A record of early to middle Holocene environmental change inferred from lake deposits beneath a sabkha sequence in the Central Sahara (Seggedim, NE Niger)

Seggedim is a remote site in NE Niger where previous studies demonstrated the presence of Holocene paleolake deposits beneath an existing sabkha. In 2005, we retrieved a 15-m core that contains a high-resolution record of early to middle Holocene environmental change. Mineralogical, chemical and petrographic data were used to infer paleoenvironmental conditions recorded by successive lake stages. An exceptionally stable lake regime existed from 10.6 to 7.3 cal ka BP. This regime, reflecting moist conditions, was characterized by deposition of continuously laminated diatomite with high organic matter content, formed under meromictic conditions, with very low detrital input. A lake regime shift occurred at 7.3 cal ka BP, interpreted as the beginning of a transition to arid conditions. This shift was initially marked by a change to predominantly clastic sedimentation, followed by increased sand input during later stages, culminating in the onset of the sabkha stage. Because of the presence of reworked organic material in the deposits, reliable radiocarbon dating of the succession of lake stages could not be achieved.