Ferromanganese nodules and micro-hardgrounds associated with the Cadiz Contourite Channel (NE Atlantic): Palaeoenvironmental records of fluid venting and bottom currents

Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf of Cadiz (850–1000 m). This channel is part of a large contourite depositional system generated by the Mediterranean Outflow Water. Ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals. We present a complete characterisation of these deposits based on submarine photographs and geophysical, petrographic, mineralogical and geochemical data. The genesis and growth of ferromanganese deposits, strongly enriched in Fe vs. Mn (av. 39% vs. 6%) in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes. The interaction of the Mediterranean Outflow Water with the continental margin has led to the formation of Late Pleistocene–Holocene ferromanganese mineral deposits, in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events. The diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons (δ13CPDB=−20 to −37‰) and organic matter within the channel floor sediments, promoting the formation of Fe–Mn carbonate nodules. High 87Sr/86Sr isotopic values (up to 0.70993±0.00025) observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep-seated fluid venting across the fault systems in the diapirs below the Cadiz Contourite Channel. Erosive action of the Mediterranean Outflow Water undercurrent could have exhumed the Fe–Mn carbonate nodules, especially in the glacial periods, when the lower core of the undercurrent was more active in the study area. The growth rate determined by 230Thexcess/232Th was 113±11 mm/Ma, supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka. Ca-rich layers in the nodules could point to the interaction between the Mediterranean Outflow Water and the North Atlantic Deep Water during the Heinrich events. Siderite–rhodochrosite nodules exposed to the oxidising seabottom waters were replaced by Fe–Mn oxyhydroxides. Slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds, which show imprints of the Mediterranean Outflow Water with low 87Sr/86Sr isotopic values (down to 0.70693±0.00081). We propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents. We also compare and discuss the generation of ferromanganese deposits in the Cadiz Contourite Channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

Exhibiting the ‘Orient’ : historicising theory and curatorial practice in UK museums and galleries

This article examines the extent to which theory emerges in practice within the context of museum curatorship and the public discourses surrounding it. The theoretical context is the legacy of Edward W. Said’s canonical study, Orientalism and its call for ‘Western’ reflexivity in the politics of representation of the Islamic Near East. We argue that Said’s study has, in its own right, engendered a field of professional academic discourse in the areas of Cultural Studies and Postcolonial Studies. We, however, begin to ask about the extent to which its arguments and insights explicitly inform the work of representation and interpretation of the material culture of the Near East in ‘Western’ institutions. This exploratory, study draws on four cases of exhibitions on Iranian, Turkish and the broader field of Islamic art in nationally funded or endorsed museums and galleries in the United Kingdom. All of the exhibitions took place following 2001 amongst cultural and political discourses concerning Islam during the so-called ‘War on Terror’. This convergence of an established ‘Saidian’ theoretical legacy and recent geopolitical events that once again raise questions about the relationship between ‘the West’ and ‘Islam’ allows these exhibitions and the discourses surrounding them to be historically emplotted in quite specific ways. Analysis of exhibition catalogues, consultants’ impact reports and interviews with curatorial staff leads us to conclude that while a specific engagement with Said’s work may not be in evidence, institutions and their staff do inhabit and act upon a discursive field that corresponds to that book’s priorities and agenda. This invites further investigation into the form and process within which critical theory makes the transition from citation and discussion in strictly academic discourse to actual implementation in historically situated organisational practice