Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea

Graham, A.G.C., Lonergan, L. & Stoker, M.S. 2010: Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea. Boreas, Vol. 39, pp. 471–491. 10.1111/j.1502‐3885.2010.00144.x. ISSN 0300‐9483. Geological constraints on ice‐sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here, we present a detailed interpretation of depositional environments from a new 30‐m‐long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British–Fennoscandian Ice Sheet. Seven units characterize a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeoregimes. These are: a period of advance and ice‐sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine‐to‐marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overriding by the SE–NW‐flowing Witch Ground ice stream. AMS ¹⁴C dating confirms ice‐stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 ¹⁴C ka BP. Sediments overlying the ice‐compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 ¹⁴C ka BP. A re‐advance of British ice during the last deglaciation, dated at 13.9 ¹⁴C ka BP, delivered ice‐proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally pervasive iceberg‐ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 ¹⁴C ka BP, and may correspond to oscillating ice‐sheet margins during final, dynamic ice‐sheet decay.     

Lunar dust and lunar simulant activation and monitoring

Abstract— NASA plans to resume human exploration of the Moon in the next decade. One of the pressing concerns is the effect that lunar dust (the fraction of the lunar regolith <20 μm in diameter) will have on systems, both human and mechanical, due to the fact that various problems were caused by dust during the Apollo missions. The loss of vacuum integrity in the lunar sample containers during the Apollo era ensured that the present lunar samples are not in the same condition as they were on the Moon; they have been passivated by oxygen and water vapor. To mitigate the harmful effects of lunar dust on humans, methods of “reactivating” the dust must be developed for experimentation, and, ideally, it should be possible to monitor the level of activity to determine methods of deactivating the dust in future lunar habitats. Here we present results demonstrating that simple grinding, as a simple analog to micrometeorite crushing, is apable of substantially activating lunar dust and lunar simulant, and it is possible to determine the level of chemical activity by monitoring the ability of the dust to produce hydroxyl radicals in aqueous solution. Comparisons between ground samples of lunar dust, lunar simulant, and quartz reveal that ground lunar dust is capable of producing over three times the amount of hydroxyl radicals as lunar simulant and an order of magnitude more than ground quartz.     

Inhibition of dissolution within shallow water carbonate sediments: impacts of terrigenous sediment input on syn-depositional carbonate diagenesis

The early diagenetic chemical dissolution of skeletal carbonates has previously been documented as taking place within bioturbated, shallow water, tropical carbonate sediments. The diagenetic reactions operating within carbonate sediments that fall under the influence of iron‐rich (terrigenous) sediment input are less clearly understood. Such inputs should modify carbonate diagenetic reactions both by minimizing bacterial sulphate reduction in favour of bacterial iron reduction, and by the reaction of any pore‐water sulphide with iron oxides, thereby minimizing sulphide oxidation and associated acidity. To test this hypothesis sediment cores were taken from sites within Discovery Bay (north Jamaica), which exhibit varying levels of Fe‐rich bauxite sediment contamination. At non‐impacted sites sediments are dominated by CaCO₃ (up to 99% by weight). Pore waters from the upper few centimetres of cores show evidence for active sulphate reduction (reduced SO₄/Cl^? ratios) and minor CaCO₃ dissolution (increased Ca²⁺/Cl^? ratios). Petrographic observations of carbonate grains (specifically Halimeda and Amphiroa) show clear morphological evidence for dissolution throughout the sediment column. In contrast, at bauxite‐impacted sites, the sediment is composed of up to 15% non‐carbonate and contains up to 6000 μg g^?1 Fe. Pore waters show no evidence for sulphate reduction, but marked levels of Fe(II), suggesting that bacterial Fe(III) reduction is active. Carbonate grains show little evidence for dissolution, often exhibiting pristine surface morphologies. Samples from the deeper sections of these cores, which pre‐date bauxite influence, commonly exhibit morphological evidence for dissolution implying that this was a significant process prior to bauxite input. Previous studies have suggested that dissolution, driven by sulphate reduction and sulphide oxidation, can account for the loss of as much as 50% of primary carbonate production in localized platform environments. The finding that chemical dissolution is minor in a terrigenous‐impacted carbonate environment, therefore, has significant implications for carbonate budgets and cycling, and the preservation of carbonate grains in such sediment systems.     

Space and sustainability: an exploratory essay on the production of social spaces through city-work

The purpose of this essay is to locate the making of social spaces as a particularly salient approach for understanding sustainability. Castells' spaces of places and spaces of flows are interpreted generically and a new social theory, Jacobs' moral syndromes, is introduced to underpin the production of these two spatial forms: commercial agents through their network practices make spaces of flows; guardian agents through their territorial practices make spaces of places. Both spaces are considered to be the outcome of city-work. A new division of labour is devised: four primary types of city-work are identified: hinter-work, net-work, territorial-work and hierarch-work. These ideas are considered as tools for thinking about developing spatial policies for sustainability. In conclusion, Jacobs' theory is used to discuss what the general strategy has to be for tackling sustainability.     

Sandwiched fossils

A little-known mode of fossil preservation-bioimmuration-is responsible for exciting new findings of soft-bodied organisms. Bioimmuration results from organic overgrowth by animals such as serpulid worms and oysters which form natural moulds of the organisms they have overgrown on their undersurfaces or sandwich overgrown organisms between themselves and their substrate. Overgrowth is a routine occurrence among the many marine organisms lacking mobility, and bioimmured fossils can be extremely common. Discoveries of bioimmured ctenostome bryozoans, hydroids and other soft-bodied animals that lived attached to hard surfaces are providing important new palaeontological perspectives, especially in the Mesozoic.