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Using a complex of analytical methods, clay minerals were studied in Pleistocene sediments from Hole ODP 1038B (120.50 m deep), drilled on the northwestern edge of the Central Hill (Escanaba Trough, Gorda Ridge) near the hydrothermal source with a temperature of 108°C, as well as in Pleistocene background terrigenous sediments from reference Hole ODP 1037B, drilled in the Escanaba Trough 5 km south of the Central Hill. The terrigenous clay mineral assemblage in sediments from Hole 1037B consists of the mixed-layer smectite-illites, smectite, chlorite, illite, and kaolinite. Sediments from Hole 1038B in the interval from the bottom surface to a depth of 5–7 m are composed of terrigenous clay minerals. In the rest of the sedimentary section, clay minerals are represented by the newly formed biotite, chlorite, and dioctahedral smectite. They were formed during the basaltic melt intrusion into the Escanaba Trough with the formation of a laccolith and the subsequent rapid cooling of its flank. The intrusion was accompanied by the ascent of high-temperature hydrothermal fluid in the central discharge channel, interacting with the adjacent sediments. As a result, the fine-dispersed biotite was formed in sediments at the high-temperature stage of this interaction due to the primary terrigenous clay minerals, K-feldspar, and amphiboles. The rapid cooling of the hydrothermal fluid to a temperature of presumably 270–330°C promoted the partial replacement of biotite by chlorite. The further rapid cooling of the hydrothermal fluid to 200°C and lower and its mixing with seawater seeping into sediments of the Central Hill fostered the formation of smectite. [ABSTRACT FROM AUTHOR]

This is the second of a two-part New Zealand Journal of Geology and Geophysics Special Issue on understanding sedimentary systems in Aotearoa-New Zealand's Hikurangi Subduction Margin (HSM). This volume includes six research papers that explore sediment-tectonic interactions operating over a range of spatio-temporal scales. We take a distinctive perspective moving from the subduction deformation front in the Hikurangi Trough, upslope to the subduction wedge, and onshore to the Coastal Ranges. Temporally, papers span the onset of subduction in the Miocene, to disentangling provenance of turbidity currents triggered by the 2016 CE Kaikōura Earthquake. Collectively, the studies in the special issue reveal a complicated and continually evolving margin, where active tectonics and volcanism, coupled with vigorous climatic and oceanographic drivers, modulate erosion, transport, and depositional cycles of vast volumes of terrigenous sediment into ocean basins. Despite decades of significant research advances in our knowledge of the HSM, considerable scope remains for future work. A deeper understanding of fundamental tectonic-sediment interactions operating on active margins, along with the significant geohazards they pose remain outstanding research needs. Collectively, Volumes 1 and 2 highlight enduring interest in the HSM as a globally important natural laboratory for the study of subduction zone geoscience. [ABSTRACT FROM AUTHOR]

Turbidity current deposition belongs to event deposition, which is of great significance to the study of neotectonic movement. However, turbidite deposits are rarely found in deep-sea basins. In this work, the particle size, mineralogy, and geochemistry of 14 deep-sea sediment cores from the Southwest Sub-basin (SWSB) of South China Sea (SCS) and its periphery are used to trace the sources of sediment and reveal the sedimentological and geochemical characteristics of deep-sea sediments. The results show that quartz and feldspar are the main minerals in the core sediments from the SWSB, and there are multiple layers of turbidites. Geochemical analysis reveals that the composition of the core sediments is close to that of the western margin of the SCS and is similar to that of the upper continental crust (UCC) and is inherited from terrigenous sediments. The Sr--Nd isotope results indicate that the sediment provenances of the SWSB are from the Mekong River, Sunda Shelf and Red River, showing the characteristics of multiple sources. Therefore, we propose that terrigenous materials from multiple sources can reach the deep-sea basin of the SWSB, and we also establish a transport model of deep-sea terrigenous sediment. Terrigenous materials were first carried by rivers and surface currents to the continental margins near the SWSB, and fine materials were subsequently transported by surface currents to the deep-sea basin, while coarse materials were subsequently transported by turbidity currents. Turbidity current deposits provide an approach for studying the transport of coarse materials in deep-sea basins of SWSB. [ABSTRACT FROM AUTHOR]

The effects of sediment contribution to the Lesser Antilles island arc have been well explored with whole-rock trace-element chemistry and isotopic studies. To better understand the source of these sediments, we analyzed >400 zircons for U-Pb ages and trace-element chemistry in eight andesiticdacitic ignimbrites and lavas younger than 100 ka from the island of Dominica in the central Lesser Antilles arc. The overwhelming majority of the zircons analyzed were magmatic in origin, with U-Pb ages younger than 10 Ma, but predominantly younger than 300 ka. Zircon trace-element chemistry is consistent with derivation from an oceanicisland arc, and positive eHf(t) values (+5 to +15) support a juvenile depleted mantle source. Rare Precambrian to Eocene xenocrystic zircons (36) were also found in the Dominican volcanics and record sediment dispersal from several different terranes as the Caribbean plate migrated eastward along the northern margin of South America. Although some previous detrital zircon studies in the region suggested zircons younger than 100 Ma were derived from the Great Arc of the Caribbean, the younger Dominican zircon xenocrysts (300-50 Ma) have elevated Th/Yb and U/Yb, as well as variable positive/negative eHf(t) values, inconsistent with an oceanic arc origin. These zircons in Dominica were most likely derived from the Eastern and Central Cordillera of the Andes, which experienced a flare-up in magmatism ca. 65-45 Ma. As the Great Arc of the Caribbean traversed along the South American margin, terrigenous sediments transported via river systems and turbidites accumulated in the forearc basin. Older zircons (1800-300 Ma) have a slightly different chemistry and equivocal source(s), including the Andes, northern Venezuelan coastal ranges, and/or the Guyana Shield. [ABSTRACT FROM AUTHOR]

Lithologic heterogeneity and the presence of fluids have been linked to seamount subduction and collocated with slow earthquakes. However, the deformation mechanisms and fluid conditions associated with seamount subduction remain poorly understood. The exhumed Chichibu accretionary complex on Amami-Oshima Island preserves mélange shear zones composed of mudstone-dominated mélange and basalt–limestone mélange deformed under sub-greenschist facies metamorphism. The mudstone-dominated mélange contains sandstone, siliceous mudstone, and basalt lenses in an illitic matrix. The basalt–limestone mélange contains micritic limestone and basalt lenses in a chloritic matrix derived from the mixing of limestone and basalt at the foot of a seamount. The basalt–limestone mélange overlies the mudstone-dominated mélange, possibly representing a submarine landslide from the seamount onto trench-fill terrigenous sediments. The asymmetric S–C fabrics in both mélanges show top-to-SE shear consistent with megathrust-related shear. Quartz-filled shear and extension veins in the mudstone-dominated mélange indicate brittle failure at near-lithostatic fluid pressure and low differential stress. Microstructural observations show that deformation in the mudstone-dominated mélange was accommodated by dislocation creep of quartz and combined quartz pressure solution with frictional sliding of illite, whereas the basalt-limestone mélange was accommodated by frictional sliding of chlorite and dislocation creep of coarse-grained calcite, with possible pressure solution creep and diffusion creep of fine-grained calcite. The mélange shear zones formed in association with seamount subduction record temporal changes in deformation mechanisms, fluid pressure, and stress state during megathrust shear with brittle failure under elevated fluid pressure, potentially linking tremor generation near subducting seamounts. [ABSTRACT FROM AUTHOR]

During the Late Cretaceous (Cenomanian), significant disruptions in the carbon cycle, global warming, and episodes of oceanic anoxia occurred, leading to the deposition of organic carbon-rich sediments. In well BED2-3, located in the BED2 gas field within the Abu Gharadig Basin (north Western Desert, Egypt), the lower-to-middle Cenomanian Bahariya Formation displays thick alternating layers of sandstones, siltstones, and shales. Detailed geochemical analyses were conducted on thirty-three cutting samples from the Bahariya Formation, focusing on total organic carbon (TOC), whole-rock elemental geochemistry, and carbonate content. These geochemical measurements provided valuable information regarding paleoredox conditions, marine biological productivity, terrigenous sediment influx, weathering and paleoclimate conditions, and mechanisms influencing organic matter accumulation. The enrichment factors (EF) of redox-sensitive trace elements were utilized to infer oxygenation conditions and marine biological productivity during the deposition of the Bahariya Formation. The stratigraphic distribution of redox-sensitive elements allowed for the Bahariya Formation to be categorized into lower and middle-upper intervals. The results revealed that the lower interval exhibited strong-to-enriched EF values of redox-sensitive elements and fair-to-rich TOC content, indicating a prevalent anoxic setting during deposition. In contrast, the middle-upper interval displayed weakly-to-slightly enriched EF values with poor-to-fair TOC content, suggesting deposition under oxic-suboxic redox conditions. By examining Al-normalized redox-sensitive ratios and their correlations with TOC content, significant relationships were observed in the lower interval, indicating a coupling between the enrichment of redox-sensitive elements and organic matter. This suggests enhanced biological productivity during deposition of the lower interval compared to the relatively low productivity during deposition of the middle-upper interval of the formation. These conditions controlled the production and preservation of organic matter in the lower interval, while the middle-upper interval suffered from organic matter dilution and destruction due to an increased influx of terrigenous material and lower biological productivity. Geochemical proxies related to detrital materials provided evidence of alternating terrigenous sediment flux, consistent with shifts between coarse- and fine-grained fractions and related facies of sandstones, siltstones, and shales. These findings align with active continental weathering in the source terrane and deposition under enhanced warm-humid climatic conditions, with intermittent arid-to-semi-arid phases. These conclusions are further supported by the palynomorph assemblages and clay mineralogy within the Bahariya Formation. [ABSTRACT FROM AUTHOR]

Authigenic dispersed biotite was discovered for the first time in Pleistocene terrigenous sediments of the Central Hill located in the Escanaba Trough in the southern part of the Gorda Ridge (northeastern sector of the Pacific Ocean). It accounts for almost the entire content of fine fractions <1 μm of most samples from ODP Hole 1038B. The authigenic nature of the biotite is associated with the metasomatic effect of hydrothermal solution on terrigenous clay minerals of sediments after the intrusion of basaltic magma in the form of laccolith with a temperature of ~1200°C. The mineral composition of fine fractions of sediments was studied using complex analytical methods, including modeling of their X-ray diffraction patterns. It has been established that the dispersed micaceous mineral (biotite) is trioctahedral, high-iron, does not swell when saturated with glycol, but contracts after heating at 550°C. It is shown that its structure is devoid of foreign layers, the height and composition of which differ from those of micaceous layers. The decrease in the height of micaceous layers upon heating biotite to 550°C is mainly related to a decrease in the height of 2 : 1 octahedra due to the difference in the Fe2+–O and Fe3+–O bond lengths as a result of the oxidation of Fe2+ cations. It has been established that a limit value for the coefficient of variation CV should not exceed 0.10 to characterize the absence of mixed-layering in a regular structure. [ABSTRACT FROM AUTHOR]

Lithogenic materials such as terrigenous lithogenic particles (TLP) can efficiently promote the formation and sinking of mineral‐associated marine organic matter, acting as important ballast and potentially playing an important role in the global carbon cycle. To assess the influence of TLP on fluxes of particulate organic carbon (POC) and other biogeochemical cycles, we construct TLP forcing fields based on global riverine suspended sediment data and then apply them to the Community Earth System Model, version 2 (CESM2) modified with the TLP ballasting effect term. Simulations forced by different concentrations of TLP transported in the surface ocean or along the bottom of continental shelves and slopes are conducted. When the TLP transports seaward along the bottom, simulated POC fluxes at 100 and 2,000 m decrease about 11% and 19%, respectively, for the global ocean, and about 9% and 12%, respectively, for the oceanic regions of continental margins. The initial abiotic ballast processes triggered by TLP input increase POC fluxes, causing additional removal and burial of dissolved iron in continental margins. This further enhances the accumulation of macronutrients in the upwelling regions and their advection transport to neighboring subtropical gyres, thus altering regional productivity when simulations reach quasi‐equilibrium. When consider the impacts of TLP in simulations, the simulated POC flux exhibits an increase in subtropical gyres but a decrease in tropical Pacific and mid‐high latitude regions. The present work highlights the importance of TLP in global biogeochemical cycles, suggesting that the amount of carbon sequestration might be overestimated without TLP in models. Key Points: The ballast effect of terrigenous lithogenic particles has been incorporated into a community earth system modelCarbon sequestration might be overestimated without terrigenous lithogenic particles in the modelWith terrigenous lithogenic ballast, simulated POC flux increases in subtropics but decreases in tropical Pacific and mid‐high latitudes [ABSTRACT FROM AUTHOR]

This paper presents the results of mineralogical, geochemical, isotope, and geochemical (Sm–Nd) studies of siltstones from the upper Bystraya subformation of the Argun continental massif, as well as U–Pb dating of detrital zircon grains from them. The main goal of the research was to identify the main sources of clastic material, to reconstruct the paleogeodynamic environment of accumulation, and to constrain the lower age limit for the formation of terrigenous rocks of the upper Bystraya subformation. The mineralogical composition of the studied rocks indicates their accumulation in an environment associated with subduction processes. The trace element composition of siltstones from the subformation suggests the presence of rocks of mixed composition in the source area in terms of their silica content. Based on Sm–Nd isotope and geochemical data, it was established that the main sources of clastic material for siltstones of the stratigraphic unit were Paleoproterozoic rocks and (or) younger rocks whose formation is associated with the reworking of the Paleoproterozoic continental crust. Most of the zircons from the studied siltstone sample of the upper Bystraya subformation are Neo- and Paleoproterozoic in age. Their sources are probably Neo- and Paleoproterozoic igneous rocks widespread within the Argun massif in China. The ages of the youngest zircons (556 ± 9 and 566 ± 10 Ma) isolated from siltstones of the upper Bystraya subformation were used to constrain the lower limit of their accumulation at the middle Ediacaran. [ABSTRACT FROM AUTHOR]

The Jurassic Period was a significant phase of variable organic matter accumulation in paleo-shelf areas of the southern Tethys (Egypt). Reconstructing the paleoredox conditions, paleoclimate, and weathering intensity, along with the role of terrigenous sediment flux and mineralogical maturity, is important for understanding basin infill history and prevalent paleoenvironmental conditions. Here, inorganic geochemical data are presented from the Middle Jurassic Khatatba Formation and two samples from the underlying Ras Qattara and the overlying Masajid formations in the Jana-1x well, Shushan Basin, Western Desert. Twenty-four (24) whole-rock samples were analyzed for their major and trace element composition and carbonate content. The Khatatba Formation represents one of the major hydrocarbon source rocks in the North Western Desert, Egypt. Redox conditions were assessed based on enrichment factors of redox-sensitive elements Mo, V, U, and Co. Results revealed that the Khatatba Formation was deposited under predominant anoxic bottom and pore water conditions, in contrast to the oxic settings that were prevalent during the deposition of the Ras Qattara and Masajid formations. Continental weathering intensity and paleoclimate were reconstructed based on several proxies, such as the chemical index of alteration (CIA), K2O/Rb, Rb/Sr, Ln(Al2O3/Na2O), and Al/K ratios, indicating that the studied succession was deposited during alternating phases between weak and moderate weathering intensity under arid and warm-humid climates, respectively. Periods of enhanced continental weathering were associated with high values of clastic ratios such as Si/Al, Ti/Al, and Zr/Al, suggesting increased terrigenous sediment supply during intensified hydrological cycling. These ratios further provided inferences about the changes in sediment grain size, such as a change from shale to coarse silt- and sand-size fractions. [ABSTRACT FROM AUTHOR]

This study focuses on characterizing a discontinuity within the Seán stalagmite (4.75–7.75 cm) by means of two nondestructive techniques: (1) high-resolution micro-computed tomography (micro-CT) and (2) X-ray fluorescence (XRF) core scanning (XRFCS). Micro-CT was used to study the stalagmite density, and XRFCS was applied to obtain the qualitative elemental composition and colour measurements. The new data obtained from nondestructive techniques have been combined with previously published geochemical data and fabric determinations from the same stalagmite found in Sa Balma des Quartó cave in Mallorca. The two methodologies applied in the present study have improved the characterization of the distinctive horizon. The micro-CT images identified the layer as a minor event due the high air content. The distinctive horizon is characterized by a high Ti-content, indicating the arrival of terrigenous particles. Based on those observations, together with the fact that the micrite layer appears filling the gaps between the older columnar fabric, we argue that the micrite layer may represent a major flooding event inside the cave after the year 1616 ± 23 CE and before the year 1623 ± 28 CE, which can be related to an extreme rainfall event. This hypothesis is further supported by the observed cave flooding during the autumn of 2018. [ABSTRACT FROM AUTHOR]

Purpose: Unpaved road erosion represents a key source of terrigenous sediment threatening Caribbean coral reefs, yet no empirical data existed to document this in Culebra, Puerto Rico. Here, we compared unpaved road erosion to that from undisturbed hillslopes and evaluated the effects of road grading frequency and slope on erosion. Methods: A total of 46 plot-scale rainfall simulation experiments were used to measure runoff response and erosion rates from undisturbed hillslopes and unpaved roads with varying slopes and time since grading. Rainfall rates recorded over a one-year period combined with empirically derived infiltration capacity curves and erosion rates allowed for annualizing runoff and sediment production for natural hillslopes and four road types representing different grading frequencies and slopes. Results: Infiltration rates from roads were between a tenth and a quarter of those from natural hillslopes and that lead to roads generating runoff five times more frequently than natural hillslopes annually. Road erosion rates were between 330 and 760 times greater than those from undisturbed hillslopes, depending on slope and grading. Roads represent a dominant source of sediments responsible for increasing watershed-scale erosion rates from 1.1 to 25 times above background rates. Conclusion: Unpaved roads represent a major source of the sediment that threatens the coral reefs of Culebra. Therefore, future new road building must be kept to a minimum and unpaved roads must be the focus of coral reef protection efforts. [ABSTRACT FROM AUTHOR]

The marine losses during the Permo-Triassic mass extinction were the worst ever experienced. All groups were badly affected, especially amongst the benthos (e.g. brachiopods, corals, bryozoans, foraminifers, ostracods). Planktonic populations underwent a fundamental change with eukaryotic algae being replaced by nitrogen-fixing bacteria, green-sulphur bacteria, sulphate-reducing bacteria and prasinophytes. Detailed studies of boundary sections, especially those in South China, have resolved the crisis to a ∼55 kyr interval straddling the Permo-Triassic boundary. Many of the losses occur at the beginning and end of this interval painting a picture of a two-phase extinction. Improved knowledge of the extinction has been supported by numerous geochemical studies that allow diverse proposed extinction mechanisms to be studied. A transition from oxygenated to anoxic-euxinic conditions is seen in most sections globally, although the intensity and timing shows regional variability. Decreased ocean ventilation coincides with rapidly rising temperatures and many extinction scenarios attribute the losses to both anoxia and high temperatures. Other kill mechanisms include ocean acidification for which there is conflicting support from geochemical proxies and, even less likely, siltation (burial under a massive influx of terrigenous sediment) which lacks substantive sedimentological evidence. The ultimate driver of the catastrophic changes at the end of the Permian was likely Siberian Trap eruptions and their associated carbon dioxide emissions with consequences such as warming, ocean stagnation and acidification. Volcanic winter episodes stemming from Siberian volcanism have also been linked to the crisis, but the short-term nature of these episodes (

The climate response of tropical Southeast Asia to abrupt climate change originating from high northern latitudes remains poorly understood. Here, marine sediments recovered from the Northwest Borneo Trough are analyzed to trace variations in terrigenous material composition associated with sea level and palaeoflood activities over the past 40 ka. We describe for the first time the influence of sea level change on terrigenous deposition from a tropical island with small mountainous rivers surrounded by narrow continental shelves and the coupling between North Atlantic dynamics and climate feedbacks in tropical Southeast Asia during the Dansgaard‐Oeschger stadials. This study demonstrates that climate oscillations occurring at high northern latitudes can be transmitted to tropical Southeast Asia through the functions of sea level, the East Asian winter monsoon and the Intertropical Convergence Zone. Such information is fundamental to correctly assessing future sea level rise and flood risks in tropical Southeast Asia. Plain Language Summary: Sea level rise and extreme climate events are two global climate issues currently faced by humanity under the background of global warming. However, the climate feedbacks in tropical Southeast Asia remain unknown, although portions of this region are now densely populated. Here, a gravity core retrieved from the Northwest (NW) Borneo Trough is employed to reveal variations in terrigenous material composition and their controlling factors over the past 40 ka. We found that the terrigenous sediments delivered to the NW Borneo Trough are primarily sourced from NW Borneo, and their deposition is mainly controlled by sea level change and flooding. Further in‐depth analysis reveals that northern high‐latitude cooling could cause floods in NW Borneo both in the modern and during the past by influencing the East Asian winter monsoon (EAWM) and/or the Intertropical Convergence Zone (ITCZ). Furthermore, our new records suggest that a stronger EAWM during cold stadials could have transported high levels of northerly moisture to NW Borneo, resulting in relatively higher speleothem δ18O values in NW Borneo. In short, abrupt climate changes in the high‐latitude Northern Hemisphere can be transmitted to tropical Southeast Asia through the functions of sea level, the EAWM and the ITCZ. Key Points: Sea level change and flooding are the main controlling factors for terrigenous deposition from tropical Southeast AsiaNorthern high‐latitude cooling could lead to the outbreak of floods in Northwest Borneo via atmospheric teleconnectionClimate oscillations occurring at high northern latitudes can be transmitted to tropical Southeast Asia [ABSTRACT FROM AUTHOR]

The peculiarities of the distribution of rare-earth elements (REEs) in the surface bottom sediments in the Gulf of Tonkin (South China Sea) are considered. According to the results of granulometric analysis, the sediments are mainly represented by pelitic silt, silty pelite, and miktites. The REE contents normalized to the chondrite composition show the absence of cerium anomaly, the presence of negative europium anomaly and significant fractionation of light and heavy REEs. The values of indicator ratios LaN/YbN, Cr/Th, Th/Co, La/Sc, and Th/Sc indicate the predominance of rocks of intermediate and acidic composition in the erosion areas, due to which sediments were formed. The values of the Ce/La and (Fe + Mn)/Ti ratios characterize the surface sediments as typically terrigenous without the admixture of endogenous exhalative material. The Eu/Sm ratio values indicate low permeability of the sediments for upward fluid flows, which is consistent with the measured methane concentrations. The analysis of correlations indicates the dominance of the terrigenous source of REEs and that clay minerals and iron hydroxides play a significant role in the migration and accumulation of REEs. [ABSTRACT FROM AUTHOR]

This editorial, published in Frontiers in Marine Science, emphasizes the importance of using high-resolution observation methods to better understand the effects and mechanisms of coastal eutrophication, deoxygenation, and acidification. The coastal ocean is facing environmental challenges due to climate change and human activities, and traditional sampling methods are insufficient to fully comprehend these issues. The editorial highlights several studies that employ high-resolution methods to investigate topics such as submarine groundwater discharge, terrigenous particle transportation, seasonal oxygen depletion, and the driving forces behind ocean acidification. These studies offer valuable insights into the impacts of these environmental problems and contribute to our understanding of coastal ecosystems. It is important to note that the claims made in this article are those of the authors and do not necessarily reflect the views of their affiliated organizations or the publisher. Additionally, the publisher does not guarantee or endorse any products or claims made by manufacturers. This article is particularly relevant to library patrons conducting research in the field of marine science. [Extracted from the article]

The results of mineralogical and geochemical studies of sandstones and siltstones of the Ernichnaya Formation of the Argun Series of the Argun continental massif and the U–Pb (LA-ICP-MS) age of their detrital zircon are presented. It is found that the youngest group of detrital zircon has the age of 549–570 Ma with a maximum on the probability density curve of zircon ages of 566 Ma. This suggests that the lower age boundary of their accumulation corresponds to the Ediacaran–Paleozoic boundary. According to the results of U–Pb (LA-ICP-MS) dating of zircon grains, the dominant zircons in sandstones of the sequence have Neo- and Paleoproterozoic ages. These zircons were probably sourced from the Neo- and Paleoproterozoic igneous and metamorphic rocks widely abundant within the Argun continental massif. The geochemical features of terrigenous rocks of the sequence together with the presence of poorly sorted and weakly rounded rock clasts in the studied samples, as well as the presence of interlayers of gravelites in structure of the sequence, indicate their accumulation in a subduction-related setting. [ABSTRACT FROM AUTHOR]

Phyllites from Patharkhola, Lesser Kumaun Himalaya have been studied to investigate the geochemical characteristics of these rocks and their formation processes and mechanism of emplacement. Petrographically, phyllites have been showing the mineral assemblages as Biotite (25% approx.)-chlorite (25% approx.)-muscovite (20% approx.)-quartz (10% approx.)-feldspar (10% approx.)-sericite (5% approx.). Geochemically, the analysed four samples of phyllites have high SiO2 and Al2O3 values. Phyllites with higher alumina have more enrichment of trace elements. The enrichment of Zr and depletion of Y and Nb indicate preferential survival of zircon in extreme weathering conditions. The HFSE has shown variation in the ratios due to decoupling with the major oxides. The enrichment of LREE and depletion of HREE suggest mixing of the terrigenous sediments with the concominant magma. Discrimination plots to classify the tectonic settings suggested that the phyllites of Patharkhola have formed in active continental margins. [ABSTRACT FROM AUTHOR]

As a repository of REE, the Paleoproterozoic phosphorite of the Aravalli Basin in India is explored time to time. Paleoproterozoic phosphorite deposits of the Sallopat sub-basin Banswara district of the Aravalli Supergroup show moderate REE concentrations much lower than that of average marine phosphorites. Different ratios and PAAS-normalized REE distribution patterns reflect MREE enrichment over LREE and HREE in these phosphorites. MREE enrichment confirmed by (Sm/Yb)N versus (Sm/Pr)N relationship and attributed to the selective uptake by cyanobacteria and mixing of riverine inputs. Y/Ho, La/Ce and Er/Nd ratios confirm that the REE in Sallopat phosphorites might have been affected by the argillaceous terrigenous and plagioclase-rich sediments probably derived from Banded Gneissic Complex. Diagenetic modeling indicates that REE were concentrated during early diagenetic processes with limited weathering influence. Moderate negative to low Ce anomaly depicts oxic to sub-oxic conditions of seawater due to oxidation of Ce3+ to Ce4+ whereas Eu3+ reduced to Eu2+ indicating positive Eu-anomaly and reducing conditions as well during the deposition. These anomalies may be due to the stratified restricted marine environment of upwelling and mingling of organic-rich anoxic deep water with oxic upper seawater prior to the formation of phosphorite deposits in the embayment. Enrichment of REE in Sallopat phosphorite relies on various physico-chemical conditions. These phosphorites may have been formed in restricted marine water which was influenced by extra clastic sediment input carried out by fluvial systems. [ABSTRACT FROM AUTHOR]

Subduction recycling of sediments plays a key role in the geochemical evolution of Earth. The presence of recycled terrigenous sediments in upwelling plumes has been cited to explain the EM2 signature in ocean island volcanics, characterized by particularly high 87Sr/86Sr (>0.706). However, the origin of such isotopic anomalies in continental regions and the role of subducted sediments in the subcontinental lithospheric mantle (SCLM) remain unclear. The Himalaya–Tibet orogen is one of the world's best places for deciphering continental subduction and the fate of subducted crustal materials in the mantle. Here we present a systematic study of the geochronology, mineral chemistry (especially clinopyroxene), whole-rock chemistry and Sr–Nd–Pb–Hf–O isotopic compositions of Cenozoic potassic–ultrapotassic lavas from the western Kunlun area of northwestern Tibet. New secondary ion mass spectrometry (SIMS) zircon U–Pb dating, coupled with published age results, constrain the timing of volcanism from ~8.3 Ma to the present. These lavas show geochemical characteristics that closely resemble the EM2 mantle end-member represented by the Samoan hotspot. Both whole rocks and individual magmatic clinopyroxenes display arc-like trace-element patterns and remarkably enriched Sr–Nd–Pb–Hf isotope compositions (87Sr/86Sr ≥ 0.7080; ε Nd ≤ −4.8; 206Pb/204Pb ≥ 18.704; ε Hf ≤ −2.6). Together with high zircon δ18O values (6.3–10.4‰), the data point to a mantle source enriched by recycled sedimentary materials. Geochemical modeling and geophysical evidence further indicate that the sediments were directly derived from the subducted Indian continental lithosphere during India–Eurasia collision. Partial melting models assuming a hybridized mantle source that contains ~5% Indian continental crust suggest that the primary melts of the potassic–ultrapotassic lavas could be formed by melting of a phlogopite-bearing garnet lherzolite at low melting degrees (1–5%). The magma geochemistry is consistent with the model of mélange melting, implying that the subducted sediments may detach from the downgoing Indian slab and rise up diapirically into the overlying mantle lithosphere. Unlike traditional models of subducted sediments entering the deep mantle, the western Kunlun EM2-like lavas reveal that subducted sediments can be rapidly recycled into the SCLM during continental subduction (probably <50 Myr). We suggest that the SCLM could be an important reservoir for subducted sediments. The findings are important to our understanding of mantle circulation rates and chemical heterogeneities. [ABSTRACT FROM AUTHOR]

The East Brazilian continental margin contains a large shelf sector called the Royal Charlotte Bank. It has terrigenous and carbonate sedimentation associated with coastal reefs. Studies using X-ray diffractometry (XRD) and the geochemistry of immobile elements were done in samples of these reefs to figure out the provenance of the mud that arrives there. In order to do this, samples of riverine sediment from the Jequitinhonha, Santo Antônio, João de Tiba, and Buranhém rivers as well as from the Barreiras Group's sedimentary cliffs were taken. The Jequitinhonha River was found to be the most significant mud source. This was supported by the mineral fingerprints of smectite and biotite, the concentrations of immobile trace elements such as Zr, Hf, Nb, Ta, and Th, and the distribution and ratio of rare-earth elements. These findings are supported by the prevailing north-to-south drift that occurs in the region due to the northeasterly trade winds and waves that blow throughout the region for the vast majority of the year. The findings have significant implications for hydrographic basin management and the protection of reef benthic populations. [ABSTRACT FROM AUTHOR]

Modern grasslands on the Indian subcontinent, North and South America, and East Africa expanded widely during the late Miocene – earliest Pleistocene, likely in response to increasing aridity. Grasses utilizing the C4 photosynthetic pathway are more tolerant of high temperatures and dry conditions, and because they induce less C isotope fractionation than plants using the C3 pathway, the expansion of C4 grasslands can be traced through the δ13C of organic matter in soils and terrigenous marine sediments. We present a high-resolution record of the elemental and isotopic composition of bulk organic matter in the Nicobar Fan sediments from IODP Site U1480, off western Sumatra, to elucidate the timing and pace of the C3–C4 plant transition within the ∼1.5 × 106 km2 catchments of the Ganges/Brahmaputra river system, which continue to supply voluminous Himalaya-derived sediments to the Bay of Bengal. Using a multi-proxy approach to correct for the effects of marine organic matter and account for major sources of uncertainty, we recognize two phases of C4 expansion starting at ∼7.1 Ma, and at ∼3.5 Ma, with a stepwise transition at ∼2.5 Ma. These intervals appear to coincide with periods of Indian Ocean and East Asian monsoon intensification, as well as the expansion of Northern Hemisphere glaciation starting at ∼2.7 Ma. Our data from the deep sea for a multi-phased C4 expansion on the Indian subcontinent are in agreement with terrestrial data from the Indian Siwaliks. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the clay mineralogy and geochemistry of surface and drill core samples from the northeastern Beibu Gulf in order to unravel the sediment provenance of, and factors controlling, the sedimentary environment. The main clay mineral assemblage in the surface sediment samples included kaolinite (27–72%), smectite (4–51%), illite (7–20%), and chlorite (8–17%). The study area comprises three major clay distribution zones (from the northeastern coastal area to central Beibu Gulf basin), i.e., the kaolinite-dominated, kaolinite–smectite, and smectite-dominated zones. The zoning of the clay mineralogy and major and trace elements indicated the mixing of coarse terrigenous sediments with distal fine sediments. Early Holocene sea level rise was documented in core B15-1, which had three sedimentary units (divided into Units 1–3 from top to bottom), as revealed by the changes in the dominant clay minerals and geochemical/oxide ratios (SiO2/Al2O3, Rb/Sr, Sr/Ba, and Ti/Ca) in Unit 2. Unit 1 and Unit 3 were likely deposited in the continental and marine environments, respectively. The low sedimentation rate and hydrodynamic disturbance may have influenced the deposition process more than climatic fluctuations. [ABSTRACT FROM AUTHOR]

Decreasing sea ice extent caused by climate change is affecting the carbon cycle of the Arctic Ocean. In this study, surface sediments across the western Arctic Ocean are investigated to characterize sources of sedimentary organic carbon (OC). Bulk organic parameters (total organic carbon, total nitrogen, δ13 C org , and δ15 N) and molecular organic biomarkers (e.g., sterols and highly branched isoprenoids – HBIs) are combined to distinguish between sympagic, pelagic, and terrestrial OC sources. Their downcore profiles generated at the Chukchi Sea R1 core site (74 ∘ N) are then used to evaluate changes in the relative contribution of these components of sedimentary OC over the last 200 years with decreasing sea ice. Our data evidence that, from the 1820s to the 1930s, prevailing high sea ice cover inhibited in situ primary production, resulting in prominent land-derived material in sediments. Then, from the 1930s to the 1980s, primary production started increasing with the gradual decline of summer sea ice. The ratio of sympagic and pelagic OC began to rise to account for the larger portion of sedimentary OC. Since the 1980s, accelerated sea ice loss led to enhanced primary production, stabilizing over the last decades due to freshwater-induced surface ocean stratification in summer. [ABSTRACT FROM AUTHOR]

Knowledge of the hydrodynamic behavior of carbonate bioclasts is essential for solving coastal morphodynamic problems in marine carbonate depositional environments. Marine carbonate grains are produced within the sedimentary system itself and are deformed by subsequent hydrodynamics, resulting in particle densities, sizes and shapes that are distinct from those of terrigenous sediments. In this study, we investigated the shapes and settling characteristics of gravel‐size natural coral debris collected from the coasts of Okinawa Prefecture, Japan. Based on the shape parameters and settling velocities obtained using image analysis techniques and settling tube experiments, respectively, a correlation model for predicting the settling velocity of coral gravel particles was developed by extending the previous formula of Dietrich (1982, https://doi.org/10.1029/wr018i006p01615) over particle Reynolds number values ranging from 384.23 to 4439.76. The model determines the settling velocity as a function of particle nominal diameter, form, roundness, and surface texture parameters that were selected after examining several other shape descriptors. Compared with other models, the proposed model showed better settling velocity predictive skills for coral gravel particles classified into four shape types. The proposed model also determines how the drag coefficient of coral gravel particles should be modified from that for spherical particles, by accounting for the abovementioned coral gravel particle shape parameters. The obtained data set of settling velocity and modification of the drag coefficient can be used for quantitative interpretation of suspension, transport, and sedimentation processes in marine carbonate depositional environments. Plain Language Summary: Coral coasts, formed by the accumulation of carbonate bioclasts, are suffering severe erosion and inundation threats due to global climate change. Understanding how these loose materials on top of coral reef platforms move under complex hydrodynamics is essential for morphodynamic predictions and developing coastal protection measures. As highly heterogeneous sediment particles, coral fragments exhibit properties distinct from those of terrestrial source sediments in terms of size, shape and density. In this work, we focused on coral debris samples collected at Okinawa Prefecture, Japan, to clarify their settling characteristics. A better prediction of the settling velocity of coral gravel particles was achieved by considering as many parameters as possible, including particle size, density, form, roundness and surface texture effects. Moreover, the drag coefficient equation for coral gravel particles was modified from that for spherical particles by accounting for particle form, roundness and surface texture effects. These findings are essential for the successful quantitative interpretation of suspension, transport, and sedimentation processes in coral reef systems. Key Points: The variabilities in the skeletal porosity, density, and shape of coral debris were found to be distinct from those of siliciclastic sedimentsThe settling velocity of coral gravels can be better predicted by accounting for the effects of particle form, roundness and surface textureWe provide a way to define the drag coefficient of coral gravels by incorporating particle shape effects into that of a sphere [ABSTRACT FROM AUTHOR]

Recycling of upper crustal sediments through slab subduction contributes to sub‐continental lithospheric refertilization and heterogeneity. However, the nature of recycled upper crustal components is unclear and direct evidence for sediment melt activity in the sub‐continental lithosphere is lacking. Here, we integrate major and trace elements, zircon U‐Pb dating, Sr‐Nd‐Zn‐Fe isotopic compositions of clinopyroxenites (crust‐mantle boundary) and a "glassy" xenolith from the North China Craton to relate their petrogenesis to the potential recycling of upper continental crust and provide direct insight into the sediment melt‐rock interaction. The clinopyroxenites have relatively uniform δ56Fe values (the permil deviation of the 56Fe/54Fe ratio from the IRMM014; −0.05‰–0.07‰, except for one outlier) and are not affected by melt metasomatism. The clinopyroxenites have highly variable whole‐rock δ66Zn values (the permil deviation of the 66Zn/64Zn ratio from the JMC‐Lyon standard) between 0.04‰ and 0.46‰, that closely correlate with Rb/La, K/U, Ba/Th, and Th/Nb ratios, and generate arrays that trend toward a composition similar to the "glassy" xenolith. The "glassy" xenolith has a high δ66Zn value (0.43‰ ± 0.05‰, 2SD) and a significantly low 143Nd/144Nd ratio (0.510991). This evidence implies that the "glassy" xenolith may represent a quenched sediment melt formed by the melting of carbonate‐bearing terrigenous sediments that may also be responsible for the metasomatism of clinopyroxenite xenoliths. The geochemical evidence from the "glassy" and clinopyroxenite xenoliths provides a direct evidence for the activity of sediment melt with upper continental crust components in the sub‐continental lithosphere. Plain Language Summary: Slab‐derived sediment melt activity in the overlying lithosphere is crucial for element cycling and lithospheric evolution. To understand the nature of recycled sediment and its impact on the overlying lithosphere, we analyzed the Zn‐Fe‐Sr‐Nd isotopic compositions of clinopyroxenites and a "glassy" xenolith from the North China Craton. The δ66Zn values of clinopyroxenites show correlations with proxies for hydrous melt metasomatism (Rb/La, K/U, Ba/Th, and Th/Nb ratios) and generate arrays that trend toward a composition similar to the "glassy" xenolith. The identification of "glassy" xenolith provides direct insight into the sediment melt‐rock interaction. Furthermore, this study proves the validity of using Zn isotopes as a powerful tool for tracing sediment melt activity in the sub‐continental lithosphere. Key Points: The Zn isotopic variations (0.04‰–0.46‰) of the clinopyroxenites are produced by melt metasomatismThe "glassy" xenolith may represent the preserved sediment melt with recycled carbonate‐bearing terrigenous componentsZn isotopes can be used to trace the activity of slab‐derived sediment melts in the sub‐continental lithosphere [ABSTRACT FROM AUTHOR]

The paper presents geochemical and isotopic characteristics of Neoarchean (2.7–2.66 Ga) mafic granulites of the Sharyzhalgay uplift in the southwestern Siberian craton. Mafic and predominant felsic granulites compose fragments of the metamorphic complex among the Neoarchean and Paleoproterozoic granitoids. The mafic granulites are characterized by the mineral association Cpx + Pl ± Hbl ± Opx ± Qz and include two types with different major and immobile trace element contents. The dominant rocks of the first type have a wide range of Mg# and concentrations of TiO2 and immobile trace elements (REE, Zr, Nb), and mainly positive εNd(Т) values. The first type of mafic granulites show elevated (La/Sm)n and enrichment in Th and LREE relative to Nb, which is typical of subduction-related or crustally contaminated basalts. The absence of negative correlation between (La/Sm)n and εNd(Т) and a clear positive correlation of TiO2 with Nb testify against the effect of crustal contamination on the composition of the mafic granulites. The magmatic protoliths of the first type of mafic granulites are suggested to form by the melting of depleted peridotites of the subcontinental lithospheric mantle modified by melts derived from basalts or terrigenous sediments of the subducting plate. Mafic granulites of the second type have a narrower range of Mg#, TiO2 content, positive εNd(Т), flat rare earth patterns and no subduction signatures, which indicates an asthenospheric depleted mantle source. Mafic granulites contaminated by the Paleoarchean crust are characterized by increased (La/Sm)n, depletion in Nb relative to Th and LREE, and negative εNd(Т) values. Post-magmatic influence of granitoids leads to the enrichment of mafic granulites in biotite and apatite, an increase in concentrations of K2O, P2O5, a significant enrichment in Zr, Nb, Th, LREE, and negative εNd(Т) values. The difference between mafic granulites of the first and second types is not related to crustal contamination, but is caused by melting of two types of sources: asthenospheric and subcontinental lithospheric mantle. The subcontinental lithospheric mantle of the Irkut block was isotopically depleted at the Neoarchean time (∼2.7 Ga), and its enrichment in incompatible trace elements was likely caused by felsic melts generated from the rocks of subducting plate immediately prior to mafic magmatism. [ABSTRACT FROM AUTHOR]

The evolutional process of palaeoceanic environment and its effect on the accumulation of organic matter during the Ordovician–Silurian transition in Lower Yangtze region has been overlooked compared to that in Upper Yangtze region of South China, although their paleogeographic settings were expected to be discrepant. This paper documents the marine depositional environment, paleoclimate, and sediment supply changes, and discusses their roles in controlling the organic matter enrichment in sedimentary rocks within the Ordovician–Silurian transition of the Lower Yangtze region, using the latest geochemical data of the continuous drilling core. The stratigraphic framework of the Ordovician–Silurian transition in the Lower Yangtze region is composed of two third-order sequences, each of which can be subdivided into a lower TST (transgressive systems tract) and an upper RST (regressive systems tract). TST1 represented an evident depositional transition stage which was marked by the ending of the underlying carbonate sediments and the initiation of the terrigenous clastic-dominated sediments. Geochemical proxies indicate that the relatively low productivity, dysoxic water column condition, and high sediment supply flux collectively resulted in inadequate organic matter hosted in deposits of the TST1. During the depositional period of RST1, the global sea level declined due to the Hirnantian glaciation age. The icehouse also caused the decrease in overall river flux and, thus, the terrigenous clastic sediment supply. The icehouse also strengthened the upwelling that occurred in the Lower Yangtze sea. The upwelling boosted the marine algae explosion through the delivery of abundant nutrients, which not only enhanced paleoproductivity but also led to an anoxic environment by oxygen consumption. Such high paleoproductivity, anoxic water column environment, and low sediment supply flux caused the deposition of organic-rich shale. The sea level rose during the TST2 due to the ending of an ice age. The relatively large water depth and high paleoproductivity associated with volcanic eruptions are the main factors that caused the enrichment of organic matter during this stage. During the deposition of RTS2, the increase of sediment supply flux resulted in a decrease in accommodation space and water depth and the dilution of organic matter in deposits, which was the primary constraint of organic matter accumulation. [ABSTRACT FROM AUTHOR]

Seafloor hydrothermal systems play a significant role in the oceanic Mg cycle due to ubiquitous deposits of secondary Mg-rich clays during the strong fluid-rock reactions. However, the magnitude of net Mg enrichment and Mg isotopic fractionation, particularly within the medium-high temperature hydrothermal systems in felsic-hosted settings, are not well studied yet. Here we report elemental and isotopic compositions of Mg in hydrothermal chlorite-rich sediments, volcanic materials, and terrigenous sediments collected during the IODP Expedition 331 drilled to the thick sediment-covered and felsic-hosted middle Okinawa Trough (Iheya North Knoll) in the West Pacific. We investigate the sources of Mg in chlorite and Mg isotopic behavior at medium-high temperature hydrothermal alteration. After 1 mol/L HCl leaching, Mg isotopic compositions of chlorite-rich sediments present overall similar values in the residual fractions and bulk samples albeit with slightly higher values in the leachates. Mineralogical differentiation primarily determines the Mg isotopic compositions, showing that siliciclastic residues have slightly higher δ26Mg values than the leachates dominated by carbonates and oxides/hydroxides. Significant Mg isotopic fractionation happened in the medium-high temperature (∼150°C to 260°C) felsic-hosted hydrothermal system, with Δ26MgChl-SW ranging from 0.15‰ to 0.71‰ and yielding a negative correlation with temperature. This observation suggests the preferential incorporation of heavy Mg isotopes by the secondary chlorite precipitation. We infer that the medium-high temperature hydrothermal systems can take up about 8–14% of riverine input of Mg in the arc and back-arc regions. Incomplete removal of aqueous Mg in porewater and vent fluids by the medium-high temperature hydrothermal alterations in the arc and back-arc basins provides constraints on the Mg budget and isotopic composition of seawater. [ABSTRACT FROM AUTHOR]

Constraining the lithological diversity and tectonics of the earliest Earth is critical to understanding our planet's evolution. Here we use detrital Jack Hills zircon (3.7 − 4.2 Ga) analyses coupled with new experimental partitioning data to model the silica content, Si+O isotopic composition, and trace element contents of their parent melts. Comparing our derived Jack Hills zircons' parent melt Si+O isotopic compositions (−1.92 ≤ δ30SiNBS28 ≤ 0.53 ‰; 5.23 ≤ δ18OVSMOW ≤ 9.00 ‰) to younger crustal lithologies, we conclude that the chemistry of the parent melts was influenced by the assimilation of terrigenous sediments, serpentinites, cherts, and silicified basalts, followed by igneous differentiation, leading to the formation of intermediate to felsic melts in the early Earth. Trace element measurements also show that the formational regime had an arc-like chemistry, implying the presence of mobile-lid tectonics in the Hadean. Finally, we propose that these continental-crust forming processes operated uniformly from 4.2 to at least 3.7 Ga. Geochemical analysis indicates a formational regime for Jack Hills zircons that is lithologically diverse and chemically similar to modern arcs. This depicts complicated geodynamics of the early Earth, which is currently proposed by many as stagnant-lid. [ABSTRACT FROM AUTHOR]

This is in sharp contrast with the Gulf of Eilat/Aqaba which is a relatively sediment-starved system, where the role of tectonics in sediment transport is explicit. The low sediment accumulation rates associated with the arid climate and the coral reefs that serve as barriers on the inner shelf, are responsible for low sediment availability, especially in the western slope of the gulf. The coarse units described from cores collected at the Gulf of Eilat/Aqaba not only include a high percentage of LBF transported from a shallower habitat and with relatively bad preservation pointing to high-energy transport, but they also correlate to documented tectonic surface rupture events. These studies should be used for the assessment of Red Sea turbidite records, south of the Gulf of Eilat/Aqaba. [Extracted from the article]

Together, the Yinggehai and Qiongdongnan basins have received a large amount of terrigenous sediments, but the provenance evolution of Cenozoic sediments in the two basins remains disputable. Combined with previous studies in the Yinggehai and Qiongdongnan basins, the elemental geochemistry of Oligocene to Pliocene sediment samples in the junction area of the two basins were analyzed to explore the tectonic implications, parent rock characteristics, and provenance evolution of the two basins during the Cenozoic. The results reveal that all the sediment samples were derived from continental island arc to passive continental margin settings. The light REE enrichment and stable content of heavy REE with large negative Eu anomalies indicate that they were probably derived from Hainan Island. The reconstructed provenance evolution model showed that the Red River Source (RRS) provided sedimentary materials for the Central Depression of Yinggehai Basin from the Oligocene to the Pliocene, and Hainan Island Source (HIS) was also one of the sources for sediments deposited in the Central Depression of Yinggehai Basin during the Miocene. However, most of the sediments preserved in the Yingdong Slope and Qiongdongnan Basin were derived from the HIS from the Oligocene to the Pliocene, and sediments deposited in the Yingdong Slope were also derived from the RRS during the Miocene. Furthermore, the junction area of the two basins had a mixed source of the RRS and HIS during the Cenozoic. [ABSTRACT FROM AUTHOR]

The continental crust is an important reservoir for incompatible elements, including the halogen elements (F, Cl, Br, and I), but their concentrations remain poorly known, thus hindering better understanding of the role of the crust in Earth's halogen cycle. We present halogen data (F, Cl, Br, and I) for twenty-four well-characterized glacial diamictite composites that derive from the upper continental crust (UCC) and were deposited during discrete glacial events at ∼2.9 Ga, ∼2.4–2.2 Ga, 0.75–0.58 Ga, and ∼0.30 Ga. A good correlation between Cl and the highly soluble Na (R2 = 0.70), together with low and scattered Cl concentrations in the diamictites (2–279 ppm), indicates significant Cl loss during chemical weathering of the continents. The other halogens (F, Br, and I), however, are not strongly affected by chemical weathering as revealed by their correlations with less soluble elements like K, P, Nd, and Lu, which may be due to their retention in secondary minerals and/or organic matter. Increasing concentrations of F in the composites through time may reflect the evolving composition of the UCC. Using the median values of the Neoproterozoic and Paleozoic diamictite composites, halogen concentrations of the present-day weathered UCC are estimated to be: 575 ± 87 ppm F, 29 ± 20 ppm Cl, 0.65 ± 0.14 ppm Br, and 0.05 ± 0.01 ppm I (errors quoted at the median absolute deviation). Linear correlations between halogens and other elements provide estimates for minimum halogen concentrations of the present-day crystalline UCC: 394 ± 67 ppm F, 83 ± 24 ppm Cl, 0.41 ± 0.04 ppm Br, and 0.03 ± 0.01 ppm I (with 2σ uncertainties). These estimates are all lower than normalized concentrations of elements of similar incompatibility during igneous differentiation, which may reflect loss of halogens via magmatic degassing/exsolution and/or chemical weathering during the formation of the continental crust. The distinct behavior of Cl compared to Br and I during continental weathering leads to a wide range of Br/Cl (2–265 * 10−3) and I/Cl (122–197,952 * 10−6) ratios, and Br/I ratios that are distinctly higher than those of pelagic sediments and marine pore fluids. Similar halogen signals have been reported from the lithospheric mantle and may reflect recycling of terrigenous sediments. The calculated weathering flux of Cl from the continents is quite small compared to the total Cl content of seawater (<8–34 %), suggesting that Cl in seawater is mainly derived from outgassing of the mantle and/or late volatile accretion. On the other hand, the significantly higher Br and I contents in terrigenous organic-rich sediments compared to those of crystalline bedrocks suggest that significant amounts of Br and I were transported from the oceans to the continents. [ABSTRACT FROM AUTHOR]

Tracking paleoenvironmental change and past event deposits is very important to evaluate the natural hazard spatially. This paper presents how the environment changes and implies the event deposit depending on the diatom assemblage change. To investigate paleoenvironmental change and identify the difference between tsunami and typhoon deposits, we analyze diatoms from the sediments in two coastal lakes in southern Japan where flood deposits have been linked to historical typhoon and tsunami events (Lakes Kawahara and Ryuo). The sediment cores extend from B.C.E. 500 to approximately C.E. 1000 and the downcore variation in diatom assemblages indicates a series of transitions from saline to fresher conditions in both Lake Kawahara and Lake Ryuo between approximately C.E. 500 and 1700. We observe an obvious deviation in diatom assemblages in event deposits previously identified to be either of tsunami or typhoon in origin. For the most prominent event deposit preserved in Lake Ryuo by the Hoei tsunami of C.E. 1707, the deposition of marine diatoms serves as evidence of marine flooding, while the subsequent deposition of soil and freshwater diatoms indicates the mobilization of terrigenous sediment during returning seaward flows. In contrast, the most prominent event deposit in Lake Kawahara is associated with freshwater flooding by the Kamikaze typhoon of C.E. 1281 and contains very low diatom abundances and a peak of freshwater taxa, followed by a peak in diatom counts potentially due to greater biological activity induced by a resultant influx of nutrients and re‐oxygenation during the event. [ABSTRACT FROM AUTHOR]

The term "appinites" refers to amphibole-rich mafic rocks, as one of the most typical products of partial melting of a metasomatic lithospheric mantle. This paper presents results of integrated geochemical and isotopic analyses for six Early Cretaceous (125-119 Ma) appinitic plutons from the Liaodong Peninsula, northeastern North China Craton (NCC), to not only investigate the properties of the metasomatic lithospheric mantle induced by variable recycled crustal components but also to discuss a hydrous mantle source. The appinites originated from partial melting of sub-continental lithospheric mantle (SCLM), and can be geochemically categorized into three groups distinguished by the input of different recycled crustal components (e.g., terrigenous sediments and delaminated lower continental crust) on the basis of two distinct Hf-O isotopic arrays. Based on the occurrence of voluminous amphiboles (50-60 vol%) and minor clinopyroxene remnants, a petrogenetic model was proposed to interpret the formation of appinites. Asthenospheric upwelling caused by the subduction and roll-back of the Paleo-Pacific plate firstly resulted in partial melting of the SCLM to yield basaltic magmas. Subsequently, numerous hydration reactions between early anhydrous minerals (e.g., olivine and pyroxene) of basaltic magmas and hydrous melts derived from terrigenous sediments and delaminated lower continental crust occurred to produce the studied appinites. Ultimately, the recycled crustal materials can serve as the metasomatic agent not only to transfer the enriched isotopic signatures into the studied appinites but also to represent hydrous components to play the part of hydrous reactions. The high abundance of amphibole in the studied appinites is indicative of a hydrous lithospheric mantle beneath the eastern NCC. [ABSTRACT FROM AUTHOR]

Although high-Mg andesites (HMA) have attracted increasing attention due to their unique geochemical composition and important geological significance, there is no consensus on their petrogenesis. The present study indicates that the subducting terrigenous sediment-derived hydrous melts were incorporated into the mantle source of Paleozoic HMA in northwestern Tianshan, western China. These HMA are composed of basaltic andesite and andesite. They generally exhibit arc-type trace element distribution patterns and weakly enriched Sr-Nd-Hf isotope compositions. Some of them show remarkably higher Ba/La, Ba/Th, Rb/Nb, and U/Th ratios than normal mid-ocean ridge basalts (MORB). Furthermore, most of them are characterized by higher Th/Nb, Th/Yb, and Th/Nd ratios but lower Nb/U ratios relative to normal MORB, similar to those of terrigenous sediments. Whole-rock Nd isotopes covary with Rb/Nb and Th/Yb ratios, indicating contributions from both oceanic crust-derived aqueous solutions and terrigenous sediment-derived hydrous melts. Together with their high zircon δ18O values, it appears that the mantle source of the target HMA contains terrigenous sediment-derived hydrous melts in addition to subducting oceanic crust-derived aqueous solutions. In the studied HMA, the andesite generally exhibits higher contents of large-ion lithophile elements and light rare earth elements and more enrichments in Sr-Nd-Hf isotopes than the basaltic andesite. These differences indicate that the mantle source of andesite would contain more subducting sediment-derived hydrous melts than that of basaltic andesite. As a consequence, relatively Si-rich and Si-poor pyroxenite sources were respectively generated as the mantle sources of the andesite and basaltic andesite. This qualitative interpretation is verified by quantitative modeling of the geochemical transfer from subducting oceanic crust into the mantle wedge. Model calculations indicate that the addition of ~3% oceanic crust-derived aqueous solutions and 4%-12% terrigenous sediment-derived hydrous melts into the mantle wedge peridotite can account for the geochemical compositions of the target HMA. Therefore, the HMA in northwestern Tianshan provide the geochemical evidence for the crust-mantle interaction during the oceanic subduction in the Paleozoic. As such, the subducting terrigenous sediment-derived hydrous melts play a dominant role in the composition of the lithochemically fertile, geochemically enriched mantle sources and thus in the origin of HMA above oceanic subduction zones. [ABSTRACT FROM AUTHOR]

Coastal sediments in the Mong Cai area were collected and analyzed for grain size, heavy metals, total organic carbon, and isotopes (210Pb, 226Ra, δ15N, δ13C) to assess sediment quality. The most common sediments were fine sand in surface sediment, very fine sand in core C1, and very coarse and coarse silt in core C2. The total organic carbon was highest in C2 next to the surface and lowest in C1, with content levels of 1.81%, 0.40%, and 0.31%, respectively. The chronology in C1 was 1877–2019 (142 years, 0–5 0 cm), with an average sedimentation rate of 0.71 cm/year. In C2, the chronology was 1944–2019 (75 years, 0–14 cm), with an average sedimentation rate of 0.27 cm/year. These δ13C and δ15N in the sediment reflect the source of the organic matter mix from the marine and terrigenous sediments. All studied heavy metals were lower than the ISQGs, with the exception of As in C1 and C2, which were higher. C1 showed a decline in As over time, while C2 As levels increased between 1996 and 2019. In terms of heavy metal pollution indexes, the geoaccumulation index (Igeo) showed that C1 and C2 were unpolluted to moderately polluted with As, with Li and Pb in C2; the enrichment factor (EF) was moderately enriched with As; the contamination factor (CF) was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and C1 (Cd, As, Li) and considerably contaminated (As) in C2. The risk factor (ER) of As showed a moderate potential ecological risk in C2. The degree of contamination (CD) ranged from moderate to considerable (C1, C2), and the ecological risk (RI) was low. Although CD ranged from moderate (C1) to considerable (C2), most contamination was concentrated at the bottom of the cores. RI was low. The Mong Cai sediment quality does not currently affect the coastal area's ecosystem and fauna. [ABSTRACT FROM AUTHOR]

Sabellaria spinulosa (Leukhart, 1849) is a suspension feeding polychaeta that lives in tubes consisting of terrigenous particles captured by the worm itself. They form impressive reefs containing millions of worm tubes. In temperate marine areas, under optimal environmental conditions, these structures can become natural breakwaters and can play an active role in sandy beaches' defense. In this work, we report procedures aimed to analyze the growth of S. spinulosa bioconstructions in laboratory. By collecting biological replicas from a wild reef, this study aimed to identify sedimentological characteristics of sands that induce faster tube growth. During the tank experiments, the grain size and mineralogy of the sand were modified. By employing thin sections and X-ray microtomography analyses, the structures observed and measured during and after the tests were analogous to those naturally formed. The fastest growth was recorded in the presence of bioclastic sands with a grain size between 125 and 350 μm. Defining the physical conditions that induce faster growth is fundamental for the defense of these vulnerable habitats but also the surrounding marine environment. This study also lays the foundations for coastal protection interventions in which bioconstructions grown in the tank could be directly implanted on submerged natural and artificial substrates that are already present in situ. [ABSTRACT FROM AUTHOR]

The compositional range of ~2,000 marine sediments and ~19,000 oceanic igneous rocks is encapsulated by a set of 12 sedimentary and 10 mafic rock compositions, allowing computation of phase relationships on P-T paths along subduction interfaces. These are described economically by a partitioning analysis, which connects the mineral assemblages to different parts of the subduction P-T space and facilitates assessment of prograde dehydration, melting, densification, and rheological systematics. Dehydration and densification occur at shallower depths than in studies that neglect shear heating. Lawsonite stability is limited to interfaces where convergence is slower than 20 mm/yr; such rates also favor transport of volatiles beyond the arc. Terrigenous sediments and mafic rocks reach their solidi close to the top of the wedge-slab interface; melt fractions are enhanced by fluid from the dehydrating slab interior. Rheological calculations show that the most abundant sediment types have interface capacities of hundreds of meters to kilometers, and that the strengths of mafic rocks comfortably exceed their buoyancy stresses. Above ~650°C sediments are weak enough to rise as diapirs into the mantle wedge. Carbonate-and serpentinite-rich lithologies are weaker than other interface rocks, and ascend most rapidly at the cessation of subduction. Ascent rates drop abruptly as rocks enter the plate interface, probably leading to retrograde equilibrium at P~1-1.5 GPa. The seismic-aseismic transition is expected at about 500°C in mafics, and 400°C in metasediments. Seamounts are weaker than most other interface rocks, and unlikely to form asperities. Slow slip and tremor may be associated with the blueschist-eclogite transition. [ABSTRACT FROM AUTHOR]

Accurate age‐depth models for marine sediment cores are crucial for understanding paleo‐oceanographic and ‐climatic changes derived from these archives. To date, information on bulk sediment composition is largely ignored as a potential source of information to improve age‐depth models. In this study, we explore how bulk sediment composition can be qualitatively used to improve age‐depth models. We developed the BomDia algorithm, which produces age‐depth models with realistic sediment accumulation rates that co‐vary in harmony with the bulk sediment composition. We demonstrate that changes in the marine versus terrigenous sediment deposition, based on bulk sediment composition, can be used to significantly improve age‐depth models of hemipelagic marine deposits. Based on two marine records—each containing more than 20 radiocarbon (AMS 14C) dated levels—we show that the mean error of prediction of unused AMS 14C ages significantly improves from 3.9% using simple linear interpolation, to 2.4% (p = 0.003), when bulk sediment composition is included. The BomDia age‐depth modeling approach provides a powerful statistical tool to assess the validity of age control points used and also may assist in the detection of hiatuses. Testing and further development of the BomDia algorithm may be needed for application in depositional settings other than tropical hemipelagic. Plain Language Summary: The age‐depth relationship in a marine sediment core is known as an age‐depth model. To build an age‐depth model, that is to produce a continuous age‐depth relationship, an accurate and precise prediction of ages in between age control points is needed. A new algorithm, which includes information on the bulk sediment composition in the prediction of ages, has been developed and tested for this purpose. The calcium carbonate content of the sediments is calibrated versus the log ratio of titanium and calcium as obtained from resolution X‐ray fluorescence and used as model input for bulk sediment composition. We tested the algorithm using data from two tropical hemipelagic cores and find that the algorithm, which we refer to as BomDia ("a good dynamic interpolation algorithm"), produces robust age‐depth models with predictive power and realistic sedimentation rates that co‐vary with sediment composition. Further application and testing of the algorithm to a wider variety of other than tropical hemipelagic sedimentary settings is recommended. Key Points: The accuracy and predictive quality of age‐depth models for tropical marine hemipelagic cores improves when bulk sediment composition is includedThe BomDia algorithm produces age‐depth models with realistic accumulation rates, which co‐vary with bulk sediment compositionThe BomDia algorithm uses a Monte Carlo approach to assess age‐depth model uncertainty [ABSTRACT FROM AUTHOR]

Summary: We present a study to estimate the large‐scale landscape history of a continental margin, by establishing a source‐to‐sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best‐fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate. [ABSTRACT FROM AUTHOR]

The formation of large‐volume silicic magmas in arc settings is fundamental for understanding trans‐crustal magmatic systems related to subduction zones. Here, we present an integrated study of the four Quaternary Toba eruptions and pre‐caldera Haranggaol Andesite on Sumatra, Indonesia. This rock suite has significantly enriched Sr‐Nd isotopes (87Sr/86Sr = 0.71220–0.71517, εNd = −8.9 to −10.6) compared with other volcanic rocks on Sunda‐Banda arc, but is similar to the post‐caldera (<74 ka) Sipisupisu basalts near the Toba Caldera. Thermodynamic modeling using Magma Chamber Simulator has revealed that the Toba silicic rocks can be produced by a two‐stage assimilation and fractional crystallization of mantle‐derived basaltic melts with compositions similar to the Sipisupisu basalts in the lower and upper crustal magma reservoirs. Binary modeling of Sr‐Nd isotopes suggests that the rocks near the Toba Caldera can be produced by mixing of 5%–10% of the subducting Nicobar Fan sediments (87Sr/86Sr = 0.73493, εNd = −14 on average) with depleted MORB mantle (DMM). Indeed, decompressional partial melting modeling of bulk mixtures of DMM with 7% subducting sediments using pMELTS indicates that the melts generated can have geochemical compositions similar to the Sipisupisu basalts. We therefore argue that hybridization of the subducting sediments with the mantle wedge could be an alternative scenario responsible for the enriched isotopic characteristics of the rocks near Toba. Prolonged fractionation of mantle‐derived enriched/depleted basaltic melts, accompanied by crustal assimilation and crystal‐melt segregation, could be common processes in generating large‐volume silicic magmas on continental arcs. Plain Language Summary: The Toba volcano in northern Sumatra is a supervolcano that has produced two super‐eruptions, one of which is the largest Quaternary eruption on Earth. The last super‐eruption of the Youngest Toba Tuff at ∼74 ka expelled ∼5,300 km3 dense rock equivalent of magmas, corresponding to a volcanic explosivity index of ∼9.1. This eruption has produced the largest collapsed caldera and caused severe global temperature decrease and environmental impacts. The silicic magmas feeding these super‐eruptions have previously been considered to be produced by melting of the continental crust. We present a new and systematic elemental and Sr‐Nd isotopic data set of the Toba eruptions. Combined with thermodynamic modeling, we show that the Toba silicic magmas were fundamentally the evolutionary products of mantle‐derived basaltic melts. The basaltic melts were isotopically enriched due to addition of subducted terrigenous sediments to the mantle wedge underneath the Toba Caldera. The basaltic melts have undergone a two‐stage evolution in the lower and upper crustal magma reservoirs. Assimilation of the continental crust and crystal‐melt segregation could have occurred accompanied by fractional crystallization in the upper crustal magma reservoir. We therefore propose that large‐volume silicic magmas commonly have a basaltic root, at least in arc settings. Key Points: Toba silicic magmas were products of a two‐stage evolution of mantle‐derived basaltic melts in the lower and upper crustAssimilation, fractionation, and crystal‐melt segregation of andesitic magma in the upper crust feed directly to the Toba silicic eruptionsThe mantle source underneath Toba is enriched due to hybridization of the subducted sediments [ABSTRACT FROM AUTHOR]

The structure, composition, and source areas of Lower Cretaceous terrigenous sediments and geodynamic conditions for their deposition in the Northern Sikhote-Alin are considered. The study established that in terms of mineralogical and geochemical parameters the sandstones, being either petrogenic or first cycle deposits formed by the products of the breakdown of bedrock from the source areas, correspond to graywackes. They are characterized by low maturity, weak lithodynamic reworking of parental rocks, and high rates of deposition. The paleogeodynamic interpretation of the data suggests sedimentation in the Early Cretaceous along the continent–ocean boundary in the basin related to large-scale strike-slip motions along the transform faults. The source area combined sialic land formed by granite-metamorphic and sedimentary rocks, a mature and deeply eroded continental-margin arc, and fragments of Jurassic–Early Cretaceous accretion prisms of the Sikhote-Alin with ophiolites incorporated into their structure. All this allows the studied deposits to be considered as a part of the Early Cretaceous Zhuravlevka pull-apart terrane. [ABSTRACT FROM AUTHOR]

Nowadays estuarine deltas are threatened by factors such as insufficient terrigenous sediment supply and rising sea levels. The Changjiang Estuary is adjacent to Hangzhou Bay, characterized by high turbidity waters, and the suspended sediment exchange between the two will inevitably affect the erosion and deposition of subaqueous delta in the future. Based on in situ observation data and numerical model, we found that suspended sediment is transported from the Changjiang Estuary into Hangzhou Bay during spring tides, while from Hangzhou Bay into the Changjiang Estuary during neap tides. The key driving mechanisms for the difference during spring-neap tides were expounded by momentum analysis and numerical sensitivity experiments. The barotropic pressure gradient force during spring tides is the key force that drives the suspended sediment from the Changjiang Estuary into Hangzhou Bay. Conversely, the baroclinic pressure gradient force during neap tides is the key force that drives the suspended sediment from Hangzhou Bay into the Changjiang Estuary. This study can provide valuable scientific evidence for erosion and deposition in estuaries and adjacent seas, as well as the sustainable utilization of regional coastal sediment resources. • Suspended sediment is transported from the Changjiang Estuary into Hangzhou Bay during spring tides, while the opposite occurs during neap tides. • During spring tides, the suspended sediment from the Changjiang Estuary into Hangzhou Bay is driven by the barotropic pressure gradient force. • During neap tides, the suspended sediment from Hangzhou Bay into the Changjiang Estuary is driven by the baroclinic pressure gradient force. [ABSTRACT FROM AUTHOR]

It is crucial to establish a robust chronology for understanding late Quaternary sedimentation processes and environment changes in response to sea-level fluctuation on shelves. The shelf of the East China Sea (ECS) is featured by huge terrigenous sediment input and striking land -sea interaction during the late Quaternary. However, there remains controversy in chronostratigraphic rebuilding of transgression and regression deposits during eustatic-glacial cycles, mainly due to a lack of reliable dating data. In this study, an extensive comparison of 17 optically stimulated luminescence (OSL) and 15 AMS 14C ages from core TBF-1 (upper 40 m) provides a constraint in chronostratigraphic reconstruction since Marine Isotope Stage (MIS) 5. OSL ages range from 9.5 ± 0.7 to 67.3 ± 4.8 ka at depths from 2.00 to 28.00 m, while 14C ages range from 6645 to 41435 cal a BP at depths from 0.02 to 17.52 m. Regression analysis demonstrates a high level of agreement between OSL and 14C ages, with r2 values of 0.91 and 0.90, respectively. For Holocene sediments (U1), both OSL and 14C methods are applicable in tidal sand ridges, however, it should be noted that 14C ages may exhibit a young bias of up to 3 ka. For pre-Holocene sediments (U6-U2), OSL ages are robust within saturation limitation of OSL signal (D e up to ca. 166 Gy), cross-checked by feldspar post-IR IRSL (pIRIR) dating protocol. Nevertheless, the shell 14C ages (11620 and 10390 cal a BP at depths of 13.95–14.56 m) in Last Glacial Maximum (LGM) fluvial sediments of U2 are significantly underestimated, because of their susceptibility to recrystallization and overgrowth, resulting in carbon exchange with environment. While the peaty layer's14C age in deltaic deposition (17.50 m, U5) was determined to be 36420 cal a BP, coincided with OSL age of 39.6 ± 3.9 ka. The chronostratigraphy since MIS 5 for core TBF-1 exhibits a significant correlation with previously published cores SFK-1, DZQ4, and DH02, on the ECS outer shelf. Through the evaluation of those underestimated 14C ages and saturated OSL ages, we re-elucidated the primary sedimentary facies and their respective formation periods. This sedimentary stratigraphic illustration exhibits significant consistency with eustatic-glacial cycles. The renewed chronological framework for ECS shelf allows better correlation between the late Quaternary sedimentary evolution and the land-sea interaction on open shelves dominated by siliciclastic sedimentation. [ABSTRACT FROM AUTHOR]

ICESat-2's Advanced Topographic Laser Altimeter System (ATLAS) has emerged as a useful tool for calculating attenuation signals in natural surface waters, thus improving our understanding of particulates from open-ocean plankton to nearshore suspended terrigenous sediments. While several studies have employed methods based on Beer's Law to derive attenuation coefficients (including through a machine-learning approach), a rigorous test of specific tuning parameters and processing choices has not yet been performed. Here we present comprehensive sensitivity tests of noise removal, choice of bin sizes, surface-peak exclusion, and beam pairing across four contrasting marine environments as well as solar background removal at an additional site to quantify the impacts of these processing choices on the derived photon-based attenuation coefficient K dph. Ultimately, calculated K dph values were not statistically sensitive to choices of horizontal bin sizes, vertical bin sizes, and surface exclusion depths with ranges of 500–2000 m, 0.25–1.0 m, and 0.5–1.0 m, respectively. Use of strong-beam data is recommended because weak-beam data introduce additional noise, though in open-ocean waters where photon counts are sparse, it may be desirable to include weak-beam data. In a daytime/nighttime data comparison, daytime data were found to be usable, though removal of the solar background increased the K dph estimates by ∼27–64%. A robust solution for removing afterpulses remains elusive, though a gaussian decomposition scheme was attempted. It did not, however, yield statistically different K dph values relative to the uncorrected dataset. Detailed information about processing choices and a suggested workflow for ocean applications are provided. Together the results pave the way for expanded K dph analyses of global datasets (including turbid coastal waters). • Study evaluates the impact of processing choices on K dph and offers a workflow. • Many processing terms have little impact on K dph , including afterpulse removal. • Using strong-beam data is recommended and using daytime data is possible. [ABSTRACT FROM AUTHOR]

In order to investigate the oil shale enrichment mechanisms and the relationship among gravity flows, volcanism, and oil shale deposition, detailed petrological, sedimentological, and organic geochemical research have been carried out on the Lower Cretaceous Jiufotang Formation in the Ludong sag, Songliao Basin, Northeast China. Seven facies were recognized and were grouped into three facies associations, namely hyperpycnites and intrabasinal turbidites, delta, and lacustrine facies associations. During the deposition of the lower Jiufotang Formation, hyperpycnites were developed during catastrophic flooding events that caused an abrupt increase in the discharge of water and sediment into the deep lacustrine environments, and a delta persisted during normal river discharge intervals and prograded into lacustrine environments. During the deposition of the upper Jiufotang Formation, deep lacustrine facies further expanded, and the extent of hyperpycnites decreased. Four types of oil shales were recognized in the Ludong sag of which those in the lower and upper Jiufotang Formation were defined as medium-to good-quality and good-to best-quality source rocks, respectively, exerting an overall thermal maturity of early oil generation. The lacustrine redox conditions show oxic to dysoxic conditions in the lower Jiufotang Formation, and anoxic to dysoxic conditions in the upper Jiufotang Formation. Oil shales were poorly-developed in the lower Jiufotang Formation and were well-developed in the upper Jiufotang Formation. During the active rift stage of the lower Jiufotang Formation, frequent occurrences of gravity flows and water-carried re-sedimentation of tuffaceous materials were unfavorable for oil shale accumulation. During the waning rift phases of the upper Jiufotang Formation, minor wind-transport of volcanic ash input into the deep lacustrine environments fertilized the lake water and supported algae blooms, leading to reduced oxygen concentrations in the bottom lacustrine waters along with high bioproductivity that were favorable for organic matter preservation and oil shale formation. • The oil shales are often associated with gravity flows and volcanic activity in rift basins. • The hyperpycnites carried terrigenous sediments and diluted organic matter abundance. • A minor input of air-fall volcanic ashes is benefit for algal blooming and oil shale formation. • High-quality and thick oil shales are developed in reduced oxygen concentrations in the bottom water. [ABSTRACT FROM AUTHOR]

As a crucial "sink" for terrigenous material entering the ocean, provenance of sediments within the coastal zone and continental shelf sea regions holds significant scientific importance in the investigation of global material cycling. Environmental magnetism was proved as an effective and rapid approach for sediment source identification. Detail and systematic magnetic measurements were performed for surface sediment samples collected from the mega Pearl River, local small rivers (Tan, Moyang and Jian rivers) of west Guangdong, coastal zone (CZ) and continental shelf (CS) to analyze the contribution of local small watersheds to marine sediments. The results indicate that detrital river input magnetite and hematite are coexisted in both CZ and CS sediments. Compared to CZ sediments, relatively higher concentration of hematite and finer grain size of magnetite are appeared at CS sediments. By comparing of magnetic parameters, it was inferred that magnetic minerals from the Pearl and Tan rivers are transported and deposited on the coastal zone by Guangdong longshore current. Meanwhile, sediment magnetic parameters in the Moyang and Jian Rivers are similar to the CS sediments, implying the two rivers-sourced materials were directly transported and deposited at the CS due to their narrow and restricted estuaries, and/or the CS preserves the residual deposits from the two rivers formed during the Last Glacial. Except for the Pearl River, sources of local small rivers significantly contribute to marine sediments at the coastal zone and continental shelf. • Detailed magnetic properties of northern SCS coast and shelf sediments were reported. • Local rivers-sourced sediment to coastal zone and continental shelf were found. • Two possible mechanisms of local river sediments supplying the shelf were proposed. [ABSTRACT FROM AUTHOR]

Cordilleran orogenic systems have complex, polycyclic magmatic and deformation histories, and the timescales and mechanisms of episodic orogenesis are still debated. Here, we show that detrital zircons (DZs) in terrigenous sediment from the late Pleistocene Amazon Fan, found at the terminus of the continent-scale Amazon River-fan system, record multiple, distinct modes of U-Pb crystallization ages and U-Th/He (ZHe) cooling ages that correlate to known South American magmatic and tectonic events. The youngest ZHe ages delineate two recent phases of Andean orogenesis; one in the Late Cretaceous – Paleogene, and another in the Miocene. Frequency analyses of the deep-time Phanerozoic record of DZ U-Pb and ZHe ages demonstrate a strong 72 Myr period in magmatic events, and 92 Myr and 57 Myr periods in crustal cooling. We interpret these results as evidence of changes in upper and lower plate coupling, associated with multiple episodes of magmatism and crustal deformation along the subduction-dominated western margin of South America. South American cordilleran orogenic systems have repeated complex magmatic and deformation histories. Here the authors analyze detrital zircons found in the Amazon deep-sea fan that record mountain-building events and reveal cycles of orogenesis with periods of ~60–90 Myr since the Phanerozoic. [ABSTRACT FROM AUTHOR]