Aquitaine Basin Research Articles

Palaeoenvironmental reconstruction of the basal Cretaceous vertebrate bearing beds in the Northern part of the Aquitaine Basin (SW France): sedimentological and geochemical evidence

The Purbeckian facies of the northern margin of the Aquitaine Basin is exposed in the Cherves-de-Cognac section (SW France), considered as basal Cretaceous in age. Two lithological units have been identified. The basal unit (U1) is composed of an alternation of gypsum and finely bedded black dolomitic marlstone, occasionally stromatolitic in nature. It represents mostly hypersaline, dolomitic tidal flat, lagoonal, and sabkha-type environments. The upper unit (U2) consists of variably fossiliferous limestone-marl alternations that contain a diverse fauna and flora. In the upper part of this unit, a 4-m-thick level has yielded a rich vertebrate fauna. The preservational quality of the vertebrate fossils varies within the section. On the basis of faunal, floral, sedimentological and mineralogical information the vertebrate remains accumulated in brackish water environments in which the influence of freshwater has progressively increased towards the top of the section. The close association of environments representing varying degrees of marine and continental influence suggest an estuarine setting.

Cristatopecten nov. gen. benoisti (Pectinidae, Bivalvia) du Chattien d'Aquitaine (France). Révision systématique et réflexions sur l'origine et l'évolution des Cristatopecten

The detailed study of a sample of “Pecten ( Amussiopecten) benoisti” Cossmann and Peyrot (1914) from the Chattian outcrops of the Adour Basin, allowed to improve our knowledge of this species poorly known till now and to show its important ornamental variability. It follows that some nomenclatural points have been clarified at the generic level: we refute the attribution of this species to the genus Amussiopecten Sacco (1897) as used by authors—genus which was besides emended several times subsequently— and we propose its allocation to Cristatopecten nov. gen. Furthermore, this study allowed to remove the ambiguity existing originally as for the attribution of the species benoisti and burdigalensis to a same genus: our comparison of the latter two taxa shows that if benoisti has to be henceforth included in the new genus Cristatopecten (as its type species), burdigalensis (which is the type species of Amussiopecten) must be incorporated in the genus Flabellipecten Sacco (1897). The two genera Amussiopecten and Flabellipecten are therefore synonymous, as Depéret and Roman had already stated in 1910. The Cristatopecten from the Old World seem to be derived from a group of “Aequipecten” notably known in the Italian Rupelian, the group of “Aequipecten deletus” (Michelotti, 1861), of which we study here a sample from the Aquitaine Chattian. In the Aquitaine Basin, the Cristatopecten are represented, in the Chattian, by Cristatopecten benoisti (Cossmann and Peyrot, 1914); in the Lower Aquitanian, by C. praehaueri (Bongrain, Cahuzac and Freneix, 1994); in the Burdigalian–Langhian of the Saubrigues paleocanyon, by C. haueri (Michelotti, 1847) and C. miogallicus (Cossmann and Peyrot, 1914). During the whole Neogene, they spread and evolved in the Tethys and the Paratethys areas, and seem to have become extinct in the Pliocene with the disappearance of C. cristatus (Bronn, 1827), a species that we consider not as an Amusium s.s., but as the last representative of the Cristatopecten phylum.

Dating multistage paleofluid percolations: A K-Ar and 18O/16O study of fracture illites from altered Hercynian plutonites at the basement/cover interface (Poitou High, France) 1

Isotopic age determination of fluid events in basement fractures is of prime importance for the reconstruction of paleo-hydraulic regimes. However, material from fracture or wall-rock is not generally easily dated. In the case of fractures filled by minerals such as phyllosilicates, it can be expected that subsequent fluid circulation may cause partial alteration or recrystallization of the previous phyllosilicates, disturbing the isotope signature. Using a specific methodology, including the extraction process without contamination of the finest (<0.2 μm) authigenic fractions, identification of clay fractions by X-ray diffraction (XRD), scanning electron microscopy, and electron microprobe, analysis of stable isotope composition (D/H, δ18O) and K-Ar dating, fluid event ages can be estimated. This methodology was applied to the northwestern margin of the French Massif Central, where basinal brines have interacted with the sedimentary cover (infra-Toarcian formations) and the fractured Hercynian crystalline basement. During periods of unknown age, precipitates from brines sealed most basement fractures as carbonates, and a recrystallization of early Hercynian phengite (+chlorite) into illite and illite/smectite minerals occurred in the earlier fractures. XRD patterns show that the clay fraction is dominated by illite and ordered mixed-layer minerals having a relatively high amount of illite (I-S R3). In the shallowest samples beneath the paleo-surface, a late assemblage is identified as a mixture of I-S minerals, a part of them being characterized by significant amounts of swelling layers (I-S R0). The δD values of the clay fractions are fairly constant around −50 ± 10‰, but δ18O values of the same clay fractions display a wide range from 8‰ to 18‰ (SMOW). The study of the size fractions between 2 and 0.2 μm reveals a correlation between K-Ar ages and δ18O values, which cannot be related to a change in the relative amounts of clay minerals. Deep fractures (at depths of 570 and 923 m) are characterized by δ18O values around 10.3 ± 0.4‰ SMOW and old ages ranging from 253 to 272 Ma. The finest fractions (<0.2 μm) of clays located at shallow level (<300 m) beneath the paleo-surface yield the highest δ18O values (15.7–18.2‰) and the youngest K-Ar dates (188 to 198 Ma). These dates are likely to record the extensional episode and thermal anomaly related to the rifting of central Atlantic Ocean (c. 190 Ma). The other important thermal/extensional episode which affected the Aquitaine Basin, namely the opening of the Gascogne gulf at c. 120 Ma, is not detected by the K-Ar method on the clay fractions. We believe that resetting of clay-type K-Ar ages linked to recrystallization was favoured in the upper part of the basement where the ancient (Hercynian) clay minerals were destabilized by subaerial low-temperature alteration during Permo-Triassic times. From a methodologic point of view, the analytical characterization of several size fractions of clays from reactivated fractures, using both stable isotope geochemistry and K-Ar isotope geochemistry, can be considered as a powerful tool for dating fluid events when no suitable material for conventional methods is available.

Dating multistage paleofluid percolations: A K-Ar and 18O/ 16O study of fracture illites from altered Hercynian plutonites at the basement/cover interface (Poitou High, France)

Isotopic age determination of fluid events in basement fractures is of prime importance for the reconstruction of paleo-hydraulic regimes. However, material from fracture or wall-rock is not generally easily dated. In the case of fractures filled by minerals such as phyllosilicates, it can be expected that subsequent fluid circulation may cause partial alteration or recrystallization of the previous phyllosilicates, disturbing the isotope signature. Using a specific methodology, including the extraction process without contamination of the finest (<0.2 μm) authigenic fractions, identification of clay fractions by X-ray diffraction (XRD), scanning electron microscopy, and electron microprobe, analysis of stable isotope composition (D/H, δ 18O) and K-Ar dating, fluid event ages can be estimated. This methodology was applied to the northwestern margin of the French Massif Central, where basinal brines have interacted with the sedimentary cover (infra-Toarcian formations) and the fractured Hercynian crystalline basement. During periods of unknown age, precipitates from brines sealed most basement fractures as carbonates, and a recrystallization of early Hercynian phengite (+chlorite) into illite and illite/smectite minerals occurred in the earlier fractures. XRD patterns show that the clay fraction is dominated by illite and ordered mixed-layer minerals having a relatively high amount of illite (I-S R3). In the shallowest samples beneath the paleo-surface, a late assemblage is identified as a mixture of I-S minerals, a part of them being characterized by significant amounts of swelling layers (I-S R0). The δD values of the clay fractions are fairly constant around −50 ± 10‰, but δ 18O values of the same clay fractions display a wide range from 8‰ to 18‰ (SMOW). The study of the size fractions between 2 and 0.2 μm reveals a correlation between K-Ar ages and δ 18O values, which cannot be related to a change in the relative amounts of clay minerals. Deep fractures (at depths of 570 and 923 m) are characterized by δ 18O values around 10.3 ± 0.4‰ SMOW and old ages ranging from 253 to 272 Ma. The finest fractions (<0.2 μm) of clays located at shallow level (<300 m) beneath the paleo-surface yield the highest δ 18O values (15.7–18.2‰) and the youngest K-Ar dates (188 to 198 Ma). These dates are likely to record the extensional episode and thermal anomaly related to the rifting of central Atlantic Ocean (c. 190 Ma). The other important thermal/extensional episode which affected the Aquitaine Basin, namely the opening of the Gascogne gulf at c. 120 Ma, is not detected by the K-Ar method on the clay fractions. We believe that resetting of clay-type K-Ar ages linked to recrystallization was favoured in the upper part of the basement where the ancient (Hercynian) clay minerals were destabilized by subaerial low-temperature alteration during Permo-Triassic times. From a methodologic point of view, the analytical characterization of several size fractions of clays from reactivated fractures, using both stable isotope geochemistry and K-Ar isotope geochemistry, can be considered as a powerful tool for dating fluid events when no suitable material for conventional methods is available.

The European Tertiary Neritiliidae (Mollusca, Gastropoda, Neritopsina): indicators of tropical submarine cave environments and freshwater faunas

The oldest freshwater neritiliid, Neritilia bisinuata, is described from the Middle Eocene of the Loire Basin. Another European species, N. neritinoides, ranging from the Lower Oligocene to Lower Miocene (Upper Burdigalian) is recognized; its habitat appears to have been freshwater, but very close to the sea. Two new marine neritiliid species from the Aquitaine Basin are described: Bourdieria favia sp. nov. from the Upper Oligocene and Pisulinella aucoini sp. nov. from the Lower Miocene. A third undescribed species from the Lower Miocene is referred to the same family and related to Pisulinella. The Oligocene species has a strong spiral sculpture, a character completely absent in previously known neritiliid species. The genus Agapilia, founded on juvenile N. neritinoides and adult Vitta picta, appears to be a junior synonym of the genus Vitta. The associated occurrence of shells of the families Neritiliidae, Neritopsidae and Pickworthiidae (well-known inhabitants of Indo-West Pacific submarine caves) at Peyrère suggest the first occurrence of a characteristic assemblage of dark submarine caves during the Oligocene. Both factorial analysis and relative abundance show that at Peyrère these families are associated with other cryptic fossils (various gastropods, bivalves, Brachiopoda, corals, Annelida). However, there are indications of other submarine cave assemblages in various Cenozoic deposits from the Palaeocene to the middle Miocene.

Morphométrie comparée de la première molaire inférieure du campagnol Microtus (Terricola) Vaufreyi tautavelensis (Rodentia, Arvicolidae) du gisement Pléistocène moyen de I'Arago (Pyrénées, France) et inférences paléoclimatiques

The morphometrical study of the first lower molar of three populations of vole Microtus (Terncola) vaufreyi tautavelensis (Rodentia, Arvicohdae) from the middle Pleistocene cave of l'Arago (Pyrenees, France) has shown a morphological change between the cold and dry isotopic stage 14 and the temperate isotopic stage 13, followed by a return to a morphology in the cold and dry isotopic stage 12 which is similar to that observed at the isotopic stage 14 A possible genetic contact with populations of the sub-species M (T) vaufreyi vaufreyi coming from the Aquitaine Basin or the western part of the Pyrenees, seems to be the must probable hypothesis for explaining this morphological evolution.

Le gisement « Purbeckien » de vertébrés de Cherves-de-Cognac, Charente (SW France) : nouvelles données biostratigraphiques

‘Purbeckian’ vertebrate deposit from Cherves-de-Cognac (SW France): new biostratigraphical data. The Purbeckian facies of the Aquitaine Basin northern margin outcrop has a thickness of about 30 m in the gypsum quarry of Champblanc, Cherves-de-Cognac, located about 10 km northeast of Cognac (Charente, SW France). Two lithological units have been identified. The basal unit (U1) is an alternation of gypsum and finely bedded black marls sometimes stromatolitic. The upper unit (U2) is a limestone-marl alternation, more or less fossiliferous. In the upper part of the unit, a one meter thick level has yielded a rich vertebrate fauna. A micropaleontological analysis of these levels, until now considered as Uppermost Jurassic age, has provided rich and diversified associations of brackish and fresh-water ostracodes and charophytes allowing them to be dated as Berriasian and to be related with the lower part of the Middle Purbeck of southern England. To cite this article: J.-P. Colin et al., C. R. Palevol 3 (2003).

High-resolution characterization and integrated study of a reservoir formation: the danian carbonate platform in the Aquitaine Basin (France)

This paper provides an example of an integrated multi-scale study of a carbonate reservoir. The Danian Lower R2 carbonate reservoir is located in the South of the Aquitaine Basin (France) and represents a potential underground gas storage site for Gaz de France. The Danian Lower R2 reservoir was deposited as a prograding carbonate platform bordered by a reef barrier. The effects of sedimentary and diagenetic events on the reservoir properties, particularly dolomitization, were evaluated. In this study, the reservoir quality has been assessed by seismic analyses at the basin scale, by log-analysis at the reservoir scale, by petrographic methods and by petrophysical tools at the pore-core scale. Two dolomitization stages, separated by a compaction event with associated fracturing and stylolites, have been identified. These diagenetic events have significantly improved the Lower R2 carbonate reservoir properties. It is demonstrated that the reservoir quality is mainly controlled by the pore-geometry, which is determined by various diagenetic processes. The permeability values of the reservoir range over 4 orders of magnitude, from 0.1 to 5600 mD and the porosity values range between 2 and 42%. Reservoir unit 4 (a karstic dolomite) shows the best reservoir properties with average porosity values ranging between 11.1% and 19.3% and an average permeability ranging between 379 and 766 mD. Reservoir unit 2 (a fine-grained limestone) shows the worst reservoir properties. The cementation factors range from 1.68 to 2.48. The dolomitic crystal carbonate texture (mainly units 3 and 4) shows the highest value of the cementation factor (1.98–2.48) and formation factor (9.54–36.97), which is due to its high degree of cementation. The saturation exponents vary between 1.2 and 3.4. Using these experimental electrical parameters and the resistivity laterolog tool we predicted the water saturation in the various reservoir units. The permeability was predicted by combining the formation factor with the micro-geometric characteristic length. The best fit is obtained with the Katz and Thompson's model and for a constant of 1/171.

Seismic evidence of Alpine crustal thickening and wedging from the western Pyrenees to the Cantabrian Mountains (north Iberia)

The Alpine collision between the Iberian and European plates resulted in a complex crustal structure beneath the northern Iberian Peninsula, as revealed from a new set of seismic refraction/wide‐angle reflection profiles. The study area is characterized by two major E‐W ranges, the Cantabrian Mountains and the Pyrenees, which are relayed to the south by the Iberian Chain. Important variations in crustal thickness and velocity distribution are found in a 560‐km‐long E‐W transect. In contrast to the typical 30‐ to 32‐km‐thick European Variscan crust of the western end of the profile, a continuous Alpine crustal root is evidenced from the Cantabrian Mountains to the central Pyrenees, with a Moho depth of 46–48 km, locally rising to ∼40 km depth in between, beneath the Basque‐Cantabrian Basin. Another outstanding feature is the inferred presence of high velocities of 6.40–6.75 km/s at midcrustal depths, which can be associated with portions of a lower crustal wedge from the northern (European) domain indenting the southern (Iberian) crust during the Alpine stage of compression. This indentation produces the delamination of the Iberian crust, with northward underthrusting of its lower half and the consequent crustal thickening. The indenting wedge has a discontinuous presence along the longitudinal section, as it was controlled and/or affected by N‐S to NE‐SW structures. Further evidence of the northward subduction of the Iberian plate is provided by another profile toward the Aquitaine Basin, while a N‐S profile across the Iberian Chain reveals an Alpine midcrustal thickening beneath this belt with Moho depths of ∼42 km.

Microbialite morphology, structure and growth: a model of the Upper Jurassic reefs of the Chay Peninsula (Western France)

During the Early Kimmeridgian, the northern margin of the Aquitaine Basin (Western France) is characterised by a significant development of coral reefs. The reef formation of the Chay Peninsula comprises two main reefal units, in which the microbial structures can contribute up to 70% of framework. The microbial crusts, which played an important role in the stabilisation and growth of the reef body, show the characteristic clotted aspect of thrombolitic microbialites. Corals are the main skeletal components of the build-ups. The bioconstructions of the Chay area are thus classified as coral-thrombolite reefs. Four main morpho-structural types of microbial crusts are distinguished: (1) pseudostalactitic microbialites on the roof of intra-reef palaeocaves; (2) mamillated microbialites, found either on the undersides or on the flanks of the bioherms; (3) reticular microbialites in marginal parts of the reefs and between adjacent bioconstructed units; and (4) interstitial microbialites in voids of bioclastic deposits. Thrombolitic crusts developed on various substrates such as corals, bivalves, or bioclasts. The thrombolites formed a dense, clotted and/or micropeloidal microbial framework, in which macro- and micro-encrusters also occur. Variations in accumulation rate strongly influenced the reef morphology, in particular its relief above the sediment surface. The coalescence of the coral-microbialite patches created numerous intra-reef cavities of metre-scale dimensions. The direction of microbial growth, which defined the macroscopic microbialite forms, strongly depended on the position within the reef framework but was also controlled by water energy, accumulation rate and light availability.

Compléments à l'étude des otolithes de poissons rupeliens d'aquitaine méridionale (Sud ouest de la France)

Otolith studies at the Lahosse, Parguie de Couston locality revealed the presence of 35 teleost taxa of which 27 were previously unknown from the Aquitaine Basin. Three of those, Dermatopsis chalossiana, Fowleria coustonis and “genus Pempheridarum” chicot, represent new species. The successive associations are indicative for a very nearshore neritic envíronment, but with normal salinity. The association of the lower levels are dominated by apogonids, but these become less abundant towards the upper part of the section. The abundance of the gobiids increases from 32 % in the lowermost sample to 95 % in the uppermost one. Comparison with deposits outside the Aquitaine Basin essentially reveals similarities of facies rather than stratigraphic correlations. This is best exemplified by the fact that the contemporaneous deposits of Lahosse and those of the southern North Sea Basin provide fundamentally different associations. From a biogeographic point of view, one can state that the fauna of the Rupelian of Aquitaine has more close Indo-Pacific than Atlantic affinities.

Otolithes de poissons du paléocanyon de saubrigues (chattien à langhien), aquitaine méridionale, France

The main interest of the otoliths collected in the Palaeocanyon of Saubrigues lies in the fact that a succession of five fish faunas from a significantly deeper environment than other places in the Aquitaine Basin can be studied there, in the same geographic area and in a sedimentary environment that remains almost constant throughout the considered time interval. A total of 170 taxa among which 109 nominal species have been identified from sediments filling the paleocanyon. Eight species are new : Halosaurus orthensis, “genus Gonostomatidarum” hoffmani, Polyipnus latus, Vinciguerria angulosa, Vinciguerria brevis, Merluccius abreviatus, Peristedion jeanbegui and Parascombrops epigonoides. The succession of fish biota in the paleocanyon is characterized by a major faunal break at the Chattian-Aquitanian boundary. Nineteen (= 45 %) of the 42 Chattian species disappear, and among the 23 species that cross the boundary, seven also disappear before the beginning of the late Burdigalian. At the beginning of the Aquitanian, a major faunal renovation is observed : 16 species appear in the palaeocanyon, which represent 59 % of a total of 27 Aquitanian species. In the succeeding levels from Early Burdigalian till Langhian, a gradual appearance of the typical Miocene fauna is observed.

Fluid transfers at a basement/cover interface: Part II. Large-scale introduction of chlorine into the basement by Mesozoic basinal brines

Significant fracture and porosity sealing characterizes the sedimentary cover-basement interface in the northwestern margin of the Aquitaine Basin (France). Dolomite and calcite (and sometimes fluorite, barite and quartz) constitute most of the fracture fillings. They contain primary inclusions of brines having chlorinities in the range of 3.3 to 5.5 mol Cl/kg solution, with total homogenization temperatures in between 65 and 130 °C for quartz and slightly lower for dolomite, barite, fluorite and calcite. Crush-leach analyses indicate that brines are characterized by Na/K ratios of 5 to 40, Na/Li ratios of 20 to 530, and Cl/Br ratios of 200 to 1000, which are rather typical of deep basinal brines. The fluid δ 18O signature is estimated to be ≈6.6±1.8‰ SMOW for a crystallization temperature of 100±20 °C between 80 and 120 °C and the δD value is −30±10‰ SMOW. The fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the Aquitaine Basin, which migrated along the sediment cover/basement interface which is characterized by high permeabilities below the Toarcian shales. The sealing is likely to be linked to the mixing of the brines with dilute ascending, hot waters. These dilute waters infiltrated from emerged zones, convected and heated at depth, reaching temperatures of 100 °C (up to 150 °C on the basis of cation geothermometry). Extensional activity, of probable Cretaceous age, related to the Gascogne Gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement/cover interface all along the margins of the French Massif Central. These processes are large scale as shown by the similarities of mineral sequences, fluid types and general features of most of the F–Ba–Pb–Zn deposits located at the basement–sedimentary cover interface. The mass transfer of Cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity. This probably explains the significant chlorine concentrations of the present-day fluids recovered in the granitoid aquifer.

Use of morphostructural analysis to show halokinesis during Mio-Plio-Quaternary in the South-West part of Aquitain Basin

In the South Aquitain sector, salt bodies of varying sizes present two geographical gradients. The first gradient, south to north, associated with the proximity of the Pyrenees shows a decreasing deformation of the structures towards the north. The second gradient explains their increasing depth of burial from the west (extrusive structures) to the east (intrusive structures). This organization has been studied from the western sector (Tercis-Benesse and Bastennes-Louer) to the eastern sector (Viella-Labarthete and Nogaro-Lussagnet). Other more modest structures, revealed by hydrographical anomalies, illustrate halokinetic events during the Quaternary. Then the detailed study of the Geaune dome shows a neotectonic phenomenon dating from the Mio-Pliocene. The radial annular drainage pattern of this structure is guided by recurrent faulting during the Quaternary. Thus the halokinetic dynamics consist in three phases: deformation of the diapirs (overthrusts) during the Oligocene, resuming of halokinesis during the middle of the Miocene and recurrent faulting during the Riss. A model of geomorphological evolution of the domes is then proposed. The first phase (stages of positive relief) is characterized by the centrifugal drainage pattern of the dome. The second phase (stages of inverted relief) is distinguished by the erosion of the center of the structure, by an inversion of the drainage pattern and by the sedimentary accretion in the central depression.

Un nouveau gisement à ambre insectifère et à végétaux (Albien terminal probable) : Archingeay (Charente-Maritime, France)

A layer of clay interbedded in sandstone, which age is likely uppermost Albian, yielded a new deposit with amber and fossil plants in Charente-Maritime (south-west France). A survey of the arthropods found in amber, the xylologic and palynologic determinations and the sedimentologic study are in progress. We already have datas to propose a palaeoenvironmental reconstruction of the coast of the northern Aquitain basin at the end of lower Cretaceous : an estuarine area under warm and wet climate.

La tectonique pyrénéenne à l'Oligocène : une phase majeure de déformation en compression méconnue du Bassin aquitain (France)

Oligocene period is well known for its episode of western European rifting. A biostratigraphic and palaeoecologic analysis has been made on the many drilling samples of the Aquitaine basin. This analysis permits to highlight a phase of compressive deformation from Oligocene. During Rupelian time, folds, unknown before, strongly structure the south of the Aquitaine basin. Meanwhile, the Basque and Corbieres nappes are thrusted over the foreland. The displacement of 40 km towards the north-north-west of the Peyrehorade unit (in the Basque nappes) is proven by the shifting of an Ilerdian isopic zone, recognized by drillholes.

Concavinae (Cirripedia, Thoracica) from the Lower and Middle Miocene of the Aquitaine Basin (France), with the description of a new genus and a new species

Concavinae (Cirripedia, Thoracica) from the Lower and Middle Miocene of the Aquitaine Basin (France), with the description of a new genus and a new species

Une faune inédite de coraux scléractiniaires dans le gisement chattien d'Escornebéou (Landes, SW France) ; stratigraphie, systématique et paléoécologie

The Escornebéou locality (Landes, SW Aquitaine Basin) is a reference site for the marine Chattian of atlantic tropical type. The abundant microorganisms allowed these outcrops to be allocated to the classic biozonations, after numerous historical controversies about their age. A fauna of Scleractinian corals has been discovered there for the first time, mainly from the ‘Le Bois’ site. About 25 taxa are listed and their systematics is analysed. They split up into 18 genera and subgenera, with stratigraphically a cachet intermediate between the Oligocene and Miocene faunas. There are as many solitary species as colonial ones (mainly hermatypics). The presence of numerous reefal genera confirms the tropical (to subtropical) paleoclimate, as well as the data from the other present organisms. Concerning the coarse zoogene calcareous deposits from ‘Le Bois’ (where the coral colonies are massive), the environment was shallow, fairly turbulent and under the effect of currents and waves. A subreefal facies locally developed (with mixed hermatypic and ahermatypic corals), belonging to the paleogeographic domain of shoal-type or barrier-type bioclastic limestones, as recognized elsewhere. At Escornebéou, the outcropping sequence is mainly marly to fine-grained sandy-marly (including such coarse calcareous intercalations), as at Lespeyrères, where few corals have also been found. These calm environments, of sheltered marine mud flat or seaweed type, were not very favourable to coral growth.

Opisthobranch molluscs from the Tertiary of the Aquitaine Basin (south-western France), with descriptions of seven new species and a new genus

An exceptionally well-preserved collection of Tertiary opisthobranch molluscs from the Aquitaine Basin, France, includes species of the order Notaspidea [Umbraculum sanctipaulensis sp. nov., Tylodina perversa (Gmelin), Spiricella unguiculus Rang and Des Moulins, Berthella aquitaniensis sp. nov., Berthella ateles sp. nov.], of the order Anaspidea [Akera cf. bullata Mu¨ller, Floribella corrugata (Cossmann), Floribella cossmanni sp. nov., Floribella rozieri sp. nov., Limondinia ornata gen. et sp. nov.] and of the order Sacoglossa [Volvatella faviae sp. nov.]. BerthellaaquitaniensisB. atelesV. faviae are the first fossil records of the families Volvatellidae and Pleurobranchidae. Floribella plicifera (Cossmann) and F.corrugata, originally assigned to the genus Philine, belong to the genus Floribella and constitute the oldest records of this genus. The fossil evidence indicates that in Umbraculum laudunensis and U. sanctipaulensis the shell probably covered most of the animal, whereas in the Recent U. umbraculum the shell only covers the central portion of the body. Tylodina perversa could be an old species that appeared during the early Miocene, more than 21 Ma. The Recent shells of Akera bullata are indistinguishable from fossils as old as the mid Eocene, but it may be biologically unrealistic to consider them to be the same species. The European species of Floribella evolved from the bullomorph shells of the early Eocene forms to the elongate shells of the early Miocene. The genus Volvatella is another example of marine tropical disjoint distributions and an excellent ecological indicator.

Haynesina germanica (Ehrenberg), Elphidium excavatum (terquem) L.S. et Porosononion granosum (d'orbigny), espèces margino-littorales de Foraminifères d'aquitaine centrale (So France) au miocène moyen (langhien). Le problème d' elphidium lidoense cushman

In the Middle Miocene (Langhian) of the Central Aquitaine Basin a margino-littoral microfauna of Foraminifera has been observed. We have mainly studied the representatives of Haynesina germanica, Elphidium excavatum and its formae and Porosononion granosum as well, basing our re-description on the original diagnosis. Moreover, we could solve the problem of the disponibility of Elphidium lidoense Cushman. The discovery of this peculiar microfauna, very close to the recent one, points out the similarity between margino-littoral Langhian and Recent environments.