Post-Archean Average Australian Shale Research Articles

Iron deposition during recovery from Late Devonian oceanic anoxia: Implications of the geochemistry of the Kawame ferromanganese deposit, Nedamo Belt, Northeast Japan

The Late Devonian, during which one of the “Big Five” Phanerozoic mass extinction events occurred, was one of the most important time intervals in Earth history. Nevertheless, the paucity of deep-sea records due to subduction has hampered elucidation of the pelagic environment during the Late Devonian in Panthalassa. However, ancient hydrothermal ferromanganese sediments, which were deposited on the abyssal seafloor and then accreted onto continental margins, are preserved as umber deposits and exposed in accretionary prisms. These sediments can provide key information to characterize the paleo-ocean. An Upper Devonian (Famennian) umber deposit is exposed in Kawame Quarry, Nedamo Belt, northeastern Japan. We investigated the bulk chemical composition and osmium isotopic ratio ( 187 Os/ 188 Os) of the Kawame umber to discuss the pelagic environment of the Panthalassa Ocean during the Late Devonian. The Kawame umber shows positive correlations between Fe content and the levels of P, V, Os, and rare earth elements, suggesting that hydrothermal Fe-oxyhydroxide particles adsorbed these elements from ambient seawater in the same way as hydrothermal ferromanganese sediments in the present-day ocean. Newly obtained initial 187 Os/ 188 Os values of Late Devonian seawater are 0.49–0.57, lower than that of present-day seawater (~1.06) and comparable to Paleogene and Late Cretaceous values. One of the most remarkable characteristics of the Kawame umber is its markedly high Fe levels (up to 90 wt%) compared to present-day seafloor hydrothermal ferromanganese sediments and younger umber deposits in Japanese accretionary complexes. Because seawater 187 Os/ 188 Os values were not notably different from those during the Paleogene and Late Cretaceous, anomalously vigorous hydrothermal activity in the Late Devonian is unlikely to have caused the increased Fe deposition. The rare earth element patterns of the Kawame umber (normalized to post-Archean average Australian shale) show weaker negative Ce anomalies than those of younger umbers and present-day hydrothermal ferromanganese sediments, suggesting that the Kawame umbers were deposited under less oxidizing conditions. Considering that many red beds were deposited at ~370 Ma, during recovery from the oceanic anoxic events (OAEs) of the Late Devonian (early Famennian), the anomalous Fe enrichment in the Kawame umber likely reflects enhanced oxidization and precipitation of abundant dissolved Fe during the post-OAE transition from anoxic to oxic conditions. • Geochemistry of Late Devonian Panthalassa was reconstructed from NE Japan. • Weakly negative Ce anomaly may reflect recovery from oceanic anoxia. • Reoxygenation of seawater caused Fe-enrichment in the Kawame umber. • Late Devonian seawater 187 Os/ 188 Os ratio was 0.47–0.57.

Rare earth elements in surface waters and sediments of the Mgoua watershed, south western Cameroon

The concentrations and distribution spectra of 14 stable rare earth elements (REE) were studied for surface waters (n = 30) and sediments (n = 30) of the tropical zone Mgoua watershed in southwest of Cameroon. Samples were analyzed using the inductively coupled plasma mass spectrometer (ICP-MS) method. The ∑REE concentrations of the surface waters vary from 0.11 to 6.60 µg/L with an average value of 1.18 µg/L. This average is 150 times lower than the average values of the Post-Archean Australian Average Shale (PAAS). In the sediments, the concentrations range from 282.12 to 727.67 ppm with an average value of 550.05 ppm, making it 2.5 times higher than the PAAS. Rare earth spectra normalized to PAAS are spread out and show heavy rare earth enrichment; positive Eu anomalies; negative, low, or no Ce anomalies; and a gradual decrease in heavy earths in river and well waters and sediments, but are sawtooth with strong negative Ce anomalies in effluent waters and sediments. A low rare earth fractionation is noted in river and well waters [(La/Yb)N ~ 0.35–1.19], while it is high in effluent waters [(La/Yb)N ~ 0.42–56.99]; a slight depletion of rare earths in all environments [(La/Sm)N ~ 0.69–2.35], as well as a depletion of heavy rare earths [(Gd/Yb)N ~ 0.58–1.94]. In the sediments, the same characteristics are found with elemental ratio values differing slightly [(La/Yb)N ~ 1.15–1.99]; [(La/Sm)N ~ 0.75–1.36]; and [(Gd/Yb)N ~ 1.15–2.01]. This study shows that the Mgoua watershed does not have a high concentration of REE, although in the sediments they are well above the average PASS value while they are insignificant in the waters.

Umber as a lithified REY-rich mud in Japanese accretionary complexes and its implications for the osmium isotopic composition of Middle Cretaceous seawater

We report geochemical and isotopic data for umber and related greenstone samples from the Aki umber deposit in the Northern Shimanto Belt, central Shikoku, southwest Japan. The greenstone underlying the umber deposit shows a geochemical signature typical for mid-ocean ridge basalts. Umber samples are characterized by notable enrichments in Fe, Mn, P, V, Co, Ni, and Zn relative to post-Archean average Australian Shale (PAAS). In addition, rare-earth elements and yttrium (REY) are markedly enriched in the umber samples (up to 1120 ppm total REY), and their PAAS-normalized REY patterns are almost identical to those of hydrothermal ferromanganese plume fall-out precipitates (suspended particulates) emanating from a mid-oceanic ridge. These geochemical features suggest that the Aki umber represents a hydrothermal iron oxyhydroxide-type REY-rich mud deposited originally in a pelagic deep-sea setting during the Middle Cretaceous (113.2–100.5 Ma), which was subsequently accreted onto the proto-Japanese Island arc. The initial 187Os/188Os ratios of the Aki umber samples range from 0.554 to 0.668. Because the umbers preserve the primary geochemical signature of hydrothermal Fe-oxyhydroxide-type REY-rich mud deposited near a mid-oceanic ridge, their Os isotopic ratios can be regarded as the marine 187Os/188Os ratios at the time of deposition (Middle Cretaceous). Our results indicate that the Cretaceous marine 187Os/188Os ratios were lower than the present day ratio, probably reflecting more intense hydrothermal activity and/or a lower continental weathering flux during that period. We also suggest that marine Os isotopic compositions during the Middle to Late Cretaceous were relatively constant (0.4–0.6), except during ocean anoxic events.

Mineralogy and geochemistry of alluvial sediments from the Kadey plain, eastern Cameroon: Implications for provenance, weathering, and tectonic setting

Mineralogical analyses by X-ray diffraction and geochemical analyses by X-ray fluorescence and inductively coupled plasma-mass spectrometry were performed on the Kadey Plain clastic sediments in order to determine their provenance and weathering. The Kadey Plain has four types of clastic sediments, shales, wackes, litharenites, and Fe-sands. The shales and wackes consist of kaolinite, quartz, muscovite, gibbsite, illite, anatase, and goethite. In the litharenites, minerals found are quartz, illite, kaolinite, gibbsite, muscovite, and goethite. Fe-sands consist of quartz, muscovite, and kaolinite, whereas gibbsite, illite, iron oxyhydroxides and anatase occur as traces. The U/Th (0.11–0.37) and V/Cr (0.99–1.73) ratios indicate an oxidising deposition environment. The behavior of trace elements is the same in these sediments, except for U content which is depleted in Fe-sands. Rare earth elements (REE) normalized with chondrite for the studied clastic sediments, demonstrate a slightly light REE enrichment (3.74 < (La/Sm)n < 5.80) and comparatively flat heavy REE patterns (1.12 < (Gd/Yb)n < 1.78) associated to negative Eu anomaly (0.51 < Eu/Eu* < 0.67). These materials disclose less fractionation of REE [7.10 ≤ (La/Yb)n ≤ 18.41]. These ratios are higher than that of Post-Archean Australian Average Shale [(La/Yb)n = 9.15], except for wackes. Al2O3/TiO2 vs. (SiO2)adj diagram, Eu/Eu*, La/Sc, Th/Sc, La/Co, Th/Co, and Th/Cr ratios suggest that the studied clastic sediments were derived from felsic sources. The REE patterns for sediments from the Kadey Plain disclosed closer resemblance to those of granites, quartzites, migmatites, and chlorite schists found relatively near to the study area. The tectonic discrimination diagrams indicate chiefly passive margin setting for these alluvial sediments.

Composition of the peninsular India rivers average clay (PIRAC): A reference sediment composition for the upper crust from peninsular India

We present a new dataset on the average composition of the clay fraction of sediments in 13 rivers draining the entire peninsular India, referred to here as Peninsular India Rivers Average Clay (PIRAC). PIRAC showed relatively low Si and high Fe, Mn and Mg compared to the other reference sediments. The total trace elements (∑TE) content of PIRAC was lower than that of Post-Archean average Australian Shale (PAAS), but close to that of Average Suspended Sediment of World Rivers (ASSWR). The total rare earth elements (∑REE) content of PIRAC was slightly lower than that of PAAS but close to that of World River Average Clay (WRAC). The ∑TE and ∑REE were much higher for PIRAC than in other reference sediments. Anomalously high Cu, Zn and Pb in PIRAC suggest that these trace elements do not reliably indicate the crustal composition. PAAS-normalised REE of PIRAC showed LREE-depleted, MREE- and HREE-enriched REE patterns with positive Ce and Eu anomalies, suggesting that PIRAC is more mafic than that of PAAS and the clays weathered from volcanic rocks and felsic component of the metamorphic rocks dominated the crustal composition of peninsular India. The REE pattern of PIRAC resembles to that of European Shale (ES) and Mud of Queensland (MUQ) but different from PAAS, WRAC, upper continental crust (UCC) and East China Post-Archean Shale (ECPAS), which exhibit LREE-enriched and HREE-depleted REE patterns. It implies that the REE composition of the upper crust is not uniform and it should be thoroughly investigated to determine the composition of PIRAC with more analyses on sediments for better understanding of the evolution of the crust.

Provenance, tectonic setting, and weathering of sediments in Tumaco-1 ST-P well, Tumaco forearc basin, Colombia: Insights from petrography, heavy minerals, X-ray diffraction, and whole-rock chemostratigraphy

A chemostratigraphic evaluation based on major and trace elements (including the REE group), heavy minerals, and whole rock petrographic analysis is applied on 300 samples from the Tumaco-1-ST-P well located in the Tumaco forearc basin, Colombia. The aim of the study is to gain a better understanding of the provenance, tectonic, and paleoweathering conditions of the succession, which contains three formations (Tumaco, Tangareal del Mira, and Cascajal) ranging in age from the late Oligocene to late Pliocene.SiO2 has the highest concentration of all major elements (mean at 52%), followed by Al2O3 (mean at 14.6%), Fe2O3, MgO, and CaO are in the range of 3.2–5.3%, Na2O and K2O oscillate between 1 and 2%, and TiO2, P2O5, MnO, and Cr2O3 are <1%. Out of trace elements, Ba, Sr, V, Cr, Cu, Zn, Ni and Zr are the most abundant; their enrichment is probably due to the marine/deltaic depositional environment conditions. Th, Cs, and Nb have the highest concentrations of all trace elements. In general, concentrations of light rare earth elements are greater than high rare earth elements (LREE > HREE). Both positive and negative Eu anomalies are present in Tumaco and Tangareal del Mira formations, suggesting that rocks have two sources, mafic and felsic; the presence of both is consistent with petrographic and heavy mineral analyses.Paleoweathering indices, such as the chemical index of alteration (CIA), plagioclase index of alteration (PIA), and index of compositional variability (ICV) in the Tumaco-1-ST-P well suggest that the source of these rocks experienced initial stages of weathering compared with Post-Archean Average Australian Shale (PAAS) and Upper Continental Crust (UCC) values, indicating that the Tumaco formation samples have undergone major alteration. The clay mineral assemblage is dominated by the occurrence of illite and illite/smectite mixed layers; when coupled with the CIA index and the Al2O3-CaO-Na2O-K2O (ACNK) plot this indicates post-depositional K-enrichment. The distribution of Al2O3, TiO2, and Zr suggests a limited recycling effect.The presence of first cycle mafic-to-intermediate igneous detritus, together with felsic to intermediate igneous and metamorphic minerals, suggest that the Tumaco forearc basin detrital material was supplied by two locations. One location corresponds to the orogenic island arc system of the Western Cordillera, which is dominated by mafic and intermediate extrusive rocks (basalt and andesite). The other source, which is volumetrically less important, is the Central Cordillera, which comprises intrusive felsic rocks and metamorphic rocks (skarn, marble, and quartz-micaceous schist). This subsidiary source represents a continental arc setting and is observed mainly in the Tumaco Formation.

Metasediments in the Alahina Sector and Associated Mineralization (North-Eastern Guinea)

The Alahina sector is located in the North-East of Guinea, precisely in the Siguiri volcano-sedimentary basin. It consists mainly of meta-sediments traversed by Paleoproterozoic pyroclastite, granite, monzogranite and granodiorite veins as well as Mesozoic dolerite and gabbros veins. This article presents new data, on the one hand, on the geochemical petrographic features and the origin of the metasediments of this zone, and on the other hand, on the genetic model of the gold mineralization that they contain. Field observations, as well as petrographic and geochemical studies reveal that the meta-sediments consist of sericite and chlorite schists. They belong to the groups of shales and grauwackes. Their protholites are moderately altered (60 N/YbN = 6.31 - 13.24) and a flat heavy rare earth patterns (HREE). This spectrum is almost identical to those of the “Post-Archean average Australian Shale” and Early Proterozoic Greywackes. Two types of polyphase gold mineralization occur in the Alahina sector: disseminated and veined. They consist of particular of grains and nanoparticles pyrite associated with gold, magnetite, hematite, ilmenite. The hydrothermal alteration accompanying this mineralization consists of silica, microcline, chlorite-epidote-sericite-carbonates.

Rare earth elements in mud volcano sediments from the Gulf of Cadiz, South Iberian Peninsula

Eight gravity cores (GC) were retrieved from the deep mud volcanoes Sagres, Bonjardim, Soloviev and Porto in the Gulf of Cadiz. Cores with 137 to 317 cm long were sliced in intervals of 15 to 20 cm thickness, and 46 samples were analyzed for grain size distribution, loss on ignition, Al, Fe, Ca, Mg, Mn, Sr, Ba and the rare earth elements (REE) La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. REE profile normalized to Post-Archean Australian Average Shale (PAAS) was dominated by a mid-REE bulge with a pronounced Eu enhancement. Sediment reducing conditions resulting from the anaerobic oxidation of methane probably contributed to the positive-Eu anomaly (1.18–2.19, PAAS normalization). Most likely, reactions near the sulfate-methane transition zone such as the precipitation of barium sulfate found at layers around 50-cm depth explain the enhancement of Eu/Eu* ratios. The Ce anomalies (0.93–1.09) were almost absent.

Effects of topography and vegetation on distribution of rare earth elements in calcareous soils

This study investigated the impact of topography and vegetation on distribution of rare earth elements (REEs) in calcareous soils using methods of single extraction and mass balance calculation. The purposes of the study were to set a basis for further research on the biogeochemical REE cycle and to provide references for soil–water conservation and REE-containing fertilizer amendments. The results show a generally flat Post-Archean Average Australian Shale—normalized REE pattern for the studied calcareous soils. REE enrichment varied widely. The proportion of acid-soluble phases of heavy REEs was higher than that of light REEs. From top to bottom of the studied hills, dominant REE sources transitioned from limestone in-situ weathering to input from REE-containing phases (e.g., clay minerals, amorphous iron, REE-containing fluids). Our results indicate that the REE content of calcareous soils is mainly controlled by slope aspect, while the enrichment degree of REEs is related to geomorphological position and vegetation type. Furthermore, the proportion of acid-soluble phases of REEs is mainly controlled by geomorphological position.

Distribution and fractionation of rare earth elements and Yttrium in suspended and bottom sediments of the Kali estuary, western India

Concentrations of rare earth elements (REE) and yttrium (Y), and major metals (Al, Fe and Mn) were measured in suspended particulate matter (SPM) and bottom sediments of the Kali estuary, western India, for their distribution and fractionation. The contents of SPM and metals in it were more uniform along the longitudinal transect during the monsoon. During the post- and pre-monsoons, low SPM in the upper/middle estuary coincided with high Fe and Mn and total REE (∑REE). But in the lower estuary SPM and its ∑REE content increased seaward, while Fe and Mn decreased. The Y/Ho ratios decreased seaward during the monsoon but increased during the post-monsoon. Sm/Nd ratios were more uniform along the transect during monsoon but decreased marginally seaward in other seasons. The Post-Archean Average Australian Shale (PAAS)-normalized REE patterns exhibited middle REE and heavy REE enrichment with positive Ce ($${\text{Ce}}/{\text{Ce}}^{*}$$ ), Eu ($${\text{Eu}}/{\text{Eu}}^{*}$$ ) and Y anomalies. The $${\text{Ce}}/{\text{Ce}}^{*}$$ increased but $${\text{Eu}}/{\text{Eu}}^{*}$$ decreased marginally seaward. The fine-grained sediments showed higher ∑REE and lower Y/Ho ratios than in coarse-grained sediments. The PAAS-normalized REE patterns of sediment were similar to that of SPM. The results revealed two processes, colloidal flocculation and coagulation of metals in the low-salinity zone and an estuarine turbidity maximum in the high salinity zone. Rare earths and yttrium (REY) in SPM and sediments primarily reflected the source rock composition than that of chemical weathering. Apart from physico-chemical processes, the mineralogy and grain size of sediments controlled the distribution and fractionation of REY in the estuary.

Distribution of some rare and trace elements in modern bottom sediments of the Caspian Sea

The features of the distribution of some rare and trace elements in modern bottom sediments of the Caspian Sea have been studied from samples collected during cruises 35, 39, and 41 of the R/V Rift and the cruise of the R/V Nikifor Shurekov in 2013. It was established that bottom sediments in different areas of the Caspian Sea vary to some degree in the contents of Zr, Hf, Th, V, Cr, Co, Ni, Cu, Sr, and Ba in comparison to suspended matter discharged by the Volga River and rivers originating in the Caucasus. As follows from the results of a comparison of the geochemical features of modern bottom sediments of the Volga River delta and different sedimentary subsystems of the Caspian Sea with the chemical composition of Middle Archean granitoids and Paleozoic and Mesozoic–Cenozoic basalts, which are regarded as geochemical images of such provenance areas as the basement of East European Platform, Urals, and Caucasus, none of these regions is considered the dominant provenance area for all sedimentary subsystems of the Caspian Sea region. Here, the revealed similarity between modern bottom sediments of the northern, central and southern Caspian Sea regions, the Volga River delta, and Post-Archean average Australian shale (PAAS) in some parameters, including REE spectra, assumes that the Volga River discharge plays a dominant role in the formation of the geochemical image of Caspian Sea subsystems. The role of clastics, including the fine-grained fraction, which is supplied to the Caspian Sea from the Caucasus region and Elburz Mountains, is insignificant already in the coastal area, which is determined both by influence of the marginal filter (MF) and large-scale cholestatic current circulation.

Dust, volcanic ash, and the evolution of the South Pacific Gyre through the Cenozoic

We examine the 0–100 Ma paleoceanographic record retained in pelagic clay from the South Pacific Gyre (SPG) by analyzing 47 major, trace, and rare earth elements in bulk sediment in 206 samples from seven sites drilled during Integrated Ocean Drilling Program Expedition 329. We use multivariate statistical analyses (Q-mode factor analysis and multiple linear regression) of the geochemical data to construct a model of bulk pelagic clay composition and mass accumulation rates (MAR) of six end-members, (post-Archean average Australian shale, rhyolite, basalt, Fe-Mn-oxyhydroxides, apatite, and excess Si). Integrating the results with Co-based age models at Sites U1365, U1366, U1369, and U1370, we link changes in MAR of these components to global oceanographic, terrestrial, and climatic transformations through the Cenozoic. Our results track the spatial extent (thousands of kilometers) of dust deposition in the SPG during the aridification of Australia. Dispersed ash is a significant component of the pelagic clay, often comprising >50% by mass, and records episodes of Southern Hemisphere volcanism. Because both are transported by wind, the correlation of dust and ash MAR depends on the site's latitude and suggests meridional shifts in the position of atmospheric circulation cells. The hydrothermal MARs provide evidence for rapid deposition from the Osbourn Trough spreading ridge before it went extinct. Excess Si MARs show that the abrupt increase in siliceous productivity observed at Site U1371 also extended at least as far north as Sites U1369 and U1370, suggesting large-scale reorganizations of oceanic Si distributions ~10–8 Ma in the southern SPG.

Geochemical fractions of rare earth elements in soil around a mine tailing in Baotou, China.

Rare earth mine tailing dumps are environmental hazards because tailing easily leaches and erodes by water and wind. To assess the influence of mine tailing on the geochemical behavior of rare earth elements (REEs) in soil, sixty-seven surface soil samples and three soil profile samples were collected from different locations near China’s largest rare earth mine tailing. The total concentration of REEs in surface soils ranged from 156 to 5.65 × 104 mg·kg−1 with an average value of 4.67 × 103 mg·kg−1, which was significantly higher than the average value in China (181 mg·kg−1). We found obvious fractionation of both light and heavy REEs, which was supported by the North American Shale Composite (NASC) and the Post-Archean Average Australian Shale (PAAS) normalized concentration ratios calculated for selected elements (LaN/YbN, LaN/SmN and GdN/YbN). A slightly positive Ce anomaly and a negative Eu anomaly were also found. For all 14 REEs in soils, enrichment was intensified by the mine tailing sources and influenced by the prevailing wind.

Petrography and geochemistry of the Kamlial Formation, southwestern Kohat plateau, Pakistan: implications for paleoclimate of the Western Himalayas

The Middle to Late Miocene Kamlial Formation that largely consists of sandstone and interbedded clay/mudstone sequences is exposed in the southwestern part of the Kohat plateau, which constitutes the westernmost extension of the Himalayan Foreland Basin. Whereas the sandstone is gray to brownish gray, fine- to medium-grained, and mostly thick-bedded, the interbedded clay/mudstone sequence is brownish gray to maroon red and occurs as continuous beds as well as lenses. Some mudstone/clay beds are bioturbated and seem to be pedogenic surfaces. Results of geochemical investigation of fresh (unaltered) representative sandstone and mudstone samples from three different sections of the formation in the southwestern Kohat plateau are presented and discussed. The average chemical index of alteration (CIA) values of both the sandstone (70-86) and mudstone (71-85) suggest moderate to slightly intense weathering in the source area. However, the high CIA values may also be due to the presence of abundant sedimentary rock fragments, which occur in the studied sandstone, rather than a result of severe weathering. Furthermore, the possibility of intensive chemical weathering in the Himalayas orogenic belt is highly unlikely, as it requires tectonic quiescence for a long period, higher temperature, and humidity. Accordingly, the range of the index of chemical variability values (0.6-2.1) of mudstone and low contents of Rb and Cs in both the mudstone and sandstone indicate somewhat moderate weathering. Furthermore, the Th/U and Rb/Sr ratios of the Kamlial Formation are lower than the corresponding average values for the upper continental crust and post-Archean average Australian shale, which shows that these sediments are first-cycled in origin. However, the Zr/Sc ratio indicates minor contributions from recycled sedimentary sources. The values of authigenic U and the U/Th, V/Cr, Cu/Zn, and Ni/Co ratios all suggest that the Kamlial sediments were deposited under oxidizing conditions.

Provenance of Early Paleozoic metasediments in the central Chinese Altai: Implications for tectonic affinity of the Altai-Mongolia terrane in the Central Asian Orogenic Belt

The Chinese Altai is one of the most typical segments of the Altai-Mongolia terrane, of which the tectonic evolution and affinity are hotly disputed and still not well constrained. Early Paleozoic metasedimentary rocks are extensive in the Altai-Mongolia terrane and their provenance is a key to unravelling the tectonic history of this terrane. Metasediments from Kulumuti Group were collected from the central Chinese Altai for geochemical study. They have low Chemical Index of Alteration (CIA = 52–54) and high Index of Compositional Variability (ICV = 0.81–1.19) values, different from the mature post-Archean Australian average shale (PAAS), indicating relatively weak chemical weathering and a source compositionally dominated by immature material that lacks alumina-rich minerals. These rocks are moderately enriched in light rare earth element (LREE) and show relatively flat heavy rare earth element (HREE) patterns (LaN/YbN = 2.36–9.80, GdN/YbN = 1.31–2.45). Compared with PAAS, they mostly have lower large ion lithophile element concentrations (e.g. Rb, Sr, Ba, Th, U and Pb) and similar contents of high field strength elements (e.g. Zr, Hf and Y), but with lower Nb and Ta. The metasediments have high Rb concentrations (> 50 ppm), relatively high K2O (> 1.1 wt.%) and low REE contents with negative Eu/Eu* anomalies, indicating that these rocks were derived from an acid-intermediate igneous source. The rocks have slightly enriched Nd isotopic compositions with calculated initial εNd(t) values mostly ranging from − 4.3 to − 0.2 and TDM2 model ages between 1.22 and 1.56 Ga. Detrital zircons from two samples of the Kulumuti metasediments have similar age spectra, dominated by Early Paleozoic to latest Neoproterozoic zircons (465–576 Ma) with a few older grains formed between 766–972 Ma and 1321–2572 Ma, remarkably consistent with those from the low-grade metamorphic Habahe Group in the western Chinese Altai. In combination with previous published data, the detrital zircons from Early Paleozoic metasediments in the Chinese Altai dominantly formed between 430–580 and 750–950 Ma, with only a minor population of Meso- to Paleoproterozoic grains. When compared with adjacent terranes, the age spectrum of the Chinese Altai is most similar to that of the Tarim Craton. This craton provided Precambrian materials for the Early Paleozoic metasedimentary rocks now exposed in the Chinese Altai, and therefore suggests that the whole Altai-Mongolia terrane has a close tectonic affinity to the Tarim Craton.

Geochemistry of Kolmani-1 Well Sediments from the Upper Benue Trough, Gongola Basin, Northeastern Nigeria

Aims: To assess the source rock characteristics and the depositional environment through Geochemical studies of sediment samples from the Upper Benue Trough. Place and Duration of Study: Department of Geology, Obafemi Awolowo University, Nigeria and The Activation Laboratory Ltd, Ontario, Canada between February 2011 and March 2012. Methodology: Eighteen samples made up of sand, shale, coaly shale, shaly sand and sandy shale, occurring between the depths of 18.3 m and 2725 m were analysed for thirty-four elements, comprising eight major, twelve trace, and fourteen rare earth elements (REE) using the Inductively Coupled PlasmaMass Spectrometry technique. Results: The results show that the sediments are compositionally rich in Al2O3 and Fe2O3. The low TiO2 values of compared to those of Post-Archean Australian average shale (PAAS) suggest that they were derived from more evolved felsic source rock. The relatively low average Rb/Sr and high Th/U ratios indicate that moderate to more intense weathering occurred in the source rock area. The absolute rare earth elements (REE) concentrations were in the order of coaly shale > shale > sandy shale > shaly sand > sand. Original Research Article British Journal of Applied Science & Technology, 4(20): 2931-2945, 2014 2932 Conclusion: The Al2O3/TiO2, Eu/Eu*, Th/Sc, La/Sc, Th/Co, La/Co, and Th/Cr ratios indicate that the sediments were probably derived from felsic source rocks. In addition, the high LREE/HREE ratios and the negative Eu anomaly also support felsic source rocks for the sediments whilst the very low V/Cr ratios indicate that these sediments were deposited under anoxic environment, consistent with the series of horst and graben structural framework model of the Benue Trough.

Geochemical constraints on provenance of the mid-Pleistocene red earth sediments in subtropical China

The source of mid-Pleistocene red earth sediments in the middle to lower reaches of the Yangtze (Changjiang) River was investigated based on their geochemical characteristics. The Xuancheng and Jiujiang red earth sediments have similar major and trace element distribution patterns. Compared to the loess and paleosol deposits of the Chinese Loess Plateau, the upper continental crust (UCC), and the post-Archean Australian average shale (PAAS), the sediments display notable depletion of CaO, MgO, Na2O, and accumulation of TiO2, Al2O3, and Fe2O3(t). The trace element distribution patterns of the red earth sediments are also different from those of loess and the PAAS, but are similar to those of the loess deposits, except for lower values of mobile trace elements Sr, Ba, and Ni, and higher values of Zr and Y. The red earth samples have uniform La/Th ratios of ~2.8, compatible with those of the UCC, loess, and paleosol. They also have similar chondrite-normalized REE patterns, characterized by enriched LREE and relatively flat HREE profiles, and consistent negative Eu anomalies, similar to those of the UCC, the loess and paleosol, and the Yangtze deposits. These results suggest that the red earth sediments have been subject to considerable mixing prior to deposition and strong subsequent chemical weathering. The sediments have very uniform 143Nd/144Nd and 147Sm/144Nd ratios, this points to well-mixed and multi-recycled sediments. The 143Nd/144Nd and 87Sr/86Sr values of the red earth sediments match well with those of the deposits in the middle to lower reaches of the Yangtze River, but are different from those of the loess and paleosols. This suggests that the red earth sediments are derived from the drainage basins of the middle to lower Yangtze River and might have experienced more intense chemical weathering relative to the Yangtze deposits, as reflected by their higher Rb/Sr ratios, intense depletion of mobile elements and accumulation of immobile elements, as well as their well-developed net-like structure.

Rare earth elements in suspended and bottom sediments of the Mandovi estuary, central west coast of India: Influence of mining

Rare earth elements (REEs) in the suspended particulate matter (SPM) of the Mandovi estuary indicated that the mean total-REEs (∑REE) and light REE to heavy REE ratios are lower than that of the average suspended sediment in World Rivers and Post-Archean average Australian shale. High ∑REE were associated with high SPM/low salinity and also with high SPM/high salinity. Although the ∑REE broadly agree with SPM levels at each station, their seasonal distributions along transect are different. SPM increased seaward in the estuary both during the monsoon and pre-monsoon, but consistently low at all stations during the post-monsoon. The mean ∑REE decreased marginally seaward and was <25% at sea-end station than at river-end station. Spatial variations in ∑REE are maximum (64%) during the pre-monsoon. Strong to moderate correlation of ∑REE with Al, Fe and Mn in all seasons indicates adsorption and co-precipitation of REEs with aluminosilicate phases and Fe, Mn-oxyhydroxides. The ratio of mean ∑REE in sediment/SPM is low during the monsoon (1.27), followed by pre-monsoon (1.5) and post-monsoon (1.62). The middle REE- and heavy REE-enriched patterns with positive Ce and Eu anomalies are characteristic at every station and season, both in SPM and sediment. They also exhibit tetrad effect with distinct third and fourth tetrads. Fe-Mn ore dust is the most dominant source for REEs. However, the seasonal changes in the supply of detrital silicates, Fe-Mn ore dust and particulates resuspended from bottom sediments diluted the overall effect of salinity on fractionation and distribution of REEs in the estuary.

Geochemistry of shales of the Upper Cretaceous Hayang Group, SE Korea: Implications for provenance and source weathering at an active continental margin

Shales of the Upper Cretaceous Hayang Group in the Yeongyang Subbasin, southeastern Korea were deposited in fluvio-lacustrine environments as the Paleo-Pacific (Izanagi) Plate obliquely subducted beneath the Asian continent. Major and trace element compositions derived from shales analyzed from the Hayang Group reveal geochemical signatures that are different from Post-Archean average Australian Shale (PAAS), but are typical of igneous rocks found in the continental-margin island arc settings. For example, most major element concentrations are depleted relative to PAAS; among them MgO and MnO depletions are most pronounced in all shales. CaO enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro-calcite nodules. Sc, Y, and Th concentrations are also slightly depleted relative to PAAS while chondrite-normalized REE data for shales from the Hayang Group show moderate to large uniform LREE enrichment but variable HREE depletions. In addition, they are more fractionated than PAAS, and have significant negative Eu anomalies. Moreover, the chemical index of alteration and A–CN–K relations comply that the source area was dominated by non-steady state weathering regimes indicative of active uplift along an active continental margin. These regions were punctuated by two periods of steady-state weathering or alternatively by enhanced recycling of sediments. The latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area. Mixing calculations based on REE data suggest that the average shale in the Hayang Group was derived from sources composed of Precambrian granitic gneiss, arc basaltic rocks, Triassic Yeongdeok Granite in the subbasin, and the Mino accretionary complex of SW Japan with ratios around 43.7 (31.8–73.2):26.4 (15.8–36.7):15.4 (2.8–33.9):14.5 (0.0–33.8). However, these proportions change up sequence.

Early Paleozoic sedimentary record of the Chinese Altai: Implications for its tectonic evolution

The Chinese Altai is a typical part of the Central Asian Orogenic Belt (CAOB), but its tectonic evolution is not well understood. Geochemical study of Early Paleozoic metasedimentary rocks was conducted to better constrain their provenance and tectonic environment. These rocks have relatively low CIA values (49 to 79), with ICV values (0.73–1.36) higher than that of post-Archean Australian average shale (PAAS), suggesting that they experienced relatively weak chemical weathering and were mainly derived from an immature source. Compared to PAAS and upper crust, the samples mostly have relatively lower high field strength elements (HFSE) (e.g. Zr, Hf, Nb, Ta) and large ion lithophile element (LILE) contents (e.g. Rb, Sr, Ba, Th, U, Pb). However, their relatively high Rb concentrations (> 40 ppm), low Rb/Sr (0.04–3.24) and Th/U (Th/U = 3–8) ratios are indicative of an acidic-intermediate igneous source that had undergone weak chemical weathering. All of the samples are moderately enriched in LREE (light REE) and show relatively flat Chondrite-normalized HREE (heavy REE) patterns (La N/Yb N = 3.2–12.6) with various negative Eu anomalies (Eu/Eu⁎ = 0.4–0.9). Meta-arenaceous samples have moderate SiO 2 (average 72.9 wt.%), Al 2O 3 (average 11.5 wt.%), Fe 2O 3 T + MgO (average 7.16 wt.%) contents and moderate Al 2O 3/SiO 2 (average 0.16), K 2O/Na 2O (average 0.93) ratios, similar to those of graywackes from continental island arcs or active continental margins. However, meta-argillaceous samples have high SiO 2 (average 60.8 wt.%), Al 2O 3 (average 17.2 wt.%), Fe 2O 3 T + MgO (average 12.2 wt.%) contents and high K 2O/Na 2O (average 3.45), Al 2O 3/SiO 2 (average 0.28) ratios similar to mudstones from continental arc basins. This kind of tectonic environment is also manifested in tectonic discrimination diagrams including Th–Sc–Zr/10 and La–Th–Sc. These geochemical characteristics suggest that the metasedimentary rocks were deposited in an active continental margin or continental arc setting. This does not favor the previously proposed passive continental margin model. Therefore, this study supports an arc accretion model for the Chinese Altai.