Contenu du sommaire

Abstract. — About two canyons of meridional Corbieres : Galamus and Pierre-Lys. A comparative study of the two most famous canyons in meridional Corbieres allows us to deal genesis and evolution of gorges. The classical explanation by tectonic movements receive here no proof and that rivers pour away in opposite directions on similar structures does not give it easily to be applied. Indeed, we can think that vertical deeping is related to the excavation of structural landforms downstream the canyons, whereas their calibrated forms are connected with the discharge of the rivers. The different parts of these parameters confers to each one its own original characters.

Abstract. — This paper aims to assess, in two instances of well stratified Urgonian calcareous massifs in a pseudo-monoclinal position, with very large coalescent dolines, the comparative roles of the structure, of karstic dissolution, and of the action of the cold in the course of morphogenesis.

Abstract. — The morphostructural analysis of three poljés (of which two are semi-poljés) of the Betic Cordilleras shows how overth- rusting structures, associated with normal faults, make easy the genesis of poljés by the intercalation, in the piling of calcareous units, of impermeable rocks which begets karsticsheet of inundation.

Summary. — The major karsts are closely bound as to their structure but their development is often dependent — in the case of subhorizontal strata — on a succession of chalk marls and hard limestone. It is in the latter that grikes are to be found, while in the former the depressions extend outwards.

Abstract. — Neogene Karst of Akhsass Table-land (N. 29° 25' - W. 9° 45') was formed on a planation surface cutting accross a complex geomorphic compression structure. Karst processing was directed by tectonic features and the pattern of fractures. Mega-structures divide the table-land in four units. Middle sized structures gave the direction of the surface shapes and underground karst. Exceptional ability of limestones and dolomites to karstic evolution is due to micro-structures. Quaternary up-lift of the table-land and a climatic change for drier conditions resulted in the selection of surface and underground drains related with the main fractures pattern.

Abstract. — This paper deals with comparisons between différent springs occuring on the western side of central Mount Liban, on its eastern side sloping to the Beqaâ, and on Anti-Liban. Bio-climatic factors (vegetation cover snow), and hydrogeologie influences (nature of Jurassic and Cenomanian pervious strata, progress in karstification) are analysed. Waters from Cenomanian aquifers in Mt. Liban are the most agressive ones ; from Jurassic calcareous rocks, they are closer to saturation ; in Anti-Liban springs, they can reach supersaturation.

Abstract. — From his researches on malagasy karsts, which show us all the types of tropical karsts (Kuppen, Kegels, Mogotes, dolinas, tsingy), the part of structural influences in determination of the various types of forms are examined.

Abstract. — Original karstic landforms (penitents, dolines...) are described along the large stripes of gypsum strata in the Rio Salado valley (Mendoza moutains, Argentine).