Oxfordian Deposits Research Articles

Stratigraphic Modelling of the Lower/Middle Oxfordian (Upper Jurassic) Outer Ramp Deposits from the NE Paris Basin (France)

We investigate herein the lateral and vertical lithological heterogeneities of the Lower/Middle Oxfordian deposits (“Terrain à Chailles” and “Marnes des Eparges” formations) in the north-eastern Paris Basin. This new detailed stratigraphic framework documents the evolution at high resolution of an outer ramp based on regional correlations in order to constrain the evolution of petrological properties between the clayey “Argiles de la Woëvre” Formation and the more calcareous “Marnes et Calcaires à Coraux de Foug Formation. The “Argiles de la Woëvre” Formation is targeted for the deep storage of nuclear waste in north-eastern France. Nine wells are correlated over the “Zone of Interest for Further Research” (ZIRA), defined by the French agency for radioactive waste management (Andra), with a resolution of 0.5–1.0 m. The architecture and the age control of these formations have been refined, revealing that the “Terrain à Chailles” Formation is characterised by a regular slightly inclined sedimentation gently deeping in the SW direction and shows a lithological evolution from silty claystones to an increased occurrence of its calcareous content towards the top (Lower Oxfordian, uppermost mariae and cordatum ammonite zones). The above “Marnes des Eparges” Formation, characterised by claystone limestone alternations, is assigned to the Middle Oxfordian (plicatilis ammonite zone), deposited during a slightly enhanced subsidence phase in the SE part of the basin and documented and associated with onlaps geometries on the more proximal areas. However, this change in geometry does not affect petrological properties over ZIRA, as this is not accompanied by lithological changes. The environmental factors controlling petrological heterogeneities over ZIRA are also discussed. The stepwise increase in the carbonate content and the decrease in the detrital content towards the Lower to Middle Oxfordian deposits was likely triggered by a climate change towards drier conditions, modulated by sea level changes on a ramp morphology. A major condensation phase encompassing most of the Lower Oxfordian cordatum ammonite zone is also highlighted. The occurrence of a maximum regressive surface associated with gentle slope topography is a probable trigger for condensation. Changes in geometries are, however, associated with the activity of the Metz Fault, which potentially had an influence on the subsidence rates of the basin at that time.

Facies analysis and depositional model for the Oxfordian Hanifa Formation, Central Saudi Arabia

The Jurassic was a time for major global changes in climate, tectonics, and oceanography, reflected in the southern Neo-Tethys Ocean by a distinct transition from carbonate-poor to carbonate-dominated sedimentation. To better constrain the effect of this turning point in the Late Jurassic, key outcrops of Oxfordian deposits of the Arabian Plate were investigated through detailed sedimentologic analysis. High-resolution (centimeter-scale) description and analysis of eight outcropping sections with a cumulative thickness of 461 m through the Oxfordian Hanifa Formation along a N–S 535 km-long transect in central Saudi Arabia are used to develop a comprehensive conceptual depositional evolution through time. Nine sedimentary lithofacies are interpreted and grouped into four facies associations. These associations include: I) outer-ramp association (FA1), II) mid-ramp association (FA2), III) inner-ramp grainy-facies association (FA3), and VI) inner-ramp reefal association (FA4). The lithofacies succession distinguishes two depositional phases, a middle Oxfordian homoclinal ramp (Phase 1) that corresponds to the Hawtah Member, and a late Oxfordian reef-bearing carbonate ramp (Phase 2) that corresponds to the Ulayyah Member. After being restricted to the high latitudes in the northern Neo-Tethys during early and middle Oxfordian ages, the carbonate ramp evolution within the Hanifa Formation reflects the expansion of scleractinian coral reefs over the southern Neo-Tethys passive margin in the late Oxfordian. However, the distribution of the corals in the Arabian Plate is mainly controlled by water salinity and siliciclastic input; they are absent northward due to hypersalinity and southward due to siliciclastic input. Furthermore, the differential subsidence and the resulting uneven topography, in addition to the eustatic sea level variation during the Oxfordian age, controls the distribution of different depositional styles over the Arabian Plate (homoclinal ramp, distally-steepened ramp, rimed shelf, and intrashelf basin).

Benthic Foraminifera from the Saïda clay formation (Djebel Brame, northwestern Algeria) biostratigraphy and paleoecology

The analysis of benthic foraminiferal assemblages was performed in the Oxfordian deposits of the “Argile de Saida” in northwestern Algeria. This formation consists mainly of clay and sandstone alternations of the Upper Jurassic. It is located in the western part of the Tlemcenian domain. The first results of the micropaleontological study of Djebel Brame indicated that the microfauna of Foraminifera was quite original and widely abundant during that period. In addition, their biostratigraphic distribution exhibited three microfaunal associations, largely dominated by Nodosariidae. These results also revealed the renewal of the assemblage composition and allowed identifying several species of biostratigraphic divisions which were found consistent with those established for the ammonites. In addition, the palaeoenvironmental interpretations were based on the spatio-temporal distribution of benthic foraminiferal associations with hyaline and agglutinated tests. Besides, the geochemical analyses (calcimetry) reflected the basin infill during the Late Oxfordian.

Sequence stratigraphy of the Upper Jurassic mixed siliciclastic-carbonate deposits in the North German Basin (Lower Saxony, Hildesheimer Wald)

The Wendhausen-6 core, drilled in the Hildesheimer Wald, 30 km SE of Hannover, provides an insight into the Oxfordian deposits of the North German Basin consisting of the Ornatenton, Heersum, and Korallenoolith formations. Eight facies are recognized based on the different fossil combinations, sedimentary structures, and the carbonate content. A facies model of a mixture of a deltaic system and a carbonate ramp is presented based on the interpretation of these facies, which helps the understanding of the facies and sequence stratigraphic evolution in the mixed system in the North German Basin and could be applied to other shallow-water mixed depositional systems. Sequences of three hierarchies are delimited. Small-scale sequences are defined by the changes in components, grain size, and the vertical facies stacking patterns. Medium-scale sequences are bounded by distinctive exposure surfaces. These surfaces are characterized either by the enrichment of iron minerals or by irregular base of the lowstand channel-fill sandstones overlying on them. Large-scale sequences are derived from the facies proportion statistics of each medium-scale sequence. The similar trend between the regional sea-level curve and the facies statistic curve implies that sea-level fluctuations have a great control on the large-scale sequence evolution during the Oxfordian age. Sequence stratigraphic correlation was achieved at the medium-scale sequence level, and four surfaces of Oxfordian age were correlated across the North German Basin.

Hydrogeochemistry of the authigenic mineral-forming processes (a case study of Oxfordian deposits in the Ob-Irtysh interfluve)

Results of the pioneering numerical physicochemical modeling of interactions in the water – rock system on the example of Oxfordian deposits in southern regions of the Ob-Irtysh interfluve (southeastern regions of Western Siberia) are presented.It has been established that, despite the groundwaters having low salinity (up to 46 g/dm3) of and their persistent interactions with rocks (during tens, or probably hundreds of millions of years), they practically have no equilibrium with primary (endogenous) minerals: albite, anortite, microcline.At the same time, groundwater is in equilibrium with micaceous minerals, Ca-, Na - and Mg-montmorillonites, kaolinite, Mg-chlorite. There is always a carbonate barrier in the way of groundwater attaining an equilibrium with primary aluminosilicate minerals. As a result of the detailed petrographic studies, the genetic series of authigenic minerals of the diagenetic and catagenetic phases were established in the studied silty-sandy rocks. Relict diagenetic minerals are represented by glauconite, pyrite, siderite, calcite of the first generation of precipitation, kaolinite, anatase and leucoxene. Catagenetic minerals are considerably dominated by calcite of the second and third generations of precipitation, quartz, kaolinite, whereas siderite, chlorite, albite, dolomite are developed in minor amounts. The results of petrographic studies have corroborated the thermodynamic calculations.

Middle to Late Jurassic carbonate-biosiliceous sedimentation and palaeoenvironment in the Tethyan Fatricum Domain, Krížna Nappe, Tatra Mts, Western Carpathians

The Jurassic of the Alpine-Mediterranean Tethys was characterized by the formation of several interconnected basins, which underwent gradual deepening and oceanization. Sedimentation in each basin was influenced by a specific set of interrelated factors, such as tectonic activity, seawater circulation, climate, chemistry and trophic state of seawater as well as evolutionary changes of the marine biota. This paper deals with the Fatricum Domain (Central Carpathians, Poland and Slovakia), which in the Jurassic was a pull-apart basin on a thinned continental crust. The sedimentation history of this domain during the Bajocian–Tithonian and its governing factors have been revealed. Facies analysis of the Bajocian–Oxfordian deposits evidences considerable relief of the basin-floor topography. Deposits in the Western Tatra Mts represent sedimentation on a submarine intrabasinal high, whereas the coeval deposits of the eastern part of the Tatra Mts accumulated in a deeper basin. The basin succession began with Bajocian bioturbated “spotted” limestones and siliciclastic mudstones (Fleckenmergel facies). These were succeeded by uppermost Bajocian – middle Bathonian grey nodular limestones, affected by synsedimentary gravitational bulk creep. The coeval deposits of the intrabasinal high are represented by well-washed Bositra -crinoidal limestones with condensed horizons. Uniform radiolarite sedimentation commenced in the late Bathonian and persisted until the early late Kimmeridgian. The basal ribbon radiolarites (upper Bathonian – lower Oxfordian), which consist of alternating chert beds and shale partings, are a record of seawater eutrophication, a related crisis in carbonate production and the rise of the CCD, which collectively resulted in biosiliceous sedimentation. The overlying calcareous radiolarites (middle Oxfordian – lowermost upper Kimmeridgian) marked a gradual return to carbonate sedimentation. The return of conditions that were favourable for carbonate sedimentation took place in the late Kimmeridgian, when the red nodular limestones were deposited. They are partly replaced by basinal platy limestones (uppermost Kimmeridgian – Tithonian) in the Western Tatra Mts. This lateral variation in facies reflects a change in the sedimentary conditions governed by a bathymetric reversal of the seafloor configuration, attributed to a further stage in the pull-apart transcurrent tectonics of the Fatricum Domain.

Ostracod Analysis of Callovian and Lower Oxfordian Deposits of the Mikhailovtsement Section (Ryazan Region): Methods and Results

Various methods of ostracod analysis with reference to paleobathymetric and paleotemperature reconstruction are considered in detail, using Callovian–Lower Oxfordian ostracod assemblages from the Mikhailovtsement reference section (Ryazan Region) as an example. Based on generalization of the data obtained by different methods, seven transgressive–regressive events are reconstructed, five of which had a pan-European scale and were accompanied by the intensified boreal effect. For the Upper Callovian of the East European Platform, ostracod index species of paleotemperatures, paleoeutrophication, and paleodepths on the upper subtidal depths are recognized for the first time.

The Structure and Formation Conditions of the Callovian–Oxfordian Deposits of Sudak Bay (Crimea)

The composition and origin of the Callovian–Oxfordian deposits of the Sudak Bay were characterized on the basis of the generalization and analysis of our own results, as well as published and unpublished data. The botanical future was first implemented for the geological mapping of the Oxfordian deposits.

COMPOSITION AND ORIGIN OF CALLOVIAN-OXFORDIAN DEPOSITS OF THE SUDAK BAY (CRIMEA)

Composition and origin of Callovian–Oxfordian deposits of the Sudak Bay based upon generalizations of our own results and analysis of published and unpublished data were specified. A botanic feature for geological prospecting of Oxfordian limestones was used for the first time.

The earliest known titanosauriform sauropod dinosaur and the evolution of Brachiosauridae.

Brachiosauridae is a clade of titanosauriform sauropod dinosaurs that includes the well-known Late Jurassic taxa Brachiosaurus and Giraffatitan. However, there is disagreement over the brachiosaurid affinities of most other taxa, and little consensus regarding the clade’s composition or inter-relationships. An unnamed partial sauropod skeleton was collected from middle–late Oxfordian (early Late Jurassic) deposits in Damparis, in the Jura department of eastern France, in 1934. Since its brief description in 1943, this specimen has been informally known in the literature as the ‘Damparis sauropod’ and ‘French Bothriospondylus’, and has been considered a brachiosaurid by most authors. If correctly identified, this would make the specimen the earliest known titanosauriform. Coupled with its relatively complete nature and the rarity of Oxfordian sauropod remains in general, this is an important specimen for understanding the early evolution of Titanosauriformes. Full preparation and description of this specimen, known from teeth, vertebrae and most of the appendicular skeleton of a single individual, recognises it as a distinct taxon: Vouivria damparisensis gen. et sp. nov. Phylogenetic analysis of a data matrix comprising 77 taxa (including all putative brachiosaurids) scored for 416 characters recovers a fairly well resolved Brachiosauridae. Vouivria is a basal brachiosaurid, confirming its status as the stratigraphically oldest known titanosauriform. Brachiosauridae consists of a paraphyletic array of Late Jurassic forms, with Europasaurus, Vouivria and Brachiosaurus recovered as successively more nested genera that lie outside of a clade comprising (Giraffatitan + Sonorasaurus) + (Lusotitan + (Cedarosaurus + Venenosaurus)). Abydosaurus forms an unresolved polytomy with the latter five taxa. The Early Cretaceous South American sauropod Padillasaurus was previously regarded as a brachiosaurid, but is here placed within Somphospondyli. A recent study contended that a number of characters used in a previous iteration of this data matrix are ‘biologically related’, and thus should be excluded from phylogenetic analysis. We demonstrate that almost all of these characters show variation between taxa, and implementation of sensitivity analyses, in which these characters are excluded, has no effect on tree topology or resolution. We argue that where there is morphological variation, this should be captured, rather than ignored. Unambiguous brachiosaurid remains are known only from the USA, western Europe and Africa, and the clade spanned the Late Jurassic through to the late Albian/early Cenomanian, with the last known occurrences all from the USA. Regardless of whether their absence from the Cretaceous of Europe, as well as other regions entirely, reflects regional extinctions and genuine absences, or sampling artefacts, brachiosaurids appear to have become globally extinct by the earliest Late Cretaceous.

First record of Late Callovian to Early Oxfordian heteromorph ammonites

The outstanding discovery of two heteromorph ammonites in Late Callovian and Early Oxfordian deposits, where such ammonites were deemed absent, substantially reduce the interval without heteromorph ammonite known into the Jurassic. A new species is described for the Early Oxfordian: Acuariceras acucostis sp. nov.; the Late Callovian Parapatoceras cf. tuberculatum is also studied. These latter expands our knowledge of the latest Parapatoceratinae and complete their stratigraphic distribution. The evolution of ornamentation between A. acuarius/Paracuariceras incisum and A. acucostis sp. nov., from which it is derived, tends toward a net reinforcement of the ribs at least on the body chamber. Without the preservation of the suture lines however, it is difficult to know the relationships maintained between the new species and the genera Acuariceras and Paracuariceras. It is not excluded that these two genera, which are distinguished only on the basis of relatively discrete suturing criteria, could be synonymous.

About the contact pads of Gryphaea Dilatata Sowerby (Dysodonta, Bivalvia) from the Oxfordian deposits of the Nizhnie Mnevniki (Moscow)

About the contact pads of Gryphaea Dilatata Sowerby (Dysodonta, Bivalvia) from the Oxfordian deposits of the Nizhnie Mnevniki (Moscow)

STRATOTYPE SECTIONS OF THE OXFORDIAN OF UKRAINIAN PRECARPATHIANS

The results of complex study of the Oxfordian deposits in Ukrainian Precarpathian are presented. According to today stratigraphic scheme, the Oxfordian deposits in the territory of Carpathian Foredeep are represented by reefogenic complex, in which Boniv, Rudky and Gorodok suites were allocated. Only Boniv suite stratotype was described by author (V.G. Dulub, 1995). In the results of our investigations the sratotypes of Rudky and Gorodok suites are determined and consistently described, and the extended stratotype of Boniv suite is specified. Section opened by the well Pidluby-105 in interval 922,5–1002,8 м is proposed as a stratotype of the Rudky suite. The stratotype of Boniv suite was opened by the well South Kochanivka-1 and by author was determined in interval 2770–2952 м. According by new data the suite is determined in interval 2720–2952 м. For the Gorodok suite is proposed the folding stratotype, which is composed of the sections opened by wells (from below to up): Dashava-405 (2180–2150 м), Rava-Ruska-2 (1189–1165 м), South Grynivka-2 (3330–3298 м), Didushychy-1 (2627–2597 м), Rudky-120 (1600–1570 м), Verchany-1 (1988–1960 м). Lithological and paleontological characteristic of these sections are given.

Comparison of benthic foraminifera and geochemical proxies in shelf deposits from the Upper Jurassic of the Prebetic (southern Spain)

Comparison of the stratigraphic distribution of major and trace elements, used as proxies for palaeoproductivity and redox conditions, and benthic foraminifera from Oxfordian shelf deposits of the External Prebetic (Betic Cordillera, South Spain) allows us to recognise two sedimentary cycles, both characterised by initial enhanced productivity and decreasing oxygen availability in the seabottom, and a subsequent decreasing productivity with a recovering in oxygenation during the second half of each cycle. Dysoxic conditions appear to coincide with maximums in marine surface productivity, thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation. The boundary between the two cycles is characterised by low contents of redox-sensitive elements and lower TOC content and Sr/Al, P/Ti, Ca/Al and Ba/Al ratios, indicating well oxygenated sea-bottom, lower productivity and lower organic matter accumulation. The geochemical proxies have also revealed as a valuable tool for interpreting the stratigraphic fluctuations of benthic foraminiferal assemblages, as well as for evaluating the palaeoecology of the main genera. Spirillina is adversely influenced by oxygen depletion independently of food availability. Ophthalmidium presents very good correspondence with palaeoproductivity fluctuations, and tolerated low oxygen levels in the sediment-water interface. Reophax was an opportunist that proliferated after adverse conditions when oxygenation and food availability were limiting factors. The variability in the microhabitat depth inside the sediment of Reophax favoured adaptation to adverse conditions. Lenticulina shows behaviour similar to Reophax. Finally, Ammobaculites shows a low degree of relation with the palaeoproductivity proxies, and is intolerant with respect to low oxygen values in shallow infaunal microhabitats

Tithonia oxfordiana, a new irregular echinoid associated with Jurassic seep deposits in south‐east France

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 distribution of calcareous nannofossils and foraminifers in the Callovian, Oxfordian, and Volgian deposits in the southwest of Moscow

The distribution of calcareous nannofossils and foraminifers occurring in the Callovian-Oxfordian deposits in the southwest of Moscow is studied. Nannoplankton-bearing beds and foraminiferal zones are distinguished. The Retecapsa incompta Beds correspond in range to the Ophthalmidium sagittum-Epistomina volgensis and Ophthalmidium strumosum-Lenticulina brestica foraminiferal zones as well as the lower part of Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria manivitae, Crepidolithus perforata, and Watznaueria fossacincta (lowermost part) beds span interval of the Epistomina uhligi-Lenticulina russiensis Zone. The Watznaueria fossacincta Beds are concurrent to the Lenticulina ponderosa-Flabellamina lidiae Zone of the foraminiferal scale.

Les ammonites du Callovien–Oxfordien des sondages Andra dans l'Est du bassin de Paris : synthèse biochronostratigraphique, intérêts paléoécologique et paléobiogéographique

The ammonites collected in nine deep bore-holes and two open wells made by ANDRA near Bure (Meuse Department, France) in the eastern Paris Basin have allowed the following: – a precise biochronostratigraphic calibration of the Callovian–Oxfordian clay-rich facies; – the correlation between the boreholes and wells by means of the ammonite biostratigraphic units that show an outstanding disparity in the sedimentary registration; – undertaking a palaeoecological and palaeobiogeographical investigation into the faunal associations; – highlighting their palaeoenvironmental and palaeogeographical applications. In the Middle Callovian–Middle Oxfordian interval, the following remarkable bio-chronostratigraphic elements are seen: – the position of the interpositum horizon (uppermost Middle Callovian, Coronatum Zone, Grossouvrei Subzone) and its importance for the localization of the Middle Callovian–Upper Callovian boundary; – the respective importance of the paucicostatum horizon (uppermost Upper Callovian, Lamberti Zone, Lamberti Subzone) and the thuouxensis horizon (lowermost Lower Oxfordian, Mariae Zone, Scarburgense Subzone) for the localization of the Callovian–Oxfordian boundary; – the validity of the woodhamense horizon based on the morphological variability of the corresponding species-index that corroborates its stratigraphic situation above the scarburgense horizon (Scarburgense Subzone, Mariae Zone, Early Oxfordian); – the consequences of the morphological variability of the successive species Cardioceras praemartini, C. alphacordatum, C. praecordatum and their selection as species-index for the three horizons of the Praecordatum Subzone (Mariae Zone, Early Oxfordian); – the difficulties of recognizing the Cordatum and Plicatilis Zones because of the scarcity, if not the total lack of characteristic ammonites of these units, which have consequences for the location of the Lower Oxfordian–Middle Oxfordian boundary. The correlations between bore-holes and wells underline that the intracratonic domain to which belongs the Paris Basin has been affected by an unceasing subsidence, which varied in both space and time from the Middle Callovian to the Middle Oxfordian. The subsidence seems to be stronger near the centre of the basin than near its margins, with a maximum activity taking place during the Lower Oxfordian, Mariae Zone, Scarburgense Subzone, woodhamense horizon. The palaeoecological interpretation of the faunal associations indicates a medium palaeodepth (lower offshore) in this eastern part of the Paris Basin, certainly a little more marked towards the centre than on its margins. If not considering the subsidence effects, the palaeodepth does not seem dissimilar to that of the southeastern basin of France. In comparison, the proximity of the former with the Tethyan oceanic domain allows us to deduce that variations of the ammonite assemblages may be related to the different modes of life of the collected taxa. Especially, if compared to the Ammonitina taxa, the selective distribution of the Phylloceratina and Lytoceratina is characteristic of open-sea distal platforms. From a palaeobiogeographical point of view, the Callovian–Oxfordian deposits of the eastern Paris Basin have recorded two boreal southward ammonite invasions: the Kosmoceratidae during the Middle–Upper Callovian, then the Cardioceratidae during the Upper Callovian and Lower Oxfordian. These invasions gave rise to heterogeneous biogeographic areas, which locate between the Boreal and Tethyan Provinces. Considered as transition areas, they are called Subboreal Province and Subtethyan Province; their ammonite associations are composite and their time and space ranges and extensions are variable. To cite this article: J. Thierry et al., C. R. Geoscience 338 (2006).

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.

TAPHONOMY OF AMMONITE ASSEMBLAGES FROM THE MIDDLE-UPPER OXFORDIAN (TRANSVERSARIUM? - BIFURCATUS ZONES) IN THE INTERNAL PREBETIC (BETIC CORDILLERA, SOUTHERN SPAIN): TAPHONIC POPULATIONS AND TAPHOFACIES TO SUPPORT ECOSTRATIGRAPHIC INTERPRETATIONS

The taphonomic analysis conducted on ammonoid assemblages has proven useful for palaeobiological and palaeoenvironmental reconstructions in upper Middle-to-lower Upper Oxfordian epicontinental deposits of the Internal Prebetic (southern Spain). Taphonic populations close to type I indicate the proximity, even coincidence, of life areas for neritic ammonites (i.e. parautochthonous assemblages). The relationships among preservation mode, shell size, within-bed position, corrasion, fragmentation, and epibionts (encrustment included), with lumpy-oncolitic and condensed & bioclasts-rich lumpy-oncolitic limestones allows us to typify two taphofacies. Taphofacies I shows higher values of mean shell size, corrasion, epibionts and encrustments, as well as a high number of specimens in quasi-horizontal settlement. The opposite characteristics serve to identify Taphofacies II. Taphonomic features, taphofacies and lithofacies combine in coherence with progressing third-order transgressive-to-highstand system-tract conditions and the resulting ecostratigraphic trends, which are registered by fluctuations in ammonite assemblages.

Palaeogeographic and stratigraphic distribution of mid-late Oxfordian foraminiferal assemblages in the Prebetic Zone (Betic Cordillera, Southern Spain)

Middle-Upper Oxfordian assemblages of foraminifera in the Prebetic Zone (Betic Cordillera, SE Spain) were analysed at the genus level to determine their composition, relative abundance, diversity, and dominance, as well as the size of the specimens. A relationship has been established between lithofacies, palaeogeography and composition of foraminiferal assemblages, the former two also determining the stratigraphic record of these microfossil assemblages. Two assemblages of foraminifera serve to identify relatively distal and proximal areas in the Prebetic shelf. The distal assemblage is characterized by higher diversity, specimens of greater size, and more abundant planktic and agglutinated forms. Benthic forms include Ophthalmidium, Epistomina and colonies of encrusting foraminifera. The proximal assemblage shows lower diversity, lower abundance of planktic forms, Epistomina and encrusting nubeculariids, and a greater abundance of spirillinids and Reofax. On the whole, planktic foraminifera decrease upwards in the studied succession, which, together with decreasing nodularity, could be related to system tract conditions previously proposed for Oxfordian deposits in the southern palaeomargin of Iberia.