The abandoned Loubieng quarry located close to Pau (France) encompasses the Danian/Selandian boundary (DSb). The section could be subdivided into three parts:i) the basal part of the section consists mostly of Danian whitish carbonate beds withonly scarce and thin marly layers, ii) several limestone/marl alternations at theuppermost part of the Danian, and iii) the Selandian marls. The transitions between those divisions are linked to the Late Danian Event (LDE) and the DSb interval respectively. The three parts are clearly distinguishable in the low-field magnetic susceptibility curve established on 272 samples collected every 10 cm along the section up to 23 m (including the first three meters of the Selandian) and then every 25 cm in the marls. The low-field magnetic susceptibility (XLF) curve could be subdivided into eight major trends (orange arrows noted from 0 to 7) as highlighted in figure 1. The lithology has clearly an influence on the XLF values as the marls have always higher XLF values compared to the Danian limestones and the Selandian sandstones. Moreover, some specific carbonate beds have very low XLF values, sometimes even negative suggesting a diamagnetic behaviour. Some of these beds clearly corresponds to mass-gravity deposits (probably debris flows) as confirmed by microfacies (thin sections) analysis. To better constrain the XLF fluctuations, hysteresis data have been obtained with a Jcoercivity magnetometer on 55 samples selected along the section including all the different lithologies and the whole range of XLF values. A very strong correlation (r = 0.93) is highlighted between XLF and XHF values suggesting that the paramagnetic particles (i.e. the clay minerals) are clearly controlling the signal. Nevertheless, ferrimagnetic particles are also detected indicating a clear contribution of these minerals on the XLF curve. The magnetic viscosity (Sd), the remanence coercive force (Hcr) and the contribution (\%) to the high-field remanence parameters have generally good correlations between them. These parameters reveal two specific intervals where their values are higher: i) around the LDE in an interval displaying yellowish colours and ii) during the DSb interval characterized by reddish marls and limestones. The behaviour of the remanent magnetization was determined in eight samples during cooling and warming cycles on a MPMS3 – VSM (vibrating sample magnetometer). These analyses confirm the presence of goethite and hematite minerals present essentially during LDE and DSb time interval, respectively. We suggest that the paramagnetic (clay minerals, i.e. illite, kaolinite and smectite) and the ferromagnetic minerals are essentially primary minerals (detrital) deriving probably from extensive soils developed on the surrounding continental areas bordering the marine realm.
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RBINS Staff Publications 2016
Between 2007 and 2015, we recorded three cases of asphyxiation of grey seals Halichoerus grypus caused by a fish lodged in the respiratory tract. In all cases, the fish involved was a common sole Solea solea, which had found its way to the trachea of the unfortunate seal, as such completely blocking it. That this fish species was involved, is not surprising: it has a very agile body, with a spectacular ability to bend longitudinally into a circular shape, as well as laterally into the form of a cigar - the way it was found in the gluttonous grey seals. The common sole currently occurs abundantly in coastal waters of the southern North Sea, and it constitutes an important part of the diet of grey seals in this area. Asphyxiation due to fish has been described in odontocetes, including in harbour porpoise Phocoena phocoena, bottlenose dolphin Tursiops truncatus, and very recently in long-finned pilot whale Globicephala melas. To our knowledge however, this cause of death has not been described before in grey seals. Furthermore, the significance of this cause of mortality in a single population has not been documented, with in particular aspects of prey abundance, seal behaviour and the limited number of stranded adult grey seals that are being investigated to be considered. Keywords: grey seal; Halichoerus grypus; common sole; Solea solea; asphyxiation; respiratory tract
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