The Rio Dell Formation: a Plio-Pleistocene basin slope deposit in Northern California

The Rio Dell Formation (Pleistocene and Pliocene), exposed south of Eureka, California, is a prograded sequence of basinal turbidites overlain by basin slope and shelf deposits. The slope deposits studied in the Centerville Beach section accumulated in a steadily shallowing environment delineated by analysis of palaeobathymetrically significant benthonic foraminiferal biofacies in turn suggesting deposition at depths of 1000–100 m. Lower slope deposits interfinger with basinal turbidites derived from the Eel River delta to the north. Slumped blocks of silty mudstone, and associated silt and mud beds, are common. The middle slope deposits are mudstones; coarser sediments bypassed this zone. Mudstones and muddy siltstones alternate on the upper slope. Shallow depressions, probably slump scars, that have been rapidly filled by upper slope sediment are common. The transition to shelf deposits is marked by an increase in sediment grain size, in the degree of oxidation, and in the abundance of megafossils. High percentages of benthonic foraminifera displaced from shelf depths indicate that resedimentation processes are most important on the upper slope.     

Experimental Study of the Composition Join NaAlSiO4-CaCO3-H2O and the Genesis of Alkalic Rock--Carbonatite Complexes

Phase equilibrium studies have been carried out on the compositionjoin NaAlSiO₄-CaCO₃-H₂O with 25 wt per cent H₂O at 1 kb pressurein the temperature range 600–960 °C. Liquid, in equilibriumwith crystalline phases and a sodic, aqueous vapor phase persistsacross the join down to temperatures of about 600 °C. Fractionalcrystallization of a carbonated nepheline-rich liquid in equilibriumwith vapor is capable of generating successively the crystallineassemblages (1) nepheline, (2) melilite+nepheline, (3) hydroxyhaüyne+melilite,(4) cancrinite+melilite, and (5) calcite+cancrinite+melilite.Late-stage liquid fractions are rich in CaCO₃, whereas the vaporphase is enriched in Na. The experimental assemblages are strikinglysimilar to rocks in alkalic rock-carbonatite complexes in generaland in the Oka, Quebec, complex in particular. The successionof assemblages at Oka and at other melilite rock-bearing complexesmay be interpreted as the products of fractionation of a carbonatednephelinite magma by analogy with the experimental results.The sodium-bearing vapor phase of the experiments may be analogousto the fenitizing agent of some carbonatite complexes.     

Petrogenesis of Group I Kimberlites from Kimberley, South Africa: Evidence from Bulk-rock Geochemistry

Fresh samples of hypabyssal kimberlite from the five major kimberlitepipes in the Kimberley area of South Africa have been analysedfor their bulk-rock major and trace element geochemistry. Thegeochemical data allow identification of the influence of crustalcontamination in certain samples, best illustrated in termsof elevated SiO₂, Al₂O₃, Pb and heavy rare earth element (HREE)contents. Samples devoid of such crustal contamination showcoherent major and fluid-immobile trace element variations,whereas fluid-mobile trace elements are scattered. Kimberlitesrich in macrocrysts are shown to reflect substantial (up to35%) entrainment of mantle peridotite, with Ni–SiO₂ andSc–SiO₂ variations defining mixing trajectories towardsgarnet lherzolite. The likely primary magma(s) parental to theKimberley kimberlites is suggested to have a composition of26–27 wt % MgO, 26–27 wt % SiO₂,     

Late Weichselian deglacial history of Disko Bugt, West Greenland, and the dynamics of the Jakobshavns Isbrae ice stream

New relative sea-level (RSL) data from Disko Bugt, a large marine embayment in West Greenland, are used to examine the deglacial history of the Jakobshavns Isbrae ice stream. RSL data show rapid deglaciation after 10.3 ka cal. yr BP. Once deglaciation began, a bedrock high in the west of the bay exerted no discernible influence on the deglacial chronology. Following initial rapid retreat, ice stream recession slowed as it approached the eastern shores of the bay. Seabed elevations increase here and the ice stream terminus lingered for several thousand years before retreating into the narrow bedrock-confined Jakobshavns Isfjord. The seabed topography of Disko Bugt includes several deep channels which probably record the former course of the ice stream. Using a simple water depth/calving velocity relationship it is estimated that the maximum calving velocity on deglaciation was c. 4.8 km a^-1. This is less than the present rate (6–7 km a^-1), although ice discharge was two to four times that observed today. Initiation of rapid ice stream retreat was probably caused by ice stream thinning and increased surface melting. A critical point in time was the retreat of the ice stream from shallow continental shelf waters ( c. 400 m) into the deep bedrock trough (>800 m) which marks the entrance to Disko Bugt.     

'The gloomy forebodings of this dread disease', climate, famine and sleeping sickness in East Africa

Identifying the nature of the association between climate, environmental, socio-economic and political context and disease remains a major challenge, yet a better comprehension of the linkages is imperative if predictive models to guide public health responses are to be devised. Our understanding of the relationships could be improved through investigations of historical epidemics. In this paper we draw on a range of published and unpublished documents to explore the complex relationship between climate, environmental change and epidemic disease (re)emergence in East Africa, and Uganda in particular. This is a region which has experienced climate variability at a range of temporal and spatial scales, but which also has a long history of episodic epidemic disease. We focus on the late nineteenth and early twentieth centuries – a time of social, economic and political reordering in East Africa associated with European colonial intervention, but also a period which witnessed a variety of climatic, ecological and disease events. It will be argued that these developments coalesced, creating a set of spatially distinctive social and environmental conditions which fostered the emergence and prolongation of one of the most deadly episodes of disease in East African history, the sleeping sickness epidemic of c.1900–20.     

CHANGING CONCEPTIONS OF SUSTAINABILITY IN BARCELONA'S PUBLIC PARKS*

ABSTRACT. In this article we explore the relationships between public parks and a broad interpretation of sustainability, taking as a case study the city of Barcelona, Spain. Recent official discourses in Barcelona insist on sustainability as one of the fundamental assets of public parks. Yet whether these urban artifacts actually contribute to sustainability objectives in environmental and social terms remains to be examined. We compare two public parks in Barcelona‐the Parc Joan Miró (1983), and the Parc de Diagonal Mar (2002)–and show how, in the former, the integration of the social, political, and environmental dimensions of sustainability was largely achieved, whereas in the latter, only the environmental dimension appears to have been considered.     

Chronology of Murrumbidgee River palaeochannels on the Riverine Plain,southeastern Australia

Four major periods of palaeochannel activity have been identified on the Murrumbidgee sector of the Riverine Plain of southeastern Australia. On the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle. The ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments. These are named the Coleambally phase, which occurred from 105 to 80 ka (the mid- to latter part of Oxygen Isotope Stage 5), the Kerarbury phase from 55 to 35 ka (Stage 3), the Gum Creek phase from 35 to 25 ka (late Stage 3 to early Stage 2) and the Yanco phase from 20 to 13 ka (late Stage 2). The present flow regime was established by about 12 ka (Stage 1). The first two phases correlate with episodes of enhanced fluvial activity in northern and central Australia and with reduced dust activity globally. The phases in Stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the Last Glacial Maximum. Source-bordering aeolian dunes associated with the Coleambally, Kerarbury and Yanco phases were found, however, the TL dates show that some have undergone aeolian reworking. Thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of Late Quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here.