Bulletin de la Societe Geologique de France最新文献

{"title":"Petrogenesis and tectonic-magmatic context of emplacement of lepidolite and petalite pegmatites from the Fregeneda-Almendra field (Variscan Central Iberian Zone): clues from Nb-Ta-Sn oxide U-Pb geochronology and mineral geochemistry","authors":"Christophe Ballouard, Patrick Carr, Flore Parisot, Éric Gloaguen, Jérémie Melleton, Jean Cauzid, Andreï Lecomte, Olivier Rouer, Lise Salsi, Julien Mercadier","doi":"10.1051/bsgf/2023015","DOIUrl":"https://doi.org/10.1051/bsgf/2023015","url":null,"abstract":"The Fregeneda-Almendra pegmatite field of the Iberian Massif represents a typical expression of peraluminous rare-metal magmatism that occurred over western Europe at the end of the Variscan orogeny. It is the host for two main types of Li-mineralized intrusions, identified at the scale of the Variscan belt, including petalite- or spodumene-rich pegmatites, as well as Li-mica-rich pegmatites, for which the origin of cristallo-chemical differences is not yet understood. Here, we provide cassiterite and columbite-group mineral (CGM) U-Pb ages along with oxide, mica and phosphate mineral compositions for Li-pegmatites from the Fregeneda-Almendra field in order to assess their petrogenesis and tectonic-magmatic context of emplacement. U-Pb geochronology indicates that petalite-rich and Li-mica-rich pegmatites were mostly emplaced sub-synchronously from 315 ± 6 to 308 ± 6 Ma, during strike-slip deformation and granite magmatism within an anatectic dome bounding the pegmatite field. U-Pb data and pegmatite geographic zonation suggest that Li-pegmatites were possibly sourced from buried equivalents of leucogranites or migmatites from the dome. Li-pegmatites experienced a complex crystallization including K-feldspar, petalite, topaz, Fe-Mn-Nb-Ta-rich cassiterite, amblygonite-group minerals (AGM) and CGM as early magmatic phases, followed by lepidolite for Li-mica-rich pegmatites. At the magmatic-hydrothermal transition, notably leading to the formation of Nb-Ta-Mn-Fe-poor cassiterite hosting CGM inclusions, earlier minerals were resorbed by muscovite and albite. A later F-rich hydrothermalism is locally reflected by zinnwaldite overgrowths on muscovite. Cassiterite, CGM and micas from petalite-rich pegmatites show lower Mn/Fe ratios and higher Ti contents, along with lower Zr-Ga contents for cassiterite, than that from Li-mica-rich pegmatites. Such behavior is consistent with a magmatic differentiation process whereby Ti content decreased and the degree of Mn-Fe geochemical fractionation and Zr-Ga solubilities increased in the melts, possibly in relation with high fluorine activities. In Li-mica-rich pegmatites, AGM equilibrated with a melt with up to 2 wt% F, similar to that in equilibrium with lepidolite (1-3 wt%). In petalite-rich pegmatite, the relatively high F concentration of the melts equilibrated with AGM (≤ 1.5 wt% F) contrasts with the liquid equilibrated with muscovite (< 0.5 wt% F). This can be accounted by muscovite crystallization after the exsolution of a F-rich aqueous phase at the magmatic-hydrothermal transition. Relatively similar F contents in the initial melts of petalite- and Li-mica-rich pegmatites supports the hypothesis that the stability of lepidolite does not only involves high F but also low H2O over F activities. For the Fregeneda-Almendra Li-mica-rich pegmatites, this could be explained by a decrease of melt H2O solubility due to a relatively low pressure of emplacement.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135547559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early, far-field and diffuse tectonics records in the North Aquitaine Basin (France)","authors":"Loïc Bouat, Pierre Strzerzynski, Régis Mourgues, Yannick Branquet, Nathan Cogné, Guillaume Barré, Véronique Gardien","doi":"10.1051/bsgf/2023014","DOIUrl":"https://doi.org/10.1051/bsgf/2023014","url":null,"abstract":"During the Mesozoic and the Cenozoic periods, Europe recorded several tectonic events that have been interpreted as far-field tectonics. This may be diffuse tectonics that occur at the onset of a major tectonic event or propagation of the deformation away from orogenic fronts. In Western Europe, the deformations related to the opening of the Bay of Biscay and the formation of the Pyrenean belt are well described in the southern part of the Aquitaine basin, but little is known about the “Northern Aquitaine Platform”. We combine field observation with Unmanned Aerial Vehicle (UAV) imagery and U-Pb laser dating on calcite to determine the tectonic evolution in the Vendée Coastal domain. Our results highlight the occurrence of two main tectonic events since the early Jurassic: (1) At the transition from the Late Jurassic to Early Cretaceous, WNW-ESE striking normal faults exhibit a horst and graben pattern that emplaced at the onset of the opening of the Bay of Biscay. Their association with reactivated Variscan strike-slip faults is consistent with oblique extension processes. Such a tectonic event was accompanied by fluid flow coming from depth. (2) During the Late Cretaceous, fractures, wide-open folds, veins, and joints are consistent with the N-S shortening direction that occurs during the earliest stages of the N-S Pyrenenan compression.&#x0D; In both cases, the early stages of the main regional deformation stages are recorded in the “Northern Aquitaine Platform” in a far-field position and before the focus of strain in rifts or orogenic belts. In the Aquitaine basin as in many other places in Europe, the tectonic study of sedimentary platforms located far from the main plate-scale deformation zone provides new constraints on the early diffuse deformation process that predate the main tectonic phases.&#x0D;","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135477196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Climate and Atlantic sea-level recorded in Southwestern Spain from 6.3 to 5.2 Ma. Inferences on the Messinian Crisis in the Mediterranean&#x0D;","authors":"Jean-Pierre Suc, Séverine Fauquette, Sophie Warny, Gonzalo Jiménez-Moreno, Damien Do Couto","doi":"10.1051/bsgf/2023013","DOIUrl":"https://doi.org/10.1051/bsgf/2023013","url":null,"abstract":"The Mio-Pliocene succession of Andalusia on the Atlantic coast (Guadalquivir Basin) is known as one of the former stratotype candidate for the Andalusian Stage, proposed during the seventies as the last stage of the Miocene. Its type section, located in Carmona, a small town east of Seville, has been the subject of mainly stratigraphic, sedimentological and micropaleontological studies. We carried out several field campaigns in this locality from 1987 to 1999, including the drilling of three cored boreholes, which allowed the acquisition of bio- and magnetic-stratigraphic data, and a high-resolution palynological analysis (including pollen, spores and dinoflagellate cysts). The pollen flora and its climatic quantification provided the mean to climatically correlate the section to the oxygen isotope curve from the Montemayor-1 borehole, located about 80 km to the West of Carmona. The variations in the ratio between dinoflagellate cysts and pollen grains were used to identify high and low oceanic levels, the two lowest levels being successively marked by the deposit of a littoral calcarenite (the Calizza Tosca Formation on which the city of Carmona is built) then by a subaerial erosive episode. Based on the correlation with the Montemayor-1 regional drilling, the two major lowering in oceanic levels observed at Carmona are linked with the two episodes of the Messinian Crisis. The interlocking position of the high-energy sandstone deposits inscribed in the Messinian valley leads to an assessment of a drop in the global oceanic level of at least 114 m at the beginning of the paroxysm of the Messinian Crisis. Comparisons are discussed with the amplitude of the Messinian Erosion Surface in the West-Alboran Basin which potentially remained suspended and fed with Atlantic waters during the height of the crisis and isolated from the rest of the almost totally dry Mediterranean Basin. The quantified climate constructed from the pollen records, compared between the Atlantic province and the Mediterranean area, confirms the climatic predisposition of the Mediterranean to desiccation. Atlantic sea-level variations observed in the Guadalquivir region and measured at Carmona suggest that global glacio-eustatism somewhat contributed to the onset and completion of the Messinian Crisis in the Mediterranean Basin.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134885434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New insights in the latest Messinian to Piacenzian stratigraphic series from the Dahra Massif (Lower Chelif Basin, Algeria): Lago Mare, reflooding and bio-events","authors":"Asma Atik, Mohamed El Habib Mansouri, Mostefa Bessedik, Mohammed Kamel Osman, Lahcene Belkebir, Jean-Paul Saint Martin, Christian Chaix, Ayoub Belkhir, Christian Gorini, Ahmed Belhadji, Linda Satour","doi":"10.1051/bsgf/2023012","DOIUrl":"https://doi.org/10.1051/bsgf/2023012","url":null,"abstract":"Recent geological studies conducted in the Dahra Massif located in the Lower Chelif Basin (specifically, the sections of Djebel El Abiod, Hgaf Tamda, Oued Tarhia and Sidi Brahim Telegraph) revealed the bio-sedimentary events that characterize the post-gypsum deposits (Messinian to Piacenzian periods). At Djebel El Abiod, for instance, variegated clays were deposited above the gypsum layer, which were later followed by alternating layers of sandy marls and sandstones (Chara cf. hispida), evolving towards (filling sequence) conglomerates with Pseudocatillus sp, inclined and fractured, whose upper surface is affected by a hardground. Above, this are marine green marls, ruby grey clays evolving to variegated clays, a sequence from which the detrital base is absent (erosion). This event (deformation, erosion) located between these sedimentary sequences, fits well with the Messinian Erosional Surface. This interpretation is supported by the palaeontological content of these deposits. The first sequence, prior to the MES, is marked by an assemblage of Cyprideis ostracodes associated with Loxoconcha muelleri, which can be linked to Lago Mare biofacies 1 ( Lago Mare 1 event, LM1); the second sequence, characterized by the assemblage with Loxocorniculina djafarovi, is linked to Lago Mare biofacies 2 (Lago Mare 3 event, LM3). The unconformable subsequent marine sedimentation (SM1, SM2), marks the reflooding ascribed to the latest Messinian; these sandy marls are sealed by an unconformity overlain by a conglomerate. In this locality, the Pliocene sedimentation begins with coralliferous white marly limestones (CWML). Unconformable marine marls follow the latter, with intercalations of sandstone bars. Simultaneously, white marls (Trubi facies) followed by sandy marls and sandstones alternation develop during the Pliocene (Sidi Brahim Telegraph: SBS). &#x0D; Ages have been established through the identification of several bioevents: Globorotalia margaritae and Reticulofenestra cisnerosii collected from the CWML with Neopycnodonte cochlear, indicating a lower Zanclean age. The succession of G. puncticulata and G. cf. crotonensis in the grey marls corresponds to the Zanclean and Piacenzian (Hgaf Tamda, Djebel El Abiod). Therefore, the deposits located between the gypsum (included) and the CWML are attributed to the latest Messinian. The underlying sandy marls (SM1, SM2) are related to the latest Messinian marine reflooding, preceding the Pliocene marine deposits. This bioevent succession is evident in the SBS section, which is of Messinian and Pliocene age defined by the calcareous nannoplankton. &#x0D; The CWML includes a coral construction (Cladocora cf. caespitosa and Dendrophyllia sp), dated between the presence of R. cisnerosii associated with Globorotalia margaritae at the base and Discoaster asymmetricus associated with G. puncticulata at the top. It indicates a relatively warm event (lower Pliocene: 3 Ma) that correlates to the TG5 stage of the oxygen iso","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"First report of an Ediacarian basement in the Western Alps: the Serre Chevalier crystalline unit (Briançonnais domain, France)","authors":"Denis Thiéblemont, Jean-Baptiste Jacob, Philippe Lach, Catherine Guerrot, Mathieu Leguérinel","doi":"10.1051/bsgf/2023011","DOIUrl":"https://doi.org/10.1051/bsgf/2023011","url":null,"abstract":"We report new LA-ICP-MS U-Pb zircon ages of varied crystalline rocks occurring in an allochtonous unit of basement terrain located at the top of the Briançonnais nappes stack ~5 km west of Briançon city. Mapped as an undifferentiated metasedimentary basement on the geological map at 1/50,000 scale, this unit actually displays varied lithologies including alternating micaschist, paragneiss, quartzite, coarse-grained conglomerate and felsic (leptynite) to mafic (amphibolite) gneiss of magmatic origin. All rocks were metamorphosed in response to a dominant pre-Alpine event under garnet-amphibolite facies conditions. Retrogression under amphibolite to greenschits facies was associated with alpine events. Zircon ages were obtained on four types of rocks: (i) a micaceous quartzite from the core of the metasedimentary unit displays a dominant age population around 610 Ma and subordinated age populations at c. 940 Ma, 1825 Ma and 2100-2560 Ma ; (ii) a granite boulder from a coarse-grained conglomerate yields a dominant magmatic age of 582 ± 5 Ma and subordinated inherited ages between 1800 and 2200 Ma. Zircon metamorphic rims provide a concordant age of 492 ± 4 Ma ; (iii) a gneissic band in the vicinity of the conglomerate is dated at 597 ± 4 Ma ; (iv) a coarse-grained garnet amphibolite yields an age of 517 ± 3 Ma interpreted as the emplacement age of the protolith. The mainly Ediacarian record in the metasediments (quartzite and granite boulder in conglomerate) with no evidence of younger zircons indicates that this material resulted from the erosion of a nearby Ediacarian (Cadomian ?) basement. The age of 517 Ma obtained on the amphibolite provide a minimum age for the sedimentary succession which deposition is therefore bracketed between 582 Ma and 517 Ma. This interval is comparable to that of the metasedimentary units of the Brioverian group of the Armorican Massif. Based on their low Th/U ratio, the 492 Ma-old zircon rims in the granite boulder are attributed to an Upper Cambrian metamorphic event, but it is not yet clear whether this event corresponds to the garnet - amphibolite facies metamorphism recorded in the Serre Chevalier crystalline terrain.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135824539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Eburnean deformation pattern of Burkina Faso and the tectonic significance of shear zones in the West African craton","authors":"D. Chardon, O. Bamba, Kalidou Traoré","doi":"10.1051/bsgf/2020001","DOIUrl":"https://doi.org/10.1051/bsgf/2020001","url":null,"abstract":"Shear zones of the Paleoproterozoic Eburnean accretionary Orogen (West African craton) are investigated by means of large-scale structural mapping. Regional scale (10-100 km) mapping was based on the aeromagnetic survey of Burkina Faso and craton-scale (1000 km) mapping on a compilation of fabric data. At both scales, shear zones are arranged as an anastomosed transpressional network that accommodated distributed shortening and lateral flow of the orogenic lithosphere between the converging Kenema-Man and Congo Archean provinces. Structural interference patterns at both scales were due to three-dimensional partitioning of progressive transpressional deformation and interactions among shear zones that absorbed heterogeneities in the regional flow patterns while maintaining the connectivity of the shear zone network. Such orogen-scale kinematic patterns call for caution in using the deformation phase approach without considering the “bigger structural picture” and interpreting displacement history of individual shear zones in terms of plate kinematics. The West African shear zone pattern is linked to that of the Guiana shield through a new transatlantic correlation to produce an integrated kinematic model of the Eburnean-Transamazonian orogen.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79116306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The stones of the Sanctuary of Delphi – Northern shore of the Corinth Gulf – Greece","authors":"Marilou de Vals, R. Gastineau, A. Perrier, R. Rubi, I. Moretti","doi":"10.1051/bsgf/2020011","DOIUrl":"https://doi.org/10.1051/bsgf/2020011","url":null,"abstract":"The choice of stones by the ancient Greeks to build edifices remains an open question. If the use of local materials seems generalized, allochthonous stones are usually also present but lead to obvious extra costs. The current work aims to have an exhaustive view of the origins of the stones used in the Sanctuary of Delphi. Located on the Parnassus zone, on the hanging wall of a large normal fault related to the Corinth Rift, this Apollo Sanctuary is mainly built of limestones, breccia, marbles, as well as more recent poorly consolidated sediments generally called poros in the literature. To overpass this global view, the different lithologies employed in the archaeological site have been identified, as well as the local quarries, in order to find their origins. The different limestones are autochthons and come from the Upper Jurassic – Cretaceous carbonate platform of the Tethys Ocean involved in the Hellenides orogen. Those limestones of the Parnassus Massif constitute the majority of the rock volume in the site; a specific facies of Maastrichtian limestone called “Profitis Ilias limestone” has been used for the more prestigious edifices such as the Apollo Temple. The corresponding ancient quarry is located few kilometers west of the sanctuary. Then, slope breccia has been largely used in the sanctuary: it crops out in and around the site and is laying on top of the carbonates. Finally, the poros appear to be very variable and seven different facies have been documented, including travertine, oolitic grainstone, marine carbonates and coarse-grained sandstones. All these recent facies exist in the south-east shore of the Gulf of Corinth, although – except for the grainstone – the quarries are not yet known.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83871350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new species of Ampulicomorpha Ashmead from Eocene French amber, with a list of fossil and extant Embolemidae (Insecta: Hymenoptera) of the world","authors":"Cédric Chény, Elvis Guillam, A. Nel, V. Perrichot","doi":"10.1051/bsgf/2020020","DOIUrl":"https://doi.org/10.1051/bsgf/2020020","url":null,"abstract":"Embolemidae is a cosmopolitan but species-poor group of chrysidoid wasps with a scarce fossil record, despite a long evolutionary history since at least the Early Cretaceous. Here, the new species, Ampulicomorpha quesnoyensis sp. nov., is illustrated and described based on a single female found in Early Eocene amber of Oise (France). The new species is compared with the three other known fossil species of the genus, and a key to all fossil species of Ampulicomorpha is provided. This is the third European fossil species of Ampulicomorpha , which suggests that the genus was once well established in Western Europe while it is more widely distributed in the Eastern Palaearctic region today. A list of all fossil and extant Embolemidae of the world, as well as a map of their geographical distribution map, are provided.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89747332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kinematics, deformation partitioning and late Variscan magmatism in the Agly massif, Eastern Pyrenees, France","authors":"J. Vanardois, P. Trap, P. Goncalvès, D. Marquer, J. Gremmel, G. Siron, T. Baudin","doi":"10.1051/bsgf/2020009","DOIUrl":"https://doi.org/10.1051/bsgf/2020009","url":null,"abstract":"In order to constrain the finite deformation pattern of the Variscan basement of the Agly massif, a detailed structural analysis over the whole Agly massif was performed. Our investigation combined geological mapping, reappraisal of published and unpublished data completed with our own structural work. Results are provided in the form of new tectonic maps and series of regional cross-sections through the Agly massif. At variance from previous studies, we identified three deformation fabrics named D1, D2 and D3. The D1 deformation is only relictual and characterized by a broadly northwest-southeast striking and eastward dipping foliation without any clear mineral and stretching lineation direction. D1 might be attributed to thickening of the Variscan crust in a possible orogenic plateau edge position. The D2 deformation is a heterogeneous non-coaxial deformation, affecting the whole massif, that produced a shallowly dipping S2 foliation, and an anastomosed network of C2 shear zones that accommodated vertical thinning and N20 directed extension. D2 is coeval with LP-HT metamorphism and plutonism at ca. 315–295 Ma. D2 corresponds to the extensional collapse of the partially molten orogenic crust in a global dextral strike-slip at the scale of the whole Variscan belt. The D2 fabrics are folded and steepened along a D3 east-west trending corridor, called Tournefort Deformation Zone (TDZ), where the Saint-Arnac and Tournefort intrusives and surrounding rocks share the same NE-SW to E-W subvertical S3 foliation. Along the D3 corridor, the asymmetrical schistosity pattern and kinematic criteria suggest a D3 dextral kinematics. The D3 deformation is a record of E-W striking dextral shearing that facilitated and localized the ascent and emplacement of the diorite and granitic sheet-shaped plutons. D3 outlasted D2 and turned compressional-dominated in response to the closure of the Ibero-Armorican arc in a transpressional regime. The progressive switch from D2 thinning to D3 transpression is attributed to the lessening of gravitational forces at an advanced stage of extensional collapse that became overcome by ongoing compressional tectonic forces at the southern edge of the Variscan orogenic plateau.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75603413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Large-sized theropod Spinosaurus: an important component of the carnivorous dinosaur fauna in southern continents during the Cretaceous","authors":"C. Candeiro, Lívia Motta Gil, P. Castro","doi":"10.1051/BSGF/2018010","DOIUrl":"https://doi.org/10.1051/BSGF/2018010","url":null,"abstract":"The Early Cretaceous of North Africa has Spinosaurinae dinosaur remains such as Spinosaurus recorded in Algeria (Guir Basin, Kem Kem beds), Egypt (Bahariya Formation), Morocco (Kem Kem beds), and Tunisia (Ain El Guettar Formation). Until now, three possible Spinosaurus species were identified: Spinosaurus aegyptiacus , Spinosaurus sp. and Spinosaurus “B”. The occurrence of this genus in the Albian-Cenomanian rocks of Africa suggests that the temporal and geographic distribution of these spinosaurines is the largest one among all genera and species of megapredators from the middle Cretaceous of Africa. The fossil record of Spinosaurus from the Albian to the Cenomanian shows a 20 million year persistence of this genus in Gondwanan ecosystems.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90616915","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}