Carboniferous diamictite dykes in the Falkland Islands     

D.M. Hyam  J.E.A. Marshall  D.J. Sanderson 《Journal of African Earth Sciences》1997,25(4):505-517

Sedimentary dykes hosted in ? Ordovician-Devonian strata on the Falkland Islands contain diamictite. The dykes, which are discordant to the host rocks, are sub-vertical, parallel-sided sheets formed by downward injection of a semi-fluidized sediment. On West Falkland palynomorphs present in 2 of the 11 dykes located demonstrate a Late Visean-Early Namurian age. This is older than the main Lafonian Diamictite Formation (Permian) and indicates that the dykes are a rare preservation of sediments formed during the main ice coverage of the Gondwana glaciation. Vitrinite reflectance from organic matter in the dykes indicates a shallow burial history (< 2–3 km) for the southwest Falkland Islands implying deposition of an incomplete or condensed sequence during Late Palaeozoic times, although the stratigraphical relationship of the dykes indicates that this may be extended back into the Mid Palaeozoic. The two diamictite dykes located on East Falkland are shown to be younger; probably Permian in age.  相似文献   

Deep-sea avulsion and morphosedimentary evolution of the Rhône Fan Valley and Neofan during the Late Quaternary (north-western Mediterranean Sea)     

J. TORRES§  L. DROZ†  B. SAVOYE  E. TERENTIEVA‡  P. COCHONAT  N. H. KENYON  M. CANALS§ 《Sedimentology》1997,44(3):457-477

The Petit-Rhône Fan Valley (north-western Mediterranean) is a broad, sinuous, filled valley that is deeply incised by a narrow, sinuous thalweg. The valley fill is differentiated into three seismic subunits on high-resolution seismic-reflection profiles. The lower chaotic subunit probably consists of channel lag deposits that seem to be in lateral continuity with high-amplitude reflections representing levee facies. The intermediate transparent subunit, which has an erosional base and clearly truncates levee deposits, is interpreted to be mass-flow deposits resulting from the disintegration of the fan-valley flanks. The upper bedded subunit shows an overall lens-shaped geometry and the seismic reflections onlap either onto the top of the underlying transparent subunit or onto the Rhône levees. Piston core data show that the upper few meters of this upper subunit consist of thin turbidites, probably deposited by overflow processes. The few available ¹⁴C ages suggest that the upper stratified subunit filled the Petit-Rhône Fan Valley between 21 and 11 kyr BP. The upper bedded subunit is deposited within the Petit-Rhône Fan Valley downslope of a major decrease in slope gradient. This upper subunit and the thalweg are genetically related and represent a small channel/levee system confined within the fan valley. Previous studies interpreted this thalweg to be an erosional feature resulting from a recent avulsion of the major channel course. Our interpretation implies that the thalweg is not a purely erosional feature but a depositional/erosional channel. This small channel/levee system is superimposed on a large muddy channel/levee system after the sediment supply changed from thick muddy flows during the main phase of aggradation of the Rhône Fan levees, to thin, mixed (sand and mud) flows at the end of Isotope Stage 2 (～16–18 ka BP). The pre-existing morphology of the Petit-Rhône Fan Valley played a determinant role in the sediment dispersal leading to the creation of this small and confined channel/levee system. These mixed flows have undergone flow stripping resulting from the changes in the slope gradient along the thalweg course. The finer sediment overflowed from the thalweg and were deposited in the Petit-Rhône Fan Valley. Coarser channelled sediment remaining in the thalweg were deposited as a ‘sandy’lobe (Neofan). As indicated by ¹⁴C dating, sedimentation on this lobe continued until very recently, suggesting a further evolution of the turbidity flows from small mixed flows to small sandy flows. the deposition of this study lobe and the sedimentary fill of the Petit-Rhône Fan Valley may be related to widespread shelf edge and canyon wall failures with a resulting downslope evolution of failed sediment into turbidity currents.  相似文献   

UV Laser Ablation ICP-MS: Some Applications in the Earth Sciences   总被引：4，自引：0，他引：4  

Robert W. Nesbitt  Takafumi Hirata  Ian B. Butler  James A. Milton 《Geostandards and Geoanalytical Research》1997,21(2):231-243

This study reports a series of applications of UV laser ablation ICP-MS in the geological sciences. The advantages and disadvantages of the PQ "S" option and the use of nitrogen in the carrier gas are discussed. A general problem common to all ablation techniques is the calibration technique and experiments involving synthetic calibration samples are covered. Zircon geochemistry and geochronology by LA-ICP-MS are discussed and data are presented for REE, Hf and U for a standard zircon (91500) as well as a series of zircons from Zimbabwe. The potential of using Ce and Eu anomalies in petrologic studies is illustrated by zircons from a fractionated gabbroic-granite in the Urals. The potential of the LA-ICP-MS method to utilise standard X-ray fluorescence glass discs is demonstrated as a useful semi-quantitative tool in determining REE patterns. LA-ICP-MS is a powerful tool in the analysis of the platinum group elements (and Re) and some examples are given in the successful application of the technique to partitioning in iron meteorites.  相似文献   

Data buoy measurements of phytoplankton dynamics in southampton water, UK, a temperate latitude estuary with high nutrient inputs     

Paul N. Wright  David J. Hydes  Mary Lou Lauria  Jonathan Sharples  Duncan A. Purdie 《Ocean Dynamics》1997,49(2-3):203-211

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The use of NOSTRADAMUS, a numerical transport model, for simulating concentrations and distributions of chromium, cadmium and lead in the Southern North Sea     

A. D. Tappin  S. Gellers-Barkmann  J. D. Burton  P. J. Statham 《Ocean Dynamics》1997,49(2-3):411-430

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Beds comprising debrite sandwiched within co-genetic turbidite: origin and widespread occurrence in distal depositional environments   总被引：11，自引：0，他引：11  

P. J. Talling  L. A. Amy†  R. B. Wynn‡  J. Peakall†  M. Robinson 《Sedimentology》2004,51(1):163-194

Co‐genetic debrite–turbidite beds occur in a variety of modern and ancient turbidite systems. Their basic character is distinctive. An ungraded muddy sandstone interval is encased within mud‐poor graded sandstone, siltstone and mudstone. The muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite. The mud‐poor sandstone, siltstone and mudstone show features indicating progressive layer‐by‐layer deposition and are thus called a turbidite. Palaeocurrent indicators, ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event. Detailed field observations are presented for co‐genetic debrite–turbidite beds in three widespread sequences of variable age: the Miocene Marnoso Arenacea Formation in the Italian Apennines; the Silurian Aberystwyth Grits in Wales; and Quaternary deposits of the Agadir Basin, offshore Morocco. Deposition of these sequences occurred in similar unchannellized basin‐plain settings. Co‐genetic debrite–turbidite beds were deposited from longitudinally segregated flow events, comprising both debris flow and forerunning turbidity current. It is most likely that the debris flow was generated by relatively shallow (few tens of centimetres) erosion of mud‐rich sea‐floor sediment. Changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition. The association with distal settings results from the ubiquitous presence of muddy deposits in such locations, which may be eroded and disaggregated to form a cohesive debris flow. Debrite intervals may be extensive (> 26 × 10 km in the Marnoso Arenacea Formation) and are not restricted to basin margins. Such long debris flow run‐out on low‐gradient sea floor (< 0·1°) may simply be due to low yield strength (? 50 Pa) of the debris–water mixture. This study emphasizes that multiple flow types, and transformations between flow types, can occur within the distal parts of submarine flow events.  相似文献   

Temporal and spatial cyclicity of accretion at slow-spreading ridges—evidence from the Reykjanes Ridge     

Christine Peirce  Alex Gardiner  Martin Sinha 《Geophysical Journal International》2005,163(1):56-78

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Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM     

J. H. C. Bosmans  S. S. Drijfhout  E. Tuenter  F. J. Hilgen  L. J. Lourens 《Climate Dynamics》2015,44(1-2):279-297

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Iodine budget in surface waters from Atacama: Natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine-129 isotopes     

《Applied Geochemistry》2016

Iodine enrichment in the Atacama Desert of northern Chile is widespread and varies significantly between reservoirs, including nitrate-rich “caliche” soils, supergene Cu deposits and marine sedimentary rocks. Recent studies have suggested that groundwater has played a key role in the remobilization, transport and deposition of iodine in Atacama over scales of millions-of-years. However, and considering that natural waters are also anomalously enriched in iodine in the region, the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained. In this study we provide new halogen data and isotopic ratios of iodine (¹²⁹I/I) in shallow seawater, rivers, salt lakes, cold and thermal spring water, rainwater and groundwater that help to constrain the relative influence of meteoric, marine and crustal sources in the Atacama waters. Iodine concentrations in surface and ground waters range between 0.35 μM and 26 μM in the Tarapacá region and between 0.25 μM and 48 μM in the Antofagasta region, and show strong enrichment when compared with seawater concentrations (I = ∼0.4 μM). In contrast, no bromine enrichment is detected (1.3–45.7 μM for Tarapacá and 1.7–87.4 μM for Antofagasta) relative to seawater (Br = ∼600 μM). These data, coupled to the high I/Cl and low Br/Cl ratios are indicative of an organic-rich sedimentary source (related with an “initial” fluid) that interacted with meteoric water to produce a mixed fluid, and preclude an exclusively seawater origin for iodine in Atacama natural waters. Iodine isotopic ratios (¹²⁹I/I) are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source (i.e., groundwater which has interacted with Jurassic marine basement), with variable influence of at least one atmospheric or meteoric source. Samples with the lowest isotopic ratios (¹²⁹I/I from ∼215 to ∼1000 × 10⁻¹⁵) strongly suggest mixing between the groundwater and iodine storage in organic-rich rocks (with variable influence of volcanic fluids) and pre-anthropogenic meteoric water, while samples with higher values (∼2000–93,700 × 10⁻¹⁵) indicate the input of anthropogenic meteoric fluid. Taking into account the geological, hydrologic and climatic features of the Atacama region, we propose that the mean contribution of anthropogenic ¹²⁹I is associated with ¹²⁹I releases during nuclear weapon tests carried out in the central Pacific Ocean until the mid 1990's (¹²⁹I/I = ∼12,000 × 10⁻¹⁵). This source reflects rapid redistribution of this radioisotope on a global scale. Our results support the notion of a long-lived continental iodine cycle in the hyperarid margin of western South America, which is driven by local hydrological and climate conditions, and confirm that groundwater was a key agent for iodine remobilization and formation of the extensive iodine-rich soils of Atacama.  相似文献   

From stormy seas to the doldrums: The challenges of navigating towards an ecologically coherent marine protected area network through England's Marine Conservation Zone process     

《Marine Policy》2016

There is an on-going process to establish Marine Conservation Zones (MCZs) in England, to form part of a coherent and representative network of marine protected areas under national and EU legislation. From 2009 to 2011, the MCZ process included strong participatory elements. Four regional multi-sector stakeholder groups developed MCZ recommendations collaboratively, in line with ecological guidance provided by the Government's nature conservation advisers. This guidance was based on Government policy principles, including that MCZs should be designated based on ‘best available evidence’. This paper analyses the multi-dimensional conflicts that emerged within the stakeholder group in south-west England, which were magnified by uncertainty about future MCZ management. In September 2011, after working through these conflicts through trade-offs and negotiations, the stakeholder groups jointly recommended 127 MCZs to Government. The process subsequently shifted to a top-down approach, with further stakeholder engagement limited to bilateral consultation. There was a concurrent shift in policy, from a broad-scale network-level focus towards single-feature conservation. A lengthy series of evidence reviews concluded that the existing evidence at the time was insufficient to progress with the designation of most sites, marking a clear departure from the policy principle of proceeding with the designation of a representative network based on ‘best available evidence’, and effectively undermining the work carried out by stakeholder groups. Though MCZ designation was originally timetabled for 2012, in November 2013 just 27 of the recommended 127 MCZs were designated in a first tranche. At the time, no clear timetable was in place for subsequent tranches.  相似文献