Quartzite Pebbles Research Articles

Extending the range of optically stimulated luminescence dating using vein-quartz and quartzite sedimentary pebbles

The feasibility of applying optically stimulated luminescence (OSL) techniques to obtain estimates of the burial age of lithic clasts in the form of pebbles of quartzose lithology is investigated in this study. We applied OSL measurement procedures to vein-quartz and quartzite pebbles from contexts at five sites with fluvial and coastal beach contexts of depositional age ranging from 500 ka to the mid Holocene. As in previous OSL studies with lithics, measured depth-dose profiles were interpreted to identify regions associated with key stages in the burial history of the pebbles, including the extent of pre-burial optical resetting, primary burial and any subsequent secondary stages of exposure to sunlight. While some of the pebbles had not been fully optically reset before burial, none were in field saturation, as commonly encountered with larger lithic clasts such as cobbles. The relatively low concentrations of radionuclides within vein-quartz and quartzite pebbles simplified the assessment of the radiation dose rate. OSL age estimates consistent with independent dating evidence were obtained for the three sites sampled in the UK (Langford Quarry, Leet Hill Quarry, Swanscombe Skull Site and Barnfield Pit) and one of two sites tested in Portugal (Forte Cão), whereas evidence of secondary optical bleaching detected in pebbles from a second site (Vale de Atela) underestimated the independent age for primary burial. The oldest depositional age of the contexts tested was ~500 ka (Leet Hill Quarry), and for some of the pebbles tested there was the capacity to extend the potential dating range further as the age equivalence of the limiting value of D e was in excess of 1 Ma. The advantages of working with smaller, portable, clasts in the form of pebbles and with a lithology of higher transparency opens up a wide range of potential applications, whether the depositional processes are environmental or anthropogenic in origin or modification. • New approach to the dating of Quaternary sediments containing vein-quartz and quartzite pebbles. • OSL techniques applied to sliced pebble cores produce depth-dose profiles that are related to optical exposure history. • Successful comparison of OSL ages with independently dated MIS 12, MIS 11, MIS 5 and Holocene depositional contexts. • Low dose rates for vein-quartz and quartzite pebbles potentially enable further extension of the dating range.

Extreme-flood-related peat blocks: An Anthropocene analogue to ancient coal-forming environments

ABSTRACT Coal clasts associated with extreme floods are prone to survive and maintain their large size, contrary to the general belief that distance from the parent peat layer reduces the size of transported clasts. Contrary to apparent logic, moreover, a second flood event favors the preservation potential of such soft organic clasts, this being the minimal fragmentation. An Anthropocene example from an urban park in Spain demonstrates that peat clasts up to 1 m long can survive due to flotation for a distance of almost a hundred meters and are well preserved and stabilized thanks to a second flood. These peat blocks were generated by catastrophic flooding of urban peatlands along the Ebro River (city of Zaragoza) during exceptional rainfalls in Iberia. The water flow from the Ebro River flooded the peatland at the surface of the meander, ripping up peat clasts from a shear or detachment level formed by an indurated level characterized by rounded quartzite pebbles, which acted as a hydrological discontinuity surface. Extensive evidence of the paleoflow direction is provided by oriented crushed reeds and the widespread occurrence of imbricated and thrusted peat blocks on the eroded and exposed peatland and in the main urban accumulation areas. To be specific, peat blocks and minor clasts accumulated in four areas associated with different modes of transport and topographic steps. From proximal to distal these are as follows: i) a proximal rim including thrusted peat blocks on the eroded peatland, ii) two intermediate accumulation zones associated with topographic steps in the park, characterized by peat-clast imbrication, iii) gravity-fall peat clasts deposited in an artificial channel in the park, and iv) peat rafts of more than 1 m in diameter scattered over the surface of the park (at a distance of 90 m from the eroded peatland).

Con Moong Cave: A Stratified Late Pleistocene and Early Holocene Site in Northern Vietnam

Here, we outline the findings of comprehensive archaeological studies in Con Moong Cave, northern Vietnam, carried out by the Russian-Vietnamese Expedition, with the participation of Australian specialists, in 2010-2014. The cave is a stratified site, whose habitation deposits span a period beginning ca 42 ka BP. A detailed description of finds is provided. Diachronic changes in artifact types, use of raw materials, and technology are presented. Lithics from layers K-S represent the Early Upper Paleolithic San Vi culture. Finds from layer K include core-shaped debris, flakes, and a discoidal side-scraper (or sumatralith). Tools were made on quartzite pebbles. Finds from layer L, dating to ca 36 ka BP, attest to substantial changes in the choice of lithic raw material: in addition to quartzite, mostly andesite and, less often, limestone, basalt, and certain sedimentary rocks were employed. Primary reduction was not preceded by preparation of nuclei. Flakes are large and medium-sized. Tools include a sumatralith and an end-scraper. The richest material comes from Con Moong layers Q and S, dating to 26-21 ka BP. Preforms consist of pebble cores with unprepared striking platforms. Nuclei include fl at-parallel, radial, and irregular varieties. New tools in the assemblage include choppers, longitudinal and transverse convergent side-scrapers, and discoidal sumatraliths, as well as Hoabinhian axes and a unilateral axe (sumatralith). We conclude that archaeological remains from Con Moong Cave provide evidence of the evolution of the San Vi culture from its emergence to its replacement by the Hoabinhian Technocomplex ~25 ka BP. Lithic industries from layers K and L correlate with one of the earliest stages in the peopling of this region by Homo sapiens.

Application of granular materials for void space reduction within packed bed thermal energy storage system filled with macro-encapsulated phase change materials

In the paper, various granular materials as potential fillers for the void space in between macro-encapsulated phase change materials of packed bed thermal energy storage are studied. Once filled with suitable granular materials, void space of the packed bed storage, which is the main drawback of this type of storage can be significantly reduced while providing improved storage capacity per designed volume. Thus, four different materials, namely, quartzite pebbles, aluminum particles, alumina particles and micro-encapsulated n-decane are considered as potential granular fillers for packed beds. Their effect on the charge and discharge time, storage efficiency and overall storage capacity are evaluated using four parametric analyses: different macro-encapsulated phase change materials, encapsulation sizes, types of granular materials and heat transfer fluid flow rates. Among the granular materials, alumina particles ensured the highest overall increment on the amount of stored thermal energy due to their high density and heat capacity, while micro-encapsulated n-decane particles provided the highest overall enhancement on the cyclic efficiency of the packed bed storage. It was noticed that the granular materials operate at their highest capacity when combined with in-house-developed phase change materials with ultra-low phase change temperature. When coupled with other phase change materials with higher phase change temperature or latent heat capacity, the advantages of filling the void space with the granular materials diminished. Moreover, void space reduction with the granular materials helps maintain the storage efficiency while allowing increase in phase change material encapsulation size to reduce its overall cost.

Glacial influence on late Pleistocene 10Be-derived paleo-erosion rates in the north-western Himalaya, India

Terrestrial cosmogenic nuclide concentrations in fluvial deposits allow estimation of paleo-erosion rates and reconstruction of the response of landscapes to climatic perturbations. In partly ice-covered landscapes, however, incorporation of subglacially-derived sediments that were shielded by ice from cosmic can lead to erroneous erosion rate calculations. Here, we combine in situ-produced 10Be-derived erosion rates, based on sand and pebbles from a fluvial fill terrace and the modern riverbed in the upper Yamuna catchment, with numerical ice flow modelling to quantify this bias. New luminescence and surface exposure ages suggest that aggradation of the exposed deposits occurred between 29.9 ± 2.5 ka and 14.8 ± 2.8 ka. During most of the deposition, glaciers probably covered ∼19% of the catchment. 10Be concentrations of terrace sand samples differ from those of pebble samples. We obtained the lowest erosion rates from quartzite pebbles, which stem from low elevations, and the highest erosion rates from crystalline pebbles, which stem from high elevations in the Yamuna catchment. We explain these different erosion rates by differences in the steepness of the source areas, an effect that prevails throughout the entire aggradation period despite significant former ice-cover. Sand samples, which are thought to be derived from all elevation parts of the catchment, however show lower 10Be concentrations during the aggradation compared to present-day. We argue that this difference is due to a substantial subglacial origin of the sand during the aggradation period, and not necessarily related to enhanced erosion. We conclude that aggradation of the valley fill in the Yamuna catchment is most likely due to reduced discharge, and only marginally related to higher erosion rates during the late Pleistocene.

A site with mixed occupation: Neanderthals and carnivores at Érd (Hungary)

The Middle Palaeolithic open-air site of Érd, near Budapest (Transdanubia, Hungary), with its specific lithic industry on quartzite pebbles, combustion structures and abundant animal bone material dominated by cave bears, was long time considered as one of the best example of a long-term camp of Neanderthals specializing in cave bear hunting. This interpretation of the site was based on the knowledge of the late 1960s. However, the association of carnivore remains and lithic artefacts found in cave or sheltered sites of the Palaeolithic period raises questions about the formation processes of the bone accumulations and about the relationships between these different agents. The development in methodology, both in archaeozoology and lithic technology, allows to apply new approaches in the study of this complex problematic. Independent new analyses of the lithic assemblage and the osteological material of Érd resulted completely new conclusions concerning past human activities at the site as well as the presence and the role of cave bear and cave hyena. An interpretation of the site as a refuge or den for these predators together with the undeniable presence of humans implies a mixed functioning through recurrent occupations.

Пещера Конмонг – многослойный памятник позднего плейстоцена и раннего голоцена Северного Вьетнама

В статье отражены результаты комплексных исследований пещеры Конмонг на севере Вьетнама, которые проводились российско-вьетнамской экспедицией при участии австралийских специалистов в 2010-2014 гг. Пещера представляет собой многослойный археологический объект, в материалах которого зафиксирована история древнего человека начиная с 42 тыс. л.н. В работе приводится их подробная характеристика. Прослеживаются изменения по слоям в составе артефактов, в использовании сырья и в методах обработки камня. Каменные артефакты, обнаруженные в слоях K — S, относятся к культуре шонви раннего верхнего палеолита. Археологический материал слоя K составляют нуклевидные обломки, сколы и дисковидное скребло (суматралит). Сырьем для изготовления орудий служили кварцитовые гальки. Материалы слоя L возрастом 36 тыс. лет свидетельствуют о существенных изменениях в отборе сырья: помимо кварцита использовался преимущественно андезит, реже — известняк, базальт, а также некоторые осадочные породы. Первичное расщепление производилось без предварительной подготовки нуклеусов. Продуктами расщепления были отщепы крупных и средних размеров. Орудия включают суматралит и скребок. Наиболее богатый археологический материал обнаружен в слоях Q и S, возраст которых определяется в диапазоне 26-21 тыс. лет. Заготовками для раскалывания являлись галечные нуклеусы с неподготовленными ударными площадками. В коллекции представлены плоскостные параллельные, радиальные и бессистемные нуклеусы. Отмечено появление чопперов, продольных и поперечных конвергентных скребел, дисковидных суматралитов. В этих слоях зафиксированы топоры хоабиньского типа и односторонний топор-суматралит. Сделан вывод о том, что материалы пещеры Конмонг фиксируют процесс формирования культуры шонви от момента становления до ее смены культурой хоабинь ок. 25 тыс. л.н. Каменные индустрии слоев K и L соответствуют одному из первых, самых древних, этапов появления современных человеческих популяций в регионе.

Conglomerate recycling in the Himalayan foreland basin: Implications for grain size and provenance

Abstract The nature of coarse sediment in rivers emerging from mountain ranges determines rates of downstream fining, the position of the gravel-sand transition, sediment entrainment thresholds, and channel morphologies. Additionally, in the stratigraphic record, clast size distributions and lithologies are used to reconstruct paleo-hydraulic conditions and source area provenance. Using Himalayan rivers, we demonstrate that the signal of first-generation clasts derived from the hinterland of a mountain range can be significantly altered by recycling older, structurally exhumed foreland deposits. The Siwalik foothills of the Himalaya comprise Neogene fluvial sandstones and quartzite-rich conglomerates with well-rounded clasts that were deposited in the Indo-Gangetic foreland basin and later exhumed by erosion, following uplift along the Himalayan mountain front. Mass balance calculations reveal that the Upper Siwalik conglomerate may contribute a significant proportion of the total gravel flux exported from the main Himalayan catchments (up to 100%) despite forming <1% of the catchment geology. Three end-member catchments with variable proportions of gravel flux from Siwalik conglomerates are analyzed to test for the effects of conglomerate recycling. Catchments that recycle the most Upper Siwalik conglomerate form quartzite-rich gravel bars comprising well-rounded pebbles and a narrow grain size distribution, mimicking the characteristics of the Upper Siwalik conglomerate. Conversely, catchments that recycle the least Upper Siwalik conglomerate form gravel bars with a range of Himalayan lithologies, angular quartzite pebbles and a wider grain size distribution. This study highlights that recycling of quartzite-rich conglomerate can dramatically modify the flux, lithology, grain size, and shape of gravel entering the Indo-Gangetic Plain.

High-Terrace Chert-Gravel Deposits in the Toledo Vicinity, Chase County, Kansas

This study examines high-terrace chert-gravel deposits preserved in several locations near and north of Toledo at the eastern edge of the Flint Hills in Chase County, Kansas. High-terrace gravel deposits are situated in ascending steps north of the Cottonwood River valley at three levels from approximately 90 to 150 feet (×28-45 m) above the Cottonwood River channel. All deposits contain exotic quartzite pebbles and represent the Old Osage River, which gradually shifted southward as it eroded into the modern valley. Assuming a late Pliocene age for the highest terrace gives a vertical incision rate of 1.5 cm/1000 years and a lateral migration rate of 2.2 m/1000 years. The Toledo vicinity provides confirmation for the asymmetric history of valley incision presumably due to regional crustal tilting downward to the south.

Detrital cosmogenic 21Ne records decoupling of source-to-sink signals by sediment storage and recycling in Miocene to present rivers of the Great Plains, Nebraska, USA

The preservation of conglomerates far from mountainous sources is commonly interpreted in terms of tectonic or climatic forcing. To relate a depositional signal to changing conditions in source areas, the process and duration of sediment routing from source to sink need to be determined. For the first time, we quantified sediment transport histories using cosmogenic 21Ne in quartzite pebbles from modern river gravels and Neogene conglomerates from the modern and ancient North Platte River of the Great Plains of Nebraska, United States. We demonstrate that at ∼400 km distance from the Front Ranges of the Rocky Mountains, the majority of pebbles were stored in older channel deposits for up to several millions of years before being recycled; this was enabled by very slow to zero basin subsidence rates. This implies that upstream tectonic or climatic controls on surface processes were decoupled from the downstream depositional record—a result supported by the similarities in cosmogenic 21Ne values among Miocene, Pliocene, and modern river channel pebbles despite known changes in tectonic and climatic forcing.

Evidence of young, proximal and primary (YPP) diamond source occurring in alluviums in the Santo Antônio do Bonito, Santo Inácio and Douradinho rivers in Coromandel region, Minas Gerais

ABSTRACT: Magmatism associated with the Alto Paranaíba structural high comprises kimberlites, kamafugites, and alkaline complexes, forming an approximately 400 x 150 km NW-SE belt in the southern São Francisco Craton. Dating of some intrusions reveals ages between 120 and 75 Ma. Chemical analyses of garnet recovered in alluvium from traditional diamond digging areas indicate peridotitic garnet windows in Três Ranchos and Coromandel. Six hundred and eighty (680) diamonds acquired or recovered during mineral exploration in the digging areas of Romaria, Estrela do Sul, Três Ranchos and Coromandel show unique characteristics, certain populations indicating young, proximal and primary sources (YPP). Analyses of 201 stones from Santo Antônio do Bonito, Santo Inácio and Douradinho rivers alluvium, Coromandel, present no evidence of transport, characterizing a proximal source. Within these river basins, exposures of the Late Cretaceous Capacete Formation basal conglomerate contain mainly small rounded and/or angular quartzite pebbles and of basic and ultrabasic rocks, as well as kimberlite minerals (garnet, ilmenite, spinel, sometimes diamond). A magnetotelluric profile between the Paraná and Sanfranciscana basins shows that the thick underlying lithosphere in the Coromandel region coincides with the peridotitic garnet window and with a diamond population displaying proximal source characteristics. Diamond-bearing kimberlite intrusions occur in different areas of Alto Paranaíba.

U–Pb detrital zircon ages from the Paleozoic Marbella Conglomerate of the Malaguide Complex (Betic Cordilleras, Spain). Implications on Paleotethyan evolution

The Marbella Conglomerate (Betic Cordilleras, SW Spain) is a poorly sorted and polymictic rock of vaguely constrained Late Carboniferous age interlayered within a sandy sequence. It contains variable amounts of pebbles of quartzite, gneiss, deformed granitoid, schist, aplite, dacite and other volcanic rocks among others, which makes it a potential target for detrital zircon provenance studies. In order to decipher provenance we combined U–Pb SHRIMP and LA–ICP-MS analyses on zircons obtained from single pebbles of deformed rocks (schist, granitoids) and detrital zircons from the sandy sequence, respectively. The age spectra of the detrital zircons indicates that at least the sedimentation took place soon after the start of the Permian according to the youngest detrital zircon age (≈286Ma), and it involved the denudation of terranes with rocks bearing Paleoproterozoic, Neoproterozoic, Cambro-Ordovician, Devonian and Carboniferous zircon age clusters. In contrast with the Permian age of the detrital zircons from the sandstones, igneous (ca. 532 and 516Ma) and metamorphic (ca. 356Ma) U–Pb SHRIMP Concordia ages were obtained from the pebbles. The different age clusters observed could be correlated to igneous, metamorphic and detrital rocks from an already eroded terrane similar to the Ossa-Morena Zone of the Iberian Variscan Belt. Therefore, we propose that most of the sedimentation of the Marbella Conglomerate took place along the western border of the Paleotethys at the north margin of Gondwana during the dismantling of the Variscan orogenic edifice and/or the Neotethys ocean opening and the birth of the Cimmerian ribbon continent.

An Early Stone Age in Western Africa? Spheroids and polyhedrons at Ounjougou, Mali

Ounjougou stratigraphic sequence (Bandiagara, Dogon Country, Mali) is the most complete record in Western Africa for the Middle Pleistocene. This paper focuses on the lithic industry unearthed in the lowest levels of the sequence. Despite the impossibility to fix the dating of those layers, the assemblage clearly presents Oldowan features. A strong erosive process, combined to the absence of Acheulean industry, strengthens the idea of a probable ancient age for the lithic industry. Morphometric, Technological and techno-functional approaches were performed to study sandstone polyhedrons, spheroids and bolas, abundant in the collection, along with a flake production on quartz and quartzite pebbles.
 This study demonstrates that polyhedrons, spheroids and bolas were shaped from independent chaînes opératoires to realize specific tasks. The hypothesis of opportunistic knapping does not fit with these materials at Ounjougou. The evidence of shaping is highlighted by diacritic schemes showing that the flakes detached are not controlled for their usability, but for shaping the morphology of the spheroid. Apart from those polyhedrons and spheroids, flake production is also identified. While the shaping process is made on sandstone cobbles, sharp flakes are produced from quartz pebbles. This clear choice of different raw materials to produce shaped heavy tools in one hand and light flake tools in another hand strengthens the idea of a deliberate shaping of spheroid tools.
 The discussion compares this assemblage with other known assemblages like Ain Hanech and Olducai Gorge. Our point focus on the methodology used to study these specific artefacts, very different from one author to another. We stress out the fact that using the term ‘polyhedron’ is not accurate to define artefacts that can refer to shape tools or multifacial cores. We suggest to avoid using it and to focus on a technical identification to name the artefacts as cores or tools. The technological and techno-functional approaches are relevant to make this distinction.
 Then we propose some hypothesis about the use of spheroid and bolas and suggest experiments and traceological analyses in the future to confirm their functionality.
 Ounjougou lithic tool kit, composed of flake débitage, retouched flakes and shaped tools on pebbles, along with the spheroids and bolas component, gives an evidence of a diversified tool kit corresponding to the Oldowan Industrial Complex, and then represents the first Early Stone Age site in stratigraphy in Western Africa.

Quartzite pebble technology in the final Middle Pleistocene of the Ribeira da Ponte da Pedra site (High Ribatejo, Central Portugal)

The lithic assemblage of Ribeira da Ponte da Pedra site (OIS8-9) was produced, almost exclusively, through the exploitation of good quality quartzite fluvial pebbles with a regular morphology. Quartzite fluvial pebbles are the most common raw material found in the Middle Pleistocene occupation sites in Portugal. Such feature results from the easy availability of these pebbles in the valleys where the great majority of the archaeological sites within this chronology are located, and also because of the quartzite’s physical properties and suitability for knapping.
 In a techno-typological point of view, its lithic assemblage is characterized by the application of two main reduction sequences that result in abundant worked pebbles, retouched pebbles, cortical and semi-cortical flakes, retouched flakes, a few cores and rare bifacial artefacts. Some artefacts present irregular and variable edge modifications described as ‘atypical’ edge modifications that could edge damage resultant from their utilization. From a strictly technical point of view the assemblage can be described as quite simple, however we can envisage an inherent complexity starting in an accurate selection and exploitation of the quartzite pebbles, whose regular morphology allows a ‘predetermined’ production of regular blanks through simple actions.
 In order to better understand patterns of raw material selection and technical schemes adopted in the exploitation of the quartzite pebbles we compared a sample of pebbles collected in the same deposits identified in the site (t4 fluvial terrace deposits) with worked pebbles that have 1 or 2 removals that had not altered significantly the original morpho-volumetry of the pebbles. The goal of this comparison was to verify if there was a selection of the fluvial pebbles based on texture and morpho-volumetry and if so, relate such selection with the technical schemes identified by technological study of the assemblage.

Experimental study on flint hammerstone use in Discoid-Levallois technologies: A comparison with the workshop assemblages of the central Iberian Peninsula

The basins of the Manzanares and Jarama rivers have been connected to human activity since the early Palaeolithic. At the boundary between these rivers the abundance of flint has given place to exploitation and mining activities even in historical times. In recent years, projects related to urban expansion in the southeast of Madrid have brought to light various Palaeolithic deposits associated with workshops and tool production. These sites do not have evidence of river pebbles of quartzite, quartz or sandstone in the immediate environment that could have been used as hammerstones, meaning that hammerstones in these raw materials had to be transported and introduced into the sites from large distances. Given this situation, attention was paid to flint elements that show clear signs of being used as hammerstones. The aim of this study is to test the effectiveness of flint as hammerstone, testing whether the use of this raw material is indifferent to other rock types or if you have limitations or advantages in this regard. An experimental protocol was developed, allowing to observe specific knapping behaviours and justifying them in the archaeological and technological context in which they are located.

Distribution, Forms and Spatial Variability of Desert Pavements in Arid Western Rajasthan

Abstract A vast area between Phalodi in Jodhpur and Pokaran in Jaisalmer district of western Rajasthan, is occupied distinctly by rocky, shallow gravelly surfaces and occasional hills. These surfaces exhibit quartz and quartzite pebbles, angular, sub-angular and few rounded sandstone gravels, have slightly convex outline and can be best described as desert pavements. Such land features assume significance because of their extent and variability under a dominantly dry aeolian environment. Morphology and distributional pattern of such formations indicate that sediments are either of in-situ origin or may have been transported to a short distance. The present study is based on field level assessment of such surfaces in the above two desert districts. Over much of the area, the profile shows a surficial concentration of gravels followed by thick sand and silt mixed with gravels and then the parent material. There are also occasional rock outcrops of very low relief exhibiting vertical, horizontal and conchoidal pattern of fractures over these surfaces near Pokaran and north of Jaisalmer which indicate disintegration of rocks under extreme diurnal fluctuation of temperature. Such manifestations in the morphology indicate impact of both thermal as well as aeolian processes. In the east of Jaisalmer town near Basanpir and Bhojka, the pavement surfaces are found covered with abundant sub-rounded to rounded pebbles and cobbles. This type of condition would indicate a profound action by fluvial activities followed by wind sorting. Our study found significant spatial variability in the distribution of pavement surfaces, which carried imprints of climatic fluctuations and environment of deposition during Holocene.

Dropstones in Rosso Ammonitico-facies pelagic sediments of the Southern Alps (southern Switzerland and northern Italy)

Sparse isolated pebbles and cobbles of extraformational lithologies are occasionally found in fine-grained deep-water sediments. In the Middle and Upper Liassic deep-water marly limestones and marlstones of Rosso Ammonitico facies (Morbio and Rosso Ammonitico Lombardo Formations) in the western Southern Alps, Lombardy and Ticino, outsized ‘exotic’ clasts of volcanic and basement rocks occur sporadically. The clasts, of pebble size, are typically rounded. The rhyolitic volcanic clasts can be related to the Permian volcanic succession of the western Southern Alps, from which they must have been reworked; a quartzite pebble is obviously derived from the Hercynian basement. The clasts are best interpreted, in analogy to other occurrences, as dropstones transported to the site of final deposition by drift wood that occasionally occurs in the pelagic sediments. The only possible source area must be situated to the west of Lago Maggiore where the Permian volcanic suite was exposed in a fault block uplifted in the course of latest Triassic–Early Jurassic rifting.

Paleodischarge of the Mojave River, southwestern United States, investigated with single-pebble measurements of10Be

The paleohydrology of ephemeral stream systems is an important constraint on paleoclimatic conditions in arid environments, but remains difficult to measure quantitatively. For example, sedimentary records of the size and extent of pluvial lakes in the Mojave Desert (southwestern USA) have been used as a proxy for Quaternary climate variability. Although the delivery mechanisms of this additional water are still being debated, it is generally agreed that the discharge of the Mojave River, which supplied water for several Pleistocene pluvial lakes along its course, must have been significantly greater during lake highstands. We used the 10 Be concentrations of 10 individual quartzite pebbles sourced from the San Bernardino Mountains and collected from a ca. 25 ka strath terrace of the Mojave River near Barstow, California, to test whether pebble ages record the timing of large paleodischarge of the Mojave River. Our exposure ages indicate that periods of discharge large enough to transport pebble-sized sediment occurred at least 4 times over the past ∼240 k.y.; individual pebble ages cluster into 4 groups with exposure ages of 24.82 ± 4.36 ka (n = 3), 55.79 ± 3.67 ka (n = 2), 99.14 ± 12.07 ka (n = 4) and 239.9 ± 52.16 ka (n = 1). These inferred large discharge events occurred during both glacial and interglacial conditions. We demonstrate that bedload materials provide information about the frequency and duration of transport events in river systems. This approach could be further improved with additional measurements of one or more cosmogenic nuclides coupled with models of river discharge and pebble transport.

Tectonic activation, source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil)

AbstractChanges in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn‐rift successions composition.

Bunter quartzites: remarkable journeys in time and space

Quartzite pebbles and cobbles, commonly known as Bunter quartzites, are widely dispersed throughout southern Britain. They can be traced back to Early Triassic pebble beds outcropping in the Wessex Basin and the English Midlands. Derived fossils within the quartzites confirm that most, if not all, were derived from Ordovician and Devonian terrains, over what is now the general region of the Armorican peninsula of north‐west France. In Early Triassic times that area of ancient rocks formed part of a chain of young Variscan mountains which were subject to a monsoonal climate, and shed vast quantities of eroded quartzite. Ultimately, this debris was transported northwards into what is now southern Britain, by the Budleighensis river system.