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• W2952397712 abstract "Abstract:During my doctoral research, I focused on deciphering the interactions between sea-level and climate change during the Late Barremian-Early Aptian, their expression in the Tethys basin and in the Helvetic carbonate platform. The research highlights are summarized here in three points: In the Helvetic Alps, the transition between the Lower Schrattenkalk (Upper Barremian) and the Rawil Member (Lowermost Aptian) is characterized by a change from a predominantly photozoan to a heterozoan carbonate-producing system, which coincides in time with a general increase in detrital and nutrient input. The clay mineral record shows the appearance of kaolinite within the Rawil Member, whereas this mineral is absent from the uppermost Lower and lowermost Upper Schrattenkalk Members. This indicates the installation of a warmer and more humid climate during this time period. A negative peak in 513C is recorded at the top of the Lower Schrattenkalk Member, and correlates with the well-known negative excursion of -l%o occurring in other basins and dated as latest Barremian, thus confirming a latest Barremian and earliest Aptian age for the Lower Schrattenkalk and Rawil Members, respectively. Furthermore, a sequence stratigraphie framework has been defined for the Rawil Member, based on both the ecology of faunal and floral assemblages, and their palaeoenvironmental interpretation, as well as on the stacking pattern of limestone beds observed during field prospection. The presence of a sequence boundary is postulated near the top of the Lower Schrattenkalk Member, which is correlated with the earliest Aptian SbAl defined in Vercors (France). The SbAl is characterized by a maximum of proximal assemblages and by the disappearance of several benthic foraminiferal species. Within the Rawil Member itself, the stacking pattern and microfacies trends are interpreted to represent the TST of the first Aptian sequence. With regards to the pelagic setting in the Tethyan realm, I investigated the Gorgo a Cerbara section (central Italy). There, thin organic-rich layers occur episodically in pelagic carbonates of the upper Barremian portion of the Maiolica Formation. They are associated with high Corg:Ptot ratios, which indicate the presence of intermittent dysoxic to anoxic conditions. Coarse correlations are also observed between TOC, Ρ and biogenic silica contents, indicating links between Ρ availability, productivity, and organic matter preservation. The corresponding 813Ccarb and δ180 records remain, however, quite stable, indicating that these brief periods of enhanced TOC preservation did not have sufficient impact on the marine carbon household to deviate 6,3C records, and are probably not the consequence of major climate change. On the other hand, organic-rich layers become more frequent around the Barremian-Aptian boundary in both pelagic and hemi-pelagic environments (Gorgo a Cerbara and La Bedoule, France), which are correlated with negative excursions in 6l3Ccarb and 613Corg records. During the earliest Aptian, at Gorgo a Cerbara, the frequency of organic-rich intervals progressively increases and redox-sensitive trace-element enrichments become more frequent, until the highest TOC-enriched level just below the Livello Selli, indicator of Oceanic Anoxic Event la (OAEla). The latter is associated with the well-known negative spike in 613Ccarb and S,3Corg records, a diminution in the δ,80 record interpreted as the consequence of a wanning interval, an important peak in Ρ accumulation and high Cor::Ptot ratios indicating the prevalence of anoxic conditions. The Selli Level (OAEla) documents a general cooling phase and coincides with maximum RSTE enrichments as well as high Corg:Ptot ratios, which confirm the importance of anoxic conditions during OAE1 a at this site.During the Early Aptian, environmental change on the platform is expressed by orbitolinids proliferation that may be induced by both climate change and sea-level rise. In the basin, the successive black shales horizons from the Late Barremian until the OAE la are interpreted as the progressive impact of palaeoenvironmental change probably linked to the formation of the Ontong- Java plate-basalt plateau.ResumeCe travail de these a permis d'investiguer les interactions entre les variations du niveau marin et les changements climatiques sur la plate-forme helvetique ainsi qu'en domaine pelagique a la limite Barremien-Aptien (Cretace).Dans les Alpes helvetiques, la limite Barremien-Aptien est marquee par la transition du Schrattenkalk inferieur, caracterise par des carbonates photozaires, au Membre de Rawil caracterise par des carbonates heterozoaires. Cette transition est marquee par une arrivee massive d'elements detritiques et un apport de nutriments ayant entraine la proliferation de foraminiferes agglutines tels que les orbitolines. L'analyse des mineraux argileux indique l'apparition de la kaolinite durant le Membre de Rawil, interpretee comme l'installation d'un climat plus chaud et humide. Un pic negatif en 513C est enregistre au sommet du Schrattenkalk inferieur correspond a l'excursion negative de -1%0 bien connue en domaine pelagique et datee comme Barremien terminal. Cette correlation apporte un controle chronostratigraphique supplementaire permettant de dater le Schrattenkalk inferieur du Barremien sup. et le Membre de Rawil de l'Aptien inf. D'autre part, une etude stratigraphique, basee sur des observations de terrain et sur l'interpretation d'assemblages floristiques et faunistiques en terme de paleoenvironnement a permis de mettre en evidence une limite de sequence au sommet du Schrattenkalk inf., correlable avec la SbAl definie dans le Vercors. Durant la mise en place du Membre de Rawil, l'evolution des microfacies est interpretee comme le « Transgressive System Tract » de la premiere sequence aptienne.En domaine pelagique, de minces couches riches en matiere organique (MO) apparaissent des le Barremien sup. dans la coupe de Gorgo a Cerbara (Italie). Elles sont associees a un ratio C:P eleve indiquant des conditions episodiquement dysoxiques a anoxiques. De plus, une correlation nette entre Carbone Organique Total (TOC), phosphore (P) et silice biogenique est observee correspondant a un lien entre Ρ disponible, productivite et preservation de la MO. Pourtant, dans le meme temps, le OI3C et le δ1βΟ restent constants indiquant des conditions environnementales stables et un cycle du carbone non perturbe par la preservation de MO qui ne serait pas la consequence d'un changement climatique global mais juste d'un effet local.Ala limite Barremien-Aptien, en domaine hemi-pelagique (La Bedoule, France) et pelagique (Gorgo a Cerbara), les couches riches en MO sont plus frequentes et plus epaisses, elles se sont deposees en meme temps qu'un pic negatif en 513CCARB et o13Coib probablement du a un episode volcanique. A l'Aptien inf. le TOC des niveaux riches en MO augmente progressivement en meme temps que la teneur en elements traces jusqu'au dernier enrichissement avant l'evenement anoxique oceanique la (OAE la) correspondant au « niveau critique inf. », indiquant des conditions anoxiques moins restreintes. Celui-ci est egalement caracterise par le fameux pic negatif en O13C (C3), une diminution du δ180 interpretee comme un rechauffement, par un pic en Ρ et un ratio C:P eleve. L'OAE 1 a, quant a lui, enregistre un refroidissement et coincide avec le maximum en elements traces ainsi qu'un fort ratio C:P mettant en valeur l'importance des conditions anoxiques pendant 1ΌΑE la dans cette coupe alors qu'aucune perturbation n'est enregistres a La Bedoule probablement a cause de conditions paleogeographiques locales.Durant l'Aptien inf., les changements environnementaux sur la plate-forme se marquent par la proliferation d'orbitolines due a un changement climatique et une hausse du niveau marin. En domaine profond, la succession de niveaux riches en MO du Barremien sup. jusqu'a l'OAE la documente l'impact progressif de changements paleoenvironnementaux, probablement lies a la formation du plateau d'Ontong Java a l'ouest de l'ocean Pacifique." @default.
• W2952397712 created "2019-06-27" @default.
• W2952397712 creator A5006225161 @default.
• W2952397712 date "2011-01-01" @default.
• W2952397712 modified "2023-09-27" @default.
• W2952397712 title "Paleoenvironmental evolution of the Helvetic shallow-water carbonate platform near the Barremian-Aptian boundary, and its relationship with paleoceanographic and paleoclimatic change in the Tethys" @default.
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