺ and HCO₃ ^? > SO₄ ^2? > Cl^?, respectively. The geochemical processes suggested that the chemical composition lake water is mostly influenced by the lithology of the basin (carbonates, silicates and sulphates) which had played a significant role in modifying the hydrogeochemical facies in the form of Ca–HCO₃, Mg–HCO₃ and hybrid type. Chemical index of alteration values of Wular Lake sediments reflect moderate weathering of the catchment area. Compared to upper continental crust and the post-Archean Shale, the sediments have higher Si, Ti, Mg and Ca contents and lower Al, Fe, Na, K, P, Zn, Pb, Ni, Cu content. Geoaccumulation index (Igeo) and US Environmental Protection Agency sediment quality standards indicated that there is no pollution effect of heavy metals (Zn, Mn, Pb, Ni and Co).The study also suggested that Wular Lake is characterised by both natural and anthropogenic influences.     

Diatoms,spatial distribution and physicochemical characteristics of the Wular lake sediments,Kashmir valley,Jammu and Kashmir

Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to understand the source of organic carbon (terrestrial or in situ) in lake systems in order to monitor the health of the lake. Wular lake, located in north Kashmir, is one of the largest fresh water lake in India, situated at an average elevation of 1580m ASL. The lake is fed by a number of watersheds that bring a diverse type of sediments and organic matter and thus deposit them into the Wular lake basin. In order to understand sediment distribution pattern, content and source of organic matter, sediment provenance and the persisting environment in the Wular lake, 32 lake floor sediment samples covering the entire lake were collected and analyzed for organic element analysis, CaCO3, organic matter, sediment texture and diatom analysis. The results indicated that sediments in the lake are dominated by silt and silty clay. The organic carbon in the lake ranged from 0.83%-4.52% and nitrogen varied from 0.06%-0.5%. The Carbon to Nitrogen (C/N) ratios (9.04 to 22.03) indicate a mixed source of organic carbon but dominated by in situ lake sources from the vascular and lake biota accumulation. The diatom analysis revealed the occurrence of a diverse type of species along the sampling sites present within the lake. The wide distribution of the diatom species such as Cymbella, Cyclotella and Tabularia etc. in the lake indicate high organic pollution and alkaline fresh water environment prevailing in the lake.     

Evaluation of environmental status and geochemical assessment of sediments,Manasbal Lake,Kashmir, India

The present study was conducted on the Manasbal Lake (34°14′N: 74°40′E) to assess the geochemical characteristics of the lake bottom sediments, its environmental implications and its response in the local catchment area. This study tracks the spatial distribution of grain size, geochemical analysis, C/N ratio, calcium carbonate (CaCO₃) and organic matter (OM) of the lake bottom sediments. It is observed that the clay fraction (49.79%) is predominant in the lake bottom sediments, followed by silt (35.88%) and sand (14.33%) and its spatial distribution is controlled by water depth. Geochemistry and normalized diagrams for the major oxides and trace elements reveal enrichment of CaO, K₂O, P₂O₅, S, Cl, Ni, Zn and Sr. Chemical index of alteration (CIA) reflects low to moderate weathering intensity and near compositional similarity with the bedrock exposed in the catchment area around the lake. Environmental indices (EF, Igeo) suggest that the sediments are enriched in Cu, Ni, Zn, Cr, Co, Pb followed by Mn content. Pollution load index (PLI) reveal that all the sampling sites reflect low to moderately polluted category except for few stations that are towards the southern and southeastern side of the lake. OM (16.85%), CaCO₃ (14.04%) and C/N ratio (15.5) of the lake bottom sediments is attributed to high organic activity within the lake, shell fragments, contributions from the lake flora and fauna adhering to the clayey silty sediments. The C/N ratio of 15.5 suggests a mixed source of organic matter both terrestrially and in situ formation within the lake. Sulphur and chlorine are high amongst the trace elements suggesting anthropogenic detritus input into the lake and this is due to the chemical fertilizers from the agricultural runoff and organic load into the lake. Thus, the present study suggests that in order to preserve the pristine lake ecology and the environment; continued monitoring and restoration efforts need to be undertaken.     

Geochemistry of sandstones from the Neoproterozoic Jinshanzhai Formation in northern Anhui Province, China: Provenance, weathering and tectonic setting

Sandstones from the Neoproterozoic Jinshanzhai Formation in northern Anhui Province, China, were analyzed for major oxides and trace elements to infer their provenance, the intensity of paleo-weathering of their source rocks and the depositional tectonic setting. Diagrams of (SiO2/20)-(Na2O+K2O)-(MgO+TiO2+FeO*), TiO2-Ni, Th-Hf-Co, Hf-La/Th and some ratios of elements indicate that felsic rocks constitute the source rocks in the provenance. The values of Chemical Index of Alteration (CIA) are low, which are considered to be affected by K-metasomatism. Whereas the high CIW (Chemical Index of Weathering) values indicate intensive weathering of the source material. Plots of sandstones on bivariate and triangle discriminant diagrams, as well as ICV (Index of Compositional Variation) values revealed that they were deposited on a passive continental margin or in an intra-plate basin. Our recent study, in combination with previous studies and the research progress of the Rodinia super continent, demonstrated that the convergence and extension of the Rodinia super continent were preserved by twice extension as expressed by petrological variation of the southeastern margin of the North China Craton (NCC) during the Neoproterozoic.     

Provenance and weathering history of the maastrichtian shale member of the Patti Formation,southern Bida Basin,Nigeria

The present study is focused on the geochemical characterization and provenance of the shale member of the Maastrichtian Patti Formation which is well represented at the centre of the southern Bida Basin in Nigeria. The major element composition of the studied shales and clays compare favourably with the reference shales, however, the trace elements vary slightly. Application of binary plot of TiO₂ versus Al₂O₃ and Al₂O₃/TiO₂ ratios of the studied shale samples show mixed mafic to felsic igneous sources. The chemical composition (plot of SiO₂ versus Log (K₂O/Na₂O) indicates active to passive continental margin province, however, a minor derivation from recycled provenance is probable. Intense chemical weathering based on the high values of Chemical Index Alteration (CIA), Chemical Index of Weathering (CIW) and Zr values obtained from the shale and clay samples a warm humid condition is suggested. The high values also probably suggest predominance of clay minerals and low feldspar. This is supported by the XRD (X-Ray Diffractometer) data which indicates predominance of kaolinite in the samples.     

Sediment and hydro biogeochemistry of Lake Nainital, Kumaun Himalaya, India

The picturesque Nainital Lake, in the Uttarakhand state of India, is one of the major tourist attractions in the northern part of India. The increasing tourism and population around these lakes are a major concern for the ecology and good sustenance of the lakes. The present study is aimed to understand the behaviour of nutrients and metals in the sediment and their association with chemical forms in the lake. The study was accomplished by studying the water, interstitial water and sediments for major oxides, nutrients and metals in the lake. The different chemical forms of phosphorus and metals in the sediments were done using sequential extraction procedures. The water chemistry (Ca + Mg:Na + K) and the sediment chemistry (CIA and Al₂O₃/K₂O) show that the rocks in the catchment area play an important role in the geochemistry of the lake. The metals in the water also show that the Tallital basin is more polluted than the Mallital basin, may be due to the influence of Bus station. The high concentration of chloride, NH₄, SO₄ and metals in the sediment water interface and the interstitial water shows denitrification, sulfidisation and sulfide oxidation in the anoxic bottom water. The sediment composition shows that the phosphorus in the water is sequestered as carbonate flour apatite, and the metals precipitate as carbonate. The geo- accumulation index shows that the metals zinc, cobalt and nickel show moderate polluted nature than other metals. In general, the lake is less affected by anthropogenic activities. The chemical processes undergoing within the lake, like sulfidisation and sulfide oxidation, oxide dissolution and denitrification and organic matter degradation play an important role in the remobilization of the metals from the lake sediments.     

Petrography and geochemistry of the Late Cretaceous redbeds in the Gan-Hang Belt,southeast China: implications for provenance,source weathering,and tectonic setting

ABSTRACT

The distinct basin and range tectonics in southeast China were generated in a crustal extension setting during the late Mesozoic. Compared with the adjacent granitoids of the ranges, the redbeds of the basins have not been well characterized. In this article, provenance, source weathering, and tectonic setting of the redbeds are investigated by petrographic and geochemical studies of sandstone samples from the Late Cretaceous Guifeng Group of the Yongchong Basin in the Gan-Hang Belt, southeast China. Detrital grains are commonly subangular to subrounded, poorly sorted, and are rich in lithic fragments. The variable pre-metasomatic Chemical Index of Alternation (CIA* = 62–85), Chemical Index of Weathering (CIW = 70.90–98.76, avg. 85.62), Plagioclase Index of Alteration (PIA = 60.23–98.35, avg. 79.91), and high Index of Compositional Variability (ICV = 0.67–3.08, avg. 1.40) values collectively suggest an overall intermediate degree of chemical weathering and intense physical erosion of the source rocks, but a relatively decreased degree of chemical weathering during the late stage (Lianhe Formation) of the Guifeng Group is observed. Several chemical ratios (e.g. Al₂O₃/TiO₂, La/Th, Cr/Th, Th/Sc, Zr/Sc) also suggest a dominant felsic source nature, significant first-cycle sediment supply, and low sedimentary recycling. Such features are consistent with active extension tectonic setting. Sandstone framework models and geochemical characteristics suggest the provenance is related to passive margin (PM), active continental margin (ACM), and continental island arc (CIA) tectonic settings. Sediment derivation from the Neoproterozoic metamorphic rocks and Silurian–Devonian granites indicates a PM provenance, whereas sediments derived from the Early Cretaceous volcanic-intrusive complexes suggest an ACM and CIA nature. Therefore, the Late Cretaceous redbeds were deposited in a dustpan-like half-graben under the back-arc extension regime when southeast China was possibly influenced by northwestward subduction of the Palaeo-Pacific plate beneath East Asia.     

Mineralogy and geochemistry of sediments from Simbock Lake,Yaoundé area (southern Cameroon): provenance and environmental implications

Two cores of sediments, named NR and EB, were collected in the Simbock Lake (Mefou watershed, Yaoundé) to assess their provenance and the degree of heavy metal pollution based on mineralogical and geochemical data. The sediments are sandy, sand-clayey to clayey, and yellowish brown to greenish brown, and with high amounts of organic matter (average value of TOC is 1.95%). The sediments are mainly composed of quartz, kaolinite, accessory goethite, smectite, rutile, feldspars, illite, gibbsite, and interstratified illite-vermiculite. Fourier transform infrared (FT-IR) spectroscopy shows that kaolinite is less crystallized in the NR core than in the EB core. The Index of Compositional Variability (ICV), Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and the Rb/Sr and K₂O/Rb ratios indicate a high weathering intensity in the source area. These sediments have low contents in Al₂O₃, Fe₂O₃, Na₂O, K₂O, MgO, and CaO as well as high values in SiO₂, P₂O₅, TiO₂, and MnO relative to the upper continental crust. The concentrations of Cr, V, Ba, and Zr are higher in the NR core than those in EB. The total rare earth element (REE) content varies between 78 and 405 ppm. The light REE are abundant (LREE/HREE ~?18–59; avg.?=?25.61). The chondrite-normalized REE patterns exhibit (i) negative Eu anomaly (Eu/Eu^* ~?0.38–0.62; avg.?=?0.5), (ii) slight positive Ce anomaly (Ce/Ce^* ~?1.11–1.34; avg.?=?1.11), and (iii) high REE fractionation ((La/Yb)_N ~?12.3–51.75; avg.?=?25.61). The enrichment factor (EF) shows that the Mefou watershed through the Simbock Lake sediments is slightly polluted by the agricultural and urban activities.     

Geological and geochemical examination of arsenic contamination in groundwater in the Holocene Terai Basin, Nepal

Geological and geochemical study has been carried out to investigate arsenic contamination in groundwater in Nawalparasi, the western Terai district of Nepal. The work carried out includes analyses of core sediments, provenance study by rare earth elements analyses, ¹⁴C dating, and water analyses. Results showed that distribution of the major and trace elements are not homogeneous in different grain size sediments. Geochemical characteristics and sediment assemblages of the arsenic contaminated (Nawalparasi) and uncontaminated (Bhairahawa) area have been compared. Geochemical compositions of sediments from both the areas are similar; however, water chemistry and sedimentary facies vary significantly. Extraction test of sediment samples showed significant leaching of arsenic and iron. Chemical reduction and contribution from organic matter could be a plausible explanation for the arsenic release in groundwater from the Terai sediments.     

华北北部中元古界洪水庄组页岩地球化学特征： 物源及其风化作用

华北北部洪水庄组黑色页岩是中元古代的富有机质沉积,它可能记录了当时重要的地球化学信息。通过对洪水庄组页岩中的常量和微量元素特征的分析,研究了洪水庄组的物源及其风化作用。高Th/Sc、Al2O3/TiO2、La/Sc、La/Cr、La/Co、Th/Cr和Th/Co值,低Cr/Zr和TiO2/Zr比值,Euan值、Co/Y Ti/Zr关系和La Th Sc组成表明洪水庄组页岩物源主要为上地壳中的长英质花岗闪长岩。洪水庄组页岩的Al、Ca、Na和K组成表明其具有较高的化学蚀变指数（CIA）,同时,元素组成的化学风化作用轨迹反映了洪水庄组页岩受到钾交代作用的影响,可能导致CIA值被低估,其原始CIA值应在90以上。高的原始CIA、化学风化指数（CIW）和斜长石蚀变指数（PIA）表明洪水庄组物源区经历了强烈的化学风化作用。化学风化作用强度以及微量元素组成特征揭示了中元古代洪水庄组沉积时期可能处于温暖潮湿的气候条件,这与中元古代时期大气高CO2浓度以及华北板块古大陆当时位于低纬度地区重建的结果不谋而合。     

Geochemistry of shales from the Upper Miocene Samh Formation,north Marsa Alam,Red Sea,Egypt: implications for source area weathering,provenance, and tectonic setting

The Upper Miocene shales of the Samh Formation, North Marsa Alam along the Egyptian Red Sea coastal plain were analyzed for major and selected trace elements to infer their provenance, weathering intensity, and tectonic setting. The Samh Formation consists of sandstone underlies by shale and marl intercalations. The Samh shales are texturally classified as mudstones. Mineralogically, these shales consist mainly of smectite and kaolinite, associated with non clay minerals (abundant quartz and trace of plagioclase, microcline, and halite). Compared to post-Archaean Australian shales (PAAS), the Samh shales are highly enriched in SiO₂, Al₂O₃, and Fe₂O₃ and depleted in TiO₂, P₂O₅, Na₂O, MgO, and K₂O contents. The K₂O/Al₂O₃ ratio values indicate predominance of clay minerals over K-bearing minerals. Trace elements like zirconium (Zr), Cr, Pb, Sc, Rb, and Cs are positively correlated with Al₂O₃ indicating that these elements are likely fixed in K-feldspars and clays. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and Chemical Index of Weathering (CIW) values indicate moderate to intense weathering of the source material in a semiarid climate. The geochemistry results suggest that the Samh shales were deposited in a passive margin of a synrift basin and derived from felsic (granitic) source rocks. The inferred tectonic setting for the Upper Miocene Samh shales in Marsa Alam is in agreement with the tectonic evolutionary history of the Eastern Desert of Egypt during the Upper Miocene.     

Geochemistry of Vellayani lake sediments: Indicators of weathering and provenance

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO₂, MnO, CaO, MgO, Na₂O, K₂O, and P₂O₅ content while TiO₂, Fe₂O₃ and Al₂O₃ are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO₂ is high in coarse fractions while Al₂O₃ is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area.     

Geochemistry and provenance of the Miocene sandstones of the Surma group from the Sitapahar anticline,Southeastern Bengal Basin,Bangladesh

Geochemical composition (major and trace elements) of Miocene sandstones of the Surma Group exposed in Sitapahar anticline, Southeastern Bengal Basin was determined to reveal their provenance, tectonic setting and source area weathering conditions. The sandstones are sub-arkosic, sub-lithic and greywacke in composition with abundant low-grade metamorphic, sedimentary lithics (mainly chert with some shale fragments), low feldspars and little volcanic detritus. Compared to the average sandstone value, the Surma Group sandstones are depleted in CaO and enriched in Al₂O₃, Fe₂O₃ and Na₂O. The Chemical Index of Alteration (CIA) values for the Miocene Surma Group sandstones vary from 57 to 73 with an average of 65, indicating low to moderate weathering of the source areas. The geochemical characteristics suggest an active continental margin to passive margin setting for the Surma Group sandstones; preserve the signatures of a recycled provenance that is agreement with sandstone petrography and derivation of these sandstones from felsic source rocks.     

Geochemistry of Renuka Lake and wetland sediments,Lesser Himalaya (India): implications for source-area weathering,provenance, and tectonic setting

The geochemical investigation of sediments deposited in the Renuka Lake basin and its adjoining wetland has shown variation in the distribution and concentration of major, trace and REEs. The major elements are depleted in the lake in relation to wetland and that of Post Archaean Australian, Shale (PAAS), except for CaO which is strikingly in excess and has a dilution effect on SiO₂ and other oxides and trace elements. The Wetland sediments, on the other hand, are enriched in Al₂O₃, Fe₂O₃, K₂O and TiO₂ and the latter three show a positive correlation with Al₂O₃ in both wetland and lake sediments suggesting their association with phyllosilicates and similar source rocks. The enrichment of Y, Zr, Ni, Th, U and Nb in wetland compared to lake and their similarity with PAAS in the former, suggests more clay fractions in the wetland. A high Zr/Hf ratio in wetland and lake sediments and a positive correlation of Zr with Y and HREE indicate Zr control on HREEs. However, higher Zr/Yb and Zr/Th ratios in wetland compared to lake indicate mineral sorting during the process of lighter particles (clays) being trapped in wetland soil. This is also reflected from negative correlation of Gd_N/Yb_N with Al₂O₃ and a strong positive correlation with SiO₂ in wetland sediments. The wetland in this context has a control on lake sediment chemistry. The chondrite normalized REE patterns are essentially the same for lake as well as wetland sediments but abundance decreases in the former. The similarity of pattern with that of PAAS and negative Eu anomaly indicates a cratonic source of sediments. In a plot of the individual samples, wetland samples cluster while lake samples are separated indicating fractionation of lake sediments. A strong positive correlation of La_N/Yb_N with Al₂O₃ and a positive correlation of Zr-∑LREE and Zr-La_N/Yb_N suggest that LREEs are controlled by both phyllosilicates and zircon. The chemical index of alteration (CIA) indices in lake sediments and in wetland are higher than PAAS indicating moderate chemical weathering in the source area. The petrography, lack of felsic magmatic rock fragments, and negative correlation between Zr-(Gd/Yb)_C indicate sedimentary source rocks for the detritus. This is in conformity with the Lesser Himalayan sedimentary sequence belonging to neo-Proterozoic–Proterozoic age and constituting lake catchment of Renuka. The tectonic delineation and discriminant function plots of lake and wetland sediments indicate their cratonic and/or quartzose sedimentary orogenic terrain source that has been deposited in a passive margin setting.     

Geochemistry of Hindoli Group metasediments,SE Aravalli Craton,NW India: Implications for palaeoweathering and provenance

The southeastern fringe of the Precambrian Aravalli fold belt has been designated as Jahazpur Belt, which includes two greenschist facies metasedimentary lithopackages, Hindoli (Late Archean/Paleoproterozoic) and Jahazpur (Paleoproterozoic) Groups. We present geochemical data on metapelite (phyllite) and metagreywackes from the Hindoli Group. Metapelites are enriched in alumina while metagreywackes show a wide range and higher abundance of silica. Covariance between TiO₂ — Al₂O₃, K₂O — Al₂O₃ pairs and moderate to high SiO₂/MgO ratios indicate a strong weathering control. Chemical Index of Alteration (CIA = 68 for metagraywackes; 75 for metapelites) reveals moderately weathered protoliths for them. Fractionated LREE pattern with almost flat HREE trend and moderate to high Eu anomalies (Eu/Eu* = 0.66 to 0.8) indicate feldspar bearing granite — granodiorite as probable compositions in the provenance. Very high PIA values (93) for metapelites reflect almost complete feldspar dissolution while the corresponding values for metagraywackes (68) are relatively lower. The diagnostic immobile trace elements (Sc, Zr, Th) can be interpreted as a variable felsic source (mainly granitic and subordinate granodioritic) for metagreywackes and a granodioritic (more mafic) one for metapelites. Considering the broad Precambrian geological set-up of NW India, the Banded Gneiss Complex (BGC), which predominantly comprises TTG gneisses and granites, amphibolite, etc. seems to be the most likely provenance for Hindoli sediments.     

Characteristics of major and trace elements in surface sediments of the Makran Accretionary Prism,Pakistan and their implications for natural gas hydrates

To accurately identify the natural gas hydrates (NGH) in the sea area of the Makran Accretionary Prism, Pakistan, this paper presents the testing and analysis of major and trace elements in sediment samples taken from two stations (S₂ and S₃) in the area by the China Geological Survey. As shown by testing results, all major elements are slightly different in content between the two stations except SiO₂ and CaO. This also applies to the trace elements that include Sr and Ba primarily and Cr, Ni and Zn secondarily. It can be concluded in this study that the tectonic setting of the Makran Accretionary Prism is dominated by oceanic island arc and that provenance of the Makran Accretionary Prism is dominated by felsic igneous provenance, which is at the initial weathering stage and mainly consists of granodiorite. Besides terrigenous detritus, there are sediments possibly originating from Makran-Bela Ophiolite from the northwestern part and Murray Ridge igneous rocks from the southeastern part. The V/Cr, Ni/Co, and V/(V+Ni) ratios indicate that sediments of the two stations are in an oxidation-suboxidation environment. However, the authors infer that the sedimentary environment of the sediments 3.0 m below the seafloor tends to be gradually transformed into a reduction environment by comparison with the Qiongdongnan Basin in the South China Sea where NGH has been discovered. The sediments in the Makran Accretionary Prism are rich in organic matter, with total organic carbon (TOC) content greater than 1%. According to comprehensive research, the organic matter in the sediments mainly originates from marine algae and has high TOC content, which is favorable for the formation of NGH.     

Fluxes and distribution of tetraether lipids in an equatorial African lake: Constraints on the application of the TEX86 palaeothermometer and BIT index in lacustrine settings

The distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (GDGT) lipids was studied in material from various sources in and around Lake Challa, a crater lake on the southeastern slope of Mt. Kilimanjaro (Tanzania), to examine the provenance of GDGTs in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies. The study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle, particles suspended in the stratified water column, profundal surface sediments, and soils surrounding the lake. The sediment trap time series revealed that crenarchaeol and related isoprenoid GDGTs were predominantly produced in January and February, following the locally prominent short rain season (November-December). The TEX₈₆-inferred temperature derived from sedimenting particles corresponded well with lake surface-water temperature at this time of largest crenarchaeol flux. Molecular ecological analysis showed that Group 1.1a and 1.1b crenarchaeota are the most likely source organisms of these GDGTs. GDGT-0 in the lake sediments does not only originate from lake surface-dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper, anoxic part of the water column. The main flux of branched GDGTs to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run-off. However, a contribution from in-situ production of branched GDGTs in the lake sediment or water, or in groundwater cannot be fully excluded. We conclude that palaeoclimatic reconstruction based on branched GDGT distributions in lake sediments should only be performed when the origin of those branched GDGTs is well constrained.     

Hydrogen sulfide and organic carbon at the sediment–water interface in coastal brackish Lake Nakaumi, SW Japan

The relationship among H₂S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H₂S concentrations and TOC content at the sediment water interface in a coastal brackish lake, Nakaumi, southwest Japan. In this lake, bottom water becomes anoxic during summer due to a strong halocline. Lake water has ample dissolved SO₄ ^2? and the surface sediments are rich in planktic organic matter (C/N 7–9), which is highly reactive in terms of sulfate reduction. In this setting the amount of TOC should be a critical factor regulating the activity of sulfate reduction and H₂S production. In portions of the lake where sediment TOC content is less than 3.5 %, H₂S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H₂S was correlated with TOC content (pore water H₂S (ppm) = 13.9 × TOC (%) ? 52.1, correlation coefficient: 0.72). H₂S was also present in areas with sediment TS above 1.2 % (present as iron sulfide), which suggests that iron sulfide formation is tied to the amount of TOC. Based on this relationship, H₂S production has progressively increased after the initiation of land reclamation projects in Lake Nakaumi, as the area of sapropel sediments has significantly increased. This TOC–H₂S relationship at sediment–water interface might be used to infer H₂S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO₄ ^2? and reactive organic matter.