PEBBLE MORPHOMETRIC ANALYSIS OF THE … AWI FORMATION, CALABAR FLANK, SOUTHEAST NIGERIA ESSIEN, NSE UDO; ITAM, ASUKWO ESSIEN; OYAMA, ADAMS A , AND OBIM, V.N DEPARTMENT OF GEOLOGY UNIVERSITY

@IJRTER-2016, All Rights Reserved 208

PEBBLE MORPHOMETRIC ANALYSIS OF THE BASAL SECTION OF

THE AWI FORMATION, CALABAR FLANK, SOUTHEAST NIGERIA

ESSIEN, NSE UDO; ITAM, ASUKWO ESSIEN; OYAMA, ADAMS A , AND OBIM, V.N DEPARTMENT OF GEOLOGY UNIVERSITY OF CALABAR, CALABAR, NIGERIA

Abstract:A pebble morphometric study was carried out on 400 pebbles samples retrieved from

conglomeritic deposits of the basal section of Awi Formation, Calabar flank, exposed along Calabar-

Oban road, Southeastern Nigeria. The three orthogonal dimensions of Long (L), Intermediate (I) and

Short(S) axes were measured and the various pebbles parameters computed. The computed pebble

morphometric parameters have ranges of values as follow; Flatness Ratio (FR =0.51 – 0.67), Flatness

Index (FI=51% - 67%), Elongation Ratio (ER= 0.70 – 0.83), Maximum Projection Sphericity Index

(MPSI= 0.72 -0.82), and Oblate – Prolate Index (OPI = -1.12-2.48) these values strongly suggest

fluvial deposits. Roundness Index determined based on Sames chart ranges between 43% and 52%

(sub angular to subrounded) and inferred short to long intermediate distance of transport from the

provenance. The diagnostic forms for pebbles of fluvial origin (Compact, Compact Bladed, Compact

Platy and Compact Elongation) of 68% predominate over beach origin (Very Platy, Very Bladed,

Bladed and Platy) of 23%. The bivariate plots of FI versus MPSI and MPSI against OPI, agreed with

this result. The results from the study area favours continental setting of dominantly fluvial origin.

Keywords: Pebble morphometric, Calabar flank, Awi Formation, provenance, fluvial origin.

I. INTRODUCTION

The recent excavations as a result of the construction and expansion of United Cement Company

(Unicem) Southeastern Nigeria (figure 1), exposed good sections of conglomeratic sand/ironstone

unit of the basal unit of the Awi Formation. The pebbly basal unit have been studied and subjected to

pebble morphometric investigation. The study area has not received any geologic attention due to the

fact that it was covered with thick layers of overburden. Pebble morphometric research studies have

has shown that pebble form indices or parameters are good indicators of paleodepositional

environment ( Sames, 1966; Stratten,1974; Nwajide and Hoque,1982; Els,1988; Inyang and Enang,

,2002; Odumodu and Ephraim, 2007a and 2007b ; Odumodu, 2014 ; Itam et al ., 2015 and Itam and

Ugar, 2016) This study will therefore attempt to use the different unweathered quartz pebbles

encountered in the investigated area to interpret the paleodepositional environment of the deposit .The

results obtained will therefore be compared with results obtained in other part of the basin previously

investigated.

International Journal of Recent Trends in Engineering & Research (IJRTER) Volume 03, Issue 01; January - 2017 [ISSN: 2455-1457]


Figure 1: Map of the study area showing location of the samples.

Location of the Study Area

The area of study is located along Calabar - Oban Road (figure 1), Cross River State, Southeastern

Nigeria. The geographic position lies within latitude N05°06ʹ 42 ́ ʹ to N05 10 ́ 05ʹʹ and longitude E008°

30 ʹ 50ʹʹ to E008° 34 ʹ 57ʹʹ and is part of Calabar Flank basin.

II. GEOLOGICAL SETTING

The Calabar Flank is an epirogenic sedimentary basin in southeastern Nigeria (Murat, 1972).The

basin according to Nyong (1995) is bounded by the Oban Massif in the north with the Calabar hinge

line separates the basin from the Niger Delta basin in the south and the Ikpe platform and Cameroon

Volcanic Line delineate it in the west and east respectively (figure 2). The origin of this basin is

associated with the opening of the South Atlantic in the Cretaceous times when the South American

plate drifted away from African plate. The major structural elements within the basin include the Ikang

Trough (graben structure) and Ituk High (horst) which were mobile depression and stable mobile

submarine ridge that influenced the distribution sedimentary of facies (Murat, 1972 and Nyong, 1995).

The stratigraphic succession in the Calabar Flank is shown in Table 1. Sediment thickness is over

3500m with the onlap (or featheredge) of the outcropping units exposed along the fringes of the Oban

Massif basement complex. The Formations are best exposed along Calabar –Ikom road and a

succession consists of five (5) Cretaceous and a Tertiary lithostratigraphic units. Awi Formation is the

oldest basal unit and sits nonconformably on the basement complex of Oban Massif. The Formation

is Aptian in Age (Adeleye and Fayose, 1978).This is overlain by Mfamosing Limestone of Middle-

Upper- Albian age (Petters, 1982) deposited during the first marine transgression in the South Atlantic.

This in turn is succeeded by Late Albian- Cenomanian to Turonian, Ekenkpon Shale. Subsidence on

the faulted blocks of horst and graben allowed wide spread deposition of shales with minor marl and

mudstone intercalation. The New Netim Marl which is Coniacian in age, succeeded the shale unit. The

Santonian period was marked by a major unconformity in the Calabar Flank. Nkporo Shale of Late



Campanian to Early Maastrichtian (Edet and Nyong, 1994) capped marine transgression and

Cretaceous sedimentation in Calabar Flank .The Tertiary continental sands and gravel of the Benin

Formation completes the sedimentation in the basin (Table 1).

Figure 2: Structural map of the Calabar Flank and adjoining areas.

(Modified after Nyong and Ramanathan, 1985)



Table 1: Lithostratigraphic correlation between Calabar Flank. Abakaliki Trough,Anambra Basin and

the Middle Benue Trough (Petters et al;2010)

III. Materials and Methods

A total of four hundred (400) unweathered quartz pebbles were collected with fifty (50) pebbles each

from eight (8) different locations (L1-L8). Pebble morphometric measurement using Vernier caliper

after Krumbeins (1941) method was used. The Long (L), Intermediate (I) and Short (S) axes of the

pebbles were measured. Pebble indices such as Flatness Ratio (FR) Flatness Index (FI), Elongation

Ratio (ER), Maximum Projection Sphericity Index (MPSI) and Oblate Prolate Index (OPI) with the

visual estimation of pebble roundness using Roundness Chart of Sames (1966).The results obtained

were compared with those recorded in other localities previously studied.

IV. RESULTS AND DISCUSSION

Field description of the study area

The lithologic description of study area consists of conglomeratic sandstone, pebbly sandstone and

ironstone (figure 3).The conglomeratic sandstone is reddish brown, clast supported to matrix

supported, imbricated conglomerate, with coarse – medium, poorly sorted. The lithologic cross section

of outcrop sample in location 5 (L5) is about 2.0m thick and made up of pebbly sandstone ( figure 3a)

.This unit is characterized by reddish brown, dominantly angular to subrounded clast supported at the

base to matrix support at the top. The top of this unit is texturally characterized by mudstone units.

The sandstone is coarse to medium, with poorly sorted grains. The overall sequence represent fining

upward succeession (graded bed). At locations 6-8 (L6-8) the thickness of the outcrop units in local

quarry ranges from 3.8m to 4.0m (figure 3b) and consists of pebbly sandstone and a thin bed of reddish

brown ironstone. The pebbly sandstone exhibits similar characteristics features as previously

described.



Thickness Lithology DescriptionDepositionalEnvironment

1.9

m

Flu

via

l -

Ch

ann

el

Dep

osit

Red

dis

h b

row

n,

matr

ix s

up

po

ted

,p

oo

rly

so

rte

d,

co

ars

e -

med

ium

gra

inp

eb

bly

san

dsto

ne

Thickness Lithology Description

Flu

via

l -

B

ea

ch

Deposits

Reddish browncoarse - medium

grain

Reddish browniron stone

0.96m

0.4m

1.4

m

.

Depositional Environment

Reddish brown, matrix suppoted,

poorly sorted, coarse - medium grain

pebblysandstone

Reddish brown, matrix suppoted,

poorly sorted, coarse - medium grain

pebblysandstone

3a

3b Figure 3: Lithostratigraphic cross sections of the mapped area in: (a) location 5, L5 (b)

location 6 – 8, L6 – L8

3b

Figure 3: Lithologic cross sections of outcrop samples from the study area of:

(a) Location 5, L5 (b) Location 8, L8



Pebble morphometric parameters

The average results of the various computed pebbles morphometric parameters and roundness values

are presented in Tables 2 and 3

Table 2: Average pebble morphometric parameters from the various study locations.

LOCATION L(cm) I(cm) S(cm) FR FI ER L-I/L-S MPSI OP R (%)

L1(n=50) 4.07 3.15 2.39 0.59 59.00 0.78 0.44 0.76 -0.20 44.34

L2(n=50) 4.03 3.11 2.22 0.55 55.38 0.78 0.51 0.73 -0.01 49.42

L3 (n=50) 3.52 2.91 2.29 0.65 64.96 0.83 0.51 0.79 -0.03 50.22

L4(n=50) 3.90 3.21 2.62 0.67 67.40 0.82 0.56 0.82 0.80 49.92

L5 (n=50) 3.67 2.81 1.94 0.54 53.76 0.77 0.49 0.72 -0.11 43.66

L6 (n=50) 3.73 2.93 2.11 0.56 56.32 0.79 0.38 0.74 -1.12 45.18

L7 (n=50) 3.94 3.25 2.37 0.60 59.94 0.82 0.44 0.75 -1.08 52.48

L8 (n=50) 3.47 2.39 1.75 0.51 50.94 0.70 0.63 0.72 2.48 43.40

OVERALL MEAN 3.79 2.97 2.21 0.58 58.46 0.79 0.49 0.75 0.09 47.33

Legend: L=Long axis, I =Intermediate axis, S = Short axis, FR =Flatness Ratio, FI= Flatness Index, ER

=Elongation Ratio, MPSI =Maximum Projection Sphericity Index, OPI = Oblate Prolate Index, R

=Roundness, n = number of samples per location.

Table 3: Characteristic features and paleoenvironmental significant of the various computed parameters.

Pebble

morphometric

parameters

Characteristics Defined limits from

previous studies

Interpretation of

depositional

environment/

processses

Flatness Index (FI) FI consists of over 84% above

fluvial limit and 16 % below

this limit

Lutig, 1962

Beach (<45%)

Fluvial (> 45%)

Predominantly fluvial

Elongation Ratio

(ER)

Over 78% has values between

0.60 -0.90

Hubert,1968

Fluvial(0.6-0.9)

Fluvial processes

Maximum

Projection

Sphericity Index (

MPSI)

85% of the MPSI sampled

occurred above the imaginary

limit (0.66)

Dobkins and Folk, 1970

Beach (< 0.66)

Fluvial (> 0.66)

Predominantly fluvial

Oblate Prolate Index

(OPI)

Characteristics by 69% of the

OPI value plotted above -1.5

limit line and 33% below

Sneed and Folk,1958

Beach ( < -1.5)

Fluvial ( > -1.5)

Dominantly fluvial

with few beach

influences.

Roundness( R) 15% has values below 0.35

,while 35% has values above

0.45

Sames,1966

Fluvial(< .35%)

Littoral(>0.45%)

Mainly littoral/beach

action with little

fluvial

Form Geometry 21%C, 7.25%E, 24%CB,

15%CE,3.5%P, .75%VB,

0.5%VP,17.25%B, 8.75%CP,

VE1%

Sneed and Folk, 1958;

Dobkins. and Folk, 1970

and Gale, 1990.

Fluvial(C,E,CB, CE)

Beach (P,VP,VB,B)

Dominantly fluvial

with few beach

influences.

The interpretation of these results are carried out in conjunction with other works (Sneed and Folk,

1958 ; Lutig 1962; Sames, 1966; Hubert, 1968 ; Dobkins. and Folk,1970 ; Gale, 1990; Odumodu and

Ephraim 2007a and b ; Ogala,et al,.2010; Udo and Mode, 2013; Odumodu,2014; Itam and David,2015;

Itam et al ., 2015 and Ideozu and Ikoro,2015).The result obtained show that the mean Flatness Ratio

(FR) has value of 0.58. The FI ranges from 50.94% to 67.40% with average mean of 58.46% indicating



fluvial depositional environment (Lutig, 1962). The mean ER for pebbles evaluated is 0.79 which is

approximately within the 0.60-0.90 range for fluvial setting (Hubert, 1968 and Itam and Inyang, 2015).

The mean value of MPSI in the study area is 0.75 and ranges from 0.72-0.82. All the sampled pebbles

have values above the 0.66 limit (Dobkins and Folk, 1970), that separates fluvial from beach pebbles

(Tables 2 and 3). These values suggest fluvial depositional environment. The OPI ranges from -1.12

to 2.48 with a total mean value of 0.09. These values are greater than -1.5; lower empirical limits

(Dobkins and Folk, 1970), which distinguishes beach dominated pebbles from river. This analysis

shows the dominance of fluvial influence over beach.

From the analysed data the mean roundness values is 47 % (43%-52% implying angular to

subroundness).This infer short/intermediate travel distance of the pebble from the provenance. This

sediments are likely to be sourced from the weathering of the basement rocks of the adjoining Oban

Massif Nigeria and intrabasinal activities (Itam and David, 2015).

The results obtained from the pebble morphometric analysis were further analysed using bivariate

plots. This was carried to further discriminate the paleoenvironment of deposition. Morphometric plots

of FI against MPSI (Stratten, 1974) and MPSI versus OPI (figure 4a and b) of all the pebbles sampled

point to predominantly fluvial influence. Also, the bivariate plot of Roundness (R) against Elongation

ratio (ER) in figure 4c using the upper limits of 35% and 45% Roundness of pebbles shaped in river

and littoral environment of Sames ( 1966 ) and the fluvial limit of Elongation ratio of 0.60 to 0.90 for

pebbles influence by fluvial processes (Hubert,1968 ), this infer fluvial–beach environment.

4a

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2

FLA

TNES

S IN

DEX

MPSI

FLUVIAL

BEACH

BEACH FIELD



4b

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-10 -8 -6 -4 -2 0 2 4 6 8 10

MP

SI

OPSI

Fluvial

Beach



4c

Figure 4: Bivariate plots of; (a) FI against MPSI (b) MPSI against OPI (c) R against ER

According to (Sneed and Folk, 1958; Dobkins. and Folk ,1970 and Gale, 1990 ), Compact (C),

Elongation ( E), Compact Bladed (CB) and Compact Elongate (CE) are most indicative of fluvial

action whereas Platy( P), Very Platy ( VP),Very Bladed (VB) and Bladed ( B ) are diagnostic of beach

setting (C), Elongation ( E), Compact Bladed (CB) and Compact Elongate (CE) are most indicative of

fluvial action whereas Platy( P), Very Platy ( VP),Very Bladed (VB) and Bladed ( B ) are diagnostic

of beach setting .The result of the analysed pebbles values of 21%C, 7.25%E, 24%CB, 15%CE,

3.5%P, 1.75%VB, 0.5%VP, 17.25%B, 8.75%CP,and 1%VE (figure 5).These values point to

predominantly fluvial than beach processes in the shaping of the analysed pebbles in the study area.

Comparing this result obtained with those recorded by previous authors (Itam and Inyang, 2015 and

Itam et al; 2015) in the distant location of the Awi Formation, the result is in agreement with

predominantly fluvial over beach processes.

0

20

40

60

80

100

120

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

RO

UN

DN

ESS

ELONGATION RATIO

Hubert , ER limit

Sames % R<35%

Sames % R>45%



Figure 5: Pie chart showing form names from the study area

Legend: C= Compact, CP =Compact Platy, CB = Compact Bladed, CE = Compact Elongate,

P=Platy, E= Elongation, VP =Very Platy, VB =Very Bladed, VE= Very Elongate

V. CONCLUSION

The pebble morphometric parameters have proven to be good indicators for distinguishing

paleodepositional environments in situations where fossils are lacking especially in a continental

setting such as Awi Formation. The various parameters obtained in the pebble morphometric analysis

together, with the different bivariate scatter plots have shown that the depositional environment of the

basal of the section of the Awi Formation is predominantly influence by fluvial processes with beach

/ littoral influence .The results obtained corroborate with the previous work, carried out on elsewhere

within the Awi Formation

REFERENCES 1. Adeleye, D.R and Fayose, E.A. (1978).Stratigraphy of type section of Awi Formation, Odukpani area, Southeastern

Nigeria, Nigeria. Journal of Mining Geology .15: 35-37.

2. Dobkins, J.E. and Folk, R.L. (1970). Shape development of Tahiti- Nui. Journal of Sedimentary Petrology, 40, pp.

1167 – 1203.

3. Edet, J.J and Nyong, .E.E. (1994). Palynostratigraphy of Nkporo Shale

4. exposures (Late Campanian – Early Maastrichtian) on the Calabar Flank,

5. Southeastern Nigeria. Paleobotany and Palynology, pp. 80, 131-147

6. Gale, J. (1990). The Shape of Beach Gravels. Journal of Sedimentary Petrology,pp. 787-789.

7. Hubert, F.L. (1968). Selection and wear of pebbles on Gravel Beach, University of Groningen, Geological Institute

Publication. Number, pp.190.144

8. Ideozu, R.U and Ikoro, D.O (2015).Sedimentology of the conglomeratic beds within Odoro Ikpe- Arochukwu Axis:

Afikpo Basin, Southeastern Nigeria. International Research Journal of Geology and Mining .Vol 5. (3), pp.31-35

9. Inyang, D.O and Enang, E.I (2002) .Use of statistical parameters in sedimentological study of conglomerates in North-

eastern Niger Delta, Nigeria. Nigerian Journal of Mining and Geology.40 (1), pp. 273-302

10. Itam, A.E and Inyang D.O (2015). Granulometry and Pebble Morphometry of Awi Sandstone, Calabar Flank Nigeria.

International Journal of Engineering and Applied Sciences. Vol 6(4), pp. 15-27

C21%

CP9%

CB24%

CE15%

P3%

B17%

E7%

VP1%

VB2%

VE1%

C

CP

CB

CE

P

B

E

VP

VB

VE



11. Itam, A.E; Inyang, D.O; Akpan E.B and Ikoro, D.O (2015).Pebble Morphometric Analysis of Awi Formation in

Calabar Flank, Nigeria: The Journal of Educational Research and Technology.4 (4), pp. 93-110

12. Itam, A.E and Ugar, S.I (2016). Sedimenatry textural parameters of outcrop sample, exposed along a road cut in

Calabar, Calabar Flank, Southeastern Nigeria. International Journal of Engineering Sciences and Research

Technology. Vol 5(10), pp.233-242

13. Krumbein, W.C. (1941). Measurements and geological significance of shape and roundness of sedimentary

particles. Journal of Sedimentary Petrology (11), pp. 64 – 72

14. Lutig, G. (1962). The shape of pebbles in the continental, fluviatile and marine facies. Int. Assoc. Science Hydro. Publ,

pp.253 – 258.

15. Murat, R. C. (1972). Stratigraphy and paleogeography of the Cretaceous and Lower Tertiary in Southern Nigeria. In:

T. J. Dessuavagie (Ed.), African Geology 251 – 266). Ibadan: University Press, pp 251 – 266

16. Nwajide, C.S and Hoque, (1982). Pebble Morphometry as an aid in environment diagnosis, an example from the

Middle Benue Trough, Nigeria. Nigerian Journal of Mining and Geology, 19, (1), pp 114-120

17. Nyong, E.E and Ramanathan, R.M. (1985). A record of oxygen- deficient

18. paleoenvironments in the Cretaceous of the Calabar Flank, Southeastern

19. Nigeria. Journal of African Earth Sciences. Vol. 5 (4), pp. 455-460.

20. Nyong, E. E (1995). Cretaceous sediments in the Calabar Flank in Geological excursion guide book. Proceedings of

the 31st Annual Conference of the Nigerian Mining and Geosciences Society.pp 13-25

21. Odumodu,C.F. (2014). Pebble form indices as signatures of the depositional environment of the Benin Formation

along the Atamiri River, Uli, South-Eastern Nigeria. International Journal of Scientific & Technology and Research.3

(1), pp 23-32

22. Odumodu, C.F.R. and Ephraim, B.E. (2007a). Paleoenvironmental analysis of the Nsukka Formation, using pebble

morphology. Natural and Applied Sciences Journal, 8 (1), pp. 73 – 84.

23. Odumodu, C.F.R. and Ephraim, B.E. (2007b). Pebble Morphometry as an indicator of the depositional environment

of the Ajali Sandstone. Natural and Applied Sciences Journal. 8 (2), pp. 132 – 143

24. Ogala,J.E; Adaikpoh, E.O; Omo-Irabor,O.O and Onotu R.U.(2010). Granulometric Analysis and Pebble

Morphometric studies as Indicators of Depositional Environments of the Sandstone Facies around Okanyan and

Evironments in the Benin Formation, Southwestern Nigeria World Applied Sciences Journal 1 (3), pp. 245-255.

25. Ojo,O J. (2012). Depositional Environment and Petrographic characteristics of Bida Formation around Pategi,

Northern Bida Basin, Nigeria. Journal of Geography and Geology pp. 224-241

26. Petters, S. W. (1982). Central West African Cretaceous – Tertiary benthic foraminifera and stratigraphy.

Paleontologica 179:1-104

27. Petters, S.W; Zarboski, P.M.P. Essien, N.U; Nwokocha, K. D and Inyang, D. (2010) Cretaceous sediments in the

Calabar Flank in Geological

28. Excursion Guidebook. Proceedings of the 46th Annual Conference of the

29. Nigerian Mining and Geosciences Society, Calabar pp.14 – 19

30. Sames, C.W.(1966). Morphometric data of some recent pebble associations and their application to ancient deposits.

Journal of Sedimentary petrology, 36, pp. 126 – 142.

31. Sneed, E.D. and Folk, R.E (1958). Pebbles in the lower Colorado River, Texas: a study of particle morphogenesis.

Journal of Geology, pp. 66, 114 – 150.

32. Stratten, T. (1974). Notes on the application of shape parameters to differentiate between beach and river deposits in

Southern Africa. Trans. Geological Society of South Africa, pp. 59 – 64.

33. Udo, I.G and Mode A.W. (2013). Use of statistical parameters in the sedimentological study of conglomerate deposits

in North Eastern part of Akwa Ibom State, Niger Delta Basin, Nigeria. IQSR Journal of Applied Geology and

Geophysics. Vol (5), pp. 21-27

Documents

PEBBLE MORPHOMETRIC ANALYSIS OF THE … AWI FORMATION, CALABAR FLANK, SOUTHEAST NIGERIA ESSIEN, NSE UDO; ITAM, ASUKWO ESSIEN; OYAMA, ADAMS A , AND OBIM, V.N DEPARTMENT OF GEOLOGY UNIVERSITY