Geology and geochemistry of Jurassic pelagic sediments, Scisti silicei Formation, southern Apennines, Italy

A better understanding of genesis and palaeoenvironmental setting of the Scisti silicei Formation (Lagonegro units, southern Italy) was achieved by means of geochemical analysis integrated with new stratigraphic information. Data show that major and trace element geochemistry of ancient clay-rich beds and banded cherts add new insights into the Mesozoic evolution of the Lagonegro basin. Sedimentary contributions to Jurassic shales sampled during this study were mainly derived from two major sources: (i) a dominant terrigenous fine-grained component, having affinity with average upper continental crust that had not undergone intense weathering and (ii) biogenic siliceous material. The latter component occurs in clay-rich layers from the “basal member” of the Scisti silicei Formation.

Composition varies up section and accounts for changes in the detrital supply due to bathymetric oscillations. The compositional variations from the basal to the overlying member are consistent with a distal source passing in time to a more “proximal” source, as indicated by sharp changes in the concentrations of detrital elements (Ti, Zr and Nb). It is likely that increased detrital input occurred through turbidity current deposition. Finally, the chemical features of the clay-rich layers from the upper cherty portion of the studied succession imply a progressive deepening of the basin.

The lack of any mafic and hydrothermal contributions in the Jurassic shales as well as the continental nature of detrital input suggests that the Lagonegro basin was located between two carbonate platforms, in accordance with the classical restoration of the African–Apulian palaeomargin. Thus, the basin acted as a preferential sink connected to the African cratonic areas through a southern entry point.     

Application of lattice gas techniques to the study of sediment erosion and transport caused by laminar sheetflow

In order to gain a deeper understanding of the dynamics of erosion and sediment transport on hillslopes, it seems important to clarify the role of some basic mechanisms involved in these processes. While there is evidence that this cannot be done using the theoretical framework of river hydraulics, the use of numerical analysis could be of considerable help. The nature of the problem requires a technique capable of solving Navier–Stokes equations at low Reynolds number, with geometrically complex boundaries and solid particles moving inside the flow field. All these requirements make a novel method, known as lattice gas automaton LGA, a natural candidate for the study of the hydrodynamics of sheetflows. However, due to the recent introduction of this technique, there is a lack of a clear definition of its operational limits. Considering the case of a viscous sheetflow on an erodible rough boundary, we argue that by using LGA the stream Reynolds number can be increased only at the expense of a reduction of the boundary shearing stress. Accordingly, LGA cannot profitably be used to study the beginning of sediment motion and transport. On the other hand, a further evolution of LGA, known as the lattice Boltzmann method, seems highly promising for the numerical study of the erosion processes that eventually lead to drainage network evolution along hillslopes. © 1997 by John Wiley & Sons, Ltd.     

Badlands as a hot spot of petrogenic contribution to riverine particulate organic carbon to the Gulf of Lion (NW Mediterranean Sea)

Determining the riverine carbon fluxes to oceans is critical for an improved understanding of C budgets and biogeochemical cycles (C, O) over a broad range of spatial and time scales. Among the particulate organic carbon (POC) involved in these fluxes, those yielded by sedimentary rocks (petrogenic POC: pPOC) remain somewhat uncertain as to their source on continental surfaces. Based on time series from long‐term observatories, we refine the POC and sediments flux of the Rhône River, one of the major tributaries to the Mediterranean Sea. Radiocarbon measurements on a set of riverine samples and forward modelling were used to (i) determine a modelled pPOC content and pPOC/POC ratio for each sample set, (ii) assess pPOC flux delivered to the NW Mediterranean Sea, and (iii) estimate the badlands contribution from the Durance catchment to both the pPOC and to sediment discharges. The weighted pPOC flux contributes up to 26% of the POC flux (145 Gg yr^‐1) discharged into the Mediterranean Sea, whereas the weighted pPOC content reaches 0.31 wt%. Despite their low contributive surface area (0.2%), badlands provide, respectively, 12, 3.5 and 14% of the pPOC, POC and sediment fluxes to the Rhône River. Consequently, such rocks can be considered as a major source of pPOC and sediments for the NW Mediterranean Sea and potentially for oceans. We suggest that river‐dominated ocean margins, such as the Rhône River, with badlands in their catchment could export a significant amount of pPOC to the oceans. Copyright © 2018 John Wiley & Sons, Ltd.     

On the stability relationships between tidal asymmetry and morphologies of tidal basins and estuaries

Simple stability relationships are practically useful to provide a rapid assessment of coastal and estuarine landforms in response to human interventions and long‐term climate change. In this contribution, we review a variety of simple stability relationships which are based on the analysis of tidal asymmetry (TA). Most of the existing TA‐based stability relationships are derived using the one‐dimensional tidal flow equations assuming a certain regular shape of the tidal channel cross‐sections. To facilitate analytical solutions, specific assumptions inevitably need to be made, for example by linearizing the friction term and dropping some negligible terms in the tidal flow equations. We find that three major types of TA‐based stability relationships have been proposed between three non‐dimensional channel geometric ratios (represented by the ratio of channel widths, ratio of wet surface areas and ratio of storage volumes) and the tide‐related parameter a/h (i.e. the ratio between tidal amplitude and mean water depth). Based on established geometric relations, we use these non‐dimensional ratios to restate the existing relationships so that they are directly comparable. Available datasets are further extended to examine the utility of these TA‐based relationships. Although a certain agreement is shown for these relationships, we also observe a large scatter of data points which are collected in different types of landscape, hydrodynamic and sedimentological settings over the world. We discuss in detail the potential reasons for this large scatter and subsequently elaborate on the limited applicability of the various TA‐based stability relationships for practical use. We highlight the need to delve further into what constitutes equilibrium and what is needed to develop more robust measures to determine the morphological state of these systems. Copyright © 2018 John Wiley & Sons, Ltd.     

Data-driven retrieval of primary plane-wave responses

Seismic images provided by reverse time migration can be contaminated by artefacts associated with the migration of multiples. Multiples can corrupt seismic images, producing both false positives, that is by focusing energy at unphysical interfaces, and false negatives, that is by destructively interfering with primaries. Multiple prediction/primary synthesis methods are usually designed to operate on point source gathers and can therefore be computationally demanding when large problems are considered. A computationally attractive scheme that operates on plane-wave datasets is derived by adapting a data-driven point source gathers method, based on convolutions and cross-correlations of the reflection response with itself, to include plane-wave concepts. As a result, the presented algorithm allows fully data-driven synthesis of primary reflections associated with plane-wave source responses. Once primary plane-wave responses are estimated, they are used for multiple-free imaging via plane-wave reverse time migration. Numerical tests of increasing complexity demonstrate the potential of the proposed algorithm to produce multiple-free images from only a small number of plane-wave datasets.     

Biogeomorphology of the Mediterranean Posidonia oceanica seagrass meadows

Here we review the multiple interactions between the endemic Mediterranean seagrass, Posidonia oceanica, and coastal geomorphologic processes as an outstanding example of biogeomorphology, taking into account recent advances in the field. Seagrass meadows are among the most important elements for the functioning of marine coastal ecosystems, and represent a major focus for research and conservation. Being considered a priority habitat, P. oceanica meadows are protected by several European Union directives and national laws. In this paper we examine: the role of sedimentary features in controlling the development of the meadows; the interplay between P. oceanica leaf litter (i.e. beached necromass) cast ashore and erosional‐depositional processes on the beaches; the interactions between meadows and nearshore hydrodynamics, and; possible linkages between geomorphological features of the seafloor and the architecture of meadows. Finally, we provide perspectives for future research on P. oceanica and other Mediterranean seagrass meadows in a biogeomorphological context with specific reference to climate change. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of seasonal forcing on habitat use by bottlenose dolphinsTursiops truncatus in the Northern Adriatic Sea

Bottlenose dolphins are the only cetaceans regularly observed in the northern Adriatic Sea, but they survive at low densities and are exposed to significant threats. This study investigates some of the factors that influence habitat use by the animals in a largely homogeneous environment by combining dolphin data with hydrological and physiographical variables sampled from oceanographic ships. Surveys were conducted year-round between 2003 and 2006, totalling 3,397 km of effort. Habitat modelling based on a binary stepwise logistic regression analysis predicted between 81% and 93% of the cells where animals were present. Seven environmental covariates were important predictors: oxygen saturation, water temperature, density anomaly, gradient of density anomaly, turbidity, distance from the nearest coast and bottom depth. The model selected consistent predictors in spring and summer. However, the relationship (inverse or direct) between each predictor and dolphin presence varied among seasons, and different predictors were selected in fall. This suggests that dolphin distribution changed depending on seasonal forcing. As the study area is relatively uniform in terms of bottom topography, habitat use by the animals seems to depend on complex interactions among hydrological variables, caused primarily by seasonal change and likely to determine shifts in prey distribution.     

Multiwavelength Study of two Unidentified γ-ray Sources

Most counterparts of the identified low-latitude γ-ray sources are isolated neutron stars (INSs). Since INSs are characterized by an extremely high value of f _X/f _opt, a systematic X-ray/optical coverage of the fields of unidentified low-latitude γ-ray sources is the best way to unveil INS counterparts of unidentified sources. Since the low-latitude sources are heavily affected by the interstellar absorption in both the X-ray and optical bands, we decided to apply the above strategy to two middle-latitude EGRET sources, which could belong to a local galactic population: 3EG J0616-3310 and 3EG J1249-8330. Here we report on the global X-ray characterization of about 300 objects, on their candidate optical counterparts and on the preliminary results of their identification.     

Post‐Variscan tectonics in eastern Anti‐Atlas (Morocco)

New field data integrated by fission‐track (FT) analysis unravel an innovative scenario for the post‐Variscan evolution of the eastern Anti‐Atlas. This area, unaffected by Meso‐Cenozoic tectonics according to most workers, is crosscut by crustal faults bearing evidence of a polyphase deformation history. Apatite FT ages, ranging between 284 and 88 Ma, point to fast Neogene exhumation and unravel contrasting cooling paths across major faults. Results show that the study area was buried beneath 2 km of allochthonous Variscan units, now eroded. The eastern Anti‐Atlas acted as the southern shoulder of the Atlasic rift in the Mesozoic, and underwent a dextral transpressional structuring of Neogene age followed by sub‐meridian shortening. The southern front of Atlasic deformation is therefore located inside the Anti‐Atlas region, and it is still active.