Gondwana breakup: Messages from the North Natal Valley

The Natal Valley, offshore Mozambique, is a key area for understanding the evolution of East Gondwana. Within the scope of the integrated multidisciplinary PAMELA project, we present new wide‐angle seismic data and interpretations, which considerably alter Geoscience paradigms. These data reveal the presence of a 30‐km‐thick crust that we argue to be of continental nature. This falsifies all the most recent palaeo‐reconstructions of the Gondwana. This 30‐km‐thick continental crust 1,000 m below sea level implies a complex history with probable intrusions of mantle‐derived melts in the lower crust, connected to several occurrences of magmatism, which seems to evidence the crucial role of the lower continental crust in passive margin genesis.     

Extra-solar planets: Detection methods and results

Since 1995, more than 200 extra-solar planets have been discovered, demonstrating not only that planetary systems are common, but also that planets may come in a large variety of flavors. As the number of detections grows, statistical studies of the properties of exoplanets and their host stars can be conducted to unravel some of the key physical and chemical processes leading to the formation of planetary systems. In this paper we describe the major techniques used to search for extra-solar planets. In particular, we discuss in more detail the radial-velocity and the transit techniques, responsible for the discovery of the bulk of the known planets orbiting solar-type stars. We then present the main results from the planet surveys, describing the global properties of the newfound worlds.     

Along-slope oceanographic processes and sedimentary products around the Iberian margin

This contribution to this special volume represents the first attempt to comprehensively describe regional contourite (along-slope) processes and their sedimentary impacts around the Iberian margin, combining numerically simulated bottom currents with existing knowledge of contourite depositional and erosional features. The circulation of water masses is correlated with major contourite depositional systems (CDSs), and potential areas where new CDSs could be found are identified. Water-mass circulation leads to the development of along-slope currents which, in turn, generate contourite features comprising individual contourite drifts and erosional elements forming extensive, complex CDSs of considerable thickness in various geological settings. The regionally simulated bottom-current velocities reveal the strong impact of these water masses on the seafloor, especially in two principal areas: (1) the continental slopes of the Alboran Sea and the Atlantic Iberian margins, and (2) the abyssal plains in the Western Mediterranean and eastern Atlantic. Contourite processes at this scale are associated mainly with the Western Mediterranean Deep Water and the Levantine Intermediate Water in the Alboran Sea, and with both the Mediterranean Outflow Water and the Lower Deep Water in the Atlantic. Deep gateways are essential in controlling water-mass exchange between the abyssal plains, and thereby bottom-current velocities and pathways. Seamounts represent important obstacles for water-mass circulation, and high bottom-current velocities are predicted around their flanks, too. Based on these findings and those of a selected literature review, including less easily accessible ??grey literature?? such as theses and internal reports, it is clear that the role of bottom currents in shaping continental margins and abyssal plains has to date been generally underestimated, and that many may harbour contourite systems which still remain unexplored today. CDSs incorporate valuable sedimentary records of Iberian margin geological evolution, and further study seems promising in terms of not only stratigraphic, sedimentological, palaeoceanographic and palaeoclimatological research but also possible deep marine geohabitats and/or mineral and energy resources.     

Contaminated soils and sediments associated with Zn ore metallurgy near the São Francisco River,Minas Gerais (Brazil)

Draining through industrial areas of the Minas Gerais mining state (Brazil), some tributaries of the São Francisco River constitute a potential environmental hazard for this great river and threaten the quality of the regional soils for agriculture and other activities. Extensive geochemistry and mineralogy of sediments, soils and alluvial plains from six selected areas within the Consciência drainage basin close to an important Zn-extraction plant, have been carried out. In this report, detailed mineralogy of those samples and supporting geochemical data are discussed, taking into account their specific climactic and environmental context. Petrographic and electron microprobe characterization of the sand-grained fraction of these materials was complemented by XRD on their finer fraction: the main contaminant minerals are willemite (one of the Zn ores used in the industrial plant) and jarosite, though their contents are quite variable in the studied areas and also with depth; minor amounts of Zn-, Pb-, Cd-, and Mn-bearing mineral phases are also frequent, usually as inclusions in willemite or in polycrystalline clasts, or adsorbed on the finer materials, such as clay minerals and associated Fe-hydroxides. Mineralogical contamination is responsible for high metal contents in the soils and sediments of the areas closer to the plant (e.g. Zn ? 2000 mg kg^?1 and Cd ? 20 mg kg^?1, which are the Intervention Values for Industrial Areas) and the greatest contamination risks are related to the more labile phases that circulate throughout the alluvial plains, the shallow sediments and the stream bed. Monitoring the mineral/chemical contamination and its extent also constitutes a useful basis for future proposals to remediate and recover this industrial area in order to decrease medium- and long-term negative impacts of metal contamination on the local and downstream environments.     

Mineralogy,composition and heavy metals’ concentration,distribution and source identification of surface sediments from the saline Maharlou Lake (Fars Province,Iran)

This study concerns the mineralogy, spatial distribution and sources of nine heavy metals in surface sediments of the Maharlou saline lake, close to the Shiraz metropolis in southern Iran. The sources for these sediments were studied by comparing the mineralogy and the distribution of heavy metals, using multivariate statistical analysis (correlation analysis and principal component analysis). The geochemical indices, including geo-accumulation index (Igeo), contamination factor (CF) and pollution load index (PLI), were used to assess the degree of heavy metal contamination in surface sediments. Sediment quality guidelines (SQGs) have also been applied to assess its toxicity. The XRD analysis shows that the main minerals of the surface sediments are aragonite, calcite, halite and quartz, with small amounts of montmorillonite, dolomite and sepiolite. The total heavy metal contents in surface sediments decrease in order of Sr?>?Ni?>?Cr?>?Zn?>?Cu?>?Co?>?Pb?>?As >?Cd and the average concentrations of Sr, Ni and As exceeded more than 10, 5 and 3 times, respectively, by comparing with the normalized upper continental crust (UCC) values. The results of pollution indices (Igeo, CF and PLI) revealed that strontium (Sr), nickel (Ni) and arsenic (As) were significantly enriched in those sediments. Based on the sediment quality guidelines (SQGs), Ni would infrequently cause toxicity. Multivariate statistical analysis indicated that the Ni, Co and Cr came mainly from natural geological background sources, while Cd, Cu, Pb, and Zn were derived from urban effluents (especially traffic emissions) and As originated from agriculture activities. Significant relationships of Sr with S, CaO and MgO in sediments suggest that Sr was derived from carbonate- and gypsum-bearing catchment source host rocks.     

Accurate seabed modeling using finite difference methods

Finite difference is the most widely used method for seismic wavefield modeling. However, most finite-difference implementations discretize the Earth model over a fixed grid interval. This can lead to irregular model geometries being represented by ‘staircase’ discretization, and potentially causes mispositioning of interfaces within the media. This misrepresentation is a major disadvantage to finite difference methods, especially if there exist strong and sharp contrasts in the physical properties along an interface. The discretization of undulated seabed bathymetry is a common example of such misrepresentation of the physical properties in finite-difference grids, as the seabed is often a particularly sharp interface owing to the rapid and considerable change in material properties between fluid seawater and solid rock. There are two issues typically involved with seabed modeling using finite difference methods: firstly, the travel times of reflections from the seabed are inaccurate as a consequence of its spatial mispositioning; secondly, artificial diffractions are generated by the staircase representation of dipping seabed bathymetry. In this paper, we propose a new method that provides a solution to these two issues by positioning sharp interfaces at fractional grid locations. To achieve this, the velocity model is first sampled in a model grid that allows the center of the seabed to be positioned at grid points, before being interpolated vertically onto a regular modeling grid using the windowed sinc function. This procedure allows undulated seabed bathymetry to be represented with improved accuracy during modeling. Numerical tests demonstrate that this method generates reflections with accurate travel times and effectively suppresses artificial diffractions.     

The Mesolithic–Neolithic transition in southern Iberia

New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover.     

Ages of Detrital Zircon from Siliciclastic Successions South of the São Francisco Craton, Brazil: Implications for the Evolution of Proterozoic Basins

In this work we report ²⁰⁷Pb/²⁰⁶Pb LA-ICPMS ages of 152 detrital zircons from lower greenschist facies quartzites from Proterozoic basin successions of the southern border of the São Francisco Craton, southern Minas Gerais State, Brazil. These are the intracratonic São João del Rei basin, the intraplate continental margin Andrelândia basin, and the Serra do Ouro Grosso sequence, developed on a crystalline basement older than 1.8 Ga, and deformed and metamorphosed during the Brasiliano Orogeny, ca. 0.59–0.50 Ga. The data constrain both the ages of the sources and the interval of sedimentation. The detrital zircons of the Serra do Ouro Grosso sequence were derived predominantly from the erosion of a Neoarchean crust, 2.5–2.8 Ga old, with only one grain showing a Paleoproterozoic age (2, 245±83 Ma) older than the Transamazonian event. Zircons extracted from a shelf quartzite of the lowermost sequence of the São João del Rei basin indicate derivation from the 1.8–2.2 Ga Transamazonian crust, with subordinate contribution from the 2.5–2.9 Ga Archean crust. The 1, 809±41 Ma age is interpreted as the maximum limit for sedimentation in this basin. The results confirm the regional correlation with the Espinhaço Rift successions. The zircons extracted from an autochthonous quartzite of the Andrelândia sequence yielded ages in the 1.0–2.2 Ga range, with a modal class at 1.2–1.3 Ga. Only two of the forty analyzed zircons yield Archean ages. The youngest zircon yields 1, 086±85 Ma. The zircons from the allochthonous quartzite yield ages between 1.0–2.7 Ga, with a modal class at 2.1–2.2 Ga. Only five of 45 analyzed grains yield Archean ages. The youngest zircon has an age of 1, 047±77 Ma. The results indicate that the detrital sediments deposited during the second marine flooding event of the Andrelândia sedimentation were mainly derived from the erosion of Mesoproterozoic and Paleoproterozic rocks. The 1, 047±77 Ma age is interpreted as the maximum depositional age for the described association.