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L'olistostrome coniacien de Lordat (Pyrénées ariégeoises) et son équivalent latéral de Vicdessos, témoins d'un nouveau bassin d'avant-pays au front nord de la Haute Chaîne Primaire

Abstract : By means of new datings and grade-datings founded on planktonic Foraminifera, ponctually identified in spite of a Campanian epimetamorphism, the extention of the Coniacian sub-basin of Lordat (« Zone des Écailles Bordières » , Ariège),partly calciturbiditic, is doubled indeed tripled at the expense of formations previously assigned to Paleozoic (particularly the ex-'Paleozoic slice of Lordat'). These last ones are only represented by very large size olistolites redeposited within a thick olistostrome (Lordat castle, Saint-Pierre hermitage), itself included within a monoclinal succession with calcareous intercalations, regarded as a probable equivalent of the 'Fucoïd flysch'. This épimetamorphic series also exists, more to the North, beyond the marbles of the Internal Metamorphic Zone, as it is evidenced by the Upper Cretaceous age assigned to the ex-Paleozoic slice of Carmilles directly overthrust by the North-pyrenean hercynian massif of Saint-Barthelemy. More to the West, the Vicdessos sub-basin is regarded as a lateral extension of the Lordat one ; it consists of a thick monoclinal Coniacian series and not of a large 'synclinorium' subdivided by Urgo-Aptian anticlines which correspond, in reality, to calcareous intercalations within the Upper Cretaceous normal succession. The herein studied terrigenous complex of Lordat-Vicdessos, partly turbiditic, is composed by, at least, two 3rd order tectono-sedimentary sequences, A and B, marking the successive infilling of foreland synsedimentary synclines supplied (olistolites) by the probably submarine erosion of the Northward migrating front of the High Primary Range (induced by successive synsedimentary probably blind overthrusts). This model of foreland sub-basin fits in perfectly with the evolutional sheme of an interplaque bivergent range, in compression during Upper Cretaceous, where followed along a N-S palinspastic section reconstructed during Coniacian, on the two sides of the future High Primary Range, at least two sub-basins linked to the European Plate (Lordat-Vicdessos and Nalzen I) and one sub-basin (San Gervas) linked to the Iberian Plate.
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Submitted on : Friday, April 15, 2022 - 1:45:59 PM
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L'olistostrome coniacien de Lordat (Pyrénées ariégeoises) et son équivalent latéral de Vicdessos, témoins d'un nouveau bassin d'avant-pays au front nord de la Haute Chaîne Primaire. Geodinamica Acta, 2001, 14, pp.289-306. ⟨10.1016/S0985-3111(01)01068-3⟩. ⟨insu-03642950⟩

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