Quantitative Provenance Analysis Research Articles

A Quantitative Provenance Analysis (QPA) Approach to Quantify Controls on Sediment Generation and Sediment Flux in the Upper Reaches of the Magdalena River (Colombia): 1. Natural and Anthropic Controls on the Sand Fraction

AbstractThis study investigates the upper Magdalena river basin (Colombia), which is characterized by tectonic activity, tropical climate, heterogeneous lithological assemblages, and anthropic influence. It aims to comprehend factors controlling sediment generation, flux, and composition by incorporating petrographic data from 27 recent fluvial samples along with geochemistry, geomorphological parameters, historical precipitation, land cover, landsliding and suspended sediment load data. The analysis shows mismatches between sand composition and drainage lithology distribution. A new set of endmember mixing models is presented, quantifying the impacts of erodibility, sand generation potential (related to lithology), and sediment connectivity between hillslopes and river outlets (related to geomorphology). Results show enhanced sediment generation from sedimentary rocks (up to 40%) due to high erodibility, and decreased sediment flux from low‐ to medium‐grade metamorphic rocks (up to 60%) due to controlling morphometric parameters. Overrepresentation of plutonic and high‐grade metamorphic rocks and underrepresentation of volcanic rocks (up to 100%) are controlled by mineralogical and textural parameters. Enhanced landsliding activity in areas with volcanic activity occasionally overshadows basin‐wide compositional trends driven by morphological and lithological characteristics, as it controls rare overrepresentation of volcanic and low‐grade metamorphic detritus in the sand fraction. Sediment retention by hydroelectric dams significantly decreases suspended sediment flux by 30%, while deforestation plays a minor role in sediment flux. This study underscores the importance of coupling sediment generation, geomorphology and the distribution of stochastic events related to seismic activity in any sediment production‐focused study and for developing numerical models in Quantitative Provenance Analysis (QPA).

A Quantitative Provenance Analysis (QPA) Approach to Quantify Controls on Sediment Generation and Sediment Flux in the Upper Reaches of the Magdalena River (Colombia): 2. Lithological Control on Contribution to Silt‐ to Clay‐Sized Fractions

AbstractThe composition of 27 fluvial silt and clay sediments was used in this study to identify and quantify the processes in the upper valley of the Magdalena river in South Colombia. The combination of seismic activity, intense precipitation, and landsliding resulted in limited chemical weathering and a very efficient transfer of weathered products to the transfer zone of both tributary rivers and the main trunk. Inputs from plutonic, high‐grade metamorphic, volcanic, and low‐ to medium‐grade metamorphic lithologies vary in coarse silt‐sized versus fine silt‐ and clay‐sized sediments, reflecting inherited textural parameters and mineralogy. Plutonic and high‐grade metamorphic rocks mostly produce sand‐sized sediments, up to two times more than coase silt and up to 10 times more than fine silt to clay. The prevalence of siltstone in the area enhances the contribution of sedimentary rocks to fine silt and clay (up to 50% higher than to sand). Volcanic rocks mainly produce coarse silt (up to 2.5 times more than sand). Low‐grade metamorphic detritus is enriched in silt and clay (up to 5–7 times). These findings highlight the critical role of lithology in regulating sediment generation. The study's approach can establish or modify factors modeling lithological control on suspended sediment flux, such as in the BQART equation.

Late Permian‐Early Triassic intracontinental tectonic inversion in the Junggar Basin, NW China: New insights from detrital zircon geochronology and seismic reflection data

AbstractThe Junggar Basin is located on the southwestern margin of the Central Asian Orogenic Belt (CAOB). Whether the Late Permian‐Early Triassic tectonic inversion there recorded the final closure of the North Tianshan Ocean or post‐accretionary intracontinental deformation remains controversial. Linking the structural style and provenance analysis of the western and northern margins of the Junggar Basin can provide a better understanding of this tectonic event and its geodynamic mechanisms. Seismic reflection profiles show that Early Permian syn‐rift half‐grabens were followed by the Middle Permian thermal sag, which is characterized by regional onlap and the migration of the depocentre to the centre of the basin. Together with the published isopach and palaeogeography maps in the western margin of the Junggar Basin, the seismic profiles demonstrate that the reactivation of the Ke‐Bai and Wu‐Xia dextral transpressive fault zones between the West Junggar terrane and the Mahu sag controlled the tilting and deformation of pre‐Permian strata and the distribution of Late Permian‐Early Triassic fan deltas. The reported igneous and sedimentological evidence indicates that the southern margin of the Junggar Basin was a rift basin controlled by transtensional strike‐slip faults in the Early Permian, and also was followed by a Middle Permian thermal sag. Quantitative provenance analysis using detrital zircon geochronology and the DZmix program shows that the West Junggar terrane and Tianshan orogenic belts experienced varied uplift, indicative of a transition from the Middle Permian thermal sag peneplanation to the Late Permian‐Early Triassic tectonic inversion involving reactivation of Early Permian normal faults. This intracontinental deformation event in the Junggar Basin was taken up by block counterclockwise rotation during the final amalgamation of the Pangea, which may be the long‐range effect of the final closure of Paleo‐Asia Ocean in the eastern part of the CAOB.

Reconstructing dust provenance from quartz optically stimulated luminescence (OSL) and electron spin resonance (ESR) signals: Preliminary results on loess from around the world

Quantitative provenance analysis studies are instrumental in understanding the tectonic and climatic processes that shape the earth's landscape. Although the most abundant mineral in the sedimentary system is quartz, almost all studies in provenance analysis investigate accessory minerals. Quartz crystals contain a vast number of point defects, intrinsic or due to impurities. For a signal to be an accurate indicator of provenance one needs to show that it is either dose independent or reaches a quantifiable steady state characteristic of the source rock. For signals used by trapped charge dating methods (optically stimulated luminescence (OSL) and electron spin resonance (ESR)), the latter option is the feasible one. By using quartz samples collected from the Chinese Loess Plateau (Luochuan loess-paleosol section), we show that the laboratory and natural dose response curves of E'1 and peroxy electron spin resonance signals of quartz (as defined later) overlap and reach a steady state for doses over about 1000 Gy. For E′1 signals we attribute this steady state to reaching an equilibrium state between diamagnetic oxygen vacancies (the oxygen deficiency centre (ODC), Si=Si) and paramagnetic oxygen vacancies (E′1). For sedimentary quartz irradiated naturally or artificially in this dose range we show a strong linear relationship with zero intercept between E′1 and peroxy signals for samples worldwide, supporting the hypothesis that these defects are Frenkel pairs. Further, we show significant correlations between the optically stimulated (OSL) sensitivity and the above two mentioned ESR signals. The very strong correlations (Pearson's r >0.9) between E′1, peroxy and OSL sensitivity remain valid after the samples have been heated for 15 min to 350 °C for E′1 to reach its maximum value, believed to be a result of the conversion of diamagnetic oxygen vacancies to E′1, clearly suggesting a relationship between OSL sensitivity and oxygen vacancies in general. Samples collected from different loess sites around the world can be distinguished based on both these OSL and ESR properties. An empirical increase in OSL sensitivity as well as oxygen related defect concentrations is observed in areas where the source material has components with older detrital zircon U–Pb ages, inferring a positive correlation between OSL sensitivity, as well as the signal intensity for E1’ and peroxy defects and the age of the source rocks.

Quantitative sediment provenance of the northwestern East China Sea: Evidence for tidal current-driven offshore transport and paleogeographic implications

In the northwestern East China Sea, sediment transport and mixing in both along-shelf and cross-shelf dimensions are distinguished using quantitative provenance analysis, with an aim to demonstrate a net transport pattern and thereby infer potential transport and dispersal processes over geological timescales. The dataset comprises 328 bottom sediment samples, which were characterized by detrital-mineral and grain-size analyses. Results show that only in the south of the study area the primary source of sediment is the Yangtze River. In the north, instead, three end-member sources, i.e., the Yangtze, Yellow and Huaihe Rivers, are quantified separately using an end-member mixing analysis. Along-coast mixing between the updrift Huaihe–Old Yellow and downdrift Yangtze River systems is minimized. In exchange, offshore sediment transport is enhanced instead. This conversion from along-shelf to cross-shelf transport is attributed to the presence of a large-scale radial tidal current system off the Jiangsu coast as well as the headland effect produced by the protruding north flank of the subaerial Yangtze delta and the Yangtze riverine plume. This radial tidal current system acts both as a trap for Huaihe–Old Yellow River sediments transported by the southward-direct longshore current, and as a transfer center for sediment dispersal offshore. Radiating transport pathways virtually indicate an extensive mixing of Yangtze sediments and Old/modern Yellow and Huaihe sediments in the southwestern Yellow and northernmost East China Seas. As an independent dynamic system, it acts as a critical link between the Yangtze and modern/Huaihe–Old Yellow River dispersal systems. Thus, we conclude that these three large-scale dispersal systems and their complex interplay dominate sediment transport, redistribution and mixing on the eastern China continental shelf.

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.

Miocene Provenance Changes in Taiwan Caused by Southward Input of Sediments From East China Sea Basin

The Cenozoic sediments in marginal basins of East Asia ultimately reflected coupling between the tectonics, landscape evolution, and drainage reorganization. Recently, the provenance of Miocene sediments in the East China Sea Basin (ECSB) and Taiwan has been in hot debate, and several models were proposed to interpret the provenance changes. Most of them are related to river reorganization in East Asia and highly relied on detrital zircon U-Pb dating. In this study, a large number of detrital zircon U-Pb ages of Miocene sediments from the ECSB, Taiwan region, and the potential source areas have been compiled for quantitative provenance analysis. The results suggested that all the early–middle Miocene sediments in Taiwan and the ECSB were closely linked to North China and the Korean Peninsula. Over 80% sediments in Taiwan were delivered from the ECSB whose sediments were predominantly contributed by North China and the Korean Peninsula (70%). However, for the late Miocene to Quaternary sediments in the ECSB, the contribution of the Yangtze River system was 72%, which indicates distinct reorganization of river networks and initial formation of the Yangtze River in the late Miocene. The quantitative provenance analysis together with southward environmental changes from dominantly fluvial sediments in the northern and middle ECSB to shallow marine sediments in Taiwan region suggested that the early–middle Miocene sediments of Taiwan were mainly sourced from the North China and the Korean Peninsula by passing the ECSB. Thus, these sediments in Taiwan region would experience the river–delta–shallow marine route from the ECSB to Taiwan region.

Reconstructing environmental signals across the Permian-Triassic boundary in the SE Germanic Basin: A Quantitative Provenance Analysis (QPA) approach

Global tectonic and climatic models for the Permian-Triassic boundary (PTB) are highly debated. One of the most disputed topics is the temperature increase associated with CO 2 emissions generated by the Siberian Trap volcanism and its potential influence on chemical weathering and associated variations in sediment fluxes. By integrating crustal architecture, plate modelling, structural kinematics, and two climatic models, we reconstruct the drainage evolution of Variscan tectonostratigraphic units from the SE portion of the Germanic Basin, from which we also extract the parameters necessary to calculate sediment flux across a time-scale of 28 Ma (Guadalupian-Lower Triassic). We reconstruct the sedimentary response to climatic and tectonic perturbations using Quantitative Provenance Analysis (QPA) and integrate compositional data into a sedimentological framework, paleodrainage and paleoclimatic models. Raman heavy mineral analysis, as well as geochronology and geochemistry of detrital apatite, zircon, and rutile, document variation in drainage lithologies and sediment flux which are controlled by regional extensional tectonics and increasingly humid conditions at the PTB. The sedimentary successions of the SE Germanic Basin record climatic perturbations on a 10 4 years timescale, while the effects of tectonics are visible on a 10 6 years timescale. The interplay of climate, tectonics and lithology, and their effects on sediment production and drainage evolution resulted in changes in sediment flux from 2.3 Mt./yr during the Guadalupian (Capitanian), to 3.80 Mt./yr in the Lopingian (Changhsingian) to 7.44 Mt./yr at the end of the Lower Triassic (Olenekian). The multifaceted workflow provided in this study represents the first step towards more precise reconstructions of sediment routing systems in deep-time and provides the first ground-truthed quantification of sediment flux across the Permian-Triassic Boundary. • Drainage modifications are efficiently identified via Quantitative Provenance Analysis. • Constraining Environmental Signals in deep-time requires paleoclimatic/tectonic models. • Paleodrainage analysis provides the parameters to calculate sediment flux. • Sediment flux increases in the Lower Triassic in response to climate change.

From a proximal-deposition-dominated basin sink to a significant sediment source to the Chinese Loess Plateau: Insight from the quantitative provenance analysis on the Cenozoic sediments in the Qaidam basin, northern Tibetan Plateau

A better understanding of the Cenozoic source to sink relationship between the Qaidam Basin and the surrounding regions allows us to reveal the topographic evolution of the northern edge of Tibetan Plateau in response to the India-Asian collision and the Asian aridification process. However, the depositional history and provenance of Paleogene strata in the southwestern/northeastern Qaidam Basin and the genetic linkage between the Qaidam Basin and Cenozoic Chinese Loess Plateau is still debated. Here we compile ca. 12,000 U-Pb zircon analyses from the Qaidam Basin, Chinese Loess Plateau and the surrounding regions, and conduct quantitative provenance analysis using a MATLAB-based Inverse Monte Carlo simulation technique. When integrated with variations in stratigraphic thickness and lithology across the basin, our analysis suggests the minor topographic relief separating the Qaidam Basin from the Hoh Xil Basin to the south, served as the major source for the sediments deposited in the SW Qaidam Basin since the Paleogene. The Qilian Shan to the north, the underlying Mesozoic strata and the local paleo-reliefs to the southwest within the basin shed materials into the NE Qaidam Basin during the Paleogene. This finding exemplifies the fact that detrital zircon geochronology alone would lead to an incorrect interpretation if independent sedimentary evidence is not considered. Based on U-Pb detrital zircon geochronology data from Pliocene-Quaternary and loess samples collected from various locations in both the Qaidam Basin and Chinese Loess Plateau, our quantitative estimate shows that approximately 30% of materials in the Chinese Loess Plateau are derived from the sediments in the Qaidam Basin, twice the previous estimate. This higher proportion of the Qaidam Basin source for the Chinese Loess Plateau highlights that using a spatially limited sample set from the Qaidam Basin would result in underrating its contribution to the sediments preserved in the Chinese Loess Plateau.

Depositional history of the Mesoproterozoic Chhattisgarh Basin, central India: insights from geochemical provenance of siliciclastic sediments

ABSTRACT The Chhattisgarh Basin is one of the most important Proterozoic basins of peninsular India. Owing to its deposition in the Mesoproterozoic, the largely undeformed and unmetamorphosed sedimentary sequence of this basin is believed to hold vital clues to our understanding of the evolution of the Indian craton subsequent to the disintegration of the supercontinent Columbia. Despite its importance, only limited studies have been carried out to decipher the depositional history of the basin and to correlate various litho-units in it. Here, we present results of quantitative provenance analysis of the sediments in the basin using trace element and Nd isotopic ratios and discuss their implications for the evolution of the basin in the context of regional tectonics. The sediment provenance analysis reveals that the spatially extensive ~2.5 Ga old granitoids of the Bastar craton were the major contributors (45% to 65%) of the total sediment budget into the basin during its initial stage of evolution. As sedimentation progressed the contribution from the Bastar granitoids was restricted to less than 30% of the total budget with the remaining supplied by younger 1.6–1.7 Ga magmatic rocks. The overall provenance of sediments appears to have remained constant throughout the evolutionary history of the basin; however, the relative contributions of various sources did change with time. The latter is highly conspicuous across the stratigraphic boundary between the Singhora and Chandarpur groups, in the lower part of the Chhattisgarh Supergroup. The geochemical data suggest that the basin developed as a result of either rift or sag into which the sea incursion occurred through the adjacent grabens during the Mesoproterozoic marine transgression.

Evolution of the Proterozoic Vindhyan Basin, Rajasthan, India: insights from geochemical provenance of siliciclastic sediments

ABSTRACTThe Vindhyan Basin of western India is a part of the largest Proterozoic sedimentary basin of the Indian subcontinent. Deposited in a largely shallow marine environment, the sedimentary sequence of the basin, known as the Vindhyan Supergroup, is believed to hold clues to our understanding of the evolution of life and climate during the Proterozoic. Inspite of multiple important paleobiological discoveries from these rocks, our knowledge about the development of the basin and responsible regional tectonics had remained rudimentary. Here, we propose a model for the evolutionary history of the Vindhyan Basin based on quantitative provenance analysis through geochemical and isotopic compositions of siliciclastic sediments. According to our model, the basin opened up in a foreland setting during an event that was contemporaneous with the amalgamation of the supercontinent Columbia. In the Lower Vindhyans, most of the sediments were derived from the basement gneisses (BGC-I & II) and a younger differentiated magmatic arc, whereas the >1.7 Ga rocks of the Aravalli and Delhi supergroups formed the source area for the Upper Vindhyans. In comparison to their counterparts in the eastern sector in the Son Valley, the Semri and Kaimur groups of the western sector had a relatively younger provenance; whereas, the Rewa and Bhander groups of both the sectors appear to have shared geochemically similar provenances. Unlike its counterpart in the eastern sector, the provenance of the sediments in the western sector had remained constant across the supposedly 400 million years break in sedimentation between the Lower and the Upper Vindhyans. However, a change in the provenance is observed during the transition from the Kaimur to Rewa group in the western sector which we infer to be a break in the deposition.

A multidisciplinary approach for the quantitative provenance analysis of siltstone: Mesozoic Mandawa Basin, southeastern Tanzania

AbstractThis paper shows how heavy minerals and single-grain varietal studies can be conducted on silt (representing c. 50% of world's sediments) sediments to obtain quantitative data as efficiently as for sand-sized sediments. The analytical workflows include heavy mineral separation using a wide grain-size window (15–355 μ) analysed through integrated optical analysis, Raman spectroscopy, QEMSCAN microscopy and U–Pb dating of detrital zircon. Upper Jurassic–Cretaceous silt-sized sediments from the Mandawa Basin of central-southern Tanzania have been selected for the scope of this research. Raman-aided heavy mineral analysis reveals garnet and apatite to be the most common minerals together with durable zircon, tourmaline and subordinate rutile. Accessory but diagnostic phases are titanite, staurolite, epidote and monazite. Etch pits on garnet and cockscomb features on staurolite document the significant effect of diagenesis on the pristine heavy mineral assemblage. Multivariate statistical analysis highlights a close association among durable minerals (zircon, tourmaline and rutile, ZTR) while garnet and apatite plot alone reflecting independence between the three groups of variables with garnet increasing in Jurassic samples. Raman data for garnet end-member analysis document different associations between Jurassic (richer in A, Bi and Bii types) and Cretaceous (dominant A, Ci and Cii types) samples. U–Pb dating of detrital zircon and their statistical integration with the above-mentioned datasets provide further insights into changes in provenance and/or drainage systems. Metamorphic rocks of the early and late Pan-African orogeny terranes of the Mozambique Belt and those of the Irumide Belt acted as main source of sediment during the Jurassic. Cretaceous sediments record a broadening of the drainage system reaching as far as the Usagran–Ubendian Belt and the Tanzanian Archean Craton.

Petrology of the Tista and Rangit river sands (Sikkim, India)

The Tista River originates from glaciers in the North Sikkim (India) and flows towards southwest draining most of the Himalaya tectonic units up to Triveni locality, where it is joined by the Rangit River (its larger tributary). Tista fluvial profile has moderate concavity (θ = 0.39) and high steepness indices (ksn = 380). In Sikkim, Tista sand is characterized by quartz, feldspars and high-rank metamorphic rock fragments from the Higher Himalayan Crystallines. After Triveni, Tista River leaves Sikkim and enters in the Indian (West Bengal) and in Bangladesh floodplain to meet the Brahmaputra River after ~ 400 km from its source. In the alluvial plain, Tista carries sand rich in quartz, feldspars and low-rank metamorphic lithic grains. The Rangit River sourced from a glacier of Mt. Kabru in the southern Kangchendzonga region (West Sikkim). Its fluvial profile display high concavity (θ = 0.75) and high steepness indices (ksn = 408). Rangit sand from the upper catchment (Chokhurang Chu and Prek Chu) includes quartz, feldspars, and biotite. Fluvial detritus from the metacarbonates of the Pandim Massif includes high-grade metamorphic lithic grains, diopsidic pyroxene and amphiboles. Sand from the Higher Himalaya Crystallines (Kalej and Ramam Khola) is characterized by high-grade gneissic rock fragments. Before the confluence with the Tista River at Triveni, Rangit sand is enriched in low rank metamorphic grains deriving from the Daling successions of the Lesser Himalaya. Quantitative provenance analysis (integrated bulk-sand petrography, statistical analysis and river-profile analysis) indicates that the Rangit River in Sikkim contributes ~ 60% to the total Tista sand flux in Bangladesh.

Physical controls on sand composition and relative durability of detrital minerals during ultra‐long distance littoral and aeolian transport (Namibia and southern Angola)

AbstractSediment in coastal Namibia to southern Angola is supplied dominantly from the Orange River with minor additional fluvial input and negligible modifications by chemical processes, which makes this a great test case for investigating physical controls on sand texture and composition. This study monitored textural, mineralogical and geochemical variability in beach and aeolian‐dune sands along a ca 1750 km stretch of the Atlantic coast of southern Africa by using an integrated set of techniques, including image analysis, laser granulometry, optical microscopy, Raman spectroscopy and bulk‐sediment geochemistry. These results contrast with previous reports that feldspars and volcanic detritus break down during transport, that sand grains are rounded rapidly in shallow‐marine environments, and that quartzose sands may be produced by physical processes. Mechanical wear is unable to modify the relative abundance of detrital components, including pyroxene and mafic volcanic rock fragments traditionally believed to be destroyed rapidly. The sole exceptions are poorly lithified or cleaved sedimentary/metasedimentary rock fragments, readily lost at the transition to the marine environment, and slow‐settling flaky micas, winnowed and deposited offshore. Coastal sediments tend to be depleted in relatively mobile amphibole, preferentially entrained offshore or re‐deposited in sheltered beaches, while less mobile garnet is retained onshore. No detrital mineral displays a significant increase in grain roundness after 300 to 350 km of longshore transport in high‐energy littoral environments from the Orange mouth to south of the Namib Erg, but all minerals get rapidly rounded after passing into the dunefield. Pyroxene and opaques get rounded faster than harder quartz and garnet, but sand mineralogy remains unchanged. Excepting strong transient selective‐entrainment effects, physical processes are unable to modify sand composition significantly. Selective mechanical breakdown can be largely neglected in quantitative provenance analysis of sand and sandstone even in the case of ultra‐long‐distance transport in high‐energy environments dominated by strong persistent winds and waves.

Multicyclic sediment transfer along and across convergent plate boundaries (Barbados, Lesser Antilles)

The main source of siliciclastic sediment in the Barbados accretionary prism is off-scraped quartzose to feldspatho-litho-quartzose metasedimentaclastic turbidites, ultimately supplied from South America chiefly via the Orinoco fluvio-deltaic system. Modern sand on Barbados island is either quartzose with depleted heavy-mineral suites recycled from Cenozoic turbidites and including epidote, zircon, tourmaline, andalusite, garnet, staurolite and chloritoid, or calcareous and derived from Pleistocene coral reefs. The ubiquitous occurrence of clinopyroxene and hypersthene, associated with green-brown kaersutitic hornblende in the north or olivine in the south, points to reworking of ash-fall tephra erupted from andesitic (St Lucia) and basaltic (St Vincent) volcanic centres in the Lesser Antilles arc. Modern sediments on Barbados island and those shed by larger accretionary prisms such as the Indo-Burman Ranges and Andaman-Nicobar Ridge define the distinctive mineralogical signature of Subduction Complex Provenance, which is invariably composite. Detritus recycled from accreted turbidites and oceanic mudrocks is mixed in various proportions with detritus from the adjacent volcanic arc or carbonate reefs widely developed at tropical latitudes. Ophiolitic detritus, locally prominent on the Andaman Islands, is absent on Barbados, where the prism formed above a westward subduction zone with a shallow decollement plane. The four-dimensional complexities inherent with multicyclic sediment dispersal along and across convergent plate boundaries require quantitative provenance analysis as a basic tool in paleogeographic reconstructions. Such analysis provides the link between faraway factories of detritus and depositional sinks, as well as clues on subduction geometry and the nature of associated growing orogenic belts, and even information on climate, atmospheric circulation and weathering intensity in source regions.

Testing provenance diagrams: Lessons from the well-constrained Cariaco Basin

The fine-grained sediments of the Cariaco Basin, Venezuela, of the last 130ky, whose deposition history is well characterized, were analyzed geochemically in order to test the validity of sediment bulk geochemistry as an indicator of detrital provenance. Several binary and ternary diagrams as well as the chemical index of alteration (CIA) were tested for their capacity to discriminate the poorly contrasted detrital sources to the Cariaco Basin, and to describe the temporal evolution of the contributions of these different sources. Most of the diagrams tested did not allow a good discrimination of sources or, when sources were well discriminated, did not allow an interpretation of the temporal variations consistent with the known history. A relatively good discrimination of sources and a consistent interpretation of temporal variations were however obtained using Hf vs. Th and La/Yb vs. Gd/Yb binary diagrams, as well as Ti–Zr–Th, Ti–Zr–La, and Lu–Hf–Th ternary diagrams. Compared to the previous studies of the detrital content of the Cariaco Basin sediments, the geochemical approach permitted the recognition of a sediment contribution eroded from the Unare platform and Gulf of Cariaco during rapid sea level oscillations, and the contribution of Saharan eolian particles during the Younger Dryas–Preboreal and MIS6-5 transition. The choice of plotted elements was determined after considering carrier minerals, so that different elements may be informative in different sedimentary contexts. Overall, mineral sorting during transport appears as a major limit to quantitative estimation of the different contributions. In particular mineral sorting leads to the selective enrichment of elements associated with clays (Al, Rb, Th and LREE) in sediments deposited in the basin. Unless the geochemical effect of mineral sorting can be measured, it appears that quantitative provenance analysis should be performed on fractions of similar grain size instead of bulk sediment.

Ultra-long distance littoral transport of Orange sand and provenance of the Skeleton Coast Erg (Namibia)

Abstract Quantitative provenance analysis based on high-resolution bulk-petrography and heavy-mineral data on beach and dune sands, integrated with detrital-zircon geochronology and chemical analyses of pyroxene, garnet and staurolite, demonstrates that sand derived from the Orange River is carried by powerful and persistent longshore currents as far as northern Namibia and southern Angola, 1750 km north of its mouth. This is the longest cell of littoral sand transport documented so far. Compositional forward modeling indicates that ≥ 80% of dune sand in the Skeleton Coast is Orange-derived, the remaining ≤ 20% being supplied by slow erosion of the Damara Orogen chiefly via the Swakop River. A decrease in basaltic rock fragments and pyroxene with relative enrichment in garnet, staurolite, tourmaline and other metamorphic minerals north of Walvis Bay indicates that only one-third of beach sand in the 350 km dune-free gap between the Namib and Skeleton Coast Ergs is Orange-derived, the remaining two-thirds being supplied largely by the Swakop River draining the Damara Orogen. Although volcanic gravel becomes dominant in beaches of the Skeleton Coast north of the Uniab mouth, detritus from Cretaceous Etendeka lavas accounts for only 4% of beach sand, reflecting limited sand generation in the arid catchment. Contributions from the Kunene River to either dune or beach sands is ruled out, indicating that gem diamonds found in placer deposits along the coast of Namibia are all derived from the Orange River.

Raman counting: a new method to determine provenance of silt

This article proposes a new integrated methodology to determine the miner- alogical composition of silt-sized sediments, reaching the same precision level required to perform quantitative provenance analysis as traditionally done on sand-sized sediments. We examine technical problems encountered in analysis of silt and illustrate how they can be solved for suspended load in a modern fluviodeltaic environment. All methods described here, and specifically the user-friendly Raman spectroscopy, can be routinely applied in mineralogical studies of ancient siltstones. Provenance information can thus be extracted from mudrocks, which represent a very conspicuous part of the stratigraphical record and are prone to preserve original detrital assemblages from diagenetic dissolution better than permeable interlayered sandstones. Quantitative mineralogical analysis of silt- sized sediments by innovative techniques opens up new frontiers in sedimentary petrology. Such an effective approach is of crucial importance to make accurate provenance diag- noses and sediment budgets and to correctly unravel the innumerable pieces of geological information stored in sedimentary archives from the alluvial plain to the deep-sea.

Tracing the drainage change in the Po basin from provenance of Quaternary sediments (Collina di Torino, Italy)

Quantitative provenance analysis of the Quaternary sediments from the Collina di Torino and the Po alluvial plain was assessed by using statistical techniques. This method, based on high-resolution heavy mineral analysis on modern and ancient sands processed by compositional biplot and linear mixing model, allowed reconstruction of the drainage change of the western Po River and its tributaries in the last 1 Ma. Mineralogical and statistical analyses discriminate three groups in the Quaternary samples. Sediments from the Po alluvial plain are rich in garnet, epidote and minor amphiboles. Detritus from the western slope of the Collina di Torino is characterized by epidote-rich assemblages, actinolite, blue-green hornblende and chloritoid. Heavy minerals from sediments of the northwestern slope include epidote-group minerals, glaucophane and hypersthene. A linear mixing model was used to compare detrital modes from modern and Quaternary detritus, and to identify the best modern analogue for any sample of ancient sedimentary deposit. Statistical analysis indicates that the first mineralogical group compares best with detritus of the modern Po River. Detritus from the second and third group compare best with sediments of the modern Dora Riparia River and Stura di Lanzo River, respectively. These results outline how the distribution of the Middle-Late Pleistocene fluvial deposits of the Collina di Torino is linked with the ancient Alpine watercourses, before the shifting of the Po River on the northern edge of the hill. During the Middle Pleistocene, rivers draining the Piedmont Zone of the Western Alps (PaleoDora Riparia and PaleoStura di Lanzo rivers) ran across the hill, while the PaleoPo River, which drained the Dora Maira Massif (Internal Massif), flowed to the south of the Collina di Torino. At the end of the Pleistocene, the PaleoPo River was diverted to the north to its present-day position in the alluvial plain. This case history shows how quantitative provenance analysis based on orogenic sediments is the key to reconstruct Quaternary drainage evolution of the foreland basin.

Tracking Paleodrainage in Pleistocene Foreland Basins

Abstract Foreland basins are comprehensive stratigraphic archives, from which many details of the tectonic history of associated orogens can potentially be retrieved by quantitative provenance analysis of sedimentary sequences. Because of complex basin‐fill architecture, however, provenance diagnoses often remain ambiguous. Trends in sediment composition cannot be safely interpreted as documenting paleotectonic or paleoclimatic changes whenever paleodrainage shifts represent an equally reasonable alternative. Understanding drainage patterns is thus a fundamental step in correctly unraveling tectonic and climatic events that punctuate the erosional evolution of mountain belts. In this study, we focus on well‐studied Quaternary subsurface successions of the Po Plain to illustrate a quantitative method of paleodrainage analysis. This method, based on high‐resolution petrographic and heavy‐mineral data from modern and Pleistocene sands, allowed us to objectively reconstruct the drainage changes of Po River tr...