Facies analysis of the Lo Valdés Formation (Tithonian–Hauterivian) of the High Cordillera of central Chile, and the palaeogeographic evolution of the Andean Basin

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Abstract
Facies descriptions and environmental interpretations are given for outstanding sections of marine Tithonian to Hauterivian strata in the High Cordillera of the central Chilean Andes. Comparisons are made with correlative strata in other regions in Chile, and with the Neuquén Basin of west central Argentina. The rich and partly endemic bivalve fauna, which has strong African affinities, shows no change up the stratigrapic sequence that cannot be related to local facies. Water depth is recognized as the main variable controlling the distribution of the bivalve and ammonite faunas. Utilizing data from both Chile and Argentina, a model is put forward for the late Jurassic to mid Cretaceous sequence whereby the facies distributions are accounted for by the interaction of global sea-level changes and regional tectonics in a shallow back-arc basin.