Temporal variability in detrital 10Be concentrations in large Himalayan catchments

Accurately quantifying sediment fluxes in large rivers draining tectonically active landscapes is complicated by the stochastic nature of sediment inputs. Cosmogenic 10Be concentrations measured in modern river sands have been used to estimate 102- to 104-year sediment fluxes in these types of catchments, where upstream drainage areas are often in excess of 10 000 km2. It is commonly assumed that within large catchments, the effects of stochastic sediment inputs are buffered such that 10Be concentrations at the catchment outlet are relatively stable in time. We present 18 new 10Be concentrations of modern river and dated Holocene terrace and floodplain deposits from the Ganga River near to the Himalayan mountain front (or outlet). We demonstrate that 10Be concentrations measured in modern Ganga River sediments display a notable degree of variability, with concentrations ranging between ∼9000 and 19 000 atoms g−1. We propose that this observed variability is driven by two factors. Firstly, by the nature of stochastic inputs of sediment (e.g. the dominant erosional process, surface production rates, depth of landsliding, degree of mixing) and, secondly, by the evacuation timescale of individual sediment deposits which buffer their impact on catchment-averaged concentrations. Despite intensification of the Indian Summer Monsoon and subsequent doubling of sediment delivery to the Bay of Bengal between ∼11 and 7 ka, we also find that Holocene sediment 10Be concentrations documented at the Ganga outlet have remained within the variability of modern river concentrations. We demonstrate that, in certain systems, sediment flux cannot be simply approximated by converting detrital concentration into mean erosion rates and multiplying by catchment area as it is possible to generate larger volumetric sediment fluxes whilst maintaining comparable average 10Be concentrations

Focused methane migration formed pipe structures in permeable sandstones: Insights from uncrewed aerial vehicle-based digital outcrop analysis in Varna, Bulgaria

Focused fluid flow shapes the evolution of marine sedimentary basins by transferring fluids and pressure across geological formations. Vertical fluid conduits may form where localized overpressure breaches a cap rock (permeability barrier) and thereby transports overpressured fluids towards shallower reservoirs or the surface. Field outcrops of an Eocene fluid flow system at Pobiti Kamani and Beloslav Quarry (ca 15 km west of Varna, Bulgaria) reveal large carbonate‐cemented conduits, which formed in highly permeable, unconsolidated, marine sands of the northern Tethys Margin. An uncrewed aerial vehicle with an RGB sensor camera produces ortho‐rectified image mosaics, digital elevation models and point clouds of the two kilometre‐scale outcrop areas. Based on these data, geological field observations and petrological analysis of rock/core samples; fractures and vertical fluid conduits were mapped and analyzed with centimetre accuracy. The results show that both outcrops comprise several hundred carbonate‐cemented fluid conduits (pipes), oriented perpendicular to bedding, and at least seven bedding‐parallel calcite cemented interbeds which differ from the hosting sand formation only by their increased amount of cementation. The observations show that carbonate precipitation likely initiated around areas of focused fluid flow, where methane entered the formation from the underlying fractured subsurface. These first carbonates formed the outer walls of the pipes and continued to grow inward, leading to self‐sustaining and self‐reinforcing focused fluid flow. The results, supported by literature‐based carbon and oxygen isotope analyses of the carbonates, indicate that ambient seawater and advected fresh/brackish water were involved in the carbonate precipitation by microbial methane oxidation. Similar structures may also form in modern settings where focused fluid flow advects fluids into overlying sand‐dominated formations, which has wide implications for the understanding of how focusing of fluids works in sedimentary basins with broad consequences for the migration of water, oil and gas

An investigation of the relationship between immune reactivity to mycobacteria and glycosylation of IgG in rheumatoid arthritis

SIGLEAvailable from British Library Document Supply Centre- DSC:DXN003269 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Carbonate sedimentation during early foreland basin subsidence: the Eocene succession of the French Alps.

The Eocene Infranummulitic Formation and Nummulitic Limestones of the external chains of the French Alps in Haute Savoie and Alpes Maritimes unconformably overlie the Mesozoic passive margin succession, and were deposited during the onset of subsidence of the underfilled Alpine foreland basin. The Infranummulitic Formation represents detrital deposition in localized structural lows in braided fluvial, fan delta, coastal plain and lagoonal environments; the resultant facies record late lowstand and early transgressive sedimentation. A transgressive surface separates the fluvial-dominated conglomerates from lagoonal facies, and a ravinement surface separates lagoonal from ramp facies of the overlying Nummulitic Limestones. The combination of infilling of topographic lows by the Infranummulitic Formation, and the transgressive ravinement process, reduced local slope gradients inherited from the topography of the European foreland, thus encouraging the subsequent development of a low-angle carbonate ramp during continued transgression. The Nummulitic Limestones represent highstand sedimentation on a low-energy, wave-dominated, carbonate ramp characterized by large benthic Foraminifera. The inner ramp accumulated bioclastic banks and shoals composed of peloids, calcareous red algae and Nummulites. The middle ramp is recorded by wackestones with a diverse assemblage of flat Foraminifera; occasional storm events generated winnowed packstones. The outer ramp is represented by mudstones and marls with a sparse biota. The Nummulitic Limestones pass upwards into hemipelagic marls. The drowning of the Nummulitid-rich ramp is unlikely to have been caused by flexural subsidence of the foreland plate. Possible other contributing factors to the demise of the carbonate ramp were nutrient excess from the siliciclastic-rich orogenic margin to the basin, and/or glacio-eustatic sea-level rise

Tectonic forcing of longitudinal valleys in the Himalaya: morphological analysis of the Ladakh Batholith, North India

Longitudinal valleys form first order topographic features in many mountain belts. They are commonly located along faults that separate tectonic zones with varying uplift histories. The Indus Valley of Ladakh, northern India, runs northwestwards following the boundary between the relatively undeformed Ladakh Batholith to the north–east and the folded and thrusted Zanskar mountains to the south–west. In this region the Shyok Valley, on the northern side of the batholith, approximately parallels the course of the Indus. This study investigates geomorphic variations in transverse catchments that drain the Ladakh Batholith, into the Indus and Shyok rivers. The batholith has been divided into three zones based on varying structural characteristics of its northeastern and southwestern boundaries. Morphometric analysis of 62 catchments that drain into the Indus and Shyok valleys was carried out using three digital datasets, and supported by field observations. Morphometric asymmetry is evident in the central zone where the Shyok valley is considered tectonically inactive, but the Indus Valley is bound by the northeastwardly thrusting Indus Molasse and the batholith. In this zone the catchments that drain into the Indus Valley are more numerous, shorter, thinner and have lower hypsometric integrals than those that drain into the Shyok. By linking these observations with the regional geology and thermochronological data it is proposed that high sediment discharge from the deformed Indus Molasse Indus Valley has progressively raised base levels in the Indus Valley and resulted in sediment blanketing of the opposing tectonically quiescent catchments that drain southwestwards off the batholith. The Indus Molasse thrust front has propagated at least 36 km towards the Ladakh Batholith over the last 20 Ma. Hence it is proposed that this long term asymmetric structural deformation and exhumation has forced the Indus longitudinal valley laterally into the Ladakh Batholith resulting in the morphometric asymmetry of its transverse catchments

The evidence for a Pyrenean Resurrection: a response to Babault et al. (2008)

No abstract availabl