Changes In Sediment Provenance Research Articles

Mio-pliocene evolution of deep-water channels on the northeastern Bengal fan: Records of signals of Himalaya uplift and South Asian Monsoon from source areas

Submarine channels, acting as major conduits for delivering terrestrial sediments into the deep sea, are sensitive to source-region uplift and climate variations. Using new 3D seismic data, previously published paleoenvironmental data, and IODP/ODP data, we characterize stratigraphic time changes in deep-water channels on the northeastern Bengal Fan and suggest that their long-term evolution relates to contemporaneous changes of Himalaya uplift and South Asian Monsoon. Our results show that around the boundary between the Miocene and Pliocene Epochs, the sedimentary characteristics of deep-water channels were changing at about the same time as decreased rates of Himalaya uplift and changes in the monsoonal climate. It is strongly suggested that environmental signals could successfully propagate from the Himalaya to the deep sea and play a dominant control on the long-term evolution of deep-water channels. During the late Miocene, orogen-wide and substantial Himalaya uplift and humid monsoonal climates (dominance of summer monsoon) generated a sediment supply with high fluxes, which allowed coarser-grained sediments to reach further into the basin and thus caused the formation of larger-scale, non-leveed erosional channels that have avulsion and confluence phenomena. After the Miocene, local and limited Himalaya uplift and arid monsoonal climates (dominance of winter monsoon) led to a sediment supply with low fluxes, during which only finer-grained sediments reached deep water and gave rise to smaller-scale, leveed aggradational channels that mainly have splay deposits. Between the late-Miocene and post-Miocene periods, detrital zircon U-Pb ages of Bengal Fan samples from IODP cores reflect a sediment provenance change from the mixing of Brahmaputra and Ganges Rivers to the end-member of Brahmaputra River, broadly coeval with the variations of Himalaya uplift and South Asian Monsoon. Moreover, Bengal Fan cores record a Mio-Pliocene decrease in sedimentation rates and maximum grain sizes and an increase in mudstone contents, consistent with the variations of sediment yield in the source catchments. Observations and interpretations from the current study, therefore, contribute to a better understanding of how the long-term evolution of submarine channels respond to tectonic and climatic perturbations in source areas and may help recognizing similar process-response relationships in other areas.

Quantifying sediment sources, pathways, and controls on fluvial transport dynamics on James Ross Island, Antarctica

Proglacial regions are enlarging across the Antarctic Peninsula as glaciers recede in a warming climate. However, despite the increasing importance of proglacial regions as sediment sources within cold environments, very few studies have considered fluvial sediment dynamics in polar settings and spatio-temporal variability in sediment delivery to the oceans has yet to be unravelled. In this study, we show how air temperature, precipitation, and ground conditions combine to control sediment loads in two catchments on James Ross Island, Antarctica. We estimate that the sediment load for the Bohemian Stream and Algal Stream over the 50 day study period, the average sediment load was 1.18 ± 0.63 t km−2 d−1 and 1.73 ± 1.02 t km−2 d−1, respectively. Both catchments show some sensitivity to changes in precipitation and air temperature, but the Algal catchment also shows some sensitivity to active layer thaw. The downstream changes in sediment provenance are controlled by underlying lithology, while differences in sediment load peaks between the two catchments appear to be primarily due to differing glacier and snowfield coverage. This identification of the controls on sediment load in this sub-polar environment provides insight into how other fluvial systems across the Antarctic Peninsula could respond as glaciers recede in a warming climate.

Eocene‐Oligocene Intensification of the Deep Western Boundary Current in the North Atlantic Ocean

AbstractThe role played by ocean circulation in major transitions in Earth's climate is debated. Here, we investigate the physical evolution of the Deep Western Boundary Current (DWBC) in the western North Atlantic Ocean through the late Eocene‐to‐mid Oligocene (35−26 Ma) using terrigenous grain size and geochemistry records of marine sediment cores. Our records cover the most pivotal transition in Cenozoic climate history, the Eocene‐Oligocene Transition (EOT; ∼33.7 Ma), when Earth first became sufficiently cool to sustain large ice sheets on Antarctica. To assess changes in deep‐water circulation in the northwest Atlantic across the EOT, we assembled sortable silt (10–63 μm) grain‐size and Nd, Hf, and Pb radiogenic isotope records at two Integrated Ocean Drilling Program (IODP) drill sites on the Newfoundland ridges (Sites U1406 and U1411). These records reveal an overall gradual increase in sortable silt abundance (SS%) at both sites with no change in sediment provenance. We interpret a steady, long‐term invigoration of the DWBC, likely driven by deepening of the Greenland‐Scotland Ridge and resultant enhanced inflow of waters sourced from deep‐water production sites in the Nordic Seas to the North Atlantic Ocean. Our results do not support abrupt and widespread invigoration of bottom current activity in the North Atlantic synchronous with accelerated cooling and Antarctic ice growth at the EOT. Instead, our records suggest that the DWBC started to intensify before this pivotal event in Cenozoic climate history (at ∼35 Ma) and then further strengthened gradually across the EOT (∼34 Ma) and through the early‐to‐mid Oligocene (∼34‒26 Ma).

Sediment provenance changes in the southwestern Okhotsk Sea since MIS 5 and their implications for sediment transport dynamics

The Okhotsk Sea, located between the Asian continent and the western Pacific, is a natural laboratory for investigating sediments source-to-sink influenced by atmosphere–ocean–land–sea ice interactions. However, despite their paleoenvironmental significance, changes in sediment provenance within the Okhotsk Sea are still debated due to the diversity of sediment sources and transport processes. Here, we investigate Sr and Nd isotope compositions in surface sediment samples from regions across the Okhotsk Sea, as well as Sr and Nd isotope compositions and elemental abundances in the sediments of core LV55‐40-1, collected from the southwestern Okhotsk Sea. Our results reveal an increasing trend of εNd values over the past ∼110 kyr, with an abrupt increase during the transition into the last deglacial/early Holocene (MIS 1). We also observed minor variations characterized by less radiogenic εNd during the glacial/stadial (G/S) periods (MIS 5d, MIS 5b, MIS 4, MIS 2), and more radiogenic εNd during the interglacial/interstadial (I/I) periods (MIS 5c, MIS 5a, MIS 3). The major terrigenous sediment sources in the northwestern Okhotsk Sea are via the Amur River and from Sakhalin Island (∼60–80%), with a minor volcanic contribution (∼20–40%) from the Okhotsk-Chukotka volcanic belt and the southern Kuril Islands/Hokkaido. Provenance variations are primarily controlled by the interplay of sea-ice drifting and ocean circulation, reflecting a dominant transport mode shift from sea ice to surface current dominance since the early Holocene. During the G/S periods with severe sea-ice condition, terrigenous materials from the Amur River and Sakhalin Island were transported to the study site, due to the southeastward drift of sea ice driven by the prevailing northwesterly winds and enhanced Okhotsk Sea Intermediate Water circulation. In contrast, during the I/I periods with moderate sea-ice conditions, an increased contribution from the Okhotsk-Chukotka volcanic belt was caused by sea-ice drifting southwestwards under the prevailing northerly and northeasterly winds, supplemented by surface currents. This study provides the first Sr-Nd isotopes record spanning the last glacial cycle in the Okhotsk Sea and it offers new insights into the relationship between sediment provenance and the interplay of sea ice and ocean currents in this region.

Sea level controls on the provenance of fine-grained sediments in the Xisha Trough, northwestern South China Sea over the last ~30 ka

The Xisha Trough situated in the northwestern South China Sea (SCS), plays a pivotal role in transporting sediments from the Red River into the deep-sea basin of the SCS, and thus is a critical place to examine variations in source-to-sink process of the Red River-derived sediments associated with past climate and oceanography changes. In this study, we analyzed clay minerals, grain size composition, and specific XRF core scanning elements of sediment core XT-1, retrieved from the northern slope of the Xisha Trough, to assess changes in sediment provenance and their primary influencing factors in the studied area over the last ~30 ka. The results show that clay minerals are primarily composed of illite+chrolite with a mean of 89%, followed by kaolinite with a mean of 9%; smectite occurs as a minor component. The mean grain size and XRF core scanning elements exhibit a three-phase change that corresponds well to variations in sediment source since the last glacial period. Over the last 29.8 ka, sea level fluctuations are the primary factor controlling changes in provenances and their contributions in the northern slope of the Xisha Trough. During the last glacial from 29.8 to 20.2 ka with lower sea levels, both the Red River and Taiwan were the primary contributors of fine-grained sediments in the lower continental slope of the Xisha Trough. However, with marine transgressions from the last deglaciation, Taiwan gradually became the dominant source of fine-grained sediments, followed by the Red River. Additionally, during the Last Glacial Maximum and the early to middle Holocene periods, the strengthened deep-water current (DWC) and East Asian summer monsoon, respectively, exerted strong impacts on the contribution of Taiwanese sediments to the Xisha Trough. The changing pattern of primary provenance in the studied core is roughly in line with those observed in the northern SCS, while differing from those in the southern regions of the western Xisha Trough. This discrepancy is likely caused by varying influences of the DWC on these regions.

Erosion regime controls sediment environmental DNA‐based community reconstruction

AbstractAnalysis of environmental DNA detected in lake sediments shows promise to become a great paleoecological technique that can provide detailed information about organism communities living in past environments. However, when interpreting sedimentary environmental DNA records, it is of crucial importance to separate ecosystem responses to large‐scale environmental change from “noise” caused by changes in sediment provenance or potential post‐depositional DNA mobility. In this study, we show that plant and mammalian communities reconstructed from sediments are strongly affected by sediment provenance, but unaffected by vertical mobility of DNA after sediment deposition. We observe that DNA from aquatic plants was abundant in background sediment, while embedded detrital event layers (sediment deposited under erosion events) primarily contained terrestrial plants; hence, vertical mobility of aquatic plant DNA across sediment layers was negligible within our studied lakes. About 33% of the identified terrestrial plant genera were only found in detrital sediment, suggesting that sediment origin had a strong impact on the reconstructed plant community. Similarly, DNA of some mammalian taxa (Capra hircus, Ursus arctos, Lepus, and Felis) were only or preferentially found in detrital event layers. Temporal changes across the Holocene were the main drivers of change for reconstructed plant communities, but sediment type was the second most important factor of variance. Our results highlight that erosion and sediment provenance need to be considered when reconstructing past mammalian and plant communities using environmental DNA from lake sediments.

Record of short-lived “orogen” on Eurasian continental margin by South China Sea obduction preserved in Taiwan collision

The Taiwan mountain belt is the result of an arc-continent collision following the total subduction of the South China Sea and subsequent closure of the Luzon forearc, a process important in the accretionary growth of continents. Due to the oblique convergence, the southern tip of Taiwan Island is experiencing incipient collision, which is key to observing the oceanic-continental subduction transition. Within the monotonous turbidite extensively exposed on the Hengchun Peninsula as an uplifted Manila Trench accretionary wedge, the Shihmen Conglomerate, as a few intercalated lenses of coarse mafic pebbles, represents a dramatic change in sediment provenance and the causal tectonic event. New zircon U-Pb and amphibole 40Ar/39Ar ages are obtained from sediments, including sands and mafic pebbles that are either gabbro or foliated amphibolite. The 22–24 Ma zircon crystallization ages confirm the South China Sea origin of the mafic clasts, while the much younger 13 ± 2 Ma amphibole 40Ar/39Ar isochron ages from foliated amphibolites suggest a later thermal-tectonic event other than seafloor metamorphism. The amphibole 40Ar/39Ar ages overlap with the biostratigraphic age (∼11–14 Ma), indicating that the mafic source rocks were exhumed and eroded in a high-relief topography immediately after metamorphism. Detrital zircon U-Pb ages from a sandy layer within the conglomerate are also mostly identical to those from the mafic pebbles. Since the paleocurrent of the Shihmen Conglomerate was similar to that of the neighboring turbidites, which were derived from major rivers draining the southeastern Chinese continent, the provenance of the mafic pebbles and sands was best explained as an isolated subaerial mountain on the Eurasian continental margin with a very limited temporal and spatial extent, as the detrital products are poorly distributed. The most likely cause of the ephemeral mountain was the obduction of the South China Sea onto the Eurasian continental margin when the latter first impinged on the Philippine Sea Plate at the Manila Trench, where the gabbroic oceanic crust was uplifted and exhumed, followed by dynamic metamorphism along the basal thrust.

Deciphering a cryptic unconformity in the Surat Basin using high frequency detrital zircon U-Pb geochronology: Insights into basin dynamics on the north-east margin of Gondwana

The Surat Basin is one of a series of shallow intracratonic basins that comprise the Great Australian Superbasin and developed in response to the initiation of Gondwanan breakup. Within the Surat Basin, the Walloon Coal Measures (WCM) are a significant target for Coal Seam Gas (CSG) production and the identification of the boundary with the overlying Springbok Sandstone (SST) is critical to the stratigraphic framework of the basin, and identification of groundwater flow units it delineates. Identification of the contact on a local (tenement) and regional (basin) scale between the SST and WCM is challenged in CSG producing areas by (i) overall lithological similarity of the units (macro- and microscopically, whole rock geochemistry, wireline signature), (ii) lateral heterogeneity of lithologies on a regional scale due to lateral facies and depositional environment variation in the uppermost WCM and lowermost SST and (iii) lack of consistent regional stratigraphic markers like erosion surfaces or correlated tuff beds. Sediment provenance analysis via detrital zircon (DZ) U-Pb geochronology allows constraint of spatial and temporal changes in sediment provenance by sampling across stratigraphic units along a lateral transect. The resulting large-scale stratigraphic correlations facilitate identification of basin dynamics within a tectonically quiescent basin. Here we present the results of DZ distributions from 26 samples that were sampled from four wells along a 300 km transect from the eastern Eromanga Basin to easternmost extent of the Surat Basin. Our data show a brief pulse of basement derived material at the base of the SST which interrupts the predominant volcaniclastic sediment provenance in the SST and WCM. This brief change in zircon provenance is interpreted as a precursor to higher energy depositional environments in the SST and can be utilised as a regional marker across the Surat and Eromanga basins, indicating a change in source provenance and basin dynamics associated with the SST – WCM boundary.

Mid-cretaceous rapid denudation of Eastern Tibetan plateau: Insights from detrital records at the Southwestern corner of Sichuan basin

Reconstruction of the Cretaceous tectonic evolution of the eastern margin of the Tibetan Plateau is of great significance to understanding the formation and early evolution of the Tibetan Plateau. The thick late Mesozoic sedimentary sequence in the Western Sichuan Basin may record the evolution of the basin itself and the tectonic uplift history of the eastern margin of the Tibetan Plateau during the Cretaceous period. Here we provide new multi-proxy provenance data from conglomerate clast populations, sandstone petrography, heavy mineral assemblages, U-Pb dating of detrital zircon, paleocurrent data, and detrital garnet geochemistry from the Cretaceous clastic units in the southwest corner of Sichuan Basin. Our analysis reveals two distinct changes in sediment provenance recorded in the Cretaceous strata at the southwest corner of the Sichuan Basin. The first significant change of detrital provenance was identified in the mid-Cretaceous Jiaguan Formation. Metamorphic rocks and volcanic rocks clast, as well as feldspar and mica, increased significantly, a heavy mineral assemblage dominated by hematite–limonite and ilmenite with high ATi and RuZi and low ZTR values, predominantly type Bi garnet and mostly 164 Ma, 207 Ma, 440 Ma, 780 Ma–824 Ma, and 1840 Ma detrital zircon ages, interpreted to be sourced from the Songpan-Ganzi fold belt and Longmenshan orogenic belt. The second shift, in the Guankou Formation, is marked by a low compositional maturity, a distinct increase in fossiliferous carbonate clasts and high GZi index with type Bii garnet, and Triassic zircon ages, indicating the exhumation of Longmenshan orogenic belt during the late Cretaceous. These data collectively indicate that the significant surface uplift and rapid denudation of the eastern margin of the Tibetan Plateau were probably initiated in the mid-Cretaceous (∼120 Ma). In conclusion, a detailed hands-on provenance analysis of the clastic sedimentary sequences in the southwest corner of the Sichuan Basin enabled us to determine catchment areas and shifts hitherto unstudied, thus contributing to the exhumation history of the eastern margin of the Tibetan Plateau.

Environmental and provenance change since MIS 2 recorded by two sediment cores in the central North Jiangsu Plain, East China

In order to reveal the evolution of sediment provenance and paleoenvironment of the central North Jiangsu Plain (NJP) since marine isotope stage 2 (MIS 2), we analyzed lithology, accelerator mass spectrometry (AMS) 14C dating, macrofossils and foraminifera, grain size, and geochemical compositions of sediments from two sediment cores (Core M and Core Y) recovered in the northern side of the Yangtze River. Our results show that fluvial environments prevailed in the central NJP during MIS 2, followed by alternations of coastal-marsh environments and shallow-bay environments in north central NJP and coastal-marsh environments in south central NJP during MIS 1. Provenance analysis suggests a major change in sediment provenance from the Yangtze River to the Yellow River at early MIS 1 in north central NJP; these Yellow River sediments might be transported from previously deposited sediments by strong tidal currents and intense waves to this area or be a reflection of a southward shift of the Yellow River during this period. However, the Yangtze River-derived sediments dominated the south central NJP since MIS 2. The depositional succession and sediment supplies since MIS 2 were dominantly controlled by sea-level fluctuations, regional geomorphic patterns, shift of the rivers, etc.

The Origin of the Paleo‐Kuril Arc, NE Japan: Sediment Provenance Change and Its Implications for Plate Configuration in the NW Pacific Region Since the Late Cretaceous

AbstractThe Nemuro Belt is a tectonic belt in the Paleo‐Kuril Arc system, the NW Pacific region. The Paleo‐Kuril Arc has been interpreted as an intraoceanic arc system between the Izanagi and Pacific Plates during the Late Cretaceous, suggesting that the boundary between these plates was a trench. However, this study shows it was a volcanic arc that developed atop a continental margin. To determine the nature of this arc during the Late Cretaceous, U‐Pb ages of detrital zircons from the Nemuro and Urahoro Groups in the Paleo‐Kuril Arc were analyzed. Our results identify two distinct types of detrital zircon U‐Pb age distributions. The first (Type 1) is characterized by multimodal age distributions with peaks ranging from ca. 1.8 Ga to 78 Ma. The other (Type 2) exhibits a unimodal age distribution with a peak at 60‐52 Ma. These different age distributions indicate a provenance transition occurred between the Late Cretaceous and Paleogene. Precambrian zircons in Type 1 sandstones indicate that the Paleo‐Kuril Arc was part of a continental plate, presumably the Okhotsk Block, in NE Asia during the Late Cretaceous. In contrast, Type 2 sandstones were supplied only from the magmatic arc region that the Izanagi‐Pacific Ridge subduction could have activated. This provenance transition suggests the initially continental arc became separated from its continental source at the beginning of the Paleogene.

Late Holocene sediment provenance change in the Red River Delta: A magnetic study

Holocene climate change and human activities can lead to sediment composition variations. In this study, two drilled cores (VN and GA) from the Red River Delta, Vietnam, were subjected to magnetic measurement, as well as particle size, diffuse reflectance spectroscopy (DRS), and geochemical analyses, to infer Holocene sediment provenance changes. Both cores VN and GA cover estuarine, shallow marine, delta front slope, delta front platform, and delta plain facies in ascending order, with the former covering the whole Holocene while the latter covering the late Holocene. In the younger core GA, the clay content has a significant positive correlation with magnetic grain-size indicators (χARM/SIRM and χfd%) and a negative correlation with demagnetization parameters (S-100 mT and S-300 mT), reflecting the enrichment of fine-grained ferrimagnetic minerals and antiferromagnetic minerals in finer sediments. On the contrary, the relationship between the above-mentioned magnetic properties and clay content is not significant in core VN, reflecting the impact of stronger post-depositional diagenesis. In addition, diagenesis in the shallow marine and delta front slope facies of two cores is more pronounced, which is due to the fact of higher input of marine-sourced organic carbon. A magnetic comparison of the upper parts of two cores indicates that there are sediment source changes within the last 2000 years, which is supported by DRS analysis. Sediments in delta front slope and delta front platform of two cores have similar goethite content, but core GA contains higher hematite content indicating a drier condition. Such a sediment source change can be interpreted by variations of monsoon climate and reworking of soil due to human disturbance. Surface soil erosion due to human activities over the last 0.5 ka is supported by the presence of ultra-fine grained magnetite. Our study demonstrates that magnetic properties together with DRS analysis can provide insights into paleoclimate and paleoenvironmental change in deltaic environments.

Late Quaternary changes in sediment sources in the Labrador Sea

Quaternary sediment in the Labrador Sea was derived from many proglacial sources in Greenland and eastern Canada. Understanding the spatial and temporal changes in sediment provenance provides information on ice extent and sediment dispersal patterns. Variations in mineral composition of sediment from late Quaternary cores has been determined by a whole pattern of quantitative X-ray diffraction procedure. Mineral facies were extracted statistically by a supervised analysis of 90 samples from bedrock and ice-rafted clasts, which were then used to predict the most probable mineral facies in 1443 marine sediment samples. We used a non-parametric Classification Decision Tree (CDT) to validate that decision. Only 26% of the samples were misclassified in the CDT. The six facies identified consisted of four facies reflecting differences in the composition of Canadian and Greenland Precambrian igneous and metamorphic bedrock, a set of samples dominated by high weight percentages of calcite and dolomite (detrital carbonate (DC) and Hudson Strait Heinrich (HS-H) events), and a “shale” facies. We isolated 284 sediments from the HS-H DC facies and determined that they could be divided into four categories based on differences in their mineral proportions. These categories vary geographically, based on non-carbonate sediment supply during these events from Greenland, the Canadian Shield, the Appalachians, and the outer continental shelf. In the Holocene of the Labrador Sea, dolomite is derived from Baffin Bay and abundance of calcite is influenced by both biogenic productivity and dissolution.

Provenance Response to Rifting and Separation at the Jan Mayen Microcontinent Margin

The Eocene-Miocene successions recovered at DSDP sites on the Jan Mayen Ridge (NE Atlantic) and on the adjacent East Greenland margin provide a sedimentary record of the rifting and separation of the Jan Mayen Microcontinent from East Greenland. A combination of palynology, conventional heavy mineral analysis, single-grain major and trace element geochemistry and radiometric dating of amphibole and zircon has revealed a major change in sediment provenance took place at the Early/Late Oligocene boundary corresponding to a prominent seismic reflector termed JA. During the Eocene and Early Oligocene, lateral variations in provenance character indicate multiple, small-scale transport systems. Site 349 and Kap Brewster were predominantly supplied from magmatic sources (Kap Brewster having a stronger subalkaline signature compared with Site 349), whereas Site 346 received almost exclusively metasedimentary detritus. By contrast, Late Oligocene provenance characteristics are closely comparable at the two Jan Mayen sites, the most distinctive feature being the abundance of reworked Carboniferous, Jurassic, Cretaceous and Eocene palynomorphs. The Site 349 succession documents an evolution in the nature of the magmatic provenance component. Supply from evolved alkaline magmatic rocks, such as syenites, was important in the Middle Eocene and lower part of the Early Oligocene, but was superseded in the later Early Oligocene by mafic magmatic sources. In the latest Early Oligocene, the presence of evolved clinopyroxenes provides evidence for prolonged magmatic fractionation. Initial low degrees of partial melting led to generation of alkaline (syenitic) magmas. The extent of partial melting increased during the Early Oligocene, generating basaltic rocks with both subalkaline and alkaline compositions. Towards the end of the Early Oligocene, the amount of partial melting and magma supply rates decreased. In the Late Oligocene, there is no evidence for contemporaneous igneous activity, with scarce magmatic indicator minerals. The provenance change suggests that the hiatus at the Early/Late Oligocene boundary represents the initiation of the proto-Kolbeinsey Ridge and separation of the Jan Mayen Microcontinent from East Greenland.

Causes of Variable Shortening and Tectonic Subsidence During Changes in Subduction: Insights From Flexural Thermokinematic Modeling of the Neogene Southern Central Andes (28–30°S)

AbstractThe Andes of western Argentina record spatiotemporal variations in morphology, basin geometry, and structural style that correspond with changes in crustal inheritance and convergent margin dynamics. Above the modern Pampean flat‐slab subduction segment (27–33°S), retroarc shortening generated a fold‐thrust belt and intraforeland basement uplifts that converge north of ∼29°S, providing opportunities to explore the effects of varied deformation and subduction regimes on synorogenic sedimentation. We integrate new detrital zircon U‐Pb and apatite (U‐Th)/He analyses with sequentially restored, flexurally balanced cross sections and thermokinematic models at ∼28.5–30°S to link deformation with resulting uplift, erosion, and basin accumulation histories. Tectonic subsidence, topographic evolution, and thermochronometric cooling records point to (a) shortening and distal foreland basin accumulation at ∼18–16 Ma, (b) thrust belt migration, changes in sediment provenance, and enhanced flexural subsidence from ∼16 to 9 Ma, (c) intraforeland basement deformation, local flexure, and drainage reorganization at ∼12–7 Ma, and (d) out‐of‐sequence shortening and exhumation of foreland basin fill by ∼8–2 Ma. Thrust belt kinematics and the reactivation of basement heterogeneities strongly controlled tectonic load configurations and subsidence patterns. Geo/thermochronological data and model results resolve increased shortening and combined thrust belt and intraforeland basement loading in response to ridge collision and Neogene shallowing of the subducted oceanic slab. Finally, this study demonstrates the utility of integrated flexural thermokinematic and erosion modeling for evaluating the geometries, rates, and potential drivers of retroarc deformation and foreland basin evolution during changes in subduction.

Persistently high efficiencies of terrestrial organic carbon burial in Chinese marginal sea sediments over the last 200 years

Constraining the origins, transport history, and burial efficiency of terrestrial organic carbon (OCterr) accumulating in marine sediments is of fundamental importance for understanding the carbon cycle on a range of spatial and temporal scales. While there is abundant evidence that OC composition and age influences the sequestration of OCterr in surface sediments, little is known about longer-term controls on OCterr sources and burial efficiencies in response to natural and anthropogenic processes that influence marginal sea sediments. Here, we use bulk and molecular-level carbon isotopic (δ13C and Δ14C) measurements to examine depth-related variations in the sources, ages and burial efficiency of OCterr in a sediment core that captures deposition over the last 200 years in the central Yellow Sea mud area, the largest mud deposit in eastern Chinese marginal seas. The similar 14C ages of terrestrial higher plant long-chain fatty acid biomarkers (1830–2700 yr) to those of sedimentary OC (1890–3360 yr) suggest the continuous and dominant supply of pre-aged OC (OCpre-aged). Two carbon isotopic mixing models are used to apportion contributions from different terrestrially-derived OC pools. A dual carbon mixing model based on bulk OC and molecular δ13C and Δ14C values showed OCpre-aged and fossil OC (OCfossil) accounted for 52 ± 3% and 13 ± 2% of sedimentary OC, respectively; while a binary mixing model based on bulk δ13C values showed OCterr accounted for 45 ± 3% of sedimentary OC. Estimates of high burial efficiency for OC (~60%) and especially for the different terrestrial OC pools (>80%) over the last 200 years highlight that refractory millennial-aged terrestrial OC inputs from the Yellow River combined with stable depositional conditions promote OC preservation in the Yellow Sea. Notably, OCpre-aged and OCfossil exhibited contrasting fates, with higher burial efficiency for the former. These observations are attributed to differences in mineral associations, transport pathways as well as changes in sediment provenance and hydrodynamic regime. Furthermore, our results suggest that initial sequestration of OCterr in surface sediments presages long-term burial in deeper sediments despite the existence of temporal variability. Although not directly influenced by riverine discharge, persistent and efficient sequestration of millennial-aged terrestrial OC renders the distal marginal sea mud area a long-term carbon sink on (at least) centennial to millennial timescales.

Chemostratigraphic Architecture of Sandstone Facies Exposed along Auchi-Ighara Road, Mid-Western Nigeria

In this work, inorganic whole-rock geochemistry was applied to characterize the exposed sandstone facies along the Auchi-Ighara road Anambra basin Midwestern, Nigeria for distinction and correlation of the depositional units on the basis of the stratigraphic variation of geochemical trait. Fourteen representative samples collected from the outcrop were analyzed using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). From our analyses, ten major elements oxides, sixteen trace elements, and thirteen rare earth elements were obtained. The concentration of major elements in the samples range from 0.13 % and 53.71 % with SiO2, TiO2, Al2O3 and Fe2O3 being predominant. Other oxides found in the samples include K2O, CaO, Na2O, MgO and P2O5 indicating a recycled orogenic source of the grits from which the sandstone is derived. Trace elements concentration ranges between 0.017 ppm and 122.25 ppm; marked by the dominance of Zircon (Zr) which further asseverates orogenic recycling. The rare earth elements range in concentration from 0.01ppm and 5.53 ppm; the modal occurrence of Praseodymium (Pr) in this category is apparently indicative of deposition in an oxidizing environment. The appreciably high SiO2/Al2O3 ratio averages 11.2 in the samples is symptomatic of several cycles of sedimentation. Variation pattern of Ga/Rb and Al2O3/(CaO+MgO+K2O+Na2O) ratios connote a cooler and drier climatic condition after the sandstone deposition, which expectedly resulted to a decrease in hydrolytic weathering. Changes in sediment provenance are predicated on Cr/Al2O3, Cr/Na2O and Nb/Al2O3 ratio which indicate grits derivation from a more quartzose sedimentary and felsic sources that resulted from fluctuating paleoclimate during deposition. From the geochemical data, the paleoclimate and provenance of the sandstone facies were modelled and used for subdivision and correlation into two geochemical packages and five geochemical units. Keywords: Chemostratigraphy; Paleoclimate; Provenance; Weathering; Whole rock geochemistry.

The Early Miocene Provenance Shift of ODP Site 1177 and Implications for the Tectonic Evolution of the Shikoku Basin, Philippine Sea Plate

The Ocean Drilling Program Site 1177 recovered the oldest (∼23 Ma) sedimentary records in the Shikoku Basin, northeastern part of the Philippine Sea Plate. Changes in sediment provenances bear important implications for the tectonic evolution of the Philippine Sea Plate, but existing data are still controversial for the early Miocene. By integrating Sr-Nd isotopes, rock-magnetic parameters, diffuse reflectance spectroscopy, and the previous data on the detrital zircons and clay minerals from Site 1177, we found that a significant provenance shift occurred at ∼16.5 Ma. The sediments of Site 1177 before ∼16.5 Ma were mainly sourced from the Pearl River and Izu-Bonin Arc, but changed to the Yangtze River and Izu-Bonin Arc sources after that. This provenance shift was strongly linked with the northward motion and clockwise rotation of the Shikoku Basin in the Miocene, which marked the final time of separation between the Shikoku Basin and the South China Sea.

Late Cenozoic channel migration of the proto-Yangtze River in the delta region: Insights from cosmogenic nuclide burial dating of onshore boreholes

A thorough magnetostratigraphic chronology of the Yangtze River Delta is problematic due to coarse-grained (i.e., poorly magnetized) deposits and sedimentary discontinuity. This study presents cosmogenic nuclide data which facilitate 26Al/10Be burial dating to determine the absolute age of horizons from four previously reported long onshore boreholes in the Yangtze Delta region that record sediment provenance change to the Yangtze River. Dates obtained close to the provenance change horizons in boreholes RGK15 and ZKJ39 from the northern delta were 4.99 (+1.26/−0.81) Ma and 4.74 (+0.94/−0.70) Ma, the oldest radiometric ages of borehole sediments yet to date. The provenance change horizon in boreholes LQ19 and LQ11 in the southern delta were dated to 0.94 (+0.17/−0.16) Ma and 0.57 ± 0.17 Ma, respectively. These new ages combined with previous lithofacies and provenance studies imply that the proto-Yangtze River first entered the northern delta prior to ~5 Ma, then migrated gradually southward to the present estuary location after 0.94 Ma and moved even further south at 0.57 Ma. The southward migration history of the proto-Yangtze River channel sheds lights not only on the tectonic subsidence widely occurring on the east China coast during the Quaternary, but also on the somewhat controversial connection history of the Yangtze River to the East China Sea.

Luminescence Sensitivity of Rhine Valley Loess: Indicators of Source Variability?

Loess provides a valuable terrestrial record of past environmental conditions, including the dynamics and trajectories of air mass circulation responsible for dust transport. Here we explore variations in the luminescence sensitivity characteristics of sedimentary quartz and feldspar as possible tools for identifying changes in source down a loess-palaeosol sequence (LPS). Luminescence sensitivity is a rapidly measurable index which is the product of interplay between source lithology and the history of the quartz or feldspar clasts. Variations in sensitivity of down profile may therefore reflect changes in sediment provenance as well as other factors such as weathering through pedogenesis. We undertake an empirical investigation of the luminescence sensitivity of quartz and feldspar from different grain-size fractions from the Schwalbenberg LPS in the German Rhine valley. We compare samples from a 30 m core spanning the last full glacial cycle with samples of oxygen isotope stage (OIS) 3–2 age exposed within nearby profile. We find an overall inverse relationship between quartz and feldspar sensitivity, as well as variability in sensitivity between different quartz grain sizes. Statistical analyses yield a significant correlation between IR50 sensitivity from unprocessed sediments and clay content, and feldspar sensitivity and Si/Al ratios down the core. Since Si/Al ratios may indicate changes in provenance, the latter correlation suggests that IR50 measurements on unprocessed samples may be used to provide a reliable, rapid scan of source variability over millennial timescales.