Diatom, phytolith, and pollen records from a 10Be/9Be dated lacustrine succession in the Chad basin: Insight on the Miocene–Pliocene paleoenvironmental changes in Central Africa

摘要: Abstract A discontinuous 200 m-long borehole drilled in the Bol Archipelago (13°N, Lake Chad) provided 25 samples, which were dated using 10 Be/ 9 Be method and analyzed for their micro-biological content. The dating ages ranging from 6.3 ± 0.1 to 2.6 ± 0.1 Ma, a period contemporaneous with Pliocene fossil localities located current Djurab desert of Chad (16–17°N). Well-preserved diatom assemblages first occurred at 4.7 ± 0.1 Ma dominated by freshwater planktonic genera Aulacoseira Stephanodiscus until end Pliocene. This supports recurrence lacustrine conditions during all presence pelite argillaceous deposits core before 4.7 ± 0.1 Ma, however, suggests that lake settled earlier, least since 6.3 ± 0.1 Ma. abundance Afromontane pollen taxa 4.2 ± 0.1 Ma occurrence trapeziform polylobate phytoliths throughout sequence suggest significant vegetation inputs southern highlands, while importance kaolinite clay sediments indicates water supply predominantly south Phytolith are lobate grass silica short cells blocky elongate types, attest herbaceous-dominated around and/or drainage basin result is also supported assemblage described 4.2 ± 0.1 Ma, shows highest affinity savanna biome. Moreover, low values Xerophytic phytolith index indicate humid-loving (mesophytic aquatic) communities this vegetation. At last, variations indicative local alternations fully marshy Bol. Particularly between 3.6 2.7 Ma, silicified bulliform combined absence diatoms support reduction favoring increasing