Dissertations / Theses on the topic 'Kimmeridgium'

The Upper Jurassic sediments of the East Coast of Sutherland and the South Brae Oilfield were deposited during the late Jurassic taphrogenic episode in which there was rapid subsidence in the grabens and uplift of the adjacent areas. The initiation of coarse-grained sedimentation in the grabens was directly related to an increase in subsidence rates. At Sutherland the most sand-rich sequences were deposited during the cymodoce zone of the Kimmeridgian, immediately after the increase in subsidence rates. Depositional environments varied from a relatively shallow water and sand-rich submarine slope during the early Kimmeridgian to a deeper water sediment starved submarine slope during the early Volgian. The sediments of the South Brae Oilfield were deposited in the channelised part of a submarine fan system which was sourced from a point which lay to the west of the 16/7a-8 well and to the southwest of the 16/7a-12 well. The South Brae sequences are part of a much larger complex which was composed of at least seven different submarine fan systems. Sediment entry points occurred along the western margin of the South Viking Graben from the T-Block in the south to East Brae in the north and each of these fed a submarine fan system. The reservoir sequences will tend to be vertically stacked and spatially restricted in proximal areas and will become less stacked and less restricted distally. Stratigraphically trapped "Brae-like" plays probably exist at the margins of many North Atlantic Continental Shelf grabens. The eastern margins of the Vøring and Træna Basins have especially high prospectivity.

The Kimmeridgian of England was characterised by the deposition of a widespread and frequently organic-rich mudrock formation, the Kimmeridge Clay. Significant lateral thickness variations are attributable to active faulting which is occasionally recorded within the sediments as a number--of earthquake-generated structures. The slowest subsidence rates occurred on the London platform and depositional depths increased away from this positive feature both to the north and the south. Organic-rich shales preferentially accumulated in the deeper basinal areas where the thickest sequences accumulated. Even in the deepest locations storms were able to influence the depositional environment. This is reflected by a range of tempestite beds and by the highly opportunistic character of the benthic fauna which responded to the brief storm-induced oxygenation events. Palaeocommunity analysis indicates that a number of variables were controlling the faunal distribution. Substrate consistency, environmental stability and oxygen levels all interacted to produce a diverse range of community types composed of a few euryoxic, opportunistic molluscs. A major change occurs in the middle of the Upper Kimmeridge Clay when softground faunas are replaced by firmground faunas. This appears to reflect a marked reduction in sedimentation rate related to a sudden increase in aridity at this time. Sandy marginal marine facies were developed on the London Platform throughout much of the Kimmeridgian; they are best seen at outcrop in the cliff sections of the Boulonnais. Facies range from shallow marine glauconitic sandstones with intensive bioturbation and a fauna of large bivalves, to shell-poor shoreface sandstones with well preserved sedimentary structures. Analysis of this latter facies indicates that storms and waves were the two principal sources of hydrodynamic energy. Tides were probably of negligible importance in the Kimmeridgian epeiric seas. Local cyclicity in the Boulonnais sediments appears to be due to small-scale fluctuations of narrow, nearshore facies belts; they are not related to the more ubiquitous shale: mudstone rhythms which characterise the offshore mudrocks. Investigation of eustatic sea level changes indicates a Jurassic highstand of sea level in the Lower Kimmeridgian followed by a slow progressive fall through the Upper Kimmeridgian. The highstand appears to have produced relatively deep water conditions in many epeiric settings throughout the world which led to organic-rich shale formation. Finer scale eustatic sea level changes are more equivocal although a highstand may have occurred in the Eudoxus zone. No substantiating evidence was found for the fine scale eustatic fluctuations recently proposed by the Vail team.

Carbon and oxygen stable isotope analyses have been performed on well preserved calcareous fossils from Callovian, Oxfordian and Kimmeridgian (Jurassic) mudrock facies of Britain. Assemblages of ammonites, bivalves and belemnites have been sampled from the Lower Oxford Clay of the English Midlands, the Kimmeridge Clay of Wiltshire and the Dorset coast, and the Staffin Shale Formation of Skye. In this way it was hoped to cover a wide stratigraphic and geographic range. Carbon isotope stratigraphy reveals a positive excursion in the Callovian, which is interpreted as an oceanic anoxic event. On the basis of palaeontological and sedimentological evidence, the Callovian has long been viewed as a time of oxygen deficiency. These views are supported by this, the first detailed isotopic study of the stage. A comparison of the 613 C values of the ammonites and infaunal bivalves reveals a major anomaly, in that the latter show very positive values. Tentative suggestions are put forward to account for this. Oxygen isotope (and hence palaeotemperature) stratigraphy reveals a cooling through the Upper Callovian and Oxfordian, consistant with the "Boreal spread" of Arkell (1956), with a warming into the Lower Kimmeridgian. Palaeotemperature variations within individual assemblages raise important questions about palaeoecology. On the basis of this data, it appears that bivalves previously considered to be nekto - or pseudoplanktonic did not occupy the upper reaches of the water column. Suggestions have been made that ammonites were benthic rather than nektonic, but the evidence presented here implies that this was not the case. Relative to the rest of the assemblage, belemnite temperatures tend to be low, highlighting their migratory nature. Boreal ammonites are found to precipitate their shells in cooler waters than those from the Tethyan Realm. The significance of this, and other factors, in terms of controls on provinciality are discussed.

Les séries d'âge oxfordien supérieur et kimméridgien inférieur de la bordure sud et sud-est du bassin de paris autorisent un découpage lithostratigraphique en huit unités d'extension variable. L'agencement géométrique de celles-ci est directement influencé par la présence d'un important complexe récifal médian et d'une zone à forte subsidence en bordure de Loire. L'étude des phénomènes diagénétiques ayant affecté certains facies ou éléments particuliers permet : de rattacher la diversité faciologique des micrites à la diversité des boues initiales, de mettre en évidence au sommet du calcaire de Tonnerre, l'existence locale d'une zone émergée temporaire sous forme de cayes sableuses, d'établir une filiation directe entre boues, pellets et oolites micritiques de cette même formation, de démontrer la nature calcitique initiale des nanoconstituants élémentaires, de préciser, par la précipitation directe, leur origine. L’étude sédimentologique des divers facies répertoriés permet de caractériser quinze milieux élémentaires de dépôt et conduit à proposer un dispositif sédimentaire virtuel de type plate-forme carbonatée insulaire. Celui-ci s'organise entre une plate-forme basse peu profonde, ouverte sur le large, soumise aux apports terrigènes et une plate-forme superficielle, vaste, très peu profonde, à hydrodynamisme variable complexe ou s'individualisent latéralement quatre zones ou domaines à sédimentation tranchée. Les deux séquences régressive et transgressive définies reflètent les phases de comblement et d'approfondissement respectives aux deux mégaséquences du jurassique supérieur

The Jurassic litho-biostratigraphy is reviewed and Jurassic depositional models are defined in order to clarify some regional stratigraphic uncertainties and to evaluate the hydrocarbon potential of the Jurassic of the United Arab Emirates (UAE). A thick succession of Triassic-Cretaceous shallow-marine carbonates is exposed in Wadi Naqab, southeast of Ras Al Khaimah in the UAE, Musandam Peninsula. The Jurassic, 1310 m thick, is examined using biostratigraphy, sedimentology and sequence stratigraphy and compared with the Abu Dhabi subsurface. Direct composition of the Jurassic foraminiferal biozones and algal assemblages can be made between Wadi Naqab and the South-Tethyan realm. Palynological data from the subsurface demonstrate that much of the Liassic, which is well represented in the Musandam Peninsula, is missing over most of the Emirates. A ca. 50 Ma time gap was defined within the Abu Dhabi clastic Minjur Formation (previously assigned to the Triassic). The age of the palynoflora of the upper Minjur is Bajocian, while the lower Minjur yielded Late Carnian palynomorphs. The Upper Toarcian and most of the Aalenian is also probably missing in the Musandam Peninsula, as in the subsurface of the Emirates and Saudi Arabia. A new Bajocian foraminifera Pseudodictyopsella jurassica, n. gen., n. sp., was recognised, and the inception of some stromatoporoids was earlier than previously thought. The Liassic of Wadi Naqab is dominantly a metre-scale 5^th-order Milankovitch-driven succession composed of peritidal cycles. Cycle tops are commonly marked by corrosion zones and/or karsts. Stacked paleokarsts are found particularly in the Sinemurian and Lower Pliensbachian. In Wadi Naqab, the Middle and Upper Jurassic seem to comprise one shallowing-upward 3^rd-order cycle built of abundant 5^th-order cycles. As a result of comparisons in this study, the Bajocian Izhara Formation is redefined and a new type-section proposed. Most of the Kimmeridgian and Tithonian are absent in Wadi Naqab, and eastern onshore and offshore Abu Dhabi, as the result of uplift and erosion before deposition of the Lower Cretaceous. Possible major Jurassic (Liassic-Early Kimmeridgian) hydrocarbon plays of Abu Dhabi are: the Marrat lowstand wedge of eastern onshore, the Jurassic onlap of Triassic high blocks in offshore areas, the Minjur lowstand clastics, the offshore Uweinat and Upper Araej and the Upper Jurassic Hadriya and Hanifa reservoirs.

Apres etude critique des techniques d'extraction des foraminiferes, deux protocoles de preparation des echantillons, reproductibles et respectueux des taphocenoses, sont proposes. L'analyse ecologique et morphofonctionnelle des petits foraminiferes actuels et jurassiques montre qu'ils sont lies a 3 super-biotopes ; un outil reproductible d'evaluation des variations bathymetriques dans les milieux marins jurassiques (valide par la confrontation de ses resultats avec ceux, sedimentologiques, macropaleontologiques. . . ) est propose sous deux formes : - un diagramme ternaire (% d'individus des 3 associations de foraminiferes), - un transect qualitatif (foraminiferes et autres organismes). L'outil est applique a 6 coupes du kimmeridgien de normandie, d'allemagne et du portugal (region du havre, souabe, montejunto), revisees en detail. Leurs associations de foraminiferes quantifiees, niveau par niveau, sont riches en especes et en individus et montrent un fond de population commun avec des variations locales parfois importantes. Leur etude permet de : - confirmer la classification en vigueur, en la modifiant un peu (vaginulinidae. . . ), - regrouper des especes, - proposer des ecosequences bathymetriques, grace au diagramme ternaire. Le reste de la microfaune est decrit brievement. Les variations de bathymetries, d'abondances et de diversites permettent : - d'etablir une interpretation sequentielle du kimmeridgien inferieur similaire a celle obtenue par d'autres methodes, - de proposer des surfaces reconnues a l'echelle europeenne ou mondiale. Les variations des teneurs en elements traces dans les carbonates sont analysees : l'evolution generale des milieux de depot et les sequences geochimiques proposees, sont en accord avec celles fournies par les foraminiferes. La methode micropaleontologique proposee et utilisee ici, est fiable dans la zone nord-tethysienne etudiee et d'une grande sensibilite pour detecter les variations bathymetriques de faible amplitude, les sequences d'ordre 3 et superieurs.

Une étude cyclostratigraphique à haute résolution a été entreprise, en utilisant les variations de la susceptibilité magnétique (SM), sur trois coupes marneuses oxfordiennes et deux coupes d’alternances marno-calcaires kimméridgiennes du Bassin du Sud-Est de la France. Les séries marneuses oxfordiennes enregistrent avec les plus fortes amplitudes de SM, les cycles d’excentricité à 100 et 405 ka. Les séries d’alternances kimméridgiennes détectent plutôt préférentiellement les cycles de précession. Les durées estimées des zones d’ammonites sont très proches de celles de l’échelle des temps géologiques GTS2004 pour le Kimméridgien inférieur, mais notablement différentes pour l’Oxfordien inférieur et moyen. Comparés aux séquences eustatiques de 3ème ordre de la charte globale de référence, les cycles d’excentricité à 405 ka semblent contrôler les variations du niveau marin relatif au moins durant le Kimméridgien inférieur et l’Oxfordien inférieur et moyen dans le Bassin du Sud-Est.

The lithologic and biostratigraphic successions of Ururoan, Temaikan and Lower - Middle Heterian (?Sinemurian, Pliensbachian - ?Kimmeridgian) strata from southwest Auckland, south Otago and Southland, New Zealand, are described and discussed. A more logical correlation of the lithologic sequence at Port Waikato with that at Te Akau is proposed. Two new formations are introduced for the sequences on the western limb of the Kawhia Regional Syncline, the Whakapatiki Mudstone for the fine grained lower Kirikiri Group strata in the Awakino Valley and the Gribbon Formation for the Rengarenga Group strata between Marokopa and Mahoenui. In Southland a new formation (Ben Bolt Formation) is proposed for the c.1340m sequence overlying the Flag Hill Sandstone, in turn overlain by a 485m thick, mudstone-dominated formation for which a long disused name is resurrected (Lora Formation). The Lora Formation is in turn overlain by a coarse-grained unit, for which the name West Peak Formation is proposed. In the absence of suitable alternatives, a subdivision of the Ururoan Stage into a Lower Ururoan, the range-zone of pseudaucella marshalli, and an Upper Ururoan, the interval-zone between the last appearance of Pseudaucella marshalli and the first appearance of a Temaikan fauna is proposed. The existing three-fold subdivision of the Temaikan Stage is emended. Belemnopsis mackayi and B. deborahae are retained as the indices of the Temaikan and its lowest subdivision, as they are present in most sections at a consistent stratigraphic position. Retroceramus (Fractoceramus) inconditus is proposed as the basal Middle Temaikan index species. Retroceramus(R.) brownei, which first appears consistently higher than R. inconditus, but below R. marwicki is proposed as the index for the upper Middle Temaikan. Retroceramus (R.) marwicki is proposed as a replacement upper Temaikan index for "Macrocephalites cf. beta-gamma" which is unsuitable. Meleagrinella n. sp. is inconsistent in its first appearance and therefore unsuitable as a Middle Temaikan index and, although confined to this stage, it ranges from Early to early Upper Temaikan. Basal Temaikan Belemnopsis spp. are absent from sections in the Catlins district whereas the earliest Temaikan taxon appearing above typical Ururoan faunas is Meleagrinella n. sp. In the absence of a better alternative Meleagrinella n. sp. is used to mark the base of the stage in the Catlins sections. However, the base of the Temaikan is here likely to be slightly younger than in other sections. Within the redefined Upper Temaikan four subdivisions based on the sequence of Retroceramus species are recognised. The lowest of these is characterised by the first appearance of R. (R.) marwicki, the second by the first appearance of R. (R.) n. sp. A., the third characterised by the first appearance of R. (R.) stehni, and the highest marked by the first appearance of either R. (R ) sp. C. (a wide triangular form) or sp. D. (an ovate flat form). The presence of these two morphologic forms indicate finer zonation of the Upper Temaikan may be possible, with further field work. The Ururoan to Middle Heterian succession of New Zealand is correlated with the international chronostratigraphic scheme based mainly on comparison of New Zealand's Retroceramus succession with that of South America and Indonesia and on relatively rare ammonites. The Ururoan is equivalent to the ?Sinemurian to Late Toarcian, Temaikan to the ?latest Toarcian to Early Callovian and the Early Heterian to the Middle Callovian to latest Middle to Late Oxfordian. Early Ururoan is correlated with the ?Sinemurian to Pliensbachian based on the presence of the ammonite Juraphyllites. Presence of the Early Toarican ammonites Harpoceras cf. falcifer and Dactylioceras spp. in the Late Ururoan indicates a potential international correlation of ?Late Pliensbachian to Late Toarcian. A ?late Toarcian to Aalenian correlation for the Early Temaikan is suggested by the presence of the European belemnite Brevibelus zieteni. Retroceramus (Fractoceramus) inconditus is similar to the Northern hemisphere Mytiloceramus lucifer and the northern hemisphere Retroceramus gr. popovi and thus suggests a latest Aalenian to Early Bajocian correlation of the Middle Temaikan. The earliest Late Middle Temaikan Retroceramus (Retroceramus) marwicki is also present in the Late Bajocian (Rotundum Zone) of Argentina. ?Teloceras gr. banksi, ?stephanoceras (S.) gr. humphriesianum, Chondroceras (C.) gr. evolvescens, C. (C.) cf. recticostatum, and C. (Defonticeras) cf. oblatum are present in the Middle Temaikan reinforcing an earliest to late Early Bajocian correlation for this substage. Toxamblyites aff. densicostatus Sturani, Chondroceras (C.) gr. Evolvescens (Waagen), C. (Schmidtoceras) orbignyanum (Wright), C. (Defonticeras?) sp. indet. occur with Retroceramus marwicki indicating an Early to Late Bajocian correlation for this zone, slightly broader than in Argentina. However, somewhat anomalously the first of these ammonites suggests a Mid Aalenian to Early Bajocian correlation. The succeeding zone (Retroceramus (R.) n. sp A. zone) has yielded the Latest Bathonian Xenocephalites grantmackiei and Lilloettia aff. boesei. Retroceramus(R.)stehni is the index for the third Upper Temaikan Retroceramus zone and is also known from the latest Bathonian to Early Callovian of Argentina. In New Zealand R. stehni is associated with Lilloettia cf. Lilloetensis and Xenocephalites cf. stipanicici which also indicate a latest Bathonian to Early Callovian correlation. The fourth and highest zone of the Upper Temaikan has yielded the ammonites Araucanites marwicki, Eurycephalites gr. extremus, Iniskinites gr. cepoides and Choffatia (Homoeoplanulites) sp. suggesting an Early to Middle Callovian correlation. The overseas relationships of the associated Retroceramus (R.) spp. C. and D. are unknown. The Heterian index Retroceramus (Retroceramus) galoi is of Oxfordian age in Indonesia where it is associated with Malayomaorica malayomaorica. In New Zealand Araucanites marwicki and Sulaites heteriense are present in the Early Heterian, below the incoming of Malayomaorica malayomaorica, low in the range of Retroceramus galoi. The presence of Sulaites high in the Early Heterian suggests a ?Middle to Late Oxfordian correlation while Araucanites indicates the lowest part of the range of Retroceramus galoi could be slightly older, perhaps Upper Callovian. The biostratigraphic scheme presented here is a significant advance on those proposed previously.

Les cinq facies carbonates (lamines paralleles ou ondulees, claires et sombres, calcaires massifs) qui composent la formation des laminites bitumineuses d'orbagnoux (france, kimmeridgien superieur), resultent de l'interaction entre l'installation de tapis cyanobacteriens et la decantation de coccolithes. Ces facies se caracterisent par des teneurs en carbone organique tres contrastees (de 0,05 a 8,63%) alors que les valeurs du potentiel petroligene et de l'indice de soufre sont toujours tres elevees (ih : 755 a 966 mg hc/g cot ; is : jusqu'a 854 mg cos/g cot) ; la matiere organique (mo) est de type i-s, rarement i/ii-s. Ce materiel sedimentaire s'est depose dans un lagon ou des episodes de pleine oxygenation de la colonne d'eau alternaient avec des periodes ou la base de la zone photique etait anoxique. Le sediment etait habituellement reducteur bien que des episodes tres oxydants, associes a l'assechement du milieu, ont ete mis en evidence. Dans tous les facies, les kerogenes sont constitues par des particules gelifiees nanoscopiquement amorphes et riches en soufre ; elles derivent uniquement du processus de sulfuration naturelle. En revanche, les etudes spectroscopiques revelent des differences dans la structure chimique de ces particules selon le facies. Un kerogene isole d'un echantillon representatif du facies lamines paralleles sombres a ete pyrolyse, liberant ainsi de nombreux composes organo-soufres. Ce kerogene apparait constitue de deux types d'unites : (i) le plus abondant correspond a des macromolecules basees sur des alcanes normaux pairs, d'origine cyanobacterienne, relies par des ponts soufre et (ii) le moins abondant constitue de composes thiopheniques, a squelette hydrocarbone lineaire et d'origine algaire. Enfin, il apparait que les conditions de pyrolyse, notamment le chauffage preliminaire a 300c, peuvent influencer les composes generes et rendre plus ou moins facile l'elucidation de la structure chimique de kerogenes riches en soufre.

Cette etude a pour objectif fondamental d'etudier l'evolution de la nature et de l'etat de preservation des constituants organiques des argiles noires du kimmeridgien d'angleterre, en relation avec la variation quantitative et qualitative de la matiere organique des differentes cyclicites. L'originalite du present sujet reside dans le fait qu'il integre un nouveau type d'approche petrologique a une reflexion sur la sedimentation et la diagenese precoce de la matiere organique ainsi que sur la problematique des cycles organiques. Les etudes ultrastructurales de la roche et de sa matiere organique petroligene montrent que la matiere organique des argiles kimmeridgiennes est composee en grande majorite d'une fraction organique totalement amorphe, meme a l'echelle nanoscopique. La geochimie, notamment les resultats moleculaires obtenus par ailleurs, montre que cette fraction organique est tres riche en composes organosoufres, ce qui permet de l'interpreter comme le resultat d'une preservation par incorporation de soufre: vulcanisation. Ce mecanisme s'accompagne d'une condensation de macromolecules dont le caractere refractaire a la degradation a ete acquis. Sa relation avec la fraction minerale montre le caractere synsedimentaire de sa formation ; sa distribution et son mode de depot dans le sediment rappelle celui des voiles bacteriens et/ou algaires qui se forment a l'interface eau/sediment. Le processus de preservation selective se trouve materialise dans les debris vegetaux terrestres, les restes algaires figures et dans la matiere organique amorphe brune du palynofacies (ultralaminae). Ces fractions organiques ne jouent pas un role quantitativement determinant dans la cyclicite organique etudiee. Les differents mecanismes decrits ci-dessus, conduisant a la formation d'une matiere organique petroligene, ont ete integres dans un schema plus general nous permettant de proposer un modele interpretatif de fossilisation des matieres organiques sedimentaires marines riche s en chaines hydrocarbonnees. Ce modele prend en consideration les resultats ultrastructuraux et moleculaires obtenus sur les echantillons du kimmeridgien mais pourrait servir d'outil de reflexion pour l'etude d'autres kerogenes. Les observations petrographiques a differentes echelles ont contribue a demontrer que les variations cycliques des teneurs en carbone organique correspondent a des accumulations variables de matiere organique d'origine phytoplanctonique liees a une variation de productivite primaire (permettant ainsi de visualiser la sensibilite de la sedimentation et de la diagenese organique aux variations induites par les cycles climatiques). La variation qualitative et quantitative du contenu organique est interpretee comme etant induite par la variation de flux organiques exportes de la zone photique, formes essentiellement d'organismes phytoplanctoniques sans test mineral. Cette matiere organique se materialise dans les sediments par la matiere organique nanoscopiquement amorphe qui dilue plus ou moins les autres flux organiques sedimentaires. Cette etude combinee aux travaux realises par les autres chercheurs du groupement de recherche 942 du cnrs, a permis aussi de mettre en exergue le double role de la sulfato-reduction. Ce processus bacterien degrade a la fois de grandes quantites de carbone organique, mais preserve d'autant mieux la matiere organique non degradee en liberant une grande quantite de soufre necessaire pour fixer les molecules qui deviennent de ce fait bioresistantes. En effet, l'h#2s produit en exces s'incorpore dans la matiere organique essentiellement lipidique en formant des composes organo-soufres leur conferant une certaine resistance. Celle-ci s'accumule de maniere cyclique sous l'effet d'une production phytoplanctonique periodique donnant lieu aux variations quantitatives (teneurs en carbone organique) et qualitatives (potentiel petroligene) du contenu organique. L'activite sulfato-reductrice est de toutes les facons induite par la production primaire qui reste le parametre precurseur dans l'accumulation de la matiere organique des argiles du kimmeridgien

The Hanifa Formation has a high-economic value in Saudi Arabia and many middle-eastern countries where it exists both as a reservoir and source rock. A few examples of the super-giant oil and gas fields that have Hanifa reservoir in the subsurface include Berri and Khurais fields. In this project, an analogue core for Hanifa reservoir facies that was drilled behind-the-outcrop, ~ 150 km south of Riyadh, along the Tuwaiq Mountain escarpment is studied. The main objective of this study is to analyze the vertical facies heterogeneity of Ullayah Member of Hanifa Formation. Thus, for this study sedimentological, petrographical, and petrophysical data have been collected and analyzed at a very high resolution. Based on the sedimentological, petrophysical and petrographic interpretation, four different vertical facies associations can be defined, representing distinct depositional environments (vertically): 1) High energy-level proximal shoreline, intraclastic grainstones deposition with moderate-Vp, relatively low-GR signature ; 2) Relatively low energy-level lagoonal depositional setting with low-Vp, high-GR represented by wackestones/packstones that has lagoonal microfossils and dasyclad algae; 3) Back barrier reefal depositional setting with moderate Vp, low-GR signature represented by stromatoporoids and corals, and 4) Oncoidal depositional setting with moderate-Vp, low- GR signature, mainly composed of ellipsoidal oncoids. Overall, the facies from these environments have been systematically vertically stacked on top of each other (in core WB-01), representing a deepening upwards trend and followed by shallowing oncoidal facies. This interpretation is also well match in regional context (GR data) and can be used as correlation reference.

The Upper Jurassic of Portugal has been globally known for its microfossil vertebrate fauna thanks to the Konzentrat-Lagerstätte of the Guimarota mine, which provided thousands of bone fragments, isolated teeth, and even complete specimens. Other vertebrate microfossil assemblages have been studied around the world. Besides Guimarota, no other Portuguese Jurassic assemblage has been extensively studied. Hereby is presented a revision of the state of the art on Portuguese microvertebrate record, and the first microvertebrate studies on three localities from the Lourinhã Formation (Late Jurassic) hosted by a Portuguese institution; Porto das Barcas, Zimbral, and Valmitão has provided 2,497 microvertebrates skeletal remains and teeth, from which 824 specimens have been identified, described and assessed to the conservative-most taxa. The stratigraphy and sedimentology of the localities suggest that Porto das Barcas and Zimbral were floodplain mud deposits, and Valmitão was an oxbow lake mud deposit, with a slow rate of sedimentation. The remains have been attributed to fishes, amphibians, squamates, crocodylomorphs, and dinosaurs; but unfortunately, no mammaliaform material has been collected. Paleoecological analyses suggest Zimbral and Valmitão were dominated by a terrestrial fauna and more diverse than Porto das Barcas, dominated by an amphibious fauna. The Lourinhã Formation appears to have been closer to the shoreline than American localities in the Morrison and Cloverly Formations were, but more continental than Buenache and Las Hoyas localities (Spain) with swamp to lacustrine paleoenvironments. A detailed study on 125 crocodylomorph teeth from Valmitão support the presence of Goniopholididae, at least two Atoposauridae taxa, and Bernissartiidae in the Late Jurassic of Portugal, with a fauna either dominated by relative small individuals, either juveniles or adults or small taxa.

Les formations, de plate-forme carbonatée, d'âge Kimémridgien à Berriasien affleurent, de part et d 'autre du synclinal molassique de Seyssel emprunté par la vallée du Rhône, dans les anticlinaux du Gros Foug, à l'Est et du Grand Colombier, à l'Ouest. Dans ces deux structures des coupes détaillées permettent de séparer les différentes formations et d'analyser les variations latérales de faciès. Les études lithostratigraphiques et pétrographiques associées amènent à distinguer, de bas en haut : - la formation des couches à Céphalopodes (Kimméridgien inférieur) et la formation des calcaires de Tabalcon (base du Kimméridgien supérieur) . Ces formations sont faites de calcaires mudstones micritiques alternant avec des lits de marnes vers la base et correspondent à des dépôts subtidaux face à la mer ouverte ; - la formation des "calcaires construits de la Haute-Chaine" (Kimméridgien supérieur) faite de calcaires boundstones biohermaux coralliens, se développe à l'Est. Il s ' agit d'une véritable barrière récifale séparant la plate-forme de la mer ouverte. En position interne, à l'Ouest donc, cette formation passe à la formation des "calcaires en plaquettes", Elle s 'est déposée dans un lagon intertidal calme , à ambiance réductrice et dans la région même de la mine d'Orbagnoux , la sédimentation est celle des calcaires véritables lemnitiques bitumineux ; - la formation des calcaires de Landaize (sommet du Kimméridgien supérieur). Il s ' agit de calcaires à texture sablo-graveleux de mer agitée surmergeant surtout le bordure externe de la plate- forme recouvrant à l'Est et au Sud la barrière récifale; - la formation des Tidalites de Vouglans (Portlandien) recouvre progressivement la paléogéographie contrastée précédente avec le dépôt des calcaires à grains fins souvent dolomitisés, de faciès supra-tidaux à intratidaux marqués par des structures sédimentaires d'émersion et également par la présence de petits cailloux noirs de composition organo-minérales témoin de quelques événements anoxyques. - Les Assises pürbeckiennes (Berriasien inférieur) correspondent à des dépôts plus calmes à fossiles laguno-lacustres par passées (Characées) de moins forte énergie mais également à cailloux noirs, structures sédimentaires d'émersion et paléosols. Il s ' agit probablement d 'un milieu de plate-forme interne de type lagunaire liée à des épisodes temporaires de régressions marquées. - L ' étude des microfacies montre que la diagenèse des roches est précoce liée à la zone de vadose et à la zone phréatique et que la compaction est faible, liée à une modeste surcharge sédimentaire. Enfin, l'étude de la matière organique effectuée selon les techniques classiques optiques ( lumière réfléchie , lumière fluorescente) et géochimiques ( dosage du carbone organique , analyse Rock-Eval, extraction chloroformique et chromatographique ) montre que seuls les calcair es en plaquettes bitumineux de la mine d ' Orbagnoux sont des roches-mères excellentes. Cette matière organique de type l, ayant une origine algaire à bactérienne est immature. On observe néanmoins la présence d' hydrocarbures en grande quantité dont une proportion non négligeable d 'hydrocarbures satures et aromatiques issus de composés organiques ayant donc subi une maturation thermique non négligeable . Le problème de leur origine est discuté .