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

ABSTACT

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 thichess 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,

siltstone 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 fluvial,

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.

laterite 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.