Oxfordian Limestones Research Articles

Large chambered sponge borings on a Late Cretaceous abrasion platform at Cracow, Poland

A new ichnospecies of the bioeroding sponge ichnogenus Entobia, i.e., E. cracoviensis isp. n., is distinguished by having a single, large, isolated chamber and radiating canals. It occurs in a rockground surface on a Turonian or Santonian abrasion platform that is cut into Oxfordian limestones as exposed at Bonarka, Cracow. The morphology of the new ichnospecies is compared with fossil and modern sponge boring morphologies. In every case, the borings lack their upper parts and are roofless. Three models are constructed for the depositional history of the rockground and its colonization by the E. cracoviensis tracemaker: (1) that the roof has been removed by physical erosion, causing, or subsequent to, the death of the sponge; (2) that the lack of the roof is primary (biological), the roof having been removed by the sponge itself; and (3) that the boring sponge was psammobiontic, initiating its boring beneath a thin sand deposit, where there was no need to maintain a roof to the boring. The third model, based on living species of Aka, fits the details of preservation best, and is considered to represent the most likely scenario.

Influence of initial iodide concentration on the iodide uptake by the argillite of Tournemire

Among the radionuclides that can migrate from radioactive wastes buried within consolidated argillaceous rocks, 129I poses a particular problem due to its high mobility in geomedia and its very long half-life of 1.6 10 7 years. Previous studies carried out on such rocks showed the existence of a low iodide retardation regarding the other anion species. The purpose of the present study was two-fold. It was hoped (1) to confirm this retardation by means of radial diffusion experiments and (2) to estimate the influence of the initial iodide concentrations towards the iodide uptake. The results obtained from in-diffusion stage show that (1) no iodide uptake occurs at high initial concentrations and (2) an uptake at low initial concentrations cannot be clearly evidenced. Finally, the most singular behaviour of iodide was highlighted for all the initial iodide concentrations, from the out-diffusion stage, during which some amount of iodide, available for out-diffusion, were not involved in the diffusion process. Although the origin of such phenomenon remains unclear, a kinetic effect for the iodide uptake was proposed, assuming that the period of 55days (corresponding to the in-diffusion stage duration) would be necessary for inducing the iodide uptake. This kinetic effect, already shown elsewhere by (Descostes, M., Blin, V., Bazer-Bachi, F., Meier, P., Grenut, B., Radwan, J., Schlegel, M.L., Buschaert, S., Coelho, D, Tevissen, E. Diffusion of anionic species in Callovo-Oxfordian argillites and Oxfordian limestones. In press for Appl. Geochem.) on similar materials, needs to be deepened.

Diffusion of anionic species in Callovo-Oxfordian argillites and Oxfordian limestones (Meuse/Haute–Marne, France)

Abstract Diffusive parameters of tritiated water (HTO) and several anionic tracers (36Cl−, 125I−, 35 SO 4 2 - and 75 SeO 3 2 - ) were determined in the Callovo-Oxfordian argillite formation (Meuse/Haute–Marne, France), and also in the Oxfordian limestone formation, located just above. Twenty two drillcore samples, from depths of 150–480 m and from almost each lithofacies along the same borehole EST205, were tested. Three distinct and complementary experimental set-ups were used (batch, column filled with crushed argillite and through-diffusion experiments) associated with a thorough characterisation of the rock, care being taken to maintain redox conditions. Tritiated water behaviour is similar to water which diffuses in the total porosity of the rock. Tritiated water and anionic tracers displayed analogous diffusive behaviour in calcareous samples with ea(anion)/ea(HTO) = 1 and De(anion)/De(HTO) close to 0.85, i.e. the ratio of their diffusion coefficients in free water. Lower and scattered values were observed in the lower part of the Oxfordian limestones which is characterized by the presence of mineralogical heterogeneities and dolomitic diagenesis. In the Callovo-Oxfordian argillite formation, diffusive fluxes of 36Cl−, 125I− and 35 SO 4 2 - are similar but lower than that of HTO. The diffusive behaviour analogy between I− and Cl− was verified, as De(halide)/De(HTO) and ea(halide)/ea(HTO) ratios were always lower than 1. This reduction in diffusivity is a consequence of the anionic exclusion, which limits the diffusion-accessible porosity to a value lower than the total porosity for anions. A weak sorption of I− and SO 4 2 - on argillite samples was always observed whatever the technique used. In the case of I−, this sorption appears to be partly reversible and kinetically controlled. Very low values of diffusive parameters were obtained for 75 SeO 3 2 - and are still not well explained. Last, diffusive parameters of each radioactive tracer tested can be plotted according to Archie’s law, which therefore allows an estimation of De(non-reactive species) from the knowledge of both the sample total porosity and the corresponding exponent m = 2 for argillite samples.

Impact of the landscape evolution on the hydraulic boundary conditions of the Callovo–Oxfordian formation

The Callovo–Oxfordian formation in the Eastern part of France was recognized as a potential nuclear waste repository layer. The Andra (National Agency for Nuclear Waste Management) has launched a few years ago a research program that aims to define the mechanisms of importance in the impact of the surface environment evolution on the site hydrogeology. Based on mapping and dating results, Andra has quantified the geomorphological evolution of the Meuse/Haute-Marne site in the past and has estimated the future evolution over 1 million years. The Callovo–Oxfordian boundary conditions depend on the hydraulic heads in the two surrounding aquifers, the Oxfordian limestone above, and the Dogger one, below. Both aquifer outcrops are modified over the next million years. For the present study, the geomorphologic evolution is considered independently of other processes and translated in the hydrogeological model in terms of changes in the hydraulic boundary conditions at the surface. The hydrodynamic simulations have been performed with the code Cast3M (implemented by CEA (Atomic Energy Commissariat)) using a mixed hybrid finite-element formulation. For these groundwater flow simulations, three modelled stages are presented: the Present, 500,000 years (500 Ky) and 10 6 years (1 Ma) in the future. The landscape evolution is merely considered through the use of three different topographies on which the boundary conditions are applied. According to Andra predictions, at the Meuse/Haute-Marne site, the valley incisions on the Bure plateau will locally reach the Oxfordian limestone. Thus, the Oxfordian aquifer exhibits more changes due to topographic evolution than the Dogger aquifer. Hydrodynamic simulations show a significant impact of the valley incisions on the groundwater flow by the creation of local outlets to the Oxfordian limestone aquifer in the North of the area for the 1 My topography. It induces local perturbations of the saturation level. The global erosion of the topography also pulls down the hydraulic heads on a regional basis. Changes induced by the geomorphologic evolution in the Dogger aquifer are located around 30 km East from the Underground Laboratory site, at the outcropping areas. Thus, at the Laboratory location, the piezometric surface does not show, for the future, significant modifications compared to the present state. The 20-m general lowering of the hydraulic heads in the Dogger is also globally less important than for the Oxfordian aquifer. The consequence on the Callovo–Oxfordian boundary conditions for the future is an increase of the internal upward vertical hydraulic gradient which, at present state, is well developed only immediately to the North of the Laboratory.

Characterization of a clay-rich rock through development and installation of specific hydrogeological and diffusion test equipment in deep boreholes

Andra (Agence Nationale pour la Gestion des Déchets Radioactifs – National Radioactive Waste Management Agency) has developed specific tools and methodologies to evaluate and understand the main transport mechanisms of solute species in an argillaceous rock in the framework of the scientific program of the Meuse/Haute-Marne Underground Research Laboratory. This paper focuses on three specific equipments already installed in boreholes for the determination of convection and diffusion parameters in a very low permeability environment. The first one is a specific borehole completion for head and permeability measurements with an integrated wireless telemetry device. In 1995, Andra devised a probe equipped with a pressure sensor to monitor the long-term evolution of electro-magnetically transmitted pore pressures. The data gathered by this first device, and a second one installed in 2001, have shown the occurrence of overpressures in very low permeability formations. The second device is derived from the multipacker system used for monitoring the drainage of the Oxfordian limestone due to the sinking of the shaft above the Callovo-Oxfordian. It is used for obtaining from a single borehole, a pressure profile of the argillaceous formation and its encasing units. To date, the major information obtained with these two borehole equipments is the existence of a 25–35 m anomalous excess hydraulic head in the 130 m thick Callovo-Oxfordian argillaceous formation. Head values in the argillaceous rock exceed those in the overlying Oxfordian limestone by 25–35 m, and those in the underlying Dogger by over 45 m. The third equipment described in the paper, is derived from the experiment carried out at the Mont Terri rock laboratory since 1996 for the characterization of diffusion and retention processes. The system is adapted for a borehole drilled from the surface. The objectives of this experiment are as follows: • Verification of the predominant role played by molecular diffusion compared with convection; • Acquisition of data required to extrapolate and /or interpolate chemical retention and diffusion parameters. The diffusion test performed from the borehole makes it possible to test in situ a small number of tracers (HTO, 36Cl, 134Cs) at a scale of 10 cm for the non sorbing tracers.

Chlorine transfer out of a very low permeability clay sequence (Paris Basin, France): 35Cl and 37Cl evidence

The marine Callovo-Oxfordian clay formation is found at a depth around 410m in the eastern part of the Paris Basin (France). It is a very low permeability formation investigated by the French agency for nuclear waste management (ANDRA) to study the feasibility of a radioactive waste disposal. Examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation. This study uses chlorine isotopes to investigate long-term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks. Detailed chlorine concentration and δ 37Cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers (the Dogger at the bottom and the Oxfordian/Kimmeridgian/Tithonian unit at the top). They are discussed in terms of chlorine budget and hydrogeological processes. Clay pore waters and aquifer waters show strong chlorine concentration depletion (<3000 mg/L) relative to the original marine interstitial water (∼19000 mg/L). This probably results from an early dilution by meteoric water in limestones (as also indicated by oxygen and hydrogen isotopes). A steep Cl-concentration gradient from the Dogger at ∼500m in depth (∼2500 mg/L) to the Oxfordian/Kimmeridgian/Tithonian aquifer near the surface (≈ 10 mg/L) is associated to a ‘v-shaped’ profile of the δ 37Cl values. Modelling Cl transport shows that a hydrodynamic dispersion process explains Cl concentration and δ 37Cl profiles in Oxfordian Limestone. This process implies a mean upward flux of chloride in the 2.6 10 −8–8.2 10 −8 mole/m 2/yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride. The modelling and knowledge of underground water transfer suggest a maximum effective Cl-hydrodynamic vertical dispersion coefficient (= vertical Cl-transport coefficient) of ∼7.6 10 −10 m 2/s. Chlorine transfer through the Callovo-Oxfordian clay, since deposition 160My ago, can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events (such as early diffusion, ion filtration etc.).

Paleoclimatic control of biogeographic and sedimentary events in Tethyan and peri-Tethyan areas during the Oxfordian (Late Jurassic)

The paleobiogeographical distribution of Oxfordian ammonites and coral reefs in northern and Central Europe, the Mediterranean area, North and East Africa, and the Middle East and Central Asia is compared with the distribution in time and space of the most important lithofacies. Interest in the Oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events. Paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data. A Late Callovian–Early Oxfordian crisis in carbonate production is indicated by the widespread absence of Lower Oxfordian reefal formations. There is a gap (hiatus) in deposition on epicontinental platforms, with Middle Oxfordian deposits resting paraconformably on Upper Callovian, while shales accumulated in adjacent intracratonic basins. Simultaneously, in Mediterranean Tethys, radiolarites accumulated in deep troughs while Rosso Ammonitico facies formed on pelagic swells. However, deposition on swells was also discontinuous with numerous gaps (hiatuses) and sequences that are much reduced in thickness. Middle Callovian deposits are generally overlain by Middle Oxfordian limestones. The dearth of carbonates is consistent with a cooling event lasting about 1 My. By the middle Oxfordian a warming, leading to “greenhouse” type conditions, is suggested on the basis of both biogeographical (mostly coral-reef distribution) and geochemical data. Carbonates spread onto an extensive European platform while radiolarites reached a maximum development in the Mediterranean Tethys. Two distinct latitudinal belts, with seemingly different accumulation regimes, are therefore inferred. Similar latitudinal belts were also present in the late Oxfordian, when carbonates were widespread. The distribution of reefal facies in the late Oxfordian–early Kimmeridgian fits relatively well with GCMs simulations that imply low rainfall in the Tethyan Mediterranean area and slightly higher precipitation in central and northern Europe. Local salinity variations, reflecting more arid or humid conditions, may bias the paleotemperature signal inferred from δ 18O values. Biogeographical and facies distributions, combined with δ 18O values, unravel the ambiguity and support a Late Callovian–Early Oxfordian cooling followed by warming in the later Oxfordian.

Oxfordian sedimentary dykes : tectonic and diagenetic implications for the eastern Paris basin

Abstract Vertical fractures in Oxfordian limestones of the eastern part of the Paris Basin are interpreted as resulting from synsedimentary extensional deformations which occurred during the Mesozoic. These NNE-SSW striking fractures are 10 to 20 meters in height, and filled with microgranular material. The fractures mainly affect crinoidal and oolitic grainstones. Their micritic to microsparitic, lithoclast-bearing infills may have resulted from the solidification of an ancient mud injected from non-lithified, overlying layers of marine sediments. They should therefore be referred to as sedimentary dykes. Graded layering suggests deposition under turbulent flow conditions, whereas later plastic deformation and breccia formation indicate a syndiagenetic reworking. Such observations are consistent with a predominance of the sedimentary dykes in grainstones, which are more rapidly lithified and therefore subject to early fracturing. On the contrary, these dykes are rare in mudstones which may constitute the source of the material for the infills in the grainstones. Both the analysis of the wall geometry and the reconstruction of the diagenetic history of the infills make possible to distinguish two types of sedimentary dykes. The first type corresponds to a fracturation characterized by irregular walls around the rock-constituting grains (i.e. crinoidal debris or ooids), whereas the walls in the second type are cross-cutting the grains and present a fringe of sparite predating the microsparite infill. The following scenario is proposed for the first type of sedimentary dykes: i) syntaxial cementation of crinoidal debris and early cementation of ooids; ii) fracturing along grain boundaries under low burial strain; iii) filling of fractures and open porosity by the mud. The second type of sedimentary dykes was formed under deeper burial conditions, which is indicated by both pre-existing bedding-parallel stylolites and the precipitation of sparite on the walls before the sedimentary infill. This early fracturation and the availability of a sedimentary filling, non-lithified material point to a late Jurassic age for these sedimentary dykes. The δ18OSMOW isotopic signatures measured for the infilling sparite and microsparite materials indicate that these were precipitated from meteoric waters, either early during the formation of the sedimentary dykes or during a later recrystallization event. The sedimentary dykes have recorded an E-W extension during the Oxfordian-Kimmeridgian period, which is in good agreement with the late Jurassic tectonic history of the western European platform. This early Oxfordian-Kimmeridgian fracturing and its associated fluid paleocirculations is of major interest in the context of the tectonic history of the Paris Basin, since most of these N-S to NNE-SSW tension gashes have been previously attributed to the Eocene Pyrenean shortening and Oligocene rifting stages.

HTO Diffusion in Oxfordian Limestone and Callovo-Oxfordian Argillite Formations

AbstractDiffusion coefficients and accessible porosities for HTO were measured on 30 samples from the Andra Underground Rock Laboratory in Meuse/Haute-Marne (France) using the through diffusion technique. Two distinct geological formations were studied: Oxfordian limestone and Callovo-oxfordian argillite between 166 and 477 m depth. The experiences were carried out with synthetic pore-water from each formation. The measured values of the effective diffusion coefficients (De) are ranging from 2.6× 10-12 to 12.4 × 10-11 m2 s-1 while accessible porosities (ε) are between 2.4 and 24%. Good correlations are found between these two parameters.

Facies, microfacies, and diagenesis of late Callovian-early Oxfordian carbonates (La Manga Formation) in the west central Argentinean high andes

At 32° 40′ south latitude the Andean orogen shows a typical thin-skinned fold and thrust belt that exposes the Mesozoic backarc basin fill. The late Callovian-early Oxfordian limestones of the La Manga Formation were studied based on lithofacies, microfacies, and diagenetic processes in order to interpret the paleoenvironment depositional setting. Five lithofacies can be recognized within the La Manga Formation: (A) stromatolite mudstone, (B) massive and laminated carbonate mudstone, (C) massive wackestone, (D) coralline floatstone, and (E) oolitic-skeletal packstone-grainstone. The vertical succession reveals six closely related microfacies grouped as follows: (1) stromatolite mudstone, (2) peloidal wackestone, (3) bioclastic peloidal wackestone, (4) oolitic bioclastic packstone, (5) coral skeletal floatstone, and (6) oolitic-intraclastic grainstone.

Jurassic corals as emersion indicators

In Recent coral reefs, emersion has resulted in the development of special growth forms of colonial corals which have been named microatolls. These colonies grow almost exclusively in a horizontal direction. In the upper part of the colony, subaerial exposure leads to the decay of the living body. The growth then stops and the skeleton is later colonized by various boring and encrusting organisms. Here we show the first record of a massive Mesozoic coral colony displaying the main features of emersion. The colony has been collected in perireefal Oxfordian (Jurassic) limestones from the Jura Mountains (France). It is situated exactly at the expected place in a shallowing-upward sequence between infralittoral buildups and supralittoral limestones. We suggest that such growth structures could be more common than previously thought in ancient coralliferous sediments and add some new details to discriminate between these colonies.

Ground penetrating radar application in a shallow marine Oxfordian limestone sequence located on the eastern flank of the Paris Basin, NE France

Abstract A Ground Penetrating Radar (GPR) survey has been carried out in Upper Jurassic limestones located on the eastern flank of the Paris Basin (NE France). The potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface. The fundamentals of the GPR technique are described. Penetration depth and vertical resolution depends on the soil conditions, the characteristics of input signal and the configuration of the transmitter–receiver assembly. In the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum (i.e. approximately 55 m). Several depositional units are outlined on the GPR profiles. Six different lithological units are recognised with distinct GPR reflection characteristics. The profiles illustrate the internal 3D organisation of the carbonate platform and its geometry. They provide detailed insight into the nature of an Oxfordian reefal build-up. The high-resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3D depositional working model. The GPR method is a non-destructive remote sensing technique that is cost effective. The method is considered complementary to other conventional high-resolution reservoir characterisation studies. It represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface.

The stratigraphy of the ‘Corallian’ facies Middle Oxfordian (Upper Jurassic) deposits at Upware, Cambridgeshire, England

At Upware, Cambridgeshire, an inlier of ‘Corallian’ facies Middle Oxfordian limestone within the more typical mudrock-dominated West Walton Formation sequence of the East Midlands Shelf, forms a topographic feature of low relief for 6 km. Recent deep excavations in the district have revealed the base of these beds, not exposed since the last century. They and the underlying mudrock have yielded prolific bivalve faunas and common ammonite faunas, including both Boreal (Cardioceratidae) and Tethyan (Perisphinctinae) elements. The stratigraphy of these Middle Oxfordian deposits is revised, and the palaeoenvironment of the benthic macroinvertebrate faunas of the succession is discussed. The Boreal bivalve Praebuchia lata (Trautschold), a new record of biostratigraphic significance, is described and figured.

Tectonic Evolution, Structural Styles, and Oil Habitat in the Sonda de Campeche, Mexico: ABSTRACT

The Sonda de Campeche is located in the southern part of the Gulf of Mexico and hosts one half of the oil reserves of Mexico. The stratigraphic section is 7500 m thick, ranging from Middle Jurassic to Holocene. The Mesozoic sequence includes Callovian salt deposits, Upper Jurassic sandstones, anhydrites, limestones, and shales; and Cretaceous limestones, dolomites, and carbonate breccias. In some places, this sequence displays condensed sections related to an early movement of salt. The Cenozoic sequence is formed mostly of benthonitic shales and minor sandstones, and shows two unconformities: the older one between the lower Miocene and the Oligocene, and the younger one between the middle Miocene and the upper Miocene. In the Sonda de Campeche, three main tectonic regimes are recorded: extensional, compressional, and extensional. The first one extended from Middle Jurassic to Late Jurassic and is related to the opening of the Gulf of Mexico. During this regime, tilted block faults trending northwest-southeast were dominant. The subsequent compressional regime took place at the end of the early Miocene and was related to northeast tangential stresses that added to the flow of Callovian salt, gave rise to huge anticlines, faulted, and often overturned. The last extensional regime extendedmore » throughout the middle and late Miocene and is related to salt tectonics and growth faults that have as a detachment surface a middle Miocene shaly horizon. The main source rocks are Tithonian shales and shaly limestones. Oolite bars, slope and shelfal carbonates, and regressive sandstones form the main reservoirs. Evaporites and shales are the regional seals. Recent information indicates that Oxfordian shaly limestones are also important source rocks.« less

Middle Jurassic calcareous algae from the circum-Arabian area

Calcareous algae of the Middle Jurassic limestones from Northern Sinai have been investigated in detail with regard to facies and palecology. The aalenian? to Callovian sequence is more than 1000 m thick. It is composed of carbonates, sandstones, siltstones and claystones; all sediments are interpreted as platform margin and extended platform deposits. Oncoids—often composed of skeletal algae—are frequent constituents in many deposits of the protected shelf areas. This algal flora is compared with algae from Oxfordian limestones of a well in Lebanon and from Aalenian?—Callovian limestones of a well in South Ethiopia. The algal flora consists of 22 taxa of Chlorophyta, Cyanophyta, Rhodophyta and 3 taxa of algae incertae sedis.

Hyperfiltration-osmosis effects in compacting sediments: Isotopic and chemical changes in pore waters

The marine Callovo-Oxfordian clay formation is found at a depth around 410m in the eastern part of the Paris Basin (France). It is a very low permeability formation investigated by the French agency for nuclear waste management (ANDRA) to study the feasibility of a radioactive waste disposal. Examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation. This study uses chlorine isotopes to investigate long-term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks. Detailed chlorine concentration and δ37Cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers (the Dogger at the bottom and the Oxfordian/Kimmeridgian/Tithonian unit at the top). They are discussed in terms of chlorine budget and hydrogeological processes.Clay pore waters and aquifer waters show strong chlorine concentration depletion (<3000 mg/L) relative to the original marine interstitial water (∼19000 mg/L). This probably results from an early dilution by meteoric water in limestones (as also indicated by oxygen and hydrogen isotopes).A steep Cl-concentration gradient from the Dogger at ∼500m in depth (∼2500 mg/L) to the Oxfordian/Kimmeridgian/Tithonian aquifer near the surface (≈ 10 mg/L) is associated to a ‘v-shaped’ profile of the δ37Cl values. Modelling Cl transport shows that a hydrodynamic dispersion process explains Cl concentration and δ37Cl profiles in Oxfordian Limestone. This process implies a mean upward flux of chloride in the 2.6 10−8–8.2 10−8 mole/m2/yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride. The modelling and knowledge of underground water transfer suggest a maximum effective Cl-hydrodynamic vertical dispersion coefficient (= vertical Cl-transport coefficient) of ∼7.6 10−10 m2/s.Chlorine transfer through the Callovo-Oxfordian clay, since deposition 160My ago, can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events (such as early diffusion, ion filtration etc.).

Upper Jurassic Ramp Carbonate and Associated Evaporite, Neuquen Province, Argentina: ABSTRACT

The Oxfordian La Manga Limestone (10-65 m) and overlying Auquilco Gypsum (315 m maximum thickness) crop out along the west flank of the Neuquen basin, Neuquen Province, Argentina (36/sup 0/40/sup 0/S lat.). The contact with the underlying Lotena Sandstone is gradational, and both formations are cut by the Late Jurassic Araucanian angular unconformity. Seven lithofacies have been identified within sections measured through the entire interval along the northeast to southwest trending, 30-km long Sierra de la Vaca Muerta ridge (38/sup 0/30'-39/sup 0/S). The La Manga Limestone is interpreted as a temperate ramp carbonate that developed over the Lotena Formation siliciclastic shelf. Interpretations of lithofacies from southwest to northeast are: behind-barrier subtidal lagoon with washovers; coral and red algae biostromes; ooid and peloid sand shoals; downslope wackestone and packstone mud mounds; and deep-water carbonate turbidites. A minor regression separates La Manga and Auquilco Formations. Lithofacies of the Auquilco Formation indicate a shallowing-up sequence comprised of initially deep (hundreds of meters) subaqueous evaporite deposition followed by shallow, subtidal carbonate peloidal and shell fragment grainstones and evaporites. Thickness of the subaqueous evaporite gives an order of magnitude estimate of Auquilco basin depths of a few hundred meters at most. The Neuquen basin hasmore » an intermediate proportion of carbonate in comparison to relatively carbonate-poor basins to the south and carbonate-rich basins to the north.« less

Activation of the plasma kallikrein system during myocardial ischemia

At Upware, Cambridgeshire, an inlier of ‘Corallian’ facies Middle Oxfordian limestone within the more typical mudrock-dominated West Walton Formation sequence of the East Midlands Shelf, forms a topographic feature of low relief for 6 km. Recent deep excavations in the district have revealed the base of these beds, not exposed since the last century. They and the underlying mudrock have yielded prolific bivalve faunas and common ammonite faunas, including both Boreal (Cardioceratidae) and Tethyan (Perisphinctinae) elements. The stratigraphy of these Middle Oxfordian deposits is revised, and the palaeoenvironment of the benthic macroinvertebrate faunas of the succession is discussed. The Boreal bivalve Praebuchia lata (Trautschold), a new record of biostratigraphic significance, is described and figured.

On the Occurrence of Terebratula Diphya in the Alps of the Canton de Vaud

I n answer to certain statements of Prof. Hébert as to the probability of the non-occurrence of Terebratula diphya in the Jurassic Series (Bulletin Soc. Géol. de France, vol. xxiii, p. 530, 1866), it may be well to put on record the following discovery of this species in strata in the Alps of the Canton de Vaud, which belong indubitably to the Oxfordian series. This is, I believe, the first time that this species has been found in Jurassic beds in the Canton. In the summer of 1867, when exploring the geology of the valley of the Sarine, near Château d’Oex (Canton de Vaud), I came upon this fossil in a block of Oxfordian limestone, among the “éboulis” around the chalets of Paray Charbon: these blocks, which are nearly all Oxfordian, have fallen from the ridge of the Vanil Noir. This range, from Merit Cray to Dent de Branleire, which forms here the boundary between the Cantons de Vaud and Fribourg, is formed by an arch of Bajocian (Inf. Ool.) dark grey limestones and shales, surmounted by the Oxfordian series at the N.E. end (Dent de Branleire, &amp;c.); but the vault rises higher where the chain becomes lower, so that at the S.W. end the Oxfordian is thrown off only at the sides, and is quite cut away from the top, the summit of Mont Cray being Bajocian. As our locality is about the middle of the range, the Oxfordian is seen at some height in the precipices above the chalet.