Deciphering signals of late Holocene fluvial and aeolian supply from a shelf sediment depocentre off Senegal (north‐west Africa)

High‐resolution climatic records of the late Holocene along the north‐west African continental margin are scarce. Here we combine sediment grain size, elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow‐marine sediment depocentre in the vicinity of the Senegal River mouth. The aim is to understand how these terrigenous components reflect climate variability during the late Holocene. Major element contents were measured and mineral identification was performed on three sub‐fractions of our sediment core: (i) fluvial material < 2 µm, (ii) aeolian material of 18–63 µm and (iii) a sub‐fraction of dual‐origin material of 2–18 µm. Results show that more than 80% of the total Al and Fe terrigenous bulk content is present in the fluviogenic fraction. In contrast, Ti, K and Si cannot be considered as proxies for one specific source off Senegal. The Al/Ca ratio, recording the continental river runoff, reveals two dry periods from 3010 to 2750 cal a BP and from 1900 to 1000 cal a BP, and two main humid periods from 2750 to 1900 cal a BP and from 1000 to 700 cal a BP. The match between (i) intervals of low river runoff inferred by low Al/Ca values, (ii) reduced river discharge inferred by integrated palynological data from offshore Senegal and (iii) periods of enhanced dune reactivation in Mali confirms this interpretation. Copyright © 2011 John Wiley & Sons, Ltd.     

Tropical glacier fluctuations in the Cordillera Blanca,Peru between 12.5 and 7.6 ka from cosmogenic 10Be dating

We report cosmogenic surface exposure ¹⁰Be ages of 21 boulders on moraines in the Jeullesh and Tuco Valleys, Cordillera Blanca, Peru (～10°S at altitudes above 4200 m). Ages are based on the sea-level at high-latitude reference production rate and scaling system of Lifton et al. (2005. Addressing solar modulation and long-term uncertainties in scaling secondary cosmic rays for in situ cosmogenic nuclide applications. Earth and Planetary Science Letters 239, 140–161) in the CRONUS-Earth online calculator of Balco et al. (2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from ¹⁰Be and ²⁶Al measurements. Quaternary Geochronology 3, 174–195). Using the Lifton system, large outer lateral moraines in the Jeullesh Valley have a ¹⁰Be exposure age of 12.4 ka, inside of which are smaller moraine systems dated to 10.8, 9.7 and 7.6 ka. Large outer lateral moraines in the Tuco Valley have a ¹⁰Be exposure age of 12.5 ka, with inner moraines dated to 11.3 and 10.7 ka. Collectively, these data indicate that glacier recession from the Last Glacial Maximum (LGM) in the Cordillera Blanca was punctuated by three to four stillstands or minor advances during the period 12.5–7.6 ka, spanning the Younger Dryas Chronozone (YDC; ～12.9–11.6 ka) and the cold event identified in Greenland ice cores and many other parts of the world at 8.2 ka. The inferred fluctuations of tropical glaciers at these times, well after their withdrawal from the LGM, indicate an increase in precipitation or a decrease in temperature in this region. Although palaeoenvironmental records show regional and temporal variability, comparison with proxy records (lacustrine sediments and ice cores) indicate that regionally this was a cold, dry period so we ascribe these glacier advances to reduced atmospheric temperature rather than increased precipitation.     

Chronology of the Last Glacial Maximum in the Salzach palaeoglacier area (Eastern Alps)

A chronostratigraphy based on luminescence data was established at a key loess profile (Duttendorf) in the northern alpine foreland of Austria. The data help to constrain the timing and duration of the Last Glacial Maximum (LGM) in the area of one of the largest east Alpine piedmont glaciers, the Salzach palaeoglacier. Climate deterioration and maximum advance of this glacier were coeval with the beginning of the main loess accumulation phase in the glacier forefield at ～29–30 ka. A late LGM‐outwash gravel layer deposited on top of the loess profile marks the end of the LGM glacier activity at ～20 ka. The geomorphological setting around the loess profile provides evidence of a major glacier oscillation during the course of the LGM, a phenomenon qualitatively known from other alpine palaeoglaciers but never interpreted in terms of palaeoclimate. A LGM glacier oscillation similar to that of the Salzach palaeoglacier was reported recently from the south Alpine Tagliamento palaeoglacier, suggesting a common forcing. The onset of loess deposition at Duttendorf and the tentatively contemporal advance of the Salzach palaeoglacier reflect, as do other data, the drastic cooling in Europe as a result of Heinrich event 3. The first glacier maximum is not well constrained in the study area but a correlation with the better dated Tagliamento amphitheatre suggests a possible response to Heinrich 2. The second re‐advance occurred synchronously (within dating uncertainties) in both palaeoglaciers forefields (at ～21 ka) but the forcing mechanism remains unknown. Copyright © 2011 John Wiley & Sons, Ltd.     

Coupling Size-Exclusion Chromatography and ICP-MS to Investigate the Speciation of Platinum-Group Elements in Environmental Samples

The applicability of size-exclusion chromatography (SEC) coupled online with a high resolution ICP-MS (HR-ICP-MS) to investigate the speciation of the platinum-group elements (PGE), Rh, Pd and Pt, was evaluated. Experiments were carried out to determine the efficiency of different hydrophilic and hydrophobic size-exclusion gel materials to select the optimal eluent in respect of resolution, recovery, reproducibility and limit of detection. The suitability of HR-ICP-MS as a reliable detection instrument at low pg ml⁻¹ levels was investigated by examining possible mass interferences with Rh, Pd and Pt. Laboratory experiments demonstrated the interaction and capability of forming complexes of humic substances with PGE, demonstrating the potential role of these ubiquitous natural substances in the mobilisation of PGE in the environment.     

Zur Messung der Fahrt über Grund an Bord von Schiffen

Zusammenfassung Es wird gezeigt, wie mit einem Zweikreiselsystem, das gleichzeitig die Nordrichtung und den Horizont liefert, ein Trägheits-Navigationssystem unter Verwendung von Beschleunigungsmessern und eines Rechenaggregates aufgebaut werden kann. Die Beschleunigungsmesser werden von einer kreiselstabilisierten Plattform getragen, die über Stützmotore in den drei Freiheitsgraden parallel zum Zweikreiselsystem gehalten wird.

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On measuring a ship's speed over ground from board of ships

Summary The following paper explains how to assemble an inertial navigation system with the aid of accelerometers, a calculating unit and a two gyro system that simultaneously indicates the north direction and the horizon. The accelerometers are carried by a gyro stabilized platform that, on its part, is kept in the three degrees of freedom parallel to the two gyro system by three torques generators.

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Sur la mesure à bord d'un bâtiment pour déterminer la vitesse par-dessus le fond de la mer

Résumé Le travail suivant expose de quelle manière on peut construire un système de navigation d'inertie en joignant des accéléromètres, un aggrégat à calculer et un système à deux gyroscopes; ce dernier fournit simultanément la direction nord et l'horizon. Une plate-forme, également stabilisée par un système à deux gyroscopes, porte les accéléromètres. Cette plate-forme se maintient à l'aide de trois génératrices du moment de couple dans les trois degrés de. liberté parallèle au système à deux gyroscopes.

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Natural and synthetic ferroglaucophane

Amphiboles approximating the composition of the ferroglaucophane end member, Na₂Fe₃Al₂Si₈O₂₂(OH)₂, have not been found in nature prior to 1969. Chemical, physical and petrologic data of four specimens of that mineral are given, two from Southern Italy and two from New Caledonia (Black, 1970). The ferroglaucophane end member was synthesized in seeded runs at 500° C, 5000 bars fluid pressure with oxygen fugacity defined by the wüstite-magnetite (WM) buffer. X-ray data and cell dimensions (a=9.686 Å, b=17.89, c=5.317, β=103° 45.2′ V=894.9 ų) are presented along with microprobe data that confirm the end member composition. Under these conditions of synthesis the ferroglaucophane grew metastably, however. Stability relations of the synthetic end member and of one natural specimen were investigated in a temperature range from 250° C to 500° C and at 3 and 5 kb with different oxygen buffers. At relatively low oxygen fugacities (WM buffer, QFM buffer) ferroglaucophane breaks down above 350–360° C. Under more oxidizing conditions (HM buffer) ferroglaucophane may not be stable even at very low temperatures. Mineral facies and chemical bulk composition of rocks that would favor the natural occurrence of ferroglaucophane are discussed. As assemblages with ferroglaucophane can have crystallized only below a very specific upper temperature limit, it is proposed to direct some attention towards that mineral.     

Laser-ablation ICP-MS analysis of silicate and sulfide melt inclusions in an andesitic complex I: analytical approach and data evaluation

Quantitative microanalysis of entire silicate and sulfide melt inclusions by Excimer Laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICPMS) has been applied to extrusive and shallow intrusive rocks from the andesitic Farallón Negro Volcanic Complex (northwestern Argentina). Silicate melts are trapped in pyroxene, amphibole, plagioclase and quartz, and sulfide melts are trapped in amphibole. Details of the analytical approach and the quantification procedure are given and the results are evaluated to test the accuracy of the technique and the validity of the interpretation of analytical signals. Similar compositions of silicate melt inclusions trapped in truly co-precipitating minerals show that the quantification approach of melt inclusion compositions from LA-ICPMS signals through an internal standard is valid. This correspondence also shows that melt inclusions investigated in this study are not significantly influenced by the boundary layer around a growing crystal or by post-entrapment modifications. Post-entrapment diffusive re-equilibration only affected the Fe and Mg content of melt inclusions in mafic phases. Thus, melt inclusions are representative samples of the melt from which the host mineral crystallized, with regard to most major and trace elements. Sulfide melt inclusions (present as pyrrhotite with exsolution of Au and Cu in phases separated during cooling) were analyzed for their bulk Fe, Cu and Au content, and the abundance of these elements was quantified using a silicate glass as external standard. The validity of this calibration was tested by comparing electron microprobe analyses of Fe, Cu, Ni and Co in homogeneous sulfide minerals with LA-ICPMS results. Identical results within calculated uncertainty (one standard deviation of five to nine analyses, mostly between 1 and 5 wt% RSD) demonstrate that for these elements, measured element ratios are independent of the matrix using our analytical setup.Editorial responsibility: T.L. Grove     

Zircon and apatite fission-track thermochronology of Late Carboniferous volcanic rocks of the NE German Basin

Zircon and apatite fission-track analyses from Late Carboniferous felsic volcanic rocks of the NE German Basin (Halle area and Friedland drilling) reveal at least two major post-emplacement thermal events. After initial cooling at ca. 300 Ma, the volcanic pile underwent a major thermal event at ca. 200 Ma that reached in most places ca. 250-280 °C and led to the new growth of clay minerals. This event is recorded in the zircon fission-track data and can be related to Jurassic-Triassic rifting in Europe. Another thermal event is recorded in the apatite samples at ca. 100 Ma. A close correlation is observed between apatite fission-track age, texture, and sample alteration. Coarse-grained samples are stronger altered and have younger fission-track ages. Hydrothermal alteration coupled with advective heating probably caused these Upper Cretaceous fission-track ages. The latter event can be related to block faulting and inversion of the European plate during the early stages of the Alpine orogeny.