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Featured researches published by François Atrops.


Earth and Planetary Science Letters | 2003

Ice age at the Middle–Late Jurassic transition?

Gilles Dromart; Jean-Pierre Garcia; Stéphanie Picard; François Atrops; Christophe Lécuyer; Simon M.F. Sheppard

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (∼0.8 Myr) temperature fall opposed to a long-term (∼1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.


Journal of the Geological Society | 2005

Jurassic evolution of the Arabian carbonate platform edge in the central Oman Mountains

Mathieu Rousseau; Gilles Dromart; Jean-Pierre Garcia; François Atrops; François Guillocheau

The Jurassic Sahtan Group exposed in northern Oman was deposited in shallow marine environments at the edge of the Arabian Platform facing the Neo-Tethys (Hamrat Duru Basin). The upper Sahtan Group is made up of a mixed siliciclastic–carbonate unit overlain by pure carbonate deposits, assigned to a Bathonian and Early Callovian age on the basis of brachiopods and foraminifers. These carbonate depositional systems were composed of outer oolitic shoals that underwent subaerial exposure, and a deeper, somewhat restricted, gently dipping shelf interior. Oolitic material was shed off the platform edge into the deep-sea depositional complex of the Guweyza Formation. The Sahtan Group is affected by an important thickness reduction towards northeastern Jabal Akhdar. The angular unconformity (0.2%) at the top of the Sahtan Group is shown to result from tilting and top truncation of genetic sequences. This unconformity is overlain by the Rayda Formation, a veneer that shows an onlap pattern including a gradual deepening upwards facies evolution. The minimal time span of the stratigraphic hiatus is Mid-Callovian–Kimmeridgian. Oxfordian and Kimmeridgian sequences were probably never deposited in this area because of lack of accommodation space and/or because of subaerial exposure. It is proposed herein that the unconformity was shaped by subaerial carbonate dissolution during a steady, tectonically driven exhumation of the platform edge. During the Tithonian, a major eustatic sea-level rise caused transgression of the Rayda Formation upon the platform edge and normal shelf marine conditions resumed in the eastern Arabian Peninsula.


Palaeogeography, Palaeoclimatology, Palaeoecology | 1997

Quantitative variations in the Valanginian ammonite fauna of the Vocontian Basin (southeastern France) within limestone-marl cycles and within parasequence sets

Stéphane Reboulet; François Atrops

Abstract The ammonite assemblages between beds and interbeds are examined. This quantitative analysis was carried out on limestone-marl alternations in the Valanginian Vergol section (Drome), located in the Vocontian Basin (southeast France). There is a strong faunal contrast between beds and interbeds. The calcareous beds are characterized by high relative abundances of Neocomitids and Olcostephanids, whereas the marls are marked by a high relative frequency of Phylloceratids. Significant modifications of the composition of ammonite spectra are also observed from the base to the top of some parasequence sets. The variations in bathymetry and trophic drifts linked to the climatic fluctuations may have controlled the ammonite assemblages. The increase in bathymetry in marls was thus probably beneficial to Phylloceratids, which are a deep-water group. The high planktonic production in limestones could explain the great relative abundance of Neocomitids and Olcostephanids, which lived in the upper part of the water column.


Journal of Paleontology | 2008

Early Tithonian Serpulid-Dominated Cavity-Dwelling Fauna, and the Recruitment Pattern of the Serpulid Larvae

Ján Schlögl; Jozef Michalík; Kamil Zágoršek; François Atrops

Abstract A Lower Tithonian cavity-dwelling community from pelagic carbonate platform deposits of the Czorsztyn Unit, Western Carpathians, represents a succession of mostly solitary coelobite organisms, dominated by scleractinian corals and small-sized serpulids during the initial recruitment stage, and by serpulids during the following recruitment stages. These bioconstructors were accompanied with other suspension feeders: thecideidine brachiopods, oysters, bryozoans, sponges, crinoids and sessile foraminifers. The boundary between the first and the second recruitment stage represents an interval of aggregate growth interruption, when a thin sheet of cyclostome bryozoans developed. Corals and serpulids Neovermilia and Vermiliopsis are primary bioconstructors; all other associated organisms profited from the free spaces between the serpulid tubes. The aggregates were already bioeroded, mineralized and encrusted during their growth. Serpulid larvae show a special recruitment pattern. Their tubes were observed attached on the inner surfaces of adult serpulid tubes only. Possible causes of such a larval behaviour involve several physical, biological or chemical factors. Except for the first recruitment stage, the rest of the succession seems to be physically controlled by the gradual infilling of cavities.


Geobios | 1993

Current trends in systematics of Jurassic Ammonoidea: The case of Oxfordian-Kimmeridgian Perisphinctids from Southern Europe

François Atrops; Guillermo Meléndez

Abstract Recent progress in the characterization of morphological variability of ammonites species has helped outline a biostratigraphic-evolutionary classification of many groups of ammonites on the basis of the concept of biospecies, or successive horizontal, homogeneous assemblages. In the case of Middle Oxfordian Perisphinctinae and Upper Oxfordian-Lower Kimmeridgian Ataxioceratinae a similar pattern can be drawn after recognizing a sharp sexual dimorphism within each group and evaluating the large horizontal continuous variability in each successive assemblage. Some prominent cases of discontinuous variability, interpreted as possible cases of intraspecific, non sexual, polymorphism, such as in Larcheria-Otosphinctes-Dichotomosphinctes, Subnebrodites-Orthosphinctes, and the forms with and without parabolic nodes of Orthosphinctes (Ardescia) and Ataxioceras (Parataxioceras), are discussed and analyzed. Taxonomic and nomenclatural problems derived from this approach are evaluated and the need for a nomenclatural revision is considered. The typological taxonomy, widely used during the last century, characterized by an abundance of morpho-taxa is however regarded as a useful tool for recognizing and characterizing morphologies and to give valid names to both sexual dimorphs until a deeper knowledge of successive dimorphic pairs is achieved.


Volumina Jurassica | 2016

Towards a consistent Oxfordian/Kimmeridgian global boundary : current state of knowledge

Andrzej Wierzbowski; François Atrops; Jacek Grabowski; Mark W. Hounslow; Bronisław Andrzej Matyja; Federico Olóriz; Kevin N. Page; Horacio Parent; M. A. Rogov; Günter Schweigert; Ana Bertha Villaseñor; Hubert Wierzbowski; John K. Wright

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r).The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.


Bulletin De La Societe Geologique De France | 2005

Palynofacies and calcareous nannofossils in the Upper Kimmeridgian, southeastern Paris basin (France)

Fabienne Giraud; Bernard Courtinat; Jean-Pierre Garcia; François Baudin; François Guillocheau; Gilles Dromart; François Atrops; Claude Collette

The Upper Kimmeridgian Members “Calcaires blancs superieurs” and the “Marnes a exogyres superieures” of the southeastern Paris basin were investigated for their palynofacies and calcareous nannofossils. These members display alternating limestone marl lithotypes and represent shallow marine paleoenvironments. The lower carbonate member is interpreted as a proximal palaeoenvironment (palaeobathymetry = 5 to 10m), where storm and swell deposits were prevalent and the salinity was occasionally weak. The relative richness of brown phytoclasts in this part is favoured by good preservation related to restricted conditions. These conditions would explain the dominance of the nannofossil Cyclagelosphaera margeretti in the nannofossil assemblages. The palynological data as those of the nannofossil assemblages show variations in the shift from carbonate member to marly member. The dominance of brown phytoclast over black phytoclast, the presence of amorphous organic matter (AOM), and the highest abundance and diversity observed within the nannofossil assemblages suggest that the maximum of distality occurred during this transition, at the basal part of the Marnes a Exogyres superieures. The upper part of the section (marly member) characterized by storm deposits an storm coquina beds is deeper (palaeobathymetry probably between 10 and 40 m depth) than the lower part. Oxidizing depositional conditions prevailed and explained the abundance of black particles found in this opper part., while proximate cysts and elevated non-placolith coccolith abundances indicate that relationships with the open sea were probably more significant compared to the lower part. Towards the top of the section, recurrences of restricted conditions are reflected by relatively elevated amounts of AOM and the abundance peak of the nonnofossil Biscutum ellipticum. This study shows that micropalaeontological signals can be well recorded in vast lagunal domains. We speculate that salinity , nutrient supply, and oxygenation of the waters control microfossil associations. In shallow environments, these parameters are particularly fluctuating, especially when freshwater dilutes marine waters in surface, on the occasion of rainy periods or of intense arrival of continental waters.


Geobios | 1999

Mise en évidence du jurassique inférieur et moyen dans la ceinture ophiolitique de sulawesi (indonésie). Conséquences géodynamiques

Jean-Jacques Cornée; Rossana Martini; Michel Villeneuve; Louisette Zaninetti; Emanuela Mattioli; Roberto Rettori; François Atrops; Wahyu Gunawan

Calcareous nannofossils, one ammonite and some benthonic foraminifera have been discovered in deposits of Upper Sinemurian (?) to Bathonian age under the ophiolite nappe in East Sulawesi. These biostratigraphical results allow to propose for the first time a general lithostratigraphic succession of the Mesozoic tectonically-dismembered sedimentary rocks under the ophiolite. This succession indicates that the Late Triassic reefal platform of East Sulawesi suffered a major subsidence event during Early Liassic times. Prior to Neogene tectonics, which strongly dismembered East Indonesia, the Ophiolitic tectonic Zone of East Sulawesi was probably part of the widest palaeogeographic block which included some of the Banda Sea continental fragments: Buru, Seram, Buton and the Sinta Ridge.


The Holocene | 2018

Tsunami sedimentary deposits of Crete records climate during the ‘Minoan Warming Period' (≈3350 yr BP)

Christophe Lécuyer; François Atrops; Romain Amiot; Delphine Angst; Valérie Daux; Jean-Pierre Flandrois; François Fourel; Kevin Rey; Aurélien Royer; Magali Seris; Alexandra Touzeau; Denis-Didier Rousseau

Earthquakes or explosive eruptions generate tsunami, which are at the origin of thick and chaotic coastal sediments. These commonly fossiliferous deposits are formed instantaneously at the historical or geological timescale and therefore have the potential to provide snapshot records of past climates. In Crete, near the city of Palaikastro, crops out a 1- to 9-m-thick sedimentary layer deposited by a huge tsunami that has been previously estimated to be about 9 m high. The presence of volcanic ash, the geometry, the archeological and faunal contents of the sedimentary deposit along with radiocarbon dating converge for interpreting this tsunamite as coeval with the Minoan Santorini (Thera) eruption ≈3350 yr BP. During its drawback, the tsunami deposited rocky blocks and a muddy matrix containing mollusc shells dredged from the seabed as well as cattle skeletal remains and various artifacts belonging to the contemporaneous Minoan civilization. While the oxygen isotope compositions of terrestrial vertebrate bone remains most likely resulted from diagenetic alteration, those of a bovid tooth revealed that air temperatures during MM3 and LM1 periods were about 4°C higher than nowadays. Oxygen isotope measurements of marine mollusc shells also revealed that sea surface temperatures were higher by about 2°C. Those results compare with the 2.5°C temperature difference already estimated according to both δ2H and δ18O values of Greenland ice cores. Incremental sampling of marine gastropods and bovid teeth suggests that the seasonal amplitude was similar to that prevailing during the second half of the 20th century.


Cretaceous Research | 2003

Report on the 1st International Workshop of the IUGS Lower Cretaceous Ammonite Working Group, the ‘Kilian Group’ (Lyon, 11 July 2002)

Philip J. Hoedemaeker; Stéphane Reboulet; Maria B. Aguirre-Urreta; Peter Alsen; Mohamed Aoutem; François Atrops; Ricardo Barragán; Celestina González; Jaap Klein; Alexander Lukeneder; Izabela Ploch; Naser Raisossadat; Peter F. Rawson; Pierre Ropolo; Zdenek Vasicek; Jean Vermeulen; Max G.E. Wippich

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Christophe Lécuyer

Institut Universitaire de France

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Mohamed Jati

University of Strasbourg

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Michel Benest

Centre national de la recherche scientifique

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