Review of the Late Cretaceous-early Paleogene crocodylomorphs of Europe: Extinction patterns across the K-PG boundary

Although the European dinosaur succession during the latest Cretaceous and its relationship with the Cretaceous-Paleogene (K-Pg) mass extinction has been the focus of recent work, other continental vertebrates, such as crocodylomorphs, have received less attention. The European continental record of crocodylomorphs in general, and of eusuchians in particular, is relatively dense through the Maastrichtian until the K-Pg boundary. Traditionally it has been argued that continental crocodylomorphs were minimally impacted by the K-Pg extinction, but they were substantially affected in Europe with the disappearance of endemic eusuchians such as Hylaeochampsidae, Allodaposuchus and their close relatives, and non-eusuchians such as Doratodon or Theriosuchus. Despite extensive sampling in Danian continental deposits, only scarce fragmentary crocodylomorph remains have been cited. It is not until the late Paleocene and Eocene that a recovery in continental crocodylomorphs is observed. The presence of taxa such as planocraniids, the alligatoroids Diplocynodon and Hassiacosuchus, and stem crocodyloids during this period provide the first reliable continental records of Crocodylia in Europe and is best explained by post-extinction immigration from Asia or North America. By contrast, marine forms such as Thoracosaurus are found on both sides of the K-Pg boundary in Europe. The adaptation of these marine animals to different environments, from shallow seas to more transitional or fluvial environments, could be the key to their success and survival across the K-Pg boundary, as seen in other marine crocodylomorph clades such as Dyrosauridae.     

Jurassic-Cretaceous (Bathonian to Cenomanian) palynology and stratigraphy of the West Tiba-1 borehole,northern Western Desert,Egypt

Land-derived pollen and spores and marine dinoflagellate cysts were extracted from the Jurassic and Cretaceous sediments of the West Tiba-1 borehole, northern Western Desert, Egypt, On the basis of the recovered palynomorphs, of known stratigraphical significance, the following stages were assessed: Bathonian-Oxfordian (Middle-Late Jurassic) and Hauterivian, Aptian-Early Albian, Late Albian-Early Cenomanian, Early Cenomanian and Late Cenomanian (Early-Middle Cretaceous). No palynomorphs diagnostic for the Berriasian, Valanginian and Barremian stages (Early Cretaceous) were depicted. Based on the nature and composition of the identified palynomorph content, five informal palynomorph assemblage zones were recognised. These are: the Gonyaulacysta jurassica-Korystocysta kettonensis Assemblage Zone (PI, Bathonian-Oxfordian), Ephedripites-Aequitriradites verrucosus Assemblage Zone (PII, Hauterivian), Afropollis jardinus-Duplexisporites generalis-Tricolpites Assemblage Zone (PIIl, Aptian-Early Albian), Nyssapollenites-Elaterosporites Assemblage Zone (PIV, Late Albian-Early Cenomanian) and Assemblage Zone PV (Early-Late Cenomanian). The latter zone was differentiated into two subzones, namely the Classopollis brasiliensis-Elaterosporites klaszii Assemblage Subzone (PVa, Early Cenomanian) and Afropollis kahramanensis-Triporates Assemblage Subzone (PVb, Late Cenomanian). The time stratigraphy of the studied interval was revised. The occurrences and types of the dinoflagellate cysts, extracted from the studied succession, reflect a general shallow (shelf) marine pal˦oenvironment.     

Tracking paleoecological and isotopic changes through the K-Pg boundary from marine ostracodes: The Poty quarry section,northeastern Brazil

Ostracode assemblages of the Poty quarry, Pernambuco-Paraíba Basin, northeastern Brazil, record an abrupt faunal change near the Cretaceous-Paleogene (K-Pg) boundary. Paleoecological and stable isotope analyses of ostracode carapaces were used to interpret the paleoenvironmental changes that took place from the Late Maastrichtian to the Early Danian. Ostracode distribution demonstrates substantial changes at and around the boundary with the last occurrences of most species and appearance of new ones. Stable isotope analyses carried out for four ostracode species distributed along the entire succession exhibit oscillations in the isotopic composition before the K-Pg boundary, thus suggesting that environmental changes may have begun slightly prior the boundary event itself. These changes may have triggered the extinctions that culminated at the K-Pg boundary, marked by positive δ¹⁸O and negative δ¹³C excursions. The K-Pg boundary is marked by cooling of bottom seawaters and a decrease in productivity, as well as the beginning of an extensive marine regression.     

An Ichthyornis-like bird from the earliest Late Cretaceous (Cenomanian) of European Russia

Ornithuromorph birds (the clade which includes modern avian radiation) first appeared in the Early Cretaceous in Asia and achieved a great diversity during the latest ages of the Late Cretaceous (Campanian and Maastrichtian). The evolutionary history of orithuromorphs during the first 17 MYAs of the Late Cretaceous (Cenomanian to Santonian ages) remains very poorly known, as the fossil record for this time interval is largely restricted to several isolated finds of the classic avian genus Ichthyornis in North America. Here we describe an isolated distal tibiotarsus of an evolutionary advanced bird, morphologically similar to Ichthyornis, from the middle Cenomanian of Saratov Province, European Russia. This is the first documentation of an Ichthyornis-like bird in the Old World. The find further constitutes only the second pre-Campanian record of the Late Cretaceous Ornithuromorpha in Eurasia, the second record of Cenomanian birds in Russia. This discovery shows that Ichthyornis-like birds enjoyed a wide geographical distribution as early as the beginning of the Late Cretaceous. Given that the earliest and the most primitive ornithuromorph birds are known from Asia, the new find supports a Eurasian origin for Ichthyornithidae.     

A stem lepidosireniform lungfish (Sarcopterygia: Dipnoi) from the Upper Eocene of Libya,North Africa and implications for Cenozoic lungfish evolution

Modern lungfish are represented by three families, Neoceratodontidae in Australia, Protopteridae in Africa, and Lepidosirenidae in South America, with the latter two comprising the Lepidosireniformes. However, the group was far more diverse as recently as the Cretaceous. Here, a new lungfish, Xenoceratodus labyrinthus is described on the basis of upper and lower tooth-bearing elements from the Late Eocene of Dur at Talah, eastern Libya. Toothplates are characterized by four denticulations, low crests and ridges, and a well-developed crushing surface. The occlusal surface bears a unique ornament of enamel lines that branch to form a reticulate pattern across the crushing surface of the jaws. The new lungfish is closely related to the Paleocene Lavocatodus giganteus and the Late Cretaceous Lavocatodus? humei, which in turn are interpreted as a clade of stem Lepidosireniformes. Along with the presence of archaic lungfish lineages in the Cenozoic of South America and Australia, Xenoceratodus suggests that a wide range of lungfish lineages crossed the Cretaceous-Paleogene boundary, only to later become extinct; climate change and teleost radiation in the Cenozoic may have ultimately led to their decline.     

Calcareous nannofossil assemblage changes and stable isotope data from Maastrichtian to Selandian in the Akveren Formation,Western Black Sea,Turkey

This study is based on calcerous nannofossil assemblages changes and fluctutions of stable carbon and oxygen isotopes was collected clayey limestones, limestones, and marls in the Maastrichtian to Selandian from Akveren Formation (Western Black Sea). As the relative abundances of species of Micula spp, Watznauera barnesiae, and Arkhangelskiella cymbiformis, which tolerated changes of temperature and nutrition, carbon and oxygen isotopes compositions, and low species richness imply strong diagenesis effect at the Maastrichtian, there is no important diagenesis effect at Paleocene. Just after the Cretaceous/Tertiary (K-Pg) boundary, Thoracosphaera spp. and Braarudosphaera bigelowi were dominant species; Danian is characterized by Thoracosphaera, Ericsonia ovalis, Cruciplacolithus spp., Coccolithus pelagicus, and Ericsonia subpertusa. Generally, the nutrition productivity is good–moderate in Lower Maastrichtian, and decreasing carbon isotope values during the Uppermost Maastrichtian shows the presence of oligotrophic environmental conditions suitable with global nutrition crises before the K-Pg boundary and diagenesis in study area. Throughout the Danian, mesotrophic–oligotrophic environmental conditions dominate; however, the decrease in nutrition before Selandian represents oligotrophic environmental conditions. The increasing nutrition at Selandian is related to the change in the environmental conditions.     

Biogeography of the Saharan Gretaceous and Paleocene epicontinental transgressions

The first trans-Saharan epicontinental transgression began in the Late Cenomanian and peaked in the Early Turonian. The sea entered through rifts (Nigeria) and subsiding areas (north Africa) and, at maximum extent, spilled out onto stable craton. The central Sahara was land in late Early Turonian time; the sea seems to have remained in the central part of the Benue rift, to sally forth again during the minor Coniacian transgressive pulse. The Coniacian transgression went no further than eastern and central Niger Republic. For a short time during the Cenomanian-Turonian link-up between the Tethys and the South Atlantic, some organisms (mainly ammonites and pelecypods) passed across the Sahara. The Coniacian marine deposits of eastern Niger contain several elements typical of the Mungo River Formation of Cameroun, and coastal Nigeria. These faunistic indications imply that the topographical obstacle formed by the Zambuk ridge of northeastern Nigeria was swamped at maximum transgression. A third, very extensive epicontinental transgression began in latest Campanian time and reached its acme in the Early Maastrichtian. In the central Sahara, at least, there was a retreat of the sea in later Maastrichtian times. A final transgression peaked during the Paleocene, after which the sea withdrew permanently from the northwest African hinterland. The same marine ostracod associations occur in the Paleocene of coastal Nigeria, the Sokoto embayment, Mali and Libya, thus providing strong evidence of a marine connexion, albeit brief, between the South Atlantic and the Tethys, despite the lack of outcrop evidence in the crucial Niger valley region.     

Cretaceous and Tertiary of the Iullemmeden Basin in Nigeria (West Africa)

The Iullemmeden Basin (Mali-Niger-Benin-Nigeria) of tectono-epeirogenic origin was invaded several times by epicontinental transgressions during the Cretaceous and Paleocene.Three major subdivisions are recognized in the Nigerian section of the basin (the “Sokoto Basin”): (1) the lower, continental beds (= Continental Intercalaire) of Late Jurassic to Early Cretaceous age, (2) intermediate marine and brackish water deposits and (3) “Continental T Terminal” of upper Eocene-Miocene age.The geology of the Iullemmeden Basin is reviewed and updated. The relationships between the “Continental Intercalaire” of francophone authors and the Illo and Gundumi Formations are analysed and the type sections of the latter described. It is suggested that the Illo and Gundumi Formations are lateral equivalents.Detailed information on the formations of the Maastrichtian Rima Group is presented. It is concluded that there is no age difference of consequence between the Paleocene Dange, Kalambaina and Gamba Formations.The epicontinental transgressions are interpreted as coming from the north-east, east of the Hoggar massif during the Cenomanian and Turonian and west of the Hoggar during the Maastrichtian and Paleocene. The Sokoto Paleocene molluscan fauna is considered to be terminal Paleocene to Eocene and somewhat younger than the Ewekoro association of coastal Nigeria.A new interpretation of the Continental Terminal is presented. The structural history of the Sokoto Basin is reviewed and partly re-interpreted in the light of new field evidence.     

Le Bassin lusitanien (Portugal) à l'Aptien supérieur–Albien : organisation séquentielle,proposition de corrélations, évolutionThe Lusitanian Basin (Portugal) during the late Aptian–Albian: sequential arrangement,proposal of correlations,evolution

. Three transgressive–regressive 2nd-order cycles were identified in the Upper Aptian–Albian fluvial and marine deposits of the Lusitanian Basin. Its widespread nature, probably including eustatic origin, allows correlation between the southern package, with precise stratigraphic positioning, and the northern series with a poorly constrained age. The main unconformities can be related to the onset of an oceanic crust, in the western margin of Galicia during the Late Aptian, in the bay of Biscay during the Early Albian, and, to the northwest of the Galicia triple point, during the Middle to Late Albian transition, and, at the Albian–Cenomanian boundary, to a probable compressive event with Africa due to the rotation of Iberia. To cite this article: J. Dinis et al., C. R. Geoscience 334 (2002) 757–764.     

Ecologic and taxonomic diversification in the Mesozoic brackish-water bivalve faunas in Japan,with emphasis on infaunalization of heterodonts

Mesozoic brackish-water bivalve faunas in Japan diversified in three steps: at the beginning of the Early Jurassic, Early and Late Cretaceous. The Hettangian Niranohama Fauna in northeastern Honshu represents the establishment of a heterodont-dominated brackish-water fauna that persisted until the early Late Cretaceous. No similar composition is known from the Triassic. The infauna consists mostly of non-siphonate and some short-siphonate heterodonts, while the epifauna is represented by diverse pteriomorphian families. In the Early Cretaceous Tetori Group in central Honshu, the long-siphonate heterodonts Tetoria (Corbiculidae) and the semi-infaunal soft-bottom oyster Crassostrea appeared. The evolutionary diversification of the latter, known as the most important element of modern brackish-water faunas, may thus originate at that time. In the early Late Cretaceous (Cenomanian) of the Goshoura and Mifune Groups in west Kyushu, several euryhaline deep-burrowing heterodont families, such as Veneridae and Tellinidae, further diversified in the brackish and marine environments. The Late Cretaceous is characterized by massive shell biolithic beds in which large Crassostrea species are common, a feature common for Cenozoic brackish-water faunas. The long-term changes in the composition of the brackish-water faunas in Japan represents thus an evolutionary record, irrespective of the severe physiological and environmental conditions imposed on the highly conservative nature of the fauna.     

论敦达古鲁巴哈里亚地区的陆相夹层及非洲其他地层中早白垩世恐龙化石的时代

列举并尝试对比了非洲早白垩世脊椎动物化石的主要产地。晚侏罗世(坦桑尼亚的敦达古鲁基默里奇期提塘期)至白垩纪最早期(南非的阿尔戈阿盆地凡兰吟期)的组合中含有剑龙、腕龙和梁龙,到前阿普特期(欧特里沃期巴列姆期?)被另一组合所取代。这一更年轻的组合中含有重爪龙亚科棘龙类、大头鳄类鳄鱼Sarcosuchus以及大型禽龙,它们主要来自尼日尔(ElRhaz组和喀麦隆(Koum组),部分来自利比亚(Cabao组)和突尼斯(Douiret组),后两组中还含有鲨鱼Priohybodus ar ambourgi。阿普特期(?)至早阿尔必期组合中仍含有禽龙,但是棘龙科棘龙类取代了重爪龙亚科。早塞诺曼期组合(Bahariya,Kem Kem)以恐龙Spinosaurus、Carcharodonto saurus,鲨鱼(Onchopris tisnumidus)和鳄鱼(利比亚鳄类、无棘腔鳄类)为特征。由此可知,中非的一些原先被认为是早白垩世的地层(坦桑尼亚的Galula组、马拉维的含恐龙层)为晚白垩世。脊椎动物化石在非洲陆相地层的对比中具有重要作用。     

Palynostratigraphy and paleoenvironmental significance of the Cretaceous succession in the Gebel Rissu-1 well,north Western Desert,Egypt

Palynological investigation of the Cretaceous Abu Roash, Bahariya, Kharita, Alamein, Alam El Bueib and Betty formations, encountered in the Gebel Rissu-1 well, north Western Desert, Egypt yielded 27 species of pteridophytic spores, 24 of gymnosperm pollen, 25 of angiosperm pollen and 11 of dinoflagellate cysts in addition to some acritarchs, foraminiferal test linings and freshwater algae. This enabled us to recognize five miospore biozones arranged from youngest to oldest as: Classopollis brasiliensis–Afropollis cf. kahramanensis–Dichastopollenites ghazalataensis Assemblage Zone (Late Cenomanian); Elaterosporites klaszii–Sofrepites legouxae–Afropollis jardinus Assemblage Zone (Middle/Late Albian–Early Cenomanian); Pennipollis peroreticulatus–Duplexisporites generalis-Tricolpates Assemblage Zone (Early Aptian–Early Albian); Tucanopollis crisopolensis–Afropollis sp. Assemblage Zone (Barremian) and Appendicisporites cf. tricornitatus–Ephedripites spp. Assemblage Zone (Late Neocomian).The Early Cretaceous Kharita, Alam El Bueib and the Betty formations encountered in the Gebel Rissu-1 well are interpreted to indicate oxic proximal and distal shelf deposits, characterized by type III/IV, V kerogen, which is gas prone but having little potential to produce hydrocarbons. The Upper Cretaceous Abu Roash and Bahariya formations are characterized by a distal suboxic–anoxic and marginal dysoxic–anoxic environment, and their kerogen type III/II indicates gas/oil prone nature. The Bahariya and Kharita Albian–Cenomanian sediments in the present study witnessed the onset of a semi-arid to arid climate, with local or seasonal humid conditions, based on the continuous high abundance of the elaterates pollen and Afropollis-producing plants that inhabited the paleotropical humid coastal plains.     

Cenomanian–Turonian carbon isotope stratigraphy of the Western Canadian Sedimentary Basin

The Cenomanian–Turonian boundary was characterized by distinctive positive carbon isotope excursions that were related to the formation of widespread oceanic anoxia. High-resolution geochemical proxies (TOC, CaCO₃, δ¹³C_org, and δ¹³C_carb) obtained from bulk rock, planktic foraminifers, and inoceramids from four marine marlstone-dominated stratigraphic sections in the Western Canada Sedimentary Basin (WCSB) were used to establish a regional carbon isotope stratigraphic framework and to investigate paleoenvironmental variability in four different depositional settings. Compared to background δ¹³C_org, (<−27‰) and δ¹³C_carb (<2‰) values which were correlative to stable isotope excursions during Oceanic Anoxic Event (OAE) II worldwide, the δ¹³C_org (>24‰), and δ¹³C_carb (>4‰) derived from inoceramid prisms in the studied sections within WCSB, were elevated during the Late Cenomanian–Early Turonian. During this interval, TOC and CaCO₃ values which increased sporadically to >40% and 7%, respectively, were not consistent enough to be used for stratigraphic correlations. Based on the δ¹³C_org excursions, two bentonite beds were regionally correlated across this portion of the Western Interior Seaway (WIS). The eruption associated with the “Red” bentonite occurred approximately coeval with the maximum δ¹³C_org-excursion during OAE II in the Neocardioceras juddii Zone, whereas the “Blue” bentonite coincides with the termination of OAE II in the latest Watinoceras devonense zone. During the Late Cenomanian–Early Turonian in the WCSB, benthic foraminifers were sparse or totally absent, indicating the existence of fully anoxic bottom-water conditions. Planktic foraminifera were common in the well-oxygenated surface waters. A benthic oxic zone characterized by several agglutinated species occurs in the eastern part of the WSCB at the beginning of OAE II in the Sciponoceras gracile zone. The termination of the OAE II in the WCSB coincides with the first occurrence of small ammonites (Subprionocyclus sp.) in the western part of the basin.     

Evidence of the transgression lake of the Subei basin during Late Cretaceous and Paleocene and its geological significance

Based on analysis of the well drilling core from Subei basin, the authors conclude that during the Late Cretaceous and Paleocene, Subei basin was linked with the sea and the deposit was affected by transgression. The cause of marine transgression may be that since Late Cretaceous and Paleocene tension power had predominated ground-stress conditions of the East China Sea and developed a series of half-graben-like basins filled by a huge thick sediment of the Early Tertiary in the shelf of Huabei-Bohai gulf, Subei-South Yellow Sea and East China Sea. Consequently, seawater transgressed from the East China Sea to the Yellow Sea and linked halfgraben-like basins on the shelf to the sea within a short period. During the sedimentation of the Late Cretaceous Taizhou Formation and Paleocene Funing Formation, the Subei basin had formed the ostracoda-enriched dark shale, including predominantly the whole basin E₁ f ₂ Formation and E₁ f ₄ Formation and local K₂ t ₂ Formation, which became the main source rocks of the basin. The evidence of paleontology, minerals in rocks and geochemistry can help confirm the environment of the lake basin that developed during the Late Cretaceous and Paleocene. We generally designate this environment as “near sea lake basin” and the sea-transgressed layer and member as “transgression lake basin”.Whereas, it is generally called “inland lake and river alluvium plain” during the sedimentation of the Eocene Dainan Formation and Sanduo Formation. This research is not only significant to the paleogeographic reconstruction of the Subei basin during the Late Cretaceous and Paleocene, but also important in understanding the development and distribution of the source rocks and evaluating the potential of oil and gas generation. __________ Translated from Acta Sedimentologica Sinica, 2007, 25(3): 380–385 [译自: 沉积学报]     

Late Maastrichtian cephalopods,dinoflagellate cysts and foraminifera from the Cretaceous–Paleogene succession at Lechówka,southeast Poland: Stratigraphic and environmental implications

The Lechówka section comprises the most complete Cretaceous–Paleogene (K-Pg) boundary succession in Poland and is among 29 sites worldwide with the youngest ammonite record. Here, cephalopods (ammonites and nautilids), organic-walled dinoflagellates (dinocysts) and foraminifera from the uppermost Maastrichtian interval are studied. In terms of ammonite biostratigraphy, the upper Maastrichtian Hoploscaphites constrictus crassus Zone is documented up to a level 120 cm below the K-Pg boundary. There is no direct, ammonite-based evidence of the highest Maastrichtian H. constrictus johnjagti Zone. However, the predominance of the dinocyst marker taxon Palynodinium grallator suggests the presence of the equivalent of the uppermost Maastrichtian Thalassiphora pelagica Subzone, which is correlatable with the H. c. johnjagti ammonite Zone. The planktonic foraminiferal assemblage is coeval with that from the H. c. johnjagti Zone as well. These data indicate that the top of the Maastrichtian at Lechówka is complete within the limits of biostratigraphic resolution, albeit slightly condensed. The dinocyst and foraminiferal assemblages are dominated by taxa that are characteristic of high-energy, marginal marine environments. A reduction in test size among the calcareous epifaunal benthic foraminifera is observed at a level 50 cm below the K-Pg boundary, which is possibly related to environmental stress associated with Deccan volcanism.     

塔里木盆地新生代海相沉积问题

基于前人文献,对塔里木盆地新生代海相沉积问题进行梳理,进而探讨该盆地新生代海侵的次数和范围以及海退的时限、原因。研究表明,新生代,塔里木盆地至少经历古近纪的阿尔塔什晚期至齐姆根早期(古新世早期至古新世晚期)、卡拉塔尔期—乌拉根期(始新世中期)、巴什布拉克中期(始新世晚期至早渐新世)等三期海侵;塔里木盆地中新世仍有海相地层这一认识获得广泛认可仍需更多的地质证据来支持。塔里木盆地海侵范围在卡拉塔尔—乌拉根组沉积时期达到最大,向东可达玛扎塔格地区,在盆地北缘和南缘分别可以到达库尔勒以东地区和洛浦县阿其克以东地区。由于受到全球海平面变化和构造运动的共同影响,副特提斯海新生代从塔里木盆地退却的沉积记录包括齐姆根组顶部、乌拉根组顶部、巴什布拉克组第四段和第五段,时间上分别对应于古新世晚期、始新世中晚期和早渐新世。     

The distribution of calcareous nannofossils in the late Santonian–Late Maastrichtian deposits in the southwest of Iran (Khuzestan Province)

The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 (Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 (Aspidolithus parcus zone), CC19 (Calculites ovalis zone), CC20 (Ceratolithoides aculeus zone), CC21 (Quadrum sissinghii zone), and CC22 (Quadrum trifidum zone) represent the Campanian. Biozone CC23 (Tranolithus phacelosus zone) indicate the Late Campanian–Early Maastrichtian. Biozones CC24 (Reinhardtites levis zone) and CC25 (Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi–Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent.     

Dinoflagellate cysts from the Upper Bajocian–Lower Oxfordian of the Dalichai Formation in Binalud Mountains (NE Iran): their biostratigraphical and biogeographical significance

The Binalud Mountains of NE Iran represent the easternmost extension of the Alborz Range. After the Mid-Cimmerian orogenic event and rapid subsidence, the deep marine sediments of the Dalichai Formation were deposited. A well-preserved section of the formation was sampled for palynological purposes. The study revealed diverse and nearly well-preserved dinoflagellate cyst assemblages. Thirty-six dinoflagellate cyst species identified lead to identification of four biozones: Cribroperidinium crispum (Late Bajocian), Dichadogonyaulax sellwoodii (Bathonian to Early Callovian), Ctenidodinium continuum (Early to Late Callovian), and Ctenidodinium tenellum (Early Oxfordian) biozones. The close similarities of dinoflagellate cyst assemblages between Binalud Mountains, NE Iran, with those of Alborz Mountains (Northern Iran) during Middle Jurassic confirm the connection between two sedimentary basins during this time in Iran. Meanwhile, this biozonation corresponds largely to that established in Northwest Europe and reveals the marine connection between NE and North of Iran with Northwest Europe and the Northwestern Tethys during the Late Bajocian to Early Oxfordian.     

Carbon and oxygen-isotope stratigraphy of the Early Cretaceous carbonate platform of Pădurea Craiului (Apuseni Mountains,Romania): A chemostratigraphic correlation and paleoenvironmental tool

Stable C and O isotope records were obtained from carbonate rocks spanning the Hauterivian to Cenomanian interval collected in several sections from the carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania). In the absence of some key biostratigraphic marker species, stable isotopes were applied as a tool for stratigraphic correlation and dating. The composite δ¹³C and δ¹⁸O curves for the Early Cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes. The Hauterivian and the Barremian limestones (Blid Formation) display lower δ¹³C values (−2.8‰ to +2.9‰) relative to the Aptian–Albian deposits (−2.6‰ to +5.4‰) (Ecleja, Valea Măgurii and Vârciorog Formations). The red detrital formation (Albian–Cenomanian) is characterized by a highly variable distribution of the δ¹³C values (−3.5‰ to +3.9‰). Based on the similarities between the C-isotope curve established in Pădurea Craiului and from other sections in the Tethyan and the Pacific regions, two major oceanic anoxic events characterized by δ¹³C positive excursions were clearly recognized. The first is the OAE1a event (Early Aptian) in the upper part of the Ecleja Formation and the Valea Măgurii Formation. The second is the OAE1b event (Late Aptian–Albian) in the upper part of the Vârciorog Formation and in the Subpiatră Member. The position of the Aptian/Albian boundary is estimated to be at the upper part of the Vârciorog Formation, immediately after the beginning of the δ¹³C positive excursion. The δ¹³C data show major negative excursions during the Barremian (Blid Formation), Early Aptian (Ecleja Formation), and Late Aptian (Vârciorog Formation). The O isotope variation pattern (−10.2‰ to −2.1‰) is consistent with progressively warming temperatures during the Early Barremian followed by a cooling period. A subsequent warming period culminated in the Early Aptian. A significant cooling phase corresponds to the Late Aptian and Early Albian and the climate cooled again during the Late Albian and into the Early Cenomanian stage. The data provide a better understanding of the Early Cretaceous sedimentation cycles in Pădurea Craiului and create a more reliable framework for regional correlations.     

Résultats préliminaires sur la sédimentation pélagique de l'Atlantique tropical au Crétacé et au Tertiaire (plateau de Demerara,Leg ODP 207)

Five sites located on a bathymetric transect of the distal Demerara Rise were studied by ODP Leg 207. Albian sediments of essentially terrigenous nature (clay, siltstone, sandstone) are the oldest drilled stratigraphic levels and form apparently the top of the synrift sequence. They are overlain by Cenomanian to Santonian finely laminated black shales, rich in organic matter of marine origin, which accumulated on a thermally subsiding ramp. Early Campanian hiatuses are thought to be the result of final disjunction of Demerara Rise (South America) from Africa and the onset of deep water communication between the two Atlantic basins (south and central). The overlying Uppermost Cretaceous–Oligocene chalk includes rich and diversified calcareous plankton assemblages, as well as two radiolarian-rich intervals (Late Campanian and Middle Eocene). A complex erosional surface developed during the Late Oligocene–Early Miocene. Sedimentation was impeded since then on the intermediate and deep sites of Demerara Rise, possibly due to the action of deep submarine currents. To cite this article: T. Danelian et al., C. R. Geoscience 337 (2005).