A Sedimentologic and Stratigraphic Study of the Maastrichtian-Pateocene Sediments in Yuil Area, Bauchi State

Abstract

The Maas trichian-Pale ocene sediments in Yuli area me composed of the Gombe Sandstone and the Kerri-Kerri Formation. They cover 400 square kilometres have a t h i c h e s s of more than 100 metres. Six stratigraphic sections were studied, representing the entire stratigraphic succession of the Gombe Sandstone i n the Yuli area, The formation has a thickness of about 30 metres in the studied area. The Gombe Sandstone consists of folded beds of sandstone, s i l t s t o n e and mudstone. The sandstone consists of well consolidated, texturally immature, feldspathic wacks which have iron oxide cement. Cross-bedding, ripple marks, bioturbations, parting lineations and laminations are the structural features present. The sandstone varieties include the ferruginous, bioturbated and cross-bedded sandstones. Dark red slabby sandstones are also present. Texturally the sandstones are G medium grained, subrounded, poorly to moderately sorted, positively skewed and leptokurtic. Based on an integrated analysis of the strati&aphic, petrographic, t e x t u r a l , faunal and structural data, three environments of deposition may be suggested, namely f l u v i a l , estuarine , and deltaic. The Kerri-Kerri Formation consists of horizontal t o near horizontal strata of sandstone, s i l t s t o n e and clay. The formation overlies the Gombe Sandstone. It a t t a i n s a thickness of about 70 metres. l a t e r i t e capping is very common. The sandstones are f r i a b l e , texturally immature feldspathic wacks and a few subarkosic arenites. The sand- I stones vary from ferruginous sandstones, cross-bedded sandstones t o pebbly sandstones. The sandstones are coarse t o medium grained, poorly sorted, very f i n e l y skewed and very platy kurtic. Textural parametres indicate s a l t a t i o n and suspension as the means of transport accompanied by rapdd sedimentation. The s t r u c t u r a l features present ,, include cross-bedding, r i p p l e marks, laminations and slump structures. The sediments were diposi ted i n Pluvial, Lacustrine and d e l t a i c environments. Paleocurrent directions f o r the two formations based on the r i p p l e marks, cross-bedding, s i z e and rounding trends of the vein quartz pebbles indicate t h a t t h e c u r r e n t flow was eastwards. The feldspathic composition of the sandstones from both formations, the dominance of non-undulose aonocrystalline quartz and quartz pebbles suggest derivation from the nearby basement complex west of the studied area. The composition and t e x t u r a l c h a r a c t e r i s t i c s of the Aeavy minerals present also suggest derivation from the basement complex west of the area as well as the reworking of the older sedimentary rocks.