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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
I dubbi metafisici di un tranviere poeta
No full textUn'introduzione all'edizione commentata del capolavoro di Luciano Erba (1922-2010), "L'ippopotamo", come occasione per riflettere sulla ricezione editoriale e critica dell'autore milanese
Calcareous nannofossil paleofluxes: proxies for pCO2 fluctuations through the Aptian
No full textThe Cretaceous has been punctuated by episodes of widespread organic matter burial in oxygen-depleted oceans known as Oceanic Anoxic Events (OAEs) (Schlanger & Jenkyns, 1976). In particular, the Aptian (~121 to ~113 Ma) has been characterized by a super-greenhouse climate and profound environmental perturbations, including the early Aptian OAE 1a, thought to be related to the emplacement of the Ontong Java Plateau.
The aim of this work is to study variations in biogenic carbonate production of calcareous nannofossils through the Aptian in order to detect if and how it has been affected by high pCO2. Calcareous nannoplankton is an excellent proxy for reconstructing present and paste surface water conditions, being extremely sensitive to changes in physical and chemical conditions of the oceans (pH). Studies on living form have attested a direct response of these organisms to changes in CO2 concentrations (e.g. Krug et al. 2010). Production of dwarf/malformed coccoliths has also been documented in the geological record through OAE 1a (Erba et al. 2010).
Here we present quantitative analyses of nannofossil micrite in thin sections, reconstructing nannofossil absolute abundances and calcite paleofluxes in three drill sites: the Cismon core (Northern Italy), Piobbico core (Central Italy) and DSDP Site 463 in the mid-Pacific Mountains. In each of the three sites, nannofossil absolute abundances and paleofluxes show a progressive drastic reduction starting in the latest Barremian. This decrease is due to a worldwide decrease in the rock-forming nannoconids, “nannoconids decline”, that culminates with the “nannoconids crisis” just prior to OAE 1a (Erba, 1994; Erba & Tremolada, 2004). At the end of OAE 1a, nannofossil biocalcification increases again, but it never reaches pre-anoxia values. In the late Aptian, nannofossil paleofluxes reach high values during the Nannoconus truittii acme, followed by a final decrease through the Aptian/Albian boundary interval.
Calcite paleofluxes fluctuations reveal a drastic reduction in nannoplankton calcification interpreted as the adaptive response of these organisms to perturbed surface-water conditions that favoured small and less calcified forms and caused false extinction among heavily calcified nannoconids (Lazarus effect). We conclude that, despite metabolic processes, CO2 concentrations influence the ocean chemistry and the carbonate system. In particular, the correlation between reduced biocalcification rates and intervals of intense volcanism, suggest that mid-Cretaceous nannoplankton biocalcification and nannofossil paleofluxes were strongly controlled by excess volcanogenic CO2.
REFERENCES
Erba, E. (1994). Nannofossils and superplumes: The early Aptian “nannoconid crisis”. Paleoceanography, 9: 483-501.
Erba, E. & Tremolada, F. (2004). Nannofossil carbonate fluxes during the Early Cretaceous: phytoplankton response to nutrification episodes, atmospheric CO2 and anoxia. Paleoceanography, 19: 1008.
Erba, E., Bottini, C., Weissert, H.J., Keller, C.E. (2010). Calcareous Nannoplankton response to surface-water acidification around Oceanic Anoxic Event 1a. Science 329: 428–432.
Krug, S.A., Schulz, K.G., Riebesell, U. (2010). Effects of CO2-induced changes in seawater carbonate chemistry speciation on Coccolithus braarudii: a conceptual model of coccolithophorid sensitivities. Biogeosciences Discuss., 7: 8763–8778.
Schlanger, S.O. & Jenkyns, H.C. (1976). Cretaceous oceanic anoxic events: causes and consequences. Geol. Mijnb., 55: 179–184
Clero secolare, storiografie, metodo critico. Sull'itinerario intellettuale di p. Achille Erba
No full textIl contributo analizza il percorso storiografico del barnabita Achille Erba con particolare riguardo per le monografie più importanti. L'analisi intreccia il contenuto delle opere con il parallelo evolvere dei rapporti intellettuali intercorsi tra lo studioso e le varie scuole storiografiche o gruppi di lavoro che fecero da sfondo al progredire delle ricerche di Erba. Ne risulta uno spaccato delle diverse tendenze che caratterizzarono tra gli anni Sessanta ed Ottanta l'evolvere europeo degli studi in ambito storico-religioso
v-erbA overexpression is required to extinguish c-erbA function in erythroid cell differentiation and regulation of the erbA target gene CAII.
No full textUdgivelsesdato: 1991-NovThe v-erbA oncoprotein represents a retrovirus-transduced oncogenic version of the thyroid hormone (T3/T4) receptor c-erbA (type alpha). It contributes to virus-induced erythroleukemia by efficiently arresting differentiation of red cell progenitors and by suppressing transcription of erythrocyte-specific genes. Here, we show that v-erbA and c-erbA bind directly to sequences within the promoter of the erythrocyte-specific carbonic anhydrase II (CAII), a gene whose transcription is efficiently suppressed by v-erbA. This erbA-binding site confers thyroid hormone responsiveness to a heterologous promoter in transient expression experiments and is a target for efficient down-regulation of CAII transcription by the v-erbA oncoprotein. In stably transformed erythroblasts coexpressing the v-erbA oncoprotein and the c-erbA/T3 receptor at an approximately equimolar ratio, c-erbA activity is dominant over v-erbA. T3 efficiently induced erythroid differentiation in these cells, thus overcoming the v-erbA-mediated differentiation arrest. Likewise, T3 activated CAII transcription as well as transient expression of a T3-responsive reporter gene containing the CAII-specific erbA-binding site. The c-erbA-dependent activation of this CAII reporter construct could only be suppressed by very high amounts of v-erbA. Our results suggest that overexpression of v-erbA is required for its function as an oncoprotein
Calcareous nannofossil paleofluxes as proxy of pCO2 fluctuations during the Early Cretaceous
No full textCalcareous nannoplankton is an excellent proxy for detecting present and paste surface water conditions, being extremely sensitive to changes in temperature, fertility, salinity and chemical conditions of the oceans. We investigated a time interval of the geological history that includes the early Aptian Oceanic Anoxic Event 1a (OAE1a) (Schlanger and Jenkyns, 1976; Arthur et al., 1990), characterized by pronounced global changes in the composition and structure of the ocean-atmosphere system due to increased volcanogenic CO2 emissions associated with the emplacement of the Ontong Java and Manihiki Plateau.
In order to detect the response of calcareous phytoplankton to global changes and C-cycle perturbation, quantitative analyses of nannofossil micrite were conducted in thin sections, reconstructing nannofossil absolute abundances and calcite paleofluxes in two drill sites: the Cismon core (Northern Italy) and the DSDP 463 Site in the mid-Pacific Mountains.
At both sites, in the Barremian –Aptian interval, nannofossil absolute abundances and paleofluxes show a progressive drastic reduction, marked by a worldwide decrease in the rock-forming nannoconids “nannoconids decline”, that culminates with the “nannoconids crisis” just prior to the Selli event (Erba, 1994; Erba and Tremolada, 2004). At the end of the OAE1a, nannofossil biocalcification increases again, but it never reaches pre-anoxia values. In the late Aptian, nannofossil paleofluxes reach maximum values during the Nannoconus truittii acme, followed by a final decrease through the Aptian/Albian boundary interval.
Calcite paleofluxes fluctuations reveal a drastic reduction in nannoplankton calcification interpreted as the adaptive response of these organisms to perturbed surface-water conditions that favoured small and less calcified forms and caused false extinction among heavily calcified nannoconids (Lazarus effect). We speculate that mid-Cretaceous nannoplankton biocalcification and nannofossil paleofluxes were strongly controlled by excess volcanogenic CO2. Despite metabolic processes, CO2 concentrations influence the ocean chemistry and the carbonate system.
Excess CO2 conditions were perhaps enhanced by introduction of biolimiting metals at hydrothermal fields during construction of submarine Large Igneous Provinces
Dr. Warren's Erba Buena Bitters
No full textTrade card advertising Dr. Warren's Erba Buena Bitters, a remedy prepared by H. Williams & Co., San Francisco. Title on verso: Dr. Warren's Erba Buena Bitters
Morphological changes of calcareous nannofossils during Oceanic Anoxic Event 2
No full textThe Cenomanian - Turonian Oceanic Anoxic Event 2 (OAE2) is one of the most pronounced perturbations of the Cretaceous that induced major changes in the marine environment and severe disturbances of the biosphere. It is thought to be linked to extensive volcanism and particularly to the emplacement of a Large Igneous Province (LIP) that acted as a natural source of excess CO2. Particularly, OAE2 seems to be strictly connected with the formation of the Caribbean Plateau, which triggered a chain of events leading to enhance ocean fertility, accelerated organic carbon burial, widespread ocean anoxia, and acidification.
Calcareous nannoplankton is sensitive to chemical - physical - trophic changes and must have reacted to the OAE2 extreme environmental conditions. Indeed, nannofossil data show that they experienced a turnover, a general decrease in species richness and locally a decline in abundance of the fertility indicator species.
In this study we present new results of a detailed morphometric analysis of 4 nannofossil species during OAE2 from two different areas: the Mediterranean area (Novara di Sicilia section, North-eastern Sicily) and the Sussex area (Eastbourne section, United Kingdom). These sections have been chosen based on integrated high-resolution stratigraphy: the C isotopic anomaly is taken as primary tool of dating and correlation of OAE2 events. Furthermore the Novara di Sicilia section represents only the lower portion of OAE2, whereas the Eatsbourne section, covering the entire OAE2 interval, provides the opportunity to characterize changes before, during and after the paleoenvironmental perturbation.
In analogy to the work of (ERBA et alii, 2010) on the Early Aptian OAE1a, biometric analyses were performed at high resolution on B. constans, D. rotatorius, Z. erectus and W. barnesiae in order to evaluate the influence of paleoenvironment on coccolith size and morphology. Size measurements of calcareous nannofossils were carried out on smear slides with a light microscope: in each sample 30 specimens of B. constans, D. rotatorius, Z. erectus and 50 specimens of W. barnesiae have been measured by using the Qcapture Pro suite.
Morphometric analyses highlight that:
1. In both sections dwarf coccoliths are present even before the OAE2 onset.
2. There is a species - specific response in both section: B. constans displays the most pronounced reduction in size, D. rotatorius records a well express reduction in size too as opposed to Z. erectus which diminishes in size to a lesser extend.
3. In both sections, the mean size of W. barnesiae is within the holotype and normal range size
4. In the Novara di Sicilia section dwarf coccoliths record the strongest reduction in size relative to Eastbourne samples.
5. Pronounced dwarfism is observed in discrete intervals before and within the carbon isotope excursion.
6. During OAE2 coccoliths return to normal sizes around the carbon isotopic peak “A”.
Comparison of morphometric analyses through OAE1a (ERBA et alii, 2010) and OAE2 shows analogies and differences. During OAE1a dwarfism and malformation are restricted to the onset of the carbon isotopic anomaly, in the core of the negative shift coeval with most profound paleoenvironmental perturbations. In the OAE2 interval dwarfism is most pronounced in the last part of the C isotopic anomaly, and coccolith deformation is negligible. During the two major Cretaceous OAEs, the ocean experienced extreme CO2 concentrations, acidification and an increase in fertility. Coccolith dwarfism suggests a link between nannoplankton calcification and high pCO2, although enhanced fertility and/or presence of toxic metals in seawater might have been instrumental as well. We speculate that during OAE1a and OAE2 excess CO2 played a fundamental role in ruling nannoplankton calcification efficiency, and that coccolith dwarfism might be a proxy of ocean acidification. Different patterns and degree of dwarfism and malformation during OAE1a and OAE2 suggest unequal volcanic CO2 emissions (rates, pulses, amount). We conclude that analogous causes (LIPs emplacement) have induced partially similar response at different times.
REFERENCE
ERBA E., BOTTINI C., WEISSERT H.J. & KELLER C.E., L., (2010) – Calcareous nannoplankton response to surface- water acidification around Oceanic Anoxic Evenet 1. Science, 329, 428-432
v-erbA oncogene activation entails the loss of hormone-dependent regulator activity of c-erbA.
No full textUdgivelsesdato: 1990-Jun-15The v-erbA oncogene, one of the two oncogenes of the avian erythroblastosis virus, efficiently blocks erythroid differentiation and suppresses erythrocyte-specific gene transcription. Here we show that the overexpressed thyroid hormone receptor c-erbA effectively modulates erythroid differentiation and erythrocyte-specific gene expression in a T3-dependent fashion, when introduced into erythroid cells via a retrovirus. In contrast, the endogenous thyroid hormone receptor does not detectably affect erythroid differentiation. The analysis of a series of chimeric v-/c-erbA proteins suggests that the v-erbA oncoprotein has lost one type of thyroid hormone receptor function (regulating erythrocyte gene transcription in response to T3), but constitutively displays another function: it represses transcription in the absence of T3. The region responsible for the loss of hormone-dependent regulator activity of v-erbA has been mapped to the very C-terminus of c-erbA, encompassing a cluster of highly conserved amino acid residues with the potential to form an amphipathic alpha-helix
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