Sediment Provenance Research Articles

Provenance of the Nb-rich bauxite and Li-rich claystone at the base of the Heshan Formation in Pingguo, Guangxi, SW China: Constrained by U–Pb ages and trace element contents of detrital zircon

The base of the Upper Permian Heshan Formation in Pingguo County, Guangxi Province, SW China, can be divided into two layers: a lower Nb-rich bauxite layer and an upper Li-rich claystone layer. The sources of these layers may have played a critical role in their formation. Detrital zircon provenance analysis is an effective method for identifying sediment provenance; however, it has not been applied previously to the Nb-rich bauxite and Li-rich claystone, thus limiting our knowledge of the sources of these two layers. Detrital zircons from the bauxite and the claystone layers yield a single age peak at ∼ 260 Ma, which is consistent with the age of the Emeishan Large Igneous Province (LIP; 263–257 Ma) and the Permian Palaeo-Tethyan magmatic arcs (300–260 Ma). In contrast, detrital zircons from the two layers yield different trace element signatures. Yttrium and Hf contents and U/Yb ratios of detrital zircon grains from the bauxite layer overlap with those of continental and oceanic crust and have similar Hf/Th, Th/Nb, Th/U, and Nb/Hf ratios to those of zircons of within-plate and magmatic arc origins. These results indicate that the bauxite was sourced from volcanic rocks or ash related to the Emeishan LIP and the Permian Palaeo-Tethyan magmatic arcs. However, detrital zircons from the claystone have similar Hf/Th, Th/Nb, Th/U, and Nb/Hf ratios to only those of zircon from magmatic arcs, suggesting a single Permian Palaeo-Tethyan magmatic arc source. Thus, our results reveal an abrupt change in the provenance of zircons at the base of the Heshan Formation. The lower Nb-rich bauxite layer was derived from the weathering of volcanic rocks or ash related to the Emeishan LIP and the Permian Palaeo-Tethyan magmatic arcs, whereas the upper Li-rich claystone layer was derived principally from the weathering of volcanic ash related to the Permian Palaeo-Tethyan magmatic arcs. Since Nb is an immobile element, volcanic rocks/ash related to the Emeishan LIP and the Permian magmatic arc could represent a source for bauxite and Nb. In contrast, Li is chemically highly mobile in the Earth’s surface environment and its origin cannot be constrained easily, further work is needed to identify the sources of Li.

Titanium and iron isotopic records of granitoid crust production in diverse Archean cratons

Archean granitoid provides critical clues on how Earth's felsic crust was established and its geodynamics evolved. In this study, we present Fe-Ti isotope and trace-element data for granitoids (mostly TTGs) from the ∼3.8-3.6 Ga Itsaq Gneiss Complex and ∼3.3 Ga East Pilbara Terrane, Pilbara Craton. TTGs from those localities and several other cratons follow the same Ti isotopic fractionation trend as modern calc-alkaline rocks. This similarity hides important petrogenetic differences as partial melting could have played a much more important role in establishing the felsic character of TTGs compared to modern granites of calc-alkaline affinity. Our thermodynamics-based modeling of isotopic fractionation shows that partial melting of hydrated metabasite can explain the Fe and Ti isotopic compositions of many TTGs but reworking of tonalite crust is needed to explain the most extreme compositions. The same Ti isotopic fractionation trends have been found now in several cratons (West Greenland, Slave, Pilbara, and Kaapvaal cratons) in granitoids formed in different geothermal gradients, meaning that it was likely a global signature of the Archean crust. Sediment provenance studies that use those TTG compositions and point to a primarily felsic crust in the Archean are therefore valid.

Initial development and sedimentary provenance of a middle Paleozoic foreland basin: Clam Bank Formation, western Newfoundland

The upper Silurian(?) to Lower Devonian (Lochkovian) Clam Bank Formation is the most northerly exposed middle Paleozoic foreland-basin succession in the Appalachian orogen. Understanding of its sedimentary history is poor, and there are contradictory interpretations of placement of its lower structural boundary. Our study redefines the lithostratigraphy and subdivides the ∼600 m thick formation into three paleoenvironmental successions: a lower coastal plain setting with fluvial channels giving way upsection to coastal flats with carbonate, colluvium with reworked paleosol material, and aeolian (silt) deposits; a middle coastal zone succession following marine transgression and deposition of shoreface sandstone; and an upper alluvial succession host to pedogenic and groundwater calcretes. A basal disconformity, though not exposed, is inferred from lithic and geochemical evidence for sediment mixing with underlying Upper Ordovician sources in the lowermost part of the formation. This supports previous interpretations of Silurian uplift along the Laurentian margin in response to the Salinian orogeny. Sedimentary provenance indicates quartzo-feldspathic sources throughout the formation, and sediment-transport indicators identify a northeast–southwest-oriented basin with northwest-directed fluvial input. U–Pb detrital zircon distributions associated with the paleocolluvium and younger transgressive sandstone document upsection loss of prominent age peaks of late Grenville (∼0.98 Ga) and pre-Grenville (1.5, 1.65, and 1.75 Ga) sources. The coastal plain succession and related detrital-zircon signature imply a mixture of distal and proximal sediment sources, the latter related to erosion of a weathered upland and exhumed Precambrian inliers in western Newfoundland. A more regional provenance signature with marine transgression suggests sediment transport in response to Acadian orogenesis.

Detrital geochronology of the Cunningham Lake formation: an overlap succession linking Cache Creek terrane to Stikinia at ∼205 Ma

Detrital zircon from three coarse-grained marine siliciclastic rocks was analyzed for U–Pb, Lu–Hf, and trace element compositions to constrain the timing of deposition and sediment provenance of the Cunningham Lake formation (formerly siliciclastic unit of the Sitlika assemblage) in north-central British Columbia. This strategy tests previously proposed sedimentary linkages between the Cache Creek terrane and the westerly rocks of the Stikine terrane. All three samples indicate maximum depositional ages at ca. 205–202 Ma (Rhaetian). The samples contain a predominant ca. 225–215 Ma detrital population, sourced from proximal contemporaneous volcanic arcs, and minor Permian to Middle Triassic and Carboniferous arc-derived detrital populations. The absence of Precambrian grains is consistent with the strongly suprachondritic zircon compositions (εHf(t) = +7 to +20), and indicates exclusively juvenile sources for the Cunningham Lake formation. Late Triassic sources of zircon are not known in the Cache Creek terrane and, except within western Stikine terrane, are uncommon among the Intermontane terranes that amalgamated with the Cache Creek terrane during Late Triassic–Early Jurassic. The Stikine suite (ca. 230–214 Ma) and coeval volcanic rocks in western Stikinia are the most probable sources of Late Triassic detritus for the Cunningham Lake formation. Stikinia’s Paleozoic basement is the probable source of Carboniferous detrital zircon. Volcanic arc–backarc complexes in the Cache Creek terrane are the most likely sources of Permian to Middle Triassic detritus in the Intermontane terranes. Accordingly, the siliciclastic rocks of the Cunningham Lake formation represent an overlap sedimentary succession that links Stikinia to the Cache Creek terrane by the latest Triassic.

Geochemical evidence of provenance diversity in Holocene sandy land of Qinghai Lake Basin in the north‐eastern margin of Qinghai–Tibet Plateau and its implications for climate change

ABSTRACTThe Qinghai Lake Basin, located in the north‐eastern Tibetan Plateau, is crucial for understanding the East Asian monsoon evolution and its interaction with westerlies. Palaeoclimatic studies in this region since the Holocene have primarily focused on interpreting proxy significance from sediments, resulting in being highly controversial. However, exploring palaeoclimate evolution through sediment provenance and proxy integration remains rare. This study analysed the elemental geochemical properties of two fluvial–lacustrine–aeolian profiles in Hudong Sandy Land, east of the Qinghai Lake Basin, and compared these with published modern basin sediments and extensively investigated Late Quaternary aeolian deposits. It was found that Hudong Sandy Land sediments exhibit similar geochemical compositions to other modern basin sediments, primarily consisting of SiO2, Al2O3 and CaO. Contrary to previous understanding, lacustrine sediments in the Hudong Sandy Land are closer to the upper continental crust average than aeolian deposits. Geochemical ratios and parameters suggested that Hudong Sandy Land sediments primarily derived from mixed source rocks of felsic igneous, quartzose sedimentary and intermediate igneous provenances. A comparison with published elemental geochemical data from the basin reveals distinct sediment sources during different periods in the Hudong Sandy Land. From 9.6 to 4.0 ka bp, Hudong Sandy Land hosted numerous lake environments, with sediments displaying a dominant role in sedimentary recycling and reworking, implying a continuously stronger East Asian summer monsoon. During 8.2 to 5.1 ka bp, the Hudong Sandy Land was a fluvial depositional sink for sediments from the Dabanshan Mountains. Bedrock clastic material generated by intense erosion and monsoonal runoff transport contributed to Hudong Sandy Land sedimentation, indicating the East Asian summer monsoon's peak since 9.6 ka bp. After 4.0 ka bp, thick aeolian sands accumulated in the Hudong Sandy Land, primarily derived from Lake Qinghai sediments due to declining water levels, indicating that westerlies and East Asian winter monsoon dominated the basin, with a weaker East Asia summer monsoon. This study facilitates a deeper understanding of the interaction between the East Asia summer monsoon and East Asia winter monsoon/westerlies.

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.

Provenance of deep-sea sediments in the eastern South China Sea since Marine Isotope Stage 5 (MIS 5) and implications for climate change and volcanic activity

The South China Sea deep-sea basin receives large amounts of marine sediments and volcanic materials from the surrounding continents and islands, and it is an ideal region to study the effects of climate change and volcanic activity on sediment provenance. Core K2 was collected in a water depth of 4078 m in the eastern South China Sea and is mainly composed of diatoms, tephra, volcanic glass and slag. The results of a total of 102 analysed grains show that the depositional processes were dominantly suspension, uniform suspension and overbank-pool facies suspension, with no rolling. Six accelerator mass spectrometry (AMS) 14C ages from planktonic foraminifers and fifty-four δ18O data points of G. ruber suggest that the age of Core K2 is 125 kyr before present (BP). Forty-four clay mineralogical data points show that the clay minerals in the sediments are mainly illite+chlorite (24.3%–49.7%), with a small amount of smectite (2.6%–11%), suggesting a sediment source mainly from Taiwan with a small amount of sediment from Luzon. Forty-five samples yield 143Nd/144Nd and 87Sr/86Sr ratios ranging from 0.512250 to 0.512769 and from 0.704383 to 0.710690, respectively, indicating that sediments in K2 represent a mixture of volcanic inputs from in or around Luzon and sediments from Taiwan and Luzon. Based on calculations of clay minerals and SrNd isotopic data, the relative proportions of sediments from Taiwan and Luzon and volcanic input vary from 8% to 88%, from 1% to 23% and from 0% to 91%, respectively, and the average proportions of sediments from Taiwan and Luzon and volcanic input are 55%, 12% and 33%, respectively. Significant temporal changes in SrNd isotopes are attributed to variations in the volcanic eruption intensity or distance to the sampling location. Moreover, high εNd values and low 87Sr/86Sr ratios of the sediments in Core K2 during interglacial periods could represent volcanic eruptions.

Tracking Sediment Provenance Applying a Linear Mixing Model Approach Using R’s FingerPro Package, in the Mining-Influenced Ocoña Watershed, Southern Peru

Stream sediments record water–rock interactions in tributaries followed by fluid mixing in larger downstream catchments, but it can be difficult to determine the relative contributions of each tributary. A good way to analyze this problem is sediment fingerprinting, which allows researchers to identify the source of sediments within a basin and to estimate the contribution of each source to the watershed. Herein, we developed a workflow using the frequentist model FingerPro v1.3 to quantify the sediment source contribution in a semiarid watershed. We applied an unmixing model algorithm to an ICP-MS geochemical database containing information on 32 elements in 362 stream sediment samples. By modeling the source contributions to these mixed samples, we infer that the main sediment contribution comes from the upper portion of the catchment (61–70%), followed by the middle (21–29%) and lower (8–10%) parts, with geochemical anomalies (As and Cu) being closely related to mining sites. Results from this study can be helpful for future management decisions to ensure a better environment in this semiarid watershed.

Sedimentology, Mineralogy of Al-Dujaila River Sediments Project, Southeastern Kut City, Iraq

A sedimentological and mineralogical study was carried out on sediments of Al-Dujaila River Project, one of the branches of the Tigris River, southeastern Kut City, Iraq. The study aims to identify the nature and maturity of sediments in order to deduce the provenance of these sediments and the source area. The results of grain size analysis of ten river sediment samples indicated that the averages are: silt (44.97%), clay (34.06%), and sand (20.96%). According to Folk's classification (1974), the sediments are classified as sandy mud. A microscopic study of five sand fraction samples has shown the presence of light and heavy minerals. Light minerals (average 94.6%) include on average: a major share of rock fragments (64.8% including dominant carbonate, chert, igneous, metamorphic, and mudstone), quartz (24.1% including dominant monocrystalline and polycrystalline), feldspars (5% including orthoclase and plagioclase) while evaporates, and coated clays are subordinate. Heavy minerals (average 5.4 %) include opaques (average 54.2%) and non-opaques (average 45.8%) including pyroxene, amphibole, epidote, garnet, staurolite, chlorite, biotite, muscovite, zircon, tourmaline and rutile. Based on the mineralogical signatures, light and heavy minerals reflect metamorphic, mafic and felsic igneous rocks of the active margin of the unstable shelf in addition to carbonate, evaporate and mud of sedimentary rocks that could be sourced from the floodplain. According to sediment diversity and very poor grain sorting in the study area, as well as the values of indices of mineral maturity MI (0.34), MMI (0.76), and the ZTR (23.5%), all these results indicate that sediments are immature to extremely immature, which means the source area represents rather elevated topography, rapid erosion and transport in arid to the semi-arid environment and a short distance of transportation. The tectonic provenance of Al-Dujaila River sediments can be characterized as a lithic reworked of the recycled orogen as a result of the collision range of Taurus and Zagros Mountain range.

Statistical self-similarity of detrital zircon U-Pb ages reveals sedimentary provenance: A case study from the Chinese Loess Plateau

A major concern of the geoscience community is often where sediments originally come from — this is a material's provenance. Tracing provenance allows us to determine how a material moved from its source to its sink, and thereby to evaluate the tectonic and paleoclimatic history. Detrital zircon UPb geochronology has long been used for this purpose. However, current approaches to measuring (dis)similarity in zircon age distributions may lead to erroneous geologic interpretations. Here we propose an Age-Number fractal model to characterize zircon age densities and perform intersample comparisons using multidimensional scaling. The advantage of the new method is that compared to such traditional methods as Kolmogorov-Smirnov test, it accentuates holistic rather than partial differences between two age distributions and is less-affected by data biases related to grain-size sorting and uneven sample sizes. We then use this model to unravel the debatable provenance of the Chinese Loess Plateau (CLP) by comparing the zircon ages of Quaternary loess on the CLP with that of loose sediments from potential source regions. The model divides the CLP into four distinct provenance zones, receiving materials primarily from the northeastern Tibetan Plateau, upper Yellow River, and/or Mu Us Desert. Our observations corroborate that the aeolian (East Asian monsoon and Westerlies) and fluvial (Yellow River) processes play a joint role in the dust deposition. A new pattern of spatial heterogeneity in the loess provenance is established and can be interpreted as a combined effect of atmospheric circulation patterns, availability of riverine sediments, and such factors as aridification, implying a more dynamically-evolved CLP than previous thought. Our results will aid future development and interpretation of the dust-based paleoclimatic proxies.

Fluvial response to Late Pleistocene–Holocene climate change in the Colorado River drainage, central Texas, USA

Abstract We documented the impact of Late Pleistocene–Holocene climate change on terrace deposits and preserved channels in the unglaciated drainage of the Colorado River in central Texas (south-central United States) using integrated channel morphology and provenance analysis. Detrital zircon (DZ) U-Pb ages (n = 1850) from fluvial terrace deposits and new quantitative analysis of fluvial channel morphology based on LiDAR data were used to reconstruct sediment provenance and shifts in paleohydraulic conditions during Late Pleistocene to Holocene aridification. These data reveal a reduction in fluvial channel size and discharge temporally coupled with a rapid shift in erosion locus and dominant sediment sourcing, from the Southern Rocky Mountains to the Llano area, during the glacial-interglacial transition. Geomorphic mapping and morphometric analysis show narrowing of river channels linked to diminishing Colorado River discharge. DZ data show an abrupt shift to erosion in the lower drainage basin and the remobilization of older terraces due to river incision and lateral channel migration. We attribute these systematic changes to upper-basin contraction caused by drainage reorganization and aridification during the Late Pleistocene, as well as the onset of enhanced convective precipitation sourced from the Gulf of Mexico, driving focused erosion along the topographic edge of the Llano uplift in central Texas since the early to mid-Holocene.

The Clay Mineralogy and Geochemistry of Sediments in the Beibu Gulf, South China Sea: A Record of the Holocene Sedimentary Environmental Change

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.

Unraveling source-to-sink dust transport in Central and East Asia by identifying provenances of aeolian sediments

Loess deposits as a unique terrestrial archive of paleo-dust contribute to understanding the wide-scale and long-term dust transport from source to sink. This study provided diagnostic constraints on the sources of clay-sized particles in the Chinese Loess Plateau (CLP) loess by expanding the potential dust source areas with the Kyzylkum Desert and the Central Asian loess. Based on the grain sizes and the particle-size-specific trace elements, we characterized the major provenance and the sedimentary process of the Kyzylkum Desert sands. The results indicate the main derivation of Kyzylkum Desert sands from the Tian Shan-derived sediments, with limited large-scale mixing. The desert was thought to be a sink region, instead of an important dust source, which was supported by its weak genetic links to the Central Asian loess. With integration of the published data set about trace element and SrNd isotopic composition and our results, combined with the simulation results, we revealed that the Badain Jaran and Tengger deserts in northwestern CLP, rather than the Taklimakan and Kyzylkum deserts further west, played an important role in supply of the clay-sized particles for the CLP loess. The findings implied that the fine particles were primarily related to the East Asian winter monsoon, instead of the high-level westerly airstreams. In this context, we attributed the asynchronous timing of enhanced dust accumulation during the last glacial maximum (LGM) over Greenland and North Pacific (early LGM) and on the CLP (late LGM) to the differences in the major dust sources and in the atmospheric circulation systems.

Geochemistry of the Lancang River (Upper Mekong River) overbank sediments: Implications for provenance, weathering and sedimentary characteristics

Large rivers originating from the Tibetan Plateau play a crucial role in sediment production and transportation and thus influence the ocean composition and global climate. This study focuses on the geochemical characteristics, including major, trace and rare earth elements of overbank sediments from the Lancang River (Upper Mekong), which drains southwest China and is one of the largest international rivers in Asia. We characterize sediment maturity and recycling, weathering and provenance in a typical, tectonically active cold-humid climate region. Lancang River (LR) sediments with an average chemical index of alteration (CIA) of 73 ± 6 and an average index of compositional variability (ICV) of 1.1 ± 0.6 suggest an intermediate mineralogy and chemical maturity corresponding to moderate weathering in a slightly warmer climate. The provenance of LR sediments is characterized by felsic source rocks, similar to the upper continental crust (UCC), followed by recycled sedimentary rocks, which were possibly derived from the Yidun, North Qiangtang (NQ) and Songpan-Ganzi (SGZ) terranes at upstream locations when the Lingcang basalt (LCB) provided mafic rocks for LR sediments. However, recycled materials have limited impacts on sediment maturity, as reflected by the degree of weathering. Highly physical weathering (erosion) has created a massive source for LR sediments due to active tectonics, while the impacts of climate on weathering processes have increased. Meanwhile, the overbank sediment in large rivers could be a good sampling medium for evaluating terrestrial weathering, provenance and sediment characteristics using geochemical evidence.

Linking sedimentary provenance, climate and tectonics in the Neoproterozoic Seridó Belt, Borborema Province (NE Brazil)

The Seridó Belt, at the extreme northeast of Brazil, is one of the several Neoproterozoic mobile belts related to the Brasiliano/Pan-African Orogeny in Western Gondwana. The lithostratigraphy of the Seridó Belt comprises basal quartzites and metaconglomerates (Equador Formation) overlain by hornblende-bearing paragneisses, calc-silicate rocks and marbles (Jucurutu Formation) and biotite-schists (Seridó Formation). We investigated the sedimentary provenance of these rocks based on an integration of compiled whole-rock geochemistry, Sm-Nd isotopes, U-Pb detrital zircon ages and a new set of whole-rock trace elements analyses. Equador Formation quartzites have major and trace elements patterns that resemble cratonic sandstones, with a typical felsic provenance consistent with the isotopic composition of plutonic Archean to Paleoproterozoic basement rocks. Geochemical proxies suggest that these rocks were deposited in fresh waters under anoxic conditions and moderate to intense weathering conditions (CIA = 58–79). A shift in provenance led to an increase in intermediate-mafic sources during the deposition of the Jucurutu and Seridó formations. Trace elements from rock types in these units are nearly identical, yet they differ on the contents of some high field-strength elements (e.g., Sc, V and Ni), which are higher in the Seridó Formation than average pelites. Geochemical proxies show similar depositional environments, with brackish to marine conditions for the Jucurutu and Seridó formations under anoxic to euxinic conditions. Weathering conditions are consistently lower in the Jucurutu Formation (CIA = 58–66) in comparison with the Seridó Formation (CIA = 60–88). Compiled U-Pb data suggest maximum depositional ages of 633 ± 11 Ma and 633 ± 6 Ma for Jucurutu and Seridó formations, respectively, suggesting deposition following the ca. 645–635 Ma Marinoan glaciation. We compared the geochemistry of the Seridó Formation schists with currently exposed basement rocks and showed a strong affinity with Neoproterozoic arc-related intermediate rocks, which is in agreement with their slightly radiogenic signature (average εNd(630Ma) = –1.68). When comparing with other pelitic sequences on the western Borborema Province, most of them fit the same sources and weathering conditions of the Seridó Formation schists and Jucurutu Formation paragneisses. We propose that the Seridó Belt represents an intracontinental rift basin (Equador Formation) that was overlain by fine-grained magmatic arc-related sediments (Seridó and Jucurutu formations) during the post-Marinoan deglaciation and sea level rise. Similar pelitic deposits in western Borborema Province suggest a large marine-influenced continental depositional system that was mostly sourced from magmatic arcs of the West Gondwana Orogen.

Effect of chemical composition on zircon radiation damage dating: Implications for low-temperature thermochronology

Zircon radiation damage dating is a low-temperature thermochronological method that can reveal the cooling histories of magmatic intrusions and discriminate sedimentary provenance in combination with other dating methods. This method has broad application prospects because of its advantages of non-destructive, high efficiency, and capable of double (or multiple) dating, involving only multiple measurements by Raman spectrometer and laser ablation-inductively coupled plasma-mass spectrometry. However, several factors, such as zircon chemical composition and the non-uniformity of radiation damage annealing kinetics, can cause poor precision when using this method and thus restricts its wide application. This study examined the effect of chemical composition (P, Ti, Dy, Th, U, and Hf) on Raman spectra using synthetic zircon crystals grown in a lithium-molybdate flux. The results show that the full width at half-maximum (FWHM) of the ν3(SiO4) band has positive linear correlations with the concentrations of P, Ti, Dy, Th, and U in decreasing order of influence, while the FWHM is unaffected by Hf at concentrations <1 wt.% but increases at concentrations >10 wt.%. Furthermore, the Raman shift is negatively correlated with Th, U, and Dy concentrations, positively correlated with Hf, and shows no obvious correlation with Ti and P. Thus, our study shows that chemical composition is a non-ignorable factor for calculating zircon radiation damage age using Raman spectroscopy, especially for zircon with relatively high concentrations of P, rare earth elements (REEs), Th, U, and Hf. The obtained multiple linear regression equation provides a potential means for estimating the FWHM at zero dose and implication for improving the dating precision of this method. In addition, the observed effects of REEs, Th, U, and Hf on the Raman shift of the ν3(SiO4) band indicate that chemical composition in zircon might affect the estimation of the P-T conditions of geological processes when using entrapped zircon inclusions in host minerals or the field of zircon as an in situ pressure sensor in hydrothermal experiments. Our study suggests that zircon radiation damage dating, excluding geochemical effects, will be more accurate for addressing lower-temperature geological processes.

Mio‐Pliocene exhumation of the hinterland and sediments provenance of the Neogene strata from Kumaun Himalaya of northwest India: Insights from detrital fission‐track thermochronology

Fission‐track (FT) thermochronological analysis of detrital apatite and zircon derived from the lower and middle Siwalik Group of the sub‐Himalaya allows the reconstruction of the long‐term exhumation history of the Higher Himalayan Crystalline (HHC) and Lesser Himalayan Sequence (LHS), and also the provenance of the Siwalik sediments. Here, we report 14 detrital apatite and zircon fission‐track (AFT/ZFT) ages of lower and middle Siwalik subgroups of the Kumaun region, northwest Himalaya. Detrital FT ages suggest that all sandstone samples were never buried below the temperature range of 90° to 100°C and remained as unreset to retain a signal of source‐area exhumation. A detrital AFT age from sandstone sample at close proximity to the Main Boundary Thrust (MBT) is 4.4 ± 0.5 Ma (Pliocene time) which is completely reset and younger than the depositional age, while the detrital ZFT ages of the same sample are unrest. The AFT age represents the time of reactivation of the MBT during which ZFT ages were not affected. This study revealed that the provenances of Siwalik sediments are located majorly in the MBT hinterland areas and the nearest sources are Amritpur granite, the outer Lesser Himalayan meta‐sedimentary (LHMS) zone, Almora klippe, Ramgarh thrust sheet, and the overlying Tethyan Himalayan Sequence. These source areas can be attributed to the development of local drainage networks in the Ramganga‐Kosi drainage basin during late Miocene to Pliocene (i.e., ~9 to 4 Ma). Based on detrital FT datasets, it has been envisaged that different tectonic activities in the MBT hinterland area between Miocene and Pliocene Periods cause the tectonic upliftment and exhumation of source areas and supply the sediment to the Siwalik foreland basin.

Decoupled local climate and chemical weathering intensity of fine-grained siliciclastic sediments from a paleo-megalake: An example from the Qaidam basin, northern Tibetan Plateau

Clay mineralogy and elemental geochemistry of lacustrine sedimentary records have been widely used in paleo-weathering and paleo-climate studies. However, different paleo-climatic interpretations may be produced via analyses on siliciclastic sediments and other sedimentary components (e.g., authigenic minerals and organic materials), especially for megalake systems. To test this hypothesis, we focus on late Cenozoic lacustrine fine-grained deposits from the northwestern Qaidam basin and combine clay mineralogical and geochemical data (including neodymium isotope) to interpret sediment provenance, reconstruct paleo-weathering history and characterize sediment-climate feedback processes. Provenance analysis results show that the lacustrine siliciclastic sediments were derived from lithologically similar sources that provided dominant felsic parent-rocks. The kaolinite/illite ratio, illite chemistry index, Chemical Index of Alteration (CIA) values are low and demonstrate overwhelmingly mild-moderate chemical weathering intensity, seemingly matching well with the middle–late Miocene regional arid climate. However, these weathering intensity index values are also highly fluctuant and display increasing trends during ~13.4–12 Ma and ~8.8–8.4 Ma. The reconstructed paleo-weathering history is discrepant with local intensified aridity conditions documented by previously published sedimentary carbonate oxygen isotope, evaporite mineral, biomarker and sporopollen data. Given the occurrence of a middle–late Miocene megalake in the Qaidam basin, the intense exhumation at ~13–12 Ma and the ~9 to ~7 Ma intensified East Asian summer monsoon precipitation in northeastern Tibet regions, we suggest that the lacustrine fine-grained siliciclastic compositions and corresponding weathering records were likely influenced by tectonic and climatic changes in far regions to the east. The observed clay mineralogical and geochemical variations reflect weathering conditions involving sediment sources and transport pathways, not merely the depositional areas. Our findings verify the possible differences in paleo-climate reconstruction results from different lacustrine sediment indicators. This study emphasizes the importance of a sediment source-to-sink perspective for paleo-climate study based on siliciclastic materials in megalake systems.

Sedimentary record off the Yangtze River estuary and its response to typhoons and human activities over the past 70 years

The muddy area off the Yangtze River estuary serves as an archive that can be investigated to unravel the impacts of environmental changes and human activities. However, in the context of increasing human activity and global climate change, it is unclear how the sedimentary records in this area respond to these changes. Radionuclide activity, magnetic susceptibility, grain size, clay minerals and chemical elements of samples in a sediment core (T1) collected off the Yangtze River estuary were analyzed in this study to identify the sediment provenance and elucidate the impacts of typhoon events and human activities on the sedimentary records over the past 70 years. Based on the analyses of clay minerals, Cr/Th vs. Sc/Al, element ratios, and correlations between grain size and magnetic susceptibility, sediments at 44–90 cm were mainly derived from the Yangtze River, while sediments at 0–44 cm were influenced by the Yangtze River, old Yellow River, and relict sand. Since AD 1950, the mineralogical–geochemical compositions of sediments in core T1 have significantly altered, which was attributed to typhoon events and human activities. Before 2003, typhoon activity influenced the frequency of sand layer deposition, which was related to El Niño-Southern Oscillation (ENSO) variations. However, following the operation of the Three Gorges Dam in 2003, the relationship between typhoon event records and ENSO was disrupted. Human activities have affected the sedimentary records of typhoon events off the Yangtze River estuary. This study emphasizes that sediments at the edge of the muddy area off the Yangtze River estuary can serve as good records of typhoon events, but the influence of human activities should be considered when studying the relationship between typhoon activity and climate change, especially during the past several decades.

Aeolian-fluvial interactions in the Yellow River Basin, China: Insights from sedimentary characteristics and provenance of the sedimentary sequences

Understanding environmental changes requires the characterization of potential interactions between aeolian and fluvial systems. This study aimed to identify the sedimentary characteristics, provenance, and transport of sediments of the Yellow River Basin, as well as the processes and geomorphological effects of aeolian-fluvial interactions using end-member modelling analysis (EMMA), multidimensional scaling (MDS), and principal component analysis (PCA). Samples (n = 107) collected from sedimentary sequences in the source area, upper, middle, and lower reaches were analyzed for grain size and major element contents. The results showed that sediments in the source area of the Yellow River mainly originated from the Tibetan Plateau, whereas the input of materials from the Chinese Loess Plateau (CLP) gradually increased from the upper to lower reaches. The sediment transport was jointly controlled by simultaneous or alternating aeolian and fluvial processes. Asynchronism in aeolian activity and rainfall and the non-uniformity of runoff and sediment sources resulted in a concentration of aeolian-fluvial interactions in the river reaches traversing through the deserts and CLP. Fluvial sediments in the upper reaches consisted of wash loads deposited in slow-moving water, whereas rapid replenishment of sediment from the CLP in the middle reaches increased sediment transport capacity, thereby enhancing the uniformity of sedimentary characteristics from the upper to lower reaches. Moreover, numerous gullies in the CLP resulted in increased intensities of aeolian-fluvial interactions, thereby accelerating severe sedimentation in the lower reaches. This study can act as a reference for paleoclimatic reconstruction and for soil and water conservation in large-scale watersheds across a range of climatic zones.