Source Area Weathering Research Articles

Petrography and geochemistry of Oligocene to Lower Miocene sandstones in the Baiyun Sag, Pearl River Mouth Basin, South China Sea: Provenance, source area weathering, and tectonic setting

There is a controversy regarding the source area and weathering intensity of Oligocene to Lower Miocene sediments in the Baiyun Sag of the Pearl River Mouth Basin. Detrital modes, geochemistry, heavy mineral data, and detrital zircon U–Pb ages were analysed to understand the provenance, source area weathering, and tectonic setting of Oligocene to Lower Miocene sandstones in the Baiyun Sag. Petrographic data reveal that the sandstones were derived from a recycled orogen. With increasing transport distance, sediment maturity increased correspondingly. The Oligocene to Lower Miocene sandstones in the Baiyun Sag have low compositional maturity and have experienced low to moderate weathering. The sediments of the Zhuhai Formation have experienced relatively strong weathering intensity compared with those of the Enping and lower Zhujiang formations. Due to low degree of illitization and differences in the geochemical compositions of the sediments, the continental island arc data from different boreholes in the Baiyun Sag are more irregularly distributed in the A‐CN‐K plot. The modal composition (e.g., quartz, feldspar, and lithic fragments) and geochemical indices (Al2O3/TiO2 ratio; Al2O3‐TiO2 diagram; discriminant F1‐F2 diagram; Eu/Eu*, La/Sc, La/Co, Th/Sc, and Th/Co ratios; Hf‐La/Th and La/Sc‐Co/Th diagrams; and rare earth element patterns) indicate that the sediments in the Baiyun Sag are mainly derived from felsic source rocks. Although the uplift around the Baiyun Sag includes multistage magmatism and basic rocks, it has little influence on the sediment in the depression, and no sediments were transported by the Han River to the Baiyun Sag. Geochemical data and detrital zircon U–Pb ages suggest that the Pearl River was formed in the Early Oligocene and became the main source for the sediments in this area. The river carried felsic material from the South China Coast forming a large delta on the northern slope of the Baiyun Sag. The ratios of Eu/Eu*, La/Sc, La/Co, Th/Sc and Th/Co, and heavy mineral data indicate that the sediments transported by the Pearl River to the Baiyun Sag were changed from the arc‐dominated coastal zone to the interior of the South China Block during the Late Oligocene to Early Miocene and even reached the south‐eastern margin of the Tibetan Plateau (West Yunnan Plateau). The La‐Th‐Sc and Th‐Sc‐Zr/10 diagrams suggest that the provenance of these sandstones is evolved continental island arc or an active continental margin setting.

Geochemistry of the Miocene Zoumi flysch thrust-top basin (External Rif, Morocco): new constraints on source area weathering, recycling processes, and paleoclimate conditions

This study focuses on the Lower-Middle Miocene syn-orogenic flysch deposits of the Zoumi basin to infer source area paleoclimatic conditions, the intensity of source rocks paleoweathering, and mechanical sorting and recycling effects. The mudrocks are enriched in Al2O3, Fe2O3, CaO, and TiO2 relative to PAAS and depleted in the other mobile major elements. There are high positive correlations between SiO2, Al2O3, and TiO2 and negative correlations between SiO2 and CaO. Geochemically, the mudstones are mainly classified as shales, Fe-shales, and wackes. Various discriminant diagrams were used to reveal the inferred tectonics, source paleoweathering intensity, and paleoclimatic conditions. Chemical index of alteration (CIA) and chemical index of weathering (CIW) values for Lower-Middle Miocene vary from 50 to 80% indicating low to moderate degree of source area weathering compatible with non-steady-state weathering under wet and humid paleoclimatic conditions. Locally (Zoumi mid-section) CIA values are higher (> 80) reflecting intense source area weathering, which may be attributed to high tectonic impulses and more humid conditions during deposition. The combination of ICV-CIA, Al2O3-Zr-TiO2, and Th/Sc-Zr/Sc values suggests the bulk rock is chemically immature and has experienced modest physical sorting and recycling reflecting little transportation until the final deposition.

Geochemistry of Ahoko claystone-shale sequence, south eastern Bida Basin, Nigeria: implications for tectonic setting, provenance and source area weathering

Results of geochemical investigation of shale and claystone samples from two different sections of the exposed Ahoko claystone-shale sequence along the Koton-Karifi/Abaji highway are presented and discussed. Chemical variation of SiO2/Al2O3 and Na2O/K2O is ascribed to varying degrees of weathering of plagioclase rich rock either at the source and/or during transportation to the depositional basin. The high Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) values indicate intense alteration/weathering and removal of mobile cations. The CIW/CIA ratios indicate material that has undergone short distance transportation before final deposition. Besides, the overall Index of Compositional Variability (ICV) values and lower contents of Rb and Cs than upper continental crust (UCC) and post Archean Australian shale (PAAS) of both profiles (i.e. AH-1 and AH-2) indicate intense weathering. The average Th/U ratio is less than the average values for UCC and PAAS, which indicates that the source area is rich in uranium. Furthermore, the average Zr/Sc values are considerably higher than the average value for both UCC and PAAS, suggesting a high recycled sedimentary source. The geochemistry of our samples is consistent with felsic rocks, mixed with some old sediment components and should be derived from UCC. On the log (Fe2O3/K2O) versus log (SiO2/Al2O3) scattergram, the Ahoko claystone-shale samples mainly plot in the shale and Fe-shale fields. The variability in the geochemical classification of our samples is attributed to variation in the relative proportion of matrix, feldspar and lithic components. The major, trace and rare-earth elements assemblage of the studied Ahoko claystone-shale samples plot on various discrimination diagrams, revealing that the tectonic setting belongs to a passive continental margin and a continental island arc.

Geochemical fingerprinting of Maastrichtian oil shales from the Central Eastern Desert, Egypt: Implications for provenance, tectonic setting, and source area weathering

Upper Cretaceous oil shales accumulated in intracratonic sedimentary basins along the Central Eastern Desert. Comprehensive geochemical analyses have been applied on 3 Maastrichtian oil shale horizons from the Duwi and Dakhla formations (El‐Beida and El‐Nakheil mines). We provide significant clues for chemical weathering, sediment recycling, petrogenesis, and tectonic setting of oil shales' source material. The mineralogical composition of the studied oil shales is generally characterized by carbonates, phyllosilicates, quartz, fluorapatite, and sulphides. The geochemistry is characterized by high Ca, P, Ni, U, and Cr values compared to standard post‐Archean Australian shales (PAAS). Their chondrite‐normalized patterns are distinguished by LREE enrichment, HREE depletion, negative Eu anomaly, and typical shale‐like PAAS‐normalized REE patterns. Furthermore, the total REE content is positively correlated with Si, K, Na, Fe, Al, Ti, and Mn, indicating that the REE of the investigated oil shales originated from terrigenous sources. Diverse proxies (e.g., CIA, CPA, and PIA) and the A–CN–K ternary diagram suppose that the source rock succession of the oil shales experienced moderate to intensive chemical weathering. Various geochemical parameters suggest that the oil shales were predominately derived from intermediate, with a minor contribution from felsic, igneous source rocks without any remarkable recycling signals. The average values of (Gd/Yb)N (1.39), Eu/Eu* (0.76), Th/U (0.29), and discrimination diagrams reveal that the oil shales were derived from Neoproterozoic island arc parent rocks. The geochemical results for oil shale provenance are in accordance with the composition and the palaeotectonic history of the igneous rocks in the Central Eastern Desert of Egypt.

Integrated Petrographic, Mineralogical, and Geochemical Study of the Upper Kaimur Group of Rocks, Son Valley, India: Implications for Provenance, Source Area Weathering and Tectonic Setting

ABSTRACT The upper Kaimur Group (UKG) of the Vindhyan Supergroup in central India, primarily consists of three rock types-Dhandraul sandstone, Scarp sandstone and Bijaigarh shale. The present study aims to reconstruct the parent rock assemblages, their tectonic provenance, mineralogy, weathering intensity, hydraulic sorting and depositional tectonic setting. Samples from the UKG rocks representing the Dhandraul sandstone, Scarp sandstone and Bijaigarh shale were studied using a combination of petrographic, mineralogical, and geochemical techniques. Texturally, medium to coarse grained UKG sandstones are mature and moderate to well sorted. Deficiency of feldspars in these sandstones indicates that the rocks are extensively recycled from distant sources. Their average modal composition for Scarp (avg. Qt99F0.2L0.8) and Dhandraul (avg. Qt99 F0.1L0.8) sandstones, classifies them as quartz arenite to sub-litharenite types, which is consistent with geochemical study. Major element concentrations revealed that sandstones have high SiO2, K2O > Na2O, and low Fe2O3, which are supported by the modal data. On the other hand, sandstone samples are enriched in most trace elements such as Ce, Sr, V, Sc and Zr and depleted in U and Th. The CIA values (43.17-76.48) of the UKG rocks indicate low to moderate weathering, either of the original source or during transport before deposition, which may have related to low-relief and humid climatic conditions in the source area. Further, petrographic and geochemical interpretations indicate that they are derived from craton interior to quartzose recycled sedimentary rocks and deposited in a passive continental margin. Therefore, granitic and low grade metamorphic rocks of Mahakoshal Group and Chotanagpur granite-gneiss, situated on the southern and south-eastern side of the Vindhyan basin are suggested as possible provenance for the UKG rocks.

Source-Area Weathering, Composition and Paleo-Redox Condition of Stream Sediments from Ijero-Ekiti, Nigeria

Source-Area Weathering, Composition and Paleo-Redox Condition of Stream Sediments from Ijero-Ekiti, Nigeria

Geochemical and Nd-isotopic compositions of juvenile-type Paleoproterozoic Birimian sedimentary rocks from southeastern West African Craton (Ghana): Constraints on provenance and tectonic setting

The Paleoproterozic Birimian Supergroup consists of sedimentary basins composed predominantly of wackes and argillites, and volcanic belts composed predominantly of basaltic rocks. Whole rock geochemical and Nd-isotopic studies were carried out on fine-grained sedimentary rocks (shales and fine-grained sandstones) from one of the Birimian sedimentary basins, the Kumasi basin. The sedimentary rocks are immature in nature, with very little recycled materials. Relative to average early Proterozoic upper continental crust, the Birimian sedimentary rocks are depleted in the alkalis and alkaline earth elements and the high field strength elements, and enriched in transition metals. Chondrite-normalized rare earth element (REE) plots for both the shales and sandstones show fractionated LREE patterns (average LaN/SmN=3.45), with slight negative Eu-anomalies (average Eu/Eu∗=0.79) and a slightly fractionated HREE patterns (average GdN/YbN=1.84). Low to moderate degree of chemical weathering in the sediment source area is indicated by Chemical Index of Alteration values of between 52 and 80. Elemental ratios such as La/Co, Th/Co, Th/Cr, and Eu/Eu∗ that are critical to provenance suggests that the sediments were derived from rocks of mixed felsic and mafic compositions. Mixing calculations based on the REEs indicate that, the shale is best modeled with a mixture having 62% TTG, 16% granite and 22% basalt whereas the sandstone is almost 100% TTG. The εNd values for the analyzed samples, calculated at the age of deposition (i.e., 2.1Ga), range from −1.69 to 1.07, suggesting derivation from an undifferentiated source. The Nd-isotopic compositions, together with Eu/Eu∗ and Th/U values and other trace element characteristics suggest Young Undifferentiated Arc provenance, and this is in agreement with previous studies that show that the Birmian crust is juvenile and little amount of Archean crust is present in the sedimentary rocks. The geochemical and Nd-isotopic systematics further suggest that the bulk of detritus was supplied by adjacent Paleoproterozoic Birimian greenstone belts with only 10% or less contribution from the Archean crust. Trace element characteristics further suggest that deposition took place in an island arc setting.

Geochemistry of claystones of the Ruteh Formation, NW Iran: Implications for provenance, source-area weathering, and paleo-redox conditions

Geochemistry of claystones of the Ruteh Formation, NW Iran: Implications for provenance, source-area weathering, and paleo-redox conditions

Petrography and geochemistry of upper Triassic sandstones from the Tumengela Formation in the Woruo Mountain area, North Qiangtang Basin, Tibet: Implications for provenance, source area weathering, and tectonic setting

AbstractThe petrography and major and trace element concentrations of the sandstones from the Tumengela Formation in the Woruo Mountain area, North Qiangtang Basin, are studied to determine their provenance, intensity of weathering and tectonic setting. The detrital compositions of the Tumengela sandstone samples are dominated by quartz (58.0–70.1 %, average 64.7 %) and lithic fragments (21.8–35.9 %, average 27.3 %), but low in feldspar content (4.9–12.9 %, average 8.0 %). The sandstones can be classified as litharenite and feldspathic litharenite according to their detrital compositions, which is consistent with the geochemical data. The detrital modal compositions reflect that these sandstones are probably derived from a recycled orogenic source. The index of chemical variability (ICV) and SiO2/Al2O3 ratio values suggest that the compositional maturity and recycling were moderate. The weathering indices such as the chemical index of alteration (CIA), plagioclase index of alteration (PIA), chemical index of weathering (CIW), and Al2O3–(CaO* + Na2O)–K2O (A–CN–K) diagram indicate that the intensities of weathering in the source area were moderate. The Al2O3/TiO2, Th/Co, La/Sc, La/Co, Th/Sc, Cr/Th ratio values and the discriminant function of the Tumengela sandstones indicate that the sediments were mainly derived from felsic source rocks, while also mixed with intermediate source rocks. The comparison of rare earth element patterns and its Eu anomalies to the probable source rocks infer that the sandstones were derived from the combination of granite, rhyolite, dacite, and gneisses. The proximal central uplift belt was probably the primary provenance area as evidenced by the petrographical and geochemical features of the Tumengela sandstones. The multidimensional tectonic discrimination diagram based on major elements show a collision setting (80 %) combined with a rift setting (20 %) for the Tumengela sandstones, which is consistent with the general geology of the study areas.

Provenance, tectonic setting and source-area weathering of the lower Cambrian sediments of the Parahio valley in the Spiti basin, India

The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K2O/Al2O3 ratio and positive correlation of Co (r=0.85), Ni (r=0.86), Zn (r=0.82), Rb (r=0.98) with K2O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K2O/Na2O] vs. SiO2; [SiO2/Al2O3] vs. log[K2O/Na2O]; [SiO2/20] – [K2O+Na2O] – [TiO2+Fe2O3+MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A–CN–K diagram indicates that these sediments were generated from source rocks of the upper continental crust.

Late Quaternary loess-like paleosols and pedocomplexes, geochemistry, provenance and source area weathering, Manasbal, Kashmir Valley, India

The late Quaternary loess and loess-like deposits in Kashmir Valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region. We present a loess-like paleosol located along the margin of the Manasbal Lake, Ganderbal, which was studied in detail for understanding the pedological processes and reconstructing the late Quaternary soil formation. In this paper we present loess-like paleosol formation of a nearly 10.6m thick sequence exposed along the margin of Manasbal Lake, Ganderbal District, Srinagar, Kashmir. Geochemical and textural data of this loess-like sedimentary sequence fluctuate reflecting the varied depositional processes operating in the valley, differential intensity of weathering, and processes of pedogenesis. Weathering indices such as chemical index of alteration, chemical index of weathering, and plagioclase index of alteration reveal weak to moderate weathering of the parent material. Provenance discrimination diagrams of the present study disclose that the Manasbal loess-like paleosol sediments are derived from the mixed source rocks suggesting a variety of provenance with variable geological settings, which apparently have undergone weak to moderate recycling processes. The Manasbal paleosol horizons have been dated by the optically stimulated luminescence (OSL) method to the marine isotope stages mid-MIS-3 (41.7±8.0ka) and late-MIS-2 (14.6±3.8ka). During the MIS-3 period, the climate was wetter, forming a strong AhBtk paleosol as inferred from the geochemical data. A steady increase in the CaCO3 content and C/N ratio in the paleosols from 6.50m (MIS-3) indicates arid and drier climatic conditions. The area around Manasbal Lake incised because of climate change and neotectonic activity since post-14ka.

Geochemistry and provenance of a multiple-stage fan in the Upper Miocene to the Pliocene in the Yinggehai and Qiongdongnan basins, offshore South China Sea

The Yinggehai and Qiongdongnan basins in the northwestern South China Sea preserve a large volume of Cenozoic sediments. However, their sources are still remain controversial and need a further research. This paper uses discriminant diagrams and bivariate plots of major, trace and rare earth elements, combined with heavy mineral data and detrital zircon U-Pb ages to determine the provenance, source area weathering and tectonic setting of the Upper Miocene to Pliocene sediments in the Yinggehai and Qiongdongnan basins, offshore South China Sea. The sandstone samples used in this study are characterized by four features: (i) The studied sandstones are first-cycle deposits, no recycling processes are recorded in these sediments, and there is a low degree of weathering conditions in the source areas. (ii) The sandstones from the DF fan, LD fan and Central Canyon System may have a similar source, being derived from an old upper continental crust mainly composed of felsic igneous source rocks. (iii) Detrital zircon U-Pb ages suggest that Central Vietnam is likely to be the dominant source of the DF fan, LD fan and Central Canyon System. (iv) The tectonic setting of the sandstones in the DF fan, LD fan and Central Canyon System belongs to the continental island arc (CIA) or the active continental margin (ACM) fields.

Geochemistry of upland lacustrine sediments from Serra dos Carajás, Southeastern Amazon, Brazil: Implications for catchment weathering, provenance, and sedimentary processes

A multi-proxy geochemical study of surficial sediments of an upland lake (Amendoim Lake), located in the Serra dos Carajás region, Brazil, was carried out to understand catchment weathering and provenance of sediments in the basin, as well as sedimentary processes. The carbon and nitrogen isotopic compositions of organic matter in the sediment were quite homogeneous, and suggest that the organic sources for this lake are mainly composed of palms and submerged macrophytes. The R-mode factor analysis indicates that most of the trace elements, including rare earth elements (REEs), are clustered with Al (Group 1), Si is grouped with Zr and Hf (Group 4), total organic carbon (TOC) with TS and Hg (Group 2), and Fe with Mn and As (Group 3). The elements of the Group 1 show strong positive correlations with Al, suggesting that these elements are hosted in detrital minerals during laterization in the catchment basin and not significantly affected by diagenesis. The high CIA values (96–99) of sediments together with their position in A-CN-K and log (Fe2O3/K2O) vs log (SiO2/Al2O3) plots indicate intense chemical weathering in source area. However, similar geochemical signatures between lake sediments and catchment lateritic crust indicates that mechanical erosion was the dominant sediment formation process. REE patterns normalized to chondrite along with geochemical indices (Al/K, Al/Ti, La/Th, La/Al, Ti/Zr, Zr/Hf, Th/Sc, Co/Th, Ba/Sr, and Eu/Eu*) also indicate that the sediments are mainly derived from laterite crust. This study provides reliable background information to reconstruct weathering processes and lake evolution in the Serra dos Carajás area.

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 the Miocene oil shale (Hançili Formation) in the Çankırı-Çorum Basin, Central Turkey: Implications for Paleoclimate conditions, source–area weathering, provenance and tectonic setting

The geochemistry of oil shale units of Hançili Formation in the Çankırı-Çorum Basin (Central Turkey) was studied using various chemical analyses. The mineralogical composition of the samples were preliminarily investigated using Pearson's correlation coefficients of selected elements, indicating that the samples contain abundant clay minerals as well as K-feldspar and carbonate. The K2O/Al2O3 and SiO2/Al2O3 ratios indicate that the major proportion of clay minerals is composed of smectite. Si, Al, Ti, K, Na, and Fe reside in clay minerals, while Ca, Mg, and Mn are mostly associated with carbonates (e.g., calcite and dolomite) and phosphorous (P) is present as apatite. The total REE content of the oil shale range from 19 to 113ppm. The chondrite-normalized patterns of the oil shale show LREE enrichments, HREE deficits, negative Eu anomalies and negligible Ce anomalies. In general, major, trace and rare earth element abundances suggest that the studied oil shale in the Çankırı-Çorum Basin are mainly from the intermediate rocks, mixed with small amounts of basic rocks, and that their source rocks are mostly deposited in the continental collision setting. The REE geochemistry of the oil shale suggests that these samples were derived from a consistent terrigenous source and the Eu anomaly was inherited from the source rocks. The paleoclimate index (C-value), varies between 0.07 and 1.22 reflecting a generally semi-arid to humid conditions. In addition, Rb/Sr (~0.22) and Sr/Cu (~9.09) ratios support the idea that warm and humid conditions prevailed during deposition of the Hançili Formation. Sr/Ba ratios (0.54–3.7) of the studied samples suggest a paleoenvironment with variable salinity. The co-variation among this factor and paleoclimate indicators suggest that variations in climatic conditions exerted a primary control on salinity. The substantially low C-value and Rb/Sr ratio and significantly high ratios of Sr/Cu and Sr/Ba and also elevated carbonate content of four samples indicate that these samples were deposited during hot and arid periods and that the paleoclimate controlled the terrigenous sediment flux to the lake basin. The chemical index of alteration (CIA), A-CN-K ternary diagram, and high Th/U ratios indicate that the parent rocks of the oil shale experienced moderate chemical weathering (steady state).

Detrital mode and whole-rock geochemistry of the Miocene-Pliocene fluvial succession, Pishin Belt, Pakistan: implications on provenance and source area weathering in peripheral foreland basins

Detrital mode and geochemical composition of sandstones and mudstones of the Miocene Dasht Murgha Group (DMG) and Pliocene Malthanai Formation (MF) of the Pishin Belt, northwestern Pakistan, have been examined to identify their provenance and source area weathering. Sandstones of the Dasht Murgha Group and Malthanai Formation are lithic to sublitharenites, rich in quartz, and metamorphic and sedimentary lithic fragments, indicating a recycled orogenic source. LmLvLs plots show that the Dasht Murgha Group is rich in sedimentary and metamorphic lithic fragments (Lm35Lv18Ls47), while samples of the Malthanai Formation are overwhelmingly rich in sedimentary fragments (Lm14Lv10Ls76). Eocene Nisai Formation and Oligocene Khojak Formation within the Pishin Belt were mainly providing the sedimentary/metasedimentary detritus. High content of monocrystalline quartz (DMG 28.21 %; MF 30.7) and higher SiO2/Al2O3 ratios in sandstones (DMG 9.86; MF 11.98) also indicate high maturity of sandstones due to recycling of source terrain in collision orogens. High Cr/Ni (DMG 5.23; MF 6.17) and moderate Cr/V (DMG 3.96; MF 3.88) ratios suggest significant contributions from mafic and ultramafic detritus derived from Muslim Bagh-Zhob Ophiolite. Malthanai Formation has higher CIA and CIW values (68.96 and 77.53) than Dasht Murgha Group (63.87 and 70.93); however, they both indicate low to moderate weathering intensities. Dasht Murgha Group and Malthanai Formation have higher ICV values which indicate abundance of aluminous silicates, hence, showing moderate weathering of the source area. In A-CN-K diagrams, the samples make linear trend towards illite which suggests that the sediments were derived from a tectonically active source going through non-steady-state weathering, where the detritus has been derived from different zones of weathering profiles.

Speciation of phosphorus in the continental shelf sediments in the Eastern Arabian Sea

The distributions of various forms of phosphorus (P) and their relation with sediment geochemistry in two core sediments near Karwar and Mangalore offshore have been studied through the modified SEDEX procedure (Ruttenberg et al., 2009) and bulk chemical analysis. The present study provides the first quantitative analysis of complete phosphorus speciation in the core sediments of the Eastern Arabian shelf. The chemical index of alteration (CIA), chemical Index of Weathering (CIW) and Al–Ti–Zr ternary diagram suggest low to moderate source area weathering of granodioritic to tonalitic source rock composition, despite the intense orographic rainfall in the source area. Due to the presence of same source rock and identical oxic depositional environment, the studied sediments show the same range of variation of total phosphorus (24 to 83µmol/g) with a down-depth depleting trend. Organic bound P and detrital P are the two major chemical forms followed by iron-bound P, exchangeable/loosely bound P and authigenic P. The authigenic P content in the sediments near Mangalore coast varies linearly with calcium (r=0.88) unlike that of Karwar coast. The different reactive-phosphorus pools exhibit identical depleting trend with depth. This indicates that the phosphorus released from the organic matter and Fe bound fractions are prevented from precipitating as authigenic phosphates in the deeper parts of the sediment column. The low concentration of total P, dominance of detrital non-reactive fraction of P and inhibition of formation of authigenic phosphate result in the absence of active phosphatization in the Eastern Arabian Shelf in the studied region. High sedimentation rate (35–58cm/kyr) and absence of winnowing effect appear to be the dominant factor controlling the P-speciation in the studied sediments.

Geochemical Classification and Determination of Maturity Source Weathering in Beach Sands of Eastern San’ in Coast, Tango Peninsula, and Wakasa Bay, Japan

<span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 10.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">Geochemistry of beach sand sediments collected from the Eastern San’in coast (n=17), Tango Peninsula (n=14) and Wakasa Bay (n=7) shorelines were investigated using XRF analyses for major and trace elements to characterize their composition, classification, maturity, provenance, tectonic setting and degree of weathering in source areas. Investigated sands from all sites were very similar showing depletion in all elements except SiO<sub>2</sub>, K<sub>2</sub>O and As relative to the UCCN and JUCN, suggesting a moderate geochemical maturation. Beach sand sediments from these locations can be classified as arkose, subarkose and litharenite that are chemically immature and formed under arid/semi-arid conditions with a tendency towards increasing chemical maturity suggesting that they are from multiple sources. The relatively low to moderate values of weathering indices of Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Chemical Index of Weathering (CIW), the beach sands from all sites in the source area have undergone low to moderate degree of chemical weathering. A-CN-K and A-CNK-FM plots, which suggest a granitic source composition, also confirm that the sand samples from these sites have undergone low to moderate degree of chemical weathering in consistent with CIA, PIA and CIW values. A plot of the analyzed beach sands data on the provenance discriminating function F1/F2 showed that most of the investigated beach sand sediments in all locations fall within mafic to intermediate ocean island arc source; similar to the tectonic setting discrimination diagrams based on major elements suggesting a passive margin.</span>

Geochemical Discriminant for Provenance Characterization and Palaeogeography of Shales from Dahomey Embayment, Southwestern Nigeria

The geochemical compositions [major, trace and Rare Earth Elements (REE)] of Cretaceous-Tertiary shales from Gbekebo-1 well were used to characterize provenance, paleogeography, source area weathering and tectonic setting of the study area located in the southwestern part of the Dahomey Embayment, Nigeria. Core samples (eight) of shales were obtained and analyzed geochemically using the combined methods of major elements Fusion Inductively Coupled Plasma (FUS-ICP) and trace elements Fusion Inductively Coupled Plasma Emission/Mass Spectrometry (FUS-ICP/MS). An A-CN-K (Al2O3-CaO + Na2O-K2O) ternary plot, geochemical discriminant function of major elements and chondrite normalized plots of REE suggest an upper continental crust provenance of felsic to intermediate or mixed igneous rocks of tonalite to granodiorite composition. High values of chemical index of alteration (CIA, 82.22 - 96.39) and chemical index of weathering (CIW, 88.10 - 99.17) indicated a palaeogeographic condition marked by wet tropical climate where intense chemical weathering and erosion prevailed. The Cretaceous-Tertiary shales from Gbekebo-1 well are inferred to have been deposited in passive margin setting based on various geochemical tectonic setting discrimination diagrams.

Occurrence of red clay horizon in soil profiles of the Yellow River Delta: Implications for accumulation of heavy metals

The source-area weathering and pedogenesis processes in the alluvial soil profiles might affect depth distribution of heavy metals. Red clay horizon (RCH) with a thickness of 5–50cm in a 1m soil profile has been found ubiquitously in the Yellow River Delta (YRD). The occurrence of this RCH was supposed to be related with the frequent shifting of the Yellow River tail channel in the Yellow River Delta (YRD). The geochemical features of the RCH were distinct from its upper or lower yellow silt horizon (YSH). The average median grain size of the RCH (10.5μm) was almost three times lower than that of the YSH (29.9μm). Meanwhile, the RCH was characterized of higher chemical index of alteration (CIA), magnetic susceptibility (χlf) and frequency-dependent magnetic susceptibility (χfd) values than the YSH, which implied a stronger source-area weathering and pedogenesis intensity of the RCH. Besides the distinctive characteristics of the RCH, it also accumulated significantly (p<0.05) higher mean contents of Cu, Zn, Pb, Cr, Ni and Co, and maximum content of Cd in the RCH than that in the YSH. The principal component analysis (PCA) suggested that distribution of the heavy metals in the YRD soil profiles was significantly related to the content of aluminosilicates, oxides, clay fraction, χlf and χfd, however, such a correlation was not found except for Pb in the YSH. In addition, result of BCR sequential extraction indicated that a higher percentage of Fe–Mn oxides associated fraction was in the RCH than in the YSH for the heavy metals of Pb and Co. Cadmium was observed at higher percentage of exchangeable fraction in the RCH than in the YSH, implying a higher environmental risk of the Cd in the RCH.