Palaeocurrent and Petrographic Evaluations of Sandstones in the Cretaceous Gulani Formation of the Eastern Gongola Basin, North-east Nigeria: Its Implication for Provenance Studies

摘要

The Turonian Gulani Formation of north-eastern Nigeria is characterized by a dominant subfacies represented by tabular cross-bedded, medium to very coarse-grained quartz arenites and granulestones with individual sets frequently several metres thick. The palaeocurrent indicates an easterly source area with the main focus of sediment influx located around latitude 10 o 46' north, the point of origin, on a gross scale, of a deltaic body. Within this body, small Gilbert-type delta lobes are thought to have formed in association with the major delta distributary channels. Petrographically the cross-bedded sandstone subfacies is medium to very coarse-grained, poorly to well sorted, sub-angular to well rounded quartz arenite, consisting of majorly monocrystalline quartz and rare polycrystalline quartz with a kaolinitic matrix. This subfacies is characterized by the extreme rarity or absence of feldspar, low diversity heavy mineral suites and the presence of sedimentary rock fragments, suggesting a sedimentary source area, probably in large part comprising Late Cenomanian to Early Turonian littoral sands deposited during a major preceding transgression.