The Parana, one of world's largest rivers, drains two main geological domains with contrasting topographic and climatic conditions: the warmer and wetter Parana intracratonic basin in Brazil and the cooler and drier Andean fold-thrust belt and Chaco retroarc basin in Argentina. Such geomorphological differences are reflected in the mineralogy and geochemistry of clay and fine silt generated in these two contrasting domains. In tropical Brazil, kaolinite is the virtually exclusive clay mineral independently of source rocks, with smectite prevailing locally in basaltic lowlands. Extreme depletion in K, Rb, Ba and Na, very high Al, Fe and P, abundant iron oxides, and highest Ce anomaly are testified in Paranaiba mud in the north, pointing to strong lateritic weathering with complete breakdown not only of plagioclase but even of K-feldspar. In stark contrast, both plagioclase and Kfeldspar are preserved and depletion in mobile elements is minor to negligible in northern Argentina, where illite characterizes mud produced by physical erosion in the semiarid Andean Cordillera and remains dominant to as far as the Rio de la Plata. Mineralogical and geochemical parameters thus consistently testify to a steady southward gradient throughout the Parana catchment, with progressively decreasing weathering intensity towards higher latitudes. Mud mineralogy and elemental and isotope geochemistry concur to indicate that the Andes - mostly the Bermejo River - supply the vast majority of mud (but little sand) to the Rio de la Plata estuary. This implies that most sediment generated in Brazil is currently trapped in large reservoirs upstream. Integrating mineralogical and geochemical data on different grain-size fractions is revealed as an indispensable tool to investigate sediment generation in continental domains, monitor the variability of chemical weathering, and obtain key information to constrain sediment budgets.

As part of a comprehensive project on sedimentary processes in South America, this study focuses on sediment generation in the intracratonic Paran & aacute; Basin and monitors the evolution of sand composition along the Paran & aacute; River from central Brazil to the R & iacute;o de la Plata estuary in Argentina. Several techniques (petrography, heavy minerals, detrital-zircon geochronology, elemental geochemistry and mineral-chemical analyses) are combined to evaluate the relative importance of the various factors that contribute to the production of pure quartzose sand. The huge Paran & aacute; River catchment consists of 79% siliciclastic sediments and sedimentary rocks, with basaltic lavas and Precambrian basement in subequal subordinate proportions. Pure quartzose sand supplied to the R & iacute;o de la Plata is largely produced by extensive recycling in intracratonic settings, but even Andean tributaries carry quartz-rich litho-quartzose sand recycled from Palaeozoic to Cenozoic siliciclastic rocks exposed along the retro-side of the cordillera. First-cycle basement-derived detritus is generated only in the headwaters of major Brazilian tributaries, where feldspatho-quartzose sand rapidly evolves into plagioclase-depleted quartzose sand as rivers incise across upper Palaeozoic siliciclastic rocks of the Paran & aacute; Basin. Basement-derived and volcanic-derived detritus is negligible in the lower Paran & aacute; course in Argentina because of the very low sand-generation potential of basaltic lavas and the impoundment of basement-derived and basalt-derived detritus into numerous artificial gigantic reservoirs as well as natural wetlands (e.g. Pantanal). Chemical weathering contributes to the increased durability of intracratonic sand in wetter subequatorial latitudes, but only the full integration of petrographic and geochemical parameters can help distinguish whether selective depletion of labile detrital components is the result of current weathering or is inherited from previous sedimentary cycles. The Paran & aacute; River offers a precious lesson to learn how the typical quartz-rich 'cratonic interior' signature of sediments is produced and evolves in continental intraplate settings to be finally transmitted to passive-margin beaches, continental embankments or deep-sea fans, with notable implications on reservoir quality and hydrocarbon exploration.

The Ganga-Brahmaputra river system transports up to 600 million tons of sediment annually from the Himalayan range to the Bengal Fan. The catchment of the Ganga-Brahmaputra river system is characterized by highly contrasting lithologies and exhumation rates which strongly influence erosion and chemical weathering processes. Recent studies have emphasized the importance and role of floodplains for the chemical weathering of sediments eroded from Himalayan mountains. Changes in sediment chemical weathering are controlled by climatic changes, such as variations in Indian summer monsoon precipitation and glacial interglacial cycles. However, further exploration is needed to understand the impact of anthropic changes and long-term climatic and tectonic forcings on the chemical weathering regime of the Ganga-Brahmaputra system. We present the bulk and clay mineralogy, obtained with XRD, of turbiditic sediments collected from the Bengal Fan in the Indian Ocean during the IODP Expedition 354. The clay mineralogical assemblages of IODP Expedition 354 present a dominance of illite and chlorite throughout the record with a relative increase of smectite and kaolinite content during the Miocene. Such clay mineralogy is consistent with the clay mineralogy of sediments from Leg 22 site 218 from DSDP (which was reoccupied for IODP Expedition 354). Miocene bulk sediments are relatively enriched in smectite, kaolinite, goethite, and terrigenous carbonates (calcite and dolomite). Therefore, our mineralogy results are showing a change in chemical weathering regime affecting the Himalaya system between the Miocene and Quaternary. The Quaternary is characterized by a lower content of smectite, kaolinite and carbonates, the presence of amphiboles and an enrichment in micaceous minerals (muscovite/illite, biotite, chlorite) and plagioclases as also inferred from Raman spectroscopy (Limonta et al., 2023). This indicates that during the Miocene the chemical weathering of ferro-magnesian minerals and calco-sodic feldspars was more efficient as shown by geochemical data (Tachambalath, 2023). The decrease in chemical weathering intensity from Late Miocene is consistent with the concurrent Late Cenozoic global cooling and drying of Himalayan front associated with the decrease in Indian monsoon seasonality and/or precipitation after 10-8 Ma (Clift and Webb, 2019). Here, we show that the change in the Indian monsoon system from 10-8 Ma is marked in the Bengal Fan turbiditic sediments mineralogy.

Quartz is the most abundant mineral in sediments and sedimentary rocks but efforts to reliably identify its provenance have been only partially fruitful so far. Even advanced methods such as cathodo-luminescence, Raman spectroscopy, synchrotron X-ray absorption spectroscopy, and laser ablation spectrometry have led to limited success. This article demonstrates how the delta O-18 of detrital quartz provides useful additional insight. The oxygen-isotope signature primarily depends on source rocks and their formation conditions, being highly different for different crustal sources and highest for carbonate rocks. This study illustrates a new protocol to analyze delta O-18 signatures of single quartz grains and shows how provenance from magmatic, metamorphic, or sedimentary domains can be discriminated. In each sand sample from rivers draining exclusively a single Himalayan tectonic domain (e.g., Trans-Himalaya, Greater Himalaya, Lesser Himalaya, and Tethys Himalaya), similar to 200 quartz grains were analyzed by ion microprobe LG-SIMS (Large Geometry Secondary Ion Mass Spectrometry) to characterize their oxygen-isotope variability. In each turbidite sample collected from the Bengal Fan during IODP Expedition 354, similar to 150 quartz grains were analyzed next to quantify the relative contribution of each Himalayan domain. This allowed us to complement data obtained with other bulk-sediment to single-mineral approaches, thus enhancing provenance resolution and highlight the erosional evolution of the Himalayan-Tibetan orogen through time.

The Uruguay River, a classic example of dome-flank drainage, traces a wide arc across the Lower Cretaceous Paran & aacute; large igneous province, thus presenting an unexcelled opportunity for studying the generation and fate of basaltic detritus in a subtropical climate. In this study we integrate new petrographic, heavy-mineral, clay-mineral, detrital-zircon geochronology, and geochemical data to monitor the compositional evolution of clay, silt, and sand throughout the Uruguay catchment, from southern Brazilian sources to the Rio de la Plata mouth. Pure basalticlastic sediment in Pelotas headwaters is progressively diluted by quartzose detritus recycled from upper Paleozoic to Cenozoic sandstones and almost no trace of volcanic-derived sand is left at the mouth. Even sand of Uruguay tributaries flowing entirely within the lava field is never purely basalticlastic but invariably contains significant or even dominant quartz recycled from underlying or locally intercalated quartzarenite layers. This testifies to the extremely low sand-generation potential of basaltic rocks in a subtropical climate. In humid southern Brazil, strong weathering intensity is attested by kaolinite-rich clay-mineral assemblages. In drier Uruguay, instead, either Fe-rich smectitic mud derived from basaltic lavas in the north or Fe-poor smectitic mud generated in non-volcanic terranes in the south is invariably dominant. The decrease in weathering intensity with increasing southern latitude is documented by the geochemistry of clay and fine silt, whereas the chemical composition of sand is overwhelmingly provenance-controlled although optical observations show much stronger weathering of basaltic glass in Brazilian headwaters than in Uruguay. Because of very low sand-generation potential and rare zircon content, Fe-rich smectite and rare chalcedony grains remain as the only testimony of basaltic provenance at the Uruguay River mouth. The worrying conclusion is that, in provenance studies of ancient analogues, even a huge basaltic lava field spanning most of the catchment and occupying the core of an intracratonic basin is quite likely to go undetected, even if weathering intensity was not extreme and even under the implausible condition of negligible postdepositional selective breakdown of mafic detritus.

Over the Tertiary, the uplift of the Himalaya combined to the development of the monsoon generated the largest erosion basins of the planet. More than 80% of the erosion is exported to the Bay of Bengal by the Ganga-Brahmaputra river system and generates turbidity currents which convey detrital sediment building the Bengal Fan. In the modern Himalaya, the monsoon rainfall and tectonic processes shape the erosion pattern. The monsoon seasonal precipitation ensures efficient transport of sand-rich sediments in the basin despite long distances through a very flat floodplain and delta. Rapid transport also acts as a limiting factor for weathering as it reduces residence time in the floodplain but favors efficient carbon burial. The IODP Expedition 354 drilled the Bengal Fan with seven sites over a 320 km E-W transect at 8°N. This construcs a composite sedimentary record of Himalayan erosion over the Neogene and Quaternary. Sediments are predominantly composed of turbidites generated from the Ganga-Brahmaputra delta. Turbiditic sediments show mineralogical, geochemical and isotopic characteristics which reveal a close analogy with those of the modern Ganga-Brahmaputra river. Sand deposition is dominant and is present in several meters thick sand lobe as well as in levee turbidite (Bergmann et al. 2020). Sand was used to determine average erosion rates of the Himalaya using quartz in situ concentrations of cosmogenic 10Be. Those show stable rate in spite of the onset of a more unstable climate from the Pliocene to the Pleistocene (Lenard et al. 2020). Major element concentrations and Sr-Nd isotopic compositions of turbidite samples reflect combined effects of geological sources exposed to erosion, weathering and mineral sorting during transport. Deciphering these controls, based on the comparison between turbidite samples and modern river sediments of the Ganga and Brahmaputra basin reveals evolution from Miocene to present. Changes appear in the abundance of detrital carbonates likely reflecting decreasing exposition of the Tethys Himalaya to erosion since Miocene. Clear increase in the silicate Na and Ca concentrations from Miocene to Pleistocene indicates major change in the weathering conditions in the basin which can be related to longer residence time of the sediment in the floodplain and lower erosion ratesin the Miocene. Bergmann et al. 2020, G. cube 10.1029/2019gc008702Lenard et al. Nat Geosc. 2020, doi:10.1038/s41561-020-0585-2

ABSTRACT High-resolution petrographic and heavy-mineral analyses of Bengal Fan turbidites from six cores drilled during IODP Expeditions 353 and 354 elucidate factors controlling their intersample compositional variability as a key to understanding sedimentary processes and erosional evolution of the Himalayan belt since the Miocene. Bengal Fan turbidites are feldspatho-quartzose to litho-feldspatho-quartzose with plagioclase > K-feldspar; slow-settling micas increase in abundance in very fine sand and coarse silt. The feldspar/quartz ratio and higher-rank metamorphic rock fragments notably increase from uppermost Miocene to Pleistocene deposits, which is ascribed to the onset of rapid exhumation of the Eastern Himalayan syntaxis since ∼ 5 Ma. The same trends are documented in Nicobar Fan turbidites, confirming that they belong to the same sedimentary system. Both Bengal and Nicobar fans record a pulse in mass accumulation rate at Tortonian times, when supply of sedimentary and very-low-grade metasedimentary detritus reflected accelerated exhumation of the Lesser Himalaya. In contrast to foreland-basin sediments, where ferromagnesian minerals have been completely dissolved in strata as young as Pliocene–Pleistocene, in both Bengal–Nicobar and Indus fans amphibole invariably represents about half of the moderately rich to rich transparent-heavy-mineral suite, demonstrating that amphibolite-facies Greater Himalaya metamorphic rocks were widely exposed in the Himalayan range well before the late Miocene and possibly since the late Oligocene, as indicated by a few sillimanite and kyanite grains in Bengal Fan sediments as old as 23 Ma and 28 Ma, respectively. Diagenetic dissolution strongly affected olivine and pyroxene in strata older than the middle and early Pleistocene, respectively, whereas amphibole decreases markedly through progressively older Miocene strata. Ferromagnesian minerals and sillimanite are almost completely dissolved in lower Miocene strata, where durable zircon, tourmaline, rutile, and apatite make up half of the strongly depleted heavy-mineral assemblage. Quaternary turbidites from the six studied cores have virtually the same compositional signatures, testifying to efficient homogenization by turbidite transport and reworking across the fan. Turbidites in western cores closer to peninsular India (U1444A and U1454B) are not different from those in eastern cores, indicating very minor supply from the subcontinent. Forward-mixing calculations based on integrated petrographic and heavy-mineral data indicate that sand supply from the Brahmaputra River to Quaternary turbidites was four times larger than supply from the Ganga River, indicating up to six times higher sediment yields and erosion rates in the Brahmaputra than in the Ganga catchment, largely reflecting superfast erosion of the Eastern Himalayan syntaxis.

Epidote group minerals are one of the three most abundant kinds of heavy minerals in orogenic sediments, the other two being amphibole and garnet. They resist diagenesis better than amphibole and resist weathering in soils better than garnet. Their chemical composition and optical properties vary markedly and systematically with temperature and pressure conditions during growth. Useful information on the metamorphic grade of source rocks can thus be obtained by provenance analysis. In this study, we combine optical, SEM–EDS, and Raman analyses of nine standard crystals of epidote group minerals collected from different rock units exposed in the European Alps and Apennines and develop a Raman library for efficient discrimination of epidote, clinozoisite, zoisite, and allanite by establishing clear user-oriented relationships among optical properties, chemical composition, and Raman fingerprint. This new library allows us to distinguish and reliably determine, directly from their Raman spectrum, the chemical compositions of epidote group minerals during routine heavy mineral analyses of sand/sandstone and silt/siltstone samples down to the size of a few microns. The validity of the approach is illustrated by its application to 41 Bengal Fan turbidites collected from five cores during IODP Expedition 354 and ranging in grain size from medium sand to fine silt.

Together with amphibole and garnet, epidote-group minerals are one of the three most important heavy minerals found in orogenic sediments (Garzanti and Andò, 2007). Their chemical composition and optical properties vary markedly with temperature and pressure conditions, and thus provide useful information in provenance analysis on the metamorphic grade of source rocks. The aim of this study is to devise an efficient and quick method, with micrometric resolution to distinguish among the different species of the epidote group during routine point-counting of heavy-mineral slides, which can be applied on a vast ranges of grain-sizes from fine silt to medium sand. The geochemical variability of epidote-supergroup minerals from different source rock collected in different sectors of the Alpine orogenic belt was first investigated by coupling Raman Spectroscopy, Scanning Electron Microscopy, and Energy-dispersed X-ray Spectroscopy (SEM-EDS). The geochemical composition, optical properties, and Raman fingerprints of these standard epidote grains were described and in-house database of Raman spectra was created, combining geochemical data and Raman response in the low wavenumbers region and OH stretching bands. A program, written in Matlab® language, has been established which allows to obtain a quick estimate of the amount of iron from the Raman spectra in the clinozoisite-epidote series. Raman spectra of detrital epidotes contained in turbiditic sediments of the Bengal Fan (IODP Expedition 354) were next compared with Raman spectra of epidote-group standards to determine their composition. The identification and relative amount of detrital epidote, clinozoisite and zoisite in silt- and sand-sized deep-sea sediments contribute to constrain the metamorphic grade of Himalayan source rocks, reconstruct the erosional evolution of the Himalayan orogen, and provide information on climate change and strengthening of the Indian Ocean monsoon throughout the Neogene and Quaternary. Key words: epidote, provenance, Himalaya, Raman spectroscopy, Microprobe analyses, optical microscope. Garzanti, E., Andò S., 2007. Plate tectonics and heavy-mineral suites of modern sands. In: Mange, M.A., Wright, D.T. (Eds.), Heavy Minerals in Use, Developments in Sedimentology Series, 58. Elsevier, Amsterdam, pp. 741-763.

The aim of the study is to implement a new protocol to analyze the isotopic signatures of single detrital carbonates, with primary application in source-to-sink studies, and to fully exploit them as a provenance tracers. While single grain approach is standard in detrital thermochronology [e.g. 1,2], it has not been applied on major minerals using classic isotopic tracers. In provenance studies, carbonate abundance and their O and C isotopic signatures partly reflects the geology of the source areas [e.g. 3,4], but depends also on chemical weathering processes acting during sediment transfer [e.g. 5]. Because isotopic analyses of bulk aliquot of carbonates mix grains with different origin and significance (e.g. pedogenetic, marine, diagenetic and detrital carbonates), part of the information carried by each detrital grain is lost. This new protocol is tested on modern sediments of Ganga-Brahmaputra Rivers and turbiditic sediments from the Bengal Fan (IODP Expedition 354). Single grain isotopic fingerprint is expected to pinpoint sediment sources eroded in the Himalayan belt and to highlight sediment mixing from specific sources enhancing provenance resolution with respect to bulk approaches. We apply an automated acid digestion with oversaturated orthophosphoric acid at 70°C followed by isotopic analyses of the evolved CO2 with a Thermo Fisher Scientific MAT 253 mass spectrometer coupled with a Gasbench gas chromatograph [6]. For each sample 100 to 200 carbonate

ABSTRACT The Congo deep-sea fan, the largest on Earth fed entirely with anorogenic detritus, is characterized by quartzose to pure quartzose sand, reflecting multiple recycling coupled with extreme chemical weathering in cratonic equatorial Africa. The very youthful lower course of the Congo River connects directly to a steep canyon, where detritus including quartz grains up to a few millimeters in diameter is funneled towards Atlantic Ocean floors and deposited at abyssal depths more than a thousand kilometers away from shore. This article illustrates for the first time in detail the mineralogical and geochemical signatures of Congo Fan sands and discusses the factors controlling their intersample and intrasample variability as a key to understand how sediment is generated, recycled, and finally transferred to the deep sea. Compositional variability is largely grain-size-dependent. Combined petrographic and Raman spectroscopy analyses demonstrate that quartz increases in coarser samples and size classes, whereas feldspars are concentrated in finer sizes, plagioclase relative to K-feldspar and orthoclase relative to microcline, defining an order of mechanical and chemical durability among detrital tectosilicates. Because of overwhelming quartz abundance and very low heavy-mineral concentration, quartz contributes significantly to the REE budget and up to 40–50% of Nd in coarser samples, characterized by εNd values as low as –21. The strong grain-size-dependent variability of εNd suggests that quartz carries a markedly more negative εNd signature than monazite and other detrital components. This is chiefly ascribed to the durability of quartz grains, able to survive repeated cycles of weathering and diagenesis through Proterozoic and Phanerozoic time better than all other minerals. Neodymium model ages are influenced less by grain size and quartz abundance but more by the Sm/Nd ratio of different detrital components, and samples hydrodynamically enriched in LREE-rich minerals display TNd,CHUR and TNd,DM ages 1.2–1.4 Ga younger than samples enriched in HREE minerals. Not all detritus in the Congo Fan is supplied transversally by the Congo River. Forward-mixing calculations based on mineralogical data indicate that sand entrained northward by longshore currents mixes progressively with Congo River sand along the northernmost Angola coast, penetrates in the Soyo estuary, and is eventually captured in the canyon and transferred to the deep-sea fan, where it is estimated to represents 7 ± 2% of turbidite deposits.

Understanding the evolution of river systems in southern Africa is fundamental to constrain the evolution of landscape and sediment dispersal patterns. It is widely considered that the upper Zambezi River was connected with the Limpopo River during the Cretaceous, forming what was then the largest river in Africa. Crustal flexure during the Paleogene severed the upper Zambezi drainage from the Limpopo, setting the framework of the modern Zambezi and Limpopo River systems. We present first evidence—based on heavy‐mineral assemblages from cores drilled offshore of the Limpopo River mouth and samples collected in different reaches of the modern Limpopo River, integrated with magnetic susceptibility, detrital‐zircon geochronology, and geomorphological analysis—suggesting that the current Limpopo River formed recently in the Plio‐Quaternary. Plio‐Quaternary climate change is envisaged to have controlled the recent dynamics of river drainage and consequent distribution of sediment loads, as observed in many other transcontinental rivers worldwide.

Large sediment masses are transferred over many hundreds of kilometres along the coast of passive continental margins worldwide. The relevance of such a phenomenon for source-to-sink studies, environmental issues, and coastal management remains largely unperceived. This study traces the paths of volcaniclastic sand along ca 2170 km of the Argentine coast and documents a 760 km long cell of littoral transport extending from the formerly larger Rio Colorado delta to the edge of the Rio de la Plata mouth. During deglaciation stages and humid periods of the Pleistocene, a much greater sediment volume than today was transferred by the Desaguadero and Colorado rivers from the highest-relief tract of the Andean Cordillera to the Atlantic Ocean. Amphibole-rich sand originally supplied by the Rio Desaguadero is being recycled today from Pampean lowlands to feed the beaches along Rio de la Plata southern shores, whereas pure quartzose sand of Rio Parana is found only adjacent to its prograding delta. Augite-rich sand supplied by the Rio Colorado is dominant along the coast of the Buenos Aires Province, where it mixes locally with coarser-grained quartz-rich detritus recycled in the urbanized Mar del Plata area. Hypersthene-rich sand of the Rio Negro is dispersed both north and south of the mouth, where heavy-mineral-rich lag deposits are formed in areas of accelerated erosion and retreating sea cliffs. Changes of mineralogical signatures during long-distance littoral transport are largely ascribed to local supply from coastal erosion or hydrodynamic effects rather than to selective breakdown of labile grains. Whereas the relative abundance of amphibole and pyroxene is largely independent of transport distance, olivine is depleted both in the northern part of the Colorado littoral cell and south of the Rio Negro mouth, which is chiefly ascribed to dilution by recycling of Neogene sediments that have undergone early intrastratal dissolution rather than to mechanical loss.

The heavy-mineral data of 18 marine sediment samples from IODP 361 Site U1478A and zircons U-Pb data from U1478A core-top sample.

Central Argentina from the Pampean flat‐slab segment to northern Patagonia (27°–41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. Combined with previous research focused on coastal sediments, this actualistic provenance study uses framework petrography and heavy‐mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ca. 1,500 km and next northwards for another 760 km along the Atlantic coast. Although detritus generated in the Andes is largely derived from mesosilicic volcanic rocks of the cordillera, its compositional signatures reflect different tectono‐stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as different character and crystallization condition of arc magmas through time and space. River sand, thus, changes from feldspatho‐litho‐quartzose or litho‐feldspatho‐quartzose in the north, where sedimentary detritus is more common, to mostly quartzo‐feldspatho‐lithic in the centre and to feldspatho‐lithic in the south, where volcanic detritus is dominant. The transparent‐heavy‐mineral suite changes markedly from amphibole ≫ clinopyroxene > orthopyroxene in the north, to amphibole ≈ clinopyroxene ≈ orthopyroxene in the centre and to orthopyroxene ≥ clinopyroxene ≫ amphibole in the south. In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds and temporarily accumulated in dune fields. During the Quaternary, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment‐laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today towards the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary.

Heavy minerals are typically rare but important components of siliciclastic sediments and rocks. Their abundance, proportions, and variability carry valuable information on source rocks, climatic, environmental and transport conditions between source to sink, and diagenetic processes. They are important for practical purposes such as prospecting for mineral resources or the correlation and interpretation of geologic reservoirs. Despite the extensive use of heavy mineral analysis in sedimentary petrography and quite diverse methods for quantifying heavy mineral assemblages, there has never been a systematic comparison of results obtained by different methods and/or operators. This study provides the first interlaboratory test of heavy mineral analysis. Two synthetic heavy mineral samples were prepared with considerably contrasting compositions intended to resemble natural samples. The contributors were requested to provide (i) metadata describing methods, measurement conditions and experience of the operators and (ii) results tables with mineral species and grain counts. One hundred thirty analyses of the two samples were performed by 67 contributors, encompassing both classical microscopic analyses and data obtained by emerging automated techniques based on electron-beam chemical analysis or Raman spectroscopy. Because relatively low numbers of mineral counts (N) are typical for optical analyses while automated techniques allow for high N, the results vary considerably with respect to the Poisson uncertainty of the counting statistics. Therefore, standard methods used in evaluation of round robin tests are not feasible. In our case the 'true' compositions of the test samples are not known. Three methods have been applied to determine possible reference values: (i) the initially measured weight percentages, (ii) calculation of grain percentages using estimates of grain volumes and densities, and (iii) the best-match average calculated from the most reliable analyses following multiple, pragmatic and robust criteria. The range of these three values is taken as best approximation of the 'true' composition. The reported grain percentages were evaluated according to (i) their overall scatter relative to the most likely composition, (ii) the number of identified components that were part of the test samples, (iii) the total amount of mistakenly identified mineral grains that were actually not added to the samples, and (iv) the number of major components, which match the reference values with 95% confidence. Results indicate that the overall comparability of the analyses is reasonable. However, there are several issues with respect to methods and/or operators. Optical methods yield the poorest results with respect to the scatter of the data. This, however, is not considered inherent to the method as demonstrated by a significant number of optical analyses fulfilling the criteria for the best-match average. Training of the operators is thus considered paramount for optical analyses. Electron-beam methods yield satisfactory results, but problems in the identification of polymorphs and the discrimination of chain silicates are evident. Labs refining their electron-beam results by optical analysis practically tackle this issue. Raman methods yield the best results as indicated by the highest number of major components correctly quantified with 95% confidence and the fact that all laboratories and operators fulfil the criteria for the best-match average. However, a number of problems must be solved before the full potential of the automated high-throughput techniques in heavy mineral analysis can be achieved.

The Nicobar Fan and Bengal fans can be considered as the eastern and western parts, respectively, of the largest submarine-fan system in the world. This study presents the integrated results of petrographic and provenance studies from the Nicobar Fan and evaluates these in the context of controls on sedimentation. Both fans were predominantly supplied by Himalaya-derived material from the main tectono-stratigraphic sequences as well as the Gangdese arc. A lack of volcanic material in the Nicobar Fan rules out sources from the Sumatra magmatic arc. Overall, the petrographic data shows a progressive decrease in sedimentary detritus and corresponding increase of higher-grade metamorphic detritus upsection. Changes in sediment provenance and exhumation rates in the Himalaya are seen to track changes in sediment accumulation rates. High sediment accumulation rates in the Bengal Fan occurred at similar to 13.5-8.3 Ma, and in the Nicobar Fan from similar to 9.5-5 Ma. Both fans show peak accumulation rates at 9.5-8.3 Ma (but with the Nicobar Fan being about twice as high), and both record a sharp drop from similar to 5.5-5.2 Ma, that coincided with a change in river drainage associated with the Brahmaputra River diverting west of the uplifting Shillong Plateau. At similar to 5 Ma, the Nicobar Fan was supplied by an eastern drainage route that finally closed at similar to 2 Ma, when sediment accumulation rates in the Nicobar Fan significantly decreased. Sediment provenance record these changes in routing whereby Bengal Fan deposits include granitoid sources from the Namche Barwa massif in the eastern syntaxis that are not seen in the Nicobar Fan, likely due to a more localised eastern drainage that included material from the Indo-Burman wedge. Prior to similar to 3 Ma, source exhumation rates were rapid and constant and the short lagtime rules out significant intermediate storage and mixing. In terms of climate versus tectonic controls, tectonically driven changes in the river network have had most influence on fan sedimentation. (C) 2020 Elsevier B.V. All rights reserved.