Cosmogenic radionuclide dating

30-Jan-2016 08:46 posted by truk26 | Leave a comment

Over the last 20 years, great progress has been made in the field of karstogenesis and in the development of multidisciplinary approaches to deciphering the palaeoenvironmental information contained within karst forms and formations (Delannoy of an international working group that was set up in 2000 at the 'Cave Genesis in the Alpine Belt' workshop in Habkern, Switzerland (Häuselmann and Monbaron, 2001).Comparisons of the methods used and the results obtained from one end of the Alpine chain to the other have provided an overview of the state of knowledge of Alpine cave genesis.

In addition, the rates of denudation estimated according to the analytical data are unusually low in this alpine context but show an acceleration during the pre-Quaternary period of interest, ranging from 7 m/Ma to 14 m/Ma.

Data from karst deposits serve as reference and comparison site for Alpine chronology as well as for cave genesis and palaeogeographical reconstructions, similar to that of the Siebenhengste massif in Switzerland.

Le mont Granier, situé à l’extrémité nord des hauts plateaux de Chartreuse orientale, est un massif karstique montagnard perché contenant un méga-réseau souterrain dont les niveaux de galeries les plus haut-perchés, soupçonnés d’être antéquaternaires, ont fait l’objet de datation par défaut par détermination de l’âge d’enfouissement de leurs remplissages détritiques à l’aide des isotopes cosmogéniques Al.

We consider here the palaeoflow path as dominant direction of karst drainage determined by the location of the input and the emergence; this direction may change from one phase of karstification to another) and different tiers of passages (Audra (ii) Morphological: Feature of the walls, ceilings and floors of passages provides information about their genesis (phreatic, vadose or epiphreatic regime, flow direction, phases of aggradation or incision, gravity movements, etc.); (iii) Sedimentological: Sediment fillings in mountain karsts are extremely important palaeogeographic archives and indicators (Audra, 1995).

Numerous techniques have been developed for analysing detrital and chemical (speleothems) deposits, thereby enabling them to be used as records of variations in continental environments, alongside other natural archives (Sasowsky and Mylroie, 2004).

Furthermore, cave deposits are the only parts of caves that can be dated directly, as the passages themselves can only be dated with reference to the age of the host rock (upper limit) and the age of the oldest sediment deposits in cavities (Häuselmann, 2007).

The results of such studies may then be combined with indicators such as palaeoflow paths (., 'chemin de drainage', Choppy, 1994.Les résultats obtenus sur deux échantillons d’un même étage mais spatialement distants donnent des âges d’enfouissement pliocènes (4,3 Ma et 3,4 Ma) conformes aux hypothèses génétiques préalables.L’âge de ces niveaux de galeries établis post-plissement est donc assurément néogène.Les taux de dénudation estimés sont étonnamment faibles dans ce contexte alpin mais montrent une accélération sensible au cours de la période considérée, passant de 7 m/Ma à 14 m/Ma.Par ces résultats, le mont Granier conforte son statut de site de référence et de comparaison pour les reconstitutions spéléokarstogéniques et paléogéographiques alpines, au même titre que le massif des Siebenhengste en Suisse.Al burial dating of two cave deposits in the oldest passages, widely spaced but belonging to a same gallery level which formed after the last folding phase, gave ages of 4.3 Ma and 3.4 Ma, indicating that these levels are of at least Pliocene age.

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