Thierry Adatte (Université de Lausanne)

&Danièle Grosheny (Université de Lorraine)

Journées en l’honneur d’Hubert Arnaud

27 & 28 novembre 2017

Salle Van Straelen77 rue Claude Bernard

75005 Paris

Organisateurs :

LES PLATES-FORMES CARBONATEES

Avec le soutien

Gro

upe

Fran

çais

du

Cr

étacé Groupe França is du Crétacé

DESASSOCIATIONSEDIMENTOLOGISTESFRANCAIS

Réun

ion spécialisée de la SGF

1

Séance Spécialisée de la Société Géologique de France Avec le soutien de l’ASF, du GFC et de l’Institut Dolomieu

LES PLATES-FORMES CARBONATEES Journées en l’honneur d’Hubert Arnaud

Livret des résumés

Organisées par Thierry Adatte et Danièle Grosheny

2

Hubert sur le terrain, au Pilatus

3

Notre collègue et ami Hubert est né le 18 novembre 1939 à Tunis. Il est parti dans la soirée du 27 novembre 2016. Il venait d’avoir 77 ans. Après des études secondaires à Bizerte, Hubert effectue son cursus universitaire à Grenoble où il devient assistant dès 1963. Il y soutient sa thèse de 3e cycle, intitulée «Contribution à l’étude géologique du Vercors méridional – Alpes françaises» en 1964, puis, obtient le titre de docteur d’Etat en 1981. Il est lauréat du prix Prouvost de la SGF en 1982. De 1982 à 1984, Hubert est spécialiste des carbonates chez Elf-Aquitaine à Pau. Il travaille alors en Italie, Tunisie et en Angola. En 1989, Hubert devient Professeur des Universités à Grenoble et continue à parcourir le monde en réalisant ses travaux sur le Crétacé inférieur en Syrie, Azerbaidjan, Géorgie, Oman, Mexique, Venezuela. Il applique alors les concepts de la stratigraphie séquentielle à la géométrie sédimentaire de l’urgonien du sud-est de la France. Hubert prend sa retraite en 2003 mais, il continue, sans discontinuer, à parcourir le monde toujours aussi passionné par son métier. En 2005, avec Annie, Hubert nous avait conduit géologiquement et culturellement dans sa Tunisie qu’il aimait tant, lors d’une excursion sur les séries de l’Aptien au Cénomanien En octobre 2016, Hubert a, une nouvelle fois, menée une excursion géologique sur son urgonien du Vercors qu’il aimait tant. Auteur de plus de cinquante articles, il laisse à la communauté géologique une somme impressionnante de connaissances et d’observations sur la sédimentologie des carbonates.

Façade Sud-Ouest du Vercors – Montagne de Glandasse

4

PROGRAMME

Lundi 27 novembre 9h30 : Accueil

10h00 : Introduction par les organisateurs

10h05 : Hommage à Hubert Arnaud

10h15 : Conférence de Maurice Tucker.- Carbonate Platforms: the Roles of Microbes.

11h10 : Pause café

11h40 : Bernard Duval, Philippe A. Lapointe.- Pétrole, carbonates, géosciences.

12h10 : Benjamin Brigaud, Simon Andrieu, Jocelyn Barbarand, Eric Lasseur.- Définir les

paléo-environnements lorsque les sédiments manquent : analyses géochimiques in situ des

ciments des discontinuités.

12h30 : Stéphane Bodin.- Responses of neritic carbonate factories to Jurassic environmental

changes Example from the Central High Atlas of Morocco

13h10 : Pause repas (non organisée par la SGF)

14h30 : Conférence de Karl Föllmi.- The evolution of the Urgonian platform in the light of late

Early Cretaceous paleoenvironmental change

15h25 : Brahimsamba Bomou.- The mexican Guerrero-Morelos carbonate platform throughout the

Cenomanian-Turonian boundary

15h55 : Pause café

16h20 : Philippe A. Lapointe .- Sequence Stratigraphy and Seismic Stratigraphy of the Lower

Cretaceous Shuaiba Formation from Abu Dhabi Ruwais Field.

16h50 : Lucie Bonvallet, Annie Arnaud, Alexis Godet, Thierry Adatte, Jorge E. Spangenberg,

Karl B. Föllmi.- Evolution of the Helvetic shelf (Switzerland) during the Barremian - early

Aptian: Paleoenvironmental, paleogeographic and paleoceanographic controlling factors.

17h00 : Débat : Appréciation du temps géologique: nouvelles méthodes versus biostratigraphie.

5

Mardi 28 novembre

9h00 : Accueil

9h30 : Rémy Richet, Jean Borgomano, Sophie Viseur, Jean-Pierre Masse.- High-resolution

stratigraphic model of the Urgonian carbonate platform in the Gresse-en-Vercors area (SE

France).

10h00 : Serge Ferry.- Growth faults affecting the internal geometry and facies of depositional

sequences, lower Barremian, southeastern Vercors carbonate platform, France.

10h30: Pause café

11h00 : Conférence de Peter W. Skelton.- Aptian carbonate platform development in the

Alicante region, SE Spain.

11h55 : Rabaa Hfaiedh Alexis Godet, Annie Arnaud Vanneau, Jamel Ouali.- Biostratigraphy

and palaeoenvironments of the Aptian sedimentary succession at Jebel Bir Oum Ali

(Northern Chain of Chotts, South Tunisia): Comparison with contemporaneous series from

the southern Tethyan margin.

12h25 : Pause repas

14h00 : Alexis Godet, Christophe Durlet, Jorge E. Spangenberg, Karl B. Föllmi.- Meteoric

diagenetic overprint on the carbon isotope composition of Urgonian-type platform

carbonates from the western Swiss Jura

14h30 : Jean-Pierre Masse, Mukerrem Fenerci-Masse.- Les rudistes et la datation des formations

carbonatées de type Urgonien du Sud-Est de la France

15h00 : Jean Vermeulen, Hubert Arnaud.- Ages of the marine series underlying the Urgonian in

the Gard

15h30 : Annie Arnaud Vanneau.- Modalities of the installation of the Urgonian during the late

Barremian on the north-Tethyan margin of France and Switzerland.

16h00 : Pause café et clôture

6

Résumés

7

Modalités de l’installation de l’Urgonien au Barrémien supérieur sur la marge nord téthysienne de France et de Suisse

Annie Arnaud-Vanneau1, Karl B. Föllmi2, Alexis Godet3, Thierry Adatte2, Lucie Bonvallet1

1Association Dolomieu, 18 Boulevard Maréchal Leclerc, F-38000 Grenoble, France 2Institute of Earth Sciences, University of Lausanne, UNIL Quartier Mouline, CH-1015, Lausanne, Switzerland 3Department of Geological Sciences, The University of Texas at San Antonio, 1 UTSA Circle, San Antonio, Texas, 78249, USA

Les calcaires à rudistes qui vont constituer l’Urgonien en France et Suisse ou le Schrattenkalk

en Suisse alémanique vont s’installer sur la marge nord téthysienne au Barrémien supérieur. Grâce aux études récentes menées dans le cadre des thèses sur le Gard, l’Ardèche et la Provence (Bastide, 2014), sur les Alpes helvétiques (Bonvallet, 2015) et les datations par ammonites situées sous la falaise urgonienne (Vermeulen, 2017 en cours), nous avons tous les éléments pour suivre précisément l’installation de cette plate-forme de calcaire à rudistes. Ainsi au cours du Barrémien inférieur les dépôts carbonatés bioclastiques peu profonds s’installent sur les bordures du bassin vocontien en formant des corps sédimentaires de superficie réduite, assimilables à des corps de bas-niveau. Au Barrémien supérieur le niveau de la mer va s’élever et ennoyer de plus en plus largement la marge nord-téthysienne au cours de la séquence B3, entrainant le développement des lagons à rudistes et des calcaires urgoniens. C’est la dynamique de dépôt de cette séquence qui va être développée à présent.

La base de la séquence B3 débute par un abaissement du niveau marin évalué à une centaine de mètres dans le sud du Vercors. Ce bas niveau est responsable de l’émersion et de l’érosion d’une partie émergée des dépôts du Barrémien inférieur, et probablement d’une partie de l’Hauterivien.

Les premiers dépôts calcaires peu profonds sous faciès bioclastiques sont limités à la bordure du bassin vocontien. Les dépôts suivants s ‘installent de plus en plus loin sur la surface antérieurement émergée.

Les dépôts de transgression (TST) se développent sur la bordure du bassin vocontien sous forme d’une frange récifale constituée de petits atolls coralliens de 500 m à 2 km de diamètre pouvant renfermer des lagons à rudistes de taille limitée. Ces atolls s’installent sur des shoals oolitiques formant une bande d’une largeur d’une dizaine de kilomètres dans le Vercors. Au-dessus, l’élévation du niveau marin devient plus importante (marnes de Font Froide dans le Vercors) et des ammonites ont été retrouvées dans les zones les plus externes proches du bassin. Ces marnes peuvent être considérées comme correspondant à la mfs de la séquence B3.

Les séries sus-jacentes sont beaucoup plus détritiques et la faune présente témoigne du changement environnemental qui devient soit mésotrophique avec la multiplication des orbitolines (Palorbitolina transiens), soit distrophique avec la pullulation d’annélides isolés. Ces dépôts vont se retrouver jusqu’à 15 à 30 de km de la bordure de la plate-forme. L’élévation du niveau marin est estimée de 30 à 40 m. La transgression arrive sur des surfaces émergées et érodées (surface d’érosion, et Barrémien inférieur partiellement manquant dans le Gard, traces de racine et galets dans le Vercors et le Jura)

Les dépôts qui viennent au-dessus forment le HST et constituent une trilogie observable de la Provence à la Suisse avec à la base des faciès bioclastiques et oolitiques, puis des faciès assez riches en coraux et éponges calcaires et enfin des faciès à rudistes, faciès urgoniens par définition.

Au sommet de la séquence B3, les derniers dépôts indiquent des faciès de plage ou d’émersion. Le sommet de cette séquence finit par émerger, les sédiments se cimentent précocement et sont en partie karstifiés. L’abaissement du niveau marin correspondant à la fin de la séquence B3 peut être de l’ordre d’une quinzaine de mètres.

La durée de cette séquence B3 a été estimée à 920 000 ans, avec une vitesse de remontée passant de 0,88 à 0,71m/1000 ans jusqu’à la mfs, puis se stabilisant autour de 0,29 m/1000 ans pour le HST.

8

Modalities of the installation of the Urgonian during the late Barremian on the north-Tethyan margin of France and Switzerland

Rudist limestones that constitute the Urgonian Formation in France and Switzerland, as well as its lithostratigraphic equivalent (the Schrattenkalk Formation) in northern Switzerland, settled on the northern Tethyan margin in the late Barremian. Recent studies performed in the Gard, Ardèche and Provence regions of France (Bastide, 2014), in the Swiss Alps (Bonvallet, 2015), are complemented by the dating of ammonites located under the Urgonian Formation in Gard and Ardèche, France (Vermeulen, 2017, in progress), and permit to precisely follow the installation of this rudists-bearing carbonate platform.

During the early Barremian, shallow water marine bioclastic carbonate deposits formed sedimentary bodies of reduced surface area on the borders of the Vocontian basin; they can be assimilated to low-stand systems tract (B1 and B2 sequences). In the late Barremian, sea level rose and inundated more and more the northern Tethyan margin during the B3 sequence, allowing the development of lagoons with rudists and limestones of the same name. It is the dynamics of deposition of this B3 sequence, which is developed in this contribution. A drop of the sea level occurred at the base of the B3 sequence. It is estimated to a hundred meters in the south of the Vercors. This low sea level induced the subaerial exposure and erosion of part of the Hauterivian (?) to lower Barremian deposits.

The first shallow-water limestone deposits of bioclastic facies are limited to the edge of the Vocontian basin. The following deposits settle farther and farther on the surface formerly emerged. On the edge of the Vocontian basin, deposits of the transgressive systems tract formed of a reef fringe, which consists of small coral atolls of 500 m to 2km in diameter, and which can define lagoons with scarce rudists. These atolls settled on oolitic shoals and formed a ca. 10 km wide strip in the Vercors. The sea-level rise subsequently became more important, reaching a maximum in the marls of Font Froide in the Vercors. Laterally, ammonites have been found in the outermost zones near the basin. These marls can be considered as corresponding to the mfs of the B3 sequence. The overlying series are much more detrital and their specific fauna reflects a change in the environment that either became mesotrophic with the multiplication of orbitolinids (Palorbitolina transiens), or distrophic with the occurrence of isolated annelids. These deposits are found up to 15 to 30 km from the edge of the platform, and imply a rise in sea level of 30 to 40m. The transgression occurs on surfaces that were previously emerged and eroded, as testified by the lost of part of the Barremian in the Gard, the occurrence of rootmarks and of perforated pebbles in the Vercors and the western Swiss Jura. The following deposits belong to the highstand systems tract and constitute a ‘sedimentological trilogy’ observable from Provence to Switzerland with a bioclastic and oolitic facies at the base, then facies rich in corals and calcareous sponges, and finally a rudists-bearing facies. Finally, the early cementation and partial karstification of the last deposits of the sequence B3 indicate a beach environment that was periodically subjected to subaerial exposure. The drop in sea level corresponding to the end of the sequence B3 may be of the order of 15 m.

The duration of the sequence B3 was estimated to 920 000 years, with a sedimentation rate ranging from 0.71 to 0.88 m.kyr-1 up from the base of the sequence to its maximum flooding surface, then stabilizing at ca. 0.29 m.kyr-1 during the highstand systems tract.

9

Responses of neritic carbonate factories to Jurassic environmental changes: Example from the Central High Atlas of Morocco

Stéphane Bodin

Department of Geoscience, Aarhus University, Denmark During the Early and Middle Jurassic, Morocco was the locus of vast neritic carbonate

production. The present-day outstanding exposures of the Central High Atlas Mountains offer an exceptional setting in which the stratigraphical and lateral evolution of these neritic carbonate deposits can be evaluated against the numerous episodes of environmental change known to occur during this time interval. We aim here at better understand the relationship between neritic carbonate production, reef evolution and environmental changes.

The foremost change affecting neritic carbonates in Morocco occurs at the Pliensbachian-Toarcian boundary. It is marked by the complete demise of the neritic carbonate factory throughout the basin and beyond, temporarily replaced by siliciclastic system in the western part of the Central High Atlas basin, whereas condensation and hiatus characterize the central and eastern part. This demise is linked to a major environmental change, from an arid to a humid climate. It however precedes the Toarcian Oceanic Anoxic Event by ca. 1 Myr, which is itself accompanied by a distinct, short-lived demise event of a mixed carbonate –siliciclastic system in the western part of the basin. Besides these early Toarcian events, two other noticeable events have impacted the neritic carbonate production in Morocco: the Sinemurian-Pliensbachian boundary event, and the late early Bajocian event. The first event is coeval to a major eustatic sea-level rise, responsible for strong backstepping (but no demise) of the microbial-dominated Sinemurian carbonate factory. The second event is marked by a short-lived neritic carbonate demise event that coincides with an episode of combined seawater eutrophication and pronounced sea-level rise. However, as soon as the adverse environmental conditions cease, the neritic carbonate factory resumes unchanged compared to its pre-event state.

In total, four groups of different carbonate factories can be observed during the early and middle Jurassic; a timespan of 30 Myr. This highlights the resilience and plasticity of neritic carbonate systems on geological timescale, and demonstrate that these latter are able to quickly adapt to new a set of environmental parameters. On shorter timescale, however, rapid environmental upheavals were often deleterious for existing carbonate factory, but frquently paved the way for a new type of factory. For instance, the Sinemurian-Pliensbachian boundary event marks the onset of Lithiotid bivalves’ dominance in the shallow marine environment until the onset of the Toarcian Oceanic Anoxic Event. This latter event marks the onset of the mid-Jurassic carbonate factory group, characterized by oobioclastic sedimentation during prograding phases, and a microbial-dominated factory during transgressive phases

Several parameters are frequently evoked as major controls on carbonate factory. These include seawater temperature, nutrient levels, or temporary reduction of carbonate saturation state. Preliminary results indicate that the main factor regulating the strength and evolution of Central High Atlas carbonate factories was regional nutrient levels changes. These latter are correlated to changes in precipitation regime in the Central High Atlas basin hinterlands, which are paced by global environmental changes. During the onset of the Toarcian OAE, additional factors such as ocean acidification, thermal stress and increased hurricane intensity might also have contributed to the demise of the earliest Toarcian carbonate factory.

10

The Mexican Guerrero-Morelos carbonate platform throughout the Cenomanian-Turonian boundary

Brahimsamba Bomou1, Annie Arnaud-Vanneau2, Thierry Adatte3

122 boulevard Emmanuel Rouquier, 06130 Grasse, France, brahimsamba.bomou@gmail.com 2Association Dolomieu, 8 Chemin des Grenouilles, 38700 La Tronche, France 3Institute of Earth Sciences, University of Lausanne, Bâtiment Géopolis, 1015 Lausanne, Switzerland The Cretaceous period is well known for the huge expansion of marine carbonate platforms around the

world, under a relative warm climate. However several intense crisis punctuated this period with the widespread development of Oceanic Anoxic Events. One of them is particularly intense and present at the global scale, the Cenomanian-Turonian Oceanic Anoxic Event or OAE2. This event is marked by strong carbon cycle perturbation highlighted by the isotopic carbon excursion world widely recorded. Massive submarine volcanic activities, as the Caribbean Plateau, have released high biolimitant metal abundance that enhanced productivity and oceanic eutrophication. Numerous and major faunal and flora extinctions occurred during this interval, in particular for large benthic foraminifera. Only few carbonate platforms survived during this crisis, in particular the Guerrero-Morelos carbonate platform (South-western Mexico) which persisted under oligotrophic to mesotrophic environments despite its proximity of the Caribbean Plateau. The δ13C curves of the studied sections (Axaxacualco and Barranca del Cañon) exhibit the typical OAE2 features including a large positive excursion. This well preserved carbon isotopic curve recorded in the platform carbonate deposits allows a better understanding of large benthic foraminifera distribution during the OAE2 event and their biotic response to these paleoenvironmental changes. The definitive drowning of Guerrero-Morelos carbonate platform takes place in the lower Turonian, well above the end of the δ13C shift, with the deposition of black shale and turbidites indicating deeper anoxic environments, which preclude large benthic fauna reestablishment.

11

Evolution of the Helvetic shelf (Switzerland) during the Barremian–early Aptian: Paleoenvironmental, paleogeographic and paleoceanographic controlling factors

Lucie Bonvallet1,2, Annie Arnaud-Vanneau2 , Alexis Godet3, Thierry Adatte1,

Jorge E. Spangenberg4, Karl B. Föllmi1

1 Institut des Science de la Terre, Université de Lausanne, CH-1015 Lausanne 2 Association Dolomieu, 8 chemin des Grenouilles, 38700 Grenoble France 3Department of Geological Sciences, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA 4Institut des dynamiques de la surface terrestre, Université de Lausanne, CH-1015 Lausanne

The Early Cretaceous has experienced the development of large shallow-water carbonate platform in tropical and subtropical regions, favoured by exceptionally warm climatic conditions, optimal trophic conditions and a suitable tectonic and paleogeographic context. This period was also characterized by shorter intervals, in which the widespread deposition of marine sediments enriched in organic matter occurred (“oceanic anoxic event”: OAE). This study focuses on the Barremian-Aptian interval, during which the Urgonian platform developed throughout the northern Tethyan passive margin. Due to the Alpine orogeny, sediments belonging to this platform - named locally Schrattenkalk Formation, are presently outcropping in the Helvetic Alps.

This study aims to reconstruct the paleogeographic evolution of the Helvetic platform, and to define the environmental and oceanographic factors, which influenced its development. Several key episodes in the life of this platform have been identified:

- The installation of the platform, covering hemipelagic sediments of the Drusberg Member, near the limit between the early and late Barremian.

- The temporary change of carbonate production type during the basal Aptian, with the deposition of the Rawil Member.

- And finally the definitive interruption of photozoan carbonate platform sedimentation in the study area, during the early Aptian.

The sedimentological, biostratigraphical and chemostratigraphic (d13C) data lead to the sequential subdivision of eleven sections and one core, located throughout the different Helvetic nappes of Switzerland. The sequence stratigraphic framework, initially defined for the Urgonian carbonate platform of the Vercors area (SE France), is confirmed in the Helvetic nappes, where the same number of sequences was observed. For instance, the sequence stratigraphic framework helped to highlight the installation of a bioclastic body, included in the Schrattenkalk Formation, since the middle Early Barremian (sequence B2). The age of the installation of the rudist-rich limestone, which corresponds to the Urgonian facies sensu stricto, is attributed to the late Barremian (maximum flooding surface of the sequence B3). This age coincides with the one determined in other northern Tethyan areas for the installation of the Urgonian platform.

The results of this study show a strong tectonic control on the platform architecture, with the presence of syn-sedimentary faults in a perpendicular position to the progradation direction of the platform. The presence of these faults was highlighted by the study of the evolution of the microfacies distribution and by thickness variations in different areas.

Sea level fluctuations also played an important role in the various life phases of the platform. Three major falls in sea level have been identified. An important drop of the relative sea level induced a ignificant emersion of the proximal domain, leading to the exposure of the Drusberg Member hemipelagic series. A second major drop in sea level is identified near the Barremian-Aptian boundary, and a third is registered on the top of the Upper Schrattenkalk Member on the whole platform; it triggered the karstification of the underlying limestones to a depth of over 20 meters. This observation sheds new light on the conditions linked to the demise of Urgonian platform, which was strongly influenced by this phase of emersion.

12

Les paléo-environnements lorsque les sédiments manquent : analyses géochimiques in situ des ciments des discontinuités

Benjamin Brigaud1, Simon Andrieu2, Jocelyn Barbarand1, Eric Lasseur2

1 GEOPS, Univ. Paris-Sud, CNRS, Université Paris Saclay, Rue du Belvédère, Bât. 504, 91405 Orsay, France 2 BRGM, 3 avenue Claude Guillemin, BP 36009, 45060 Orléans, France Les roches carbonatées déposées sur les plate-formes sont de formidables archives de

l’histoire de notre planète et des bouleversements environnementaux qu’elle a connus. Néanmoins, les plate-formes carbonatées sont souvent marquées par des périodes d’arrêt de sédimentation, à l’origine de la formation de surfaces clefs appelées « discontinuités sédimentaires », dont l’origine est difficile à caractériser. Lors de ces périodes de non-dépôt, des ciments dits « précoces », dont la taille ne dépasse généralement pas quelques dizaines de micromètres, précipitent et participent à la genèse des discontinuités. Au-delà de leur observation au microscope, leur petite taille rend leur caractérisation chimique compliquée car les méthodes d’analyse par spectrométrie de masse après attaque acide nécessitent de prélever des quantités trop importantes de carbonate (1mg). La taille d’investigation est dans le cas de la caractérisation des discontinuités un verrou important à leur compréhension. Dans cette étude, le couplage (1) de la sonde ionique (Secondary Ion Mass Spectrometry – SIMS 1280), et (2) d’un spectromètre de masse à source « plasma » couplé avec un système d’ablation laser (Laser Ablation Induced Coupled Mass Spectrometer High Resolution LA-ICPMS-HR) est proposé afin de travailler directement sur les lames minces à l’échelle des ciments. Ces deux méthodes permettent de déterminer les rapports isotopiques en oxygène et en carbone ainsi que les concentrations en éléments traces comme les Eléments des Terres Rares (ETR) ou majeurs (Mg, Al, Mn, Fe) des ciments carbonatés. Le but de cette étude est de tester, comme marqueur paléo-environnemental, l’analyse des ciments calcitiques cristallisant dans l’espace inter-granulaire pendant la période de non-sédimentation par ces deux méthodes. Plusieurs discontinuités clefs d’âge Jurassique moyen et supérieur (environ 170 millions d’années) du Bassin de Paris ont été sélectionnées.

Les observations aux microscopes photonique, électronique et à cathodoluminescence montrent que les ciments calcitiques cristallisant dans l’espace inter-granulaire pendant la période de non-sédimentation sont diversifiés, composés de onze types différents incluant des ciments fibreux de quelques dizaines de micromètres d’épaisseur entourant les grains, de minuscules rhomboèdres de moins de 100 micromètres, des ciments microstalactitiques à l’extrémité des grains ou encore des ménisques sparitiques à micritiques. Les analyses isotopiques et géochimiques des éléments majeurs et traces (ETR) réalisées sur ces ciments montrent que ces derniers cristallisent dans des environnements très variés pendant les périodes de non sédimentation. Il s’avère que les discontinuités sédimentaires enregistrent une succession de nombreux évènements, incluant des périodes d’émersion, de recouvrement par la mer, des variations des conditions oxydo-réductrices ou encore des changements de l’activité microbienne. Bien que le temps enregistré dans les discontinuités reste compliqué à estimer (pouvant aller de la dizaine d’années à plusieurs millions d’années), l’étude des phases calcitiques permet une caractérisation précise des conditions environnementales et de la succession d’évènements ayant lieu pendant les périodes de non-sédimentation. Cette méthodologie adoptée pour l’investigation des discontinuités ouvre de nouvelles perspectives pour remonter à l’histoire des périodes de non-sédimentation et proposer des modèles de formation de ces discontinuités sédimentaires tenant compte de l’hydrodynamisme, de l’activité microbienne, du pH, ou encore des conditions redox.

13

Pétrole, Carbonates, Géosciences

Bernard Duval, Philippe A. Lapointe

bernard.duval@orange.fr - lapointe-philippe@orange.fr Plus de 60% des réserves mondiales de pétrole et 40% des réserves de gaz se trouvent dans

des réservoirs carbonatés. Très présents au Moyen-Orient les carbonates représentent 80% des réserves de pétrole et 90% des réserves de gaz régionales. Dans le futur cette situation prépondérante devrait encore évoluer en faveur des carbonates en raison d’une déplétion plus progressive que celle des clastiques, soumise à un plateau de production relativement plus court. On décrira brièvement 3 exemples qui illustrent les liens entre l’utilisation des méthodes de géosciences, principalement la stratigraphie, et les performances de l’industrie dans l’exploration et l’exploitation des ressources.

1/ Champs « géants » du bassin de Précaspienne : positionnement des meilleurs réservoirs sur le profil de la rampe carbonatée (Kazakhstan)

2/ Développement des carbonates « pré-sel » dans les régions distales de l’Atlantique Sud-Centrale (Brésil, Angola)

3/ Récentes perspectives sur un thème nouveau ouvertes en Méditerranée orientale (Egypte, Chypre, Liban)

On souligne la diversité des faciès des réservoirs concernés (lacustres, récifaux, plateforme, dépôts de pente) et des conditions d’exploitation (tranches d’eau de quelques mètres aux très grandes profondeurs)

De la rubrique 1 (province productrice) à la rubrique 2 (province en cours de développement puis à la rubrique 3 (province « frontière » émergente), les connaissances vont par maturité décroissante du contrôle de détail à une plus grande rareté d’informations géologiques. Les approches de l’exploration évoluent d’une catégorie à l’autre, avec une prépondérance de la technologie sismique au début du processus (phase « frontière ») et une intervention croissante des méthodes géologiques dont la stratigraphie séquentielle et la prise en compte de modèles analogues de terrain, permettant de caractériser les réservoirs après découverte

Références bibliographiques : ARNAUD H., ARNAUD-VANNEAU A., CODET A., ADATTE T. (2017) – Barremian platform carbonates from the Eastern

Vercors Massif, France, organization of deposition geometries. In: AAPG Bulletin V. 101, N°14, 485-493 COLLINS J.F., KATZ D., HARRIS P.M., (2014) – Basin sedimentation and dissolution in carbonate slope facies, Tengiz Field,

Kazakhstan: evidence for hydrothermal activity. In: AAPG Search and Discovery, Article 20234 ESTRELLA G. (2009) – Breaking paradigms. Giant and supergiant discoveries in Brazil. In: AAPG Search and Discovery, Article

110074 RONCHI P., ORTENZI A., BORROMEO O., CLAPS M., ZEMPOLICH W. G. (2010) – Depositional setting and diagenetic

processes and the impact on the reservoir quality in the late Visean-Bashkirian Kashagan carbonate platform (Pre-Caspian Basin, Kazakhstan). In: AAPG Bulletin V.94, N°9, 1313-1348

14

Growth faults affecting the internal geometry and facies of depositional sequences, lower Barremian, southeastern Vercors carbonate platform, France

Serge Ferry

Retired from the University of Lyon - 6D avenue Général de Gaulle, F-05100 Briançon serge.ferry@yahoo.fr The Bi5 and Bi6 calcarenite units (Arnaud, 1981) from the Glandasse Plateau (Archiane

Cirque) and the nearby Rocher de Combeau-Montagnette are at base of the quick progradation of the Vercors “Urgonian” platform to the Vocontian Trough to the south. These two lithologic units comprises a thick, reddish, bedded calcarenite at base and a thin cap of true Urgonian facies (massive, white limestone bearing corals and rudistids) at their top. The internal geometry of the calcarenite show strong lateral variations, especially in the Bi5 lithologic unit.

In the western cliff of the Cirque d’Archiane, Bi5 begins with a flat, quickly prograding sigmoidal offlap geometry (indicating limited available space) that becomes gradually aggradational to the top (meaning increasing available space). Patches of corals appear in the uppermost part of the calcarenite which also becomes progressively poorly sorted vs that in the basal sigmoidal offlap. The transition to the true Urgonian facies at its top is gradational, suggesting for the whole unit an overall rise in relative sea level from the basal sigmoidal offlap. The same relationships are found in the thinner overlying Bi6 unit. In the eastern cliff of the Archiane Cirque, the Urgonian facies cap of Bi5 is lacking and, especially, the internal geometry of the calcarenite is completely different. It begins with a thick progradational geometry somewhat resembling that of the western cliff but without any evidence of restricted available space at base. Then, a depositional break occurs, centered on a hinge point located close to the well-known Belvedere observational site. An aggradational wedge opens to the North (platform), while a retrogradational pattern is seen on the southern side (basin). The geometry is interpreted as the result of a growth fault interrupting the progradational geometry, confining the calcarenite deposition on the northern side, and starving the southern side. In the Montagnette cliff, a few kilometres to the east, the growth fault-induced geometry is larger. The accommodation space created allowed the occurrence of huge progradational clinoforms filling a “hole” during the early part of the overall progradation. The last subunits of Bi5 are less sloped because the morphological anomaly upslope had healed. These can be traced to the south to the Rocher de Combau where they pass to finer-grained slope limestone. The global picture is therefore interpreted as a result of a progressive growth fault beginning at base of the Bi5 deposition at La Montagnette, reaching the eastern cliff of the Archiane Cirque in the mid part of Bi5, but sparing the deposits of the western cliff.

The Bi6 unit do not show differences on both sides of the Archiane Cirque. But in the Rocher de Combau, a curious facies is found. Most of the calcarenite beds found in the whole area are swell-dominated. But the lateral equivalent (according to Arnaud (1981) of the Bi6 unit bears instead, here, pure tidal features (megaripples never reactivated by the swell). Such a facies cannot be preserved without a protection from the swell. Again, the occurrence of a temporary barrier created by the rotational play of a growth fault is thought to have permitted the local occurrence of this particular facies. Closely-spaced sections from north to south over a few kilometres illustrate the process.

The very thick Barremian slope succession (around 1,000 m) below the first calcarenite units of the overall Urgonian progradation probably explains that the wedge was unstable and affected by the inferred growth faults. This should be taken into account when doing sequence stratigraphic interpretations through changes in accomodation space. This is especially true in such a famous location which has been called by some the “Mecca of geology” where the seismic scale is visible at outcrop. A Figure explains how sequence stratigraphy may be distorted, even to the opposite, depending on the places the section is logged in the Bi5 unit.

Reference : ARNAUD H. (1981).- De la plate-forme urgonienne au bassin vocontien: le Barrémo-Bédoulien des Alpes occidentales entre Isère et

Buëch (Vercors méridional, Diois oriental et Dévoluy. Thèse Doct. Etat Université de Grenoble, Géologie Alpine, Mémoire 12, 2 vol.

15

The evolution of the Urgonian platform in the light of late Early Cretaceous paleoenvironmental change

Karl B. Föllmi1, Arnaud-Vanneau, A.2, Adatte, T.1, Spangenberg, J.3, Sophie Gauthey1,4, Lucie Bonvallet1,2,

Melody Stein1,5, Jean Vermeulen6, Alexis Godet7, Stephane Bodin8

1Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland 2Association Dolomieu, 8 Chemin des Grenouilles, 38700 La Tronche, France 3Institute of Earth Surface Dynamics, University of Lausanne, 1015 Lausanne, Switzerland

4Champs-du-Soleil 26, 2504 Bienne, Switzerland 5 Institut de Physique du Globe de Strasbourg, Université Strasbourg, 67074 Strasbourg, France 6Grand Rue, 04330 Barrême, France 7Department of Geological Sciences, University of Texas, San Antonio, U.S.A. 8Department of Geoscience, University of Aarhus, Aarhus, Denmark The Early Cretaceous greenhouse world witnessed different episodes of pronounced

paleoenvironmental change, which were associated with substantial shifts in the global carbon and phosphorus cycles. They impacted the growth of carbonate platforms on the shelf, lead to the development of widespread anoxic zones in deeper water, and influenced evolutionary pattern in general. A particular good example is given by the evolution of the Urgonian platform along the northern Tethyan margin, which was very sensitive to paleoenvironmental change. The latest Hauterivian Faraoni oceanic anoxic episode (OAE) went along with a widespread phase of condensation, phosphogenesis and glauconite formation, which was characterized by minimal carbonate accumulation and which lasted until the late early Barremian. The first traces of renewed platform growth appeared in the late early Barremian and Urgonian-type platform carbonates became only important during the late Barremian. The onset of platform growth is traced by a positive carbon-isotope excursion near the early-late Barremian boundary, which becomes more important in areas close to the platform margin. The excursion is explained by the increased shedding of aragonite. Although mostly in the classical rudist-green algae-coral-stromatoporoid mode, the Urgonian platform experienced a phase of mesotrophic conditions during the mid-late Barremian, where platform facies became rich in annelids. This phase went along with a renewed phase of phosphogenesis in the outer shelf. Near the Barremian-Aptian boundary, the Urgonian-type platform shifted progressively into a heterozoan mode of carbonate production, which was accompanied by an increase in kaolinite and phosphorus contents, and which is documented in the so-called “Lower Orbitolina Beds”. The onset of this important and widespread facies change coincided with the deposition of organic-rich sediments and a negative carbon-isotope excursion, which may have been related to a decrease in aragonite shedding. In the early Aptian, a second phase of Urgonian-type platform carbonate production occurred, which terminated in the middle early Aptian. Three successive phases of phosphogenesis interfered negatively with platform growth, first forcing the platform to go into a heterozoan mode (“Upper Orbitolina Beds”) and finally to cease in the latest early Aptian. The Selli OAE coincided with the second phase of phosphogenesis, suggesting that paleoenvironmental change related to this episode affected the platforms earlier than the open oceans.

16

Meteoric diagenetic overprint on the carbon isotope composition of Urgonian-type platform carbonates from the western Swiss Jura

Alexis Godet1*, Christophe Durlet2, Jorge E. Spangenberg3, Karl B. Föllmi4

1Department of Geological Sciences, The University of Texas at San Antonio, 1 UTSA Circle, San Antonio, Texas, 78249, USA 2University of Bourgogne Franche-Comte, CNRS, Biogeosciences UMR 6282, F-21000 Dijon, France 3Institute of Earth Surface Dynamics, University of Lausanne, Geopolis, CH-1015 Lausanne, Switzerland 4Institute of Earth Sciences, University of Lausanne, Geopolis, CH-1015 Lausanne, Switzerland

*Corresponding author: alexis.godet@utsa.edu - Phone: +1 (210) 458 - 4782

Deposited in the inner portion of the northern Tethyan margin, Urgonian-type sediments from

the western Swiss Jura experienced several phases of emersion as testified, for example, by the polygenic nature of the infill of karstic cavities, dated as old as the early Aptian based on ammonites and large benthic foraminifera. We aim to highlight the stratigraphic repartition of meteoric diagenetic products as well as their impact on the carbon isotope composition of whole-rock carbonates, and thus provide insights on the limitations of this tool that is often used for long-distance chemostratigraphic correlations.

Petrographic observations under conventional and cathodoluminescence microscope revealed the presence of five generations of calcitic cements. Punctual carbon and oxygen stable isotope composition (δ13C and δ18Ovalues, respectively) measurements help define diagenetic environments: blocky calcite cements (fC1 and C1) exhibit an enrichment in light isotopes (12C, 16O), indicative of a meteoric eogenesis origin, whereas very negative δ18O values link the most recent phase of cementation C2 to mesogenesis. Meteoric calcitic cements formed during karstification that initiated at the top of the upper Barremian series in the latest Barremian since karst pockets are filled with marls containing lower Aptian ammonites. Based on their luminescence pattern and crosscutting relationships, we estimated the ratio of early meteoric versus burial cements: its stratigraphic evolution reveals that lower Aptian eogenesis influenced the isotope geochemistry of platform carbonates as deep as 45 m below the exposure surface. In this interval, negative whole-rock δ13C values do not reflect contemporaneous variations of the δ13C curves documented in other sections devoid of such a strong meteoric diagenesis. This impact of eogenesis is a function of the amount of meteoric cement in the porosity as well as of the primary carbon isotope composition of the carbonate sediments and of the meteoric cement. In the case of these sediments of the Urgonian platform, the perturbation of isotope systems is not necessarily accompanied by an alteration of microfacies, and the vertical influence of a karst is not restricted to the first meters directly below the exposure surface. Consequently, the application of δ13C chemostratigraphy to platform carbonates can only be performed with great caution, after a careful examination of diagenetic features.

17

Biostratigraphy and palaeoenvironments of the Aptian sedimentary succession at Jebel Bir Oum Ali (Northern Chain of Chotts, South Tunisia): Comparison with contemporaneous

series from the southern Tethyan margin

Rabaa Hfaiedha, Alexis Godetb,, Annie Arnaud Vanneauc, Jamel Oualid

aDépartement des Science de la Terre, Faculté des Sciences Gafsa, Tunisie

bDepartment of Geological Sciences, the University of Texas at San Antonio, TX-78249 San Antonio, U.S.A. cAssociation Dolomieu, 18 Bd Mal Leclerc, 38000, Grenoble, France dLaboratoire Eau-Energie et Environnement, Ecole Nationale d’Ingénieurs de Sfax, University of Sfax, Tunisia The Aptian sedimentary succession of the Chott region from Tunisia was deposited on the

edge of the Saharan shield, and is punctuated by numerous hiati that separate seven 3rd-order depositional sequences. Lower Aptian deposits correspond to the Berrani Member (lower Bedoulian), which is contemporaneous with the large carbonate platforms with rudists that developed under oligo-mesotrophic, tropical environmental conditions on both margins of the Tethys. Upper Bedoulian sediments were deposited under mesotrophic conditions characterized by seagrass, algae, abundant orbitolinids and aragonite-producers organisms. The lower to upper Aptian boundary is marked by the temporary disappearance of carbonate platforms and an important renewal of the microfauna, whose tests and skeletons become less and less aragonite-rich and more and more calcite-rich and arenaceous. This episode is reported from both Tethyan margins. The platform is subsequently flooded, and dysoxic environments with annelids mark the end of the lower Aptian carbonate platform development. An arid and probably colder episode (lowermost upper Aptian) induced the deposition of gypsum in an intrashelf basin. Following on top, the return to more humid conditions triggered an enhanced input of detrital material in fluvio-deltaic environments (upper Aptian). Finally, the return to oligo-mesotrophic, marine conditions allowed the temporary installation of wide lagoons with rudists in the uppermost Aptian and probably in the lowermost Albian. Long-distance correlations have been established by means of benthic foraminifera occurrences. They highlight the importance of stratigraphic gaps linked to low sea levels, which have been tentatively estimated.

18

Les rudistes et la datation des formations carbonatées de type urgonien du Sud-Est de la

France

Jean-Pierre Masse et Mukerrem Fenerci-Masse

Aix Marseille Université, Centre Saint-Charles, 3 Place V. Hugo, 13331 Marseille, Cedex 03 C’est d’Orbigny (1850) qui a démontré, lors de l’établissement de son étage Urgonien, que les

rudistes pouvaient jouer le rôle de marqueurs stratigraphiques, suivant une hypothèse déjà formulée par Matheron (1842-43). Les premières tentatives de datation des formations urgoniennes s.l. , basées sur ces organismes, étant dues principalement à Paquier (1900, 1903, 1905), Toucas (1907), Haug (1907) et Kilian et Reboul (1915). Le développement de la micropaléontologie stratigraphique, les progrès enregistrés dans la taxonomie et la biozonation des ammonites, et l’intercalibration des échelles correspondantes, ont permis par la suite d’améliorer considérablement le cadre biochronologique des carbonates de plate-forme du Berriasien-Aptien du Sud de la France et des faunes de rudistes qui leur sont inféodées.

Notre contribution est basée sur l’étude de la distribution dans le temps d’environ 70-80 espèces qui se rattachent à une vingtaine de genres et 6 familles ; le pas de temps de référence est précisé à l’échelle de la zone d’ammonite. Cette présentation actualise un travail publié précédemment (Masse, 1996) concernant le Sud de la France. Elle s’appuie sur les révisions taxonomiques et biostratigraphiques effectuées et publiées depuis, et tient compte de travaux en cours. Six associations fauniques, notées de 1 à 6, se succèdent dans le temps, du Valanginien au Bédoulien p.p. La discrimination des faunes successives est basée sur celle de coupures liées aux crises évolutives et aux évènements d’apparitions ou d’extinctions, contemporain de perturbations du système carbonaté (drowning events principalement). La faune 1disparait vers le milieu du Valanginien (sous la zone à B. campylotoxum), la faune 2 s’éteint à la limite Hauterivien inférieur-Hauterivien supérieur (sous la zone à S. sayni), la faune 3 est datée de l’Hauterivien supérieur (B. balearis ?-P. ohmi), la faune 4 débute au Barrémien basal et s’éteint au milieu du Barrémien supérieur (« Agriopleura event » du milieu de la zone à G. sartousiana), la faune 5 lui succède et disparait et à la fin du Barrémien supérieur (sous la zone à I. giraudi), la faune 6 à Caprinidae débute dans la zone à M. sarasini et se poursuit dans l’Aptien inférieur. Une faune spécifique, datant de la fin du Bédoulien, est bien individualisée en Aquitaine et en Espagne, mais n’existe pas dans le SE de la France de même que celle du Gargasien. La limite Bédoulien-Gargasien est un évènement majeur d’extinction associé à un renouvellement remarquable, téthysien, de la composition des assemblages à rudistes.

Les coupures fauniques sont couplées avec celles d’autres organismes cardinaux des plates-formes carbonatées : algues calcaires et foraminifères en particulier, et sont synchrones de crises de la sédimentation calcaire correspondante. Les coupures fauniques ne coïncident généralement pas avec les limites des étages, à noter pour le seul Barrémien l’existence de trois faunes successives calées sur les zones d’ammonites.

Référence bibliographique : MASSE J.-P. 1996. Lower Cretaceous rudist biostratigraphy of southern France: a reference for Mesogean correlations. Revista

Mexicana de Ciencias Geologicas, Universidad Nacional Autonoma de Mexico, Instituto de Geologia Mexico D.F., 12, 2, 236-256.

19

Sequence Stratigraphy and Seismic Stratigraphy of the Lower Cretaceous Shuaiba Formation from Abu Dhabi Ruwais Field.

Philippe A. Lapointe

lapointe-philippe@orange.fr The Ruwais field is a 4-way structural closure discovered in 1968. Drilling penetrated a thick

sequence comprising reservoir facies of carbonate ramp Rudist shoals of Aptian age, in the Upper Thamama Group, namely the Shuaiba Formation.

The seismic stratigraphy may by-pass the actual sequence stratigraphy scheme. A combined approach of facies and sedimentoloy description supported by biostratigraphy, carbon-isotope stratigraphy and strontium-isotope stratigraphy was used to constrain the sequence stratigraphic correlation (Ghani et al., 2008).

The reservoir lithofacies paleobathymetry profile was compared to the one proposed by Al Ghamdi and Read (2010) and Strohmenger et al. (2010). Some facies were not described from the cores cut in the different wells drilled on the Ruwais structure. With respect of the general Shuaiba paleogeography and the well position on the structure, no intra platform or lagoon related facies were specifically identified. Rudists are accumulated as rudstone grainstone or floatstone packstone to grainstone in large shoals.

The Shuaiba transgressive and early highstand sequence sets were built by the Ap2 and Ap3 sequences. The Shuaiba late highstand sequence set is comprised of the Ap4 and Ap5 sequences, and the Bab lowstand sequence set is represented by the Ap6 sequence (Ghani et al., 2008). A marked late-Aptian regional unconformity and sedimentary hiatus separates rocks of Aptian age (Shuaiba Formation) from those of Albian age (Nahr Umr) (Ziegler, 2001). However, the platform margin appears to be steeper in northwest Abu Dhabi, as the area of the interpreted Upper Aptian (Ap4 and Ap5 sequences) distal clinoform belt is narrower than the one encountered in central Abu Dhabi.

The Shuaiba deposits of the Ruwais Field conform to a sequence stratigraphic framework established for Bu Hasa giant oil field of central Abu Dhabi. Several publications provide a validated general sequence stratigraphic chart for second and third order cycles based on publications by Yose et al. (2006, 2010), Strohmenger et al. (2010), Van Buchem et al. (2010).

Taking in account the seismic stratigraphy performed on the available 3D seismic, combined with the electric logs and core description performed, then with the published results from Ghani et al. (2008) and Strohmenger et al. (2010), a revised sequence stratigraphy framework was devised:

• Ap1 sequence corresponds to the Hawar Member • Ap2 and Ap3 belong to the early Aptian. Ap3 is subdivided on the basis of the

seismic in Ap3a and Ap3b. • Ap4 and Ap5 correspond to the Upper Shuaiba (Late Aptian). Ap4 encompass the

former Ap4a and Ap4b, has no subdivisions were apparent from seismic stratigraphy. • Ap6 correspond to the Nahr Umr Formation.

Based from the core descriptions and logs a more detailed sequence stratigraphy scheme was intended at 4th or 5th order but this his scheme was not used for the static model development.

References : GHANI A. A., C. J. STROHMENGER, D.G. BARWICK, T. STEUBER, S.H.A. AL-MAZROOEI, N. O. AL-ZAABI 2008.-

Sedimentology, sequence stratigraphy and seismic stratigraphy of the Lower Cretaceous Shu’aiba Formation of northwest Abu Dhabi, United Arab Emirates, GeoArabia, V., No. 4, 2008.

ZIEGLER M.A. 2001.- Late Permian to Holocene paleofacies evolution of the Arabian Plate and its Hydrocarbon Occurrences, GeoArabia, V. 6, No. 3, p. 445-504.

YOSE, L., A,S. RUL C,]. STROHMENGER, J.S. SCHUELKE, A. GOMBOS, I. AL-HOSANI, S. AL-MASKARY, G. BLOCTU Y AL-MEHAIRI, LG. JOHNSON 2006.- Three dimensional characterization of a heterogeneous carbonate reservoir, Lower Cretaceous, Abu Dhabi (United Arab Emirates). In P.M. Harris and L.]. Weber (Eds.), Giant Hydrocarbon Reservoirs of the World: From Rock to Reservoir Characterization and Modeling. American Association of Petroleum Geologists Memoir 88, Society of Economic Paleontologists and Mineralogists Special Publication, p. 173-212.

YOSE, L., C.J. STROHMENGER, I. AL-HOSANI, G. BLOCH, Y. AL-MEHAIRI 2010.- Sequence stratigraphic evolution of an Aptian carbonate platform (Shu'aiba Formation), eastern Arabian Plate, onshore Abu Dhabi, United Arab Emirates. In F.S.P. Van Buchem, M.I. Al-Husseini, F. Maurer and H.J. Droste (Eds.), Barremian - Aptian stratigraphy and hydrocarbon habitat of the eastern Arabian Plate, GeoArabia Special Publication 4, Gulf Petrolink, Bahrain, V.2, p.309-340.

20

STROHMENGER C. J., T. STEUBER, A. GHANI, D. G. BARWICK, A. H. A. AL-MAZROEI, N. O. AL-ZAABI 2010.- Sedimentology and chemostratigraphy of the Hawar and Shuaiba depositional sequences, Abu Dhabi, United Arab Emirates, GeoArabia Special Publication 4, V.2, p. 341-365.

VAN BUCHEM F.S.P., M.I. AL-HUSSEINI, F. MAURER, H.J. DROSTE, L.A. YOSE 2010a.- Sequence-stratigraphic synthesis of the Barremian - Aptian of the eastem Arabian Plate and implications for the petroleum habitat. In F.S.P. Van Buchem, M.I. - Al-Husseini, F. Maurer and H.J. Droste (Eds.), Barremian - Aptian stratigraphy and hydrocarbon habitat of the eastern Arabian Plate, GeoArabia Special Publication 4, Gulf Petrolink, Bahrain, V. 7, p. 9-48.

AL GHAMDI, N., READ F. J. 2010.- Facies-based sequence stratigraphic framework of the Lower Cretaceous rudist platform, Shu’aiba Formation, Saudi Arabia, In: F.S.P. Van Buchem, M.I. Al Husseini, F. Maurer and H.J. Droste (Eds.), Barremian-Aptian stratigraphy and hydrocarbon habitat of the eastern Arabian Plate, GeoArabian Spec. Publ. 4, Gulf Petrolink, Bahrain, 2, 367-410.

21

High-resolution stratigraphic model of the Urgonian carbonate platform in the Gresse-en-Vercors area (SE France).

Rémy Richet1, Jean Borgomano2, Sophie Viseur2, Jean-Pierre Masse2

1 Géologue Indépendant, Le Canoubier, Bât G, 40 Rue Floralia, 13009, Marseille 2 AIX-MARSEILLE UNIVERSITE, Centre Européen de Recherche et d'Enseignement de Géosciences de l'Environnement, 3 pl. Victor Hugo, 13331 Marseille.

. Carbonate platforms are characterized by complex sedimentary and stratigraphic architectures

that can be expressed at length scale exceeding single outcrops, thus preventing the realisation of valid 3D facies models. This work focuses on the Barremian (Lower Cretaceous) deposits of the Gresse-en-Vercors cliff (southeastern France) that provide a seismic-scale slice though a platform margin - analogous to Middle East reservoirs - ideal to study laterally continuous and large scale carbonate platform developments. The cliffs are 500 m high and extend for 25 km along depositional dip, straddling the transition from shallow water platform to deeper basin. New biostratigraphical data shows that the Vercors platform is mainly Lower Barremian. Four stratigraphic sequences were defined, with two complete platform stages, separated by three drowning events.

New high-resolution numerical data (LIDAR point-set and high-resolution georeferenced

photos) obtained by helicopter survey, allowed the realization of a 3D high-resolution digital elevation model (DEM) over the entire outcrops. Integrating the stratigraphic observations and the DEM in gOcad result in a continuous 3D stratigraphic architecture and facies model of the carbonate outcrop that can be used for stratigraphic and sedimentological interpretations.

The resulting geological model demonstrates that outcrop numerical data and 3D geological

modeling are pertinent methods for improving carbonate outcrop characterization and conceptual models of carbonate platform systems. It allows to establish subtle sedimentary profiles, with geometrically constrained paleo-bathymetry and high resolution facies mosaic along seismic scale platform trend. This approach is particularly critical for the 3D characterization of clinoforms and stratigraphic system tracts of non-cylindrical carbonate systems, especially in the platform-to-slope transition: for exemple, apparent low stand wedge or distal onlapping lobes in 2D are in reality prograding high stand systems in 3D.

Stratigraphic models based on classic stratigraphic correlations of distant locations and on

LIDAR-based DEM stratigraphic mapping can be compared. The two approaches show the same general results: two Lower Barremian platform stages marked by the southward progradation stages (in basinward direction) separated by several drowning events. In addition the stratigraphic numerical model highlights some important differences:

1. Four stratigraphic sequences were defined in the digital outcrop model separatedby three drowning events (D1, D2, and D3), whereas only two of these drowning events were defined with the classic field section correlation.

2. It shows the occurrence of clinoforms that are onlaping updipin the general direction of the platform progradation (Unit 3) that can be the consequence of the lateral migration of the depositional system from north-west to west-north-west.

3. It shows that some progradational-retrogradational interpreted trends defined with the classic approach are apparent in 2D but not real in 3D (especially the three shallowing-up facies sequences recorded in the Unit 3).

These results can be used to constrain more regional stratigraphic models of the Urgonian

platform and to calibrate process-based stratigraphic forward models of carbonate platforms.

22

Aptian carbonate platform development in the Alicante region, SE Spain.

Peter W. Skelton1, José Manuel Castro Jiménez2, Pedro Alejandro Ruiz Ortiz2

1 The Open University, Walton Hall, Milton Keynes, MK/ 6AAUK 2 Universidad de Jaén, Campus Las Lagunillas, 23701 Jaén, Spain

As part of a multi-national project investigating the record of environmental and biotic events and their controls in the Aptian of the Prebetic Zone in SE Spain*, this presentation reports on the paleoecological aspects of carbonate platform development in the Alicante region, emphasising changes in macrobiotic constitution, especially among the richly represented rudist bivalves.

Previous regional stratigraphical studies by Castro et al. (2008) had identified two platform developments in, respectively: (1) the lower Bedoulian Llopis Formation; and (2) the upper Gargasian to Lower Albian Seguilí Formation. They are separated by the marly, hemipelagic Almadich Formation into which both platform successions wedge out basinwards towards the south-east, the second platform over-stepping the limits of the first.

Progradation of the Llopis Formation platform is clearly displayed in the Sierra de Mariola, in the NE part of the study area, where SE-facing clinoforms are succeeded by flat-lying platform-top beds. Rudists are well represented in the upper clinoform and platform-top deposits. Their distribution across the platform top can be studied in detail further east, in roadside sections on the northern flank of the Sierra de Seguilí. Here, a regressive succession passes up from thick external platform-top beds, dominated by fragmented colonial corals and rudists, to tabular beds of 1-2 m individual thickness, each one consisting mostly of rudist-dominated bioclastic floatstone – but including some clusters of elevator rudists preserved in life position – capped by miliolid-rich wackestones with sparser macrofossils. These beds are interpreted to represent minor regressive cycles. Consistently with previous studies of co-eval Tethyan platforms (Fenerci-Masse, 2006), caprinid rudists, with robust, originally almost wholly aragonitic shells, dominate the external platform-top facies, while relatively more internal facies contain a mix of monopleurid, polyconitid and requieniid rudists, showing slightly thicker development of the calcitic outer shell layer, together with some slender caprinids. Other macrofaunal elements include chondrodontid bivalves, nerineid gastropods and regular echinoid spines.

The Llopis Formation platform is abruptly terminated by a hardground surface, with evidence suggestive of prior emergence. The overlying Almadich Formation commences with dark shales corresponding to those seen in the hemipelagic Cau section, to the south, which have in turn been isotopically correlated with OAE1a (Ruiz-Ortiz et al., 2016). Upward, the succession passes via nodular marly limestones with sparse ammonites and irregular echinoids to pale buff sandy limestones in which first corals, then rudists re-appear, heralding renewed platform progradation in the Seguilí Formation. As before, tabular platform-top beds show a pattern of repeated cyclic regression, though with a strikingly altered cast of rudists: thus, caprinids, previously so prominent, are now absent, while polyconitids, requieniids and radiolitids, some of large size and all with appreciably thickened calcitic outer shell layers, accompany the remaining tubular monopleurids. In another section to the south-east (‘Barranco Alcaida’), dense clusters of Chondrodonta, with thick, oyster-like foliaceous calcite shells, additionally feature prominently in the upper parts of relatively thicker cyclic beds.

Platform successions of late Bedoulian age elsewhere in Spain, outside the present study area, reveal a mixed, transitional phase between the typical early Bedoulian, and the Late Aptian rudist faunas illustrated above. Particularly striking is a greatly increased abundance of polyconitids in the outer platform-top to upper slope facies, at the expense of caprinids, the distribution of which became more localized, prior to their (‘Lazarus’-style) disappearance at the close of the Bedoulian.

*Acknowledgment: Spanish Government funded Project REF. CGL2014-55274-P.

References

CASTRO, J. M., de GEA, G. A., RUIZ-ORTIZ, P. A., NIETO, L. M. (2008).- Development of carbonate platforms on an extensional (rifted) margin. The Valanginian–Albian record of the Prebetic of Alicante (SE Spain). Cretaceous Research, 29, 848–860.

FENERCI-MASSE, M. (2006).- Les communautés à rudistes du Crétacé inférieur de la marge ouest Européenne de la Tethys. Thèse doct., Univ. de Provence, FRE-2761. 436 pp.

RUIZ-ORTIZ, P. A., CASTRO, J. M., DE GEA, G. A., JARVIS, I., MOLINA, J. M., NIETO, L. M., PANCOST, R. D., QUIJANO, M. L., REOLID, M., SKELTON, P. W.n WEISSERT, H. J. (2016).- New drilling of the early Aptian OAE1a: the Cau core (Prebetic Zone, south-eastern Spain). Scientific Drilling, 21, 41-46.

23

Carbonate Platforms: the Roles of Microbes

Maurice Tucker

School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, England maurice.tucker@bristol.ac.uk Carbonate platforms, thick successions of mostly shallow-water limestones and dolomites,

occur throughout the geological record. In general they are a feature of times of minimal siliciclastic influx to the oceans, as during transgressive and highstand states of sea-level, and most were deposited in low latitude regions. Microbes have been a major player in carbonate precipitation since their evolution in the early Archaean, some 4 billion years ago. Bacterial processes of photosynthesis, bacterial sulphate reduction and denitrification may all lead to carbonate precipitation. The products of these activities are well seen in the form of stromatolites, well developed throughout the Precambrian of course but also common in more Recent times in situations where there was little competition from higher organisms for one reason or another. However, throughout the record there are numerous examples of fine-grained limestones with no direct evidence of microbes being involved, especially in shallow shelf to deeper-water facies. Are these also microbial or were they direct precipitates ? Direct precipitation, i.e. homogeneous nucleation, of CaCO3 is not simple – some say impossible, with seeds needed (then it is heterogenous nucleation). But what could these nuclei be ? (apart from tiny !). How about viruses ? Yes – this ‘life’-form has been completely neglected in Earth Sciences – especially carbonate sedimentology, but being present in numbers 10 to 100 times more abundant than bacteria (106-7 in a cu cm of sediment), surely they must play a role. Recent work on microbial mats (Perri, Tucker et al. 2017) is showing that viruses, which are closely associated with bacteria of course, are being per-mineralised in the top mm of the mat (as is EPS, extracellular polymeric substances / mucus), as a result of a negative charge which attracts cations. The several 10s nm-diameter nanospheres produced have been illustrated before (e.g. in Palaeoproterozoic cherts and phosphates, Edwards et al. 2012) but either not interpreted, regarded as abiotic or ‘microbial’ or thought to be nanobacteria (e.g. Folk 1993) which are now considered to not to exist. The nanospheres, under appropriate conditions produced in great abundance in the oceans, could well have provided the nuclei for carbonate precipitation (including dolomite) – throughout the geological record. Fine-grained carbonate sediment, as generated by whitings, and peloidal-micritic limestones, including automicrite in reefs and the matrix to mud-mounds, could also be attributed to the activities of viruses. Proving that is the task. Viruses are the new frontier.

24

Notes

25

Liste des Participants

Adatte Thierry Anguenot François Arnaud-Vanneau Annie Baudin François Bernardez Enrique Bodeur Yves Bodin Stéphane Bomou Brahimsamba Bonvallet Lucie Borgomano Jean Brigaud Benjamin Cao Henri Caus Esmeralda Debrenne Françoise Deconninck Jean-François Domange -Brown de Colstoun Isabelle Duval Bernard Ferry Serge Föllmi Karl Fort Pierre Frau Camille Gaspard Danièle Godet alexis Gorini Christian Groené Yves Grosheny Danièle Lafay Philippe A.

Lansigu Christophe Lapointe Philippe Leparmentier François Manz Bruni Mariton Daniel Martin Guillaume Mascle Georges Masse Jean-Pierre Mcnaughton Niel Montardet Lucien Pagnoux Bruno Philip Jean Ravenne Christian Reyx Jean Richet Rémy Sanchez Pellicer Raquel Schoumacker Denis Skelton Peter W. Robaszynski Francis Tendil Antony Thomas Audrey Thommen Patrick Toullec Arnaud Tucker Maurice Vaskou Philpppe Vermeulen Jean Vincent Benoit

26e Réunion des Sciences de la Terre | 26th Earth Sciences Meeting

LILLE22 - 26 OCTOBRE

2018

Conférences Grand Public | Sessions spécialisées

Forum Enseigner les géosciences | Forum Métiers

Excursions | Visites géologiques

Espace professionnel

www.rst-sgf.fr Evo-Eco-Paléo

© D

R - Fo

tolia