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Calcareous nannofossils biostratigraphy (Upper Bajocian – Lower Bathonian) of the Ravin du Bès section (Bas Auran, Subalpine Basin, SE France), evolutionary trends of Watznaueria barnesiae and new enigmatic morphotypes of genus Rucinolithus
No full textA biostratigraphic and evolutionary study based of calcareous nannofossils was performed on the Ravin du Bès section (Bas Auran area, SE France), proposed as formal candidate of Global Boundary Stratotype Section and Point (GSSP) for the base of the Bathonian stage (Fernàndez-Lòpez et al., 2007). Semiquantitative estimates of total nannofloral abundance and single species abundance were carried out. The following biohorizonts were identified and calibrated to ammonite biostratigraphy: the first occurrence (FO) of Watznaueria aff. W. barnesiae, the FO of Pseudoconus enigma; the FO of Rucinolithus sp.; the last occurrence (LO) of Hexalithus magharensis; the FO of Stephanolithus speciosum octum and the FO of Watznaueria barnesiae. These results, consistent with biostratigraphic scheme previously proposed (Erba 1988, 1990; de Kaenel & Bergen 1993; de Kaenel et al. 1996; Bown & Cooper 1998; Mattioli & Erba 1999) confirm that the calcareous nannofossils are good biostratigraphic markers for the Bajocian/Bathonian boundary interval. Moreover, the finding of P. enigma within of the Sub-Mediterranean province allows a direct calibration between Tethyan and Boreal nannofossil events and biozones.
This study showed an evolutionary trend from Watznaueria communis to Watznaueria barnesiae that seems to support the theory of punctuated equilibria rather than a phyletic gradualism.
We also documented the occurrence of new morphotypes of uncertain polycycloliths. These enigmatic nannoliths are very similar to specimens of the Cretaceous taxon R. terebrodentarius, whose peculiar structure poses doubts on its origin. In fact, as previously speculated (Tremola & Erba 2002; Erba 2004), R. terebrodentarius nannoliths might be CaCO3 precipitates or biocalcification by bacteria under peculiar oceanographic conditions rather than products of coccolithophorid algae.
REFERENCES
Bown, P.R., Cooper, M.K.E, 1998. Jurassic. In: Bown, P.R. (EDS.), Calcareous Nannofossil Biostratigraphy. British Micropaleont. Soc. Publ. Series. Kluwer Academic Publishers, London: 34-85.
De Kaenel, E., Bergen, J.A., 1993. New early and Middle Jurassic coccolith taxa and biostratigraphy from the eastern proto-Atlantic (Morocco, Purtugal and DSDP Site 547B). Eclogae Geol. Helv., 86: 861-907.
De Kaenel, E., Bergen, J.A., von Salis Perch Nielsen, K., 1996. Jurassic calcareous nannofossils biostratigraphy of western Europe. Compilation of recent studies and calibration of bioevents. Bull. Soc. Geol. Fr., 167: 15-28.
Erba, E., 1988. Calcareous nannofossils from the Bas Auran section. In: M., Innocenti, C., Mangold, G., Pavia and H. Torrens, A proposal for the formal ratification of the basal boundary stratotype of the Bathonian stage based on a Bas Auran section (S.E. France). 2nd International Symposium on Jurassic Stratigraphy, 333-346.
Erba, E., 1990. Calcareous nannofossil biostratigraphy of some Bajocian sections from Digne area (SE france). Mem. Descr. Carta geol. Ital.,40: 237-356.
Erba, E. 2004. Calcareous nannofossils and Mesozoic Oceanic Anoxic Events. Marine Micropaleont. 52, 85-106.
Fernando-Lòpez, S.R., Pavia, G., Erba, E., Guiomar, M., Henriques, M.H., Lanza, R., Mangold, Morton, N., C., Olivero, D., Tiraboschi, D., 2007. Formal proposal for the Global Boundary Stratotype Section and Point (GSSP) of the Bathonian Stage, at the base of the Zigzag Zone in the Ravin du Bès Section (Bas-Auran, Sudalpine Basin, SE France). International Subcommission of Jurassic Stratigraphy. Bathonian Working Group Ballot: 1-43.
Mattioli, E., Erba, E., 1999. Synthesis of calcareous nannofossil events in Tethyan Lower and Middle Jurassic successions. Riv. Ital. Paleontol. Stratigr., 105: 373- 376.
Tremolada, F., Erba, E., 2002. Morphometric analyses of Aptian Assipetra infracretacea and Rucinolithus terebrodentarius nannoliths: Implications for taxonomy, biostratigraphy and paleoceanography. Marine Micropaleont., 44: 77-92
Il pianeta si copre di fiori in una "super-serra" (120 milioni di anni fa)
No full textStorie del pianeta terra.il pianeta si copre di fiori in una super-serra (120 milioni di anni fa)
Possible effects of excess pCO2 on the oceanic ecosystem : Is the Cretaceous super-greenhouse replicable in the future?
No full textUpwelling in the Jurassic-Cretaceous Pacific Ocean : biota changes and sedimentary evidence for paleoequatorial crossings of the Pacific Plate
No full textCalcareous nannofossils and Mesozoic Oceanic Anoxic Events
Full text linkTwenty-five years ago, Mesozoic oceanic anoxic events (OAEs) were documented and formalised as intervals of widespread to global deposition of organic matter. The Toarcian, Early Aptian (OAE1a) and latest Cenomanian (OAE2) OAEs are truly global in nature, commonly carbonate-poor, and typically represented by organic carbon-rich black shales. In some areas, these OAEs are also characterised by abundant radiolarian-sands and silts. They are associated withnegative and positive excursions in the 87Sr/86Sr record, in addition to large global carbon-isotope anomalies in carbonateand/or organic matter, caused by a major perturbation of the global carbon budget. Increased rates of volcanism during theformation of the Ontong Java (and Manihiki) and Caribbean Plates, and the Karoo-Ferrar Traps, are believed to havecaused the geological responses associated with OAE1a, OAE2, and the Toarcian OAE, respectively. Excess volcanogenic CO2 in the atmosphere most probably turned the climate into a greenhouse mode, accelerating continental weathering and increasing nutrient content in oceanic surface-waters via river run-off. Higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes. Because Mesozoic OAEs are often represented by carbonate-poor sediments, quantitative studies of calcareous nannofossils have been applied to explore (a) the causes and effects of igneous/tectonic events and climate changes, relative to nannofloral increases and crises, as well as (b) dissolution events, and (c) diagenetic modifications.
Characterization of calcareous nannofloras in OAE intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis (biological pump) and biomineralisation (carbonate pump) that affect the organic and inorganic carbon cycle, as well as adsorption of atmospheric CO2 in the oceans. Types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events. In selected sections, it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pCO2 by drastically reducing calcification. As in the modern oceans, during OAEs the increase of nutrients and atmospheric CO2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep-photic zone nannoconids and schizosphaerellids. Similarly to the ‘nannoconid crisis’ preceding deposition of the Early Aptian OAE1a black shales, a ‘schizosphaerellid crisis’ is detected prior to the Toarcian OAE. Both OAEs are further characterised by a rapid nannofloral speciation, beginning approximately 1.5 myr before the OAE, but without extinctions. Global changes during the latest Cenomanian OAE 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions. This event, in fact, was a time of extinctions followed by originations within calcareous nannofossils. Precise timing of the events before, during and after OAE1a, OAE2 and the Toarcian OAE indicates that they were intervals of enhanced oceanic productivity and that anoxia/dysoxia post-dated biotic changes
Challenges in Mesozoic paleoceanography
No full textThe Cretaceous ocean was unusual in many aspects and provide opportunities to explore, quantify, and model processes that might impact our current ocean in the (near) future. A pressing issue for humankind is the understanding of the future state of the planet within the context of increasing carbon dioxide (CO2) and other greenhouse gas concentrations, climate change, and the adaptations or extinctions in the Earth’s biosphere in response to Anthropocene perturbations.
The ocean is the oldest and largest ecosystem on Earth, and biodiversity changes at one trophic level (primary producers) lead to a variety of responses at higher levels. To predict future effects of increasing atmCO2 and other greenhouse gases, global warming, sea level rise, ocean acidification, and eutrophication, short-term current changes require integration with long-term variations. Thus, the geologic record of past environmental perturbations is relevant for understanding current and future global changes, biotic responses, and how and at what rate pre-perturbation conditions are eventually restored.
Cretaceous examples of coupled excess CO2 (and other greenhouse gases) and extreme climates are also associated with global anoxia, making the recognition of individual causes and their role extremely challenging. Major information on Cretaceous oceans was obtained from the early stages of scientific ocean drilling (DSDP), and augmented subsequently (ODP), but significant geographic and stratigraphic limitations prevent a thorough understanding of the causes and consequences of environmental changes. Cretaceous sediment in the global ocean is largely under-sampled, despite its vast geographic extent. Moreover, Cretaceous pelagic sections from the Pacific and Indian oceans, characterized by alternating hard-soft (e.g., chert-chalk) layers, have been exceedingly difficult to core dur¬ing DSDP, ODP, and IODP. It remains a major technical challenge to improve upon sparse core recovery in such section, and lack of such sections pre¬cludes systematic studies of the geological past and applications to our future.
An ad hoc Magellan Workshop will be held in April 2013 to foster new scientific (ocean and continental) drilling projects that will advance understanding of the Cretaceous world, and develop a long-term strategy of drilling targets. Some priority targets require Chikyu, a unique platform that has deep riser drilling capabilities to core (and recover) Cretaceous sedimentary sections.
This white paper focuses on major challenges in Mesosozic paleoceanography—Oceanic Anoxic Events, (super)greenhouse climates, marine biota and environment co-evolution—in the Pacific Ocean and the in situ Tethys. In the Pacific, Chikyu riser drilling will allow good recovery of Cretaceous and Upper Jurassic sedimentary sections from the Magellan Rise, Shatsky Rise, Ontong Java Plateau, Manihiki Plateau, Hikurangi Plateau, and Hess Rise, where chert and chert-chalk alternations have hampered core recovery. The POP (Pacific Ocean Plateaus) project comprises a number of sites located in water depths currently within Chikyu’s range (≤2500 m); other key sites in greater water depths (2500-4000 m) may be drilled when Chikyu gains such capabilities.
Recent investigations suggest that the Ionian Abyssal Plain of the Eastern Mediterranean might be the oldest in situ ocean fragment of the world, with ocean crust of Late Triassic age. Here, the TOIS (Tethys Ocean In Situ) project proposes to sample a Cretaceous-Jurassic and Upper Triassic section uncontaminated by the Alpine orogeny and subsequent tectonics. The current water depth of the Ionian Abyssal Plain is ~4000 m, and the sedimentary section is estimated to be ~ 7000 m thick. Coring of Tethys in situ is thus an extremely ambitious target comparable to the Moho project.The deep riser-drilling vessel Chikyu is the only scientific platform capable of retrieving key data from the oceans and provides the scientific community with the opportunity to reach targets inaccessible by any other platform. Implementation of its technical capabilities in the next decade (greater water depths and deeper drilling) will be constitute milestones in scientific exploration of ocean and Earth history
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