Morphosedimentary study of a cave deposit at bois du clos cave (charente, france): Geometric constraints and Hydrological Dynamics

摘要

A section in a remarkable sequence of detrital deposits of more than 5 m high, filling in the cave of the Clos du Bois (La Rochefoucauld karst, Charente) allowed a morphosedimentary analysis of a discontinuous and complex sequence. Three major phases of submergence/dewatering of the cave have been identified by the combination of a grain-size analysis, Passega diagrams, a mineralogical analysis of sands and clays, and a geochemical analysis. Despite the lack of chronological milestones within the sedimentary sequence, a chronostratigraphy and time setting are proposed following the study of a stalagmite that seals the filling and is dated from marine isotopic stage 3. The results are correlated with episodes highlighted in nearby sites. They show in our case the palaeofunctioning of an initially open karst system heavily influenced by the fluctuation of a large karst water table (the Touvre) and by nearby flows (palaeostreams and palaeovadose flows), but gradually closing down. The palaeoclimatic and palaeoenvironmental interpretation of the sediments is discussed. Notions of endokarstic trap and sedimentary gap are developed. The "site effects" on the sedimentary record of the influences of climate variability are shown.