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Poster De Conférence Année : 2023

Interbedded history of Holocene tufa and alkaline peat formations in the Somme valley (France)

Résumé

During the Holocene, concomitant formations of peat and calcareous tufas are recorded on chalky basins of north-west Europe (Belgium, Netherlands, Germany, Poland). Since the 19th century, geologists have recorded tufa-peat formations on the valley floor of the Middle Somme valley. Two systems of calcareous tufa have been identified in the midst of the peat deposits: 1) in dome-shaped tufas that wind through the valley and overhang the actual peaty valley floor by about three metres and 2) in lateral banks below the chalky cliffs. The interstratification with the peat deposits shows both simultaneous growth and different hydraulic conditions. The relationship between these sediments is still poorly documented, but offers possibilities for complementary palaeoenvironmental reconstruction. New fieldworks have provided a better understanding of these tufa-peat alternations. Stratigraphic surveys (tufa-peat sections and auger coring) of the Bourdon-Tirancourt sector and a GIS study of the valley floor were carried out, in order to characterise the geometry of the deposits and the environmental evolution during the Holocene. These surveys showed that the tufa domes developed in a paleochannel and at the bottom of dry valleys. Supplemented by a malacological study of a tufa dome in Bourdon and radiocarbon dating on peat, a first chronology of interstratification and environmental conditions is emerging to document the evolution of the water regime and aquifers of the valley floor during the Holocene. The development of tufas begins in the Preboreal period, according to the dating and several archaeological artefacts embedded in tufas. From 2300 BP the deposits became more silty and their formation was interrupted during the Iron Age. The peat preserved alongside the tufa dates from the Subboreal (around 3500 BP). Thus, the altitude of the top of tufas would indicate a more important peaty filling which has undergone a strong degradation (erosion, mineralization) and heights of water tables much higher than those observed nowadays.

Domaines

Géomorphologie
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Dates et versions

hal-04176817 , version 1 (11-10-2023)

Identifiants

  • HAL Id : hal-04176817 , version 1

Citer

Léa Beaumont, Chloé Garcia, Pierre Antoine, Boris Brasseur, Julie Dabkowski, et al.. Interbedded history of Holocene tufa and alkaline peat formations in the Somme valley (France). INQUA, Jul 2023, Roma, Italy. ⟨hal-04176817⟩
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