Record of warm temperate pollen from the Palaeogene-Neogene lignite of southeast Nigeria: Consequences of regional palaeoclimatic changes or tectonics?

摘要

Fossil microflora of warm temperate climate affinities were recovered with those of tropical rainforest from brown coal sample of Mpu Formation. Among the most abundant species were Psilatricolporites medius (15%), Echitricolporites maristellae (11%), Alnipollenites verus (8%), Psilastephanocolporites laevigatus (8%), Retibrevitricolporites protrudens (8%), and Fenestrites spinosus (7%). Less abundant but stratigraphically and ecologically important were: Retitricolporites irregularis, Zonocostites ramonae, Inaperturopollenites dubius/hiatus, Spinizonocolpites prominatus, Racemonocolpites hians, Margocolporites umuahiaensis and Echiperiporites icacinoides. The area is presently situated within the equatorial rainforest climatic region. Podocarpus milanjianus, a wind-pollinated gymnosperm, found by earlier authors in the Miocene-Recent sediments of the Niger Delta has been attributed to wind-transport from the Cameroon Highlands. However, the abundance of the wind pollinated angiosperm A. verus in the coal, which is a closed system, excludes any such transport. Along with I. dubius/hiatus. this temperate pollen is the record of montane climate resulting from the middle Cenozoic uplift which raised the area as high as the present Cameroon Highlands. Pollen results substantiated vertical tectonic movements in Nigeria during the Middle-Late Cenozoic which resulted in local montane climate.