Sediments and micronodules in the northern and central Peru Basin

The mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the Peru Basin are discussed. Because of the proximity of the basin to the Carbonate Compensation Depth (C.C.D.), surface sediments vary between calcareous oozes and siliceous muds. Besides biogenic components clay minerals are important. By far the most abundant clay mineral is smectite which is thought to be of diagenetic origin. On a carbonate-free basis, the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial Pacific. Sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm/ 1000 yr.Micronodule compositions show significant variations related to the size class of the micronodules and the depth of occurrence within the sediment column. In general, the chemistry of the micronodules can be explained by the reductive mobilization of Mn within the sediment column and by oxic diagenetic reactions between ferromanganese hydroxides and biogenic opal. The dominant mineral phase is todorokite.

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Zusammenfassung Mineralogie und chemische Zusammensetzung von Sedimenten und Manganmikroknollen aus dem nördlichen und zentralen Teil des Peru-Beckens werden beschrieben. Die Oberflächensedimente bestehen je nach der Lage zur Karbonatkompensationstiefe (C.C.D.) aus karbonatischen bzw. kieseligen Ablagerungen. Neben den biogenen Komponenten sind Tonmineralien (Smektit, Illit) von Bedeutung. Das häufigste Tonmineral ist diagenetisch gebildeter Smektit. Auf karbonatfreier Basis ist die chemische Zusammensetzung der Sedimente sehr einheitlich, vergleichbar mit dem Chemismus zentralpazifischer Sedimente.²³⁰Th-Datierungen ergeben eine Sedimentationsrate von 3–5 mm/1000 a für die obersten Sedimentschichten.In Abhängigkeit von der Korngrößenklasse und der Tiefe in der Sedimentsäule zeigen die Manganmikroknollen große Schwankungen im Chemismus. Remobilisationsprozesse unter reduzierenden Bedingungen in der Sedimentsäule sowie die diagenetischen Reaktionen zwischen Fe-Mn-Hydroxiden und biogenem Opal bestimmen die chemische Zusammensetzung der Manganmikroknollen. Die vorherrschende Mineralphase ist Todorokit.

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Résumé Cette note décrit la minéralogie et la composition des sédiments et des nodules polymétalliques de la partie septentrionale et centrale du bassin de Perou. Les sédiments de surface consistent en dépôts calcaires ou siliceux selon leur situation par rapport à la profondeur de compensation des carbonates (C. C. D.). A côté des composants biogènes, des minéraux argileux (smectites, illites) sont présents en quantité importante. Le minéral argileux le plus fréquent est une smectite diagenétique. La composition chimique de la fraction non carbonatée des sédiments est uniforme, comparable au chimisme de ceux du Pacifique central. Dans les couches les plus élevées, la vitesse de sédimentation, basée sur des datations par²³⁰Th, est de 3 à 5 mm/1000 ans.Le chimisme des micronodules polymétalliques est très variable et dépend de leur profondeur dans le sédiment et de leur dimension. Le chimisme est déterminé par des processus de remobilisation en conditions réductrices dans la colonne sêdimentaire, ainsi que par des réactions diagénétiques entre les hydroxydes de Fe-Mn et l'opale biogène. Le minéral dominant est la todorokite.

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High resolution Thex stratigraphy of sediments from high-latitude areas (Norwegian Sea, Fram Strait)

We present data on the average sedimentation rates (ranging from 1.6 cm/kyr to 3 cm/kyr) for the last 300.000 years based on δ¹⁸O analyses of foraminifera in a core from the Norwegian Sea and ²³⁰Th_ex measurements in cores from the Norwegian Sea and the Fram Strait (Arctic Ocean). Furthermore, we relate ²³⁰Th_ex variations downcore to the various oxygen isotope stages. This correlation is tentatively interpreted as being a result of the paleoceanographic and paleoclimatic control of bioproductivity. It is shown that based on the average sedimentation rates and characteristic ²³⁰Th_ex variations carbonate-poor sediment cores from northern latitudes can be correlated.     

How precise are U-series coral ages?

U-series dating of fossil reef corals is a well established and widely applied technique in paleoclimate research. Many fossil corals, however, show evidence for post-depositional diagenetic alteration, and it is generally accepted that the accuracy of U-series coral ages is more limited due to coral diagenesis than analytical precision. In recent years, three models have been published that try to correct the effects of diagenesis and allow the calculation of model ages [Thompson W. G., Spiegelmann M. W., Goldstein S. L., and Speed R. C. (2003) An open-system model for U-series age determinations of fossil corals. Earth and Planetary Science Letters210, 365-381; Villemant B., and Feuillet N. (2003) Dating open systems by the ²³⁸U-²³⁴U-²³⁰Th method: application to Quaternary reef terraces. Earth and Planetary Science Letters210, 105-118; Scholz D., Mangini A., and Felis T. (2004) U-series dating of diagenetically altered fossil reef corals. Earth and Planetary Science Letters218, 163-178].Here, we assess the age variability of both conventional ²³⁰Th/U-dating and the three models by application to different sub-samples of individual coral specimens. The age variability, estimated as the 2σ-standard deviation on the individual ages, is compared with the errors quoted by the different methods. Our results show that the errors of conventional ²³⁰Th/U-dating as well as those of the method of Thompson et al. (2003) do not account for the true age variability. The age variability of both methods is in the range of the errors given by the models of Villemant and Feuillet (2003) and Scholz et al. (2004).Furthermore, we show that the widely used reliability criteria are not sufficient to identify all diagenetically altered corals. In contrast, analysis of different sub-samples of one coral specimen allows (i) to estimate the real age variability, (ii) to test if the assumptions of the models are fulfilled, and (iii) to investigate the diagenetic processes in more detail. Thus, this method should generally be applied to obtain more reliable U-series coral ages and errors.     

The World Karst Aquifer Mapping project: concept,mapping procedure and map of Europe

Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.

     

Comparative biomonitors of coastal trace metal contamination in tropical South America (N. Brazil)

Samples of 5 bivalve molluscs (Crassostrea rhizophorae, Mytella charruana, Anomalocardia brasiliana, Anadara ovalis, Phacoides pectinata), 2 barnacles (Fistulobalanus citerosum, Balanus amphitrite) and leaves of the mangrove tree Rhizophora mangle were collected from up to 11 sites in two estuaries in Natal, Brazil--the comparatively contaminated Potengi estuary and the comparatively uncontaminated Curimataú estuary. Specimens were analysed for the trace metals Zn, Cu, Cd, Fe, Mn and Ni, and a comparative assessment made of the power of the different species as trace metal biomonitors. Four of the 5 bivalves (not P. pectinata) take up metals from solution and suspended material (food source), while P. pectinata as a lucinid with symbiotic chemosynthetic bacteria takes up metals from dissolved sources only. The organisms with the strongest net accumulation of particular metals showed the greatest discrimination between trace metal bioavailabilities between sites. Barnacles (F. citerosum) showed the best discrimination, but oysters (C. rhizophorae) are particularly recommended as biomonitors given their strong accumulation patterns for many trace metals, their large size and their local abundance.     

An initial evaluation of drone‐based monitoring of boulder beaches in Galicia,north‐western Spain

Low altitude flights by a micro‐drone were made in 2012 and 2013 over two boulder beaches in north‐western Spain. Geographical information system software was used to map the data. Boulder outlines from the first flight were recorded on 4796 clasts at Laxe Brava and 2508 clasts at Oia. Changes in location were identified by overlaying these outlines on the 2013 images. About 17.5% of the boulders (mean surface area 0.32 m²) moved at Laxe Brava and about 53% (mean surface area 0.23 m²) at Oia. Most movement on both beaches was between the mid‐tide to about 2 m above the high tidal level. The location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at Laxe Brava and 3324 boulders at Oia. These elevations were compared with the elevations at the same locations in 2013. The occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines. The study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution, micro‐drone technology. Copyright © 2014 John Wiley & Sons, Ltd.     

Multipurpose geochemical maps produced by integration of geochemical exploration data sets in The Paraná Shield, Brazil

Old geochemical datasets from the Paraná Shield of southern Brazil have been integrated into a new geochemical database and the results are presented as a series of multipurpose geochemical maps. Although the 24 datasets retrieved were analysed by three different laboratories, the maps produced correlate surprisingly well with bedrock geological features.The retrieval of old geochemical exploration data sets for the purpose of generating maps showing element depletions and enrichments is a powerful tool with a wide range of applications: trace elements such as Zn, Cu and Mo can significantly affect crop productivity; areas with high abundances of harmful elements such as As and F can be delineated in order to identify public health hazards; heavy metals such as Cd, Pb and Hg can be measured in order to better constrain knowledge of chemical background levels for environmental monitoring. The integration and manipulation of different data sets can however be complicated by the heterogeneity in sampling and analytical procedures.