Reconstructing Mid-Holocene palaeoenvironmental dynamic in the Middle Atlas (Morocco) inferred from non-marine molluscs succession of the Aït Said ou Idder tufa sequence

The Mediterranean area is particularly sensitive to environmental changes. In Morocco, research undertaken over the past ten years has shown that continental sedimentary archives are useful to document Holocene environmental and climatic variability. However, palaeoenvironmental reconstruction using non-marine molluscs is in an early stage of research. This paper aims to present a new chronostratigraphical and malacological analysis from a Middle-Holocene and Upper Pleistocene tufa sequence in the Middle Atlas (Ait-Said-ou-Idder). Results highlight that the lower part of the sequence is dated from the Upper Pleistocene which corresponds to a fluvio-paludal model of deposition. Radiocarbon dates assign the upper part of the sequence to the Middle Holocene. During the Pleistocene phase, the environment is a reed swamp that turns to permanent body water. During the Middle Holocene, three main environmental phases have been identified. Between 6600 and 6100 cal BP, a mesophilic environment is characterised by open and dry areas with some paludal zone. Between 6100 and 5600 cal BP, a durable marshland developed. Between 5600 and 4600 cal BP, the paludal zone tended to disappear while an open and sclerophyllous environment developed. The malacological study provides important elements to the construction of a Holocene malacological framework in Morocco initiated at Blirh (Upper Moulouya). Both records identify a drastic switch to environmental aridification at the end of the Middle Holocene. By recording at the same time local evolution and regional trends and events, Ait Said ou Idder results provide material to understand environmental variability in north-eastern Morocco.