Donnees biostratigraphiques nouvelles sur l'oxfordien et le kimmeridgien du djebel nador de tiaret (avant-pays tellien,algerie); consequences paleogeographiques

In “Djebel Nador de Tiaret” area two calcareous and marly intercalations situated in the upper part of the “Argiles de Faidja” formation contain ammonites of late Oxfordian (Planula zone) and lower Kimmeridgian (Hypselocyclum and Divisum zones). These new biostratigraphic data allow precise correlations with ammoniteless formations. So, the installation of the carbonate platform can be placed in upper Kimmeridgian in all the Western Algeria foreland. Moreover the development of the facies “Argiles de Saïda” into the upper part of lower Kimmeridgian, shows that the closing of the tlemcenian trough begins later in Djebel Nador than in the Ilemcen mountains.     

Sequence stratigraphy of Upper Jurassic deposits in the North German Basin (Lower Saxony,Süntel Mountains)

A core recovered in the North German Basin at the locality of Eulenflucht in the Süntel Mountains, 30 km SE of Hannover, Germany, is interpreted in terms of Oxfordian to Kimmeridgian sequence stratigraphy of this basin. Thirteen different facies are recognized which record the evolution of an outer ramp into a restricted hypersaline lagoon. Changes in grain size, variations in the amount of components, fluctuations of the matrix content and of the microscopic texture, as well as vertical lithofacies stacking patterns, were integrated to define small-scale sequences. Medium-scale sequences were identified by changes in facies combinations of the constituent small-scale sequences. Large-scale sequences were differentiated by facies proportion statistics in the distinct medium-scale sequences. This allows the complete sequence stratigraphic subdivision of the Oxfordian and Kimmeridgian succession to be interpreted. The stable carbon isotopic composition of bulk samples enables a correlation with chemostratigraphic records found elsewhere. This result is supported by an ostracod biostratigraphy that allows a chronostratigraphic assignment of the succession. The large-scale sequences were controlled by climate and local tectonic movements. It is proposed that a long-term shallowing trend during the Kimmeridgian time was induced by regional uplift.     

On the First Reliable Record of the Ichthyosaur <Emphasis Type="Italic">Ophthalmosaurus icenicus</Emphasis> Seeley in the Oxfordian–Kimmeridgian Beds of European Russia

An incomplete skeleton of the ichthyosaur Ophthalmosaurus icenicus Seeley, 1874 excavated in the Oxfordian–Kimmeridgian beds south of the town of Syzran (Samara Region) is described. Members of the genus Ophthalmosaurus are characterized by a unique combination of characters, most of which are well-pronounced in the specimen described here: the extracondylar area of the basioccipital is reduced, but still visible beyond the occipital condyle and has a well-pronounced ventral notch; the scapular shaft is mediolaterelly flattened; the humerus has three distal facets: the anterior facet is the smallest; the facet for the accessory preaxial element has a sharpened anterior margin; the facet for the radius faces distally; the facet for the ulna faces posterodistally; the posterior margin of the ulna is concave and sharpened, involved in the perichondral ossification; the intermedium is rhomboid, with two distal facets equal in size for the second and third distal carpals; the epipodial and autopodial elements are round and thickened, loosely arranged in the fin. This specimen is the first reliable evidence of the presence of Ophthalmosaurus in the Oxfordian–Kimmeridgian of Russia. The previously described remains of a Kimmeridgian ichthyosaur referred to as O. undorensis Efimov, 1991 should be identified as Ophthalmosauridae indet.     

Stratigraphie du Jurassique supérieur du djebel Bechtout au Nord-Ouest de tiaret (Bordure sud-tellienne,Algérie); Comparaison avec le Bou Rheddou

The study of the Upper Jurassic of the Bechtout Mountain (Southern Tellian border) allows us to distinguish five formations and to precise their age assignment owing to new collections of ammonites. Previous stratigraphic assignments are modified. Stratigraphic and sedimentologic data give evidence that each of the five Bechtout formations can be correlated with those encountered in the Bou Rheddou Mountain. As in the Bou Rheddou, first beds with ammonites are Middle Oxfordian in age. The Oxfordian «Ammonitico rosso facies begins in the Transversarium Zone up to the Planula Zone. The uppermost formation (Calcaires médians du Bou Rheddou) that begins in the Upper Oxfordian (Planula Zone) is essentially Kimmeridgian what causes us to exclude the time range Portlandian-Lower Cretaceous previously assumed.     

New Data on Jurassic Cerithiopsidae (Gastropoda) from European Russia

Paleontological Journal - The Oxfordian–Kimmeridgian Cerithiopsidae, represented by two genera Cosmocerithium Cossmann, 1906 and Dragonia gen. nov. are re-investigated. Three species (C....     

A review of the chronostratigraphical ages of Middle Triassic to Late Jurassic dinoflagellate cyst biozones of the North West Shelf of Australia

The chronostratigraphical ages of the 20 dinoflagellate cyst zones and one dinoflagellate cyst assemblage for the Middle Triassic (Ladinian) to the Jurassic-Cretaceous transition of the North West Shelf of Australia are comprehensively reviewed. Evidence from macro- and micropalaeontology, palynology and strontium isotopes made available after the establishment of these biozones in the 1980s has been used to reassess the ages of this important zonal scheme and to calibrate it to the international stratigraphical stages. The Shublikodinium Superzone is renamed herein as the Rhaetogonyaulax Superzone, and based on conodont evidence is determined to span the Ladinian to Early Sinemurian. This is significantly shorter in duration than was originally envisaged (Late Anisian to Late Pliensbachian). The Luehndea Assemblage is a low diversity dinoflagellate cyst association which marks a eustatic rise; it is subdivided into two subzones. It is of latest Pliensbachian to Early Toarcian age, based largely on palynological evidence. The Bajocian to earliest Oxfordian Pareodinia ceratophora Superzone represents the inception of a continuous Mesozoic-Cenozoic dinoflagellate cyst record in Australia. It comprises seven zones, which are considered to be slightly older than originally interpreted. The overlying Pyxidiella Superzone is characterised by diverse dinoflagellate cyst associations. It is Early Oxfordian to Kimmeridgian in age, and comprises three zones. The bases of the Wanaea spectabilis and Wanaea clathrata zones are reinterpreted as being slightly older than originally proposed. The superjacent Fromea cylindrica Superzone is Tithonian to earliest Valanginian and modified ages are indicated for four of the nine zones. This unit is dominated by endemic dinoflagellate cysts, reflecting a global trend towards provincialism at this time due to a regressive eustatic regime.     

Microbial encrustations from the Middle Oxfordian-earliest Kimmeridgian lithofacies in the Prebetic Zone (Betic Cordillera, southern Spain): characterization, distribution and controlling factors

Two main types of microbial encrustation were identified in Middle Oxfordian to lowermost Kimmeridgian deposits in the Prebetic Zone (southern Spain), showing existing relationships between skeletal content, fabric and morphology of these organosedimentary structures. Laminated planar and concentric encrustations relate to peloidal fabrics (mainly constituted of microbes = microbial laminated fabrics s. str. and microbial oncoids s. str.), as well as to dense microbial fabrics periodically colonized by encrusting foraminifera (microbial laminated fabrics with nubeculariids and microbial oncoids with nubeculariids). Sedimentation rates, substrate stability and grain size, as well as illumination, influenced microbial growth pattern as major controlling factors in low-energy conditions, and forced palaeogeographic and stratigraphic patterns of distribution. Significant encrustation was identified in terrigenous-poor lithofacies from the middle (Transversarium-Bifurcatus zones) to the outer (Transversarium-Bimammatum zones) shelf in the Prebetic Zone. Rare-to-absent encrustation characterized terrigenous-rich deposits (Bimammatum and Planula zones) in the area.     

Platform-basin transect of a middle to late Jurassic large-scale carbonate platform system (Shotori mountains,Tabas area,east-central Iran)

Summary Following a phase of predominantly siliciclastic sedimentation in the Early and Middle Jurassic, a large-scale, low-latitude carbonate depositional system was established in the northern part of the Tabas Block, part of the central-east Iranian microplate, during the Callovian and persisted until the latest Oxfordian/Early Kimmeridgian. Running parallel to the present eastern block margin, a NNW/SSE-trending carbonate platform developed in an area characterized by reduced subsidence rates (Shotori Swell). The growth of this rimmed, flat-topped barrier platform strongly influenced the Upper Jurassic facies pattern and sedimentary history of the Tabas Block. The platform sediments, represented by the predominantly fine-grained carbonates of the Esfandiar Limestone Formation, pass eastward into slope to basin sediments of the Qal'eh Dokhtar Limestone Formation (platform-derived allochthonites, microbialites, and peri-platform muds). Towards the west, they interfinger with bedded limestones and marlstones (Kamar-e-Mehdi Formation), which were deposited in an extensive shelf lagoon. In a N−S direction, the Esfandiar Platform can be traced for about 170 km, in an E-W direction, the platform extended for at least 35–40 km. The width of the eastern slope of the platform is estimated at 10–15 km, the width of the western shelf lagoon varied considerably (>20–80 km). During the Late Callovian to Middle Oxfordian, the Esfandiar Platform flourished under arid climatic conditions and supplied the slope and basinal areas with large amounts of carbonates (suspended peri-platform muds and gravitational sediments). Export pulses of platform material, e.g. ooids and aggregate grains, into the slope and basinal system are interpreted as highstand shedding related to relative sealevel variations. The high-productivity phase was terminated in the Late Oxfordian when the eastern platform areas drowned and homogeneous deep water marls of the Upper Oxfordian to Kimmeridgian Korond Formation onlapped both the Qal'eh Dokhtar Limestone Formation and the drowned Esfandiar Limestone Formation. Tectonic instability, probably caused by faulting at the margins of the Tabas Block in connection with rotational movements of the east-central Iranian block assemblage, was responsible for the partial drowning of the eastern platform areas. In some areas, relicts of the platform persisted to produce shallow-water sediments into the Kimmeridgian.     

Stable isotope records (O, C) of Jurassic aragonitic shells from England and NW Poland: palaeoecologic and environmental implications

Shells of fully marine Middle to Upper Jurassic molluscs from England and north-western Poland were analysed with respect to their stable isotope (δ¹⁸O, δ¹³C) compositions, and palaeoecological and environmental life conditions of these molluscs were inferred from them. Light microscopical and SEM inspection and an analysis of the minor element content (Fe, Mn, Mg, Sr) suggest rather unaltered isotope signals. The δ¹⁸O and δ¹³C values show a characteristic distribution among three groups of co-occurring organisms. Benthic (adult) bivalves generally preserved higher δ¹⁸O and δ¹³C values than ammonites, whereas planktic bivalve larvae tend to possess the lowest δ¹⁸O but higher δ¹³C than adult bivalves. As this distribution pattern is found in numerous horizons and sections of Bathonian to Kimmeridgian age in NW Poland and England, it is thought to reflect real palaeoenvironmental parameters. All observations can be incorporated in a single model that assumes (i) seasonally induced temperature stratification of the water column, (ii) a correlation between phytoplankton blooms and reproduction season of planktic-planktotrophic bivalves, and (iii) insignificant vital effects with respect to the δ¹³C in bivalves, but strong biological control in ammonites. In addition, the δ¹⁸O evolution suggests that the Late Bajocian to Middle/Late Bathonian and Early Oxfordian to Late Kimmeridgian were considerably warmer than the latest Bathonian to Late Callovian time interval. The oxygen isotopic records from other European regions indicate a similar pattern of long-term palaeotemperature evolution. The comparatively high water temperatures during the Callovian to Oxfordian of the Isle of Skye (NW Scotland) are enigmatic, however. In the Early Oxfordian, sea surface and bottom temperatures began to rise in continental Europe and England. These changes coincide with a south-westward drift of the West European crustal plate, but a causal relationship remains to be demonstrated.     

Le genre Postepithyris makridin (térébratulidés,brachiopodes) dans l'oxfordien et le kimméridgien Français

The questions relating to the type-species of genus PostepithyrisMakridin and to its systematic position within Terebratulids are discussed.The French species are described: besides the type-species P. cincta (Cotteau) from Upper Oxfordian, two species from Inferior Kimmeridgian can be included in this genus: P. minor (Douvillé) and P. dubisensis nov. sp.A new subspecies P. cincta mosensis nov., recently discovered in Oxfordian from East of the Paris Basin, can also be assigned to the genus.Postepithyris did not evolve through a single special facies: the species could supported different environmental conditions.     

Skeletal completeness of the non‐avian theropod dinosaur fossil record

Non‐avian theropods were a highly successful clade of bipedal, predominantly carnivorous, dinosaurs. Their diversity and macroevolutionary patterns have been the subject of many studies. Changes in fossil specimen completeness through time and space can bias our understanding of macroevolution. Here, we quantify the completeness of 455 non‐avian theropod species using the skeletal completeness metric (SCM), which calculates the proportion of a complete skeleton preserved for a specimen. Temporal patterns of theropod skeletal completeness show peaks in the Carnian, Oxfordian–Kimmeridgian and Barremian–Aptian, and lows in the Berriasian and Hauterivian. Lagerstätten primarily drive the peaks in completeness and observed taxonomic diversity in the Oxfordian–Kimmeridgian and the Barremian–Aptian. Theropods have a significantly lower distribution of completeness scores than contemporary sauropodomorph dinosaurs but change in completeness through time for the two groups shows a significant correlation when conservation Lagerstätten are excluded, possibly indicating that both records are primarily driven by geology and sampling availability. Our results reveal relatively weak temporal sampling biases acting on the theropod record but relatively strong spatial and environmental biases. Asia has a significantly more complete record than any other continent, the mid northern latitudes have the highest abundance of finds, and most complete theropod skeletons come from lacustrine and aeolian environments. We suggest that these patterns result from historical research focus, modern climate dynamics, and depositional transportation energy plus association with conservation Lagerstätten, respectively. Furthermore, we find possible ecological biases acting on different theropod subgroups, but body size does not influence theropod completeness on a global scale.     

Kimmeridgian hardground-sequence boundary from the Mesozoic margin of the Holy Cross Mountains (central Poland): implications for the evolution of the northern Tethyan carbonate shelf

The sedimentary succession in central Poland records significant changes in facies at the turn of the Planula and Platynota zones in the Upper Jurassic, expressed by the drowning of the ramp-type platform and development of an extensive isochronous marl horizon. The topmost level of the marl horizon is a regional hardground, which is interpreted as the third-order sequence boundary Kim 1. In some areas, the hardground was eroded and is only preserved as bored and encrusted clasts. The composition of the borings may indicate that colonization and recolonization of the clasts took place in an extremely shallow water environment. The overall low level diversity of clast-encrusting organisms and their occurrence on both sides of clasts indicates frequent overturning and high current activity. However, other extrinsic factors, such as salinity fluctuations, may have been involved. The final redeposition and burial of the clasts were related to subsidence through widespread reactivation of Paleozoic faults. Comparison with Middle Oxfordian–Lower Kimmeridgian sequences of central and southern Poland indicates that the carbonate ramp morphology and paleoenvironmental conditions were periodically subjected to significant modification during phases of extensional tectonics, with the development of fault-controlled intra-platform ridges and basins. These features may have been the NE continuation of parallel swells and basins developed in the southern part of the carbonate platform adjacent to the Tethys.     

Stable isotope analyses of belemnites from the Kachchh Basin,western India: paleoclimatic implications for the Middle to Late Jurassic transition

Stable isotope analyses of 61 diagenetically unaltered belemnite rostra from the Middle to Late Jurassic of the Kachchh Basin of western India suggest stable paleotemperatures across the Callovian-Oxfordian boundary (~14°C). Only at the end of the Middle Oxfordian water temperatures drop for more than 3°C before reaching again higher values during the Kimmeridgian (~12.3°C). The data do not support polar glaciations proposed for the Middle to Late Jurassic transition, which necessarily would have led to a global temperature and sea-level minimum at the boundary. Callovian to Oxfordian rocks in the Kachchh Basin point to a gradual shallowing corresponding to a slight fall in relative sea level. However, the magnitude of this regression is comparatively small, and the sea-level minimum is reached in the late Early Oxfordian and not close to the boundary. Results from the Kachchh Basin therefore, imply almost stable climatic conditions during the Middle to Late Jurassic transition and do not show any evidence for polar glaciations.     

Biometric methods for species recognition in <Emphasis Type="Italic">Trigonia</Emphasis> Bruguière (Bivalvia; Trigoniidae): a case study from the Upper Jurassic of Western Europe

From its first occurrence in the Middle Triassic to the Late Cretaceous, and thus for almost 200 Ma, Trigonia, type genus of the family Trigoniidae, has been a common constituent of global shallow-marine benthic faunas. The genus is highly over-split at the species level, which hampers sound biostratigraphic, palaeobiogeographic, and palaeoecologic applications. The present study focuses on two closely related species, i.e. Trigonia reticulata Agassiz and Trigonia pseudomeriani Choffat, and illustrates typical problems of species identification in Trigonia. T. reticulata is a well-known representative of the genus with a significant fossil record in Lower Oxfordian to Upper Kimmeridgian strata of western and central Europe, and likely is the ancestor of T. pseudomeriani, which is endemic to the Upper Oxfordian to Lower Kimmeridgian Alcobaça formation of the Lusitanian Basin (central Portugal). In order to effectively display intraspecific variability, digital analyses of a set of metric and non-metric parameters, including outline analysis, were applied to a representative number of specimens from different localities and stages. Originally, these methods were intended to show that both forms are conspecific. Instead, the analysis supports the distinctness of both species based on a very limited number of non-plastic characters. The methods applied can be transferred to other species in Trigonia and may lead to a modern species concept for the genus. Also, they may be successfully applied to other members of the Trigoniinae.     

Mise en évidence de la zone à Platynota (Kimméridgien inférieur) dans le Massif du Montejunto (Portugal); conséquences stratigraphiques et paléontologiques

The section has been logged on the southern slope of the Montejunto Mountain, near Cabanas de Torres (North of Tage River, Portugal). Typical ammonites of the Platynota zone with species-index Sutneria platynota (Reinecke) have been found in the lower part of the «Marnes d'Abadia formation. Orthosphinctes and Desmoides subzones of early Kimmeridgian are paleontologically well characterized. Unlike what is usually thought, the lower Kimmeridgian does occur. More fossiliferous beds of the «Marnocalcaires de Tojeira formation are coincident with Upper Oxfordian (Planula zone and Upper part of the Bimammatum zone). They yield Ardescia gr. enayi Atrops which appear earlier in Portugal than in South-eastern France.     

Comparison of carbonate C and O stable isotope records across the Jurassic/Cretaceous boundary in the Tethyan and Boreal Realms

Carbon and oxygen stable isotope records were compared for Jurassic/Cretaceous (J/K) boundary sections located in the Tethyan Realm (Brodno, Western Slovakia, and Puerto Escaño, Southern Spain; bulk limestones), and the Boreal Realm (Nordvik Peninsula, Northern Siberia, belemnites). Since a detailed biostratigraphic correlation of these Tethyan and Boreal sections is impossible due to different faunal assemblages, correlation of the isotope records was based on paleomagnetic data. This novel approach can improve our understanding of the synchroneity of individual isotope excursions in sections where detailed biostratigraphic correlation is impossible. No significant excursions in either the carbon or oxygen isotope records to be used for future Boreal/Tethyan correlations were found around the J/K boundary (the upper Tithonian and lower Berriasian; magnetozones M20n to M18n) in the studied sections. At the Nordvik section, where a much longer section (middle Oxfordian–basal Boreal Berriasian) was documented, the transition from the middle Oxfordian to the Kimmeridgian and further to the Volgian is characterized by a decrease in belemnite δ¹⁸O values (from δ¹⁸O values up to + 1.6‰ vs. V-PDB in the Oxfordian to values between + 0.3 and ? 0.8‰ in the late Volgian and earliest Boreal Berriasian). This trend, which has previously been reported from the Russian Platform and Tethyan Realm sections, corresponds either to gradual warming or a decrease in seawater δ¹⁸O. Supposing that the oxygen isotope compositions of seawater in the Arctic/Boreal and Tethyan Realms were similar, then the differences between oxygen isotope datasets for these records indicate differences in temperature. The Boreal/Tethyan temperature difference of 7–9 °C in the middle and late Oxfordian decreases towards the J/K boundary, indicating a significant decrease in latitudinal climatic gradients during the Late Jurassic. Two positive carbon isotope excursions recorded for the middle Oxfordian and upper Kimmeridgian in the Nordvik section can be correlated with a similar excursion described earlier for the Russian Platform. Minor influence of biofractionation at the carbon isotopes, and the influence of migration of belemnites to deeper, slightly cooler water at the oxygen isotopes, cannot be excluded for the obtained belemnite data.     

The oldest turtle from Portugal corresponding to the only pre-Kimmeridgian plesiochelyid (basal Eucryptodira) recognized at the generic level

A shell coming from an upper Oxfordian section of the Lusitanian Basin located in Alqueidão da Serra (Municipality of Porto de Mós, West Central Portugal) is here presented. It corresponds to the oldest remain of a turtle identified in Portugal. In fact, the record of Jurassic turtles identified in pre-Kimmeridgian levels of Europe is very scarce. The new specimen represents the second worldwide identification of a Plesiochelyid turtle (basal Eucryptodira) performed in pre-Kimmeridgian levels, being the only one recognized at generic level. Therefore, this specimen corresponds to the oldest identification of Craspedochelys, a genus well-represented in Kimmeridgian and Tithonian levels of several European countries. This finding contributes the first evidence on the synchronous coexistence of more than a member of Plesiochelyidae in pre-Kimmeridgian levels, which provides arguments to justify the relatively wide diversity known for this exclusively Jurassic clade during the Kimmeridgian and the Tithonian.     

Dinoturbation in Upper Jurassic siliciclastic levels at Cabo Mondego (Lusitanian Basin,Portugal): evidences in a fluvial-dominated deltaic succession

At Cabo Mondego (western central Portugal), the Upper Jurassic marine to coastal succession contains several stratigraphic levels preserving dinosaur footprints on the surface bedding plane, as well as convolute bedding and soft sediment injection structures interpreted as dinoturbation structures. At least nineteen new three-dimensional structures observed in cross-sections are interpreted as produced by dinosaur trampling. The identification of three-dimensional structures of dinosaur footprints provides an important complement to the information obtained from footprints preserved on single bedding surfaces, such as the substrate consistency, potential trackmaker identification, and the possibility to enhance the distinction of sauropods and tridactyl dinosaurs, and paleoenvironmental interpretations. In the lower part of the Arenitos da Boa Viagem Formation, eight levels of probable lowermost Kimmeridgian age (ca. 157–156 Ma), displaying the above-mentioned deformational structures, were analyzed in detail. They support interpretations concerning the relationship between the footprints and the substrate consistency at the time of their formation. Three distinct cohesiveness patterns, defined by the penetration of the feet from the paleosurface, are the result of different degrees of substrate cohesiveness. Identifying the trackmakers of levels belonging to the middle Oxfordian–lower Kimmeridgian has important implications for Late Jurassic ecosystem reconstructions, as the footprints observed in Cabo Mondego indicate a change in the morphotypes throughout the Upper Jurassic succession.