Detrital Sediments Research Articles

Erosional Response to Pleistocene Climate Changes in the Brazilian Highlands

AbstractPlio‐Quaternary climatic changes are considered to be a key driver of landscape evolution, but many unresolved questions remain, such as the extent of the impact of major climatic shifts such as the Mid‐Pleistocene Transition (MPT). Various geochronological methods are available to infer changes in surface processes over the Plio‐Quaternary, and Terrestrial Cosmogenic Nuclides (TCN) have proven to be one of the most efficient tools to reconstruct paleo‐denudation. Implementing these approaches requires very specific conditions, such as well‐preserved and extensive sediment sequences. Developing alternative methods to document the evolution of denudation is thus of major interest to retrieve information on the evolution of denudation in places where recent detrital sediment records are absent. We explore the evolution of landscape erosion over a 1 Ma timescale in an intra‐cratonic setting, the Espinhaço mountain range (Brazil), with a new data set of detrital cosmogenic nuclide concentrations (26Al–10Be). We observe a systematic disequilibrium in the 26Al/10Be ratio, which we interpret as resulting from the combination of soil mixing and a significant increase in the intensity of surface processes, close to the MPT. We discuss the different scenarios with respect to available local and global data concerning the relationships between climate evolution and erosion over this time period. Our results have important implications for the interpretation of the denudation rates derived from TCN concentrations under steady states assumption, in landscapes with low erosion rates, which have a long memory for surface processes history.

Formation mechanism and oil-bearing properties of gravity flow sand body of Chang 63 sub-member of Yanchang Formation in Huaqing area, Ordos Basin

Abstract Gravity flow sand body is an important reservoir for deep water deposition. The in-depth study of its formation mechanism and oil enrichment law can provide important guidance for oil and gas exploration in deep water areas. In this article, taking the deep-water gravity flow sand body of the Triassic Chang 63 sub-member in the Huaqing area as an example, the identification characteristics, formation mechanism, and oil-bearing characteristics of the gravity flow sand body are systematically discussed. The results show that sandy debris flow, turbidite flow, and mixed event flow present different superposition combination modes on vertical gravity flow deposition. The lithofacies of the gravity flow sandstone complex are mainly affected by lake level fluctuation, provenance supply, and hydrodynamic conditions. According to the formation conditions, sedimentary types. and distribution characteristics of deep water gravity flow sand bodies, a three-dimensional sedimentary mode of deep water gravity flow sand bodies is established. It is found that the physical and oil-bearing properties of the sandy debris flow sand body are better than those of the turbidity flow sand body. The reason is that the proportion of debris in the sand body of sandy debris flow is high, and the content of debris particles is generally greater than 70% according to the statistics of thin sections, which is conducive to the formation of pores. Second, sandy debris flow belongs to block transport, and the mixing of lithology is not sufficient in the process of block flow transport, so some pores will be preserved. Finally, gravity flows, which are dense at the beginning, become less dense later as detrital sediments unload, allowing them to be transported to distant regions. Therefore, the monolayer thickness of the sandy debris flow sand body is large (generally greater than 0.5 m), and the particle size of the debris ranges from 0.03 to 0.3 mm. Finally, the physical and oil-bearing properties of the sandy clastic flow sand body are better than those of the turbidity flow sand body.

Hf Isotopes and Detrital Zircon Geochronology of the Silasia Formation, Midyan Terrane, Northwestern Arabian Shield: An Investigation of the Provenance History

ABSTRACTU–Pb ages and Hf isotopic data from detrital zircon of the Silasia Formation in the Midyan Terrane record evidence for the provenance and tectonic evolution of the northern Arabian Shield. Given that the youngest acknowledged age of these detritus sediments is 735 ± 13 Ma, it is likely that the Silasia Formation was deposited during the closure of the Mozambique Ocean. The U–Pb ages define a major Mesoproterozoic peak, with two minor peaks of Neoproterozoic and Archean age. Combined with zircon Hf isotopic compositions, the sedimentary detritus of the Silasia Formation was mainly derived from source rocks formed during the Grenville Orogeny during the assembly of Rodinia, with a minor contribution from Archean and Paleoproterozoic crustal material, in addition to a limited arc‐basement supply related to the early Mozambique Ocean. The youngest Concordia age of 735 ± 13 Ma with highly variable εHf(t) values (11 to −35) indicates a complex mixture of sources from juvenile to extremely ancient. The Concordia ages at 1113 ± 11 and 1046 ± 10 Ma have positive hafnium isotope signatures (up to +10.45) that are consistent with juvenile source rocks formed during the Grenville Orogeny. Several detrital zircons with ages of 2622 ± 22 Ma and 2690 ± 7 Ma are similar to those reported in Yemen, whereas 1818 ± 19 Ma, 2071 ± 8 Ma and 2001 ± 19 Ma Paleoproterozoic ages are similar to dated outcrops in the Khida terrane in the eastern Arabian Shield.

Sedimentological, Geochemical, and Environmental Assessment in an Eastern Mediterranean, Stressed Coastal Setting: The Gialova Lagoon, SW Peloponnese, Greece

This study describes the prevalent sedimentological and geochemical patterns and investigates the environmental status of the bottom of Gialova lagoon, a highly vulnerable coastal site of the EU’s Natura 2000 network. For this task, lithological, geochemical, and microfaunal analyses of sediment samples were combined with a high-resolution bathymetric survey. Potential pollution was determined using geochemical-based (EF, I-geo, and PLI) and faunal (Foram-AMBI) indices. We find that sedimentation is mainly controlled by the bottom morphology, hydrodynamic variations, and biogenic productivity of the lagoon. The application of the multivariate factor analysis technique revealed four dominant factors explaining the geochemical processes occurring in the lagoon. The first factor, namely “terrigenous aluminosilicates associated with Corg vs. autochthonous biogenic carbonates”, discriminates the deposition of detrital sediments, related to the high adsorption of heavy metals—versus bioclastic sediments. The “sulfides” factor represents an anoxic phase of the lagoon floor, whereas the “Mn-oxyhydroxides” factor indicates increased manganese content with several compounded trace elements. The “phosphate” factor reveals multiple sources of phosphorus in the lagoon. The lagoon bottom shows negligible to minor contamination in heavy metals, except Mo and Pb, which induce moderate pollution levels. The maximum contamination and environmental stress concern two small-sized, shallow basins within the lagoon.

Deep recycling of volatile elements in the mantle: Evidence from the heterogeneous B isotope in intra-plate basalts

Volatiles in the mantle are crucial for Earth’s geodynamic and geochemical evolution. Understanding the deep recycling of volatiles is key for grasping mantle chemical heterogeneity, plate tectonics, and long-term planetary evolution. While subduction transfers abundant volatile elements from the Earth’s surface into the mantle, the fate of hydrous portions within subducted slabs during intensive dehydration processes remains uncertain. Boron isotopes, only efficiently fractionating near the Earth’s surface, are valuable for tracing volatile recycling signals. In this study, we document a notably large variation in δ11B values (−14.3‰ to +8.2‰) in Cenozoic basalts from the South China Block. These basalts, associated with a high-velocity zone beneath East China, are suggested to originate from the mantle transition zone. While the majority exhibit δ11B values (−10‰ to −5‰) resembling the normal mantle, their enriched Sr-Nd-Pb isotope compositions and fluid-mobile elements imply hydrous components in their source, including altered oceanic crust and sediments. The normal δ11B values are attributed to the dehydration processes. Remarkably high δ11B values in the basalts indicate the presence of subducted serpentinites in their mantle source. A small subset of samples with low δ11B values and radiogenic isotope enrichments suggests a contribution from recycled detrital sediments, though retaining minimal volatile elements after extensive dehydration. These findings provide compelling evidence that serpentinites within subducted slabs predominantly maintain their hydrous nature during dehydration processes in subduction zones. They may transport a considerable amount of water into deep mantle reservoirs, such as the mantle transition zone.

Exploring electron backscatter diffraction analysis as a tool for understanding stromatolite: Quantitative description of Cretaceous lacustrine stromatolite reveals formative processes and high‐resolution climatic cycles

AbstractLacustrine stromatolites serve as important archives for recording environmental changes, and the detailed examination of their microfabrics is essential for understanding their formative processes and the environmental changes embedded within them. This study explored the application of Electron Backscatter Diffraction combined with Energy‐Dispersive X‐ray Spectroscopy to investigate a well‐preserved middle Cretaceous lacustrine stromatolite from south‐eastern Korea, unveiling ultra‐high‐resolution sedimentary processes that are often challenging to observe using conventional methods. Two types of microsparitic layers and one type of crystalline layer are distinguished based on their texture, crystal morphology and elemental composition. Both microsparitic layers are micrometre‐thick and are characterized by poorly co‐oriented calcite grains, but differ in their composition. Type 1 is depleted in magnesium but enriched in detrital elements such as silicon and aluminium, likely originating from the trapping and binding of detrital sediments on microbial mats during rainy seasons. In contrast, type 2 is enriched in magnesium but devoid of detrital elements, interpreted to have formed by the precipitation of calcium carbonate during dry seasons. The crystalline layers comprise fan‐shaped calcite crystals (ca 500 μm in length) with radiating internal structures, with their c‐axes oriented perpendicular to the stromatolite layers. These structures resemble those observed in some modern freshwater stromatolites, which are interpreted as imprints of cyanobacterial fascicules. While the cyclic occurrence of types 1 and 2 microsparitic layers might imply annual seasonal cycles, the less frequent crystalline layers are interpreted as a result of environmental changes occurring every 27 to 30 years. This is the first study to apply Electron Backscatter Diffraction to stromatolites, showcasing its potential in unravelling both the formative and diagenetic processes of ancient stromatolites.

Provenance of clay-sized detrital sediments in the North Sea and the Skagerrak region based on radiogenic Nd-Sr-Hf isotopes and clay mineral compositions: assessing the impact of coastal and seabed erosion

The Skagerrak basin represents the main sink area for fine-grained sediment in the North Sea region and constitutes a natural deposition center for sediments that are supplied from the Atlantic, the Baltic Sea and the surrounding continental margins and coasts. However, the exact sources and their proportional contributions to the North Sea sediments and to the Skagerrak deposits are not well understood. To trace the predominant sources of the sediment and to gain a better understanding of the sedimentary processes in the North Sea and the Skagerrak basin, radiogenic Sr, Nd, and Hf isotope signatures and clay mineral compositions of the detrital clay fraction of surface sediment samples from the North Sea, the Scandinavian margins and the Baltic Sea were measured. The results indicate that the major source for Skagerrak clay-size sediments is the northern North Sea but Scandinavia as well as the southern North Sea including the southern England coast also contribute material. Seabed and coastal erosion in the northern North Sea are enhanced by the inflowing Atlantic Currents, which provide the Skagerrak with high amounts of clay size sediments. In contrast, the southern North Sea, the Baltic Sea and mid-European rivers such as Weser, Elbe and Ems are only minor contributors. As Skagerrak deposits are dominated by clay sized material (up to 60%), the reconstructed sediment processes in this study deviate from findings in previous sediment budget studies, which were based on both clay and silt fraction and indicated predominant influences from the southern North Sea. These results highlight that coastal and seabed erosion in the North Sea is a previously underestimated source of fine-grained sediments for depocenters in the entire North Sea. With regard to climate change, the global sea-level rise will likely enhance erosional processes and can therefore significantly influence the sediment budget of the entire North Sea.

Geochemistry of BIF in the Quadrilátero ferrífero, Brazil, as a proxy to neoarchean paleoenvironmental and depositional conditions

Precambrian Algoma-type banded iron formations (BIFs) are biochemical metasedimentary rocks formed in the deep water environment relatively close to centers of volcanic expansion and can be characterized on the basis of their paleodepositional environment and the associated rock types. These rocks may contain geochemical signatures indicative of changes in the redox conditions of the Archean ocean. Such variations in the Meso- and Neoarchean are crucial in understanding the processes that led to the gradual increase of oxygen in the early atmosphere, culminating in the Great Oxidation Event (2.4–2.3 Ga). Oxide- and carbonate-facies BIFs were intercepted by drill cores in the Pilar gold deposit in the NE sector of the Quadrilátero Ferrífero (QF), Brazil, located in the Neoarchean Rio das Velhas greenstone belt. These rocks are interbedded with mafic and ultramafic metavolcanic rocks and carbonaceous phyllites. In light of the potential to reconstruct paleodepositional evidence indicative of the Earth's atmospheric redox history based on this stratigraphy, we have considered specific proxies from geological and geochemical observations. Pilar BIFs geochemistry exhibits positive anomalies of La, Eu, and Y, indicating characteristics inherited from seawater and high-temperature hydrothermal fluids. In addition, a superchondritic Y/Ho ratio further supports the influence of seawater. The signatures of the major elements Al2O3 and other immobile elements typical of detrital sediments corroborate the interpretation that these rocks were deposited in a deep marine environment with low clastic influence. Furthermore, negative Ce/Ce*SN anomalies in some sections of the Pilar BIF indicate limited oxygen availability which, together with Mo, U, V, and Zn trace-element enrichment factors, indicate deposition under suboxic/euxinic conditions. This research, together with other similar BIF data from the NW QF provide new insights into the paleoenvironmental conditions prevailing during the formation of the Archean volcano sedimentary basins that compose the southern São Francisco craton (SFC).

Influence of changing water mass circulation on detrital component and carbon burial of late Pleistocene and Holocene sediments in the eastern-central Mid-Adriatic deep

A sediment core was retrieved in the eastern-central Mid-Adriatic Deep (MAD) to study the changes in the water mass circulation and their effect on carbon burial efficiency and the provenance of a detrital sediment component. An age-depth model of the sediment core POS-514-40-11 is based on radiocarbon dating and tephrochronology. Two tephra were correlated to the Neapolitan Yellow Tuff and Pomici di Mercato eruptions, extending the previously known distribution of Pomici di Mercato tephra. Based on the analysis of heavy mineral (HM) assemblages throughout the core, for the first time the occurrence of Eastern Adriatic current (EAC) was estimated at ca. 15 ka BP, i.e., at the beginning of the post last glacial maximum (LGM) transgression. During the late Pleistocene, the detrital component was dominated by Paleo-Po river sediments, which gradually shifted toward the Albanian province as a basin-wide counterclockwise circulation was established. Mass accumulation rates of organic carbon (OC), stable isotopes of carbon (δ 13C) and nitrogen (δ 15N) as well as C/N ratios, showed that carbon burial was affected by sea level rise and climatic changes. Climatic effects are observed during cold periods i.e., the Younger Dryas and the 8.4–7.9 ka cold period when terrestrial OC was dominant. In the latter case dominance of terrestrial carbon was due to the North Adriatic dense water (NAddW) influence. On the other hand, sea level rise increased MAD distance from the main river mouths/deltas, resulting in decreased influx of terrestrial organic carbon and lower accumulation rates of organic carbon in general. This reconstruction of the oceanographic setting is valuable considering that the Adriatic Sea is one of the key locations for the formation of DW and thus affects the overall Mediterranean circulation.

Clay minerals control silicon isotope variations of fine-grained river sediments: Implication for the trade-off between physical erosion and chemical weathering

Stable silicon (Si) isotopes in fluvial sediments can provide insights into understanding silicate weathering processes on the Earth's surface. However, a lack of comprehensive studies has hindered full understanding of the factors influencing Si isotope fractionation during continental weathering. In this study, through the analysis of Si isotopes in fine-grained sediments from 13 rivers surrounding the South China Sea, significant variation of Si isotopes in bulk detrital sediments (<63 μm) was observed, with δ30Si values ranging from −0.17‰ to −1.09‰. At basin scale, the δ30Si values are influenced by multiple controlling factors such as climatic conditions, lithology, and tectonic settings, which have a close relationship with the content of clay minerals. The characteristics of weathering types and intensities are ultimately reflected in the weathering products, specifically clay minerals. Compiling data across multiple grain sizes from major rivers globally, robust correlations based on clay mineral classification between δ30Si and Al/Si ratio have been observed, which are unaffected by regional and grain-size variations. As the dominant clay mineral group transitions from illite/chlorite to smectite and kaolinite, the degree of Si isotope fractionation increases progressively. This sequence indicates a shift from stronger physical erosion to more intensive chemical weathering, suggesting a transition in the weathering regime from weathering-limited to transport-limited. This study reveals the intrinsic link between Si isotopic compositions and clay mineral assemblages, providing implications for similar stable isotope research and offering a potential indicator for understanding continental weathering processes and their contributions to the global carbon cycle.

Multidisciplinary characterisation of the biodiversity, geomorphology, oceanography and glacial history of Bowditch Seamount in the Sargasso Sea

The first multidisciplinary characterisation of Bowditch Seamount in the Sargasso Sea was conducted to provide new baseline knowledge of the biodiversity, geomorphology, oceanography and glacial history of this seamount. A dropframe camera transect 1483–1562 m deep on the seamount documented 77 megafaunal taxa including Vulnerable Marine Ecosystem indicator taxa such as sponges, cold-water corals, and stalked crinoids. Seabed terrain analysis of multibeam echosounder data showed species varied significantly along this transect in response to local geomorphological variability (R2adj = 31%, p < 0.0001), with changes in seafloor relief and substrata driving species composition over the seamount. 14C-calibrated and 230Th-ages of fossil corals (Desmophyllum dianthus) collected by Van Veen grabs 1517 m deep showed corals thrived on the seamount ∼24 ka BP and ∼17 ka BP. Abrupt excursions between higher and lower radiogenic εNd-composition values of the skeletons suggested that D. dianthus persisted on the seamount over times of southern source water input and detrital sediments from the melting Laurentide Ice Sheet, respectively. In agreement with other studies from the western North Atlantic, living D. dianthus were absent in the contemporary setting at these depths, and suggest a significant re-organisation of the seamount community since the deglacial when ice-rafted debris of carbonates likely resulted in a lower aragonite compensation depth allowing D. dianthus to proliferate at deeper depths. New conductivity-depth-temperature profiling revealed the seamount at these depths is now bathed by highly oxygenated Labrador Sea Water (LSW) formed at high latitudes. Co-analysis of a newly constructed 70-year long time series of temperature and salinity for the Labrador Sea and Bermuda regions revealed a 10-year transit time from high latitudes to Bowditch Seamount. This multidisciplinary approach shows how geomorphology drives local biodiversity patterns, but also how upstream climatic forcing in subpolar regions may influence Bermuda's subtropical seamount ecosystem.

Multiple Ba Phases in Marine Sediments elucidate environmental processes and conditions for the Holocene Mediterranean

Mediterranean sediments are known for their major shifts in sedimentary composition associated with dramatic changes in environmental and climate conditions. A typical expression for this in Holocene sediments is the occurrence of a distinctly organic-rich unit, sapropel S1, thought to be related with humid climate conditions. The S1 is accompanied by major changes in Ba content and in other elemental composition, respectively related to biological upper water column productivity and shifts in detrital sediment provenance. Here, we focus on changes in Ba and in its various phases to unravel shifts in environmental conditions around S1.Using selective extractions for sediments in cores MP37PC, MP39PC and MP50PC, respectively at 1908, 1359 and 775m water depth, we distinguish different Ba-phases: detrital Ba (Ba-det), barite Ba (Ba-bar), Mn-oxide-related Ba (Ba-ox), carbonate- and pyrite-associated Ba (Ba-carb and Ba-pyr). The predominant Ba-phase during S1 is Ba-bar (∼70%), whereas before and after S1 it is Ba-det (>90%). All other phases are mostly relatively small but have diagnostic value for environmental conditions and processes.The detrital (Ba/Al) is distinctly lower during S1 than before and after. The (Ba/Al). det variability, and enhanced values for Ba-carb and Ba-ox may have substantial influence on the traditional way to derive barite-Ba or excess-Ba content.The steep gradients in Ba-bar at onset and ending of S1and its high level during S1, clearly identify this period. In addition, and due to the exclusive nature of extraction results, we unequivocally demonstrate for the first time that there is a small gradual ‘early onset’ Ba-bar preceding the major increase in sapropel S1 formation sensu stricto.The ending of S1 formation is relatively abrupt with a well-defined reventilation event (’6 ka reventilation event’). This reventilation is associated with a rapid change in environmental conditions such as oxygenation and related remineralization of organic matter and recrystallization of carbonate. This rapid change and associated diagenetic processes are authentically recorded in Ba-carb and Ba-ox. For the period during sapropel S1 formation, the Ba-carb and Ba-ox results point to different levels of ventilation in the Eastern Mediterranean, i.e. a relatively mixed water mass down to ∼800m, a moderately mixed water mass from ∼800-to ∼1500 m, and a more stagnant water mass below 1500 m.

Provenance signature and tectono–sedimentary setting of the Permian Shihezi formation (Ordos basin, China): Insights from geochemistry and detrital zircon U–Pb dating

During the depositional period of the Permian Shihezi Formation, the southern margin of the Ordos Basin was a key location for studying the tectonic movement of the North China Craton (NCC) and South China Blocks. The sedimentary environment was the first period of complete transition from marine to continental. However, the distribution of sediments controlled by a multi–provenance supply and the response of deposition to tectonics remain ambiguous, and the restoration of paleogeography remains in the qualitative stage, restricting the study of larger-scale tectono–sedimentary patterns. Based on field profiles and core observations, the paleocurrent direction, lithic fragments, heavy mineral assemblages, rare earth element distribution patterns, 11 detrital zircon U–Pb age datasets, and discrimination diagram of major and trace elements, the provenance signature and tectono–sedimentary setting were revealed. The results indicated that there are three main provenances in the southern margin of the Ordos Basin: North Qilian and western and eastern sections of the North Qinling Orogenic Belt. The tectonic setting of the North Qilian was a continental island arc, and the North Qinling was transformed from a passive to an active continental margin. Owing to the continued intense tectonic activities of the North Qilian, a braided river delta with a large sedimentary range developed in the west, and it was mixed with detrital sediments from the western section of the North Qinling with weak tectonic activity in the central. Affected by the uplift of the southern North China Craton, the sedimentary environment in the eastern range was unstable, and the thickness distribution of sandy sediments in the braided river delta was uneven. Refinement of provenance and deposition has important implications for the study of basin–mountain coupling relationships and paleogeographic reconstruction in the southern Ordos Basin and provides a basis for the study of collision evolution of the North and South China Blocks in the Permian.

Elemental composition of smectite minerals in continental rise sediments from the Amundsen Sea, West Antarctica, as a tool to identify detrital input from various sources throughout late Quaternary glacial-interglacial cycles

Detrital smectite is a ubiquitous clay mineral in marine sediments and has a variable total Fe, Al, and Mg composition depending on the source, i.e., bedrock or unconsolidated sedimentary strata, the smectite is derived from. Analyses of elemental composition of smectite minerals in marine sediments can help to differentiate the smectite sources and, thus, sediment provenance, with potentially far-reaching paleo-environmental implications. In this study, we investigated the smectite compositions of modern-latest Holocene seafloor surface sediments deposited offshore from the Amundsen Sea drainage sector, where the West Antarctic Ice Sheet is currently unstable and losing mass due to ocean-forced melting, to detect and understand the variabilities of their elemental composition and geographical distribution. The smectite composition in continental rise sediments was compared to that of potential source areas on the Amundsen Sea continental shelf and in the sub-Antarctic South Pacific basin. Furthermore, we analyzed the smectite composition of sediments in continental rise cores deposited during the last glacial and last interglacial periods to reconstruct source variations over glacial-interglacial cycles. In particular, high contents of Al–Fe-rich smectite indicate that the glacial sediments had been supplied from the coastal region around Pine Island Bay by the cross-shelf advance of the West Antarctic Ice Sheet during the last glacial period. This clearly contrasts with the smectite minerals in rise sediments deposited during the present and the last interglacial periods that are composed of two distinct smectite types (Mg-rich and Al-rich, respectively), indicating their supply from multiple sources. During interglacials, Mg-rich smectite is probably transported by Circumpolar Deep Water from the sub-Antarctic South Pacific basin to the continental rise, while Al-rich smectite is supplied as part of ice rafted debris and by marine currents from the coasts around the Amundsen Sea embayment. Our research demonstrates that analysis of the elemental composition of smectite minerals on the Amundsen Sea continental margin provides a valuable tool to trace variations in sources for detrital sediment components and their pathways throughout glacial-interglacial cycles.

3.7 billion year old detrital sediments in Greenland are consistent with active plate tectonics in the Eoarchean

AbstractPlate tectonic processes modulate element cycling, crust generation, and differentiation, yet at what point in Earth’s history these processes emerged remains debated. Here we present evidence that parts of the &gt;3.7 Ga Isua Supracrustal Belt formed within a fore-arc setting, consistent with the operation of plate tectonics in the Eoarchean. We show that the oldest known sequence of detrital meta-sedimentary rocks were deposited conformably above chemical sediments on a volcanic basement. Mineral and trace elemental compositions show that turbiditic and pelagic detrital sediments were derived from terrains, comprising both basalts and differentiated tonalitic igneous rocks. The boninitic volcanic basement would have formed in a tensile environment before the adjacent terrains which sourced the clastic sediments. This suggests formation within a fore-arc during the initial few million years of subduction. This environment may have facilitated the local proliferation of life suggested by the frequent occurrence of layers rich in biogenic graphite.

Detrital zircon U–Pb geochronology and geochemistry of sandstones in the Siziwang Banner, Central Inner Mongolia: Implication for tectonic evolution

The central Inner Mongolia, located at the intersection of the northern margin of the North China Craton (NCC) and the Central Asian Orogenic Belt, is crucial for deciphering the Late Palaeozoic tectonic evolution associated with the subduction and closure of the Palaeo‐Asian Ocean (PAO). Our study focused on petrology, detrital zircon LA–ICP–MS U–Pb geochronology and whole‐rock geochemistry for the Late Carboniferous to Permian sandstones within the Shuanmazhuang, Dahongshan, Naobaogou, and Laowopu formations in Siziwang Banner, central Inner Mongolia. This comprehensive analysis shed light on the dynamic interplay between the NCC and the South Mongolia Block. Detrital zircon U–Pb ages in investigated samples mainly cluster between 250 and 2650 Ma, with significant peaks at 2.4–2.5 Ga, 1.8–2.0 Ga, 400–430 Ma, and 250–320 Ma, respectively. The geochemistry data are characterized by SiO2 contents (56.29–77.95 wt. %), Na2O / K2O ratios (0.45–1.58) and SiO2/Al2O3 ratios between 4.33 and 7.44. Moreover, they exhibit the slight enrichment in large ion lithophile elements (Rb and Ba) and the depletion in high field strength elements (Nb, Ta, Th, and U). These facts indicate that the sedimentary detritus predominantly originates from felsic sources, probably deriving from the Late Carboniferous–Permian continental island arc‐related intermediate‐acid igneous rocks, the Late Ordovician‐Silurian magmatic rocks in the Bainaimiao arc and the basements of the NCC. Furthermore, our present results also suggest that during the Early–Middle Permian, accelerating oceanic crust subduction triggered significant magmatic events in Siziwang Banner, leading to rapid uplift and the erosion of arc magmatic rocks, as well as the abundant corresponding sediments. Subsequently, the gradual convergence and eventual collision between the NCC and the Southern Mongolian Block took place at the end of the Permian, representing final closure of the PAO.

Contribution of Asian dust into the sediment budget of the Parece Vela Basin over the last 1 Ma: Implications for the climate change in East Asia

By quantifying the deposition of Asia-derived dust in the Western Pacific Ocean it is possible to constrain the consequences of climate change in East Asia. However, the rates of eolian dust deposition and its transport mechanism in the low-latitude Pacific remain uncertain. Core CP19 recovered sediment dating from ∼1 Ma to the present in the Parece Vela Basin (PVB). In this study we present bulk-rock major and trace element geochemistry, and Sr and Nd isotopic compositions from this sediment. The results reveal that these clastic sediments are a mixture of volcanic materials derived from the adjacent island arcs and eolian dust material originating from the arid regions of East Asia. Within the PVB, the proportion of Asian dust in the detrital sediment ranges from 30% to 50%, with an average of 44%. The majority of the dust originated from Eastern Asian deserts. Sr and Nd isotopes indicate that there is a significant increase in the overall proportion of eolian dust in the PVB starting at ∼0.64 Ma, influenced by an enhanced East Asian winter monsoon. In contrast, strengthening of the East Asian summer monsoon led to a decrease in the proportion of the eolian dust from the Ordos deserts. The notable alteration in eolian dust flux to the PVB corresponds to an abrupt intensification of aridity and monsoon climate in the East Asian continent at ∼0.64 Ma, caused by the Middle Pleistocene Climate Transition.

Glacial melt impacts carbon flows in an Antarctic benthic food web

Most coastal glaciers on the West Antarctic Peninsula are in retreat. Glacial ice scouring and lithogenic particle runoff increase turbidity and shape soft sediment benthic communities. This, in turn, has the potential to induce a shift in these systems from an autotrophic to a heterotrophic state. In this study, we investigated the influence of glacial runoff on carbon flows in the soft-sediment food web of Potter Cove, a well-studied shallow fjord located in the northern region of the West Antarctic Peninsula. We constructed linear inverse food web models using a dataset that includes benthic carbon stocks as well as carbon production and respiration rates. The dataset offers detailed spatial information across three locations and seasonal variations spanning three seasons, reflecting different degrees of disturbance from glacial melt runoff. In these highly resolved food web models, we quantified the carbon flows from various resource compartments (phytoplankton detritus, macroalgae, microphytobenthos, sediment detritus) to consumers (ranging from prokaryotes to various functional groups in meio- and macrofauna). Locations and seasons characterized by high glacial melt runoff exhibited distinct patterns of carbon flow compared to those with low glacial melt runoff. This difference was primarily driven by a less pronounced benthic primary production pathway, an impaired microbial loop and a lower secondary production of the dominant bivalve Aequiyoldia eightsii and other infauna in the location close to the glacier. In contrast, the bivalve Laternula elliptica and meiofauna had the highest secondary production close to the glacier, where they are exposed to high glacial melt runoff. This study shows how the effects of glacial melt propagate from lower to higher trophic levels, thereby affecting the transfer of energy in the ecosystem.

Sediment provenance variations driven by sea level in the eastern Arabian Sea since the MIS 9 period: Evidence from geochemical proxies

Although the uplift of the Tibetan Plateau has led to strong land-sea interactions, the characteristics of sediment transport and their controlling factors in typical marine areas in the northern Indian Ocean since the Quaternary are not clear. This work aimed to reconstruct the pattern of change in the sources of sediments since the Marine Isotope Stage 9 (MIS 9) period and to explore the mechanism of their response to changes in the marine environment in the Arabian Sea. To this end, a comprehensive multi-indicator study of the chronology and geochemical elements was carried out in core AS05-7 from the eastern Arabian Sea. Major trace element factor analysis and rare earth element (La/Yb)N-δEuN mapping suggested that sediments in the eastern Arabian Sea were mainly derived from terrestrial inputs from the Indus River and the Deccan Plateau. The sediments showed a clear glacial-interglacial cycle of change, with the contribution of the Indus River increasing during the interglacial period and that of the Deccan Plateau increasing during the glacial period. On average, the Indus River and Deccan Plateau contributed 71 % and 29 %, respectively, to the total amount of sediment. Indicators such as mass accumulation rate and Ca/Ti showed that the inputs from the terrestrial sources showed clear glacial-interglacial characteristics, with inputs during the glacial period being higher than those during the interglacial period. The lowering of the sea level during the glacial period led to an increase in the exposed area of the shelf, the shifting of deposition centers closer to the core, an increase in the rate of mass accumulation, and an increase in riverine inputs to the sea when clastic sediments from the Deccan Plateau increased. The elevation of the sea level during the interglacial period led to the inundation of the shelf, the shifting of deposition centers away from the core, a decrease in the rate of mass accumulation, and a reduction in riverine inputs to the sea when detrital sediments from the Deccan Plateau decreased. Changes in terrestrial inputs and sources revealed the orbital-scale control of sea-level change on sedimentary processes in the Arabian Sea and provided direct evidence for the “source-sink” model of sedimentation in the tropical Indian Ocean.

Byrd Ice Core Debris Constrains the Sediment Provenance Signature of Central West Antarctica

AbstractProvenance records from sediments deposited offshore of the West Antarctic Ice Sheet (WAIS) can help identify past major ice retreat, thus constraining ice‐sheet models projecting future sea‐level rise. Interpretations from such records are, however, hampered by the ice obscuring Antarctica's geology. Here, we explore central West Antarctica's subglacial geology using basal debris from within the Byrd ice core, drilled to the bed in 1968. Sand grain microtextures and a high kaolinite content (∼38–42%) reveal the debris consists predominantly of eroded sedimentary detritus, likely deposited initially in a warm, pre‐Oligocene, subaerial environment. Detrital hornblende 40Ar/39Ar ages suggest proximal late Cenozoic subglacial volcanism. The debris has a distinct provenance signature, with: common Permian‐Early Jurassic mineral grains; absent early Ross Orogeny grains; a high kaolinite content; and high 143Nd/144Nd and low 87Sr/86Sr ratios. Detecting this “fingerprint” in Antarctic sedimentary records could imply major WAIS retreat, revealing the WAIS's sensitivity to future warming.