Response of littoral chironomid communities and organic matter to late glacial lake—level,vegetation and climate changes at Lago dell’Accesa (Tuscany,Italy)

This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes.     

Use of targets to track 3D displacements in highly vegetated areas affected by landslides

Monitoring landslides with terrestrial laser scanning (TLS) is currently a well-known technique. One problem often encountered is the vegetation that produces shadow areas on the scans. Indeed, the points behind a given obstacle are hidden and thus occluded on the point cloud. Thereby, locations monitored with terrestrial laser scanner are mostly rock instabilities and few vegetated landslides, being difficult or even impossible to survey vegetated slopes using this method with its classical non-full wave form. The Peney landslide (Geneva, Switzerland) is partially vegetated by bushes and trees, and in order to monitor its displacements during the drawdown of the Verbois reservoir located at its base, an alternative solution has been found. We combined LiDAR technique with 14 targets made of polystyrene placed at different locations inside and outside the landslide area. The obtained displacements were compared with classical measurement methods (total station and extensometer), showing good resemblance of results, indicating that the use of targets in highly vegetated areas could be an efficient alternative for mass movements monitoring.     

The Saint-Georges-sur-Loire olistostrome,a key zone to understand the Gondwana-Armorica boundary in the Variscan belt (Southern Brittany,France)

In the southern part of the French Armorican massif, the Ligerian domain is located along the boundary between Gondwana and Armorica. Lithological, geochemical and structural data on the Saint-Georges-sur-Loire Unit, which is the northern part of the Ligerian domain, allow us to distinguish two sub-units. A southern sub-unit, formed by various blocks (chert, limestone, sandstone, rhyolite, mafic rocks) of Silurian to Middle Devonian age included as olistoliths in a Middle-Late Devonian terrigeneous matrix, overthrusts a sandstone-pelite northern sub-unit. Both units experienced two deformation events. The first one is a top-to-the-NW thrusting and the second one is a left-lateral wrenching. The Saint-Georges-sur-Loire Unit is an accretionary prism formed during the Late Devonian closure of the Layon rift, coeval with the main phase of the Variscan orogeny. The Layon rift, which according to the mafic olistoliths was partly floored by oceanic crust, appears as a buffer structural zone that accounts for the lack in Central Brittany of any tectonic or sedimentary echo of the closure of the Medio-European Ocean. The tectonic evolution of the Saint-Georges-sur-Loire Unit supports a polyorogenic model for this part of the Variscan Belt.     

A tracer study in an Alaskan gravel beach and its implications on the persistence of the Exxon Valdez oil

Despite great efforts including bioremediation, the 1989 Exxon Valdez oil spills persist in many gravel beaches in Prince William Sound, Alaska, USA. To explore this mystery, a lithium tracer study was conducted along two transects on one of these beaches. The tracer injections and transports were successfully simulated using the 2-dimensional numerical model MARUN. The tracer stayed much longer in the oil-persisting, right transect (facing landwand) than in the clean, left transect. If the tracer is approximately regarded as oils, oils in the upper layer would have more opportunities to enter the lower layer in the right transect than in the left one. This may qualitatively explain the oil persistence within the right transect. When the tracer is regarded as nutrients, the long stay of nutrients within the right transect implies that the oil persistence along the right transect was not due to the lack of nutrients during the bioremediation.     

Deep crustal structure and rheology of the Gascoyne volcanic margin,western Australia

Interpretation of deep seismic reflection data across the Gascoyne Margin reveals six distinct seismic facies units related to the tectono-magmatic breakup history. On the outer Exmouth Plateau four large scale units are identified: (1) an extensively block-faulted upper crust; (2) a middle-crustal unit of discontinuous, undulatory reflectors; (3) a reflection-free deep crustal unit; and (4) a lower-crustal band of low-frequency, high-amplitude reflectors. Two additional units are found near the continent-ocean boundary (COB); (5) seaward-dipping reflectors (SDR); and (6) landward-dipping reflectors in the lower crust below the SDR. The lower-crustal high-reflectivity band, located near the top of a high-velocity unit (V_p > 7 kms^–1), is interpreted as magmatic underplating. There is a spatial correlation between the underplated area and the presence of extensive upper-crustal block-faulting and intrusive rocks in the shallow crust. The undulatory middle-crustal reflector unit is also only identified in the outer plateau area, and is interpreted as a zone in which the upper-crustal faults terminate. The inner parts of the margin consist of a deep basin showing little upper-crustal faulting and no evidence of middle crustal deformation or underplating. Theoretical modeling of the effect of rifting and magmatic underplating on crustal strength profiles suggests that the brittle-ductile transition may migrate at least 5 km upwards during several million years after the underplating event. Based on the seismic interpretation and crustal strength modeling we propose that the seismic structure of the outer Exmouth Plateau is severely modified by a transient change in the crustal rheological structure associated with magmatic underplating.     

Evidence for slope instability and current-induced sediment transport,the RMSTitanic wreck search area,Newfoundland rise

The first map of the sea bed morphology and sedimentary features within the RMSTitanic search area is proposed from the interpretation of SAR side-scan sonar images. Downslope sedimentary features such as erosional furrows and crown scarps constitute a 7 km wide instability corridor. A large field (15 km²) of asymmetrical sediment waves indicating a downslope transport is identified. Current-induced features corresponding to associated sand ribbons and barchan dunes resulting from the Western Boundary Undercurrent action are mapped. The morphology of theTitanic Canyon is also precised from the SAR images. Finally, the origin of the sea bed features is discussed in an attempt to link each bed form to a sedimentary process.     

Rejection of Intracoelomic Invading Material by Leptosynapta inhaerens (Echinodermata: Holothuroida): A Process of Ecological Significance?

Abstract. The synaptid holothuroid Leptosynapta inhaerens has the ability to expel unwanted particles that enter its body cavity. Intracoelomic particles ( viz. experimentally injected carmine particles) are trapped either by a coelom-produced mucoid net or by specialized organs (the vibratile urnae) that occur in bands in some interradial areas. Whatever the trapping method, particles are incorporated into dense mucoid masses that move towards the posterior part of the body cavity, in the vicinity of the rectum. These aggregates then cross the rectal wall through rectal pores, mix with the faeces, and are eventually incorporated into the wall of the synaptid burrow. Clearance of foreign particles requires 2 to 3 days. The coelom-cleaning system of synaptids appears to be the most effective within the class Holothuroidea , being well designed for endofaunal organisms whose walls are delicate and easily rupture.