Chemical Index Of Weathering Research Articles

Provenance and weathering of sediments in the deep basin of the northern South China Sea during the last 38 kyr

Deep-sea sediments are ideal recorders for studying the provenances and relevant chemical and physical weathering of adjacent lands. Major, trace (Fe, K, Al, Ti, V, Rb, Th, and Cr), and rare earth elements (REEs), grain size, and AMS 14C ages were studied on a 4-m-long core CS11 collected from a deep basin in the northern South China Sea (SCS). Core CS11 sediments were mainly derived from southwestern Taiwan Island and transported by the southward bottom current during most of the study periods, except from 37 to 35 kyr BP, when northern Luzon inputs temporarily had influence. For the past 35 kyr, the stacked chemical weathering index (SCWI) correlated well with the worldwide Younger Dryas (YD), Heinrich 1 (H1), Heinrich 2 (H2), and Heinrich 3 (H3) events, indicating global climate control on weathering intensity in this area. However, the SCWI showed the strongest chemical weathering intensity during the low sea level at the Last Glacial Maximum (LGM) when Taiwan-derived sediments were subaerially exposed on the shelf, chemically weathered and increasingly transported to the deep basin of the SCS. The major factors influencing chemical weathering intensities for sediments in the deep basin of the northern SCS varied on different geological time scales, with climate changes on millennial scales and sea-level changes on orbital scales.

Provenance of sediments from Barra del Tordo and Tesoro beaches, Tamaulipas State, northwestern Gulf of Mexico

The mineralogy, bulk sediment geochemical composition, and U–Pb ages of detrital zircons retrieved from the Barra del Tordo (Tordo) and Tesoro beach sediments in the northwestern Gulf of Mexico were analyzed to determine their provenance. The beach sediments are mainly composed of quartz, ilmenite, magnetite, titanite, zircon, and anorthite. The weathering proxies such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA), reveal a moderate-to-high intensity of weathering in the source area. The chondrite-normalized rare earth element (REE) patterns are similar to felsic igneous rocks, with large negative europium anomaly (Eu/Eu* = ~ 0.47–0.80 and ~ 0.57–0.67 in the Tordo and Tesoro beach sediments, respectively).Three major zircon U–Pb age groups are identified in the Tordo and Tesoro beach sediments, i.e., Proterozoic (~ 2039–595 Ma), Mesozoic (~ 244–70.3 Ma), and Cenozoic (~ 65.9–1.2 Ma). The differences of the zircon age spectrum between the Tordo and Tesoro beach sediments are not significant. The comparison of zircon U–Pb ages in this study with ages of potential source terranes suggests that the Mesozoic and Cenozoic zircons of the studied Tordo and Tesoro beach sediments were derived from the Eastern Alkaline Province (EAP) and Mesa Central Province (MCP). Similarly, the likely sources for the Proterozoic zircons were the Sierra Madre Oriental (SMOr) and Oaxaquia in the northwestern Gulf of Mexico. The results of this study further indicate that the sediments delivered to the beaches by rivers and redistributed by longshore currents were crucial in determining the sediment provenance.

Denudation rates of granitic regolith along climatic gradient in Eastern China

In order to assess the impact of the monsoonal climate on denudation, physical erosion, and chemical weathering processes, we measured cosmogenic nuclides 10Be, 26Al and immobile element Zr in five granitic regolith profiles across Northeast to South China. The 10Be and 26Al concentrations are 2.98 × 104–25.20 × 104 atoms g−1 and 2.18 × 105–16.62 × 105 atoms g−1, respectively. Compiling previous depth profile data from Leymon and Beacon Heights, we find that the 26Al/10Be ratios systematically increase or decrease with the depth. Our numerical model shows that muons contributions can produce higher 26Al/10Be ratios (greater than 6.75) in both steady-state and non-steady state scenarios, which can result in underestimated burial age (initial 26Al/10Be ratio) and exaggerated denudation rates (due to non-negligible production from muons) for the application of dual-nuclide in Earth Science. The denudation rates, chemical weathering rates and physical erosion rates derived from cosmogenic nuclides and Zr are 28–45, 9–31 and 6–22 m Ma−1, respectively. Chemical weathering rates, excluding the JLN profile, comprise a large proportion of the denudation rates (greater than 50%). Despite the wide range of mean annual precipitation (MAP) and mean annual temperature (MAT), the denudation rates vary without an apparent gradient from northeast to south. However, the physical erosion and chemical weathering results show good relationships with climate, suggesting the limitation type changed from kinetic-limited in the north, to supply-limited in the south. Chemical weathering indices (chemical index of alteration, CIA and weathering intensity factor, WIF) also indicate that the extent of chemical weathering strengthens from northeast to south and increases with chemical weathering rates, but decreases with physical erosion rates.

Terrestrial records of the early Albian Ocean Anoxic Event: Evidence from the Fuxin lacustrine basin, NE China

The early Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the Tethys, Pacific and North Atlantic, but few studies have evaluated whether or not terrestrial records of OAE 1b exist. In order to identify terrestrial records of the early Albian OAE 1b and to infer possible driving mechanisms, an integrated multi-proxy study from the late Aptian to Albian in the Fuxin lacustrine basin was conducted, including thick, organic-rich black mudstones, total organic carbon (TOC), organic carbon isotopes (δ13Corg), mercury concentration (Hg) and results from pyrolysis analyses (S2, Tmax and HI). Results show three distinct short-term negative δ13Corg excursions corresponding with relatively high TOC values, which could be counterparts of the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Atmospheric CO2 concentration (pCO2) recovered from C3 plant δ13Corg compositions indicates an increasing trend in Unit C during the early Albian, and there are three short-term increases of pCO2 corresponding to the three sub-events of OAE 1b at this time interval. We infer that a trend of increasing pCO2 during the Kilian sub-event in the study area is closely related to volcanism. Continental weathering calculated using chemical weathering indices (CIA, WIP and MIA(O)) show an increasing trend during the OAE 1b interval, likely resulting from warmer and more humid conditions. Mixed sources of terrestrial plants and lacustrine plankton demonstrated by pyrolysis analyses (HI vs. Tmax and S2 vs. TOC), indicate a terrestrial contribution to the organic-rich sediments of the Kilian, Paquier and Leenhardt sub-events of OAE 1b. We suggest that a CO2-forced greenhouse effect during the early Albian might have triggered the relatively warm and humid palaeoclimatic conditions, and intensified chemical weathering that combined to create high nutrient and organic matter levels that were flushed into lakes contributing to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.

Weathering and pedogenesis of mafic rock in the Brazilian Atlantic Forest

The effects of parent material on soils tend to be stronger than those of temporal and environmental conditions that interfere with weathering and pedogenesis. The main objective of the present study was to characterize and evaluate rock weathering and pedogenesis in the toposequence of gabbro-derived soils using geochemical and micromorphological data. Four profiles were sampled from a toposequence in the highlands of the Atlantic Forest region of Rio de Janeiro, Brazil. We carried out chemical and physical characterization of samples from disturbed soil horizons, followed by soil classification. Samples from undisturbed soil horizons were subjected to mineral weathering and micromorphological analyses, and scanning electron microscopy was used for microanalyses. We determined the total content of elements (SiO2, Al2O3, Fe2O3, TiO2, CaO, MgO, Na2O, K2O, Mn, P2O5, and Zr) and calculated the following weathering indices: chemical alteration index, chemical weathering index, and weathering index scale. We observed the progressive alteration of olivine into chlorite, weathering of clinopyroxenes and plagioclase, and neoformation of clay minerals such as kaolinite and iron oxyhydroxides such as goethite and hematite. The weathering of magnetite and ilmenite resulted in hematite and leucoxene, respectively. The high quantities of Si and Al in the soil matrix and the presence of iron oxyhydroxides and nodules indicated that fersialitization was the predominant pedogenetic activity associated with soil formation. Moreover, partial hydrolysis favored the formation of 2:1 clay minerals. Other processes included eluviation and illuviation, evidenced by the micromorphological analysis that indicates clay coating on pores, cavities, and aggregates.

Provenance Characterization and Palaeoenvironmental Analysis of the Meta-Sedimentary Rocks of Sonaghati Formation, Betul District, Madhya Pradesh Using Geochemical Approach

Betul belt, ENE-WSW trending, 135 km long, prominent litho-tectonic unit exposed in the central part of Central Indian Tectonic Zone (CITZ) is composed of meta-sedimentary & meta-volcanic rocks intruded by mafic-ultramafic and granitic suite of rocks, belonging to Palaeoproterozoic to Neoproterozoic age. This belt is traversed by several ENE-WSW trending, sub-vertical ductite shear zones. The meta-sedimentary rocks of Sonaghati Formation were geochemically characterized and their geochemical composition was interpreted for provenance characterization and paleo-environmental assessment. The weathering indices including Chemical index of Alteration, Chemical index of Weathering, Plagioclase Index of Alteration and Weathering Index of Parker indicate that theses meta-sedimentary rocks have witnessed the substantial amount of weathering at the source without any evidence of potash metasomatism. The Bivariate plots using the major and trace element composition show co-linear trends, which reflect that all these samples belong to co-genetic population and the visible compositional variation could be attributed to chemical, mineralogical and textural maturity. The Sonaghati metasedimentary rocks are enriched in REE with negative Eu anomaly. The LREE enrichment varies from 122 to 174 times and that of the HREE enrichment ranges from 12 to 31 times of Chondrite indicating highly varied protoliths. The provenance characterization was attempted using the large ion lithophile elements and high field strength elements. The results show that the precursor for these meta-sedimentary litho-units are mixed source with the major contributor being felsic to intermediate and minor contribution has come from the mafic end members. These meta-sedimentary rocks were deposited in the overall semi arid climate with a sequential transition, suggesting the variable climatic conditions ranging from semi-arid to arid. The Cu/Zn, V/Cr ratios, and presence of pyrites dissemination and stringers eventually indicate the prevalence of reducing environmental conditions during the deposition of these meta-sediments.

Abrupt aridification in the upper eocene of the western Qaidam Basin, northeastern Tibetan Plateau

The Qaidam Basin in the northeastern part of the Tibetan Plateau preserves a continuous and thick Cenozoic sedimentary succession, which is of great significance to studying the aridification of inland Asia. Based on the normalized concentrations (element/Al) and chloride content records of the lacustrine sediments in deep drilling well SS9 in the western Qaidam Basin, the change in the aridity of inland Asia during the late Middle Eocene was investigated. The results show that the Al-normalized concentrations of Na and Cl, which are indicator elements of saline lake sediments, increased sharply at ~38 Ma. The peaks in the Ga/Al and chloride values indicate that the salinity of the lake was extremely high at ~38 Ma. Based on these results, the sudden decrease in the sedimentation rate, the chemical weathering index, the hematite content, and the (smectite + illite/smectite)/illite ratios, the Qaidam Basin experienced abrupt aridification during this period. The decrease in water vapor transport caused by the final retreat of the Paratethys Sea from the southern Tarim Basin may have been the main reason for the changes in the arid environment in the Qaidam Basin during the late Middle Eocene. Long-term global cooling and the uplift of the Altyn Tagh may have played a role in the background conditions.

Predicting weathering indices in soils using FTIR spectra and random forest models

Weathering indices based on the relative proportions of different chemical elements are a useful tool to investigate the degree of weathering of soils. This characterization is missing in West Azerbaijan, northern Iran, and thus the main goals of this work were to assess the suitability of different indices to determine soil weathering, and to predict weathering indices using Fourier Transform Mid-infrared (FTIR) spectroscopy and Random Forest (RF) models. Soil major elemental oxides were determined in 12 profiles by X-ray Fluorescence (XRF), and the degree of chemical weathering was characterized using various indices: Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Mineralogical Index of Alteration (MIA), Weathering Index of Parker (WIP), SiO2/R2O3, Vogt Index (V) and Chemical Proxy of Alteration (CPA). For each index, a RF model based on the FTIR spectra of the samples was optimized and calibrated. The soils showed a weak to moderate degree of weathering, and CIA, CIW, MIA and V were the most appropriate for this characterization. The constructed models showed R2 values of 0.79, 0.75 and 0.71 for MIA, CIA, and CIW, respectively. The important spectral bands for prediction were those related to the presence of smectitic clays, which indicates that weathering is related to the alteration of primary minerals and the neoformation of smectites. The predicted spatial distribution of the weathering indices showed that Typic Haplocalcids and Typic Haploxerepts are at an earlier stage of weathering compared to Haplargids and Haplocambids in the area. The combination of FTIR spectroscopy and RF models is a rapid, efficient, and cost-effective technique to predict weathering indices in large datasets when XRF data are limited.

Estimation of Pressuremeter Modulus and Limit Pressure in Weathered Granite Based on the SPT-N Value and Chemical Weathering Index: A Case Study in South Korea

A pressuremeter test (PMT) is a representative and highly reliable in situ test for assessing the stress–strain behavior of weathered granite. Its application, however, is restricted by its cost and time requirements. Many researchers have also investigated the correlations between the SPT-N value and the pressuremeter modulus (Em) and limit pressure (PL) of soils, but they have mostly focused on sand, silt, and clay and have employed simple regression analysis. In this study, equations for Em and PL were derived for weathered granite through multiple nonlinear regression analyses using a chemical weathering index that quantitatively represents the degree of weathering. Nonlinear multiple regression analyses were conducted by combining the allometric models that produced the optimal correlations between Em, PL, energy corrected SPT-N (SPT-N60), and normalized VR (Vogt’ ratio) with vertical effective stress. The obtained equations for Em and PL had higher R2 values (0.76 and 0.46, respectively) compared with the simple regression equations reported in previous studies. Because local characteristics are important determinants of the engineering properties of geo-materials, the Em and PL equations proposed in this paper are intended for use in geotechnical surveys of weathered granite in South Korea.

Habitat specificity and co-occurrence network of bacterial communities in the Xincuntun Cave, Guilin, Guangxi

<p indent=0mm>Although karst systems comprise approximately 5%−20% of the Earth’s ice-free land surface, only 10% of them have so far been explored. Karst caves are important components of karst systems and represent one of the most unique and poorly understood ecosystems on Earth. They are extreme environments in terms of nutrition deficiency, permanent darkness, and isolation from other ecosystems, and serve as a natural laboratory to study the deep biosphere. Caves are also ideal places to discover microbial dark matter such as microbial biodiversity and novel metabolic pathways and metabolites. Microorganisms in caves have been demonstrated to be involved in the dissolution and formation of minerals, biogeochemical cycles, and degradation of organic matter and thus have a fundamental role in sustaining the cave ecosystems. However, knowledge about microbial distribution, diversity, potential functions, and interactions in subsurface caves has remained limited to date particularly in different niches, which limits the utilization of microbial resources and hampers our understanding of biogeochemical processes in the deep biosphere. To address these issues, bacterial communities from seven different niches including cave wall, weathered crust, loose sediments, biofilms from the wet surface of stalagmite, biofilms from the dry surface of stalagmite, microbial mat on rock surface, and overlying soils in the Xincuntun Cave, Southwest China, were investigated via high-throughput sequencing and bioinformatics. Alpha diversities of bacterial communities significantly differed from one niche to the other. Specifically, bacterial diversity was the highest in the overlying soil, followed by those in weathering crust, sediments, wet surface of stalagmite, cave wall, dry surface of stalagmite, and microbial mat. Bacterial communities were dominated by <italic>Actinobacteria</italic> and <italic>Proteobacteria</italic> and showed high specificity for their niches as indicated by principal coordinates analysis (PCoA) and bacterial indicator groups identified by the linear discriminant analysis effect size (LEfSe) method. <italic>Nitrospira </italic>and <italic>Polycyclovoran </italic>were indicator genera on the dry surface of stalagmite. <italic>Candidatus </italic>Udaeobacter, <italic>Vicinamibacter</italic>, <italic>Bacillus</italic>, and <italic>Longimicrobium </italic>were indicator genera in overlying soils, microbial mat, sediments, and weathering crust, respectively. Redundancy analysis was conducted to investigate the relationship between environmental factors and bacterial communities. Results showed that pH, TOC, and Mg/Si (chemical weathering index) were of significance to construct bacterial communities. The pH had significantly positive association with<italic> Gammaproteobacteria</italic>,<italic> Rokubacteria</italic>, and <italic>Nitrospirae</italic>, whereas it was negatively related with<italic> Actinobacteria</italic>. TOC had a significantly positive correlation with <italic>Alphaproteobacteria</italic>,<italic> Gammaproteobacteria</italic>,<italic> </italic>and <italic>Planctomycetes</italic> and negative correlation with <italic>Acidobacteria</italic>. Bacterial interactions among different groups were analyzed via co-occurrence networks. The results indicated a high-modularity network with <italic>Gammaproteobacteria</italic>, <italic>Candidatus</italic> Udaeobacter, and <italic>Thermoleophilia</italic>, being the top-three keystone members, which may contribute to the stability of microbial network. The high proportion of positive links between nodes inferred fundamental cooperation among different microbial groups surviving under the extreme conditions in karst caves. Our results revealed habitat specificity of bacterial communities, microbial interactions, and environmental driving forces for bacterial communities in the Xincuntun Cave, enhancing our understanding of the deep terrestrial biosphere.

Sedimentary environment and provenance of sandstones from the Qadir member in the Nayband Formation, Tabas block, east-central Iran

Qadir Member of Nayband Formation, located in East of Central Iran, has developed to a great extent. Investigation of the lithofacies and sedimentary environment, resulted in identification of the deltaic and marine deposits. Based on field evidence and facies features, Qadir Member consists of two lithofacies, including carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies including Sr, Sh, Sp, St, three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies. Also, regarding the field, laboratory studies, and identification of lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member which is is under the impact of tidal currents. The chemical weathering index (71%) indicated semi-arid to semi-humid conditions and plotting the geochemical data showed the provenance of re-cycling and active continental margin and because of Chemical Index of Alteration, the weathering rate was found to be rather medium to high. The geochemical diagrams also showed a probable source of the intermediate igneous and sedimentary rocks. The active continental margin conditions for this deposit could suggest the Neotethys subduction under Iran’s plate and volcanic activity at the end of Triassic, which coincided with the early Cimmerian orogeny in Alborz and Central East Iranian Microcontinent.

Increased aridity across thePermian–Triassictransition in the mid‐latitudeNEPangea

The Dalongkou section in Xinjiang, Northwest China has preserved a continuous terrestrial Late Permian–Early Triassic sequence with well‐studied information of biota evolution and isotopic excursion. In order to know the corresponding palaeoclimatic and palaeoenvironmental evolution in this critical transition, chemical weathering indexes (chemical index of alteration [CIA], plagioclase index of alteration [PIA], and chemical index of weathering (CIW)) are analysed in high resolution across the Permian–Triassic Boundary. Results show that the declining trend of the CIA, PIA, and CIW was related to the continuous decrease of the chemical weathering in the latest Permian. The climate in the mid‐latitude NE Pangea was becoming increasingly arid in a generally greenhouse warm climate, causing widespread wildfire and turnover of the fauna and biota, coupled with the environmental deterioration expressed by the anomalies of carbon and mercury. Climatic conditions oscillated in the Early Triassic with possible intermittent rainfall and was likely affected by the strengthening of the megamonsoon. In the latest Permian–earliest Triassic, whether chemical weathering strengthened or weakened, as well as whether the climate was increasingly arid or humid, varied in the different places. The possible reasons inducing this need to be further explored.

Sedimentary geochemistry of the Weihe River sediments, Central China: implications for provenance and weathering

Modern river sediments sampled from the Weihe River, Central China, were analyzed in regard to facies, grain size, major and trace element, and rare earth element (REE). The main aim of the study was to investigate source rock provenance and paleoweathering intensity. Grain-size and outcrop analyses indicate that sediments from the Weihe River are predominantly slit (< 62 μm) and sand (62 μm to 2000 μm). Major and trace element concentrations show inverse correlations with SiO2 content and grain size. Silty sediments are enriched in REE relative to upper continental crust (UCC), whereas sandy sediments tend to be depleted. UCC-normalized REE distribution fingerprints indicate that the silt sediments are mainly derived from the Loess Plateau, while sandy sediments are mainly sourced from the Qinling Mountains. Discrimination functions and La/Th ratio and Hf abundance discrimination diagram also show that silty sediments are mainly derived from quartzose sediments, the main components of Loess Plateau, while sandy sediments are mainly derived from felsic igneous source, the main components of Qinling Mountains in the region where tributaries flow. The chemical index of alteration (CIA), plagioclase index of alteration(PIA), and chemical index of weathering (CIW) suggest that Weihe River sediments are immature and have experienced relatively minor chemical weathering. This work has an important bearing on the general understanding of the role that source rock characteristics and weathering regime have on the formation of clastic sediments in modern rivers and provides a critical baseline for which future work on the Weihe River sediments can be evaluated against.

Factors Controlling the Lower Radioactivity and Its Relation with Higher Organic Matter Content for Middle Jurassic Oil Shale in Yuqia Depression, Northern Qaidam Basin, China: Evidence from Organic and Inorganic Geochemistry.

Organic-rich oil shale with unusual lower radioactivity (expressed by GR) was found in Member 7 of Dameigou Formation, middle Jurassic (J2d7) in Yuqia depression of northern Qaidam Basin, China. In order to systematically and contrastively investigate the factors controlling the lower GR and its relation with higher organic matter (OM) content (expressed by total organic carbon, abbr. TOC), organic and inorganic geochemical analyses were performed on samples consisting of oil shale and the underlying conformable contact dark shale from Well YQ-1Y. Our study shows that GR of J2d7 oil shale is mainly derived from uranium and thorium. Compared with dark shale, oil shale is characterized by higher OY and TOC, lower GR, and clay mineral content. During oil shale deposition, the paleoclimate was relatively arid, indicated by a decreased C value and siderite content as well as an increased carbonate content and Classopollis. Under such paleoclimate conditions, sedimentary water became more anoxic, suggested by higher V/(V + Ni), pyrite content and lower pristane/phytane (Pr/Ph). From oil shale to dark shale deposition, according to analyses of Al2O3/TiO2, TiO2 versus Zr, La/Sc versus Th/Co, La/Th versus Hf, and La–Th–Sc, the felsic igneous rock could always be deduced as the parent rock of provenance; however, the increasing arid paleoclimate resulted in weakened chemical weathering of provenance, inferred by relatively low chemical index of alteration, chemical index of weathering, and plagioclase index of alteration corresponding to the input degree of radioactive materials and other terrigenous detrital materials (TDMs), evidenced by Ti and Al contents and terrigenous (%). Meanwhile, the relatively high P/Ti and Ba/Al both indicated increased primary paleoproductivity. Together with the maximum flooding stage of oil shale deposition, the relatively low radioactivity tends to be associated with the inhibited input of clay minerals and radioactive materials, largely caused by increasing arid paleoclimate. The accompanying decreased TDM benefited primary paleoproductivity and anoxic conditions; their combined influence could induce sapropelic OM accumulation.

Geochemical Characteristics of Quartzite in Parts of Paleoproterozoic Dhanjori Group, Singhbhum Craton, Eastern India: Implications for Provenance and Paleoweathering

Abstract Singhbhum craton preserves the records of sedimentation, magmatism, and tectono-thermal events from Mesoarchaean to Neoproterozoic. The Dhanjori Group (DG), located on the northeast margin of the Singhbhum craton, comprises of a variety of rocks including quartz pebble conglomerate, quartzite, schist, interlayered with mafic to intermediate and rarely acidic lava flows, tuff and agglomerate. Petrography and geochemical characteristics of the Dhanjori quartzite have been undertaken to interpret paleoweathering and provenance characteristics. Studied quartzites are made up of abundant quartz, feldspar, mica, and lithic fragments. With the help of geochemical data, the studied quartzites are classified as quartz-arenites and sub-arkoses. In addition to the A-CN-K plot, various chemical indices such as the chemical index of weathering (CIW), chemical index of alteration (CIA), and plagioclase index of alteration (PIA) indicate moderate to intense chemical weathering of the provenance under semi-humid climatic conditions. Rare earth element (REE) chondrite normalized patterns of the studied samples illustrate enriched light rare earth elements (LREEs) (LaN/SmN = 3.11 – 6.19), depleted heavy rare earth elements (HREEs) (GdN/YbN = 0.35 – 3.12) and negative Eu anomaly (Eu/Eu* = 0.55 - 0.87, ~ 0.68). Such patterns are similar to that of the upper continental crust (UCC). In the discrimination function diagram, studied samples of the Dhanjori Group fall in quartzose sedimentary field. In addition, La/Sc vs. Th/Co and La-Th-Sc diagrams, various ratios like Th/Sc (~0.61), La/Sc (~4.42), Th/Co (~0.03), La/Co (~0.11), and Cr/Th (~141.62) imply a mixed provenance for the studied samples. Hence, it has been inferred that the meta-sediments and orthoamphibolites of the older metamorphic group, Singhbhum granitoid complex, as well as associated Archaean metavolcanic suites, would have acted as the probable source rocks for the studied Dhanjori quartzites.

Geochemical, mineralogical and sedimentological analyses of reworked sediments (new) in the syn- to post-rift Middle Cretaceous-Quaternary detrital deposits from western Atlantic margin of Cameroon: evidence from sedimentation-erosion alternation in the context of passive margin evolution

Reworked detrital sediments were discovered in the syn-rift to post-rift Cretaceous to Quaternary (Pleistocene) detrital deposits of the Douala coastal sub-basin in the eastern margin of the South Atlantic Ocean at West Cameroon. This contribution presents the geochemical, mineralogical, and sedimentological data to constrain the origin of these reworked sediments. The investigated samples are characterized by the high values of Plagioclase Index of Alteration (PIA, 97.83–99.90), Chemical Index of Alteration (CIA, 71.9–99.08), and Chemical Index of Weathering (CIW, 98.67–99.90). Data gleaned from these indices suggest that the reworked sediments and their potential source rocks experienced severe weathering. The A-CN-K plot along with the mineralogical indicates a probably post-depositional K-enrichment. The high light rare earth elements (LREE)/heavy rare earth elements (HREE) ratios (15.82–79.13) suggest that the reworked were mainly derived from felsic igneous rocks. This interpretation is further confirmed by the Zr versus TiO2, TiO2/Al2O3, Th/Co versus La/Sc, and La/Th versus Th/Yb plots, which indicate felsic igneous and silicic source rocks. Meanwhile, the high variability of LREE/HREE ratios (15.82–79.13) and the positive Eu anomalies (1.10–1.32) of studied samples could indicate a little contribution of mafic source rocks. Analysis of the distribution of the heavy minerals (e.g. tourmaline, aluminum silicate, and rutile) revealed that these felsic and silicic source rocks are mainly granite and gneiss, probably belonging to the Nyong Group and the Western part of the Neoproterozoic Yaounde Group. The morphoscopic analyses of the host rocks (very angular to angular shapes) have revealed that the reworked sediments have proximal to subproximal onshore origins, probably from former sedimentary deposits, as is indicated by variation of their color. The tectonic discriminant diagram indicates the Oceanic Island Arc and Active Continental Margin which are inconsistent with the geological history of the Douala coastal sub-basin and could be explained by the recycling effect experienced by studied sediments which have been deposited in the coastal plain to the fluvial environment in the Low System Track context.

Relationship between Chemical Weathering Indices and Shear Strength of Highly and Completely Weathered Granite in South Korea

In South Korea, weathered granite is widely distributed and has been used as a bearing stratum for various structures. Therefore, it is important to determine the shear strength of the weathered granite. However, it is difficult to obtain reliable shear strength parameters with laboratory tests or standard penetration test (SPT) because weathered granite is easily crushed during the sampling process, and the penetrability of SPT is not secured. On the other hand, it is well known that weathering affects the variation of geotechnical properties. Based on this concept, this study reports a correlation between the shear strength parameters and the chemical weathering indices of the weathered granite. In this study, the pressuremeter test (PMT) was adopted to determine the friction angle of the weathered granite. For the identical granite, the chemical weathering indices (Vogt’s Ratio (VR), Chemical Index of Alteration (CIA), and Mobiles Index (Imob)) were measured by X-ray fluorescence (XRF). An estimating model considering both site-specific characteristics and degree of weathering was used, and the CIA showed the best correlation (R2 = 0.66) with friction angle among the weathering indices. Since the ratio of measured friction angle over the predicted one was distributed in the range from 0.8 to 1.2, it is more reasonable to predict friction angles based on CIA comparing to using the SPT-N value. It can contribute to a better estimation of friction angles of weathered granite.

Quaternary record of terrestrial environmental change in response to climatic forcing and anthropogenic perturbations, in Puerto Rico

We present cospatial, contemporary archival records of biotic and abiotic terrestrial processes operating over the past ∼25 ky within the Rio Fajardo watershed, in northeastern Puerto Rico. The proxy records were derived from a 5-m-thick stratigraphic section exposed by cut bank incision. We interpreted ecosystem dynamics from changes in the stable carbon isotopic ratio of sedimentary organic material compared to δ13C ratios of contemporary carbon sources. Sedimentary organic material had δ13C values ranging from −29.715 to −15.291. We derived a record of paleo-erosion rates in the catchment from the concentration of meteoric 10Be in layers of the floodplain sediments. Paleo-erosion rates ranged from 13 to 356 mm ky−1. The chronology of the sediments was constrained with the radiocarbon ages of organic deposits, the oldest age was calibrated to ∼22.4 ky BP (thousand years before present) and retrieved at 440 cm depth. We collected grain size data, clay mineralogies, and analyzed geochemical indices including the chemical weathering index, salinization, and base cation loss down profile. This stratigraphic sequence captures major shifts in the Caribbean climate, the intensification of the El Nino-Southern Oscillation, and the arrival of humans on the island. During the last glacial and early Holocene epochs both biotic (δ13C) and abiotic proxies (10Bemet and geochemical data) indicated dynamic equilibrium with climate. The past five thousand years (ky) of record are characterized instead by pulsed responses to disturbances in both systems. Colonial-era land use drove changes that significantly exceeded natural variability in any proxy over the period of record.

Geochemical assessment of mud rocks intervals from well X boundary of Nigeria and Benin Republic sectors of the offshore Dahomey Basin: Implication for provenance studies.

This work describes the nature of rocks, tectonic setting and paleoenvironmental conditions of the upper Cretaceous grayish - dark shale from an offshore well-X from Dahomey Basin, Nigeria. The selected samples were analyzed using x-ray fluorescence analysis. Indices obtained from various ratios were used for some deductions and interpreted using plots based on some previous works. By plotting Al2O3/TiO2 againstSiO2,and also TiO2 plotted against Zr, it was indicated that an intermediate igneous rocks were the parent rock of the analyzed shales. Using the plot of K2O/Na2O and SiO2 (Roserand Korsch, 1986), an intracratonic nature of the basin was indicated. Ratios of Cu/Zn and Cr/Ni in this work range from 0.23 to 0.63 and 1.61 to 2.55 respectively and these indicate an oxidizing condition of deposition. Additionally, chemical index of weathering (CIW) and plagioclase index of alteration (PIA) values (58.36-86.53 and 33.43-84.09 respectively) indicated a higher degree of weathering of at the source area compared to the extent of weathering inferred from our CIA values.

Sedimentological and Geochemical Charectesization of Manaveli and Cuddalore Formations, Puducherry Basin, India

Sedimentological and Geochemical Charectesization of Manaveli and Cuddalore Formations, Puducherry Basin, India &#x0D; &#x0D; Shyam N. Mude, Shyam Yawale and Vishal Choudhari &#x0D; &#x0D; Department of Geology, Fergusson College (Autonomous), Pune- 411004, India&#x0D; Email: shyam.mude@fergusson.edu; shyammude25@yahoo.co.in&#x0D; &#x0D; Abstract: The lithostratigraphically rocks of Puducherry basin (Sub-basin of Cauvery Basin) have been classified as Valudavur, Mettuveli, Karasur, Manaveli, Cuddalore formations in ascending order of deposition. The sedimentological and geochemical studies of sediments from Manavali (Paleocene) and Cuddalore (Mio-Pliocene) formations were carried out to understand grain size variation and distribution of major oxides and trace elements. &#x0D; The sieve analysis was used to study grain size variation and on the basis of grain sizes various geo-statistical parameters were calculated to understand depositional environment. The discriminant function analysis of the sediments from the Cuddalore Formation infers that mostly the sedimentation was occurred in fluvio-deltaic environment with incursions of shallow marine environment whereas bivariate plots suggests that the deposition was occurred in riverine to deltaic environment.&#x0D; The major element geochemistry of the Manaveli and Cuddalore formations have been carried out to understand the provenance, paleoclimate and source area weathering conditions. The values of CIA (Chemical Index of Alteration), CIW (Chemical Index of Weathering), ICV (Index of Compositional Variability) and PIA (Plagioclase Index of Alteration) of the sediments infer high weathering was occurred in source area of sediments for Manaveli and Cuddalore formations. The ratio (Al2O3+K2O+Na2O)/SiO2 indicate semi-humid climatic conditions during deposition of Cuddalore Formation whereas Manaveli Formation was deposited in semi-arid climatic conditions. The discriminant function diagram (A-CN-K Plot), suggest Quartzose sedimentary provenance for Cuddalore and Mafic igneous provenance for Manaveli Formation. &#x0D; &#x0D; Keywords: Grain Size, Geochemistry, Manaveli, Cuddalore, Puducherry Basin