Modern Sand Research Articles

Automated determination of transport and depositional environments in sand and sandstones

As sand moves across Earth's landscapes, the shapes of individual grains evolve, and microscopic textures accumulate on their surfaces. Because transport processes vary between environments, the shape and suite of microtextures etched on sand grains provide insights into their transport histories. For example, previous efforts to link microtextures to transport environments have demonstrated that they can provide important information about the depositional environments of rocks with few other indicators. However, such analyses rely on 1) subjective human description of microtextures, which can yield biased, error-prone results; 2) nonstandard lists of microtextures; and 3) relatively large sample sizes (>20 grains) to obtain reliable results, the manual documentation of which is extremely labor intensive. These drawbacks have hindered broad adoption of the technique. We address these limitations by developing a deep neural network model, SandAI, that classifies scanning electron microscope images of modern sand grains by transport environment with high accuracy. The SandAI model was developed using images of sand grains from modern environments around the globe. Training data encompass the four most common terrestrial environments: fluvial, eolian, glacial, and beach. We validate the model on quartz grains from modern sites unknown to it, and Jurassic-Pliocene sandstones of known depositional environments. Next, the model is applied to two samples of the Cryogenian Bråvika Member (of contested origin), yielding insights into periglacial systems associated with Snowball Earth. Our results demonstrate the robustness and versatility of the model in quickly and automatically constraining the transport histories recorded in individual grains of quartz sand.

An Ediacaran orogeny in subglacial East Antarctica is uncovered by detrital garnet geochronology

Detrital minerals provide valuable insights into the tectonic history of continents. Uranium-lead dating of detrital zircon is widely used to characterize the magmatic history of continents but is generally insensitive to metamorphism accompanying the production and reworking of crust during orogenesis. Garnet is the most important mineral for recording prograde and peak orogenic metamorphism and can occur as a common detrital phase. Here, we demonstrate laser-ablation lutetium-hafnium (Lu-Hf) geochronology of detrital garnet as a provenance tool for reconstructing orogenic histories at (super)continental scales. Detrital garnet (n = 557) from modern sands and Permo-Carboniferous glacial strata in South Australia faithfully record local garnet-grade metamorphic events but also include a major population at ca. 590 million-years with no known source in South Australia. We trace the ca. 590 million-year-old detrital garnets to a largely ice-covered orogenic province in East Antarctica, uncovering the inception of convergent margin tectonism along the palaeo-Pacific margin of Gondwana.

Discrimination of tectonic provinces using zircon U-Pb ages from bedrock and detrital samples in the northern Andes

Abstract The northern Andes of southern Colombia contain a rich geologic history recorded by Proterozoic to Cenozoic metamorphic, igneous, and sedimentary rocks. The region plays a pivotal role in understanding the evolution of topography in northwestern South America and the development of large river systems, such as the Amazon, Orinoco, and Magdalena rivers. However, understanding of the basement framework has been hindered by challenging access, security concerns, tropical climate, and outcrop scarcity. Further, an insufficient geochronologic characterization of Andean basement complicates provenance interpretations of adjacent basins and restricts understanding of the paleogeographic evolution of southern Colombia. To address these issues, this paper presents a zircon U-Pb geochronological dataset derived for 24 bedrock samples and 19 modern river samples. The zircon U-Pb results reveal that the Eastern Cordillera of southern Colombia is underlain by basement rocks that originated in various tectonic events since ca. 1.5 Ga, including the accretion of discrete terranes. The oldest rocks, found in the Garzon Massif, are high-grade metamorphic rocks with contrasting Proterozoic protolith crystallization ages. Whereas the SW part of the massif formed during the Putumayo Orogeny (ca. 1.2–0.9 Ga), we report orthogneisses for the NE segment with protoliths formed at ca. 1.5 Ga, representing the NW continuation of the Rio Negro Jurena province of the Amazonian Craton. In contrast, crystalline rocks of the Central Cordillera primarily consist of Permian–Triassic (ca. 270–250 Ma) and Jurassic–Cretaceous (ca. 180–130 Ma) igneous rocks formed in a magmatic arc. In southernmost Colombia, the Putumayo Mountains mainly consist of Jurassic–Cretaceous (180–130 Ma) plutonic and volcanic rocks. Furthermore, we analyzed the heavy mineral abundances in modern river sands in southern Colombia (spanning 1°N–5°N) and found that key minerals such as garnet and epidote can be utilized to trace high-grade metamorphic and igneous lithologies, respectively, in the river catchments. The differentiation of basement ages for separate tectonic provinces, combined with heavy mineral abundances in modern sands, can serve as unique fingerprints in provenance analyses to trace the topographic and exhumational evolution of different Andean regions through time.

Revisiting a proof of concept in quartz-OSL bleaching processes using sands from a modern-day river (the Séveraisse, French Alps)

Conditions of sediment transport and deposition in highly dynamic fluvio-glacial environments enhance incomplete bleaching of luminescence signals during sunlight exposure. Whatever the geomorphic context or application, partial bleaching has been widely reported and remains a methodological limitation for application of Optically Stimulated Luminescence (OSL) dating methods, potentially resulting in sediment-burial age overestimation. This study focuses on the highly dynamic Séveraisse River (SW French Alps) where modern-day alluvial sands of a braided reach were sampled to assess the degree of quartz-OSL partial bleaching associated with superficial pre- and post-deposition geomorphic processes. Our original approach combines (i) a photogrammetry-based survey, (ii) sediment grain-size analysis, and (iii) measurements of both portable OSL luminescence signals and conventional quartz OSL equivalent doses in modern superficial (from 0.1 to 1 cm) and sub-surface (up to 30 cm) alluvial sands exposed to sunlight for at least 19 days. Our results show high but spatially variable residual luminescence signals at the surface, measured in all grain-size fractions with both the portable luminescence reader (≥5 x106 cts/g) and conventional quartz-OSL doses (≥80 Gy), even within the uppermost millimetres of the exposed alluvial surface. Our data thus highlight poor luminescence bleaching in the Séveraisse's modern sands, during both pre-depositional transport and post-depositional exposure. In addition, our study reveals, for the first time, the significant sunlight attenuation over a few millimetres within modern alluvial sediments, perhaps conditioned by dark sand grains, and/or by superficial blanketing by silts (i.e. waning flow stage) that leads to a porosity decrease and very low sunlight penetration. We suggest the occurrence of a critical sediment layer (i.e. only a few mm thick) that could play a key role in bleaching processes for alluvial surfaces, with strong implications for our understanding of residual doses in braided systems' sandy deposits and the dynamics of such alluvial surfaces.

Early Miocene sand wedge deposits in Southwestern Tarim Basin and Implications for the Uplift of the Northern Tibetan Plateau

The uplift of the Tibet Plateau and its climatic effects have long been a hot topic in academic research. However, there is still significant controversy regarding the uplift history and related climate changes along the northern margin of the plateau. In this paper, we present sand wedge deposits from the base of the Wuqia Group (∼20 Ma) on the southwestern Tarim Basin, representing the oldest reported sand wedges in the Tibetan Plateau. A comprehensive study was conducted on lithostratigraphy, sedimentary environment, and macroscopic–microscopic features of the sand wedge deposits. The results indicate that the lithostratigraphic succession preserving the sand wedge deposits consists mainly of lenticular conglomerates and cross-bedded gravelly sandstone interbedded with medium–thin-bedded mudstone, consistent with the braided fluvial environment. The sand wedge deposits commonly exhibit a V-shape geometry and are filled with gravelly sandstone, with the gravels arranged parallel to the walls of the wedge. The clasts of the wedge-filled sandstone are well-rounded and show a unimodal grain size distribution. The quartz surfaces commonly display dish-shaped and crescent-shaped impact features, indicating an eolian origin and an arid climate. Based on the relationship between the formation temperature of modern sand wedges, the atmospheric temperature gradient, and altitude, the reconstructed paleo-elevation of the sand wedge deposits at the base of the Wuqia Group in the southwestern Tarim Basin is approximately ∼ 1000 m. These results indicate that the northern margin of the Tibet Plateau had already reached an elevation of ∼ 1000 m during the Early Miocene, forming a seasonal arid and cold climate.

Provenance of modern sands from Baja California rivers (Mexico): petrographic constraints from light and heavy minerals

ABSTRACT We used high-resolution petrographic and dense-mineral data on modern sand to investigate erosion patterns of the El Rosario, San Fernando, and San Vicente river basins of Baja California (Mexico) to better understand the interrelationships between a complex magmatic arc terrane and surface processes. Modern sand composition of these three rivers reflects the nature of the source region, which lies in the central part of the Alisitos arc (Peninsular Ranges, Baja California, Mexico). The sand detrital modes correspond well with the main structural units drained by the El Rosario, San Fernando, and San Vicente rivers: 1) the Early Cretaceous oceanic arc of the Alisitos Group, 2) the Paleozoic to Mesozoic continental-margin metasedimentary rocks, 3) the Cretaceous plutons, 4) the Upper Cretaceous to Tertiary sedimentary rocks, and 5) the Tertiary volcanics. The modern sand of the San Vicente, San Fernando, and El Rosario rivers is fed chiefly from erosion of a magmatic arc and consists mostly of minor feldspatho-lithic (Fl) to quartzo-litho-feldspathic (qFL) sand and dominant quartzo-feldspatho-lithic (qLF) and litho-feldspatho-quartzose (lQF) sand. Framework petrography also suggests a progressive increase in quartz, K-feldspar, sedimentary and metamorphic lithic fragments, and a decrease in volcanic lithic fragments. Sand, in the Lv field, microlitic (Lvmi), felsitic (Lvf) and lathwork (Lvl) types, and trace amounts of vitric grains (Lvv), such as pumice particles. The andesitic volcanic province of the Alisitos arc sheds quartz-poor sand containing mainly microlitic lithic fragments and plagioclase, whereas sand derived from more felsic rhyolites and rhyodacitic and trachyandesitic products contains largely felsitic volcanic lithics and minor lathwork lithics are mainly derived from subordinate basalts. The abundance of intrusive rock fragments and volcanic and sedimentary lithics of the sampled river sands faithfully represents the relative abundance of a heterogeneous bedrock exposure consisting of sedimentary and metasedimentary rocks, as well as volcanic, plutonic, and medium- to high-grade metamorphic rocks in each drainage basin. Transparent heavy-mineral assemblages including major amounts of amphibole, pyroxene, epidote, titanite, zircon, and minor amounts of staurolite, rutile, actinolite, tourmaline, garnet, kyanite, andalusite, sillimanite, and apatite are in good agreement with a mixed provenance characterized mainly by magmatic, primarily volcanic (andesite, rhyolite, and basalt) and secondarily plutonic (granitoid rocks) and metamorphic source rocks. Some labile species such as hornblende and pyroxene grains show mainly corroded to etched morphologies due to dissolution processes and by chemical weathering processes occurring in a paleo and current semiarid climate. The Zircon+Tourmaline+Rutile index of the heavy-mineral modes, coupled with their subrounded to rounded grain surface texture, indicates recycling from the sedimentary source rocks. Heavy-mineral abundance and weathering textures in the San Fernando and San Vincente river sands match predominantly volcanic bedrock lithologies, while the El Rosario river sands match sedimentary and metasedimentary source rocks.

Modern sand provenance and transport across the western Gulf of Mexico margin

Petrographic and detrital zircon U-Pb analysis of modern beach sands and river sands from major catchments in northeastern Mexico draining to the Gulf of Mexico provides evidence for a minimum of 650 km of littoral sand transport southward from the mouth of the Rio Grande at the Mexico-U.S. border to the central part of the state of Veracruz, Mexico. Principal tracers of Rio Grande sand include: (1) quartzose composition that contrasts with lithic compositions of sand in eastern Mexico rivers and (2) detrital zircon ages with Mesoproterozoic modes at 1.8−1.5 Ga and 1.4 Ga, age groups that are typical of basement and derivative sediment of the SW United States but are uncommon to rare in Mexican river catchments. In contrast, abundant Miocene and younger grains in beach sands of Veracruz indicate primary sediment derivation from active and recently active volcanoes in the Trans-Mexican volcanic belt in central Mexico. A proportional decrease in sand of Rocky Mountain provenance with distance southward along the coast from the mouth of the Rio Grande and absence of Miocene and younger zircon grains in beaches north of rivers draining the Trans-Mexican volcanic belt indicate net littoral sand transport southward along the eastern coast of Mexico, demonstrating that wintertime shoreline-parallel surface currents rather than north-directed summertime currents dominate sediment transfer. Sand samples of Tamaulipas beaches in northeastern Mexico commonly have equal or higher proportions of U.S.-derived Mesoproterozoic zircon grains than are present in river bar sand of the lower Rio Grande and the Rio Grande delta, and thus require that littoral processes rework and incorporate coastal dune and beach sands of northeastern Mexico that are enriched in predam Rio Grande sediment. Implied coastal erosion may be related to Holocene transgression or interruption of sediment supply to the coastal sediment transport system by dams in the Rio Grande drainage basin. Such coastal erosion is impacting long-term shoreline stability and viability of the littoral environment.

Cretaceous source to sink system reconstruction of northeastern Asian continental margin: Insight from integrated detrital geochronology in NE China

The Cretaceous sedimentary successions in NE China are largely incomplete as the basins are inverted and younger strata are eroded. Except for the Songliao Basin, whose depositional record has remained relatively intact, the burial record to the east was interrupted in the late Early or Late Cretaceous. There is still controversy on the possible connection between the Songliao Basin and the eastern basin group, as well as the extent of the previously suggested “pan-Sanjiang” proto-basin that covered most current eastern satellite basins. To address these questions, we studied modern river catchments of variable sizes from sediment-supplying basement highs that cover most of eastern NE China to track the intense denudation events and provenance changes through the Cretaceous. We found a great inconsistency between detrital age patterns of the modern river sands and the spatial proportions of the source units. The detrital age distributions allow to re-evaluate the basement units that are mostly composed of the Triassic–Jurassic igneous suite and some metasedimentary units with Paleozoic ages, but the contribution from Proterozoic formations is negligible. Combining the newly dated modern catchment detrital U-Pb ages, the region-wide compilation of the basement emplacement ages, and the U-Pb ages in the Cretaceous formations in NE China, we systematically refine the Cretaceous provenance history. In the Early Cretaceous, the eastern satellite basins accumulated sediments from the Lesser Xing’an range (LXR) in the west, Zhangguangcai range (ZGCR) in the south, and the Nadanhada terrane (NT) in the east. The sediment of the southern Songliao Basin derived from the North China Craton (NCC) and from ZGCR but barely from the Great Xing’an Range (GXR). The Jiamusi uplift (JU) did not provide sediments to the eastern satellite basins and the Songliao Basin.In the Late Cretaceous, the eastern satellite basins received sediments from the exhumed JU but barely from ZGCR and LXR. The Songliao Basin still accumulated the sediments from the NCC, some south part of ZGCR, and GXR but minor from the central and northern ZGCR and LXR. Between the latest Early Cretaceous and early Late Cretaceous, a much wider proto-basin was suggested in NE China than previously assumed. It covered during its maximum extension period the current Songliao Basin, the eastern satellite basins, the LXR, ZGCR, JU, and partial GXR basement areas. The provenance change is induced by the Paleo-Pacific plate motion change, i.e., with the subduction direction change, the roll-back, and two-stage limited flat slab subduction trigged the formation of the basin-and-range system in NE China since the Early Cretaceous. Moreover, we suggest conducting modern sand provenance analysis to detect, verify or re-classify the ages of the zircon-bearing units, especially at a reconnaissance prospecting on areas covered by imprecise large-scale geological maps only to reveal the catchment better.

Periglacial–Aeolian Polygonal Surface Structures in the Tibetan Plateau

Abstract—The surface pattern of permafrost area in the Tibetan Plateau, with 15–20 m polygons, resembles the patterned ground of the Arctic periglacial loess plains in northeastern Eurasia and North America. However, unlike the Arctic plains, it consists of semi-stabilized modern sand dunes, up to 2.5–3.0 m high, and U-shaped epigenetic ice wedge casts inherited from an ancient polygonal network on the surface of a 10–12-m terrace of the Yangtze River. The polygonal dunes and the U-shaped sand wedges were studied in the Yangtze head-waters in the vicinity of the high-altitude research station Bei-Lu-Xe. The polygons have desert pavement floors with ventifacts, composed of Late Pleistocene alluvial gravel and debris. The dunes and wedges consist of well sorted quartz-carbonate sand with an average grains size of 2.0–2.2 mm. Ground Penetrating Radar surveys in the area revealed the permafrost table at depths varying from 2 to 4 m below the dunes. The polygonal dunes may have formed by biogenic-aeolian deposition over an ancient system of ice wedges.

Which is the dominant source for the aeolian sand in the Badain Jaran Sand Sea, Northwest China: Fluvial or gobi sediments?

Fluvial and gobi sediments play significant roles in the formation of modern sand seas and their evolution. However, little is known about their respective source contributions, especially in quantitative terms. In the present study, we selected the Badain Jaran Sand Sea in Northwest China to quantitatively identify the sediment sources. To achieve this goal, we collected Heihe River sand and gobi sediments (Ejin gobi and the Beida–Yabrai gobis) as the potential sand sources. We performed provenance identification based on robust geochemical indicators, and found that both of these potential sources provided sand materials to the sand sea. Our quantitative analysis based on novel fingerprinting methods, namely consensus ranking (CR) and consistent tracer selection (CTS), suggested that the gobi sediments supplied more sand than the fluvial sand, accounting for 76.85 % and 23.15 % of the total (goodness of fit is 95.8 ± 3.89), respectively. Therein, the Ejin gobi was the dominant source for most regions of the sand sea (63.17 ± 21.43 %), but the Heihe River mainly fed sand source to the southern part of the sand sea (23.15 ± 18.66 %) and the Beida–Yabrai gobis provided the most sand to regions near the fan (13.68 ± 11.49 %). The source supply areas largely control above contribution difference. Our results demonstrate the critical role of gobi sediments for sand accumulation of the Badain Jaran Sand Sea.

PENGETAHUAN PENAMBANG PASIR DESA KALIURANG KECAMATAN SRUMBUNG KABUPATEN MAGELANG MENGENAI ANCAMAN LAHAR DINGIN DI KALI BEBENG GUNUNG MERAPI

The threat of cold lava from Mount Merapi is a secondary hazard causing an increasing impact on the number of casualties. Knowledge of sand miners is the key to success in anticipating the threat of cold lava disaster. So that the sand miners are able to respond and determine the appropriate action based on the knowledge they have. The purpose of this study was to analyze the knowledge of sand miners regarding the threat of cold lava in Bebeng River. The population in this study was taken using a total sampling technique with a sample of 63 respondents in the category of traditional sand miners and modern sand miners who live in Kaliurang Village. The results show that the knowledge of sand miners is included in the fairly good category with a knowledge index value of 72%. Based on the comparison of the categories of miners, it is known that modern sand miners have a 6% higher value than modern miners. Knowledge of distance, signs and causes of cold lahar threats has higher results than knowledge of triggers of lahar threats and elements of cold lahar threats. Experience, place of residence and participation in disaster organizations greatly affect the knowledge of sand miners regarding the threat of cold lava

Growth of the southern Tian Shan-Pamir and its impact on central Asian climate

Uplift and amalgamation of the high-elevation (>3000 m) Tian Shan and Pamir ranges in Central Asia restricts westerly atmospheric flow and thereby limits moisture delivery to the leeward Taklimakan Desert in the Tarim Basin (<1500 m), the second largest modern sand dune desert on Earth. Although some research suggests that the hyper-arid conditions observed today in the Tarim Basin developed by ca. 25 Ma, stratigraphic evidence suggests the first erg system did not appear until 12.2 Ma. To address this controversy and to understand the tectonic influences on climate in Central Asia, we studied a continuous, 3800-m-thick stratigraphic section deposited from 15.1 to 0.9 Ma now exposed within the western Kepintagh fold-and-thrust belt in the southern Tian Shan foreland. We present new detrital zircon data (n = 839), new carbonate oxygen (δ18Oc) and carbon (δ13Cc) stable isotope compositions (n = 368), structural modeling, and stratigraphic observations, and combine these data with recently published magnetostratigraphy and regional studies to reconstruct the history of deposition, deformation, and climate change in the northwestern Tarim Basin. We find that basins along the southern (this study) and northern (i.e., Ili Basin) margins of the Tian Shan were likely receiving similar westerly precipitation by 15 Ma (δ18Oc = ∼−8‰) and had similar lacustrine-playa environments at ca. 13.5 Ma, despite differences in sedimentary provenance. At ca. 12 Ma, an erg desert formed adjacent to the southern Tian Shan in the northwestern Tarim Basin, coincident with a mid- to late Miocene phase of deformation and exhumation within both the Pamir and southern Tian Shan. Desertification at ca. 12 Ma was marked by a negative δ18Oc excursion from −7.8 ± 0.4‰ to −8.7 ± 0.7‰ in the southern Tian Shan foreland (this study), coeval with a negative δ18Oc excursion (∼−11 to −13‰) in the Tajik Basin, west of the Pamir. These data suggest that only after ca. 12 Ma did the Pamir-Tian Shan create a high-elevation barrier that effectively blocked westerly moisture, forming a rain shadow in the northwestern Tarim Basin. After 7 Ma, the southern Tian Shan foreland migrated southward as this region experienced widespread deformation. In our study area, rapid shortening and deformation above two frontal foreland faults initiated between 6.0 and 3.5 Ma resulted in positive δ13Cc excursions to values close to 0‰, which is interpreted to reflect exhumation in the Tian Shan and recycling of Paleozoic carbonates. Shortening led to isolation of the study site as a piggy-back basin by 3.5 Ma, when the sediment provenance was limited to the exhumed Paleozoic basement rocks of the Kepintagh fold belt. The abrupt sedimentologic and isotopic changes observed in the southern Tian Shan foreland appear to be decoupled from late Cenozoic global climate change and can be explained entirely by local tectonics. This study highlights how tectonics may overprint the more regional and global climate signals in active tectonic settings.

Machine Learning Applied to a Modern‐Pleistocene Petrographic Data Set: The Global Prediction of Sand Modal Composition (GloPrSM) Model

AbstractPetrography has long been used as a tool to decipher the sedimentary provenance of sand and sandstone based on relative proportions of detrital grain types. However, there is not yet a predictive framework that constrains the relationship between sand grain composition and the factors that influence it, including bedrock lithology, elevation, slope, basin area, precipitation, and temperature. We used a globally extensive modal point‐count data set of 3,522 Pleistocene to modern sand samples to train an inline series of random forest meta‐estimators to predict relative abundances of quartz (Q), feldspar (F), and lithic (L) grain types and eight subcompositions. The trained random forest models were fit to a global data set of fluvial watersheds to produce the global prediction of sand modal composition (GloPrSM) model which predicts Q‐F‐L of fluvially transported sediment. GloPrSM predicts quartz enrichment in low latitudes (35°N to 35°S), feldspar enrichment near plutonic and metamorphic crystalline terranes in middle to high latitudes, and lithic enrichment near modern and ancient collisional plate boundaries and flood basalts. Our analyses reveal that slope, temperature, and the relative abundance of exposed metamorphic and felsic to intermediate plutonic rocks are the most important predictors of Q‐F‐L composition. In addition, temperatures higher than 15°C and large drainage areas appear to promote quartz enrichment, while steeply sloping environments favor lithic enrichment. The GloPrSM model represents the first global‐scale estimate of fluvial sand compositional modes and illustrates that the spatial distribution of Q‐F‐L at Earth's surface can be predicted from the first‐order factors that generate sediment.

Modern sand supply of the Tengger Desert and temporal variations in sand provenance driven by northern Hemisphere glaciation

Knowledge of surface processes in source-to-sink system of sand is important for the development and utilization of natural resources in desert. However, the surface processes within Chinese deserts, especially their response to long-term global cooling since the Late Pliocene, are still poorly understood. Here, we use geochemical analyses of aeolian sand (63–500 μm) samples from a drill core in the central Tengger Desert of China, together with widely-distributed surface samples, to elucidate the present and past surface processes. The main sand provenances for the southwestern and northeastern parts of the Tengger Desert are the northeastern Tibetan Plateau and the Alxa Block, respectively. After the inception of Northern Hemisphere glaciation at ∼2.7 Ma, the expansion of ice sheets in high northern latitudes was the major trigger of an increased sand supply from the Alxa Block to the desert hinterland, via the strengthening of the Siberian High. After the Mid-Pleistocene Transition (MPT), during ∼1.2–0.8 Ma, the development of mountain glaciers in the Tibetan Plateau was the major trigger of an enhanced fluvial sand supply from the northeastern Tibetan Plateau to the hinterland. Further, we propose that these two triggers may subsequently have caused substantial variations in the sand supply to most of the deserts surrounding the northern Tibetan Plateau rather than only the Tengger, due to the similarity of their sand supply mechanisms. And the enhanced fluvial sand supply from the northern Tibetan Plateau may be of significance to the continuous existence of a sand sea landscape in the surrounding basins during the post-MPT interval. Overall, our study suggests that glaciation in the high latitudes and the high mountains of the Northern Hemisphere have a significant impact on the two sand supply agents, i.e., wind and water, of Chinese deserts respectively.

Detrital orthopyroxene as a tracer of geodynamic setting:: A Raman and SEM-EDS provenance study

Raman spectroscopy is a powerful and efficient tool that is being used more and more frequently in high-resolution provenance analysis. This study is dedicated to Ca-poor orthorhombic pyroxene, which for its low durability during diagenesis can be considered as a diagnostic first-cycle phase. We focused on 15 samples of modern sands representing a full range of rock units exposed at different structural levels of continental, arc, or oceanic lithosphere and generated in diverse geodynamic settings. By coupling optical observations, SEM-EDS mineral-chemistry and Raman spectroscopy analyses on the same grains we show how orthopyroxene from mantle, deep crustal, and volcanic rocks ranging in composition from andesite to dacite and felsic differentiates can be robustly distinguished. The Mg# [Mg/(Mg + Fe)] content of orthopyroxene grains can be accurately estimated by recording the characteristic position of their six main characteristic peaks (ν1 to ν6, vibrational modes) even during routine point-counting under the Raman spectroscope. In particular, the position of the strong and narrow ν3 peak (~655 cm−1) also allows estimation of the Ca content when compared to the position of other peaks (especially ν1, ~330 cm−1). High-Mg orthopyroxene is exclusively derived from mantle rocks, whereas metagabbros of the lower continental crust and gabbroic rocks of arc crust are distinguished by their lower Ca. The lowest Mg# was recorded in detrital orthopyroxene derived from the silicic Amiata Volcano in central Italy, whereas trachytes in rift-related settings did not show unique characteristics apart from their slightly higher Ca content.

Oligocene onset of uplift and inversion of the Cascadia forearc basin, southern Oregon Coast Range, USA

Abstract An extensive detrital zircon U-Pb data set (n = 6324 dates) from Eocene to Miocene sandstones and modern river sands establishes the onset of arc magmatism and forearc uplift along the Cascadia convergent margin in southwestern Oregon (United States). Middle to late Eocene marine strata in the Coos Bay area were primarily sourced from the Klamath Mountains and coeval Clarno-Challis volcanoes in central Oregon and/or Idaho. Ancestral Cascades arc magmatism initiated at 40 Ma and supplied sediment to a broad forearc basin in western Oregon during late Eocene time. Major reduction of Ancestral Cascades arc (40–12 Ma) and Clarno-Challis (52–40 Ma) zircon in the Tunnel Point Sandstone (ca. 33–30 Ma) records the isolation of the Coos Bay area from the Ancestral Cascades arc due to Oligocene onset of forearc uplift, basin inversion, and emergence of the southern Oregon Coast Range. The Tarheel formation (ca. 18–15 Ma) is characterized by disappearance of Ancestral Cascades arc zircon and a substantial increase in Clarno-Challis zircon recycled from underlying forearc strata. The ~15–20 m.y. delay between subduction initiation (ca. 49–46 Ma) and the onset of forearc uplift (ca. 33–30 Ma) supports insights from thermomechanical models that identify tectonic underplating and thermally activated lower-crustal flow as major drivers of deformation and uplift in active forearc regions.

Release of Fluoride in Groundwater from Various Rock Forming Minerals and Sandy Aquifer of Central Ganga Basin, India

Abstract Fresh and pure water has an important role to play for healthy life. Currently, in many studies higher concentrations of contaminants like calcium, sodium, nitrate, lead, chromium, arsenic, fluoride etc. have been reported that makes the water unfit for its direct consumption. Sources and release mechanism of many such pollutants is still not known. These sources can be anthropogenic or geogenic. This paper deals with one of such contaminants namely fluoride and emphasizes on its release from various minerals viz. Gypsum, fluorite, tourmaline, actinolite, plagioclase, biotite, quartz, kayanite, epidote and orthoclase under different pH environment. It has been noted that maximum fluoride has been released from the fluorite at all pH environment (acidic, normal and alkaline) of water while minimal fluoride was released from kayanite. However, orthoclase, tourmaline and biotite can release fluoride in considerable amount. The attempts were also made to compare the release of fluoride from modern sand (Ganga sediments) with ancient sand (from sandy aquifer) under different pH condition. Outcome of studies shows that maximum fluoride released from the sand at the pH range of 6.1 to 8.2.

Implications for sedimentary transport processes in southwestern Africa: a combined zircon morphology and age study including extensive geochronology databases

Extensive morphological and age studies on more than 4600 detrital zircon grains recovered from modern sands of Namibia reveal complex mechanisms of sediment transport. These data are further supplemented by a zircon age database containing more than 100,000 single grain analyses from the entire southern Africa and allow for hypothesising of a large Southern Namibian Sediment Vortex located between the Damara Orogen and the Orange River in southern Namibia. The results of this study also allow assuming a modified model of the Orange River sand highway, whose origin is likely located further south than previously expected. Moreover, studied samples from other parts of Namibia give first insights into sediment movements towards the interior of the continent and highlight the potential impact of very little spatial variations of erosion rates. Finally, this study points out the huge potential of detrital zircon morphology and large geo-databases as an easy-to-use additional tool for provenance analysis.

Clinical and instrumental associations of knee osteoarthrosis and pathology of the veins of the lower extremities

Knee osteoarthritis (OA) and varicose disease of the lower extremities (VD) are two diseases common in middle– aged and older women. Questions about whether their combination is accidental or natural and whether VD affects the course and severity of OA, remain unresolved.The aim of the study was to look for the possible association between knee OA and lower limb vein pathology on the basis of clinical and modern instrumental investigation sand to study the effect of the VD on the clinical manifestations and severity of knee OA.Materials and methods. A case-control study was conducted in 85 women 40–60 years old with knee OA diagnosed in accordance with the criteria of ACR (1986) and 50 women of the same age without signs of knee OA. Women of both groups were evaluated for complaints and objective examination with an emphasis on diseases of the joints and veins of the lower extremities, radiography of the knee joints, ultrasound duplex scanning of the veins of the lower extremities. The severity of OA was assessed by the Lequenne indices. The clinical assessment of venous pathology was carried out according to the CEAP classification.Results. Patients with knee OA more often than their peers without joint pathology have VD (43% vs 22%; p=0.015), signs of chronic venous insufficiency (28% vs 12%; p=0.03), as well as valve failure of several lower limb veins simultaneously (53% vs 20%; p=0.0004). After correction by body mass index, the association of knee OA with detected vascular pathology remained clinically and statistically significant. The presence of VD with moderate manifestations of chronic venous insufficiency, as well as ultrasound signs of venous pathology, was not associated with the clinical signs and course of knee OA.Conclusions. Knee OA in middle-aged and older women, regardless of body mass index, is associated with VD and ultrasound signs of simultaneous valves failure of several veins. Manifestations of chronic venous insufficiency did not affect the clinical picture and severity of knee OA.

Petrographic analysis of Pre-Columbian pottery from Nevis, Eastern Caribbean

Prehistoric Indigenous groups in the Eastern Caribbean often used local materials in the manufacturing of ceramics and frequently transported raw materials and/or finished pottery as they traveled between the islands. Given the ubiquity and diversity of ceramics in the Caribbean they are particularly amenable for helping to discern past movements, exchange systems, and spheres of interaction. Curiously, however, the compositional analysis of ceramics is understudied in the region despite its great potential for answering questions regarding provenance and distribution patterns. In this paper, we conducted the first mineralogical study of pottery from the island of Nevis (northern Lesser Antilles). Using the Gazzi-Dickinson method of point counting—initially applied in Oceania with great success—20 non-diagnostic potsherds from the Late Ceramic Age (A.D. 600–1440) site of Coconut Walk were analyzed along with 11 modern sands collected from across the island. Descriptions focused on sand and matrix characteristics such as composition, size, sorting, angularity, and firing environment. Representatives of descriptive groups from both sherd and sand were identified based on composition. Two compositional groups were defined based on description and point count analysis: group 1 (Felsitic) and group 2 (Volcanic). Results indicate that these compositional groups match both local geologic description and several of the modern local sands, suggesting a local provenience for pottery production and use of multiple tempering agent sources.