Sedimentary Provenance Analysis Research Articles

Episodic magmatism of the Gongga batholith (eastern Tibet) revealed by detrital zircon U-Pb geochronology: Insights into phased Xianshuihe fault activity and plateau growth

Understanding the onset and episodes of magmatism is essential for comprehending tectonic history, crustal extension, and geodynamic processes. However, due to physical constraints, many places have remained unexplored, which makes it difficult to understand their geological evolution. Following thorough sedimentary provenance analysis, the chronology and periods of magmatism within a drainage area can be revealed through the detrital zircon U-Pb dating method. Here, we present detrital zircon U-Pb ages (n = 1429) obtained from sediments in modern rivers of the Gongga batholith in the eastern Tibetan Plateau. Our results reveal five major magmatic episodes since the early Mesozoic. Three episodes of magmatism occurred in the early to middle Mesozoic (ca. 230–200 Ma, ca. 200–180 Ma, and ca. 180–160 Ma), followed by a protracted period of magmatic quiescence. During the Cenozoic, there were two main periods of magmatism at ca. 50–25 Ma and ca. 25–5 Ma. This is consistent with bedrock geochronological data acquired previously. We propose that the Mesozoic magmatism was most likely caused by post-collisional extension after the closure of the Paleo-Tethys Ocean. The two Cenozoic magmatic episodes are coeval with the progressive intensification of Xianshuihe fault activity. Consequently, these episodes highlight two significant phases of plateau growth in the eastern Tibetan Plateau: the northward push of the Indian plate and “lateral extrusion,” which is consistent with the ongoing subduction of the Indian plate beneath the Eurasian plate.

From Outcrop to Spectrum—An Automated Approach to Modal Mineralogy of Silt‐Sized Sediment Applied to Central European Loess

AbstractProvenance information from recent and ancient sedimentary archives is obscured by several factors and for disentangling these intermingled signals, analysis by multiple methods is paramount. In sedimentary provenance analysis (SPA), single‐grain methods determining mineralogy, chemical composition, or radiometric ages are of key importance but are mostly applied to sand‐sized sediments or sedimentary rocks. Finer grained sediments or sedimentary rocks are usually analyzed by whole‐rock geochemical means and seldom by single‐grain methods. Considering the abundance of fine‐grained sedimentary archives, a strong need for single‐grain, multi‐method analyses of silt‐sized sediments is obvious. Thus, we propose a workflow that is optimized for sample throughput and correlative analysis of fine‐grained sediments based on machine learning methods. The feasibility of the workflow is demonstrated by differentiating three Central European loess‐paleosol‐sequences. The increased sample throughput enables access to sedimentary archives at high spatial and/or temporal resolution, which will open up new research pathways in SPA of silt‐sized sediments.

A database of detrital zircon U–Pb ages and Lu–Hf isotope of sediments in the South China Sea

AbstractSource‐to‐sink analysis examines the effects of source areas and basin (sink) dynamics on the generation, transport, composition, distribution and deposition of sediment in modern and ancient sedimentary systems. Detrital zircon, as one of the most stable detrital minerals, its U–Pb geochronology and geochemistry is pivotal for sedimentary provenance analysis and reconstructing palaeogeography. The South China Sea (SCS), as the largest marginal sea in the Southeast Asia, is closely related to the uplift of the Tibetan Plateau and the evolution of Chinese rivers. In this study, we mainly collect published detrital zircon of Cenozoic sediments in the SCS (include Hainan and Taiwan Islands). These detrital zircon were concentrated on Cenozoic multiple episodic rift basins in the northern part of the SCS. A total of 21,760 detrital zircon U–Pb data from 293 samples and 995 detrital zircon Lu‐Hf isotope data from 22 samples were collected in this dataset, with the main study epochs being the Palaeogene and Neogene. Best ages of these grains are range from 4,691 to 10 Ma and more than half of them within age less than 500 Ma. The 176Hf/177Hf ratios of the SCS samples ranging from 0.280509 to 0.28306 and the εHf(t) values from −63.8 to 24.6. The main age group of the SCS Cenozoic sediments were at 130–95 Ma, 175–130 Ma and 265–230 Ma. The detrital zircon U–Pb age and Lu–Hf isotope data contained in this dataset is an important geological record of the sedimentary and tectonic evolution of the SCS and the evolution of rivers such as the ancient Pearl River and the ancient Red River, which can provide a basis and important clues or exploring the source of sediments in the SCS, the dynamical processes of basin evolution, the evolution of the coastal drainage system and the tectonic uplift of the Tibetan Plateau.

A zircon classification scheme for sedimentary provenance analysis using radiation damage

Detrital single‐grain zircon U–Pb geochronology is a powerful tool for provenance studies if information on the source rocks is available. This paper proposes a new source‐rock classification tool that uses the degree of annealing of radiation damage in detrital zircon; the annealing is expressed by the relationship between the width (full‐width at half‐maximum; FWHM) of the v3[SiO4] Raman band at ~1008 cm−1 and the calculated α‐dose. The host rocks of the zircons are classified into three types according to their emplacement process and/or thermal history: volcanic and rapidly cooled plutonic and high‐grade metamorphic rocks (type 1); rocks with hydrothermal zircons (type 2); slowly cooled igneous and metamorphic rocks (type 3). We construct a naive Bayes prediction model by training it with a collection of zircons of known types. The unknown zircons are assigned a probability of derivation from a specific host‐rock type. This classification scheme is best used as an accessory tool in provenance studies that apply detrital zircon U–Pb geochronology.

Impact of the Yellow River capture on the paleoenvironmental changes of Hongze Lake, China

The Yellow River (YR) capture of the Huai River had a profound effect on the landscape evolution, ecology, and social development in China, disrupting the evolution of some vital shallow floodplain lakes. Because of the absence of lacustrine sediment provenance analysis, previous studies were inadequate in distinguishing the influence of YR capture on paleoenvironmental changes in these lakes, especially on landscape evolution, redox conditions, lake level changes, and organic productivity. The current study aims to use X-ray fluorescence-core scanning (XRF-CS) and multivariate statistics on a 9.8 m sediment core from Hongze Lake (HZL), China, to analyze the impact of the YR capture on the lake's paleoenvironmental changes and the sediment provenance simultaneously. High-resolution images, magnetic susceptibility, and XRF-based multi-element data were obtained using a GEOTEK Multi-Sensor Core Logger. The calcium (Ca) content indicates the presence of YR sediment in HZL, given the high Ca content in YR sediment and the identification of mainly exogenous sources of Ca in HZL. The high values of Ca indicate that 48.7% of the sediment in the center of HZL is related to the YR's incursion. Periods of higher Ca content coincide with periods of higher oxygenation levels of the lake (as indicated by the ratio of manganese to titanium) and lower organic content in the lake sediment (as indicated by the ratio of incoherent to coherent scatter). These analyses reveal that the YR's capture of HZL significantly increased the lake's oxygen level. Furthermore, the decrease in the organic content of sediment tends to be the result of the accelerated deposition caused by the YR. The decrease in Ca content coincides with an increase in lake levels (as indicated by magnetic susceptibility). Thus, it can be inferred that the embankment on the eastern side of HZL, built to increase lake storage, has reduced the incursion frequency of the YR.

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.

Basin formation, magmatism, and exhumation document southward migrating flat-slab subduction in the central Andes

The Central Andean Plateau is the largest plateau formed in a non-collisional setting and is taller, wider, has thicker crust, and has greater retroarc shortening than any other region of the modern Andes. It also hosts some of the thickest Cenozoic strata in the Andes, which were deposited synchronously with punctuated widening and narrowing of the magmatic arc. Multiple hypotheses have been advanced to explain these unique characteristics, yet the detailed, plateau-scale Cenozoic basin history needed to test these hypotheses remains unavailable and therefore has not been integrated into the established records of deformation and magmatism. Here we synthesize new detrital zircon maximum depositional ages (MDAs) and sediment provenance analysis of non-marine strata from ∼15°–16.5°S with existing records of sediment accumulation, deformation, and magmatism from ∼14°–24.5°S to develop a model of the Eocene–early Miocene evolution of the Altiplano-Puna plateau region. Stratigraphic correlations based on the new MDAs show a Paleocene–Eocene unconformity/condensed section followed by resumption of rapid sediment accumulation. Rapid sediment accumulation resumed at 46–43 Ma at 15–16°S, at 36 Ma at 18°S, and as young 19 Ma at ∼23°S. Provenance data presented herein indicate that Eastern Cordilleran detritus appeared in Altiplano strata at progressively younger ages to the south. The southward progression of this basin reorganization proceeded in lockstep with initiation of exhumation in the Eastern Cordillera, and also a lull in the magmatic arc followed by widespread volcanic flare-up. We present a model in which the observed stratigraphic hiatus, along with the magmatic lull and flare-up, orogenic widening, and high-magnitude shortening, are upper plate responses to shallowing and resteepening of an late Paleocene–early Miocene flat slab beneath the Altiplano-Puna plateau. In the proposed model initial slab flattening was driven by late Paleocene–early Eocene subduction of buoyant oceanic crust: potentially a Manihiki Plateau Conjugate. Subsequently, southward shallowing and resteepening of a late Eocene–early Miocene flat slab beneath the Altiplano-Puna Plateau was driven by subduction of an asperity on the Nazca Plate which we tentatively identify with the Juan Fernandez Ridge. The geographic coincidence of all of these features suggests that the flat slab hydrated and weakened the upper plate lithosphere, thereby facilitating later development of the suite of unique features which characterize the Central Andean Plateau.

Quartz OSL sensitivity from dating data for provenance analysis of pleistocene and holocene fluvial sediments from lowland Amazonia

Quartz OSL sensitivity from dating data for provenance analysis of pleistocene and holocene fluvial sediments from lowland Amazonia

Contribution Of The Different Sources To The Formation Of Alluvial Sediments In The Selenga River Delta. (Eastern Siberia, Russia)

Unraveling sources of sediment supply, their temporal and spatial variability is of key importance to determine origin of deposits and to explore the formation mechanism of Selenga Delta landscape units. From an environmental point of view this solution would help to identify the particle-bound pollution sources. We used geochemical fingerprinting (the FingerPro R package), which is a modern quantitative implementation of the method of sedimentary provenance analysis. The main aim was to recognize the main patterns of sediment and associated particle-bound pollutants transport and deposition within the delta. At the old floodplain from 55% to 90% of sediments were delivered from the eroded floodplain and terrace banks upstream and only about 10-15% originates from the remote basin sources. Sedimentary environment in the Khlystov Zaton reveals a greater variety than on the floodplains. 40% of sediments from the upper 5 cm-layer originated from the flood, taking place in 2013, and 30% were the product of floodplain and terraces banks erosion. Nevertheless, analysis of the fine-grained component of suspended sediment sets the material from eroded floodplain banks as the dominant source of accumulation within the delta. This means that the self-absorption is the leading process in the Selenga delta at the moment. Heavy metals and metalloids accumulates in the lower reaches of the Selenga on the floodplain surface, deltaic lakes and oxbows during high floods. Runoff decrease during floods can lead to the release of pollutants into the Lake Baikal.

Multiproxy sediment provenance analysis of two megafans in the Owambo Basin, northern Namibia

The sediments in two stacked megafans in the Owambo Basin of northern Namibia and southern Angola were made accessible by a c. 400 m long, continuously cored borehole. Previous studies have indicated that the lower buried Paleocene–Eocene Olukonda Megafan was deposited by a palaeo-Kunene River transporting material from the NW (i.e. from the Kunene Intrusive Complex and the adjacent Angola Shield). The morphology of the overlying Eocene–Pliocene Cubango Megafan suggests the input of sediments from the north via the Cubango River. Mineralogical and geochemical data from the upper fan indicate felsic metamorphic and granitoid sources. Previous studies, however, did not provide a unique provenance identifier. Combining detrital zircon U–Pb data from both megafans with previously published and newly obtained mineralogical and geochemical data confirms two distinct provenances. The Olukonda Megafan can now be uniquely attributed by means of its detrital zircon ages to the Kunene Intrusive Complex and the surrounding Epupa Metamorphic Complex. In good agreement with the geochronologically more varied geology of the source region in the north, the Cubango Megafan detrital zircon record shows a wide distribution of Paleoproterozoic to Archean ages, but also a younger age range, probably related to a later Damaran/Pan-African source, which is absent in the Olukonda detrital zircon record. Supplementary material: Data obtained for this study, e.g. geochemical data, heavy mineral composition, heavy mineral morphology, zircon morphology, U-Th-Pb isotopes and ages on zircon, instrument settings, and U-Th-Pb isotope data of analysed reference zircon are available at https://doi.org/10.6084/m9.figshare.c.6280517

Detrital Mica Composition Quantitatively Indicates the Sediment Provenance along the Subei Coast to the Yangtze Estuary

The influence of large rivers on the Subei littoral plain area requires more research than the results that have been available up to now. Thus, specific diagnostic indices of detrital mica are successfully applied for the first time to identify the detritus of the Yangtze River and the ancient Yellow River and to analyze their influence on the coast in the Subei littoral plain area. Based on field investigation and sample collection, detrital mica minerals within the 0.063–0.125 mm grain size fraction were selected and identified. Their content/ratio differentiations and possible origins were analyzed. Moreover, specific diagnostic indices were evaluated for detritus identification considering these two large rivers in addition to their provenance influences on the Subei littoral plain area. The results indicate that the detrital mica contents in the Yangtze River Estuary differed from those in the ancient Yellow River Estuary. The mass percentage in the former (average value of 32.2%) was much higher than that in the latter (average value of 13.1%). The former contained abundant weathered mica, with a particle percentage of approximately 50.6%, while the latter contained abundant biotite (with a particle percentage of approximately 40.9%). Differences, including but not limited to those above, could be attributed to basic geological, climatic and hydrodynamic conditions. In particular, the mica indices were clearly distinguished between these two river estuaries. These indices constitute specific diagnostic indices for differentiating river detritus and quantitative contribution analysis of detritus provenance in the Subei littoral plain area. Finally, the changes and quantitative contributions of four diagnostic indices demonstrated that in the Subei littoral plain area, northward from the Yangtze River Estuary to sample site SBY11 located in Yangkou town, Rudong County, detrital micas were mainly affected by the Yangtze River, and southward from the ancient Yellow River Estuary to sample site SBY12 located in Bengcha town, Rudong County, detrital micas were largely affected by the ancient Yellow River. The main mixing area should be located between these two towns. This study provides both a good example and an efficient approach to the application of detrital mica in detritus identification, mixed zone determination, sediment provenance analysis and transport tracing.

Beyond Zircon: Incorporating Detrital Feldspar Pb Isotope Analysis into the Multiproxy Toolbox for Sedimentary Provenance Analysis—an Example from a Long-Lived Eastern Laurentian Clastic System

Previous article No AccessBeyond Zircon: Incorporating Detrital Feldspar Pb Isotope Analysis into the Multi-Proxy Toolbox for Sedimentary Provenance Analysis - an Example from a Long-Lived Eastern Laurentian Clastic SystemDavid P. Moecher, Eszter Badenszki, J. Stephen Daly, and David ChewDavid P. Moecher Search for more articles by this author , Eszter Badenszki Search for more articles by this author , J. Stephen Daly Search for more articles by this author , and David Chew Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Just Accepted Article DOIhttps://doi.org/10.1086/724287 Views: 33Total views on this site HistoryAccepted January 06, 2023 © 2023 The University of Chicago. All Rights reserved.PDF download Crossref reports no articles citing this article.

Quantitative provenance analysis through deep learning of rare earth element geochemistry: A case from the Liuling Group of the East Qinling Orogen, Central China

With the ever-growing availability of massive geo-data, deep learning has been widely applied to geoscientific questions such as sedimentary provenance analysis. However, randomly selected initial weights (and also biases) and possible loss of population diversity in traditional neural network learning remain problematic. To address this issue, in this study, we proposed a new deep neural network model by incorporating genetic algorithm (GA) and simulated annealing algorithm into the BP neural network, i.e., the GA-SA-BP model. We then applied this new model to rare earth element (REE) geochemical data of the Liuling Group of the East Qinling Orogen to investigate its provenance. Our results showed that among other deep learning algorithms, the new model presents the best performance with good measuring metrics (e.g., over 85% of accuracy, over 0.82 of F1-macro-average, F1-micro-average, and Kappa coefficient, and smallest (<0.15) Hamming distance). Here, we interpreted in accordance with the classification results that the southern margin of the North China Craton and the South Qinling Orogen are likely two major sources of the Liuling Group, suggesting a bidirectional deposition route of sediments from the north and south. Therefore, we proposed a foreland basin environment as the likely tectonic setting for the Liuling Group, which is consistent with current geological understanding. Our observations suggested that the GA-SA-BP model (or improved deep learning models) coupled with REE geochemistry is capable of provenance analysis.

Indian plate paleogeography, subduction and horizontal underthrusting below Tibet: paradoxes, controversies and opportunities.

The India–Asia collision zone is the archetype to calibrate geological responses to continent–continent collision, but hosts a paradox: there is no orogen-wide geological record of oceanic subduction after initial collision around 60–55 Ma, yet thousands of kilometers of post-collisional subduction occurred before the arrival of unsubductable continental lithosphere that currently horizontally underlies Tibet. Kinematically restoring incipient horizontal underthrusting accurately predicts geologically estimated diachronous slab break-off, unlocking the Miocene of Himalaya–Tibet as a natural laboratory for unsubductable lithosphere convergence. Additionally, three endmember paleogeographic scenarios exist with different predictions for the nature of post-collisional subducted lithosphere but each is defended and challenged based on similar data types. This paper attempts at breaking through this impasse by identifying how the three paleogeographic scenarios each challenge paradigms in geodynamics, orogenesis, magmatism or paleogeographic reconstruction and identify opportunities for methodological advances in paleomagnetism, sediment provenance analysis, and seismology to conclusively constrain Greater Indian paleogeography.

AnalyZr: A Python application for zircon grain image segmentation and shape analysis

Zircon grain shape is traditionally interpreted as a product of the physico-chemical conditions during crystal growth and may be modified during grain transport processes. The analysis of magmatic zircon grain shape has been proposed to inform on crystallization conditions, whereas detrital zircon grain shape has been proposed to complement traditional sediment provenance analysis. Shape parameters can be automatically measured from digital images of zircon mounts; however, this requires extraction of individual grain boundaries for measurement. Existing image segmentation software may require the use of proprietary languages, or knowledge of scripting to develop automated image segmentation routines, and is typically not tailored towards the geosciences. Furthermore, the separation of touching zircon grains in images remains a challenge for existing algorithms. To facilitate zircon grain shape analysis, we present AnalyZr, an open-source graphical Python application designed to segment reflected and transmitted light images of zircons mounted in resin. A new segmentation algorithm is implemented to improve the separation of touching zircon grains. Shape parameters are automatically measured from the segmented images and may be output to a .csv or .mdb file. Two case studies demonstrate the use of the application in resolving geologically relevant information in zircon grains sourced from: i) compositionally and age-distinct granite, diorite, and gabbro samples from across Western Australia, and ii) age-distinct detrital zircons from the Canning Basin, Western Australia.

Provenance of upper Permian–Triassic sediments in the south of North China: Implications for the Qinling orogeny and basin evolution

The Triassic Qinling Orogenic Belt was formed during the closure of the Paleo-Tethys Ocean, and its evolution can be traced by provenance analysis of sediments in the south of North China. We present detrital zircon ages, sandstone petrographic observations, paleocurrent data, and paleogeographic reconstructions that allow the evolution of this basin–mountain system to be reconstructed. Detrital zircons from upper Permian sedimentary rocks yield two major age peaks at 1876 and 259 Ma, and two minor age peaks at 2526 and 363 Ma. These zircons were likely sourced from recycled sediments in the Southern North China Block. Detrital zircons from Lower Triassic sedimentary rocks have multiple age peaks at ca. 2500, 1850, 950, 745, 450–430, and 310–250 Ma, reflecting a mixed provenance from the Qinling Orogenic Belt and Southern North China Block. Zircons from a Middle Triassic sandstone have a concentrated age peak at ca. 250 Ma and two subordinate age peaks at ca. 1800 and 2500 Ma. Hafnium isotope data for the late Paleozoic detrital zircons are characterized by negative εHf(t) values of −23.11 to −0.11, and only two grains have positive εHf(t) values of +1.45 and +2.10. We infer that these zircons were derived from recycled sediments in the Southern North China Block. The provenance data show that the North Qinling Belt and Southern North China Block had been uplifted prior to the Early Triassic. The uplift was mainly related to the continental collision between the South China and North China blocks. These and previously published data indicate the Southern North China Block experienced exhumation during the Middle−Late Triassic, firstly involving Permian cover rocks, followed by Cambrian and Neoproterozoic strata, and finally Mesoproterozoic basement rocks. The fold-and-thrust belt in the Southern North China Block probably formed during the Middle Triassic. Uplift and denudation of the Qinling Orogenic Belt controlled Triassic basin evolution in the south of North China.

Provenance analysis of sediments in the south-east Aegean during the Upper Quaternary: a composite approach based on bulk and clay mineralogy and geochemistry

AbstractSediments from the ST5 deep-sea bottom core collected from the south-east Aegean Sea between Symi and Tilos islands, Greece, were examined by quantitative mineralogical analysis and geochemical analysis to infer provenance and palaeoenvironmental control over sediment deposition. The mineralogical composition comprises carbonates (mainly calcite and Mg-calcite), quartz, feldspars, serpentine, amphibole and clay minerals. Chlorite is the most abundant clay mineral, whereas smectite and illite are less abundant than in the sediments in the south-west Aegean and the Cretan Sea. Semi-quantitative analysis of clay minerals from oriented clay fractions overestimates significantly the smectite content and underestimates the abundances of illite, chlorite and kaolinite. The studied sediments are enriched in MgO, Ni and Cr, which decrease in abundance with decreasing depth, following the distribution of serpentine. By contrast, the abundances of SiO2, Al2O3, Fe2O3, Na2O and K2O increase upcore. The regional S1 sapropel horizon is enriched in V and Co and has considerably greater Ba/Al ratios than the remaining sequence. The mineralogical and geochemical relationships indicate a strong ultrabasic influence, probably from the Marmaris ophiolite in the Lycian nappes. The clay mineral distribution suggests that the smectite was mainly of volcanogenic origin, the illite was supplied by the nearby landmasses of west Anatolia and the islands of Rhodes, Tilos and Symi and the contribution from the south-east Mediterranean was limited or totally lacking. The combined use of the mineralogical and geochemical analysis of bulk sediments rather than the clay fractions is not only extremely useful in tracing sediment provenance in relatively closed basins, but it also enables a more realistic assessment of the importance of water circulation patterns on sedimentation processes in such environments.

Cosmogenic and Geological Evidence for the Occurrence of a Ma-Long Feedback between Uplift and Denudation, Chur Region, Swiss Alps

We used concentrations of in situ cosmogenic 10Be from riverine sediment to quantify the basin-averaged denudation rates and sediment fluxes in the Plessur Basin, Eastern Swiss Alps, which is a tributary stream to the Alpine Rhine, one of the largest streams in Europe. We complement the cosmogenic dataset with the results of morphometric analyses, geomorphic mapping, and sediment fingerprinting techniques. The results reveal that the Plessur Basin is still adjusting to the landscape perturbation caused by the glacial carving during the Last Glacial Maximum c. 20,000 years ago. This adjustment has been most efficient in the downstream part where the bedrock comprises high erodibility North Penninic flysch and Bündnerschist, whereas glacial landforms are still prominently preserved in the upstream region, comprising low erodibility South Penninic and Austroalpine bedrock. This geomorphic observation is supported by the 10Be based denudation rate and sediment provenance analysis, which indicate a much faster sediment production in the flysch and schist lithologies. Interestingly, the reach of fast denudation has experienced the highest exhumation and rock uplift rates. This suggests that lithologic and glacial conditioning have substantially contributed to the local uplift and denudation as some of the driving forces of a positive feedback system.

Closure of the Paleo‐Asian Ocean in the Middle‐Late Triassic (Ladinian‐Carnian): Evidence From Provenance Analysis of Retroarc Sediments

AbstractA major current debate in Asian tectonics concerns the time of closure of the Paleo‐Asian Ocean (PAO) and the collision between the Central Asian arcs and the Tarim and North China cratons (NCC). This has led to much uncertainty about the reconstruction of proto‐Asia and tectonic configuration of northeast Pangea. Here we report Triassic provenance change in the foreland of the Alxa Block by field‐based zircon U‐Pb and Hf isotopic analysis. Nonmarine sediments, unconformable on or in fault contact, with the Alxa basement yield Precambrian and Paleozoic–Triassic detrital zircon ages with maximum depositional ages of Middle‐Late Triassic (∼244–224 Ma). Hf isotopic data indicate that Middle Triassic sandstones were sourced from the NCC basement and a continental arc, whereas Late Triassic sediments received an additional input from a juvenile arc. This provenance change in the foreland sedimentation indicates that the final closure of the PAO was in the Middle‐Late Triassic.

Seesaw longitudinal–transverse drainage patterns driven by Middle and Late Pleistocene climate cycles in the foreland basin of the south-eastern European Alps

The multi-proxy sediment provenance analysis of two sedimentary successions (GER1 core, 130 m long, and CB core, 103 m long) provides new data for detecting the temporal and spatial variations in fluvial drainage patterns and landscape evolution of the Venetian Plain (NE Italy) in relation to Middle–Late Pleistocene climate fluctuations. Detailed petrographic analyses, compared to present-day river signatures, highlight compositional variations of the sediments, providing crucial information for detecting the depositional histories of the two sites, which lie about 15 km apart, and considering a source-to-sink multi-source context. The successions span from a cold phase older than MIS 9/11 to MIS 1, and are chronostratigraphically well correlated from the MIS 7.3 marine transgression. Despite belonging to the same alluvial system since the Last Glacial Maximum, the GER1 and CB cores show different depositional histories during previous Marine Isotopic Stages, starting at least from MIS 8 (i.e., ca 300–250 ka). A glacial interval older than MIS 9/11, is encountered only within records of the GER1 core. Due to its composition and the particularly coarse grain size, it represents a key element for detecting the depositional dynamics of megafans during past climate oscillations. Conversely, the presence of sediments not fully ascribable to any of the present-day catchment suggests the existence of a trunk paleo-river, longitudinal to the foreland axis, flowing from west to east along the Po Plain and occasionally draining the Venetian Plain. A causal relationship between prograding mechanisms of transverse alluvial megafans and Pleistocene climate variations is detected, taking into account responses of local alluvial systems to glaciers' development, sediment yield from the orogenic hinterland, and sea-level lowstands and highstands. A focus on glacial termination phases allows identification of two additional incised valleys, established at the end of the pre-MIS 9/11 glaciation and of MIS 6.