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Abstract: There are certain controls which operate to demarcate the nature and size range of quartz particles in terrestrial detrital sediments. The particles fall into discrete and definable populations, which are separated by ‘Tanner gaps’. Quartz sand nature is determined largely by a eutectic-like reaction, which takes place in the original igneous rock. This reaction delivers a fine mix of quartz and feldspar units, which on weathering deliver quartz sand. The formation of quartz silt is more contentious; it appears that silt production is essentially controlled by the presence in larger quartz particles of ‘Moss defects’, crystalline defects introduced into the quartz structure by earlier events, e.g. the high-low displacive transformation in cooling quartz. There appear to be two modes in airborne quartz particles (which have been called large dust and small dust). The larger mode is the loess mode (around 20–60 μm) and the smaller mode falls into the classification with high-level, long-travel dust (mode around 2–6 μm). The quartz in small dust is around the same size as the clay mineral agglomerate particles (CMA) which form a considerable proportion of high level dust clouds. The CMA particles form from lake deposits; the size is controlled by the openness of the packing in the lake sediments. This can be demonstrated by a simple Monte Carlo model. [Copyright &y& Elsevier]

Abstract: Annually laminated sediments can provide an absolute time scale (by varve counting) and a high-resolution palaeoclimate information (from varve thickness). Both types of information may be directly measured from sediment core surfaces. In this paper, we stress that varve counting and varve thickness measurements derived from fresh core surfaces could not systematically reveal the internal sedimentary structure, even if assisted by high resolution image analysis. We present an example of a homogeneous sediment core for which the varves were only observable after core impregnation and polishing steps. Because the impregnation methods are not yet standardized, the aim of this paper is to give an updated review of the methodology. In this review, we present the major critical points during impregnation steps. In particular, we focus on all of the post-treatment sediment disturbances that can alter the laminated micro-structure and, consequently, varve measurements. Finally, we propose a modified impregnation protocol, especially adapted for tracking varved intervals in long cores. [Copyright &y& Elsevier]

Abstract: Multi-beam bathymetry and backscatter, 3.5 kHz pinger profiles, side-scan sonar and seabed samples have been examined to evaluate along- and down-slope sedimentary processes along the Celtic Margin shelf and upper slope in water depths of 200 to 1500 m. The continental shelf and slope are indented and dissected by major canyon systems. The shelf is characterised by major northeast–southwest trending sand banks that are orthogonal to the shelf edge. Along the shelf edge, several fields of asymmetric sandwaves oriented orthogonal to the canyon axes indicate sediment transport into the canyon heads. Less commonly, sandwaves with weak asymmetry suggest sediment transport onto the shelf. These may be reworked and are partly overprinted by more recent sandwaves. Down-slope sediment transport by turbidity currents is the dominant process through the major canyons. Recent faulting has also played a role in canyon development. Turbidity currents are most likely initiated by faulting, and/or slope failure of the walls that bound the canyon head drainage basins and sediment migration from the shelf. This leads to deep incision of sinuous thalwegs in the upper reaches of canyon floors and downcutting and sediment transport on the mid to lower continental slope. The canyons are V-shaped in the upper reaches and become U-shaped progressively down-slope, suggesting they represent either a transition from erosive to depositional processes or sediment bypass conduits carrying sediment between the shelf and abyssal plain. Over-bank spill from canyons leads to deposition of unconfined turbidite deposits (muds) on the intervening canyon spurs. [Copyright &y& Elsevier]