Freshwater fish δ18O indicates a Messinian change of the precipitation regime in Central Africa

Abstract

Tracking terrestrial environmental change throughout the Neogene is a challenge, notably in areas such as Central Africa where the few available data consist of a few vertebrate fossil assemblages. Here we aim to quantify the evolution of the δ 18 O of the main water body between four Neogene wet episodes in the Chad basin, ranging from the Late Miocene to the early Pliocene. The δ 18 O of the open water body was inferred from oxygen isotope measurements of phosphate in the apatite of open water fish tooth enamel. The more open the fish habitat, the lower the δ 18 O, as revealed by the teeth of the large tiger fish ( Hydrocynus ) sampled in the four available Chadian vertebrate fossiliferous areas, i.e., Toros-Menalla (anthracotherid unit), Kossom Bougoudi, Kolle, and Koro Toro, all located in the Djurab Desert (Chad) and dated at 7.04 ± 0.18 Ma, 5.26 ± 0.23 Ma, 3.96 ± 0.48 Ma, and 3.58 ± 0.27 Ma, respectively. The δ 18 O values increased by ∼2‰ between the two sites having ages that bracket the Messinian time period, and there was a slight increase of ∼0.6‰ difference between the three Pliocene sites. These results reflect unambiguously change in the water cycle in Central Africa during the late Neogene, interpreted as a constant drying trend between the four successive wet episodes registered in the Djurab and a shift during the Messinian.