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In-field compositional analysis of large prehistoric relics, such as the Altar Stone at Stonehenge (England), is limited due to the size of the relics and difficulty in obtaining samples that can be analyzed in a laboratory. In this study, a portable Raman spectroscopy system was used to analyze the Altar Stone to help determine its origin and classification, which appears to differ from other bluestones at Stonehenge. While the study is ongoing and the definitive origin of the Altar Stone is not yet known, this study demonstrates the applicability of a portable Raman spectroscopy system in the compositional analysis of large samples in the field.

The Thar Desert is a major sediment depocenter located in southwestern Asia and bordering the Indus drainage system to its east. It is unclear where the sediment that built the desert is coming from, and when the desert experienced phases of construction. In particular, we seek to establish the role of the South Asian monsoon in the initial formation and subsequent expansion of the desert. Here we integrate bulk-petrography and heavy-mineral data with U-Pb ages of detrital zircon grains to understand how the Thar Desert relates to the major potential sediment sources in the Himalayan orogen and to the large rivers that adjoin it to the west and north. Bulk petrography and heavy-mineral data from eolian sand in Cholistan (NE Pakistan) show closer similarity with that of Himalayan tributaries than eolian sand in Sindh (S Pakistan), which contains heavy-mineral suites close to those of mainstream Indus sand largely supplied by erosion of the Karakorum and Kohistan ranges. Kohistan is a particularly rich source of heavy minerals and is thus over-represented in provenance budgets based on that proxy alone. U[sbnd]Pb ages of detrital-zircon fail to show a sharp difference between dune sands in Sindh and Cholistan but confirms a somewhat greater supply from the Himalaya in Cholistan and from the Karakorum, Kohistan, and Nanga Parbat in Sindh. Zircon ages are similar in Sindh desert sand and in the Indus Delta, and are most similar to deltaic sand dated as 7 ka or older in the deglacial period. In parallel, the age signature of Cholistan sand resembles more that of older river channels found along the northwestern edge of the desert (e.g., paleo-Ghaggar-Hakra) than that of modern Himalayan tributaries (e.g., Sutlej). Both Cholistan and Sindh sands suggest that sediment supply to the desert was greater during the early Holocene when the summer monsoon was stronger. The southwesterly summer monsoon was the most effective agent of eolian transport and recycling of Indus delta

Detrital geochronology employing the widely-used zircon U-Pb proxy is biased toward igneous events and metamorphic anatexis; additionally, zircon is highly refractory and frequently polycyclic. Garnet, a rock-forming and thus commonly occurring mineral, is predominantly metamorphic and much less refractory. Here, we report in situ U-Pb and Lu-Hf ages from detrital garnet hosted in ancient and modern sediments of the European Alps. Both geochronometers are biased toward the most recent garnet-crystallizing metamorphic event in the source area, with fewer inherited ages. This likely reflects efficient removal of inherited garnet during diagenesis and metamorphism, and is in contrast to detrital zircon, apatite, and rutile U-Pb data, which largely record pre-Alpine ages. Neither the U-Pb nor Lu-Hf system in garnet exhibits a relationship between age recovery and composition. However, the Lu-Hf system in garnet yields significantly better age recovery than the U-Pb system. Estimated initial 238U/206Pbc values at the time of crystallization are near unity, suggesting that garnet does not significantly partition U from Pb during crystallization, at least for the generally almandine-rich garnets analyzed in this study. Hence, Lu-Hf geochronology of detrital garnet offers an effective method to detect and date the most recent phase of mid-grade metamorphism in sub-anatectic source areas, in which detrital zircon U-Pb analysis may be of less utility.

There is no consensus about the geological nature of the westernmost portion of the Iberian Massif. In the present research, the detrital zircon U–Pb signatures of Jurassic strata of the Lusitanian Basin, known to be west-sourced, are combined with published U–Pb data for the Precambrian-Palaeozoic basement and other Lusitanian Basin units to better understand this poorly exposed portion of the Iberian Massif. Cryogenian to Ediacaran ages prevail in a northern Upper Jurassic unit, while Lower and Upper Jurassic rocks in southern locations yield mostly Carboniferous to upper Permian zircons. These age results, coupled with their respective U/Th ratios, suggest that the basin covers two distinct terranes of the Iberian Massif. Another noteworthy feature of west-derived deposits is the abundance of < 310 Ma ages. It is proposed that a combination of crustal thinning in the West Iberian Margin with regional eastward basement tilt, favoured the enrichment of relatively young zircon in the western shoulder of the basin relative to its eastern margin. The detrital zircon age signatures also reveal a middle to late Permian thermal event in restricted areas, which is probably associated with the oldest stages of Alpine extension in West Iberia.

In this study, we use provenance analysis to shed light on the Neogene evolution of river drainage and sediment dispersal in eastern Asia as a consequence of the Himalayan orogeny and topographic rise of the Tibetan Plateau. As an attempt to envisage how sediment-routing systems operated in the past, and to identify the ultimate source of siliciclastic detritus originally generated in mainland China and now incorporated in, and recycled from, the western Taiwan accretionary prism, we have used Raman spectroscopy of detrital garnet in modern river sands and upper Neogene sandstones, complemented by detrital-zircon geochronology and by petrographic and heavy-mineral analysis. Garnet grains are relatively abundant and largely represented by almandine with various percentages of pyrope molecules in Yangtze sand as in western Taiwan sandstones and modern river sand derived from them. Instead, they are rare and largely represented by grossular or andradite in the sand of the Pearl River and of coastal rivers of SE China facing the Taiwan Strait. This finding supports the result of detrital geochronology, which documents a sharp difference between U-Pb age spectra of Pearl River and coastal SE China zircons (characterised by a Paleozoic-Mesozoic triple peak) and Yangtze and western Taiwan zircons (characterised by prominent Neoproterozoic, Paleoproterozoic, and latest Archean clusters). The Pearl River and minor rivers facing the Taiwan Strait are thus ruled out as ultimate sources of upper Neogene sandstones exposed today along the western front of the Taiwan fold-thrust belt. In the envisaged scenario, sand mostly supplied by the paleo-Yangtze River was entrained for ~ca.1,000 km southward by longshore currents and deposited on the Chinese passive margin before being accreted along the front of the Taiwan orogen since ~6 Ma. Littoral sand drift represents a major factor of long-distance sediment transport in modern shelves and needs to be taken into full accoun

Together with the companion article dedicated to sedimentary geochemistry and clay mineralogy, this study investigates the interplaying controls on the generation and composition of river sediments across South China. In the Pearl River and southern Yangtze catchments, dominantly sedimentary and basaltic rocks of the Yangtze block shed quartzo-lithic sedimentaclastic sand, whereas mostly granitic and sedimentary rocks of the Cathaysia block generate feldspatho-quartzose sand. Rivers of the Fujian and Zhejiang Provinces draining the SE Coast Magmatic Belt carry feldspatho-litho-quartzose volcaniclastic sand containing epidote with minor clinopyroxene and olivine locally. Within the Pearl River catchment, 35–40% of the sand is derived from the Yangtze block, and 60–65% from the Cathaysia block. Erosion rates are fairly evenly distributed across the basin, reaching higher values in the Hongshui headwaters where topographic relief is greater. South China hosts one of the largest and most spectacular karst areas on Earth, where two landscape types are characterized by different intensity of chemical dissolution. In fengcong (cone) karst, carbonate detritus attacked by carbonic and sulfuric acids is partly preserved, whereas carbonate grains are completely dissolved in fenglin (tower) karst developed in wetter regions to the east. The strong climatic gradient from the dry Tibetan plateau in the west to monsoon-drenched coastal areas is faithfully reflected in illite-rich vs. kaolinite-rich clay-mineral assemblages, but in sand the weathering effect is much harder to isolate from the dominant effects of source-rock lithology and recycling. The different durability of tectosilicates (quartz > microcline > orthoclase > plagioclase) and the degree of corrosion displayed by detrital minerals offer essential qualitative information but cannot represent robust proxies to quantify weathering intensity. The sand generation index SGI reveals whether lithologies are under

This study illustrates the clay mineralogy and sedimentary geochemistry of the Red River and its major tributaries and distributaries in northern Vietnam and shows how these methods can be used to unravel grain size, provenance, hydraulic-sorting, and chemical weathering effects. All sand samples are SiO2-rich and consequently depleted in most chemical elements (but Sn and Pb) relative to the upper continental crust (UCC). The order of element mobility indicated by aAlE values, which estimate the degree of depletion in mobile element E relative to the UCC standard, is Ca Na . Sr . Mg . Ba K Rb. In mud fractions, SiO2 decreases, and other elements consequently increase. The grain size-dependent intrasample chemical variability of fluvial sediments reflects the grain size distribution of detrital minerals, which is strictly controlled in turn by the settling-equivalence principle. The 87Sr/86Sr ratio in Red River sands varies widely between 0.716 and 0.748, and eNd ranges from8.5 to13.8. The negative eNd values and high 87Sr/86Sr ratios point at a significant contribution from Precambrian crystalline basement, directly or through recycling of Triassic siliciclastic strata. Clay-mineral assemblages, dominated by illite and smectite with subordinate kaolinite and minor chlorite, suggest largely physical erosion in the upper catchment and stronger weathering in the monsoon-drenched lower catchment. Extremely intense weathering is demonstrated by a Quaternary soil sample from the Red River valley in northernmost Vietnam, which is a pure quartzose sand yielding a tourmaline-dominated heavy-mineral suite and a kaolinite-dominated clay-mineral assemblage. In the humid landscapes of northern Vietnam, no detrital mineral, excepting quartz, muscovite, tourmaline, prismatic sillimanite, anatase, and zircon, can resist even shallow early pedogenesis.

The interplay of tectonic and climatic forcing in the development of Alpine deep-seated gravitational slope deformations (DSGSD) is still poorly understood. We investigate a giant DSGSD affecting the Piz Dora slope (Val Müstair, Switzerland) by geological, structural and geomorphological analyses, spaceborne SAR interferometry and numerical modelling. The DSGSD affects Permian terrigenous and volcanoclastic successions folded into a kilometre-scale asymmetric anticline during the Alpine orogenesis. The area is characterized by active tectonic uplift and widespread shallow seismicity with dominant dip-slip fault mechanisms, experienced fast deglaciation after the Last Glacial Maximum and periglacial conditions between the Lateglacial and Holocene. The slope is affected by morpho-structural features testifying to the deep-seated gravitational sliding of 1.85 km3 of rock along a basal shear zone over 400 m deep. Analysis of rock glaciers and DInSAR data show that the DSGSD was active in Lateglacial times and is presently deforming at rates ö 15 mm/yr. Integrated kinematic analysis of field and radar data outlines a key control of the inherited fold structure on the DSGSD, with a transition from deep compound sliding to the West, controlled by massive conglomerates (Chazforà Formation), to shallower roto-translational sliding to the East, controlled by volcanoclastic foliated rocks (Ruina Formation). 2DFEM stress-strain numerical models, simulating the post-LGM slope evolution in static, pseudo-static and dynamic conditions allowed evaluating the contribution of long-term seismicity to DSGSD in a paraglacial setting. Dynamic modelling was performed starting from the characterization of a real earthquake, representative of the recent local seismotectonic activity, and scaled to obtain dynamic scenarios with different return periods. Results suggest that deglaciation-related perturbations promoted the inception of the DSGSD but not its complete development, that was li

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 f

We analysed the Piz Dora deep-seated gravitational slope deformation by integrating field surveys, 3D structural analysis and numerical modelling. The DSGSD affects meta-sandstones, meta-conglomerates and phyllites of the Austroalpine S-Charl cover nappe, involved in a slopescale, WNW trending closed anticline fold. The area is seismically active and experienced extensive glaciation during the LGM. The slope is affected by spectacular gravitational morphostructures (double-crested ridges, scarps and counterscarps) associated to the deep-seated sliding of 1.85 km3 of rock along a basal shear zone up to 300 m deep. The DSGSD deformed recent periglacial features and partially collapsed. Finite-Element modelling suggests that earthquake shaking and related damage may have enhanced the triggering role of postglacial debuttressing, suggesting the importance of active tectonic conditioning in relevant alpine sectors. .