Occurrence of nannoplankton observed in Early Pliocene samples from Zanclean stratotype of Capo Rossello, Sicily (Table I)

Calcareous nannoplankton biostratigraphy has been worked out in the eastern Mediterranean utilizing deep-sea sediments recovered from DSDP Leg 42A Sites 375 and 376. These two drill sites were located approximately 55 km west of Cyprus on the Florence Rise. Sediments, ranging in age from early Miocene (Helicosphaera ampliaperta Zone) through Holocene, contain sufficient age-diagnostic species to recognize essentially all of the lowlatitude nannoplankton zones described by Bukry, although regional, secondary marker species are needed to define some zonal boundaries. Reworked Cretaceous and Paleogene nannoplankton occur throughout the stratigraphic interval studied, but not in quantities large enough to mask indigenous species. Sedimentation rates at Sites 375 and 376 were highest in the late Miocene and late Pleistocene. Open-marine, warm-water species of discoasters are present in significant numbers throughout the Miocene and Pliocene. Earliest Pliocene assemblages contain numerous specimens of ceratoliths. Nannoplankton in post-Messinian sediments at the drill sites and the Zanclean stratotype at Capo Rossello, Sicily, indicate that the base of the Amaurolithus tricorniculatus Zone (base of Triquetrorhabdulus rugosus Subzone) corresponds with the Miocene-Pliocene boundary.

Pliensbachian/Toarcian boundary: the proposed GSSP of Peniche (Portugal)

The Peniche section (Portugal) is considered as a potential stratotype (GSSP) for the Pliensbachian/Toarcian boundary and it is analysed on the background of the available data on the ammonite successions from other Tethyan and NW European areas.

Toarcian GSSP candidate: the Peniche section at Ponta do Trovão

The Peniche section (Ponta do Trovão) in Portugal is presented as potential stratotype (GSSP) for the Pliensbachian/Toarcian boundary. The lithostratigraphic succession is described and the chronostratigraphy, based on ammonite assemblages, is presented; the change in foraminifera assemblages occurs later, only at the base of beds 16 (base of Semicelatum Subzone, Crosbeyi ? Horizon). An extensive bibliographical list of all scientific articles containing specific reference to this stratigraphic boundary, whether from the Lusitanian or Algarve basins, is also presented.

1st datings of ammonite-bearing Bajocian suites from Caucasus (Georgia) - K-Ar ages of volcanic hornblendes

Volcanic flows and tuffs interbedded with ammonite-bearing sediments directly correlatable with the stratotype section of the Bajocian stage have been dated for the first time within the Caucasus area. Three samples, each from a different section, allowed separation of well-preserved brown hornblende; these are considered reliable geochronometers in a region where subsequent volcanic activity occurred. The dated separates are V139: a volcanic layer probably near the base, V142 another layer near the top of the Lower Bajocian substage; V141 a boulder from a latest Bajocian volcanic conglomerate. From bottom to top, apparent ages at 173.5 +/- 2.6, 164.8 +/- 2.5 and 167.1 +/- 1.9 Ma (analytical uncertainty, 95% confidence level) respectively, can be calculated. The consistency of the results is obtained if the dated boulder is interpreted as derived from an underlying layer, The Bajocian-Bathonian boundary is much younger than commonly accepted and younger than 164 Ma.

The prelude of the end-Permian mass extinction predates a postulated bolide impact

The mass extinction at the Permian-Triassic Boundary (PTB) is said to have been abrupt and probably caused by an extraterrestrial impact. However, evidence from the Global Stratotype Section and Point (GSSP) of the base of the Induan at Meishan, China, shows that the biotic crisis began prior to the level, in beds 25 and 26 at which the postulated impact event occurred. Evidence of such an earlier biotic crisis occurs in other sections in South China, and in central and western Tethyan regions. This event is characterized by the extinction of a range of faunas, including corals, deep-water radiolarians, most fusulinids and pseudotirolitidammonoids, and many Permian brachiopods. In all sections, this extinction level is usually a few decimeters to meters below that of the main mass extinction in the event beds (25 and 26) at Meishan, and their correlatives elsewhere. This earlier extinction event happened before the postulated bolide impact at the level of beds 25 and 26, and constrains interpretation of the mechanisms that brought about this greatest mass extinction.

Integrated Ladinian bio-chronostratigraphy and geochrononology of Monte San Giorgio (Southern Alps, Switzerland)

New biostratigraphic data significantly improve the age assignment of the Ladinian succession of Monte San Giorgio (UNESCO World Heritage List site, Southern Alps, Switzerland), whose world-famous fossil marine vertebrate faunas are now dated to the substage and zone levels. High-resolution single-zircon U-Pb dating was performed using ID-TIMS and chemical abrasion (CA) pre-treatment technique on volcanic ash layers intercalated in the biostratigraphically-defined intervals of the Meride Limestone. It yielded ages of 241.07 +/- 0.13 Ma (Cava superiore beds, P. gredleri Zone), 240.63 +/- 0.13 Ma (Cassina beds, P gredleri/P. archelaus transition Zone) and 239.51 +/- 0.15 Ma (Lower Kalkschieferzone, P. archelaus Zone). Our results suggest that the time interval including the vertebrate-bearing Middle Triassic section spans around 4 Myr and is thus significantly shorter than so far assumed. The San Giorgio Dolomite and the Meride Limestone correlate with intervals of the Buchenstein Formation and the Wengen Formation in the reference section at Bagolino, where the Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian was defined. The new radio-isotopic ages of the Meride Limestone are up to 2 Myr older than those published for the biostratigraphically-equivalent intervals at Bagolino but they are consistent with the recent re-dating of the underlying Besano Formation, also performed using the CA technique. Average sedimentation rates at Monte San Giorgio are by more than an order of magnitude higher compared to those assumed for the Buchenstein Formation, which formed under sediment-starved pelagic conditions, and reflect prevailing high subsidence and high carbonate mud supply from the adjoining Salvatore/Esino platforms. Finally, the high-resolution U-Pb ages allow a correlation of the vertebrate faunas of the Cava superiore/Cava inferiore beds with the marine vertebrate record of the Prosanto Formation (Upper Austroalpine), so far precluded by the poor biostratigraphic control of the latter.

Phosphorus and carbon burial during cretaceous oceanic anoxic events, links with climatic changes

According to Jenkyns (2010), oceanic anoxic events (OAE) record profound changes in the climatic and paleoceanographic state of the planet and represent major disturbances in the global carbon cycle. One of the most studied OAEs on a worldwide scale is the Cenomanian-Turonian OAE 2, which is characterized by a pronounced positive excursion in carbon-isotope records and the important accumulation of organic-rich sediments. The section at Gongzha (Tibet) and the sections at Barranca and Axaxacualco (Mexico) are located in remote parts of the Tethys, and show δ13C records, which are well correlated with those of classical Tethyan sections. Both sections, however, do not exhibit the presence of organic-rich sediments. Phosphorus Mass Accumulation Rates (PMAR) in Tibet show a pattern similar to that observed in the Tethys by Mort et al. (2007), which suggests enhanced Ρ regeneration during the OAE 2 time interval, though there is no evidence for anoxic conditions in Tibet. Ρ appears here to have been mainly driven by detrital influx and sea-level fluctuations. The sections at Barranca and Axaxacualco show that the Mexican carbonate platform persisted during this anoxic event, which allowed the evolution of platform fauna otherwise not present in Tethyan sections. The persistence of this carbonate platform close to the Caribbean Igneous Plateau, which is thought to have released bio-limiting metals, is explained by local uplift which delayed the drowning of the platform and a specific oceanic circulation that permitted the preservation of oligotrophic conditions in the area. The Coniacian-Santonian OAE (OAE3) appears to have been more dependent on local conditions than OAE2. The presence of black shales associated with OAE3 appear to have been restricted to shallow-water settings and epicontinental seas in areas located around the Atlantic Ocean. The sections at Olazagutia (Spain), and Ten Mile - Arbor Park (USA), two potential Global Boundary Stratotype Sections and Points (GSSP) sites, are devoid of organic-rich sediments and lack a δ13C positive excursion around the C-S boundary. The Gabal Ekma section (Sinai, Egypt) exhibits accumulations of organic-rich sediments, in addition to phosphorite bone beds layers, which may have been linked to an epicontinental upwelling zone and/or storm inputs. Our data suggest that OAE 3 is rarely expressed by truly anoxic conditions and seems to have been linked to local conditions rather than global paleoenvironmental change. The evidence for detrital-P being the likely cause of Ρ fluctuations during the OAEs studied here does not negate the idea that anoxia was the principal driver of these fluctuations in the western Tethys. However, an explanation is required as to why the Ρ accumulation signatures are mirrored in both oxic and anoxic sedimentary successions. 'Eustatic/climatic' and 'productivity/anoxic' models may have both operated simultaneously in different parts of the world depending on local conditions, both producing similar trends in Ρ accumulation. - Selon Jenkyns (2010), les événements anoxiques océaniques enregistrent de profonds changements dans le climat et la paléoceanographie de la planète et représente des perturbations majeures du cycle du carbone. L'un des plus étudiés à l'échelle mondiale est l'ΟΑΕ2 du Cénomanien-Turonien, qui est caractérisé par une très forte excursion positive des isotopes du carbone et une importante accumulation de sédiments riche en matière organique. La section de Gongzha (Tibet) et les sections de Barranca et Axaxcualco (Mexique) sont situées aux confins de la Téthys, et enregistrent une courbe isotopique en δ13C parfaitement corrélable avec les sections téthysiennes, mais ne montre pas d'accumulation de black shales. Le taux de phosphore en accumulation de masses (PMAR) au Tibet montre un pattern similaire observé également par Mort et al. (2007) dans la Téthys, suggérant un model de régénération du Ρ durant l'anoxie, cependant aucune conditions anoxiques régnent dans la région du Tibet. Ρ apparaît donc principalement guidé par le détritisme et les fluctuations du niveau marin. Les sections de Barranca et d'Axaxacualco montrent que la plateforme carbonatée mexicaine persiste durant cet événement anoxique, et permet le développement d'une faune de plateforme qui n'est pas présente dans les sections téthysiennes. La persistance de cette plateforme carbonatée si proche du plateau Caribéen, qui est connu pour le relâchement de métaux bio-limitant, peut être expliqué par un soulèvement tectonique local qui inhibe l'ennoiement de la plateforme et une circulation océanique spécifique qui permet la préservation de conditions oligotrophiques dans cette région. L'événement anoxique océanique du Coniacien-Santonien apparaît plus dépendant des conditions locales que pour l'ΟΑΕ2. Les black shales associés à POAE3 sont restreints aux zones situées autour de l'océan Atlantique et plus particulièrement aux eaux peu profondes et épicontinentales. Les sections d'Olazagutia (Espagne), Ten Mile Creek et Arbor Park (USA), qui sont deux potentielles sections GSSP (Sections de stratotype de limite globaux et de points), ne montre pas d'accumulation de black shales et pas de forte excursion positive en δ13C autour de la limite C-S. La section de Gabal Ekma (Sinai, Egypte) montre des accumulations de black shales, en plus des couches de phosphorites et d'accumulation d'os (« bone beds »), vraisemblablement lié à des zones active d'upwelling épicontinentale et/ou d'apport de tempêtes. Nos données suggèrent que l'OAE 3 est rarement exprimé par de vraies conditions anoxiques et semble être plus lié à des conditions plus locales que des changements paléo-environnementaux globaux, comme observés pour le Cénomanien- Turonien. Les arguments pour un modèle lié au phosphore détritique qui serait la cause des fluctuations du phosphore total durant les OAEs, n'écartent pas l'idée que l'anoxie est la principale cause de ces fluctuations dans les sections riches en matière organique de l'Ouest téthysien. Cependant une explication est nécessaire pour comprendre pourquoi la signature de l'accumulation du phosphore est semblable dans les successions sédimentaires déposées dans des conditions oxygénées et anoxiques. Les modèles « Eustatisme/Climat » et « Productivité/anoxie » ont simultanément opéré dans les différentes parties du monde dépendant de conditions locales, et ont produit des tendances similaires en accumulation de phosphore.

Cenomanian-Turonian transition in a shallow water sequence of the Sinai, Egypt

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, delta(13)C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian-early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak delta(13)C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the delta(13)C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the delta(13)C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first delta(13)C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous delta(13)C shift, but delayed effects of OAE2 dependent on water depth.

Late Barremian-Early Aptian palaeoenvironmental change: the Cassis-La Bedoule section (SE France)

The well-dated section of Cassis-La Bédoule in the South Provencal Basin (southern France) allows for a detailed reconstruction of palaeoenvironmental change during the latest Barremian and Early Aptian. For this study, phosphorus (P) and clay-mineral contents, stable-isotope ratios on carbonate (δ13Ccarb) and organic matter (δ13Corg), and redox-sensitive trace elements (RSTE: V, U, As, Co, and Mo) have been measured in this historical stratotype. The base of the section consists of rudist limestone, which is attributed to the Urgonian platform. The presence of low P and RSTE content, and content of up to 30% kaolinite indicate deposition under oligotrophic and oxic conditions, and the presence of warm, humid climatic conditions on the adjacent continent. The top of the Urgonian succession is marked by a hardground with encrusted brachiopods and bivalves, which is interpreted as a drowning surface. The section continues with a succession of limestone and marl containing the first occurrence of planktonic foraminifera. This interval includes several laminated, organic-rich layers recording RSTE enrichments and high Corg:Ptot ratios. The deposition of these organic-rich layers was associated with oxygen-depleted conditions and a large positive excursion in δ13Corg. During this interval, a negative peak in the δ13Ccarb record is observed, which dates as latest Barremian. This excursion is coeval with negative excursions elsewhere in Tethyan platform and basin settings and is explained by the increased input of light dissolved inorganic carbon by rivers and/or volcanic activity. In this interval, an increase in P content, owing to reworking of nearshore sediments during the transgression, is coupled with a decrease in kaolinite content, which tends to be deposited in more proximal areas. The overlying hemipelagic sediments of the Early Aptian Deshayesites oglanlensis and D. weissi zones indicate rather stable palaeoenvironmental conditions with low P content and stable δ13C records. A change towards marl-dominated beds occurs close to the end of the D. weissi zone. These beds display a long decrease in their δ13Ccarb and δ13Corg records, which lasted until the end of the Deshayesites deshayesi subzone (corresponding to C3 in Menegatti et al., 1998). This is followed by a positive shift during the Roloboceras hambrovi and Deshayesites grandis subzones, which corresponds in time to oceanic anoxic event (OAE) 1a interval. This positive shift is coeval with two increases in the P content. The marly interval equivalent to OAE 1a lacks organic-rich deposits and RSTE enrichments indicating that oxic conditions prevailed in this particular part of the Tethys ocean. The clay mineralogy is dominated by smectite, which is interpreted to reflect trapping of kaolinite on the surrounding platforms rather than indicating a drier climate.