Se estudian 195 ejemplares de ammonoideos de la subfamilia Reineckeiinae pertenecientes a 20 taxones diferentes y procedentes del Calloviense de la Cordillera Ibérica (Aragón). La distribución cuantitativa y cualitativa muestra que los Reineckeiinar suponen el 10,75% del total de la fauna de ammonoideos del Calloviense, siendo más abun­dantes en las Zonas Gracilis y Anceps. Los taxones de Reineckeiinae coinciden con la distribución bioestratigráfi­ca de la Provincia Submediterránea. Se han identificado los horizontes 111 (Rehmanni), Vlla y Vllb (Boginense y Kiliani), VIII (Bannense), IX (Turgidum), XII (Baylei), XVI (Piveteaui), la parte superior de la Zona Athleta (horizonte XVII) y tal vez la base de Lamberti (horizonte XVIII).

An integrated biostratigraphic approach, based on ammonites, calcareous nannofossils, dinoflagellates, combined with sedimentology, carbon-isotope and physical stratigraphy, is proposed for the Subalpine Basin (Thuoux and Saint-Pierre d'Argencon sections). Within the expanded marl deposits of the Terres Noires Fm., the Callovian-Oxfordian boundary is particularly well defined by ammonite taxa from different families (i.e. Cardioceratidae, Oppeliidae, Aspidoceratidae and Perisphinctidae), calcareous nannoplankton (first occurrence of large-sized Stephanolithion bigotii) and dinoflagellate cysts (first occurrence of Wanaea fimbriata). This precise biostratigraphy and diversity of ammonites permit long-range correlations with Boreal and Pacific domains. The exceptional outcrop conditions and continuous sedimentation allow high-resolution chemostratigraphy and cyclostratigraphy to be used. Variations of the δ13C record (1.5‰ increase during the Lamberti Zone), consistent with data from other sections of the Subalpine Basin and with the Paris Basin, provide additional markers to characterise the Callovian-Oxfordian boundary. Promising results from cyclostratigraphy should serve to constrain the duration of biostratigraphic units and thus improve the Late Jurassic Geologic Time Scale. Comparisons are made with the two other candidates for an Oxfordian GSSP, Redcliff Point (UK) and Dubki (Russian Platform). Finally, the advantages of the Subalpine Basin sections support the proposal of Thuoux as a suitable GSSP candidate for the base of the Oxfordian Stage.

The Thuoux and Saint-Pierre d’Argençon sections (Subalpine Basin, southeastern France) display a thick silty–clayey sedimentation with abundant and diversified ammonite faunas, free of detectable hiatuses. The Callovian–Oxfordian boundary is biostratigraphically located between the Lamberti and the Mariae zones or, more precisely, between the Lamberti Subzone (paucicostatum horizon) and the Scarburgense Subzone (thuouxensis horizon). The mixing of Boreal–Sub-Boreal Cardioceratinae and Sub-Mediterranean–Tethyan Hecticoceratinae, Peltoceratinae, and Perisphinctinae in this basin allows reliable worldwide correlations that enhance the choice of the Thuoux and Saint-Pierre d’Argençon sections as a Callovian–Oxfordian GSSP candidate.

(1) EA 4592 G&E, ENSEGID, University of Bordeaux, 1, allée F. Daguin, 33607 Pessac Cedex, France, (2) Sorbonne Universités, UPMC Univ. Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France, (3) CNRS, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France, (4) GeoZentrum Nordbayern, Fachgruppe PaläoUmwelt, Friedrich-Alexander Universität Erlangen-Nürnberg, Loewenichstr. 28 91054 Erlangen, Germany, (5) UMR CNRS 6282 Biogéosciences, Université de Bourgogne, 6, Bd Gabriel, 21000 Dijon, France, (6) TOTAL S.A., Tour Coupole, 2 Place Jean Millier La Défense 6, 92078 Paris La Défense Cedex – France, (7) Institute of Geology and Geophysics of Uzbek Academy of Sciences, Tashkent, Uzbekistan

High-resolution carbon and oxygen isotope data from the Paris Basin and the Subalpine Basin (France) are available in a precise biostratigraphic framework for the Callovian-Oxfordian stages. A biostratigraphically well-constrained delta C-13 curve, derived from bulk carbonates in the Paris Basin and the Subalpine Basin, is provided in order to document carbon-cycle evolution and to serve as a chemostratigraphic reference for the Callovian-Oxfordian in the Tethyan domain. Sea-temperature reconstructions, using diagenetically screened belemnite and oyster data, reveal major climate perturbations at the Middle-Late Jurassic transition.

The Thuoux and Saint-Pierre d’Argençon sections (Subalpine Basin, southeastern France) are proposed as a potential GSSP candidate for the Callovian–Oxfordian boundary. Several aspects of stratigraphy that have recently been applied in the two selected sections are discussed, including ammonite and nannofossil biostratigraphy, palynology, physical stratigraphy, and cyclostratigraphy.

A very high-resolution carbon and oxygen stable isotope analysis (bulk-carbonate) of a biostratigraphically well-constrained Callovian–Oxfordian series is provided here for the first time. The homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin. A prominent and brief negative excursion in the δ13C curve (−2‰), occurring at the start of the Middle Callovian (Jason Zone – Obductum Subzone) and correlated regionally, suggests a possible methane release. The increasing δ13C values thereafter up to the Early Oxfordian, concomitant with a warming episode, highlight the burial of carbon in organic-rich layers which, in return, may have triggered a decrease in atmospheric pCO2. At higher frequencies, observed fluctuations of the δ13C and δ18O values are orbitally driven (405-kyr and 100-kyr eccentricity cycles) and may correspond to the salinity and temperature variability recorded in sea water. The δ18O isotopic measurements from well-preserved diagenetically screened belemnites and bivalves along the series, compared to available data from Tethyan domains, agree with the scenario of a global cooling at the Middle-Late Jurassic transition. The well-dated δ18O isotopic curve suggests that the onset of this cooling event occurred at the end of the Coronatum Zone (Middle Callovian).

Chronostratigraphy and geochronology: A proposed realignment1 By "formed" we mean when the main fabric of the rock was constructed; in sedimentary rocks, this is taken as when the sedimentary particles were deposited; in igneous rocks, this typically means intrusion or crystallization (although these processes may not be precisely synchronous).The "timing of formation" of any individual metamorphic rock is often more problematic, because such a rock commonly includes components that crystallized at different times along a pressure-temperaturetime path.

Abstract:  The infaunal irregular echinoid, Tithonia oxfordiana, is described and compared to congeneric species previously described from Upper Jurassic and lowermost Cretaceous strata. This new species characterizes a monospecific echinoid assemblage, which occurs only in some places where deep‐marine middle Oxfordian deposits are exposed in south‐east France. Specimens are closely packed and clearly concentrated at the top of small carbonate chemoherms; a close connection of the echinoids with the emission of reduced chemicals, which were oxidized by chemoautotrophic bacteria, is highly probable. Based on general test shape and plate architecture, T. oxfordiana probably was a deposit feeder on chemosynthetic organic matter produced by such bacteria. In view of the fact that T. oxfordiana is the sole species of the Jurassic genus Tithonia known from Oxfordian strata, it is postulated that chemoherms possibly acted as refugia for these peculiar echinoids, which have an episodic record between the Callovian and Valanginian.

The Middle jurassic carbonates of the eastern part of the Paris Basin display surprisingly low values of porosity and permeability (Phi<15%o and K<0.5 mD). The main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs; a fate that did not befall their equivalents in deeper, central parts of the Paris Basin. Using petrographic and geochemical analyses (stable O and C isotopes, Sr isotopes, major elements), we identify six calcitic spar stages, two dolomite stages, and several episodes of fracturing and stylolitization ordered in paragenetic sequence. Cement quantification shows the predominance of two blocky calcite cement stages (75% of total cementation). O and Sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped Jurassic seawater and meteoric water, or from buffered meteoric waters. In the geological history of the Paris Basin, major meteoric water inputs were possible during the Early Cretaceous, when the Middle Jurassic carbonates cropped out at its northern and eastern borders. Lateral meteoric recharge may have occurred as a result of two separate uplift events (Late Cimmerian Unconformity and Late Aptian Unconformity) and the related exposures of carbonates to the north of the study area. This palaeohydrological circulation brought about a significant reduction of porosity (from 40% to 10%) through calcite cement precipitation. The Early Cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the London-Brabant Massif across all of northwestern Europe. A subsequent dolomite and calcite cementation stage accounts for about 5% of the total cement volumes. This late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the Late Oligocene extension episode. (C) 2009 Elsevier B.V. All rights reserved.

Key-words : Stratigraphy - Dogger - «Lusitanian» - Serra de Candeeiros. New elements about the stratigraphy of the Serra de Candeeiros Dogger and Lower «Lusitanian» are presented. The Lower Aalenian was recognized for the first time. Bathonian (more than 50 metres thick) is dated on brachiopods and foraminifera. It corresponds to a series of massive micritic, biadetritical, coral-reef, chaetetid, bryozoa and oolitic-limestones. Callovian (120 m) begins by whitish or yellowish limestones with ammonites and brachiopods of rhe Gracilis zone. Ir is followed by regressive limesrone sequences ending with thick oncolitic layers. The «Lusitanian» base is farmed by greyish lagoon brackish limesrones; it lies unconformably on the Dogger, with or without angular and/or cartographic uncanfarmiry. This radical facies change is related tO tecronic deformation of severa! blocks between the Nazare and Tagus faults during Oxfordian rimes.

A detailed sedimentological, geochemical and mineralogical study is carried out on the Early Bajocian to Early Callovian (Middle Jurassic) limestones of the Paris Basin. Objectives are to document and explain the facies changes in the context of the climate/environmental evolution at the NW European scale. Deposits include 18 lithofacies which are stacked into 10 third-order depositional sequences. At a greater time scale, 4 biosedimentary packages are distinguished by their allochems associations. (1) An intracratonic carbonate environment with coral reefs and crinoid-rich facies is typical of the Early Bajocian. (2) A major facies change occurred at the Early/Late Bajocian transition with a shift from crinoid- and coral-rich facies to ooid-rich facies. During the Late Bajocian, a southward-dipping ooid ramp with successive progradational trends was emplaced. (3) A large lagoon protected by ooid shoals developed during the Bathonian in a muddy ramp setting. (4) At the Bathonian/Callovian boundary, a second major change occurred with the lagoonal facies being superseded by an ooid-bioclastic (crinoids, corals) ramp associated with a waning of carbonate productivity (retrogradational trend). Our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern. A cooling from the latest Early Bajocian to the Late Bajocian and a subsequent warming from the earliest Callovian to the Early/Middle Callovian transition are described using a proxy of sea surface temperatures. Together with δ13C and mineralogical data, our new δ18O values suggest a palaeo-climatic/palaeo-environmental control of facies in this shallow carbonate ramp environment.

Magnetic susceptibility (MS) variations record Earth's orbital parameters in the clays and marls of the Early Oxfordian in the Paris and Vocontian basins of France. Climatically driven weathering of surrounding emergent areas and the resulting detrital input to the basins is a significant source of the MS signal. MS proves to be an effective tool for deciphering the orbital forcing signal in these sediments, and for assessing the chronology of these formations. The 405-kyr orbital eccentricity cycle is clearly visible in the MS signal and, consequently, is a valuable geochronometer for this portion of the Jurassic time scale. Astronomical calibration of the Mariae ammonite zone (basal Oxfordian stage) indicates a duration of -2.2 myrs, whereas current time scales assign only 0.6 myrs to this biozone. However, the Late Jurassic time scale has large uncertainties in stage boundary ages (4 myrs), hence of interval durations. These results could lead to significant revisions in the M-sequence magnetic anomaly block model, and greatly improve the resolution of the Jurassic time scale. (C) 2008 Elsevier B.V. All rights reserved.

The aim of this paper is to study the evolution of the architecture of the << apical system-periproct complex >> of the genus Collyrites (Echinoidea, Disasteroidea) for species from the Bathonian and Callovian stages (Middle Jurassic). The studied material comes from several localities of the Paris basin. The apical system of the genus Collyrites is subdivided in two parts: (i) an anterior part composed by four genital (1, 2, 3, 4) and three ocular (II, III, IV) plates, called trivium; (ii) a posterior part composed by two ocular plates (I, V) and one genital plate (5), without gonopor, which circle the periproct, called bivium. The genital plate 5, which may collapse in the periproct, is not always visible. The Bathonian-Callovian transition is marked by a subdivision of the bivium in two parts: the periproct breaks up from the posterior ocular plates (I, V). These morphological changes are associated with architectural modifications. The trivium stays relatively stable during the Bathonian and the Callovian, but a supplementary plate may be inserted into the trivium. The bivium shows important modifications linked to the separation of the periproct and the ocular plates (I and V). Such a separation is marked by a strong development of supplementary plates, these ones keeping in connection with the periproct and the ocular plates I and V. The supplementary plates are more and more developed whereas the distance between the periproct and ocular plates increases. The connection between the trivium and the bivium is similarly provided by supplementary plates. The size of these plates seems to significantly increase between the Bathonian and the Callovian. Moreover, some specimens from the Bathonian and the Callovian may have an atypical architecture with a supplementary genital plate or a genital plate with two pores. The "extraxial axial theory" allows to recognize two types of skeleton: (i) an "axial skeleton" corresponding to ocular plates and plates of the ambulacra and interambulacra; (ii) an "extraxial skeleton" corresponding to the genital and supplementary plates, and the periproct. Architectural modifications between the Bathonian and the Callovian is a result of a more important development of the "extraxial skeleton" while the "axial skeleton" shows few modifications during this time interval. (C) 2007 Publie par Elsevier Masson SAS.