Microflores des formations du Gabon attribuées au Karroo

Abstract

In Gabon the thick Cretaceous and Tertiary successions are found lying on a sedimentary sequence which is now considered to be a correlative of the Karroo formations. This correlation has been established on the basis of well-preserved and characteristic palynological assemblages. Unfossiliferous glacial deposits, probably assignable to the Dwyka, are overlain by the clastics and dolomites of the “Série de l'Agoula”. The latter formation is characterized by the occurrence of three distinctive palynological assemblages: 1. (1) An assemblage in the lower part of the formation is composed of monosaccates, striate monosaccates, striate disaccates, and some characteristic pollen grains such as Walikalesaccates,ellipticus, Hoegiasaccites transitus, Fusacolpites ovatus and Fusacolpites fusus. This assemblage can be compared with assemblages from the “Série des Schistes Noirs de Walikale et Lukuga” in Zaire (Congo Kinshasa) which has been assigned to the Early Permian (Sakmarian) Ecca formations. 2. (2) An assemblage in the middle part of the formation includes Corisaccites spp., Lueckisporites spp., Hamiapollenites karrooensis and Protohaploxypinus spp. This assemblage compares with assemblages from the Lower Coal Measures of Tanganyika (Ecca), the Upper Barakar and Raniganj of India, and the Lower Permian of the Salt Range; it is considered to be diagnostic of the upper part of the Lower Permian (Artinskian-Kungurian). 3. (3) After an important unfossiliferous interval the upper part of the formation is characterized by an assemblage with Klausipollenites schaubergeri, Lueckisporites virkkiae and Taeniaesporites noviaulensis. This Late Permian assemblage has a European appearance. The “Serie de l'Agoula” is overlain by the clastics of the “Série de M'Vone” yielding a Middle Jurassic palynological assemblage with Classopollis torosus, Callialasporites dampieri and Spheripollenites scabratus. After another unfossiliferous interval (N'Dombo), Cretaceous sedimentation commences with the dominantly argillaceous deposits of the “Série de Kango” yielding a palynological assemblage with Dicheiropollis etruscus, Classopollis classoides, Ephedripites spp. and Cicatricosisporites spp.