30 research outputs found
Calcareous nannofossil assemblages across the Pliensbachian/Toarcian boundary at the Peniche section (Ponta do Trovão, Lusitanian Basin)
The Peniche section has revealed moderately-to-well preserved calcareous nannofossil assemblages across the Pliensbachian/Toarcian boundary. This good record has allowed the proposition of a refined biostratigraphic scheme. The stage
boundary, as defined by ammonites, is comprised within the NJ5b C. impontus (NW Europe; BOWN & COOPER, 1998) or the
NJT5b L. sigillatus (Mediterranean Tethys; MATTIOLI & ERBA, 1999) nannofossil subzones. Since in the Lusitanian Basin a mixing of N- and S-Tethyan taxa is observed, both biozonation schemes can be applied. Some nannofossil events (mainly first
occurrences) are observed earlier in Portugal than in other Tethyan settings. It is still unclear if these events are real first occurrences. A diversification phase occurred across the Pliensbachian/Toarcian boundary.
This phase is well recorded at Peniche, where a change is observed passing from the Pliensbachian, when assemblages are
dominated by muroliths, to the Toarcian showing assemblages where placoliths are abundant. A quantification of nannofossils
per gram of rock shows that absolute abundances are the highest across the Pliensbachian/Toarcian boundary. Indeed, Peniche exhibits nannofossil abundances very high with respect to correlative levels in other Tethyan settings. The pelagic carbonate
fraction (produced by nannofossils) is important in the marly hemi-couplets of Peniche. In some levels, nannofossils account for more than 50% of the total carbonate fraction
Base of the Toarcian Stage of the Lower Jurassic defined by the Global Boundary Stratotype Section and Point (GSSP) at the Peniche section (Portugal)
This is the final version of the article. Available from the publisher via the DOI in this record.The Global Stratotype Section and Point (GSSP) for the base of Toarcian Stage, Lower Jurassic, is placed at the base of micritic limestone bed 15e at Ponta do Trovão (Peniche, Lusitanian Basin, Portugal; coordinates: 39°22'15''N, 9°23'07''W), 80km north of Lisbon, and coincides with the mass occurrence of the ammonite Dactylioceras (Eodactylites). The Pliensbachian/ Toarcian boundary (PLB/TOA) is contained in a continuous section forming over 450m of carbonate-rich sediments. Tectonics, syn-sedimentary disturbance, metamorphism or significant diagenesis do not significantly affect this area. At the PLB/TOA, no vertical facies changes, stratigraphical gaps or hiatuses have been recorded. The base of the Toarcian Stage is marked in the bed 15e by the first occurrence of D. (E.) simplex, co-occurring with D. (E.) pseudocommune and D. (E.) polymorphum. The ammonite association of D. (Eodactylites) ssp. and other species e.g. Protogrammoceras (Paltarpites) cf. paltum, Lioceratoides aff. ballinense and Tiltoniceras aff. capillatum is particularly significant for the boundary definition and correlation with sections in different basins. Ammonites of the PLB/ TOA are taxa characteristic of both the Mediterranean and Northwest European provinces that allow reliable, global correlations. The PLB/TOA is also characterized by other biostratigraphical markers (brachiopods, calcareous nannofossils, ostracods and benthic foraminifers) and by high-resolution stable carbon and oxygen isotopes, and 87Sr/86Sr ratios that show distinctive changes just above the PLB/TOA, thus providing additional, powerful tools for global correlations. The PBL-TOA lies at the end of a second (and third) order cycle of sea-level change, and the top of bed 15e is interpreted as a sequence boundary. Cyclostratigraphy analysis is available for the Lower Toarcian of Ponta do Trovão. Detailed correlations with the Almonacid de la Cuba section (Iberian Range, Spain) provide complementary data of the ammonite succession in the Northwest European Hawskerense and Paltum Subzones, and magnetostratigraphical data that allow supraregional correlations. The proposal was voted on by the Toarcian Working Group in June, 2012, and by the International Subcommission on Jurassic Stratigraphy in September, 2012, approved by the ICS in November, 2014, and ratified by the IUGS in December, 2014. With this Toarcian GSSP, all international stages of the Lower Jurassic have been officially defined.Several scientists have been members of the Toarcian Working Group. We would like to acknowledge all of them. We are also grateful to the ISJS and ICS members who have made valuable comments on a previous version of this manuscript. We warmly thank Marc Philippe for his help with the literature on Pliensbachian/Toarcian continental successions. We warmly thank Christian Meister and Jim Ogg for their helpful review. Constructive remarks by Jim Ogg on an early
version of the paper were greatly appreciated. We also acknowledge the precious help of David Besson for providing the ammonite specimens from the Mouterde collection (Musée des Confluences, Lyon). Ammonite photographs were taken by Emmanuel Robert (Collections de Géologie de Lyon). This paper is dedicated to the memory of Abbé René Mouterde and Serge Elmi, who died in 2007 after having been for years the main supporters of the Peniche section as GSSP of Toarcian Stage. Calcareous nannofossil slides are curated at the Collections de Géologie de Lyon (No. FSL 766535-766617). This work has been supported by the BIOSCALES Project (POCTI/
36438/PAL/2000), coordinated by the Universidade NOVA de Lisboa; R. B. Rocha thanks the support of A. F. Soares, J. C. Kullberg, P. S. Caetano and P. H. Verdial. Financial support was provided to L. V. Duarte, S. Pinto and M. C. Cabral by Projects PDCTE/CTA/44907/2002 and PTDC/CTE-GIX/098968/2008
On the structure and function of the phytoene desaturase CRTI from Pantoea ananatis, a membrane-peripheral and FAD-dependent oxidase/isomerase
CRTI-type phytoene desaturases prevailing in bacteria and fungi can form lycopene directly from phytoene while plants employ two distinct desaturases and two cis-tans isomerases for the same purpose. This property renders CRTI a valuable gene to engineer provitamin A-formation to help combat vitamin A malnutrition, such as with Golden Rice. To understand the biochemical processes involved, recombinant CRTI was produced and obtained in homogeneous form that shows high enzymatic activity with the lipophilic substrate phytoene contained in phosphatidyl-choline (PC) liposome membranes. The first crystal structure of apo-CRTI reveals that CRTI belongs to the flavoprotein superfamily comprising protoporphyrinogen IX oxidoreductase and monoamine oxidase. CRTI is a membrane-peripheral oxidoreductase which utilizes FAD as the sole redox-active cofactor. Oxygen, replaceable by quinones in its absence, is needed as the terminal electron acceptor. FAD, besides its catalytic role also displays a structural function by enabling the formation of enzymatically active CRTI membrane associates. Under anaerobic conditions the enzyme can act as a carotene cis-trans isomerase. In silico-docking experiments yielded information on substrate binding sites, potential catalytic residues and is in favor of single half-site recognition of the symmetrical C(40) hydrocarbon substrate
The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)
The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of “dead zones” in modern oceans
Pseudohyperphosphorylation has differential effects on polymerization and function of tau isoforms
The microtubule-associated protein tau exists as six isoforms created through the splicing of the second, third, and tenth exons. The isoforms are classified by their number of N-terminal exons (0N, 1N or 2N) and by their number of microtubule-binding repeat regions (3R or 4R). Hyperphosphorylated isoforms accumulate in insoluble aggregates in Alzheimer’s disease and other tauopathies. These neurodegenerative diseases can be categorized based on the isoform content of the aggregates they contain. Hyperphosphorylated tau has the general characteristics of an upward electrophoretic shift, decreased microtubule binding, and an association with aggregation. Previously we have shown that a combination of seven pseudophosphorylation mutations at sites phosphorylated by GSK-3β, referred to as 7-Phos, induced several of these characteristics in full-length 2N4R tau and led to the formation of fewer but longer filaments. We sought to determine whether the same phosphorylation pattern could cause differential effects in the other tau isoforms, possibly through varied conformational effects. Using in vitro techniques, we examined the electrophoretic mobility, aggregation properties and microtubule stabilization of all isoforms and their pseudophosphorylated counterparts. We found that pseudophosphorylation affected each isoform, but in several cases certain isoforms were affected more than others. These results suggest that hyperphosphorylation of tau isoforms could play a major role in determining the isoform composition of tau aggregates in disease
Dimethyl Sulfoxide Induces Both Direct and Indirect Tau Hyperphosphorylation
Dimethyl sulfoxide (DMSO) is widely used as a solvent or vehicle for biological studies, and for treatment of specific disorders, including traumatic brain injury and several forms of amyloidosis. As Alzheimer’s disease (AD) brains are characterized by deposits of β-amyloid peptides, it has been suggested that DMSO could be used as a treatment for this devastating disease. AD brains are also characterized by aggregates of hyperphosphorylated tau protein, but the effect of DMSO on tau phosphorylation is unknown. We thus investigated the impact of DMSO on tau phosphorylation in vitro and in vivo. One hour following intraperitoneal administration of 1 or 2 ml/kg DMSO in mice, no change was observed in tau phosphorylation. However, at 4 ml/kg, tau was hyperphosphorylated at AT8 (Ser202/Thr205), PHF-1 (Ser396/Ser404) and AT180 (Thr231) epitopes. At this dose, we also noticed that the animals were hypothermic. When the mice were maintained normothermic, the effect of 4 ml/kg DMSO on tau hyperphosphorylation was prevented. On the other hand, in SH-SY5Y cells, 0.1% DMSO induced tau hyperphosphorylation at AT8 and AT180 phosphoepitopes in normothermic conditions. Globally, these findings demonstrate that DMSO can induce tau hyperphosphorylation indirectly via hypothermia in vivo, and directly in vitro. These data should caution researchers working with DMSO as it can induce artifactual results both in vivo and in vitro
The Early Toarcian anoxia, a synchronous event in the Western Tethys? An approach by quantitative biochronology (Unitary Associations), applied on calcareous nannofossils
During the Early Toarcian, major paleoenvironnemental and
paleoceanographical changes occurred, leading to an oceanic anoxic event
(OAE) and to a perturbation of the carbon isotope cycle. Although the
standard biochronology of the Lower Jurassic is essentially based upon
ammonites, in recent years biostratigraphy based on calcareous
nannofossils and dinoflagellate cysts is increasingly used to date
Jurassic rocks. However, the precise dating and correlation of the Early
Toarcian OAE, and of the associated delta C-13 anomaly in different
settings of the western Tethys, are still partly problematic, and it is
still unclear whether these events are synchronous or not. In order to
allow more accurate correlations of the organic rich levels recorded in
the Lower Toarcian OAE, this account proposes a new biozonation based on
a quantitative biochronology approach, the Unitary Associations (UA),
applied to calcareous nannofossils. This study represents the first
attempt to apply the UA method to Jurassic nannofossils. The study
incorporates eighteen sections distributed across western Tethys and
ranging from the Pliensbachian to Aalenian, comprising 1220 samples and
72 calcareous nannofossil taxa. The BioGraph [Savary, J., Guex, J.,
1999. Discrete biochronological scales and unitary associations:
description of the Biograph Computer program. Memoires de Geologie de
Lausanne 34, 282 pp] and UA-Graph (Copyright Hammer O., Guex and Savary,
2002) softwares provide a discrete biochronological framework based upon
multi-taxa concurrent range zones in the different sections. The
optimized dataset generates nine UAs using the co-occurrences of 56
taxa. These UAs are grouped into six Unitary Association Zones (UA-Z),
which constitute a robust biostratigraphic synthesis of all the observed
or deduced biostratigraphic relationships between the analysed taxa. The
UA zonation proposed here is compared to ``classic'' calcareous
nannofossil biozonations, which are commonly used for the southern and
the northern sides of Tethys. The biostratigraphic resolution of the
UA-Zones varies from one nannofossil subzone or part of it to several
subzones, and can be related to the pattern of calcareous nannoplankton
originations and extinctions during the studied time interval. The Late
Pliensbachian - Early Toarcian interval (corresponding to the UA-Z II)
represents a major step in the Jurassic nannoplankton radiation. The
recognized UA-Zones are also compared to the carbon isotopic negative
excursion and TOC maximum in five sections of central Italy, Germany and
England, with the aim of providing a more reliable correlation tool for
the Early Toarcian OAE, and of the associated isotopic anomaly, between
the southern and northern part of western Tethys. The results of this
work show that the TOC maximum and delta C-13 negative excursion
correspond to the upper part of the UA-Z II (i.e., UA 3) in the sections
analysed. This suggests that the Early Toarcian OAE was a synchronous
event within the western Tethys. (c) 2006 Elsevier B.V. All rights
reserved
Late Pliensbachian-Early Toarcian (Early Jurassic) environmental changes in an epicontinental basin of NW Europe (Causses area, central France): A micropaleontological and geochemical approach
We present an integrated work based on calcareous nannofossil and
benthic foraminiferal assemblages, and geochemical analyses of two Upper
Pliensbachian-Lower Toarcian sections located in the central-South
France. The studied sections, Tournadous and Saint-Paul-des-Fonts,
represent the proximal and the distal part, respectively, of the
Jurassic Causses Basin, one of the small, partly enclosed basins
belonging to the epicontinental shelf of the NW Tethys. At the
transition from Late Pliensbachian to Early Toarcian, the Causses Basin
recorded an emersion in response to the global sea-level fall. Our data
indicate severe environmental conditions of marine waters, including
salinity decrease and anoxia development, occurring in the Early
Toarcian. The acme of this deterioration coincides with the Early
Toarcian Anoxic Event (T-OAE) but, due to the restricted nature of the
basin. anoxia persisted until the end of the Early Toarcian. mainly in
the deeper parts of the basin. The micronutrients and organic
organic-matter fluxes were probably high during the entire studied time
interval, as shown by nannofossil and foraminiferal assemblages.
However, nannoplankton production drastically decreased during the
T-OAE, as demonstrated by very low nannofossil fluxes, and only taxa
tolerant to low-saline surface waters could thrive. At the same time,
benthic foraminifers temporarily disappeared in response to sea-bottom
anoxia. Our study demonstrates that environmental changes related to the
T-OAE are well-recorded even in small, partly enclosed basins of NW
Europe, like the Causses Basin. Within this area, the effects of global
changes. like sea sea-level and temperature fluctuations, are modulated
by local conditions mainly controlled by the morphology of the basin.
(C) 2008 Elsevier B.V. All rights reserved