Magnitude 5.0 Earthqauke in the Charente-Maritime Department of southwestern France.

The Centre Sismologique Euro-Méditerranéen recorded a Magnitude 5.0 Earthquake at a depth of about 10 km, roughly 11 km to the northwest of the commune of Surgères in the Charente-Maritime Department of southwest France, slightly before 6.40 pm local time (slightly before 6.40 pm GMT) on Friday 16  June 2023. The Earthquake is reported to have been felt across much of western France, with one person is reported to have received treatment for minor injuries in the Deux-Sevres Department, and reports of damage to buildings in the Charente-Maritime and Deux-Sevres departments.

The approximate location of the 16 June 2023 Charente-Maritime Department Earthquake. Centre Seismologique Euro-Méditeranéen.

The precise cause of Earthquakes in France can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

France is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally, the country is subject to glacial rebound; until about 10 000 years ago much of the mountainous and upland areas of the country were covered by a thick layer of glacial ice, pushing the rocks of the French lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 

Glacial rebound seems an unlikely cause of Earthquakes in the Channel region, an area that was never glaciated, but this is not entirely the case. The northwest of Scotland is rising up faster than any other part of the UK, but the Earth's crust on land in the UK is fairly thick, and does not bend particularly freely, whereas the crust beneath the Channel is comparatively thin and more inclined to bend under stress. Thus, uplift in Scotland can cause the entire landmass of Great Britain to pivot, causing movement in the rocks beneath the Channel, and affecting both the English and French coasts.

(Top) Simplified diagram showing principle of glacial rebound. (Bottom) The extent of glaciation in Europe at the last glacial maximum. Wikipedia.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The Centre Seismologique Euro-Méditeranéen is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to them here.

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Glenrosa carentonensis: A new species of Conifer from the Early Cretaceous of Charente-Maritime, France.

Conifers of the genus Glenrosa were first recorded from the Early Cretaceous Glen Rosa Formation of Texas in 1984 (although specimens of the plant had been collected in the area since the 1890s), and subsequently recorded from widely distributed Early Cretaceous from North America, Europe and Asia, suggesting that for a while it was a widespread and dominant plant in the Northern Hemisphere. Glenrosa is distinguished by having small fleshy triangular leaves held close to the stems, with stomata (breathing pores) grouped together in deep stomatal crypts (indentations on the leaves). Such crypts are known only from a single other species of Conifer, Sedites rabenhorstii, which also lived in the Cretaceous, making interpretation of its ecological significance difficult, however similar structures are found in some modern Angiosperms (flowering plants), the majority of which live in arid climates, suggesting that the pores may help to regulate water loss in dry conditions.

In a paper published in the journal PLoS One on 19 August 2015, Jean-David Moreau of Géosciences Rennes at Université Rennes and the European Synchrotron Radiation Facility, Didier Néraudeau, also of of Géosciences Rennes at Université Rennes, Paul Tafforeau also of the European Synchrotron Radiation Facility and Éric Dépré of the Groupement d’Etude et de Contrôle des Variétés et Semences, describe a new species of Glenrosa from material included in flint nodules collected from Early Cretaceous deposits at Font-de-Benon Quarry, between the villages of Archingeay and Les Nouillers in the Charente-Maritime Department of western France.

The new species is named Glenrosa carentonensis, meaning ‘from Charente’ (Carentonia is the Latin name for the River Charente). The species is described from a number of specimens of fragmentary material up to 50 mm in length preserved in flint nodules. Since it is essentially impossible to extract plant remains from hard flint, the specimens were examined using propagation phase-contrast X-ray synchrotron microtomography at the European Synchrotron Radiation Facility.

Plant fossils embedded inside flint nodules. (A) Broken flint nodule with diverse conifer inclusions, SIL_ARC_2. (B) Leafy twigs of Glenrosa carentonensis. (C) Leafy twigs of Glenrosa carentonensis. (D) Leafy axis of Glenrosa carentonensis bearing distally a microsporangiate cone on its distal tip. (E) Detail of the same cone. Moreau et al. (2015).

The leaves of Glenrosa carentonensis are arranged helically around the stems; they are flesh and somewhat claw-shaped, with a waxy cuticle and numerous stomatal crypts, each containing 7-12 stomata. Several male cones were found in the sample, the first time these have been recorded for any species of Glenrosa. These are 2.8–5.0 mm long and 2.3–4.1 mm wide and bear up to 40 microsporophylls regularly distributed along the cone axis. Each microsporophyll bears 6-7 pollen sacs in clusters up to 0.5 mm wide. The pollen could be determined to be 17.3–20.3 μm long and 10–16 μm wide, but no details could be discerned.

Propagation phase-contrast X-ray synchrotron microtomograph, virtual sections of Glenrosa carentonensis reconstructed using a single distance phase retrieval process. (A) Longitudinal section of leafy axis. (B) Transversal section of leafy axis. (C) Longitudinal section of twig and cone. Moreau et al. (2015).

The stomatal crypts, fleshy leaves and thick waxy cuticles of Glenrosa carentonensis all appearto be adaptations to an arid climate, while the inclusion of the material in flint nodules implies a coastal environment (all flint deposits are thought to have originated in shallow-marine environments). Moreau et al. suggest the plants were a major component of a dry coastal Conifer forest, with occasional storm events and possibly haline influences (salt laden winds).

Propagation phase-contrast X-ray synchrotron microtomograph 3D renderings of Glenrosa carentonensis. (A) Helically arranged leafy axis. (B–C) Leafy axes bearing a microsporangiate male cone. Moreau et al. (2015).

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A Polypore Fungus Beetle from the Early Cretaceous of France.

Beetles first appear in the fossil record in the Early Permian. And by the Triassic were already beginning to dominate Insect faunas, with many modern groups in existence by the end of the Cretaceous. However the majority of Beetle groups were defined from extant species, and many are hard to differentiate in the fossil record because of this, with the result that many fossil Beetle groups are not well studied, and fossil collections in museums and universities often include many undescribed Beetles.

In a paper published in the journal Acta Palaeontologica Polonica on 9 August 2013, Carmen Soriano of the European Synchrotron Radiation Facility, DarrenPollock of the Department of Biology at Eastern New Mexico University, Didier Néraudaeu of Géosciences Rennes and the Centre national de la recherche scientifique, Andre Nel of the MuséumNational d’Histoire Naturelle and Paul Tafforeau, also of the European Synchrotron Radiation Facility, describe a Polypore Fungus Beetle from Early Cretaceous Amber from Archingeay-Les Nouillers in the Charente-Maritime Department in southwest France.

The amber is opaque, as is the majority of amber from the Early Cretaceous of France (and Mesozoic amber in general). However it has proven possible to build up three-dimensional models of Insects trapped in such amber using X-ray synchrotron microtomography. This method enables the fossil to be examined at any angle desired, and even for internal features, not usually available to palaeoentomologists, to be examined.

The new Beetle is named Synchrotronia idinineteena, where ‘Synchrotronia’ refers to the European Synchrotron Radiation Facility in Grenoble, where the specimen was detected and reconstructed, and ‘idinineteena’ refers to the beamline in which the specimen was detected and imaged (ID19). It is a 3.2 mm long, 1.4 mm wide Beetle with a narrow head and lateral eyes close to the antennae. Based upon careful examination of the limbs of the specimen it was possible to place it within the Tribe Holostrophini, which is in the Subfamily Eustrophinae of the Family Tetratomidae (Polypore Fungus Beetles). This is not only the oldest known member of the Family Tetratomidae, it is the first Mesozoic fossil to be assigned to the group at all.

3D reconstruction of the holotype of Synchrotronia idinantinensis. Specimen tomographied in beamline ID19 of the ESRF, at 30keV and 5.06 μ voxel size. Scale bar 2 mm. Soraino et al. 2014.

In modern times the Tribe Holostrophini is largely restricted to north and east Asia, with only a single species found in Europe. The Beetles feed on wood rotting Fungi, which would be a plausible diet for a Cretaceous Beetle found in amber (which is preserved tree resin). The specimen is about 140 million years old, dating to a time when the climate was extremely warm, and the amber is believed to have been produced by a Gymnosperm tree living in a warm, humid, estuarine forest.

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