Stratigraphy of the Lower Cretaceous Sediments from the Carpathian Bend Area, Romania

The Lower Cretaceous sediments of the Ceahl?u Nappe (from the bend region of the Romanian Carpathians) were investigated from lithological and micropaleontological (calcareous nannoplankton) points of view. Our investigations revealed that the studied deposits were sedimented within the latest Tithonian-Albian interval. The calcareous nannofossil assemblages of the turbidite calcareous successions (the Sinaia Formation) were assigned to the NJK-?NC5 calcareous nannofossil zones, which cover the Late Tithonian-Early Barremian interval. The sandy-shaly turbidites, which followed the calcareous turbidites of the Sinaia Formation, are Early Barremian-Early Albian in age (interval covered by the ?NC5-NC8 calcareous nannofossil zones). Because the studied deposited are mainly turbidites, many reworked nannofossils from older deposits are present in the calcareous nannofloras. Thus, some biozones (i.e., NC5), defined based on the last occurrences of nannofossils, could not be identified. The calcareous nannofossil assemblages are composed of Tethyan taxa (which dominate the nannofloras) and cosmopolitan taxa. During two intervals (the Late Valanginian and across the Barremian/Aptian boundary), Tethyan and cosmopolitan nannofossils, together with Boreal ones, were observed. This type of mixed calcareous nannoplankton assemblage is indicative for sea-level high-stand, which allows the nannofloral exchange between the Tethyan and Boreal realms, within the two-above mentioned intervals.     

Palaeoceanography of Lower Cretaceous (Barremian–Lower Aptian) black shales from northwest Germany evidenced by calcareous nannofossils and geochemistry

During the Barremian–Early Aptian, the Lower Saxony Basin (LSB) of northwest Germany was covered by a shallow epicontinental sea where restricted conditions resulted in the formation of black shales. This study focuses on a 103-m-thick succession of Lower Barremian–Lower Aptian dark claystones and black shales exposed in a temporary road cut in northwest Germany (A39). Calcareous nannofossils and the δ¹³C_org record have been used to determine the timing of black shale deposition (Hauptblätterton, Blätterton, Fischschiefer events). Redox-sensitive trace elements indicate anoxic conditions with free H₂S causing the formation of black shales and dysoxic conditions during deposition of the dark claystones. The palaeoecological reconstructions based on calcareous nannofossils suggest that during the Lower Barremian Hauptblätterton event a stratification of water masses existed, caused by high surface water temperatures and reduced terrigenous run-off. During the deposition of the Upper Barremian clay-Blätterton alternation warm surface water prevailed, accompanied by meso-eutrophic surface water conditions. The formation of the Barremian black shales was mainly caused by restricted conditions related to the palaeogeography and palaeoceanography of the LSB. Global processes associated with the Oceanic Anoxic Event 1a most likely induced the deposition of the Lower Aptian Fischschiefer. High weathering rates, high primary production, and restricted conditions in the LSB led to increased burial of organic matter and thereby to the formation of the Fischschiefer.     

Integrated biostratigraphy and carbon isotope stratigraphy of the Lower Cretaceous (Barremian to Albian) Adriatic-Dinaridic carbonate platform deposits in Istria, Croatia

The Adriatic-Dinaridic carbonate platform (ADCP) was one of the largest and relatively well preserved Mesozoic platforms in the Mediterranean region (central Tethys). The peninsula Istria, in the northwestern part of the ADCP, is built up predominantly of shallow-water carbonates of the Middle Jurassic (Dogger) to Eocene age and, to a lesser extent, of Paleogene clastic deposits (flysch and calcareous breccia). This study focuses on a Lower Cretaceous (Barremian to Albian) succession of strata at five localities in western Istria. Stratigraphic determinations are based on identification of nine microfossil assemblages (benthic foraminifera and calcareous algae Dasycladales) and on using their taxa as index fossils. The age of strata with these microfossil assemblages, however, is questionable. Most of the age uncertainties are associated with a regional emersion, which occurred on the ADCP during the Aptian or close to the Aptian-Albian transition. It is unclear what portions of the Upper Aptian and/or Lower Albian are missing along this unconformity. A stable isotope study was conducted on homogenous micritic matrix samples in an attempt to resolve some of these uncertainties. Variations in carbon isotope compositions proved useful for stratigraphic correlation between the examined successions of strata, for improving their age determination, and for relating them to other coeval successions that span an important time interval of major oceanographic changes and carbon-cycle perturbations associated with the Early Aptian oceanic anoxic event (OAE 1a).     

Correlation of Barremian-Aptian (mid-Cretaceous) dinoflagellate cyst assemblages between the Tethyan and Austral realms

Quantified organic-walled dinoflagellate cyst (dinocyst) assemblages are presented for two sedimentary successions deposited in neritic environments of the Tethys Ocean during the Barremian and Aptian in an attempt to reconcile established dinocyst biostratigraphic schemes for Tethyan and Austral regions. One section is at Angles, southeast France (the Barremian stratotype section); the other is at Deep Sea Drilling Project Site 263, off northwest Australia. We also construct a carbon isotope record for Site 263 using bulk organic carbon.Both sections contain abundant, well-preserved dinocyst assemblages. These are diverse, with 89 taxa identified at Angles and 103 taxa identified at Site 263. Of these, more than 93% are cosmopolitan. When combined with other work at Angles and Site 263, we found that nine dinocysts have their first occurrence (FO) or last occurrence (LO) at both locations. These dinocyst events are, in alphabetical order: LO of Cassiculosphaeridia magna, FO of Criboperidinium? tenuiceras, LO of Kleithriasphaeridium fasciatum, LO of Muderongia staurota, FO of Odontochitina operculata, LO of Phoberocysta neocomica, FO of Prolixosphaeridium parvispinum, FO of Pseudoceratium retusum var. securigerum, and FO of Tehamadinium sousense. Although these events support a Barremian–Aptian age for both sections, their stratigraphic order is not the same in the sections. The δ¹³C_org record at Site 263 displays a characteristic series of changes that have also been recorded in other carbon isotope curves spanning the Late Barremian–Early Aptian. Such independent dating (along with ammonite zones at Angles) suggests that three of the nine dinocyst events are approximately isochronous at Angles and Site 263: the LO of K. fasciatum in the mid Barremian, the FO of P. retusum var. securigerum and the FO of C.? tenuiceras in the earliest Aptian; the other six dinocyst events are diachronous. Dinocyst assemblages at Site 263 can be loosely placed within existing Australian zonation schemes, providing much-needed calibration. Our data suggest that the Muderongia testudinaria Zone ends in sediments of mid Barremian age, the succeeding Muderongia australis Zone extends into the Early Aptian, and the younger Odontochitina operculata Zone begins in Early Aptian deposits. The boundary between the M. australis and O. operculata zones, and the Ovoidinium cinctum (as Ascodinium) Subzone, positioned at the top of the M. australis Zone when present, could not be recognized incontrovertibly. Interestingly, however, this horizon broadly correlates with the onset and extent of the Selli Event, a time of major biogeochemical change.     

Aptian bio-events—an integrated biostratigraphic analysis of the Almadich Formation, Inner Prebetic Domain, SE Spain

The Upper Barremian to Aptian Almadich Formation (Inner Prebetic Domain of the Betic Cordillera) is composed of hemipelagic sediments deposited on a distal carbonate ramp in the southern Iberian Palaeomargin. Within this facies we have found a thick interval of blue to black shales and marls that is interpreted as deposited under oxygen-depleted conditions. We think that this interval, dated as early Aptian, represents the local record of Ocean Anoxic Event 1a. The integrated biostratigraphic analysis of a section in the Almadich Formation, by means of planktonic foraminifera, calcareous nannofossils and ammonites, enables us to recognize most of the biostratigraphic units based on these three fossil groups and to correlate between them. The Sartousiana, Sarasini, Weissi, Deshayesi and Furcata (ammonite) Zones were identified for the Upper Barremian–Lower Aptian interval. By means of calcareous nannofossil biostratigraphy the Micrantholithus hoschulzii, Hayesites irregularis and Rhagodiscus angustus Zones, plus several additional biohorizons, were identified. A quantitative study performed on a set of 27 Lower Aptian samples has enabled the precise identification of the ‘nannoconid crisis’, the lower limit of which clearly precedes the main anoxic event, and its correlation with other bioevents. Planktonic foraminifera occur consistently throughout the Lower to Upper Aptian of the Cau section and are moderately well preserved. This fact allows us to use the most recent taxonomic framework, based on wall texture, to identify the Blowiella blowi, Schackoina cabri, Globigerinelloides ferreolensis, Globigerinelloides algerianus, Hedbergella trocoidea andTicinella bejaouaensis Zones. Coincident with the anoxic episode, the planktonic foraminiferal assemblages are composed of a significant number of forms with elongated chambers and/or tubulospines assigned to the genera Claviblowiella,Lilliputianella , Leupoldina and Schackoina. Most of the planktonic foraminiferal and nannofossil taxa are illustrated.     

Calcareous Nannofossils and Molecular Fossils in Cobalt-rich Crusts and their Response to the P/E Global Event

A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age.The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous,late Paleocene,(early,middle,late) Eocene,middle Miocene,late Pliocene,and Pleistocene.Gas chromatography(GC) and gas chromatography-mass spectrometry(GC-MS) were used to test the Co-rich crusts,and a variety of molecular fossils were detected,such as chloroform bituminous "A",n-alkane,isoprenoid and sterol.Peak carbon and molecular indices(such as ΣC23 /ΣC24 +,CPI,Pr/Ph,Pr/nC17,Ph/nC18 and δ13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter.Researches on calcareous nannofossils,molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene(P/E) global event is recorded in the cobaltrich crusts from the northwestern Pacific Ocean.A succession of biomes can be observed near the 85 mm boundary(about 55 Ma),i.e.,the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis,and Broisonia parka microbiotas above the P/E boundary,and the bloom of Coccolithus formosus,Discoaster multiradiatus,Discoaster mohleri and Discoaster sp.below the boundary.Typical parameters of molecular fossils,such as saturated hydrocarbon components and carbon-number maxima,Pr/Ph,Pr/C17,Ph/C18,distribution types of sterols,Ts/Tm ratios and bacterial hopane,also exhibit dramatic changes near the P/E boundary.These integrated results illustrate that the biome succession of calcareous nannofossils,relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.     

松辽盆地海侵事件——松科1井钙质超微化石新证据

松辽盆地作为中国最大的陆相含油气盆地,是否发生过海水侵入一直存在争议,化石能为该科学问题提供直接解释。在松科1井嫩江组一、二段发现了少量的钙质超微化石,初步鉴定出Calculites obscurus,Calculites ovalis,Quadrum sp.,Micula sp.等属种。上述钙质超微化石广泛分布于晚白垩世海相地层中,通过与国际标准海相化石的对比,将嫩江组一段中、下部的时代限定为Turonian晚期—Maastrichtian期。松辽盆地嫩江组一、二段下部的钙质超微化石保存总体一般,有一定的多样性,具有海相钙质超微化石的特征。松科1井钙质超微化石的分布、古生态及其与有孔虫化石的对应关系表明,松辽盆地嫩江组一段中-下部、二段下部沉积期湖泊水域广阔,全球海平面较高,间歇性的海水侵入事件导致西北太平洋中的钙质超微浮游生物和有孔虫等海洋生物被带入松辽盆地。     

Biostratigraphic studies of the lower cretaceous (Upper Barremian—lower Aptian) Sarcheshmeh and Sanganeh Formations in the Kopet Dagh basin, NE Iran: An integration of calcareous nannofossil and ammonite stratigraphies

Lower Cretaceous sediments of the northwestern part of the Kopet Dagh sedimentary basin have been sampled with the purpose to study stratigraphic distribution of calcareous nannofossils. A total of 87 samples from the 1900-m-thick marly limestones, shales and siltstones of the Sarcheshmeh and Sanganeh Formations (late Barremian-early Aptian) displayed diverse nannofossil assemblages. Representative species of the following genera were recorded from the Sarcheshmeh Fm.: Braarudosphaera, Calcicalathina, Calciosolenia, Chiastozygus, Conusphaera, Cretarhabdus, Cyclagelosphaera, Eprolithus, Haqius, Hayesites, Lithraphidites, Manivitella, Micrantholithus, Nannoconus, Radiolithus, Retecapsa, Rhagodiscus, Rucinolithus, Watznaueria, and Zeugrhabdotus. In the Sanganeh Formation, Biscutum, Broinsonia, Cribrosphaerella, Crucicribrum, Cyclagellosphaera, Diazomatolithus, Discorhabdus, Eiffellithus, Lithraphidites, Nannoconus, Prediscosphaera, Rhagodiscus, Tranolithus, and Watznaueria were found. The identified nannofossil assemblages enabled the recognition of NC5-NC7A zones in the studied part of the section. Paleoecologically, these nannofossil assemblages are typical for the Lower Cretaceous of the Tethyan realm and indicate warm surface water conditions.     

Micropaleontological record of Holocene estuarine stages in the Bahía Blanca estuary,Argentina

Holocene paleoenvironmental changes have been interpreted on the basis of benthic foraminifera and calcareous nannofossils recovered in samples from Napostá Grande Stream, Bahía Blanca estuary, southern Buenos Aires Province. Samples are fine sands and clay sediments from a Holocene outcrop and were studied with quantitative techniques. The benthic foraminiferal assemblage is dominated by Ammonia parkinsoniana, Ammonia tepida, Bolivina pseudoplicata, Bolivina striatula, Bolivina sp., Buccella peruviana, and Elphidium spp. The calcareous nannofossil assemblage recovered is a typical cold-water association, dominated by Calcidiscus leptoporus, Coccolithus pelagicus, Emiliana huxleyi and Gephyrocapsa oceanica. A dendrogram classification by cluster analysis was made for each microfossil group. The results of these analyses were coincident, showing a liaison between changes in the assemblages of benthic foraminifera and calcareous nannofossils. Those results, jointly with the sedimentological information, lead to the identification of three different paleoenvironments along the Napostá N1 site. The lower part of the succession represents an estuarine environment with larger marine connection. The middle part represents a gradual passage to a more restricted estuarine environment, and the upper part represents the establishment of the modern continental fresh-water environment.     

Ecological succession, palaeoenvironmental change, and depositional sequences of Barremian–Aptian shallow-water carbonates in northern Oman

Abstract Barremian and Aptian shallow‐water carbonate facies (uppermost Lekhwair, Kharaib and Shuaiba Formations) are described from outcrops in northern Oman. Based on facies analysis and bedding pattern, three orders of depositional sequences are defined (third to fifth order) and correlated between sections. Over the course of three third‐order sequences, covering the Barremian to Lower Aptian, a third‐order depositional pattern is documented that consists of a succession of three distinct faunal assemblages: discoidal orbitolinids and calcareous algae were deposited during early transgression; microbialites and microencrusters dominate the late transgressive to early highstand facies; and a rudist‐ and miliolid‐dominated facies is typical of the highstand. This ecological succession was controlled largely by palaeoenvironmental changes, such as trophic level and clay influx, rather than sedimentological factors controlled by variations in accommodation space. Orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow‐water carbonate response to global changes affecting Late Barremian to Aptian palaeoclimate and palaeoceanography.     

Lower Aptian ammonite biostratigraphy and potential for further studies of OAE 1a in Bulgaria

Sediments of Early Aptian age in Bulgaria can be assigned to four different facies: platform carbonates (Urgonian complex), shallow-water siliciclastics, hemipelagic and flyschoid siliciclastics. The taxonomic analysis of the ammonite faunas of 18 sections from these four different facies resulted in a revision of the existing ammonite zonation scheme so far applied in Bulgaria and adjoining areas. A new biostratigraphic scheme, which bridges the western and eastern Tethys, is thereby proposed for the Lower Aptian of Bulgaria.The Upper Barremian Martelites sarasini Zone is characterized in its upper part by the Pseudocrioceras waagenoides Subzone in the shallow-water sections and by a horizon with Turkmeniceras turkmenicum in the deep-water settings. The Upper Barremian/Lower Aptian boundary is fixed by the first appearance of Paradeshayesites oglanlensis. For the Lower Aptian the following ammonite zones were established (from bottom to top): The Paradeshayesites oglanlensis Zone, the Deshayesites forbesi Zone (= formerly Paradeshayesites weissi Zone) including the Roloboceras hambrovi Subzone in the upper part, the Deshayesites deshayesi Zone including the Paradeshayesites grandis Subzone in the upper part and the Dufrenoyia furcata Zone. The Lower–Middle Aptian boundary has been defined by the appearance of species belonging to the genera Epicheloniceras and Colombiceras.The Lower Aptian ammonite faunas of Bulgaria, allow an interregional correlation with other areas of the Tethyan Realm. The presence of Turkmeniceras in the Upper Barremian enables a correlation with the Transcaspian region, whereas Roloboceras, Koeneniceras and Volgoceratoides found in the middle part of the Lower Aptian are more typical representatives of the ammonite faunas in northern Europe (England, Germany, Volga region).The analysis of the ammonite successions in combination with sedimentological observations enable us to conclude that the marls and marly limestones of the Lower Aptian studied here also cover the interval of the Oceanic Anoxic Event 1a. An interval of thin-laminated clays, rich in organic matter, was identified in the upper part of the D. forbesi Zone (Roloboceras hambrovi Subzone). This interval is characterized by a total lack of benthic faunas.     

Geodynamic significance of the Cretaceous pillow basalts from North Anatolian Ophiolitic Mélange Belt (Central Anatolia,Turkey): geochemical and paleontological constraints

The most widespread blocks within the Cretaceous ophiolitic mélange (North Anatolian ophiolitic mélange) in Central Anatolia (Turkey) are pillow basalts, radiolarites, other ophiolitic fragments and Jurassic-Cretaceous carbonate blocks. The pillow basalts crop out as discrete blocks in close relation to radiolarites and ophiolitic units in Cretaceous ophiolitic mélange.

The geochemical results suggest that analyzed pillow basalts are within-plate ocean island alkali basalts. The enrichment of incompatible elements (Nb, Ta, Light REE, Th, U, Cs, Rb, Ba, K) demonstrates the ocean island environment (both tholeiites and alkali basalts) and enriched MORB. Dated calcareous intrafills and biodetrital carbonates reveal an age span of Callovian—Early Aptian. The thin-shelled protoglobigerinids, belonging to the genus Globuligerina, in the calcareous intrafills between pillow basalt lobes indicates a Callovian—Barremian age interval, most probably, Valanginian to Late Barremian. The volcanic and radiolarite detritus-bearing orbitolinid—Baccinella biodetrital carbonates dated as Late Barremian-Early Aptian in age, were probably deposited around atolls and have a close relationship with the ocean island pillow basalts.

The results collectively support the presence of a seamount on the Neo-Tethyan oceanic crust during the Valanginian—Late Barremian and atolls during the Late Barremian-Early Aptian interval. The presence of an oceanic crust older than that seamount along the Northern Branch of Neo-Tethys is conformable with the geodynamic evolution of the Tethys.     

Albian and Cenomanian palaeobathymetry in the Pieniny Klippen Belt Basin, Polish Carpathians

During the Albian and Cenomanian, the Pieniny Klippen Belt Basin, a part of the Carpathian geosynclinal domain, showed a clear differentiation into an axial deepest part represented by the Pieniny and Branisko successions and two marginal zones, a southern (Nizna and Haligovce successions, in Slovakia) and a northern zone (in Poland and Slovakia) represented by the Niedzica, Czertezik and Czorsztyn successions, becoming progressively more shallow towards the north. Five palaeobathymetric foraminiferal associations have been distinguished in the axial and northern marginal zone sediments of the Klippen Basin, corresponding to: ‘A’ shelf and upper slope: relatively large proportion of nodosariids and miliolids (Czorsztyn succession); ‘B1’ middle part of slope; oligotaxic planktonic assemblage dominant (Niedzica through Branisko successions and northern part of the Pieniny succession); ‘B2’ middle part of slope: larger proportion of agglutinated foraminifers, association characteristic of sediments influenced by turbidites (submarine flyschoid channels in the Branisko succession); ‘Cl’ middle and lower parts of slope: scarce microfauna, Hedbergella and textularids dominant (Pieniny succession, middle part); ‘C2’ slope/abyssal plain transition, close to foraminiferal lysocline (probably about 3500m below sea level): scarce specimens corroded and slightly dissolved (Pieniny succession, southern part).     

Calcareous nannofossils from late Jurassic sediments of the Volga Basin (Russian Platform): evidence for productivity-controlled black shale deposition

The Jurassic/Cretaceous boundary interval in the northern hemisphere is characterized by the widespread occurrence of black shales. About 60% of all petroleum source rocks comprise sediments of late Jurassic and early Cretaceous age with the origin of such black shales still under discussion. In order to better understand the factors that controlled black shale sedimentation, 78 samples were analyzed for calcareous nannofossils from two sections (Gorodische, Kashpir) of the Volga Basin (NE Russia). Calcareous nannofossils are ideal proxies for deciphering nutrient, temperature and salinity fluctuations. Additionally 58 samples from both sections were also analyzed for clay mineralogy, ¹³C_org , TOC and CaCO₃ composition. Both sections contain calcareous claystones and intercalated organic rich shales overlain by phosphorite beds. The presence of the calcareous nannofossil species Stephanolithion atmetros throughout both successions allows a biostratigraphic assignment to the S. atmetros Nannofossil Biozone (NJ 17), which corresponds to the Dorsoplanites panderi Ammonite Biozone of the Middle Volgian. The marlstones of the Kashpir section yield a well-preserved rich and diverse nannoflora, whereas all black shale beds are essentially barren of calcareous nannofossils. Only the uppermost black shale layers yield an impoverished assemblage of low diversity and abundance. Geochemical data suggest an early diagenetic nannofossil dissolution in the black shales of the Kashpir section. This is supported by the occurrence of coccoliths in black shale horizons of the Gorodische section. The assemblages in both sections are dominated by coccoliths of the Watznaueriaceae group (Watznaueria barnesae, Watznaueria fossacincta, Watznaueria britannica, Watznaueria communis), Biscutum constans and Zeugrhabdotus erectus. In Kashpir rare specimens of Crucibiscutum salebrosum occur in the higher part of the section. These taxa indicate boreal affinities. B. constans and Z. erectus are considered to be taxa indicative of a higher productive environment, while C. salebrosum is a cool-water species. From base to top of the Kashpir section, consecutive mass occurrences of different taxa/groups were observed: W. barnesae–W. fossacincta acme, W. britannica–W. communis acme, Z. erectus acme, B. constans acme (including sparse occurrences of C. salebrosum).The observed distribution patterns have been interpreted as characterizing a transition from a low productive, oligotrophic setting with high abundances of K-selected cosmopolitan species (Watznaueriaceae) and predominating marlstone sedimentation to a higher productive, mesotrophic setting. Cooler water temperatures marked by r-selection and acmes of opportunistic species (Z. erectus, B. constans) are coincident with the deposition of black shales and phosphorites in the higher part of the section. Interpretation of clay mineral distribution indicates that black shale deposition occurred under semi-arid hinterland climatic conditions concomitant with a sea level rise. This induced dysoxic conditions in the deeper parts of the Volga Basin, favoring the preservation of organic matter. The cause of the nutrient enrichment in the surface water is still unclear, but possible river water input from the continents does not seem to have been the controlling factor under a semi-arid climate. The occurrence of phosphorites in the upper part of both sections presumably indicates that enhanced productivity may be better explained by the upwelling of nutrient-rich bottom water and thereby causing the recycling of nutrients from oxidized phytoplankton back into the photic zone. This recycling effect finally may have led to an intensified phytoplankton growth which seemed to be a sufficient source for the enrichment of organic matter. This is well correlated with the increase in black shale horizons in the upper part of the Kashpir section.     

Charophyte biostratigraphy of the non-marine Lower Cretaceous in the Central Tunisian Atlas (North Africa): Palaeobiogeographic implications

The chronostratigraphic framework of the non-marine deposits of the Central Tunisian Lower Cretaceous (Kebar Formation) is reviewed from a biostratigraphic viewpoint. The outcrops located in the Jebel Kebar, Jebel Ksaïra and Jebel Koumine localities provided charophyte assemblages belonging to two biochronozones: Ascidiella cruciata-Pseudoglobator paucibracteatus (upper Barremian–lower Aptian) and Clavator grovesii lusitanicus (upper Aptian–lower Albian). Clavatoraceans from the upper Barremian–lower Aptian in the Tunisian Atlas are reported here for the first time. The assemblage consists of Atopochara trivolvis var. triquetra, Ascidiella iberica var. inflata, Globator maillardii var. trochiliscoides, Globator maillardii var. biutricularis, Echinochara peckii var. lazarii, Clavator harrisii var. harrisii and Clavator harrisii var. reyi. In addition, a new characean species, Mesochara magna nov. sp. Trabelsi and Martín-Closas, is described herein. The results show that the Kebar Formation is diachronous in Central Tunisia, with a more complete record to the north (Jebel Koumine) than in the type locality (Jebel Kebar). Barremian–Aptian diapiric activity is proposed as the factor that controls the diachronous nature of this formation.The late Barremian–early Aptian charophyte assemblages from the Kebar Formation display strong affinities with the contemporaneous floras of the European basins, thus suggesting that intense supraregional floristic exchanges occurred between the Tethyan islands scattered throughout what is now Western Europe and North Africa. The biogeographic distribution of these charophytes leads to the hypothesis that the peri-Tethyan Archipelago acted as an effective bridge for the intercontinental exchanges of these plants between Laurasia and Gondwana.     

Ammonites (Phylloceratina,Lytoceratina and Ancyloceratina) and organic-walled dinoflagellate cysts from the Late Barremian in Boljetin,eastern Serbia

Late Barremian ammonite fauna from the epipelagic marlstone and marly limestone interbeds of Boljetin Hill (Boljetinsko Brdo) of Danubic Unit (eastern Serbia) is described. The ammonite fauna includes representatives of three suborders (Phylloceratina, Lytoceratina and Ancyloceratina), specifically Hypophylloceras danubiense n. sp., Lepeniceras lepense Rabrenović, Holcophylloceras avrami n. sp., Phyllopachyceras baborense (Coquand), Phyllopachyceras petkovici n. sp., Phyllopachyceras eichwaldi eichwaldi (Karakash), Phyllopachyceras ectocostatum Drushchits, Protetragonites crebrisulcatus (Uhlig), Macroscaphites perforatus Avram, Acantholytoceras cf. subcirculare (Avram), Dissimilites cf. trinodosus (d'Orbigny) and Argvethites? sp. The taxonomic composition and percent abundance of the identified ammonites indicate that their taxa are predominantly confined to the Tethyan realm. Ammonites with smooth and slightly sculptured shells predominate among the studied fauna. The ammonite-bearing succession from Boljetin represents the lower part of the Upper Barremian, ranging in ammonite zonation from the Toxancyloceras vandenheckei Zone to the lower part of the Imerites giraudi Zone. The associated organic-walled dinoflagellate cysts confirm the Late Barremian age of the ammonite-bearing levels.     

Nannofossils and biostratigraphy: An overview

Intensive biostratigraphic studies of calcareous nannofossils have been carried out for only about a decade, even though nannofossils have been known for over a century. Although coccoliths have been reported from various Paleozoic deposits, datable assemblages are known only from Liassic (early Jurassic) and younger strata. Today nannofossils are one of the best correlation tools available to the biostratigrapher in marine sediments that contain pelagic constituents. Precise age determinations and correlations can be made in Cretaceous and Cenozoic strata for which numerous reference sections have been studied. The Jurassic nannofossil succession is less completely known mainly because of a lack of good reference material.The very large number of specimens per sample and the minute size of calcareous nannofossils create both advantages and disadvantages in their utilization. Variability of synchronous assemblages may occur latitudinally as well as from the oceanic to the hemipelagic realms.     

Stratigraphic framework and calcareous nannofossil productivity of the Essaouira-Agadir Basin (Morocco) during the Aptian–Early Albian: Comparison with the north-Tethyan margin

In the southern Tethyan margin, the Essaouira-Agadir Basin (EAB), south of Morocco, exhibits well-exposed and fossiliferous sections of Aptian–Albian age. Biostratigraphy by ammonoids and sedimentological analysis have been realized for five sections located along an E-W transect in the EAB. The studied successions were dated from the latest Early Aptian to the Early Albian and are characterized by five major sedimentary discontinuities defining at least four main sedimentary sequences. The Late Aptian–Early Albian succession can be considered a gently westward-dipping ramp, marked by a deepening upward evolution. A quantitative study of calcareous nannofossils and calcium carbonate content has been performed on three of these sections. At this time, the EAB was located in the tropical-equatorial hot arid belt. The decrease in both calcium carbonate content and Nannoconus abundances at the Aptian–Albian transition could be the result of cooler climatic conditions recognized in the EAB, and/or of the associated increasing terrigenous input and nutrients, which hindered carbonate production. In the EAB, the nannofossil productivity is higher below the deposition of dark levels, which are coeval with the Niveau Paquier, recognized as the expression in southern France of the OAE 1b (Early Albian). During the Early Albian, the EAB was characterized by nannofossil fluxes two times lower than the upwelling-influenced Mazagan Plateau (southern Tethyan margin) and eight times lower than the Vocontian Basin (northern Tethyan margin). These results show that, with respect to the northern Tethyan margin, trophic conditions in sea surface waters of the pelagic realm of the southern Tethyan margin were lower. Comparable results obtained by Heldt et al. in the neritic realm of the southern Tethyan margin have been ascribed to more arid climatic conditions.     

日本早白垩世非海相软体动物群组合

日本具有4个标志早白垩世的半咸水和淡水软体动物群组合:欧特里沃期—早巴列姆期的立川和菖蒲动物群组合,晚巴列姆期的濑林动物群组合和早阿普特期动物群组合。纯非海相下白垩统大量分布于日本东北部(本州岛北部)的部分地区,以及日本中部、西南部的内带。在日本东北部的部分地区以及日本西南部的外带(四国岛与本州岛中部),从巴列姆阶下部往上有一些海相地层夹在非海相层中,这为研究非海相动物群提供了准确的年代依据。生物组合之间在种一级水平上的区别,主要由环境的差异而引起。1)立川动物群组合(欧特里沃期—早巴列姆期),含有半咸水Hayamina naumanni组合和淡水Megasphaerioides okurodaniensis组合;手取群的Okurodani、Kuwajima和Izuki三个组内的淡水软体动物可与本动物组合相对比;2)菖蒲动物群组合(欧特里沃期—早巴列姆期),含有Eomiodon nipponicus组合;3)濑林动物群组合(晚巴列姆期),含有Costocyrena radiatostriata组合,可与手取群的Kitadani组和日本东北部关门群的Sengoku组以及Monomiyama组的淡水软体动物组合相对比;4)日比原动物群组合(早阿普特期),含有Costocyrena minor组合,关门群Wakamiya组的淡水软体动物可与本动物组合相对比。