Gramineae cuticle: a key indicator of Late Cenozoic climatic change in the Niger Delta

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Charred Gramineae (grass) cuticle stomatal cells and pollen have been recorded in many well sections of Early Miocene to Pleistocene age from the coastal and offshore region of the Niger Delta. Gramineae microfossils were examined from approximately 4000 samples during the course of a palynological study aimed at establishing a high resolution biostratigraphic zonation scheme for the Niger Delta. Opaque (charred) cuticle, formed as a result of savanna fires, is intermittently abundant from the basal Middle Miocene and provides an excellent tool for stratigraphic correlation and palaeoclimatic interpretation. Intervals of abundant charred cuticle are considered to represent essentially dry periods when savanna vegetation extended over most of the delta. The Gramineae cuticle and pollen record suggests that climates became increasingly dry from the latest Early Miocene and that Late Miocene climates were particularly arid. After a return to a mainly everwet regime in the earliest Early Pliocene, the Late Pliocene and Pleistocene climates were characterised by alternating dry and uniformly moist climates. The pollen record suggests an expansion of Gramineae into swamp habitats during the Pleistocene. The period of Late Miocene dessication may have been responsible for the extinction of much of the West African humid tropical flora.