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Source‐to‐sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post‐extensional subsidence in the Jurassic‐Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source‐to‐sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source‐to‐sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta‐sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near‐source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post‐rift stage. Key Points: Provenance changed from a point source from skarns during the syn‐rift stage to multiple sources during the post‐rift stageHigher relief in the Tianshan in the Triassic was reduced during the Jurassic‐CretaceousSediment recycling took place in the Early Cretaceous [ABSTRACT FROM AUTHOR]

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well. [ABSTRACT FROM AUTHOR]

Abstract Source‐to‐sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post‐extensional subsidence in the Jurassic‐Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source‐to‐sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source‐to‐sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta‐sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near‐source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post‐rift stage.

The Himalayan orogen exports millions of tons of sediment annually to the Indo‐Gangetic foreland basin, derived from both hinterland and foreland fold‐thrust belts (FTB). Although erosion rates in the hinterland are well‐constrained, erosion rates in the foreland FTB and, by extension, the sediment flux have remained poorly constrained. Here, we quantified erosion rates and sediment flux from the Mohand Range in the northwestern Himalaya by modeling and measuring the cosmogenic radionuclide (CRN) 10Be and 26Al concentrations in modern fluvial sediments. Our model uses local geological and geophysical constraints and accounts for CRN inheritance and sediment recycling, which enables us to determine the relative contributions of the hinterland and foreland FTB sources to the CRN budget of the proximal foreland deposits. Our model predictions closely match measured concentrations for a crustal shortening rate across the Mohand Range of 8.0 ± 0.5 mm yr−1 (i.e., approximately 50% of the total shortening across the Himalaya at this longitude) since 0.75−0.06+0.02 $0.7{5}_{-0.06}^{+0.02}$ Ma. This shortening implies a spatial gradient in erosion rates ranging from 0.42 ± 0.03 to 4.92 ± 0.34 mm yr−1, controlled by the geometry of the underlying structure. This erosion pattern corresponds to an annual sediment recycling of ∼2.0 megatons from the Mohand Range to the downstream Yamuna foreland. Converted to sediment fluxes per unit width along the Himalaya, the foreland FTB accounts for ∼21% ± 5% of the total flux entering the foreland. Because these sediments have lower 10Be concentrations than hinterland‐derived sediment, they would lead to ∼14% overestimation of 10Be‐derived erosion rates, based on Yamuna sediments in the proximal foreland. Plain Language Summary: Cosmogenic radionuclides such as beryllium‐10 (10Be) are important tools for tracking erosion processes at the Earth's surface. However, they are challenging to apply when sediment remains temporarily stored for millions of years before being re‐eroded. We call this sediment recycling. We quantified sediment recycling in the Mohand Range, at the foothills of the northwestern Himalaya, based on the present‐day 10Be concentration in fluvial sediments recycled from tectonically uplifted older foreland deposits. We do this by modeling how the 10Be concentrations change as sediment is first eroded in the Himalayan source region, then deposited in the foreland, and finally eroded again. By comparing modeled and measured concentrations, we find that erosion rates in the Mohand Range vary from 0.42 ± 0.03 to 4.92 ± 0.34 mm yr−1, corresponding to about 2.0 megatons of sediment recycling from this range to the downstream Yamuna foreland. Because the 10Be concentration in recycled sediment is lower than that in sediment eroded from the high Himalaya, admixing high Himalayan sediments with recycled material may result in erosion rates that are higher than the actual erosion rates in the high Himalaya. Key Points: Novel approach for tracking cosmogenic nuclide accumulation in fluvial sediments through each step of a fold‐thrust belt sediment routing system10Be‐derived erosion rates and sediment flux from the Mohand Range in the northwestern HimalayaOnset of Main Frontal Thrust motion and rate of crustal shortening across the Mohand Range constrained by modeling 10Be concentrations in present‐day river sediments [ABSTRACT FROM AUTHOR]

Subduction recycling of sediments plays a key role in the geochemical evolution of Earth. The presence of recycled terrigenous sediments in upwelling plumes has been cited to explain the EM2 signature in ocean island volcanics, characterized by particularly high 87Sr/86Sr (>0.706). However, the origin of such isotopic anomalies in continental regions and the role of subducted sediments in the subcontinental lithospheric mantle (SCLM) remain unclear. The Himalaya–Tibet orogen is one of the world's best places for deciphering continental subduction and the fate of subducted crustal materials in the mantle. Here we present a systematic study of the geochronology, mineral chemistry (especially clinopyroxene), whole-rock chemistry and Sr–Nd–Pb–Hf–O isotopic compositions of Cenozoic potassic–ultrapotassic lavas from the western Kunlun area of northwestern Tibet. New secondary ion mass spectrometry (SIMS) zircon U–Pb dating, coupled with published age results, constrain the timing of volcanism from ~8.3 Ma to the present. These lavas show geochemical characteristics that closely resemble the EM2 mantle end-member represented by the Samoan hotspot. Both whole rocks and individual magmatic clinopyroxenes display arc-like trace-element patterns and remarkably enriched Sr–Nd–Pb–Hf isotope compositions (87Sr/86Sr ≥ 0.7080; ε Nd ≤ −4.8; 206Pb/204Pb ≥ 18.704; ε Hf ≤ −2.6). Together with high zircon δ18O values (6.3–10.4‰), the data point to a mantle source enriched by recycled sedimentary materials. Geochemical modeling and geophysical evidence further indicate that the sediments were directly derived from the subducted Indian continental lithosphere during India–Eurasia collision. Partial melting models assuming a hybridized mantle source that contains ~5% Indian continental crust suggest that the primary melts of the potassic–ultrapotassic lavas could be formed by melting of a phlogopite-bearing garnet lherzolite at low melting degrees (1–5%). The magma geochemistry is consistent with the model of mélange melting, implying that the subducted sediments may detach from the downgoing Indian slab and rise up diapirically into the overlying mantle lithosphere. Unlike traditional models of subducted sediments entering the deep mantle, the western Kunlun EM2-like lavas reveal that subducted sediments can be rapidly recycled into the SCLM during continental subduction (probably <50 Myr). We suggest that the SCLM could be an important reservoir for subducted sediments. The findings are important to our understanding of mantle circulation rates and chemical heterogeneities. [ABSTRACT FROM AUTHOR]

Detrital zircon (DZ) geochronology has become a popular tool in provenance studies during the past two decades. However, similar zircon crystallization ages from different source regions greatly hamper the interpretation of sediment dispersal and recycling processes. The Alleghenian–Ouachita–Marathon (AOM) foreland and vicinity in North America is a region where some dominant DZ age groups could come from both the southern Appalachians in the eastern United States and the Gondwanan terranes in Mexico. In this study, we present 1045 new DZ U–Pb ages and 81 DZ core–rim age pairs in lower Permian sandstone in the Permian Basin and Miocene sandstone in the eastern Gulf of Mexico (GOM). These new data were integrated with published DZ single U–Pb age and core–rim ages from syn‐ to post‐orogenic strata in the Permian Basin, Marathon foldbelt, southern Appalachian foreland basin and eastern GOM to interpret the sediment‐dispersal models in the AOM foreland and eastern GOM. Our models show that during the Leonardian Stage, sediments derived from the Appalachians were first delivered to the US midcontinent and then recycled to the Permian Basin; during the Miocene, sediment from the Appalachians fluxed to the eastern GOM, with no longshore mixing from the western GOM. These models based on the integration of single U–Pb and core–rim ages are consistent with published results that used other methods, including zircon single U–Pb age, zircon Hf isotopic data, zircon (U–Th)/He age, sedimentology and stratigraphy. Our results demonstrate that although some limitations exist, zircon core–rim age is a powerful tool, adding an extra constraint on the interpretation of sediment‐dispersal systems. This tool is particularly applicable to the post‐orogenic stage, during which the sediment pathways are more complicated because of the dominant input from distal sources. Insights gained in this study imply that this novel strategy of using core and rim ages could be integrated with other methods to better understand sediment dispersal. [ABSTRACT FROM AUTHOR]

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well.

In many parts of the world, ports and harbours lie adjacent to ecologically important areas of coastal habitat. In such areas port authorities, coastal managers and regulators are required to negotiate the tension between the demands of making ports ever more efficient, with wider and deeper approaches to accommodate vessels of deeper draft and larger handling areas, and the preservation of coastal habitats which are vitally important for bird and fish populations and which help protect the coast from flooding and erosion. The deepening of approach channels and berths usually results in an increased rate of sedimentation and maintenance dredging. There is an increasing recognition that such dredged sediment is a resource which should be utilised beneficially for human development activities and/or enhancement of ecological habitats. One form of beneficial use of dredged material, is termed “sediment recycling” or “strategic placement”. This form of beneficial use consists of the placement of cohesive sediment into the water column or onto the bed in such a way so that currents and waves then transport the released sediment onto the desired habitats. Sediment recycling is less widely practiced because the changes in bed level resulting from placement are generally of the order of a few centimetres/year or less and it is difficult to demonstrate whether such recycling is successful. This paper describes a methodology for the assessment of the effectiveness sediment recycling, implementing the methodology on a case study of a large-scale sediment recycling scheme in the Stour/Orwell Estuary system in the United Kingdom, designed to offset the identified adverse effects of an approach channel deepening on the estuary system. The study represents a major contribution to the consideration of non-direct beneficial use of cohesive sediment. For the first time a methodology for reliably evaluating the effects of sediment recycling, separating the effects of natural changes in morphology from the beneficial use, has been shown to be effective. This method, which is applicable anywhere where there are sufficient data, allows a robust evaluation of the effectiveness of such methods and crucially enables these methods to be tested and optimised using modelling before implementation.

Over 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of north‐west Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across north‐west Africa indicate significant and sustained shifts in source regions in Meso‐Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from north‐west Africa—often described as the 'Mesoproterozoic Gap', which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa. [ABSTRACT FROM AUTHOR]

An implicit assumption of most sedimentary provenance analyses is a direct link between source and sink. However, recycling of sedimentary detritus from pre‐existing strata interrupts the direct source‐to‐sink link and can result in incorrect interpretations of paleogeography and paleodrainage. Detrital zircon is the favoured proxy of contemporary provenance studies, but its physiochemical resilience makes it particularly prone to recycling. In this study, we integrate geochemical (age, isotope, and trace elements) and grain roundness data of multiple detrital minerals with different physiochemical stabilities (zircon, tourmaline, rutile, and apatite) to evaluate the importance of recycling in an ancient sedimentary basin. We focus on the early Cambrian Lalun Formation of Iran, which forms part of a laterally extensive sandstone‐rich succession deposited along the northern margin of Gondwana. The Lalun Formation preserves a distinct change of compositional maturity between lower arkose and shale units and an upper unit of quartz‐rich sandstone. Detrital zircon, rutile, and apatite data demonstrate that all units of the Lalun Formation share a common source in the Arabian‐Nubian Shield. Whole‐rock geochemical data further indicate that all units have similar chemical alteration indices, suggesting the change in compositional maturity is not a product of differential weathering of the source region. Analysis of grain roundness reveals that detrital zircon, rutile, and tourmaline in the upper quartz‐rich unit are typically more rounded than those in the underlying arkose and shale units. In contrast, detrital apatite grains are nearly all angular in the quartz‐rich unit but mostly rounded in the lower arkose and shale. Together, the detrital mineral provenance, whole‐rock geochemistry, and morphological data are consistent with recycling of the lower arkose and shale units of the Lalun Formation into the uppermost quartz‐rich unit, with the latter also receiving a component of first‐cycle detritus represented by angular detrital apatite. Our findings demonstrate that integrating the features of detrital minerals acquired during a sedimentary cycle (grain rounding and diversity of mineral assemblages) with features inherited from their ultimate source rocks (age, isotopic, and geochemical proxies) can assist in recognising sediment recycling in ancient strata. [ABSTRACT FROM AUTHOR]

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range. • We characterized the Quartz OSL sensitivity in a thick Cenozoic sedimentary basin-fill sequence of the Northern Andes. • OSL sensitivity is compared with shifts in provenance constrained by mineralogical composition and detrital zircon U-Pb ages. • OSL sensitivity varies according to the main shifts in provenance and episodes of recycling recognized in the Northern Andes. [ABSTRACT FROM AUTHOR]

Luminescence characteristics of quartz and feldspar allow to discriminate sediments from different source areas. Particularly, sensitivity of optically stimulated luminescence (OSL) and thermoluminescence (TL) signals of quartz and infrared‐stimulated luminescence (IRSL) of feldspar from Quaternary sediments has been used for provenance analysis. These properties change due to source area denudation rates and sediment reworking, which drive the number of burial irradiation‐solar exposure cycles of sediment grains in surface systems. Here, we use for the first time a similar approach to interpret the geomorphic conditions of source areas of Silurian to Triassic siliciclastic sedimentary units of the intracratonic Parnaíba Basin in northeast Brazil. Luminescence measurements were performed on sand grains, and statistical tests were applied to evaluate differences in luminescence properties within and across stratigraphic units. We explored the position of well‐known "110°C" (TL110) and "325°C" (TL325) TL peaks of quartz as proxies to discriminate stratigraphic units with similar lithological assemblages. OSL and TL sensitivities as well as the dominance of the so‐called fast OSL component increase from Silurian to Triassic sedimentary units, while the IRSL sensitivity decreases towards younger stratigraphic units. These patterns point to source areas with decreasing denudation rate and higher sediment recycling over basin filling time, leading to decreasing feldspar concentration and quartz luminescence sensitisation. Major changes in luminescence properties coincide with regional unconformities. This is attributed to physical landscape changes leading to shifts in the relief of source areas and basin sediment recycling. The TL110 peak position is similar across stratigraphic units, but the TL325 peak position has significant variation, with values between 324°C and 334°C, allowing its use for stratigraphic discrimination. Changes in OSL and TL characteristics of quartz sediment grains are preserved during long‐term burial (108 Ma), representing a new tool for interpreting basin evolution and to perform stratigraphic analysis of ancient siliciclastic successions. [ABSTRACT FROM AUTHOR]

An important gap in the management of land erosion in mining‐affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining‐affected Santa Cruz and Pamalabawan catchments in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub‐catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub‐catchments, with as little as 10–22% of relative disturbance area being enough to generate four‐fold to eight‐fold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub‐catchments with > 10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km−2 d−1) compared with sub‐catchments with < 10% disturbance (3.6 ± 17.7 t km−2 d−1) and undisturbed catchments (2.0 ± 5.7 t km−2 d−1). We also show that sediment flushing predominantly occurs in the most disturbed sub‐catchments at the onset of the wet season. A small number of flood events transports the bulk of the sediment, with hysteresis effects being most pronounced in disturbed areas. Lastly, we show that floodplain sediment recycling exerts a key control on sediment delivery at both reach and catchment scales, with the relative contribution of floodplain sources to the sediment budget becoming dominant in the latter stages of the wet season‐ up to 89% of the total sediment export per storm event. This study highlights the importance of both degree of disturbance and sediment pathways in controlling sediment transport in mining‐disturbed areas, and that considering the entire sediment routing system including intermediate stores is crucial to optimizing existing and future measures against siltation and potential contamination of trace metals and metalloids downstream of mining areas. [ABSTRACT FROM AUTHOR]

Salt marshes are valuable ecosystems that must trap sediments and accrete in order to counteract the deleterious effect of sea level rise. Previous studies have shown that the capacity of marshes to build up vertically depends on both autogenous and exogenous processes including ecogeomorphic feedbacks and sediment supply from in‐land and coastal ocean. There have been numerous efforts to quantify the role played by the sediments coming from marsh edge erosion on the resistance of salt marshes to sea level rise. However, the majority of existing studies investigating the interplay between lateral and vertical dynamics use simplified modeling approaches, and they do not consider that marsh retreat can affect the regional‐scale hydrodynamics and sediment retention in back‐barrier basins. In this study, we evaluated the fate of the sediments originating from marsh lateral loss by using high‐resolution numerical model simulations of Jamaica Bay, a small lagoonal estuary located in New York City. Our findings show that up to 42% of the sediment released during marsh edge erosion deposits on the shallow areas of the basin and over the vegetated marsh platforms, contributing positively to the sediment budget of the remaining salt marshes. Furthermore, we demonstrate that with the present‐day sediment supply from the ocean, the system cannot keep pace with sea level rise even accounting for the sediment liberated in the bay through marsh degradation. Our study highlights the relevance of multiple sediment sources for the maintenance of the marsh complex. Key Points: The sediment eroded from marsh edges helps to build the remaining marshesMarsh erosion has a twofold effect: more sediment available for the remaining marshes but decrease in the trapping capacity of the lagoonManagement actions should consider the effects associated with wetland edge erosion at basin scale [ABSTRACT FROM AUTHOR]

Detrital zircon (DZ) analysis has become the standard tool for source‐to‐sink sediment routing studies at many spatial and temporal scales. In North American source‐to‐sink studies, DZ distributions are commonly classified according to the presence/absence and proportions of DZ age groups associated with North American crustal provinces as well as peri‐Gondwanan and Cordilleran terranes. Although such a classification scheme is descriptive, these age groups typically do not uniquely identify most recent DZ source areas. Using a compilation of >19,000 individual DZ ages for Mesoproterozoic‐Paleogene strata of the northern Rocky Mountains, including 2,053 new analyses from the Paleogene Renova Formation and its equivalents in southwestern Montana, we demonstrate periodic derivation of first‐cycle DZ from crystalline sources and widespread recycling of poly‐cycle DZ from sedimentary sources over multimillion‐year timescales. Results show that (1) DZ age distributions become increasingly complex between Mesoproterozoic and Paleogene time with the introduction of new DZ sources to the study area, but (2) once an age group appears in the northern Rocky Mountains stratigraphy, grains of that age persist up‐section. These trends show that most DZ age groups are spatiotemporally ubiquitous and nonunique. We largely attribute this to periodic, tectonically induced recycling of DZ into progressively younger sedimentary systems, rather than prolonged derivation of DZ from crystalline basement sources, a trend that reflects the growth of increasingly complex topography associated with the North American Cordillera. Key Points: Detrital zircons with North American basement ages are spatiotemporally ubiquitous in the stratigraphy of western North AmericaUbiquity is due to orogenic recycling of detrital zircons through multiple phases of basin evolutionThe presence of North American basement ages alone does not identify unique sediment source areas [ABSTRACT FROM AUTHOR]

Mafic arc igneous rocks with oceanic crust-derived fluids in their mantle sources generally show heavy Mo isotope compositions. However, these rocks may exhibit variable Mo isotope compositions due to involvement of seafloor sediments under different redox conditions. Thus, it is intriguing how Mo isotope recycles with sediment subduction and how Mo isotope fractionation occurs during this process. Here we report Mo isotope data for Paleozoic mafic arc igneous rocks from the Qinling-Tongbai orogenic belt in Central China. The Qinling mafic rocks have δ98Mo values of −0.03 to 0.40‰, and the Tongbai mafic rocks have δ98Mo values of −0.26 to 0.17‰. These values are considerably higher than the normal mantle values of −0.20 ± 0.01‰. In combination with low Mo/Ce ratios, enriched Sr Nd isotope compositions, and high melt-mobile incompatible trace element contents for these rocks, the high δ98Mo values suggest that anoxic sediment-derived melts with heavy Mo isotopes were incorporated by oceanic subduction into the mantle sources. The high δ98Mo values of the mafic rocks indicate the limited Mo isotope fractionation during subduction of the anoxic sediment. This inference is further verified by modeling of Mo isotope fractionation under reducing conditions in the subduction zone. In this regard, Mo isotopes can be used to identify the recycling of sediments in different types and thus provide geochemical constraints on the redox conditions of oceanic subduction zones. [ABSTRACT FROM AUTHOR]

Sediment recycling has important impacts on the differentiation of the continental crust, and is considered to mainly occur in arc settings. In collisional orogenic belts, however, sediment recycling processes are comparatively less well understood. In general, sedimentary rocks or tourmaline with continental affinities have boron (B) isotope compositions that differ from marine sedimentary rocks, magmatic rocks undergoing seawater alteration or tourmaline originating from these rocks or fluids. This study uses laser-ablation multi-collector, inductively coupled plasma-mass spectrometry (LA-MC-ICPMS) for in-situ B isotope analyses of tourmaline from the northern and southern margins of Tibet. Tourmalines from the Hudongliang Pliocene two mica rhyolites in the Songpan-Gangzi block and the Cuonadong Miocene two mica granites in the Himalayan Block have δ11B values of −10.47 ± 0.54‰ and −12.48 ± 1.04‰, respectively. Combined with petrological and Nd–Sr isotope data, we suggest that these strongly peraluminous magmatic rocks from the northern and southern margins of Tibet were mainly generated by partial melting of subducted or overridden metasedimentary rocks with continental affinities due to the contraction caused by the collision between the Indian and Asian plates. Given the widespread occurrences of strongly peraluminous Neogene magmatic rocks in the southern and northern margin of Tibet, we suggest that the recycling of sediments with continental affinity played an important role in the evolution of continental crust during the collisional orogenic process.

Abstract This work aims to unravel the provenance, depositional tectonic setting and source area weathering of the cretaceous Debre Libanos Sandstone in the Blue Nile Basin, Ethiopia from its petrographic and geochemical signatures. Both the average chemical index of alteration (CIA) and chemical index of weathering (CIW) of sandstones (CIA = 91.08, CIW = 96.75), shales (CIA = 81.89, CIW = 98.17) and siltstones (CIA = 98.10, CIW = 99.35) of the Debre Libanos Sandstone indicate very strong chemical weathering. The low Th/Sc ratio of sandstones (1.46), shales (0.85) and siltstones (0.81), and Th/Sc versus Zr/Sc relationship indicate sediment recycling that leads to a progressive enrichment of heavy minerals such as zircon which is the major host for Zr and Th. The increase of quartz content in sandstones and dense minerals in siltstones and shales can be related to hydraulic sorting, grain-size controlled fractionation and source composition. Trace element concentration and their ratios (La/Th, Cr/Th, Th/Sc, Cr/V, Y/Ni) with rare earth element proxies (Eu/Eu*, La N /Yb N) of the studied samples revealed felsic to mixed source rocks of upper continental crust with some input from recycled old sediments. The source area of the Debre Libanos Sandstone is from the northern and northwestern Ethiopia during the time of marine regression, retreat of the Indian Ocean from NW Ethiopia back to SE Somalia. Tectonic discrimination diagrams revealed continental rift setting for the sandstones and collision setting for shales and most of the siltstones. Furthermore, the studied sandstones were partly deposited in a passive margin setting which had undergone post-depositional K-metasomatic alteration. The shales and siltstones were deposited in active margin setting. [ABSTRACT FROM AUTHOR]

Abstract In this study, we present the element geochemical data of Core XK08-A2 drilled from Lake Xingkai (Khanka), northeast China. The study aims to examine the changes of sediment provenance and geochemical composition in response to Asian summer monsoon variability since the last interglacial period. Major elemental analyses on lacustrine samples and sand samples from Lake Xingkai and the surrounding sandy ridges in northeast China indicate that their abundance varied in relatively narrow ranges. The samples had only undergone the primary stage of chemical weathering. Similar Ti/Al and K/Al ratios between the lacustrine samples from Lake Xingkai and the loess-paleosol samples in north China were observed, which suggests that they come from broadly similar desert sources. Due to the significant dependence on grain-size and influence of sediments recycling, Chemical Index of Alteration of the lacustrine sediments could not be regarded as sensitive indicators of source regions' weathering on the glacial-interglacial timescale. Alternatively, the geochemical proxies of the lacustrine sediments could be linked to the Asian summer monsoon through the development of runoff and physical erosion in the catchment. Weakened Asian summer monsoon caused more fine particles transported to the lake basin by reduced runoff in the last glacial period. In contrast, coarser and less-weathered detritus are transported into the lake accompanying strengthened Asian summer monsoon during the warm periods. Highlights • Lacustrine sediments from Lake Xingkai are likely lacustro-aeolian deposits. • Chemical weathering indices are grain-size dependence and influenced by recycling. • Less-weathered detritus are transported into the lake accompanying strengthened runoff transporting capacity. [ABSTRACT FROM AUTHOR]

This paper revisits the intermediate sediment repository (ISR) concept applied to provenance, using a comparison of the detrital zircon population of Holocene beach sand from the southwest Portuguese coast with populations from their potential source rocks. The U–Pb age of detrital zircon grains in siliciclastic rocks allows for the interpretation of provenance by matching them with the crystallization ages of igneous source (protosource) rocks in which this mineral originally crystallized or which was subsequently recycled from it, acting as ISRs. The comparative analysis of the Precambrian, Paleozoic, and Cretaceous ages using recent statistical tools (e.g., kernel density estimator (KDE), cumulative age distribution (CAD), and multidimensional scaling (MDS)) suggests that the zircon age groups of Carboniferous, Triassic, and Pliocene-Pleistocene ISRs are reproduced faithfully in Holocene sand. Furthermore, the recycling of a protosource (Cretaceous syenite) in a sedimentary system dominated by ISRs is evaluated. It is argued that the ISR concept, which is not always taken into account, is required for a better understanding of the inherent complexity of local provenance and to differentiate sediment recycling from first- cycle erosion of an igneous rock.

Lattice fixed nitrogen component in arc lavas from Kick'em Jenny (KEJ) was investigated for improving our understanding of two long-standing controversies in the recycling of subducting slab material. One is whether the crustal signatures in the Lesser Antilles arc rocks originated from slab recycling or crustal assimilation. The other is the budget of fixed nitrogen in arc crust, which is still a missing piece in the modeling of geodynamic nitrogen cycle. Our results show that the KEJ basaltic lavas contain variable amounts of labile nitrogen (removable by 400 °C heating) and 2.6–5.3 ppm refractory nitrogen with δ 15 N values of +0.8‰ to +6.6‰. The labile nitrogen was likely introduced on seafloor although the KEJ lavas appear to be strikingly fresh, whereas the refractory nitrogen was likely inherited from their magmatic source. Nitrogen isotopic signature of the refractory nitrogen cannot be explained by magmatic degassing, fractional crystallization and/or crustal assimilation. Instead, the data can be best explained by a mixing between the mantle and two δ 15 N-distinct endmembers, which are consistent with the two types of subducting sediments (i.e., marl/ooze and shale) recovered from the reference site (DSDP Site 144). This supports sediment recycling into the mantle source of the Lesser Antilles arc. Our modeling also yielded a nitrogen fixation flux of 2.3–4.7 × 103 moles N⋅yr ⋅ − 1 km−1 (or 1.8–3.8 × 106 moles N⋅yr−1 for the 800 km arc) in the Lesser Antilles arc crust. This is 2–3 orders of magnitude smaller than the nitrogen input flux into the Lesser Antilles trench solely from subducting sediments (1.3 × 106 moles N⋅yr ⋅ − 1 km−1 or 1.0 × 109 moles N⋅yr−1 for the entire 800 km trench). This suggests that arc crust is not a major repository of subducted nitrogen, at least in the Lesser Antilles. Instead, most of the crustal nitrogen subducted to the sub-arc depths is either retained in the subducting slab, stored in the metasomatized lithospheric mantle, and/or released back to the surface by volcanic emission. • N fixed in the Kick'em Jenny arc lavas show crustal isotopic signatures. • Little N isotopic effect from magmatic degassing and AFC processes. • Our data support recycling of both marl/ooze and shale below the Lesser Antilles arc. • 80–90% of the N in the arc lavas originated from recycled sediments. • N budget in the arc crust only accounts for <0.3% of the N in the subducting slab. [ABSTRACT FROM AUTHOR]

Abstract Negative Cerium (Ce) anomalies are observed in chondrite-normalized Rare Earth Element patterns from various volcanic arc suites. These anomalies are well defined in volcanic rocks from the Mariana arc and have been interpreted as the result of addition of subducted sediments to the arc magma sources. This study combines 143Nd/144Nd and 138Ce/142Ce isotope measurements in Mariana volcanic rocks that have Ce anomalies ranging from 0.97 to 0.90. The dataset includes sediments sampled immediately before subduction at the Mariana Trench (Sites 801 and 802 of ODP Leg 129) and primitive basalts from the Southern Mariana Trough (back-arc basin). Binary mixing models between the local depleted mantle and an enriched end-member using both types of sediment (biosiliceous and volcaniclastic) found in the sedimentary column in front of the arc are calculated. Marianas arc lavas have Ce and Nd isotopic compositions that require <2.5% of a sediment component derived from the volcaniclastics. With this proportion of sediment, most of the Ce/Ce* range measured in lavas is reproduced. Thus, this study confirms that the origin of the Ce anomalies in the Mariana arc magmas can be principally attributed to recycling of trench sediments through active subduction. The participation of a component derived from biosiliceous sediments does not explain the Ce-Nd isotope composition of the lavas because the involved proportion is too high (up to 8%) in comparison to results obtained from other geochemical proxys. Using this end-member, the modeled Ce anomalies are also too high (0.91–0.84) in comparison to those measured in lavas. Various processes and conditions are able to generate Ce anomalies: oxygen fugacity, residual mineral phases, partial melting, fractional crystallization and tropical weathering. Their influence in the case of Mariana volcanic arc magmas seems to be very limited but partial melting effect may explain the lowest measured Ce/Ce* values. Magmatic processes cannot be definitely ruled out in producing Ce anomalies in other arc system environments. Additional experimental data, however, are needed for a better understanding of the behavior of cerium relative to its neighboring elements. Also, this study highlights the importance of using local depleted mantle and sediments to model the isotopic compositions of arc lavas. Highlights • Origin of negative Ce anomalies in Mariana arc magmas. • Coupled 138Ce/142Ce and 143Nd/144Nd isotope measurements in Mariana arc magmas, sediments and back-arc basalts. • Ce-Nd isotopic binary mixing models coupled with Ce/Ce* prove that volcaniclastics control the Ce/Ce* in Mariana lavas. [ABSTRACT FROM AUTHOR]

Detrital zircon U–Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia. [ABSTRACT FROM AUTHOR]

Highly variable molybdenum (Mo) isotope compositions have been reported for mafic arc volcanics above oceanic subduction zones. The heavy Mo isotope signatures of mafic arc magmas are generally attributed to addition of high δ98Mo oceanic crust-derived fluids to the subarc mantle sources. However, subduction zone fluids at subarc depths may occur in the forms of aqueous solution and hydrous melts, and seafloor sediments would also be subducted to subarc depths to produce hydrous melts. If such sediment-derived melts were incorporated into the mantle wedge, it is intriguing what is their effect on the Mo isotope composition of mafic arc magmas. Here we report Mo isotope data for Early Jurassic mafic igneous rocks from Northeast China, which was an active continental margin during subduction of the Paleo-Pacific Plate in the Mesozoic. These rocks have δ98Mo values of −0.26‰ to 0.17‰, which are mostly higher than the normal mantle value of −0.20‰ ± 0.01‰. They also exhibit arc-like trace element compositions, moderate (87Sr/86Sr) i ratios of 0.7042 to 0.7047, and neutral ε Nd (t) values of −2.8 to 2.2. The high δ98Mo values are associated with low Mo/Ce ratios, enriched Sr Nd isotopes, and high melt-mobile element contents in the mafic igneous rocks. These geochemical features indicate that the heavy Mo isotope signatures in these rocks were mainly inherited from subducting sediment-derived melts. Subducting Paleo-Pacific oceanic crust-derived aqueous solutions and seafloor sediment-derived hydrous melts would metasomatize the overlying mantle wedge beneath the northeastern China continent, and the sediment-derived melts would have contributed the heavy Mo isotope signatures to the mantle sources of mafic arc magmas in the active continental margin. Therefore, the Mo isotope study of mafic igneous rocks is a powerful means to decipher the recycling of crustal components at convergent plate margins. [ABSTRACT FROM AUTHOR]

Sand grains from Quaternary glacial, aeolian and fluvial deposits in the Mazovian Lowland, central Poland, were examined to characterize the effects of different Quaternary processes on sand-grain surfaces that experienced repeated cycles of intense polar-desert-like conditions during the Middle and Late Pleistocene. A cold, dry and windy periglacial environment prevailed here at least twice between the Saalian (Marine Isotope Stage (MIS) 6) and Holocene (MIS 1) stages. Because the surface characteristics of quartz sand grains can provide important palaeoenvironmental information, we examined grains extracted from sediment samples in different landforms to determine their surficial features from scanning electron microscope images. The grain surfaces were dominated by microtextures characteristic of aeolian-induced grain transformation, indicated by a high percentage of well-rounded, low-relief-worn grains with dish-shaped depressions, bulbous edges and upturned plates. Although remnants of previous sedimentary cycles were occasionally observed, aeolian effects were dominant even in glacial and fluvial settings. Quartz microtextures indicated that none of the examined grains represented their original setting, but rather suggested remobilisation under periglacial conditions. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As a result of recycling, the mineralogical and chemical compositions of riverine sediments may reflect the combined effects of the present-day weathering regime as well as previous weathering and diagenetic alteration history. River sediments can be interpreted as a mixture of non-weathered bedrock-of igneous, metamorphic, or sedimentary origin-and solids formed by the modern weathering system. The correlation between the weathering proxies chemical index of alteration and weathering index of Parker offers an approach to distinguish fine suspended particles, coarse bedload sediments, and recycled sediments under the influence of quartz dilution. Recycling of cation-depleted source rocks formed during past geological weathering episodes may have great impacts on the weathering indices of sediments from the Changjiang (Yangzte) and Zhuoshui Rivers. Special caution is required when using chemical weathering indices to investigate the intensity of chemical weathering registered in fluvial sediments. To minimize the effect of hydrodynamic sorting or sediment recycling, we suggest that the fine sediments (e.g. suspended particles and <2 μm fractions of bedload sediments) in rivers better reflect the average of weathered crust in catchments and the terrigenous end-member in marginal seas. [ABSTRACT FROM AUTHOR]

Felsic igneous rocks are common constituents of volcanic arcs, and contain valuable information about subduction-related magmatism. In this study we investigate nine granitoids with S-type volcanic arc affinity from the Chinese Altay, emplaced from 507 to 391 Ma in an active subduction zone during the early–middle Paleozoic. These granitoids are characterized by moderate to high SiO 2 contents (61.01–75.30 wt.%), moderate total alkalis (Na 2 O + K 2 O, 3.43–7.64 wt.%), and high Al 2 O 3 contents (13.29–17.18 wt.%). Negative εNd(t) values (− 6.1 to − 1.0), the wide range of εHf(t) values (− 7.0 to + 9.0), and enrichment of LILEs such as Pb, Th and U, all suggest that the granitoids were probably derived from the partial melting of subducting oceanic sediments and the associated mantle wedge. This inference is further supported by the Nd-isotope data. The high initial 87 Sr/ 86 Sr ratios (0.703963–0.719428), low Ba/Th ratios (7.00–118.93), and uniformly negative εNd(t) values (− 6.1 to − 1.0) indicate that slab-derived aqueous fluids were vital in generating the initial magma of these granitoids, and assimilation played only a minor role. Our data demonstrate that residual zircon retains a substantial amount of Hf during the partial melting of oceanic sediments, therefore, Hf may not be an effective tracer for the input of recycled sediments. We conclude that sediment recycling played an important role in the generation of arc magmatism and the growth of the Central Asian Orogenic Belt (CAOB). [ABSTRACT FROM AUTHOR]

Deciphering the slab melt contribution to arc igneous rocks in orogenic belts is of great importance for unraveling the fate of subducted slabs, adakite petrogenesis and geochemical recycling process. The fact of subducted slabs, particularly how different sections of the oceanic crust including its overlying sediment react during slab melting, remains poorly understood. Here we present a detailed study of the Leigongshan (LGS) tonalite pluton in the eastern section of the North Qilian suture zone (NQSZ). The tonalites are geochemically similar to low-Mg adakitic rocks characterized by high Sr/Y and (La/Yb) N ratios with low MgO, Cr, and Ni concentrations, indicating limited/no mantle interaction. They exhibit moderately radiogenic Sr, Nd, and Pb isotope compositions with initial 87Sr/86Sr ratio of 0.706216–0.708267, εNd(t) value of −0.7 to −2.1 and (206Pb/204Pb) t of 18.52–18.90, most likely a mixed melt derived from the mafic oceanic crust plus ca. 10–25% overlying sediments. Morphology, internal structure, and U Pb dating of zircon crystals indicate a common preservation of old cores aged at ca. 470–2733 Ma. The sharp truncation of core zoning and embayed boundaries with the rims further indicate that the cores are probably clastic, abraded materials inherited from a (meta)sedimentary precursor from which the tonalitic magma was derived. The younger mean ages of ca. 453–450 Ma are interpreted as the emplacement age of the pluton. They have ε Hf (t) values of +0.5–7.0 and δ 18 O Zrc values of 4.9‰ to 8.7‰, which somewhat deviate from those of the parent mafic oceanic crust, indicating the involvement of subducted sediments as well. The LGS adakitic tonalite represents mixed melts of the subducted slab including the overlying sediment that accounts for the enriched Sr–Nd–Pb isotope compositions. Future detailed research on the zircons of adakite/adakitic rocks would provide new important clues on their petrogenesis. • Newly identified old zircon cores (ca. 470–2733 Ma) are clastic, abraded materials inherited from a sedimentary precursor. • Bulk-rock Sr–Nd–Pb and zircon Hf O isotopes confirm the contribution of oceanic crust with ca.10–25% subducted sediments. • Sediment contribution to slab melts accounts for the enriched bulk-rock isotopes (also common in LCC-derived adakitic rocks). [ABSTRACT FROM AUTHOR]

Although it has been argued that sediment recycling plays an important role in the differentiation of the continental crust, boron (B) isotopic data does not support a direct input of subducted sediments into arc magmas. This raises questions about the viability of sediment recycling as a process in the differentiation of continental crust. Here, we report B isotopic data from Miocene–Quaternary lavas derived from different sources in the northern margin of Tibet. These lavas have high B contents and negative δ11B values close to those of continental sediments. Strongly peraluminous rhyolites have the highest B (93 to 1559 ppm) contents with negative δ11B (−9.7 to −17.9) values. Adakitic dacites and trachyandesites exhibit the lowest B (18 to 29 ppm) contents with markedly negative δ11B (−12.0 to −35.7) values whereas olivine leucitites have B (37.2 to 59.3 ppm) contents with negative δ11B (−8.3 to −15.6) values. These lavas also have enriched Hf-Pb-Nd isotopic compositions similar to those of sediments. This data, combined with numerical modelling and geophysical and tectonic data for Cenozoic continental subduction in the northern margin of Tibet, indicates that: (1) the strongly peraluminous rhyolites were generated by partial melting of mica-bearing continental sedimentary rocks subducted to the depth of mid-to-lower crust; (2) adakitic lavas were derived by partial melting of sediment-bearing thickened lower crust underwent dehydration and eclogites-facies metamorphism; and (3) olivine leucitites were generated by partial melting of enriched mantle metasomatized by sediment-bearing eclogite-facies crust-derived melts. Thus, at continental convergent margins, continental subduction is an important mechanism for sediment recycling and the evolution of continental crust. • B-Hf-Pb-Nd isotopes show that subducted continental sediments entered the mid-to-lower crust and mantle of northern Tibet. • Subducted sediments in mid-to-lower crust and mantle were recycled to the continental crust via magmatism. • Continental subduction is an important mechanism for sediment recycling and the evolution of continental crust. [ABSTRACT FROM AUTHOR]

In order to improve techniques for provenance studies, and especially to address the question of sediment recycling, morphological changes of two minerals with contrasting durability (zircon and apatite) were tracked during both fluvial transport and littoral reworking. The Sefidrud river system in northern Iran, which drains the Alborz volcano-sedimentary range into the Caspian Sea, and the Sarbaz river system in southeastern Iran, which drains the Makran Accretionary Prism into the Oman Sea, were chosen for this study. To determine source rocks of the grains, and thus their nature in terms of sedimentary cycles, zircon geochronology was conducted on both rivers. The zircon data indicate that most of the Sefidrud sediments are first cycle, derived from crystalline rocks, and the Sarbaz sediments are generally recycled from older wedges of the Makran. Results from SEM analysis show significant differences between the roundness of associated zircon and apatite grains. Zircon grains remain unrounded through several cycles, while apatite grains show abrasion from the early stages of their first cycle. [ABSTRACT FROM AUTHOR]

Detrital zircons from Holocene beach sand and igneous zircons from the Cretaceous syenite forming Cape Sines (Western Iberian margin) were dated using laser ablation - inductively coupled plasma - mass spectrometry. The U-Pb ages obtained were used for comparison with previous radiometric data from Carboniferous greywacke, Pliocene-Pleistocene sand and Cretaceous syenite forming the sea cliff at Cape Sines and the contiguous coast. New U-Pb dating of igneous morphologically simple and complex zircons from the syenite of the Sines pluton suggests that the history of zircon crystallization was more extensive ( ca 87 to 74 Ma), in contrast to the findings of previous geochronology studies ( ca 76 to 74 Ma). The U-Pb ages obtained in Holocene sand revealed a wide interval, ranging from the Cretaceous to the Archean, with predominance of Cretaceous (37%), Palaeozoic (35%) and Neoproterozoic (19%) detrital-zircon ages. The paucity of round to sub-rounded grains seems to indicate a short transportation history for most of the Cretaceous zircons ( ca 95 to 73 Ma) which are more abundant in the beach sand that was sampled south of Cape Sines. Comparative analysis using the Kolmogorov-Smirnov statistical method, analysing sub-populations separately, suggests that the zircon populations of the Carboniferous and Cretaceous rocks forming the sea cliff were reproduced faithfully in Quaternary sand, indicating sediment recycling. The similarity of the pre-Cretaceous ages (> ca 280 Ma) of detrital zircons found in Holocene sand, as compared with Carboniferous greywacke and Pliocene-Pleistocene sand, provides support for the hypothesis that detritus was reworked into the beach from older sedimentary rocks exposed along the sea cliff. The largest percentage of Cretaceous zircons (< ca 95 Ma) found in Holocene sand, as compared with Pliocene-Pleistocene sand (secondary recycled source), suggests that the Sines pluton was the one of the primary sources that became progressively more exposed to erosion during Quaternary uplift. This work highlights the application of the Kolmogorov-Smirnov method in comparison of zircon age populations used to identify provenance and sediment recycling in modern and ancient detrital sedimentary sequences. [ABSTRACT FROM AUTHOR]

Laser ablation ICP-MS U–Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U–Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U–Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa–Morena and Central Iberian zones that outcrop in and close to the Porto–Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian–Carboniferous ages (< ca. 315 Ma) found in detrital zircons provide evidence of the denudation of Variscan and Cimmerian granites during the infilling of continental rift basins in western Iberia. The zircon age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U–Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia. [ABSTRACT FROM AUTHOR]

The Upper Devonian Munster Basin of southern Ireland has traditionally been viewed as a post-orogenic molasse deposit that was sourced from the Caledonides of central Ireland and subsequently deformed by the end Carboniferous Variscan orogenic event. The basin fill is composed of super-mature quartz arenite sandstone that clearly represents a second cycle of deposition. The source of this detritus is now recognized as Lower Devonian Dingle Basin red bed sequences to the north. This genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units; micas plot in identical fields and define the same trends. In addition, the two sequences show increased textural and chemical maturity up-sequence and define indistinguishable 40 Ar/ 39 Ar age ranges for the detrital mica grains. Partial resetting of the Ar ages can be attributed to elevated heat flow in the region caused by Munster Basin extension and subsequent Variscan deformation. The combined evidence from southwest Ireland therefore points to a Caledonian or possibly Taconian primary source area that initially shed detritus into the Lower Devonian Dingle Basin which was subsequently recycled into the Upper Devonian Munster Basin following mid-Devonian Acadian basin inversion. [ABSTRACT FROM AUTHOR]

The relationship between tectonic uplift, climate change and continental silicate weathering has long been debated because deconstructing the tectonic and climatic impacts on continental silicate weathering is challenging. To address this issue, we present long-term climatic and silicate weathering records since 7.3 Ma on tectonically active NE Tibet retrieved from the SG-1 and SG-1b lake sediment drill cores in the western Qaidam Basin. We find distinct correlations between silicate weathering and regional climate on long-term (>106 years) and short-term (105–106 years) time scales. On long-term scales, silicate weathering intensity exhibits a consistent evolution with regional climate, both of which are dominantly controlled by global climate change. This evolution resulted in a stable weathering intensity during 7.3–~3.6 Ma and a weakening of weathering intensity since ~3.6 Ma, followed by a continuous decreasing trend after 2.6 Ma. However, on short-term scales, silicate weathering intensity displays out-of-phase changes with the regional climate at 6.9–3.7 Ma and 0.2–0.1 Ma and in-phase changes at 7.3–6.9 Ma and 3.7–0.2 Ma. We attribute this long-term consistency between the weathering intensity and climate to aridification in inland Asia, but the short-term inconsistencies at 6.9–3.7 Ma and 0.2–0.1 Ma to the change in the sediment routing system impacted by the regional climate within a tectonically active setting. Such a change in the sediment routing system along with sediment recycling may bias weathering indication on orbital time scales, and our study therefore suggests a more complex response of silicate weathering to tectonic and climatic forcings. [Display omitted] [ABSTRACT FROM AUTHOR]

Mineralogical and textural analyses of 45 undisturbed short cores and 80 grab sediment samples, collected from five frequently dredged navigational areas within harbors and water pathways of the Nile delta littoral system, were utilized for evaluation of these sediments as potential source of economic heavy minerals (EHMs). Results of mineralogical characterization indicate that the average total heavy mineral (HM) concentrations are as follows: Abu Qir Bay (1.7%), Rosetta estuary (3.1%), Burullus fishing port (4.5%), Damietta Harbor (2.9%), and El Gamil lagoon inlet (1.9%). Assessment of HM grades indicates predominance of magnetite, ilmenite, hematite, leucoxene, garnet, zircon, and rutile. Results of the feasibility analysis indicate that dredged sediments at these study areas are considered as a potential source of EHMs and economically promising to be mined for HMs. The present study suggests a practical operative plan of two successive phases for HMs recycling: (1) in-situ initial separation of HMs on the dredger deck using wet-gravity spirals, then (2) transportation of the recovered HM concentrates to an onshore processing plant to selectively separate individual HMs via wet and dry magnetic and electrostatic separators. Alternatively, dredged sediments can be directly pumped to a nearby onshore area as stockpile to be recycled afterward in inland processing plant. [ABSTRACT FROM AUTHOR]

We present new He-Sr-Nd-Pb-Os isotopic compositions and major and trace-element concentrations for ten subaerially-erupted lavas and one seamount lava associated with the Pitcairn hotspot. The most geochemically-enriched lavas at the Pitcairn hotspot have signatures that are consistent with recycled sediments derived from upper continental crust. Pitcairn lavas have elevated Ti, which also supports the presence of a mafic protolith in the Pitcairn mantle. A subset of Pitcairn seamount samples, including the seamount sample presented here, are tholeiitic. Tholeiitic lavas are uncommon at ocean hotspots located far from mid-ocean ridges. Like tholeiites that erupted in Hawaii, the presence of tholeiites in the Pitcairn magmatic suite can be explained by melting a silica-saturated recycled mafic component in the Pitcairn mantle source. We also present the highest 3 He/ 4 He ratio (12.6 Ra, ratio to atmosphere) from the Pitcairn hotspot. This sample anchors the high 206 Pb/ 204 Pb portion of the Pitcairn array and provides evidence for a plume component in the Pitcairn mantle. In contrast, Pitcairn lavas that have the lowest 206 Pb/ 204 Pb are the most geochemically enriched, and have the highest 87 Sr/ 86 Sr and lowest 143 Nd/ 144 Nd in the Pitcairn suite; these EM-1 end-member lavas have MORB-like 3 He/ 4 He (~ 8 Ra, ratio to atmosphere). Recycled oceanic crust and sediment suggested to be in the Pitcairn EM-1 mantle are expected to have low 3 He/ 4 He (< 0.1 Ra). Therefore, the higher, MORB-like 3 He/ 4 He in Pitcairn EM-1 lavas is paradoxical, but might be explained by diffusive exchange of helium, but not the heavy radiogenic isotopes, with the ambient mantle over billion-year timescales. [ABSTRACT FROM AUTHOR]

Management of port development is increasingly challenging because of the competitive requirement for deeper channels and because of the need to preserve important coastal wetlands which function as both habitat and flood defence. This paper describes the management of the Stour/Orwell Estuary system, Eastern England, an estuary system which has experienced considerable development and morphological change. The estuary is internationally important for its wetland bird populations and the intertidal areas of the estuary system are protected under European legislation. It is also the location of the Port of Felixstowe. In 1998/2000 the approach channel to the Port of Felixstowe was deepened from −12.5 mCD to −14.5 mCD. This paper describes the effects of the approach channel deepening, the approach taken to identifying the potential impact to intertidal habitat resulting from the deepening, the sediment recycling implemented as mitigation to prevent increased loss of habitat and the subsequent response of the estuary system to this intervention. [ABSTRACT FROM AUTHOR]