Pb isotopic constraints on the formation of the Dikulushi Cu–Pb–Zn–Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo)

Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago) in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram (²⁰⁶Pb/²⁰⁴Pb = 18.66–23.65; ²⁰⁷Pb/²⁰⁴Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides, whereas the U most likely originated from external sources. Local metal sources are also suggested by the ²⁰⁸Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu Plateau clearly record a diachronous evolution.     

<Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr anomalies in Late Cretaceous-Early Tertiary strata of the Cauvery basin,south India: Constraints on nature and rate of environmental changes across K-T boundary

The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This paper documents the occurrences of two positive ⁸⁷Sr/⁸⁶Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise extinction of biota across KTB.     

Morphology and recent history of the Rhone River Delta in Lake Geneva (Switzerland)

The current topographic maps of the Rhone Delta—and of Lake Geneva in general—are mainly based on hydrographic data that were acquired during the time of F.-A. Forel at the end of the nineteenth century. In this paper we present results of a new bathymetric survey, based on single- and multi-beam echosounder data. The new data, presented as a digital terrain model, show a well-structured lake bottom morphology, reflecting depositional and erosional processes that shape the lake floor. As a major geomorphologic element, the sub-aquatic Rhone Delta extends from the coastal platform to the depositional fans of the central plain of the lake at 310 m depth. 9 canyons cut the platform edge of the delta. These are sinuous (“meandering”) channels formed by erosional and depositional processes, as indicated by the steep erosional canyon walls and the depositional levees on the canyon shoulders. Ripples or dune-like morphologies wrinkle the canyon bottoms and some slope areas. Subaquatic mass movements are apparently missing on the delta and are of minor importance on the lateral lake slopes. Morphologies of the underlying bedrock and small local river deltas are located along the lateral slopes of Lake Geneva. Based on historical maps, the recent history of the Rhone River connection to the sub-aquatic delta and the canyons is reconstructed. The transition from three to two river branches dates to 1830–1840, when the river branch to the Le Bouveret lake bay was cut. The transition from two to one river branch corresponds to the achievement of the correction and dam construction work on the modern Rhone River channel between 1870 and 1880.     

Determination of Trace Elements in the Quartz Reference Material UNS-SpS and in Natural Quartz Samples by ICP-MS

A procedure for the digestion and analysis of quartz samples was developed to measure trace element concentrations in natural quartz. The certified glass sand reference material UNS-SpS was chosen to assess the precision, accuracy and detection limit of the analytical method. Quartz was digested with HF/HNO₃ in a closed glassy carbon vessel and analysed by means of quadrupole ICP-MS with external calibration. Analyte concentrations of the sand UNS-SpS were compared with certified and other values from the literature. The abundances of a number of elements (Pr, Gd, Ho and Er) in the reference material are reported here for the first time. The procedure was then applied to three quartz samples from different geological settings to show that trace element data by ICP-MS can distinguish the origin of the sample.     

High resolution climate simulations over the Arctic

The regional atmospheric climate model HIRHAM has been applied to the Arctic. Simulations for the whole year 1990 and for an ensemble of winter months (January of 1985-1995) have been performed. The comparison of the simulations with observational data analyses shows that the general spatial patterns are in good agreement with the data, in both the vertical structure and the annual cycle. For an additional validation of the model results, a multivariate classification of large-scale circulation patterns has been applied to the January ensemble model simulations.     

Cenomanian oysters from the Sergipe Basin, Brazil

Cenomanian (mid Cretaceous) oysters from the Sergipe Basin in northeastern Brazil are described, with revisions of previously described forms. Nine genera and subgenera, including eleven species, are distinguished: Rastellum diluvianum (Linné, 1767), Amphidonte (Ceratostreon) reticulata (Reuss, 1846), A. (Ceratostreon) flabellata (Goldfuss, 1833), Exogyra (Costagyra) olisiponensis Sharpe, 1850, Ilymatogyra (Afrogyra) africana (Lamarck, 1801), Rhynchostreon (Rhynchostreon)mermeti (Coquand, 1862), R. (Laevigyra) obliquatum (Pulteney, 1813), R. (Laevigyra) sp., Pycnodonte (Phygraea) vesiculosa (J. Sowerby, 1823), Curvostrea rouvillei (Coquand, 1862) and Ambigostrea sp. No undoubted Turonian oysters are known from Sergipe, althoughR. (R.) mermeti possibly straddles the Cenomanian–Turonian boundary. This is in sharp contrast with the situation in the more northerly Brazilian basins, from where several Turonian but no Cenomanian forms have been described. Well-preserved material from Sergipe confirms the close relationship between Exogyra (Costagyra) Vialov andVultogryphaea Vialov. The palaeobiogeographical affinity of the oyster fauna is typically Tethyan with many taxa that are known particularly from the southern Tethys. The inferred palaeoenvironment as implied by the oysters is that of a shallow shelf.     

An alternative approach to overcome shortcomings with multiple testing of binary data in ecotoxicology

Binary data such as survival, hatching and mortality are assumed to be best described by a binomial distribution. This article provides a simple and straight forward approach for derivation of a no/lowest observed effect level (NOEL/LOEL) in a one-to-many control versus treatments setup. Practically, NOEL and LOEL values can be derived by means of different procedures, e.g. using Fisher’s exact test in coherence with adjusted p values. However, using adjusted p values heavily decreases statistical power. Alternatively, multiple t tests (e.g. Dunnett test procedure) together with arcsin-square-root transformations can be applied in order to account for variance heterogeneity of binomial data. Arcsin-square-root transformation, however, violates normal distribution because transformed data are constrained, while normal distribution provides data in the range \((-\infty ,\infty )\). Furthermore, results of statistical tests relying on an approximate normal distribution are approximate too. When testing for trends in probabilities of success (probs), the step down Cochran–Armitage trend test (CA) can be applied. The test statistic used is approximately normal. However, if probs approach 0 or 1, normal approximation of the null-distribution is suboptimal. Thus, critical values and p values lack statistical accuracy. We propose applying the closure principle (CP) and Fisher–Freeman–Halton test (FISH). The resulting CPFISH can solve the problems mentioned above. CP is used to overcome \(\alpha\)-inflation while FISH is applied to test for differences in probs between the control and any subset of treatment groups. Its applicability is presented by means of real data sets. Additionally, we performed a simulation study of 81 different setups (differing numbers of control replicates, numbers of treatments etc.), and compared the results of CPFISH to CA allowing us to point out the advantages and disadvantages of the CPFISH.     

Perfect partial reconstructions for multiple simultaneous sources

A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test.     

Acoustic and petrophysical properties of mechanically compacted overconsolidated sands: part 1 – experimental results

This paper part one is set out to lay primary observations of experimental compaction measurements to form the basis for rock physics modelling in paper part two. P- and S-wave velocities and corresponding petrophysical (porosity and density) properties of seven unconsolidated natural sands with different mineralogical compositions and textures are reported. The samples were compacted in a uniaxial strain configuration from 0.5 up to 30 MPa effective stresses. Each sand sample was subjected to three loading cycles to study the influence of stress reduction on acoustic velocities and rock physical properties with the key focus on simulating a complex burial history with periods of uplift. Results show significant differences in rock physical properties between normal compaction and overconsolidation (unloaded and reloaded). The differences observed for total porosity, density, and P- and S-wave velocities are attributed to irrecoverable permanent deformation. Microtextural differences affect petrophysical, acoustic, elastic and mechanical properties, mostly during normal consolidation but are less significant during unloading and reloading. Different pre-consolidation stress magnitudes, stress conditions (isotropic or uniaxial) and mineral compositions do not significantly affect the change in porosity and velocities during unloading as a similar steep velocity–porosity gradient is observed. The magnitude of change in the total porosity is low compared to the associated change in P- and S-wave velocities during stress release. This can be explained by the different sensitivity of the porosity and acoustic properties (velocities) to the change in stress. Stress reduction during unloading yields maximum changes in the total porosity, P- and S-wave velocities of 5%, 25%, and 50%, respectively. These proportions constitute the basis for the following empirical (approximation) correlations: Δϕ ∼ ±5 ΔV_P and ΔV_P ∼ ±2ΔV_S. The patterns observed in the experiments are similar to well log data from the Barents Sea. Applications to rock physics modelling and reservoir monitoring are reported in a companion paper.     

Upper Cretaceous bottom current deposits,north-east Greenland

Reported ancient bottom current deposits in deep marine settings are scarce and most of them remain contentious. This study describes sedimentological, ichnological and petrographical characteristics of a drill core that covers ca 10 Myr of Upper Cretaceous stratigraphy at Hold with Hope, north-east Greenland. The core is divided into four facies associations, which are interpreted to reflect deposition from bottom currents, turbidity flows and hemipelagic settling in slope and/or near slope environments. The evidence for bottom current influence is three-fold. Firstly, pervasive indications of winnowing such as marine bioclast-rich lags and outsized clasts on ‘mud on mud’ contacts are suggestive of low-sediment concentration flows capable of transporting up to pebble-sized clasts. Common Mn–Fe–Mg rich carbonate matrix cements and various types of hiatal chemogenic lag deposits showing glauconite, apatite and carbonate clasts also point to condensation, prolonged exposure at the sediment–water interface and recurrent phases of sea-floor erosion. Secondly, such deposits can show indicators for tidal processes such as double mud-drapes, tangential bottom sets in dune-scale cross-bedding and cyclic rhythmites. Thirdly, inverse to normal grading at various scales is common in fully marine, commonly seafloor-derived sediments. Ichnological data indicate considerable taxonomic variability in the bottom current deposits, but recurrent fabrics are characteristically dominated by morphologically simple burrows such as Thalassinoides and Planolites, with secondary Phycosiphon, Nereites, Zoophycos and/or Chondrites. In general, opportunistic taxa are common whereas mature composite ichnofabrics are rare. The omission surfaces are locally burrowed with stiffground to firmground trace fossil suites. The results contribute to establishing sedimentological, ichnological and mineralogical criteria for recognition of bottom current deposits as well as to the understanding of the Late Cretaceous palaeoenvironmental evolution of the Arctic region.