1,377 research outputs found
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
Kinetic and thermodynamic analysis of leech-derived tryptase inhibitor interaction with bovine tryptase and bovine trypsin
Get PDFThe interaction of leech-derived tryptase inhibitor (LDTI) with bovine liver capsule tryptase (BLCT) and bovine trypsin has been studied using both thermodynamic and kinetic approaches. Several differences were detected: (i) the equilibrium affinity of LDTI for BLCT (K-a = 8.9 x 10(5) M-1) is about 600-fold lower than that for bovine trypsin (K-a = 5.1 x 10(8) M-1); (ii) LDTI behaves as a purely non-competitive inhibitor of BLCT, while it is a purely competitive inhibitor of bovine trypsin. These functional data are compared with those previously reported for the LDTI binding to human tryptase, where tight inhibition occurs at two of the four active sites of the tetramer (K-a = 7.1 x 10(8) M-1). Amino acid sequence alignment of BLCT, human beta II-tryptase and bovine trypsin allows us to infer some possible structural basis for the observed functional differences
Efficient Reduced Basis Algorithm (ERBA) for Kernel-Based Approximation
Get PDFThe main purpose of this work is to provide an efficient scheme for constructing kernel-based reduced interpolation models. In the existing literature such problems are mainly addressed via the well-established knot insertion or knot removal schemes. Such iterative strategies are usually quite demanding from a computational point of view and our goal is to study an efficient implementation for data removal approaches, namely efficient reduced basis algorithm (ERBA). Focusing on kernel-based interpolation, the algorithm makes use of two iterative rules for removing data. The former, called ERBA-r, is based on classical residual evaluations. The latter, namely ERBA-p, is independent of the function values and relies on error bounds defined by the power function. In both cases, inspired by the so-called extended Rippa’s algorithm, our ERBA takes advantage of a fast implementation
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
Autoimpollinazione e impollinazione incrociata in erba medica
No full textAnalizzando la distribuzione bi-modale delle altezze e delle masse verdi di piante di erba medica, e' stato possibile stimare la percentuale di individui di ciascuna delle due popolazioni (piante da incrocio e piante da auto-fecondazione). La chiave del lavoro consiste nel supporre la distribuzione bi-modale miscuglio di due distribuzioni normali
Nannofossil carbonate fluxes during the Early Cretaceous : phytoplankton response to nutrification episodes, atmospheric CO2 and anoxia
No full textGreenhouse episodes during the Valanginian and Aptian correlate with major perturbations in the C cycle and in marine ecosystems, carbonate crises, and widespread deposition of Corg-rich black shales. Quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the Southern Alps (northern Italy), where high-resolution integrated stratigraphy allows precise dating of Early Cretaceous geological events. Rock-forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean-atmosphere system. Increased rates of volcanism during the formation of Ontong Java and Manihiki Plateaus and the Paranà-Etendeka large igneous province (LIP) are proposed to have caused the geological responses associated with early Aptian oceanic anoxic event (OAE) la and the Valanginian event, respectively. Calcareous nannofloras reacted to the new conditions of higher pCO2 and fertility by drastically reducing calcification. The Valanginian event is marked by a 65% reduction in nannofossil paleofluxes that would correspond to a 2-3 times increase in pCO2 during formation of the Paranà-Endenteka LIP. A 90% reduction in nannofossil paleofluxes, which occurred in a 1.5 myr-long interval leading into OAEla, is interpreted as the result of a 3-6 times increase in pCO2 produced by emplacement of the giant Ontong Java and Manihiki Plateaus. High pCO2 was balanced back by an accelerated biological pump during the Valanginian episode, but not during OAE1a, suggesting persisting high levels of pCO2 in the late Aptian and/or the inability of calcareous phytoplankton to absorb excess pCO2 above threshold values. Copyright 2004 by the American Geophysical Union
Stress ed invecchiamento cerebrale: un approccio multiintegrato
No full textStudio dei correlati neuroendocrini nell'invecchiamento cerebrale, con particolare riferimento alla misurazione dei ritmi circadian
Substituted spiro{2-aza-7-thiabicyclo[2.2.1]heptane-[5.4']-1',2',3'-triazoles} from 4-methylene-v-triazolines and thiazolones: NMR structural and configurational determination
No full textA conserved C-terminal sequence that is deleted in v-erbA is essential for the biological activities of c-erbA (the thyroid hormone receptor)
No full textThe thyroid hormone (T3) receptor type alpha, the c-ErbA alpha proto-oncoprotein, stimulates transcription of T3-dependent promoters, interferes with AP-1 activity, and induces erythroid differentiation in a ligand-dependent manner. The v-ErbA oncoprotein does not bind hormone and has lost all of these activities. Using c-ErbA/v-ErbA chimeras, we found that a deletion of 9 amino acids, conserved among many members of the nuclear receptor superfamily, which are located at the extreme carboxy terminus of c-ErbA alpha is responsible for loss of both transactivation and transcriptional interference activities. Single, double, and triple amino acid substitutions within this region completely abolished T3-dependent transcriptional activation, interference with AP-1 activity, and decreased T3 binding by c-ErbA alpha. However, the lower T3 binding by these mutants does not fully account for the loss of transactivation and transcriptional interference, since a c-ErbA/v-ErbA chimera which was similarly reduced in T3 binding activity has retained both of these functions. Deletion of homologous residues in the retinoic acid receptor alpha (RAR alpha) resulted in a similar loss of transactivation and transcriptional interference activities. The ability of c-ErbA alpha to induce differentiation of transformed erythroblasts is also impaired by all of the mutations introduced into the conserved carboxy-terminal sequence. We conclude that this 9-amino-acid conserved region is essential for normal biological function of c-ErbA alpha and RAR alpha and possibly other T3 and RA receptors
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