Reconstructing the palaeoenvironment of the Middle Russian Sea during the Middle–Late Jurassic transition using stable isotope ratios of cephalopod shells and variations in faunal assemblages

Oxygen and carbon isotope data of well-preserved belemnite rostra and ammonite shells are presented from the Callovian–Oxfordian boundary (uppermost Lamberti to lowermost Cordatum zones) of the Dubki section near Saratov in the Russian Platform. Palaeotemperatures calculated for nektobenthic belemnites (averages of 5 °C and 8 °C for cylindroteuthids and belemnopseids, respectively) show the presence of cold bottom waters in the central part of the Middle Russian Sea during the studied interval. Palaeotemperatures calculated for ammonites, which are assumed to have lived in near-surface waters, are considerably higher (average 13 °C). The presented data show a vertical thermal gradient in the Middle Russian Sea. The belemnite oxygen isotope record and the relative abundances of ammonite families in the Dubki section do not correlate with each other probably as a result of different depth habitats of ammonites and belemnites. A review of literature isotope data shows the climatic zonation in European seas at the Middle–Late Jurassic transition. Despite the flux of cold polar waters to the Middle Russian Sea and the area of Scotland there is no evidence for glaciation at the Middle–Late Jurassic transition. Changes in water circulation during a sea-level highstand were likely a source of spreads of cold bottom waters and cardioceratid ammonite fauna in this time period.The belemnite isotope record of the Callovian–Oxfordian boundary in the Russian Platform is characterized by significant scatter of δ¹³C values. No temporal carbon isotope trend is observed. The δ¹³C values of Russian belemnite rostra average 2.6‰ VPDB being 1 to 2‰ higher than the values of coeval Lower Oxfordian belemnites from the area of the Submediterranean ammonite province. Higher (than Submediterranean) δ¹³C values of Russian belemnite rostra are likely related to high biologic productivity and/or high organic matter burial in semi-isolated Boreal–Subboreal marine basins.     

Sclerochronological study of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from Hokkaido,northern Japan

Here, we present the first sclerochronological investigation of shells of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from the middle Campanian cold seep carbonate‐bearing strata of the Yezo Basin in Hokkaido (northern Japan). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were measured in the aragonitic and calcitic shell layers of both species and compared to those of other co‐occurring benthic (mainly bivalves and gastropods) and demersal molluscs (ammonites). Sedimentological and stable isotope data suggest that these bivalves lived near cold seeps and were exposed to high H₂S level in the seawater. The inoceramid shells exhibited higher δ¹³C and lower δ¹⁸O values than the coeval non‐cold seep molluscs. We ascribed the anomalous isotopic pattern to a combination of vital and environmental effects determined by the hosting of chemosymbionts and the exposure to warm interstitial waters. Inoceramid δ¹³C minima coincided with growth lines and likely reflect changes in nutrient supply by the chemosymbionts. Absolute temperatures estimated from δ¹⁸O values of Sphenoceramus schmidti and S. sachalinensis were, on average, ca. 4–5°C warmer than those reconstructed for the non‐seepage environment (19.3 ± 0.7°C). Short‐term δ¹⁸O fluctuations of the inoceramid material indicate local temperature ranges of up to 5.2°C, that is four times larger than those reconstructed from the benthic and demersal fauna (1.3°C). In general, our data suggest that the stable carbon and oxygen isotope values of the studied Sphenoceramus spp. were strongly affected by short‐term fluctuations in seepage activity and do not reflect seasonal fluctuations.     

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.     

L’assemblage à Cardioceras (Cardioceras) cordatum (J. Sowerby, 1812) et sa place au sein de la succession ammonitique de l’Oxfordien Inférieur (Jurassique Supérieur). Apport des données ardennaises (Province Subboréale)

Some temporary outcrops at Villers-le-Tourneur/Neuvizy (Ardennes, France), made possible the observation and biostratigraphical dating of Uppermost Callovian to Early Middle Oxfordian poorly known formations. Especially, the “Oolite Ferrugineuse de Villers-le-Tourneur–Neuvizy” is a quite thick marly unit, yielding some silicified fossils well known since the XIX^th century. With details, the Formation displays the succession of several faunal associations, characterizing the main subzones of the Cordatum Zone (Late Lower Oxfordian) and the Plicatilis Zone (Early Middle Oxfordian). Amongst many other species, Cardioceras cordatum (Sowerby, 1812) corresponds to a rare taxon or morphotype, yielded by the bottom part of the Formation. Then, the ultimate Lower Oxfordian faunal association is dominated by ammonites related to C. persecans. These Early Oxfordian are widely dominated by the family Cardioceratidae, commonly associated with Aspidoceratidae; such a structure is related to the “subboreal associations”, typically represented in Great Britain. Immediately after the Middle Oxfordian boundary, some “subtethysian” ammonites (mainly Perisphinctidae), occur in a larger number without being dominant, that emphasizing the northern location of the Ardennes margin. Then locally, two faunal associations succeed, which are characterized by C. cordatiforme (with Euaspidoceras perarmatum), and C. densiplicatum, respectively. Both are typical associations of the Vertebrale Subzone (Early Middle Oxfordian).     

The role of <Emphasis Type="Italic">Salvelinus</Emphasis> in contemporary studies of evolution,trophic ecology and anthropogenic change

The aim of this study was to better understand the relations between carbon and oxygen stable isotope values of ambient water, mollusc shells, macrophytes and their carbonate encrustations, commonly used in palaeolimnological studies. Water, molluscs and macrophytes were sampled from the littoral zone in Lake Lednica, NW Poland. The influence of carbon species assimilated during photosynthesis and the net intensity of photosynthesis resulting from the size of charophyte species and the density of their stands were postulated to be the most important factors causing the species-specific δ¹³C values of charophyte thalli and encrustations. It was suggested that photosynthetic activity of charophytes affected not only the δ¹³C values of charophyte encrustations but also mollusc shells by changing δ¹³C values of DIC within charophyte stands. In addition, incorporation of metabolic carbon into the shell was proposed as the main cause of both the ¹³C depletion of mollusc shells relative to δ¹³C values of DIC and the species-specific δ¹³C values of shells. Mollusc shells were precipitated at the isotope equilibrium or close to the equilibrium with δ¹⁸O values of lake water. Charophyte encrustations were found to be ¹⁸O depleted due to the kinetic isotope effects during intense photosynthesis and thus fast precipitation of the calcite.     

Episodic sedimentation on a peri-Tethyan ridge through the Middle–Late Jurassic transition (Villány Mountains, southern Hungary)

The Villány area, as a central part of the Tisza microcontinent/terrane along the European margin of Tethys, was characterized by intense subsidence in the Early and Middle Triassic, followed by a long interruption of subsidence in the Late Triassic to Middle Jurassic. During the Middle–Late Jurassic transition, marine sedimentation started with three distinct sedimentary episodes dated as Late Bathonian, Early Callovian, and Middle–Late Callovian, respectively. The succession is terminated by a thick limestone of Middle Oxfordian age. The sedimentary features, microfacies, and macroinvertebrate associations of these four stratigraphic units are documented and illustrated. The Middle to Late Jurassic sedimentary episodes of the Villány succession record an interplay of local and global factors and paleogeographical changes. At the beginning, local tectonic movements governed the main features of sedimentation, though the role of eustasy was also essential. From the mid-Callovian onwards, global climatic, biotic, and paleoceanographical changes controlled the nature and formation of the local carbonate sediments. The Callovian stromatolites are attributed to the activity of sulphate-reducing bacteria in a deep sublittoral, current-swept environment. Upwelling of eutrophic Tethyan waters is recorded by the prevalence of the Bositra filament microfacies in the Callovian. The long submarine hiatus at around the Callovian–Oxfordian transition mirrors a serious restriction of the carbonate budget, due to sudden cooling and a change in the oceanic current system (opening of a circumglobal Tethyan Passage), and to a higher amount of dissolved CO₂. In the Middle Oxfordian, the carbonate production considerably increased in accordance with the sudden global warming.     

Seasonal stable isotope variations of the modern Amazonian freshwater bivalve Anodontites trapesialis

In a floodplain lake of the Amazon River near the city of Iquitos, northeastern Peru, a one-year monitoring experiment was conducted during which water samples and living bivalves (Anodontites trapesialis) were collected with the aim to investigate seasonal δ¹⁸O variation in and fractionation between bivalve aragonite and host water. Both host water and molluscan growth increments show more than 8‰ seasonal variation in δ¹⁸O. In the floodplain lake under study the δ¹⁸O variation of the water is controlled by contrasting dry and wet season evaporation-precipitation regimes. Molluscan δ¹⁸O appears to be in equilibrium with the host water. Although an approximately 4.0‰ offset occurs, δ¹³C records of water and bivalves are in good agreement, suggesting that both δ¹⁸O and δ¹³C of the shells of freshwater bivalve A. trapesialis are good recorders of (palaeo-)environmental conditions. The δ¹³C of Dissolved Inorganic Carbon (DIC) is governed by plant growth and/or by changes in aquatic chemistry, affecting the DIC pool.     

Paléobiogéographie de quelques Stephanocerataceae (Ammonitina) du Jurassique moyen et supérieur; une confrontation avec la théorie mobiliste

From Bajocian to lower Kimmeridgian, the subfamilyStephanocerataceae represents a large stock of the ammonite fauna. Though it is tributary of author's stratigraphical correlations and systematical interpretations, its geographical distribution with a drifting continents concept gives many teaching about the study of this superfamily, the continental drift and its consequences. Showing a world wide repartition at its apparition this stock then presents branches; the one (Stephanoceratidae) is not envisaged here; the second (Sphaeroceratidae and Cardioceratidae families) characterises rather the «boreal province; the third (Macrocephalitidae family) is chiefly specific of the «tethysian province. A «north-east pacific province with boreal affinities and a «south-east province with tethysian affinities are delimited. It is probably from its fauna that the tethysian macrocephalitid stock appears; first represented by ammonites specifically north american in middle and upper Bathonian stage, they extend during upper Bathonian and lower Callovian and reach South America and the Tethys. The presence of a narrow sea, on Patagonia, West Antarctica, East Africa, Madagascar and India, joining the Tethys and the south edge of Gondwania, is proved at various times, at Bajocian and Callovian stages.     

西藏北部安多地区中侏罗统(巴通阶-卡洛夫阶)菊石

最近从藏北安多地区中侏罗统发现较丰富的菊石类化石,巴通期的菊石有OxyceritesoppeliElmi,Ho moeoplanulitescf. homoeomorphus(Buckman),H. cf. acuticosta(Roemer), Choffatiacf. vicentiMangold, Siemiradzkiacf. matisconensis(Lissajous), Proceritessp., Neuquenicerascf. yokoyamaiKobayashiandFukada和Indosphinctessp.。卡洛夫期的菊石有Oxyceritescf. subcotarius(Oppel), Macrocephalites? sp., Homoeoplanulitescf. furculus(Neumayr),Indospinctes(Elatmites) cf. reveliMangold和Reineckeitessp.。其中Indosphinctes,Indospinctes(Elatmites),Neu queniceras,Siemiradzkia和Procerites等属(或亚属)在西藏北部地区为首次报道。安多地区中—晚巴通期和早卡洛夫期菊石动物群凸现较强的地方性色彩; 晚巴通期ORBIS菊石带和早卡洛夫期KOENIGI菊石带是藏北地区菊石动物群扩散的重要时期。     

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.     

Stable isotopes (δC and δO) of charophyte gyrogonites: example from the Brochene Fluh section (Late Oligocene-Early Miocene, Switzerland)

A synthetic curve based on the δ¹³C and δ¹⁸O variation measured on Oligocene-Miocene charophyte gyrogonites is presented. Such a synthetic curve cannot be interpreted without taking into account facies relationships. Thus, we present a detailed analysis of the Brochene Fluh section (Late Oligocene, MP29, to early Miocene, MN1), in which more than 30 charophytes levels have been recorded. It is possible to subdivide the section into six cycles: cycles one to four, Late Oligocene in age, present a covariance in the δ¹³C and δ¹⁸O variation, and are typical of small closed lakes subject to great seasonal changes (especially humidity). The last two cycles, of Aquitanian age, show a diminution of seasonality perhaps due to the ingression of the future Burdigalian sea.     

First description of axymyiid fossils (Insecta: Diptera: Axymyiidae)

Two species of fossil insects from the Daohugou Formation of Chifeng City in Nei Monggol Autonomous Region, northeastern China are described, and recognized as Psocites pectinatus (Hong, 1983) nov. emend., nov. transl. and P. fossilis nov. sp. They are the oldest representatives of the family Callovian or Axymyiidae, and first described of this family in the Mesozoic. Although early the age of the fly-bearing beds is controversial, it is probably Oxfordian or Kimmeridgian (Late Jurassic) rather than Early Cretaceous or Middle Jurassic.     

The genus Kepplerites Neumary et Uhlig (Kosmoceratidae,Ammonoidea) in the Bathonian-Callovian beds (Middle Jurassic) of the Russian Platform

The succession of early species of the genus Kepplerites is established in the Upper Bathonian-Lower Callovian beds of Central Russia and compared with the ammonoid succession of East Greenland and Western Europe. Late Bathonian members of the genus Kepplerites from the Middle Volga Region are generally similar, though not identical to those from Greenland, whereas the Early Callovian Kepplerites species and their immediate Bathonian ancestors are represented by species common to all three regions. The analysis of the ammonoid distribution suggests a connection between the East Greenland and Central Russian marine basins in the Early and Middle Bathonian and in the Early Callovian, and their short-term isolation in the Late Bathonian. A new species, Kepplerites (Kepplerites) aigii sp. nov., is described from the Upper Bathonian (keuppi Zone) of the Alatyr River basin (Middle Volga Region).     

Toarcian–Kimmeridgian depositional cycles of the south-western Morondava Basin along the rifted continental margin of Madagascar

After rifting and final breakup of Gondwana along the former East-African-Antarctic Orogen during the Toarcian–Aalenian, passive margins formed around the Proto-Indian Ocean. Sedimentological and stratigraphic studies in the southern Morondava Basin contribute to an improved reconstruction of palaeoenvironmental changes during the syn-rift and post-rift margin formation. Depositional models based on outcrop and literature data in combination with subsurface data sets provide a stratigraphic framework of four transgressive-regressive (T-R) cycles. The incorporation of stratal architecture models derived from seismic images is essential. After a syn-breakup T-R cycle (T-R1), the post-breakup succession commenced with a Bajocian – Early Bathonian carbonate platform (T2). Middle–Late Bathonian sandstones (R2) formed when a global sea-level fall forced the shoreline to move basinward. Incised valleys and palaeokarst known from seismic lines are typical for forced regression cycles. In the Early Callovian again a widespread transgression occurs (T3). During a short regressive phase from the Late Callovian(?) to Early Oxfordian (R3), the siliciclastic shoreface deposits prograded onto the shelf. From the Early Oxfordian onwards a transgressive trend continued (T4). T1–T3 can be explained as the response to the structural development of the breakup rifting but they follow sea-level changes observed in other parts of the world. R3 and T4, in contrast, reflect eustacy.     

Middle Lutetian climate in the Paris Basin: implications for a marine hotspot of paleobiodiversity

The present study reports the evolution of environmental conditions and seawater temperatures during the establishment of a marine hotspot of paleobiodiversity that took place in the Paris Basin during the Lutetian. The stable isotope compositions (δ¹⁸O and δ¹³C) of three species of molluscs (two bivalves: Cubitostrea plicata and Venericardia imbricata, and one gastropod: Sigmesalia multisulcata) collected along the reference section of Grignon (Falunière) are used for paleoenvironmental and paleoclimatic reconstructions. Additional high-resolution analyses on one specimen of Haustator imbricatarius allow the documentation of seasonal changes for temperature. The high-resolution profiles of the δ¹⁸O signatures of S. multisulcata reveal that these gastropods mineralized their shell during the warm months of the year, as did V. imbricata, which probably had a short life span (less than 1?year). These two species thus only yield temperatures for the summer period, from 22 to 30?°C. The δ¹⁸O of C. plicata shells indicate mean annual sea surface temperatures ranging between 15 and 23?°C during the Middle Lutetian, with minimal temperatures probably reflecting greater depth at the base of the section. The seasonal contrasts reconstructed in the upper part of the section, from the large gastropod H. imbricatarius, ranged between 18 and 30?°C. Comparison of the isotopic values of the species indicates that the δ¹³C of the three taxa seems to be mostly influenced by ecological features, leading to differences between endobenthic (V. imbricata) and epibenthic species (C. plicata); or the food habits. The paleoclimatic reconstructions show that the Lutetian climate was relatively stable in the Paris Basin with long-term cooling of the mean annual sea-surface temperatures. Nevertheless, this study shows that despite a context of colder conditions compared to the Early Eocene, the climate provided a favorable context for the increase of marine biodiversity in the Paris Basin during the Middle Lutetian.     

Recent and historical discharge of a large European river system - oxygen isotopic composition of river water and skeletal aragonite of Unionidae in the Rhine

Seasonal variations in the oxygen isotopic composition of Rhine River water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves (Unionidae). The purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge, and thereby infer climate change. Seasonal variations in the river water δ¹⁸O are on the order of 1-2‰. During summer, Alpine melt-water contributes significantly to the total discharge, resulting in average values of −10 to −10.5‰, whereas the non-Alpine contribution is higher during winter, as indicated by mean δ¹⁸O values of −8.5 to −9‰. The basic pattern of the modern seasonal variation of δ¹⁸O of river water can be described by a numerical mass balance approximation of the various contributions from the Alpine and non-Alpine catchments with their average δ¹⁸O composition. The δ¹⁸O of growth increments in the prismatic shell layer of Anodonta corresponds perfectly to what is predicted by known fractionation of ¹⁸O between water and aragonite. Shell growth is restricted to water temperatures above 8-10°C, so variations in δ¹⁸O and the river water temperature are faithfully recorded by relatively large growth increments during summer. The distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells.     

Stable carbon and oxygen isotopes in human tooth enamel: Identifying breastfeeding and weaning in prehistory

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used δ¹³C to document the introduction of solid foods to infant diets and δ¹⁸O to monitor the decline of breastfeeding. We report enamel carbonate δ¹³C and δ¹⁸O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO₂ liberated by reaction of enamel with H₃PO₄ in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in ¹³C and more depleted in ¹⁸O than teeth developing at younger ages. Premolars average 0.5% higher in δ¹³C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the δ¹³C in childhood diets did not change systematically. First molars and premolars are similar in δ¹⁸O, but third molars average 0.7% lower than first molars (P = 0.0001) and 0.5% lower than premolars (P = 0.0003). First molar and premolar δ¹⁸O is heavier, because breast milk is more enriched in ¹⁸O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later. Am J Phys Anthropol 106:1–18, 1998. © 1998 Wiley-Liss, Inc.     

The dendroclimatic value of oak stable isotopes

Tree-ring stable oxygen and carbon isotope ratios (δ¹⁸O and δ¹³C) are an important archive for climate reconstructions. However, it remains unclear whether the polyvinyl acetate emulsion, often used for the preservation and fixation of wood samples, influences δ¹⁸O and δ¹³C signals. Further uncertainties are associated with the possible effects of geographical origin and cambial age of historical samples. Here, we present annually-resolved and absolutely-dated δ¹⁸O and δ¹³C measurements of 21 living oaks (Quercus robur and Q. petraea) from the Czech Republic. We find that the δ¹⁸O and δ¹³C signals in the extracted alpha-cellulose are not affected by polyvinyl acetate treatment. Covering the entire 20^th century and reaching until 2018 CE, our dataset reveals spatial and temporal coherency within and between the individual δ¹⁸O and δ¹³C chronologies of different oak species, sample locations, and tree ages. Highly significant (p < 0.01) Pearson’s correlation coefficients of the site-specific δ¹³C and δ¹⁸O chronologies range from 0.48–0.77 and 0.36–0.56, respectively. The isotopic inter-series correlations of Q. robur and Q. petraea from the same site are 0.75 and 0.43 for the mean δ¹³C and δ¹⁸O values, respectively. Significant (p < 0.01) correlations of 0.49 and 0.84 are found for δ¹³C and δ¹⁸O, respectively, when all measurements from all sampling locations and tree ages are included. Our study shows that non-pooled oak δ¹⁸O and δ¹³C measurements from both species, different locations, and diverse tree ages can be combined into robust isotopic chronologies for climate reconstructions.     

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.