Abstract

The Aquitanian deposits of the quarry of Montaigu-le-Blin, located in the ≪ Limagne bourbonnaise », are characterized by lacustrine marl and limestone alternations. They display well-developed vegetal and fauna associations. The sedimentary deposits show an environment which allowed settlement of fresh water fauna. The deposits reveal variations of the water level and consequently of the water chemistry. These variations are characterized by alternations of anoxic and oxidizing lacustrine environments, which are due to periodic climatic changes (alternating more or less humid periods). These variations induced changes in freshwater faunal and plant associations : there are thanatocoenosis during the anoxic periods and an increasing of development of encrusting algae, responsible for the formation of algae concretions, during the oxidizing period. These oxidizing periods are also characterised by an increased hydrodynamism and terrigenous deposits from watershed. The stromatolites are numerous in the study area and show various shapes, depending on main algae, bacterial communities, and the faunal associations (caddisfly pupal cases) on the one hand, and their growth environment on the other hand. The stromatolites associations can form plurimetrical complexes which are studied in detail, and situated relatively to a paleoshoreline.

You do not currently have access to this article.