Les tufières du Vormy et des Fontinettes (Aisne-Marne, France) : marqueurs de la faible karstification des calcaires lutétiens de l'Est du Bassin parisien ?
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Title:
Les tufières du Vormy et des Fontinettes (Aisne-Marne, France) : marqueurs de la faible karstification des calcaires lutétiens de l'Est du Bassin parisien ?
Description:
Les formations travertineuses et tufeuses holocènes dans le Bassin de Paris sont relativement rares comparées à celles du sud de la France. Pourtant, dans le Soissonnais et le Laonnois, on observe des tufières holocènes associées aux calcaires lutétiens. Les tufières du Vormy et des Fontinettes, prises comme exemples, se situent respectivement à Mont-Saint-Martin et à Baslieux-Ies-Fismes. Elles correspondent à des tufières de source, météogènes et perchées dans la partie supérieure des versants. Cependant, leur morphologie est contrastée et originale, à rigole suspendue de type «Steinerne Rinne ». Les observations géomorphologiques et le suivi physico-chimique interannuel et spatial témoignent d'une vidange lente et régulière de l'aquifère multicouche des Marnes et caillasses qui constitue une couverture semi-perméable sur les calcaires lutétiens. Cette dernière entretient une drainance d'eau peu agressive vers les calcaires sous-jacents ce qui explique, en partie, le faible degré de karstification du massif lutétien.
Vormy and Fontinettes tufas (Aisne-Marne, France) : a marker of east Paris Basin Lutetian limestone low karstification ? The travertine and tufa formations from Holocene in the Paris Basin are relatively rare compared to those of southern France. However, in the Soissonnais and in the Laonnois area, in the lutetian limestone, some calcareous tufas are observed. The tuffaceous of Vormy and Fontinettes are taken as examples. They are located respectively in Mont-Saint-Martin and Baslieux-les-Fismes. They correspond to tuffaceous springs, weather-linked and perched on the upper slopes. Their morphology is complex and presents domes, cascades, levels dams of travertines, tubes and specific morphology of «rigole suspendue». This one is very few observed in France but is studied in Bavarian Alps (Steinerne Rinne). Those calcareous tufas are actives and are layered on older calcareous tufas in domes which are vaster but fossils. Moreover, they are covered by vegetation. That means that suddenly, the conditions of the flows have changed. The examination of transversals sections and thin samples taken at Vormy and Fontinettes, shows that those travertine buildings are associated to a moss (Cratoneuron co mmutatum) which covers it and takes part to its genesis. However, their morphology is mixed with an original suspended-type «self built canal». The measures of spatial changing of conductivity and temperatures along the calcareous tufas are showing a decreasing of minerality and an increase in the water at the springs of calcareous tufas. These are actives tufas with water precipitating in the integrality of the progression. The physico-chemical interannual monitoring evidence of a slow and steady draining of the aquifer layered «Marnes et caillasses» which is a semi-permeable coverage on the Lutetian limestone. The latter has a water drainance low aggressive towards the underlying limestones which partly explains the low degree of the karstification of the Lutetian area.