Facies analysis of the Bida sandstone formation around Kajita, Nupe basin, Nigeria

Journal

of African

Earth Sciences. Vol. 23. No. 2. pp. 253.256, 1996 CopyrIght o 1996 Elsewer Science Ltd

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Facies analysis of the Bida Sandstone Formation around Kajita, Nupe basin, Nigeria

0. OLANIYAN’

’Department

of Geology,

* Department

Abstract-A

Federal

program

sandstones,

facies,

was

occur

in a succession

are truncated

in places.

fine deposits

in overbank

streams.

Copyright

Resume-Un

la regron

grossiers

d’une

des

a des depots de levees

argilites,

trop

grossiers

improves

par extraction

1974,

1976).

of field

sequences

traction

observations

whose

deposits

cyclothems

in channels,

and

as deposits of braided ephemeral

a ete applique

sur une matrice

de la Formation

de grappes.

et de gres grossiers,

fin pour

de trainage

dtre

tamise,

D 1996

de cinquante

du Gres

n’a

II s’agit

de Bida dans

de conglomerats,

moyens

de gres

et fins. Un septieme

pu etre

caracterise

dans des chenaux interpret&

Elsevier Science

8 June

1994:

that

que

facies

sur base

A

and by

six

was used as input

into

correspond

et a des depots

comme

version

fifty

an area of about area

20 km SE of 215

km2 (Fig.

are part

deposited (Adeleye,

decroissante

respectivement

fins sediment&

des depots

recerved

de fleuves

2 May

The Bida sub-basin

au-dela

ephemores

trending

feature

1996)

OF THE BIDA SUB-BASIN of the Nupe basin is a NW-SE

which

extends

from

Kotangora

to Lokoja over a distance of about 400 km in the central part of Nigeria. Sediment fill in the basin exceeds

about

Nupe Group conditions

a granulometrie

cyclotheme

Ltd.

revised

cluster

recognition

is located of this

de sequences

Chaque

STRATIGRAPHY

facies.

data matrix program.

verticale

tronques.

Ils sont

is to show

the of

late Cretaceous fluviatile-marine

basis

pebbly

sandstones.

Ltd.

en une succession

naturelles.

Copyright

of this paper

The sediments

coarse

and fine-grained

on the

They are interpreted

INTRODUCTION

I).

are conglomerates,

upwards coarse

granulometrique

sont localement

(Received

and covers

from

de terrain.

de rive

divaguants.

fining

en grappes

etude

de gres graveleux

dont les cyclothemes

Pategi

derived

au Nigeria.

Les facres se repartissent

area

only

represents

Elsevier Science

ont Bte distingues

d’observations

The study

These

medium-grained

of multistorey

d’analyses

8 partir

graveleux,

comportant

granulometric the computer

Zimbabwe

Nigeria

around Kajita, Nigeria.

of clusters.

areas respectively.

c 1996

de Kajita

Six lithofacies

characterization

Harare.

Minna,

on a fifty by six data matrix

Formation

characterised

Each cyclothem

programme

par six donnees

analysis

167,

it was too fine for sieving.

The facies

The objective

MP

of Technology,

was performed

coarse-grained,

claystones,

PO Box

University

were derived from extraction pebbly

seventh

because

analysis

and S. B. OLOBANIY12 of Zimbabwe,

study of the Bida Sandstone

Six lithofacies sandstones, The

of Geology,

cluster

a granulometric

University

1000

The oldest

m (Ojo and Ajakaiye, stratigraphic

the basal conglomerates,

sequence consists

1976). in the area, of rounded

to

of the

subrounded

under 1971,

to be of an alluvial fan origin (Russ, 1931, Adeleye, 1976). These conglemerates are conformably overlain by the Bida Sandstone Formation, a lateral

rock fragments.

The sequence

is said

Journal of African Earth Sciences 253

0.

OLANIYAN

and S. B. OLOBANIYI

5-O E

7OE

6 “E

8”N

lzzzl

Study

Figure

1. Location

equivalent

of the study

of the Lokoja

Sandstone

former

consists

claystones. Formation

Formation

of

The Enagi Siltstone the Ironstones. The

laminated

fine grained The dominantly is the youngest

y

x

siltstones

sandstones oolitic

with

and kaolinitic Batati

MATERIALS AND METHODS

to

of predominantly siltstones and

The Bida sandstones are overlain by oolitic and pisolitic ironstones of the

Sakpe Ironstone Formation. Formation directly overlies subordinate

x

area.

the South. The formation consists sandstones with subordinate claystones. goethitic,

x

Area

Ironstone

in the sequence.

Several mesas in the study area were mapped in order to identify the various aspects of constituent lithofacies. Fifty representative samples were taken from cliff faces covering all the lithotypes. All the samples were allowed to dry, following which the partially consolidated ones were disaggregated with

the use of a porcelain

cement

was removed

(Folk, 1980). treated

mortar

by treatment

and pestle. with

dilute

Fifty grams of each disaggregated

sample

was

sieved

with

the

formation consists of conglomerates, sandstones and claystones which occur as flat and massively bedded strata with local occurrences of small scale planar cross beds. They are built up in fining-upward multistorey sequences, similar to the fluviatile cyclothems of Allen (1965).

4$. The claystones were not sieved because their grain size was finer than the range of these sieves. Similarly, the cobble- and boulder- sized fragments in the conglomerates were removed leaving the granule- and pebble-sized grains in a generally sandsized matrix.

254 Journal of African Earfh Soences

with

apertures

a set

use of an

electromagnetic sieves

and

HCI and

The Bida Sandstone Formation forms mesas with a local relief of up to 300 m occasionally. The

DN4188

shaker

The

ranging

of standard from

24 to

Facies

analysis

of the Bida Sandstone

Formation

around

Kajita,

Nupe

Basin,

Nigeria

Conglomerates Coarse-pebbly sandstones Pebbly sandstones Coarse sandstones Medium- grained sandstones Fine-grained sandstones

Figure

I

I

25

20

2. A dendrogram

showing

of the samples analysed,

individual and cumulative

of each fraction

Cumulative frequency latter and statistical

were

showed

of

curves were plotted from the parameters - phi-mean,

all

unimodal

the modes

the

analysed

distributions.

however

varied.

samples

The position

The coarse

grained

samples

sorted,

positively

are generally

The fine-grained

of

grained

samples are poorly sorted, positively and platykurtic or mesokurtic. The

skewed medium-

moderately

Figure

well

5

Formation.

2 is a dendrogram

extraction

of clusters

of the similarity sediment

determined.

phi-median, sorting, skewness, and kurtosis were determined using the formulae of Folk and Ward (1957). Histograms

10 coefficient

of the Bida Sandstone

RESULTS of fractions in 50 grams of each

From the weights percentages

the six lithofacies

coefficients

samples

lithofacies on the basis conglomerates, namely, pebbly

sandstones,

sandstones,

medium

sandstones

sandstones. The inter-relationships shaped similarity

between

diagram

which

between

shows

in a cluster indicates

into

coarse fine

the analysed the

the sediment

This

texture pebbly and

samples were also revealed

are generally

poorly

of their coarse

sandstones,

samples

and

of the samples

six

of similarity coefficient level at which adjacent

skewed

among the different

figure shows the segregation

sediment

from the

on the basis

based on the data matrix.

and very leptokurtic.

finely

compiled

amalgamated

skewed

sorted, strongly platykurtic.

1 0

I

I

I

15 Similarity

by the treedegree

of

facies on a scale

(Fig. 2). On this scale, the sediment types are joined

their degree

of similarity.

very DISCUSSION

CLUSTER ANALYSIS The cluster analysis was performed using the weight of each fraction in 50 grams of sample as data matrix. In this analysis,

the Euclidean

and the agglomeration and complete linkage separately.

measure

was used

schedules, using the single methods, were carried out

A cluster analysis of the Bida Sandstone Formation has generated six lithofacies - characterized by conglomerates,

coarse pebbly sandstones,

pebbly

sandstones, coarse sandstones, medium sandstones and fine sandstones. The conglomerates consist of subrounded to well rounded rock fragments ranging in size from 3 to 50

mm and yellowish-brown.

They

are poorly

0.

OLANIYAN

and S. B. OLOBANIYI

sorted and lack imbrication. Commonly, they overlie low relief erosional surfaces and may be

The sandstone mesas in the study area exhibit a succession of the above lithofacies and

interbedded

subfacies. They depict the identified sediment

lower

with

the

coarse

sandstones

The coarse pebbly sandstone individual

beds varying

pebbles well

which

is thickly

from

and make

up about

The brownish

pebbly

arkosic

to subarkosic

are poorly 10

sorted

mm.

arenaceous

with

conglomerate, coarse pebbly sandstone, coarse sandstone, fine sandstone is repeated

and

carbonaceous

are

different

subfacies. are whitish

0.5

massive

or

they giving

The massive

- brown

of They

from

compositionally, or ferrugineous

varieties

are

consists

sediments.

they

to

1 O-l 5% of the

grain size ranging

Structurally,

laminated

show a fining upwards

Constituent

sandstones

moderately to poorly sorted. The coarse sandstone lithofacies

a cyclothemic variation of facies. The successions

bedded with

1 to 1.5m.

are 2 to 30 mm in size are angular

rounded

sediments.

to

in the

part of the succession.

are

rise

to

and laminated

and consist

times

incomplete.

Although

Thus a cyclothem

with any cyclothems

member of the are characteristic

(Olobaniyi,

1988).

facies

i.e. the conglomerates

sorting is minimal.

carbonaceous

average

thickness

restricted

variety

is about

to a few

is dark,

and thickly

non-

bedded.

Its

in the lower

parts

of

The medium-grained between

brownish

colour,

sandstone

0.2

whose

is poorly to moderately

small-scale

to

sorted,

and

brownish

and is thickly

of these

sediments

contain

bedded. The moderate is dictated

are whitish,

anastomosing

or

sorting

by the limited massively

plant rootlet

clay

bedded and

impressions

and

base. the application

facies

differentiation

of cluster

has shown

analysis

univariate

method statistical

is more approach

to

Earfh Sctences

have

following

of the ephemeral

might

of lower

been

in

and claystones deposited

a reduction

have

energy

from

or loss of velocity

stream.

REFERENCES

can achieve

D. R., 1971.

Upper 297p

Stratigraphy

Cretaceous University

Adeleye,

D.,

sandstone

strata

a

reliable

than

the

because

every

size

Geology

(Cretaceous)

In: Geology

The Geology Edited

Ife, Nrgeria, pp 283-287. Allen, J. R. L., 1965. A review sediments. Petrology

Co., Texas.

the

significance

Nigeria. University Olobaniyi,

grain

of the mrddle

Brda

Geology Niger Basrn.

C. A., University

Sedimentology of sedimentary

of

5, 89-l 91 rocks. Hemphrll

size

Brazes river bar; A study parameters.

Journal

Prelrmrnary

interpretatron

rn the

middle

Niger

of Nigeria,

Edited

by Kogbe,

of Ife, Nigena, S. B., 1988.

fluvral

182~.

measurements In: Geology

the

of the origin and charactenstrcs

Sedimentary Petrology 27, 3-26. OJO, S. B., and Ajakaiye, D. E., 1976. of gravity

of the

PhD thesis

Sedimentary

by Kogbe

W. C., 1957. of

Nigeria.

of

Nrgeria.

of Nigeria.

of recent alluvial Folk, R. L., 1980.

Bida,

Nigeria.

The

12,1-24. Adeleye, D. R., 1976.

and sedrmentatron

around

of Ibadan, 1974.

Folk, R. L., and Ward,

fraction is taken into account in the former. This multivariate statistical treatment has made possible the identification of facies and their interrelationships based on their grain size distribution.

256 Journal of African

sorting

by currents

suggested

Publishing

that

characterization of sediments and therefore confirm and refine the results from the field. Secondly, this multivariate

during floods The medium-

areas. The fine sandstones

suspension

Adeleye,

burrows. Coarse to fine sand-size grains are disseminated in the claystones especially at the The above

facies with its improved

low angle planar cross beds

The grain size varies from 0.1 to 2 mm.

The claystones,

High energy currents pebbles occasionally.

deposited

and the

in channels or where effective

variety of the thin laminations

whereas the massive variety is about 7 m thick. The fine-grained sandstone facies is whitish

matrix.

been are

grain-size

to 5 mm has a purplish

commonly fnable. The laminated medium-grained facies possesses and locally

introduce

overbank

the succession. ranges

would grained

0.3 m and it is usually

horizons

Such streams

The poor sorting, positive skewness and platykurtic unimodal grain size distribution of the coarse

beds.

unconsolidated

of

may terminate

sequence. of braided

pebbly facies, suggest a deposition proximal overbank areas by traction

The

this cycle

in an array

sequence, in some of each cyclothem are

sands. The coarse subfacies is thinly laminated with local occurrences of small scale planar cross pebbly,

from a basal

sandstone, pebbly medium sandstone,

resulting

fining upward multistorey instances, the components often

starting

and claystones.

several

sediment

of friable

pattern

Basrn

In of

Area, C. A.,

pp 295-307.

A geological

study

of part

of South

Central Bida Basrn, MSc fhesis 107~. University of Ilonn, Ilorin, Nrgeria. Russ, W.. 1931. The Minna Birnin GwariBelt. Part 38 Annual Report. Geological Survey of Nigeria 1930.