Les séries mésozoïques subbriançonnaises du massif du Morgon. Evolution paléogéographique du secteur durancien de la paléomarge téthysienne. ( Nappe de l'Embrunais-Ubaye, Alpes occidentales françaises).

Abstract : The Morgon mountain belongs to the Embrunais-Ubaye Nappes, in the Southern French Alps, near Serre-Ponçon lake on the Durance river. It is a structural part of the Subbriançonnais Zone of the Western Alps. Its present tectonic litnits are in large part inherited from Jurassic structuration. The studied stratigraphic series range from Late Triassic to Late Cretaeeous. It can be divided into 5 megasequences corresponding with the main structuration stages of the European Tethyan Paleomargin, that are: 1) pre-rift period up to Early Hettangian, 2) riftjng period from Hettangian to Aalenian, and 3) post-rift period from Bajocian to Cretaeeous. Each lithostratigraphic horizon shows many lateral variations of facies, both transverse and lengthwise. Some of them closely foilow the present limits of the tectonic units. The analysis of these variations allows a coherent palinspastic diagram to be reconstituted, if two left-wrench alpine faults, each of them with about 10 km displacement, are assumed. From Late Triassic to Hettangian, the Morgon realm is a carbonate platform with minor subsidence. During Sinemurian time it begings to cut up into high and low areas delimited by tensional faults. These structures are sealed by a generaI unconformity below the Middle Jurassic platform carbonates in which indications of emersion are found. Since Callovian time, the basin is deeping down and some places receives coarse materials supplied by fault unstable slopes (Brèche du Cap), which show a lateraI transition into turbidites fining away in an black marIs Oxfordianformation (Terres noires). From Late Oxfordian to the end of Early Cretaceous, the basin is a place of a reduced deep carbonate sedimentation, with chert and slumps levels. The begining of Late Cretaceous correspond with important paleogeographic change, according with active synsedimentary fault tectonics. A large erosion channel appears, in which Black shales, with a number of olistolites, are deposited. This formation contains a Triassic and Liassic body, including gypsum, which indicates the presence of a Triassic synsedimentary diapir in the environment of Morgon realm. During Senonian and Paleocene times, planctonic deposits spread out int the whole area. When replaced in a more general context, this study leads to a "puzzle like" palinspastic reconstitution for the Morgon and Durancian Subbriançonnais "corridor", the main features of which are built before Bajocian time. This scheme helps to explain the stratigraphic complexity of the subbriançonnais domain. It fits rather weil into the paleogeographic model of the North Tethysian margin as proposed by Lemoine, although with some added complications.
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Mineralogy. Université Scientifique et Médicale de Grenoble, 1986. French


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Christine Lereus. Les séries mésozoïques subbriançonnaises du massif du Morgon. Evolution paléogéographique du secteur durancien de la paléomarge téthysienne. ( Nappe de l'Embrunais-Ubaye, Alpes occidentales françaises).. Mineralogy. Université Scientifique et Médicale de Grenoble, 1986. French. <tel-00562458>

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