This study deals with the litho-biostratigraphic analysis of the Holocene fluvial and tufa deposits of the Middle Moulouya valley, near to Ksabi, with a view to a chrono-stratigraphic and paleoenvironmental reconstruction of the Early Holocene period through the associated malacological assemblages.

The malacological study is based on the description and detailed statistical processing of the species collected. In this Early fine floodplain Holocene sequence alternating with tuffaceous horizons of 5.5m depth, 26 species were collected and studied.

The number of shells is generally low and undiversified in the oldest levels dated between 11000cal BP & 10000cal BP, and indicate a maximum of regional humidity, but the malacological communities develop and diversify rapidly in the upper levels in the second part of the Early Holocene( 9800 cal BP & 7780+/-70 cal BP), indicating a change in environmental conditions with an increase in dry periods (decrease of aquatic species, increase of hygrophilous and xerophilous species), synchronous of an increase in river energy. To explain these environmental changes, the hydrogeomorphological, climatic and/or environnemental forcings have to be discussed.