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7/30/2019 assessment of depositional environment using lithofacies association and petrophysical analysis
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CHAPTER 1
1.0 IntroductionToday there are numerous description indices for clastic shape and size each
one trying to show the influence of dynamic conditions and clastic petrography
that are mobilised in certain transportation or depositional environment and
their shapes at certain moments. Particle morphometry or form (sieve analysis)
refers to the sum of the surface characteristics of sedimentary grains. Processes
of weathering, erosion, and transport may all leave distinctive imprints on
particles, in the form of fractures, worn surfaces, and particular surface textures
(Benn, 2010).
Resolving the stratigraphic patterns along the spread of a geographical area
entails an integrated approach of petrophysical analysis for the paleo-
enviromental events to be decrypted properly.
The facie characterisation of the outcrop section has a lot to do with the
deposition of sediments, the environment of deposition of the sediments and the
mineral contents to some extent.
1.1 Aims and objectives
The aim of this research is to describe the depositional environment of the
sediments in the study area which lies on Niger delta basin. The objective on the
other hand is to evaluate and analyse the petrophysical parameter of the
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sediments of the Benin formation, interpreting the identified and observed
patterns in other to evaluate and correlating them to some of the previously
devised models.
This is also aimed to give insight on the initial observation during this work.
1.2. Location and accessibility
The study area is a remote village of Ikot Amama which lays within the range
of longitude 0703050 and latitude 0501030 at Ibiono Ibom local government
area of Akwa Ibom state south-eastern Nigeria. Accessibility is highest when
most of the streams and marshy area are dried up. The high lands, elevations
and stream are highly dense with concentrated vegetation especially the under
growths causing limitation to accessibility of path connected area.
1.3 LIMITATIONS
The limitations encountered during this study include inaccessible roads
and uneasy walk paths. It was also quite difficult to get sample from the
outcrops or litho unit because of the height of some of the litho-section of
which some were about 8meters high and knowing that most exposed
surface s were weathered, the need of hammer to dig in for unexposed
unit to get un-3weathered deposits was required .the fear that some of
the lithosections might cave in and have one buried.
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1.4 Climate and Vegetation
Because of the effects of the Maritime and the Continental Tropical air masses,
the climate of this area is characterised by two seasons, namely, the wet or rainy
season and the dry season. The wet or rainy season lasts for about eight months
but towards the far north, it is slightly less. The rainy season begins about
March-April and lasts until mid-November. Relatively, this area which is
located in Akwa Ibom State receives relatively higher rainfall totals than most
other parts of southern Nigeria. The total annual rainfall varies from 4000mm
along the coast to 2000mm inland.
The dry season begins in mid-November and ends in March. During this brief
period, the whole Continental Tropical air mass and its accompanying north-
easterly winds and their associated dry and dusty harmattan haze. However, as a
result of the proximity of the area to the ocean, the harmattan dust haze, (locally
known as "ekarika") is not usually too severe as in the Sahelian zone of northern
Nigeria. Sometimes it lasts for only a few weeks between December and
January. The harmattan period is usually advantageous to the farmers because it
is congenial for harvesting and the storage of food crop. Temperature values are
relatively high in throughout the year, with the mean annual temperatures
varying between about 26C to 36C. The relative humidity of the study which
varies between about 75 per cent to 95 per cent, with the highest and lowest
values in July and January respectively. In January, areas which lie within 30 to
40 km from the coast experience mean relative humidities of more than 80 per
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cent, while values in areas further north vary between about 70 per cent a to 80
per cent Vegetation And Fauna. The existing climatic factors in this area would
have favoured luxuriant tropical rainforests with teeming populations of fauna
and extremely high terrestrial and aquatic biomass. The vegetation of the area is
still intact and concentrated with some of the native vegetation being almost
replaced by secondary forests of predominantly wild oil palms, woody shrubs
and various grass undergrowth. Mangroves cover extensive parts of the area.
1.5 Drainage, Topography and Soil
The area under study is drained by two rivers; the north-eastern and south-
eastern are drained by the Cross River while the north-western is drained by the
Kwa-Ibeo River. Most of other streams that are found in the area are seasonal
that is; the dry up during that dry season. The flow direction of these streams
and rivers are to the north-west and south. The streams are characterised by
igneous intrusion and laminated shale as the bedrocks. In general, the
topography of the area is flat with few steep and elevated areas.
Weathering and erosion constitutes the major soil forming agents in the area.
The debris derived from the weathering of the intrusive rocks are mainly
lateritic while the erosion and weathering of the shale bed provides excellent
humus due to incorporation of decayed organic materials. The soil in the area
has colour ranging from black to dark reddish and they have high clay content.
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Figure 1: Topographic map of study area
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CHAPTER TWO
2.1 Literature Review
With the general increasing interest of geologist to understand and describe the
lithological facies of the sedimentary deposits in the south eastern Nigeria, a lot
of works have been and is being done using different approaches.
Most recent works focuses on the use of geophysical analysis like the well log,
wire line logging, and electric soundings in combination with petrophysical
analysis to interpret the lithological sequence and facies. While others include
the use of paleo-environmental signatures analysed from the study area.
Previous investigation on the Paleoenvironmental Interpretation of the Nkporo
Formation Afikpo Sub-Basin, Nigeria by Okoro Anthony. U Onuigbo
Evangeline N., Akpunonu Eliseus O and Obiadi Ignatius I.
Department of Geological Sciences, Nnamdi Azikiwe University of Nigeria also employed
this same technique of lithofacies analysis and pebble morphormetry.
Pebble Morphometry and Particle Size Distribution as Signatures to
Depositional Environment of Maestrichtian Ajali Sandstone 1977; Banerjee,
1979; Ladipo, 1985; Amajor, 1986a, 1989; Reijers and Nwajide, 1996; Awalla
and Eze, 2004, and Nwajide, 2005). These studies which are now used as
models to understand the geological structure of the Niger delta basin
Wright, 1968; Murat, 1972; Olade, 1975; Whiteman, 1982 and Nwajide and
Reijers, 1996 all studied the evolution of the Niger delta basin as a result of the
regional folding and uplift of the Benue Trough during the Santonian to Early
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Campanian. Describing the formation of the Anticlinorium (Abakaliki
Anticlinorium) dislocated the depositional axis from the Benue Trough to the
Anambra Basin which was indicated to be a stable platform before the tectonic
event
2.2 Geologic study of the Area
The study area lays in the Niger delta basin underlain by the Benin
sedimentary formations of Late Tertiary and Holocene ages. Also, this area
consists of coastal plain sands, now weathered into lateritic layers. The latter
lithologies include the late abgada Formation at the base followed by akata
Formation. Upwards, the geologic succession passes imperceptibly into thick
sequences of clays, sands and gravel. Gravel beds and pebbly sands are
commonly exposed on hillsides, road-cuts and stream channels. Generally, the
sands in this area are mature, coarse and moderately sorted
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Figure 2: geologic map of study area
The Niger Delta is situated in the Gulf of Guinea and extends throughout the
Niger Delta Province as defined by Klett and others (1997). From the Eocene to
the present, the delta has prograded southwestward, forming depobelts that
represent the most active portion of the delta at each stage of its development
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(Doust and Omatsola, 1990). These depobelts form one of the largest regressive
deltas in the world with an area of some 300,000km2(Kulke, 1995), a sediment
volume of 500,000 km3
(Hospers, 1965), and a sediment thickness of over 10
km in the basin depocenter (Kaplan et al,1994).
Fig.3 Structural units of Niger Delta basin (Short and Stauble 1967)
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The formations of the study area are mainly:
1. Benin Formation (Youngest)
2. Agbada Formation and
3. Akata Formation (Oldest)
2.2.1. The Benin formation
This formation constitutes mainly of sand stones which make up of mainly 90%
of it and it stretches from the west through the Niger delta and extends up north
towards part of the Anambra basin where it transverses to the Mamu formation.
The sandstone of this formation is also intercolated with shale units and there is
poor sorting of the unit grains which include the fine sand, coarse sand, sub
angular to well-rounded pebbles, gravels and the angular cobbles units.
The presence of light streak and wood fragments suggests that they are mainly
of continental deposit of upper deltaic environment
The variability of the shallow water deposition is indicated basically by most structural units
that could be spoted within the benin formation. The thickness of this formation ranges from
about 6000ft and above. Just little collection of hydrocarbon could be found within this
formation. In addition to a surface formation the Benin Formation crops out
widely at surface across the delta province. Its limits shows below (figure 4)
based on Short and Stauble (1967) are much more extensive than those shown
by Dessauvagre (1974).
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The sequence encountered in Elele-1 contains more than 90% sand and a few
shaley intercalations. Shale content increases towards the base as shown in
(figure 4) below.The sand and sandstone are coarse to fine grained and
commonly granular in texture. The sand and sandstone are poorly sorted, and
partly unconsolidated. The sands and sandstones are white or yellowish brown
because of limonitic coats. Lignite occurs in thin streaks or a finely dispersed
fragment. Heamatite and feldspar grain are common. The members of the
formation shales are grayish brown, sandy and silty and contain plant remains
and dispersed lignite. Shales constitute only a very small part of the sequence.
2.2.2 Agbada formation
This formation is intermediate in age and position of the three formation found
in the study area (Use Ikot Amama) and is a sequence of sandstone and shale
Unit i.e. an interfingering of sandstone and shale at the bottom. The shale unit
that underlies the sand is quite thicker than the sand unit. It has high microfauna
content at the bottom which decreases upwards, indicating an increased rate of
deposition at the deltaic point.
The Agbada formation is not exposed in the Niger-delta region rather they occur
as subsurface rock between the Benin formation and the Akata formation. The
agbada formation is a replica of what is seen at ogwasi, Asaba and Ameki
formations which are Eocene and Oligocene the thickness of this rock unit
ranges from 1000ft (304.8 m) and above.
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The ages of this formation ranges from Eocene in the northern part to Pliocene/
Pleistocene in the south.
2.2.3 Akata Formation
This formation underlies the two formation mentioned above and its the oldest
amongst them in age. This formation is uniform clay with dark sandy, silt clay
with scanty plants remains occurring at the top especially close to the contact of
the overlying Agbada formation.
The Akata Formation is thought to be the main source rock for Niger Delta
complex oil and gas. The formation probably underlies the whole of the Niger
Delta complex south of the Imo shale outcrop which itself probably deposited
under similar condition of deposition and may be considered an up-dip
equivalent of Akatafacies The top of the Akata Formation is taken arbitrarily at
the deepest development of deltaic sandstone at 7810Ft in the type section. The
base of the formation was not reached at a depth of 11121Ft in Akata-1 but the
base has been penetrated in wells situated on the Delta Flanks.
The age of the formation ranges from Eocene to present day but conceptually
deep water Paleocene Imo shale and even late CetaceousNkporo Shale (Late
cretaceous) could be classed as AkataFacies.
The Akata Fauna is rich in planktonic foraminifera which indicate deposition on
a shallow marine shelf. Akatafacies extends into deep water and must contain
deep water assemblages. Akata also must be graded laterally and vertically into
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the deep water turbidities of the Avon-Mahin Fan, the Niger Fan, and the
Calabar Fan.
The arbitrary nature of the boundary between the Agbada and Akatafacies has
been commented upon. At the present day, Akatafacies are being deposited on
the continental shelf and slope and perhaps on the lower part of the pro-delta
slope, the present day outcrop of the Akata then is completely submarine. The
upper boundary is markedly time transgressive and has been deformed
structurally (synsedimentary) on large scale. The Imo Shale (Palaeocene)
represents up-dip subaerial outcrops of AkataFacies (Short &Stauble). We do
not have much data on the Akata Formation depth beneath the delta. Diapirs and
high pressure tones are developed on a grand scale but details are limited.
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Figure 4: extent of erosional truncation
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2.3 THE NIGER DELTA TECTONICS
Rapid sedimentation along the edge of the Niger delta resulted in faulting
contemporaneous with sedimentation, thus producing an abrupt thickness of
sediments across the fault line on the down thrown block. This is the well-
known growth fault line on the down thrown block. This is the well-known
growth fault structure. If sufficient movement occurs, an elongate anticline
(roll-over anticline) may form in front of the fault. Stoneley (1966) ascribed the
structures in the offshore areas to salt movement at depth. There appears to be
no doubt that the diapiric structures off the Niger delta are of the same origin as
those farther south and are possibly of AptianAlpian age.
The tectonic framework of the continental margin along the West Coast of
equatorial Africa is controlled by Cretaceous fracture zones expressed as
trenches and ridges in the deep Atlantic. The fracture zone ridges subdivide the
margin into individual basins, and, in Nigeria, form the boundary faults of the
Cretaceous Benue-Abakaliki trough, which cuts far into the West African
shield. The trough represents a failed arm of a rift triple junction associated with
the opening of the South Atlantic. In this region, rifting started in the Late
Jurassic and persisted into the Middle Cretaceous (Lehner and De Ruiter, 1977).
In the region of the Niger Delta, rifting diminished altogether in the Late
Cretaceous. Figure 3 shows the gross Paleogeography of the region as well as
the relative position of the African and South American plates since rifting
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began. After rifting ceased, gravity tectonism became the primary deformational
process. Shale mobility induced internal deformation and occurred in response
to two processes (Kulke, 1995). First, shale diapirs formed from loading of
poorly compacted, over-pressured, prodelta and delta-slope clays (Akata Fm.)
by the higher density delta-front sands (Agbada Fm.). Second, slope instability
occurred due to a lack of lateral, basinward, and support for the under-
compacted delta-slope clays (AkataFm). For any given depobelt, gravity
tectonics were completed before deposition of the Benin
Formation and are expressed in complex structures, including shale diapirs, roll-
over anticlines, collapsed growth fault crests, back-to-back features, and steeply
dipping, closely spaced flank faults (Evamy and others, 1978; Xiao and Suppe,
1992). These faults mostly offset different parts of the Agbada Formation and
flatten into detachment planes near the top of the Akata Formation.
2.3.1 Lithology
The Cretaceous section has not been penetrated beneath the Niger Delta Basin,
the youngest and southernmost sub-basin in the Benue-Abakaliki trough
(Reijers and others, 1997). Lithologies of Cretaceous rocks deposited in what is
now the Niger Delta basin can only be extrapolated from the exposed
Cretaceous section in the next basin to the northeast--the Anambra basin. From
the Campanian through the Paleocene, the shoreline was concave into the
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Anambra basin (Hospers, 1965) (see fig. 3 in this paper), resulting in
convergent longshore drift cells that produced tide-dominated deltaicn
sedimentation during transgressions and river-dominated sedimentation during
regressions (Reijers and others, 1997). Shallow marine clastics were deposited
farther offshore and, in the Anambra basin, are represented by the Albian-
CenomanianAsu River shale, Cenomanian-SantonianEze-Uku and Awgushales,
and Campanian/MaastrichtianNkporo shale, among others (Nwachukwu, 1972;
Reijers and others, 1997). The distribution of Late Cretaceous shale beneath the
Niger Delta is unknown in the Paleocene, a major transgression (referred to as
the Sokoto transgression by Reijers and others, 1997) began with the Imo shale
being deposited in the Anambra Basin to the northeast and the Akata shale in
the Niger Delta Basin area to the southwest.
Deposition of the three formations occurred in each of the five off lapping
siliciclastic sedimentation cycles that comprise the Niger Delta. These cycles
(depobelts) are 30-60 kilometers wide, prograde southwestward 250kilometers
over oceanic crust into the Gulf of Guinea (Stacher, 1995), and are defined by
synsedimentary faulting that occurred in response to variable rates of
subsidence3 and sediment supply (Doust and Omatsola, 1990). The interplay of
subsidence and supply rates resulted in deposition of discrete depobelts, when
further crustal subsidence of the basin could no longer be accommodated, the
focus of sediment deposition shifted seaward, forming a new depobelt (Doust
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and Omatsola, 1990). Each depobelt is a separate unit that corresponds to a
break in regional dip of the delta and is bounded landward by growth faults and
seaward by large counter-regional faults or the growth fault of the next seaward
belt (Evamy and others, 1978; Doust and Omatsola, 1990). Five major
depobelts are generally recognized, each with its own sedimentation,
deformation, and petroleum history. Doust and Omatsola (1990) describe three
depobelt provinces based on structure. The northern delta province, which
overlies relatively shallow basement, has the oldest growth faults that are
generally rotational, evenly spaced, and increases their steepness seaward. The
central delta province has depobelts with well-defined structures such as
successively deeper rollover crests that shift seaward for any given growth fault.
Last, the distal delta province is the most structurally complex due to internal
gravity tectonics on the modern continental slope.
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Figure 5: tectonic frame work of Niger delta
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CHAPTER THREE
3.1 Method of Study
The method of study applied in this work ranges from field-work which
involves working on the field to laboratory practical work and finally the data
analysis of which include the sieve and pebble morphometric analysis.
3.2Field work
This involves the study of the geology of the area and gathering information
from all observable geologic activities in the area. The data gathered in the field
depends on the following.
First is the scope of work which was predetermined before the field work. The
scope of work revolves around understanding the geologic as well as physical
processes of deposition in the area. Other points put in place included the
weathering activity, the relief, soil type, soil colour, soil texture, topography,
vegetation.
The data gathered also depended on the students level of involvement and
ability to see, visualise and take notes of the thing that he observes.
Finally is the materials used in the field observation.
The following materials were used for the field work
- Sample bags and small polythene bags for sample collection and storage
- The clinometers
- The GPS
- Steel tapes for mapping and analogue outcrop logging
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- Cameras for photography and digital logging
- Hammers for breaking rock and digging out rock sections.
- Pen, pencils and notes for recording observations
- Paper cello tapes for labelling the samples
- Field bags for carrying the samples.
3.3 Particle-Size analysis
Particle-size analysis comprises the measurement and analysis of the three
particle axes that define the three-dimensional shape of a particle. For many
applications, it is much more convenient to characterize particle size by only
one variable, such as the length of the intermediate particle axes or the size of
the sieve on which a particle was retained. Once the sizes of particles are
determined, they are statistically analysed, so that particle size distributions and
statistical parameters characterizing them can be compared between streams or
over time. The mean particle size on a streambed, a particular particle-size
percentile, a characteristic large particle size, as well as the entire spectrum of
particle sizes all affect the hydraulics of flow as well as bedload transport rates.
Studies concerned with the mechanics of particle entrainment, particle transport
and deposition need to include the description and comparison of particle
shapes.
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Pebble morphometric studies involves measurement (using vernier calliper) of
the long (L), intermediate (I), and short (S) axes of pebbles from pebbly
sandstones. The three mutually perpendicular axes of each pebble were
measured and the roundness estimate with the aid of a roundness image
set. Morphometric parameters such as size, flatness ratio, elongation
ratio, elongation ratio, maximum projection sphericity, form geometry and
oblate index were computed.
Figure 6: pebble geometric axis
The three mutually perpendicular axes (S, I and L) of each of the 90 pebbles
were measured using some set of instruments which include:
The venier callipers
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G cramp
The rulres
Table 3.1 Morphometric parametersIndices Formulae Author
elongation ratio
Sneed &Folk (1958)
Zingg (1935)
Zingg (1935)
Maximum projection sphericity
index (MPS) Sneed and Folk, 1958
Disc-Rod Index (DRI) Sneed & Folk (1958)
Oblate-Prolate Index (OPI)
[ ] Dobkins & Folk (1970)
Elongation index (IE) The percentage by weight of particles whose long
dimension is greater than 1.8 times the mean dimension measured with a
standard gauge. The elongation, n, is length divided by breadth and the
elongation ratio is 1/n
Roundness index The average radius of curvature of the corners of a particle,
divided by the radius of the maximum inscribed circle for a two-dimensional
image of the particle, i.e. (r/N)/R, where ris the average radius of curvature
at the corners,Nis the number of corners, andR is the radius of the largest
inscribed circle. In practice, it is used empirically and other techniques are also
used. For example, a pebble may be compared with a set of standard silhouettes.
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The resulting index figure allows inferences to be made about the nature of the
depositing process.
Sphericity An expression of how closely the shape of a grain resembles the
shape of a sphere. Sphericity can be determined by examining the relation
between the long (L), intermediate (I), and short (S) axes of the particle, the
maximum projection sphericity, , being given by the expression = 3(S2/LI).
For a perfect sphere, = 1. Values less than one relate to increasingly less
spherical shapes.
The bivariate plots of M.P.S. vs. OP Index,
The sphericity form diagrams were very useful in the environmental
discrimination of the pebbles.
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3.4 Sieving of particle size
The size of sand particles was measured manually by sieving. The different
equipment used in both approaches can affect the results. This makes it
necessary to compare different methods of particle-size
The primary purpose of sieve analysis is to determine particle size distribution
in sands which directly relates to;
Availability of different sizes of particles in parent material.
Processes operating where sediments are deposited, particularly
competency of the flow.
Concentration of particles in suspension and source rocks (Friedman,
1979; Lewis and McConchie, 1994).
Equipment
1. Sample splitters,
2. Plexiglas plate and 18 inch steel rulers,
3. shaker.
4. Miscellaneous pans, brushes, scoops, etc.
5. Sieves.
Eighteen samples from the exposure were analysed according to the technique
of Friedman (1979). The nests of sieve were arranged with the coarsest at the
top and the pan at the bottom. The disaggregated and weighed samples of each
of the sands were poured in to the uppermost sieve and shook for 15minutes.
The frequency curves of the samples were plotted and critical percentiles (5,
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16, 25, 50, 75, 84 and 95) were obtained and the t extural parameters of
the sands which include the graphic mean, median, graphic standard deviation,
inclusive graphic skewness and graphic kurtosis were calculated using the
following McManus(1995) statistical parameters
Table 3.2 McManus statistical parameters
Graphic mean Mcmanus, 1995
Median 50
Graphic standard deviation (1) + Inclusive graphic skewness (SKI) + Graphic kurtosis (KG)
The bivariate plots of
Skewness vs. standard deviation,
Mean vs. standard deviation,
Simple skewness vs. simple sorting (after Friedman, 1979) was used in
the environmental discrimination.
These results are plotted on graph of which the sieve scale is logarithmic. To
find the percentage of aggregate passing through each sieve, first the percentage
retained in each sieve was found using the following equation:
%retained =
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Where
= weight of aggregate in the sieve = total weight of aggregateThe next step was finding the cumulative percentage of aggregate retained in
each sieve which was done by adding the total amount of aggregate that is
retained in each sieve to the amount retained in the previous sieves.
The cumulative percentage passing was found by subtracting the percentage
retained from 100%
%cumulative passing = 100% - %cumulative retained
The values were plotted on a graph with cumulative percentage passing on the
y-axis and the logarithmic sieve size on the x axis (the semi-log graphic sheet).
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CHAPTER FOUR
4.1 Results and Interpretation
4.2 Field observations
The lithostratigraphic descriptions of the six outcrop sections studied are
presented in figures below. The lithofacies in most consists of repeated cyclic
deposition of fine sand, medium sand and pebbly sand. The fine sands are not
characterized by any form current ripples and parallel laminations or other
features associated with sand medium in the area.
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Table 4.1: Location 1 section 1
Three different facies (A-C) have been identified in the above chart. Also from
the stratigraphic sequence it can be seen that there is a sequence of repetition
(memory) of facie A and B until 1.6m were C come in and then at 2.0m the
memory sequence is continued.
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Table 4.2 Location1 section 2
Here, only two facies are identified and only little can be deduced form this
outcrop model.
Table 4.3 Location1 section3
Two different facies have been identified in the above chart. it can also be seen
that there is a sequence repetition of facies A.
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Table 4.4 Location3 section1
Table 4.5 Location3 section2
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Table 4.6 Location3 section3
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4.2.1 Facie association
Facie type A [para-conglomeratc bed]
is a matrix-supported rock that contains more than 15% of sand and restly
pebbles (para-conglomerates). This facie has colour ranging from white to light
brownish clast. This is the most prominent facie occurrences; it is a massive bed
with evidence of bioturbation. The poorly sorted pebbles (randomly packed
clast of different sizes) and sandstone showing that the pebbles and sandstone
were deposited by a highly flowing channel giving no time for the sediments to
properly settle in therefore indicative of a fluvial environment of deposition.
The members of this bed includes; L1S1U1, L1S1U3, L1S3U1, L1S3U3,
L3S1U2, L3S2U3. Represented as A in the lithologs above
Figure 7 Facie type A [para-conglomeratc bed]
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Facies type B massive sandstone
This facies is a massive brown medium to coarse grained sand. There are little
occurrences of fringinised sand in this facies sections as a result of the iron-III-
oxide content of the sand
Figure 8: Facies type B massive brown sandstone
Facies type c [massive sandstone]
This is a massive reddish brown sandstone facies. This is a fine sand bed with
no evidence of bioturbation. The members of this facies include; L1S1U2,
L1S3U2, L3S1U5, L3S3U2. This facie is indicated as B in the lithology.
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Figure 9: Facies type c [massive sandstone]
Facie type D [ ortho-conglomeratic beds]
It is a clast (pebble)-supported sedimentary bed with sand as matrix with 15%
or less in any mass of the bed. This is a massive brown colour bed with no
evidence of bioturbation or imbrication. The deficiency of the matrix was
probably caused by a fast flowing channel not giving in for the settlement of
debris of very less density. There is only a single occurrence of this facies in the
bed unit L3S3U1. This bed has an approximate thickness of about 2.5m
occurring from the 0m ground point. Represented as D in the litholog
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Figure 10: Facie type D [ ortho-conglomeratic beds]
Facies type E [massive intercalation of breccia debris]
This is a dark brown massive intercalation of breccia debris, pebble and fine
sand matrix with bioturbation. This bed has a thickness of approximately a
meter thick. The bed unit L1S2U2 falls into this type. The dark colour is as a
result of bio activities. Represented as E in the litholog
Figure 11: Facies type E [massive intercalation of breccia debris]
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4.3 Sieve Analysis Results
The sieve analysis for a select number of the sample recovered in the field was
carried out in other to assess the particle size distribution across each bed unit.
The picking of this sample was made base on the sections logged in the field.
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Table 4.7 Sample 1: Location 1, Section 1, Unit 1
W1 106.9g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 22.7 21.23 21.23 78.77
0 1 25.8 24.13 45.37 54.63
1 0.5 29.8 27.88 73.25 26.75
2 0.25 15.9 14.87 88.12 11.88
3 0.125 8.6 8.04 96.16 3.84
4 0.063 3.4 3.18 99.35 0.65
PAN pan 0.2 0.19 99.53 0.47
106.4
Table 4.8 Sample: Location 1, Section 1, Unit 2
W1 74.8g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 5.4 7.22 7.22 92.78
0 1 11.7 15.64 22.86 77.14
1 0.5 27.6 36.90 59.76 40.24
2 0.25 17.6 23.53 83.29 16.71
30.125 7.5 10.03 93.32 6.68
4 0.063 2.9 3.88 97.19 2.81
PAN pan 1.7 2.27 99.47 0.53
74.4
Table 4.9 Sample: Location 1, Section 1, Unit 3
W1 66.7g
grain size in
phi sieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 16.4 24.59 24.59 75.41
0 1 13.4 20.09 44.68 55.32
1 0.5 16.4 24.59 69.27 30.73
2 0.25 13.7 20.54 89.81 10.19
3 0.125 4.3 6.45 96.25 3.75
4 0.063 1.7 2.55 98.80 1.20
PAN pan 0.6 0.90 99.70 0.30
66.5
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Chart 1
1.00
10.00
100.00
-1 0 1 2 3 4 PAN
cumulative%retained
Grain size in phi
L1S1U1
L1S1U2
L1S1U3
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Table 4.10 Location 1, Section 1, Unit 4
W1 97.8g
grain size inphi sieve size wt. retained %retainedcumulative%retained
-1 2 16.5 16.871 16.871 83.129
0 1 20 20.450 37.321 62.679
1 0.5 22.2 22.699 60.020 39.980
2 0.25 17.3 17.689 77.710 22.290
3 0.125 13.2 13.497 91.207 8.793
4 0.063 4.8 4.908 96.115 3.885
PAN pan 3.6 3.681 99.796 0.204
97.6
Table 4.11 Location 1, Section 1, Unit 5
W1 89.5g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 24.3 27.15 27.15 72.85
0 1 29.9 33.41 60.56 39.44
1 0.5 19.6 21.90 82.46 17.542 0.25 8.6 9.61 92.07 7.93
3 0.125 3.7 4.13 96.20 3.80
4 0.063 1.7 1.90 98.10 1.90
PAN pan 1.3 1.45 99.55 0.45
89.1
Table 4.12 Location 1, Section 1, Unit 6
W1 97.6g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 24.9 25.512 25.512 74.488
0 1 20.1 20.594 46.107 53.893
1 0.5 26.5 27.152 73.258 26.742
2 0.25 17.1 17.520 90.779 9.221
3 0.125 5.5 5.635 96.414 3.586
4 0.063 2.8 2.869 99.283 0.717
PANpan 0.4 0.410 99.693 0.307
97.3
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Chart 2
1.000
10.000
100.000
-1 0 1 2 3 4 PAN
cumulative%retained
grain size in phi
L1S1U4
L1S1U5
LIS1U6
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Table 4.13 Location 2, Section 1, Unit 1
W1 114.9g
grain size inphi
sieve size wt. retained %retained cumulative%retained
cumulative%passing
-1 2 45 39.164 39.164 60.836
0 1 24.4 21.236 60.400 39.600
1 0.5 17.4 15.144 75.544 24.456
2 0.25 15.3 13.316 88.860 11.140
3 0.125 7.6 6.614 95.474 4.526
4 0.063 4.6 4.003 99.478 0.522
PAN pan 0.6 0.522 100.000 0.000
114.9
Table 4.14 Location 2, Section 1, Unit 2
W1 92.6g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 12.6 13.607 13.607 86.393
0 1 19.7 21.274 34.881 65.119
1 0.5 23.4 25.270 60.151 39.849
2 0.25 20.7 22.354 82.505 17.495
3 0.125 9.5 10.259 92.765 7.2354 0.063 4.3 4.644 97.408 2.592
PAN pan 1.9 2.052 99.460 0.540
92.1
Table 4.15 Location 2, Section 1, Unit 3
W1 65.8g
grain size in
phi
sieve size wt. retained %retainedcumulative
%retained
cumulative
%passing
-1 2 22.3 33.89 33.89 66.11
0 1 15.1 22.95 56.84 43.16
1 0.5 12.9 19.60 76.44 23.56
2 0.25 9.1 13.83 90.27 9.73
3 0.125 4.3 6.53 96.81 3.19
4 0.063 1.7 2.58 99.39 0.61
PAN pan 0.2 0.30 99.70 0.30
65.6
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Chart 3
1.000
10.000
100.000
-1 0 1 2 3 4 PAN
cumulatitive%retained
grain size in phi
L2S1U1
L2S1U2
L2S1U3
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Table 4.16 Location 2, Section 2, Unit 1
W1 160.7g
grain size inphi
sieve size wt. retained %retained cumulative%retained
cumulative%passing
-1 2 73.1 45.49 45.49 54.51
0 1 32.8 20.41 65.90 34.10
1 0.5 28.4 17.67 83.57 16.43
2 0.25 15.2 9.46 93.03 6.97
3 0.125 6.8 4.23 97.26 2.74
4 0.063 3.3 2.05 99.32 0.68
PAN pan 0.3 0.19 99.50 0.50
159.9
Table 4.17 Location 2, Section 2, Unit 2
W1 168.6g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 39.4 23.37 23.37 76.63
0 1 41.4 24.56 47.92 52.08
1 0.5 42.9 25.44 73.37 26.63
2 0.25 29.7 17.62 90.98 9.02
3 0.125 12.3 7.30 98.28 1.72
4 0.063 2.4 1.42 99.70 0.30
PAN pan 0.3 0.18 99.88 0.12
168.4
Table 4.18 Location 2, Section 2, Unit 3
W1 92.4g
grain size inphi
sieve size wt. retained %retained cumulative%retained
cumulative%passing
-1 2 18.6 20.13 20.13 79.87
0 1 20.4 22.08 42.21 57.79
1 0.5 24.4 26.41 68.61 31.39
2 0.25 13.5 14.61 83.23 16.77
3 0.125 9.7 10.50 93.72 6.28
4 0.063 2.3 2.49 96.21 3.79
PAN pan 1 1.08 97.29 2.71
89.9
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Chart 4
1.00
10.00
100.00
-1 0 1 2 3 4 PAN
cumulative%retained
grain size in phi
L2S2U1
L2S2U2
L2S2U3
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Table 4.19 Location 2, Section 3, Unit 1
W1 165.4g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 65.5 39.60 39.60 60.40
0 1 42.8 25.88 65.48 34.52
1 0.5 29.5 17.84 83.31 16.69
2 0.25 16.4 9.92 93.23 6.77
3 0.125 6.3 3.81 97.04 2.96
4 0.063 4 2.42 99.46 0.54
PAN pan 0.2 0.12 99.58 0.42
164.7
Table 4.20 Location 2, Section 3, Unit 2
W1 92.9g
grain size in
phisieve size wt. retained %retained
cumulative
%retained
cumulative
%passing
-1 2 16.5 17.76 17.76 82.24
0 1 20 21.53 39.29 60.71
1 0.5 22.2 23.90 63.19 36.81
2 0.25 17.3 18.62 81.81 18.19
3 0.125 6.5 7.00 88.81 11.19
4 0.063 4.8 5.17 93.97 6.03
PAN pan 3.4 3.66 97.63 2.37
90.7
Table 4.21 Location 2, Section 3, Unit 3
W1 70.0g
grain size in
phi sieve size wt. retained %retainedcumulative
%retained
cumulative
%passing
-1 2 16 22.86 22.86 77.14
0 1 14.7 21.00 43.86 56.14
1 0.5 14.8 21.14 65.00 35.00
2 0.25 13.9 19.86 84.86 15.14
3 0.125 5.9 8.43 93.29 6.71
4 0.063 3.6 5.14 98.43 1.57
PAN pan 1 1.43 99.86 0.14
69.9
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Chart 5
1.00
10.00
100.00
-1 0 1 2 3 4 PAN
cum
ulative%retained
grain size in phi
L2S3U1
L2S3U2
L2S3U3
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Table 4.22 summaries of various percentile values of the analysed samples.
UNITS 5 16 25 50 75 80 84 95
L1S1U1 0.00 0.00 -1.70 0.20 1.10 1.45 1.74 2.74
L1S1U2 0.00 -0.20 -1.75 0.30 1.50 1.27 2.00 3.00
L1S1U3 0.00 0.00 -1.63 0.28 1.25 1.10 1.74 2.75
L1SS1U4 0.00 0.00 -1.40 0.65 1.90 2.40 2.90 4.40
L1S1U5 0.00 0.00 0.00 -1.50 -0.70 0.90 1.25 2.68
L1s1u6 0.00 0.00 0.00 -0.30 -0.65 0.83 1.30 2.49
L2S1U1 0.00 0.00 0.00 -1.60 1.00 1.43 1.76 2.20
L2S1U2 0.00 -1.13 -1.68 0.70 1.75 1.90 2.20 3.30
L2S1U3 0.00 0.00 0.00 -0.40 0.60 0.80 1.00 3.70
L2S2U1 0.00 -1.20 -1.60 0.40 1.13 1.35 1.60 2.25
L2S2U2 0.00 0.00 -1.10 0.15 1.15 1.40 1.65 2.59
L2S2U3 0.00 0.00 -1.25 0.36 1.45 1.80 2.20 3.25
L2S3U1 0.00 0.00 0.00 -1.48 0.51 0.80 1.20 2.20
L2S3U2 0.00 0.00 -1.40 0.50 1.65 1.90 2.30 4.00
L2S3U3 0.00 0.00 -1.10 0.10 1.13 1.40 1.70 2.55
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Table 4.23 description of the various sieve analysis parameters
UNITS MEAN KURTOSIS SKEWNESS SORTING
standard
deviation REMARKS
L1S1U1 -0.08 0.40 0.81 0.87 0.85
poorly sorted, very
positively skewed,
Very platy kurtic, very
coarse sand
L1S1U2 -0.16 0.38 0.75 1.00 0.95
Very Poorly sorted, very
positively skewed,
Very platy kurtic, very
coarse sand
L1S1U3 -0.18 0.39 0.74 0.87 0.85 Poorly sorted, very
positively skewed,
Very platy kurtic, very
coarse sand
L1SS1U4 0.33 0.55 0.63 1.45 1.39
Very poorly sorted, very
positively skewed,
Very platy kurtic, coarse
sand
L1S1U5 0.30 -1.57 2.76 0.63 0.72
Moderately well sorted,
very positively skewed,
Very platy kurtic, coarse
sand
L1s1u6 0.28 -1.57 1.35 0.65 0.70
Moderately well sorted,
positively skewed,
Very platy kurtic, coarse
sand
L2S1U1 0.48 0.90 2.64 0.88 0.77
poorly sorted, very
positively skewed,
platy kurtic, coarse sand
L2S1U2 0.07 0.39 0.24 1.67 1.33 Very Poorly sorted,
positively skewed,
Very platy kurtic, coarse
sand
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L2S1U3 0.27 2.53 1.51 0.50 0.81
Moderately well sorted,
very positively skewed,
Very lepto kurtic, coarse
sand
L2S2U1 -0.08 0.34 0.25 1.40 1.04
Very Poorly sorted,
positively skewed,
Very platy kurtic, very
coarse sand
L2S2U2 0.10 0.47 0.85 0.83 0.80
Poorly sorted, positively
skewed,
Very platy kurtic, coarse
sand
L2S2U3 0.18 0.49 0.73 1.10 1.04
Very Poorly sorted, very
positively skewed,
Very platy kurtic, coarse
sand
L2S3U1 0.27 1.77 2.91 0.60 0.63
Moderately well sorted,
very positively skewed,
Very lepto kurtic, coarsesand
L2S3U2 0.17 0.54 0.66 1.15 1.18
Very Poorly sorted, very
positively skewed,
Very platy kurtic, coarse
sand
L2S3U3 0.10 0.47 0.90 0.85 0.81 Poorly sorted sorted,
very positively skewed,
Very platy kurtic, coarsesand
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4.3.1 The bivariate plots of the sieve analysis parameters
Chart 6:bivariate plot of skewness vs. Standard deviation
After Friedman, (1961)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
SKEWNESS
STANDARD DEVIATION
BEACH
RIVER
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Chart 7 bivariate plot of mean vs. Standard deviation
Chart 8:bivariate plot of skewness vs. simple sorting after friedman, (1979)
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
MEAN
STANDARD DEVIATION
RIVER
BEACH
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80
SKEWNESS
SORTING
RIVER
BEACH
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4.3.2 Sieve analysis interpretation
The cumulative graph which is self-explanatory has pictorially shown using the
cumulative curves the grain size proportions. When trending along the
horizontal axis from Phi -1 to 2.0, the curve tend to have a very steep upward
Shows the high content of coarse to medium grained particles. But moving from
2.0 up to pan the curve slope becomes gentle indicating reduction in fine
particle contents.
The sieve analysis data for all sample has indicated that modal particle size
occurrence is the particle size of -1 having an average percentage retained
value of 25.9% which is the gravel sized particle followed by the 1coarse
grained particles of average percentage retained 21.56% while others are
0(21.56), 2(16.70), 3(7.74), 4(3.38) pan(1.21).
In the bivariate plot, most of the samples are located within the river sediment
zone( the upper right sections of the thre plots.
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4.4 Pebble morphometric results and interpretation
4.4.1 Results
The pebble morphometric also was carried out on a set of sample collected from
the initially mentioned lithology sections. The samples which include ten
pebbles used for the morphometric analysis were collected from pebble
containing units.
Table 4.24 Sample 17: Location 1, Section 1, Unit 1
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 4.0 2.6 1.8 0.450 0.650 0.636 0.825 3.030
2 3.4 2.2 1.8 0.529 0.647 0.750 0.920 4.722
3 3.3 1.8 0.9 0.273 0.545 0.625 0.497 4.583
4 3.1 1.7 0.9 0.290 0.548 0.636 0.517 4.697
5 2.5 2.0 1.2 0.480 0.800 0.385 0.702 -2.404
6 3.6 1.7 1.4 0.389 0.472 0.864 0.765 9.351
7 2.5 1.8 1.5 0.600 0.720 0.700 0.909 3.333
8 2.3 1.9 1.5 0.652 0.826 0.500 0.917 0.000
9 2.0 2.1 1.5 0.750 1.050 -0.200 0.930 -9.333
10 2.3 1.4 1.0 0.435 0.609 0.692 0.677 4.423
Table 4.25 Sample 18: Location 1, Section 1, Unit 2
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 3.3 1.9 1.2 0.364 0.576 0.667 0.651 4.583
2 3.8 2.7 1.8 0.474 0.711 0.550 0.828 1.056
3 3.9 2.9 1.2 0.308 0.744 0.370 0.535 -4.213
4 3.0 2.2 1.2 0.400 0.733 0.444 0.640 -1.389
5 2.3 1.7 1.2 0.522 0.739 0.545 0.762 0.871
6 3.8 2.8 1.8 0.474 0.737 0.500 0.818 0.000
7 2.6 2.4 1.5 0.577 0.923 0.182 0.815 -5.515
8 2.7 2.2 1.4 0.519 0.815 0.385 0.773 -2.225
9 2.3 1.6 0.7 0.304 0.696 0.438 0.453 -2.054
10 1.8 1.4 1.0 0.556 0.7780.500
0.735 0.000
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Table 4.26 Sample 19: Location 1, Section 1, Unit 3
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 3.3 1.9 1.2 0.364 0.576 0.667 0.651 4.583
2 3.7 2.7 1.8 0.486 0.730 0.526 0.836 0.541
3 3.9 2.9 1.2 0.308 0.744 0.370 0.535 -4.213
4 3.0 2.2 1.2 0.400 0.733 0.444 0.640 -1.389
5 2.3 1.7 1.2 0.522 0.739 0.545 0.762 0.871
6 3.8 2.8 1.8 0.474 0.737 0.500 0.818 0.000
7 2.6 2.4 1.5 0.577 0.923 0.182 0.815 -5.515
8 2.7 2.2 1.4 0.519 0.8150.385
0.773 -2.225
9 2.3 1.6 0.7 0.304 0.696 0.438 0.453 -2.054
10 1.9 1.4 1.0 0.526 0.737 0.556 0.722 1.056
Table 4.27 Sample 20: Location 1, Section 2, Unit 1
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 4.1 2.5 1.9 0.463 0.610 0.727 0.875 4.904
2 6.5 3.7 2.8 0.431 0.5690.757
0.970 5.960
3 5.3 2.7 1.6 0.302 0.5090.703
0.659 6.715
4 4.5 2.6 1.9 0.422 0.5780.731
0.837 5.466
5 3.1 2.5 2.0 0.645 0.8060.545
1.011 0.705
6 3.6 2.7 1.5 0.417 0.7500.429
0.703 -1.714
7 3.1 2.0 1.4 0.452 0.6450.647
0.762 3.256
8 2.6 2.1 1.6 0.615 0.8080.500
0.909 0.000
9 2.5 1.8 1.3 0.520 0.7200.583
0.787 1.603
10 2.1 1.7 1.3 0.619 0.8100.500
0.851 0.000
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Table 4.28 Sample 21: Location 1, Section 3, Unit 1
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 6.4 3.7 3.3 0.516 0.578 0.871 1.149 7.195
2 8.3 4.7 3.3 0.398 0.5660.720
0.973 5.533
3 4.0 2.7 2.5 0.625 0.675 0.867 1.131 5.867
4 4.7 3.7 3.0 0.638 0.787 0.588 1.158 1.382
5 4.2 2.0 1.7 0.405 0.476 0.880 0.836 9.388
6 5.2 4.4 2.5 0.481 0.846 0.296 0.881 -4.237
7 5.8 4.3 2.5 0.431 0.741 0.455 0.856 -1.055
8 4.1 2.7 1.6 0.390 0.659 0.560 0.718 1.538
9 5.7 2.9 2.0 0.351 0.509 0.757 0.785 7.318
10 5.3 3.5 2.5 0.472 0.660 0.643 0.944 3.029
Table 4.29 Sample 22: Location3, Section 3, Unit 1
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 3.0 2.4 1.8 0.600 0.800 0.500 0.932 0.000
2 4.5 2.8 2.6 0.578 0.622 0.895 1.117 6.829
3 3.3 1.4 1.5 0.455 0.424 0.778 0.538 6.105
4 3.9 2.0 1.4 0.359 0.513 0.737 0.706 7.242
5 2.5 2.0 1.4 0.560 0.800 0.455 0.8I9 -1.266
6 4.1 2.9 2.0 0.488 0.707 0.571 0.876 1.464
7 3.3 2.3 1.5 0.455 0.697 0.556 0.763 1.222
8 2.7 2.0 1.9 0.704 0.741 0.875 1.083 5.327
9 3.8 1.5 0.9 0.237 0.395 0.793 0.504 12.367
10 4.5 2.0 1.8 0.400 0.444 0.926 0.865 10.648
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Table 4.30 Sample 23: Location 3, Section 1, Unit 1
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 5.6 3.7 3.1 0.554 0.661 0.760 1.129 4.697
2 3.2 2.3 1.9 0.594 0.719 0.692 0.977 3.239
3 3.4 2.8 2.0 0.588 0.824 0.429 0.944 -1.214
4 3.8 2.5 1.7 0.447 0.658 0.619 0.803 2.661
5 3.2 2.8 2.0 0.625 0.875 0.333 0.963 -2.667
6 5.2 3.9 2.5 0.481 0.750 0.481 0.917 -0.385
7 5.2 3.1 2.0 0.385 0.596 0.656 0.792 4.063
8 3.9 2.9 2.4 0.615 0.744 0.667 1.069 2.708
9 3.5 2.9 1.6 0.457 0.829 0.316 0.739 -4.030
10 3.2 1.8 11.0 3.438 0.563 -0.179 6.136 -1.977
Table 4.31 Sample 24: Location 3, Section 1, Unit 2
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 8.6 5.1 4.1 0.477 0.5930.778
1.163 5.827
2 5.8 4.1 3.1 0.534 0.7070.630
1.078 2.425
3 4.6 3.1 2.2 0.478 0.6740.625
0.907 2.614
4 4.0 2.9 2.4 0.600 0.7250.688
1.060 3.125
5 4.7 2.8 2.3 0.489 0.5960.792
0.974 5.960
6 5.4 4.1 2.9 0.537 0.7590.520
1.033 0.372
7 7.0 4.3 3.4 0.486 0.6140.750
1.093 5.147
8 4.3 2.8 1.8 0.419 0.6510.600
0.785 2.389
9 4.4 3.3 2.7 0.614 0.7500.647
1.107 2.397
10 4.6 2.9 2.3 0.500 0.6300.739
0.970 4.783
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Table 4.32 Sample 25: Location 3, Section 2, Unit 3
s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)
1 3.9 2.9 1.5 0.385 0.7440.417
0.668 -2.167
2 3.5 1.9 1.3 0.371 0.5430.727
0.691 6.119
3 2.4 1.8 1.2 0.500 0.7500.500
0.737 0.000
4 3.5 2.3 2.0 0.571 0.6570.800
0.998 5.250
5 2.5 1.4 1.1 0.440 0.5600.786
0.724 6.494
6 2.5 1.8 1.3 0.520 0.7200.583
0.787 1.603
7 3.0 2.2 1.4 0.467 0.7330.500
0.746 0.000
8 2.7 1.8 1.6 0.593 0.6670.818
0.945 5.369
9 2.1 1.4 1.2 0.571 0.6670.778
0.838 4.861
10 2.6 1.5 1.0 0.385 0.5770.688
0.635 4.875
4.4.2 Pebble Morphometry Interpretation
In pebble morphometric interpretation, the dominant forms of the sample were
obtained from the available data. The mean value of 10 pebbles was taken from
the result obtained.
According to Hubert (1968), the elongation ratio values for fluvial
environments range from 0.6 to 0.9. most values gotten from the morphometric
data for ratio of elongation falls within this range. The maximum projection
sphericity of pebbles ( ) is generally high for fluvial environment than forbeaches.
From the result, the maximum value for the projection sphericity falls above
0.65 which indicates fluvial activity. In terms of geometric which describe the
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three dimensional aspects of a pebble proposed by folk,(1974) , which include
compact, compact bladed, compact elongated, compact platy, bladed elongated,
platy, very platy, very bladed and very elongated.
Since dominant forms for river pebbles are compact, bladed, compact bladed
and compact elongated, it can be deduced from the above data results that the
pebbles are of fluvial environmental deposits.
Table 4.33 total mean values for all pebbles.
Parameters mean count
Oblate-Prolate Index (OPI) 2.14
Maximum projection sphericity index (MPS) 1.04
Disc-Rod Index (DRI) 0.59
Flatness ratio 0.69
Elongation ratio 0.52
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4.4.3 Bivariate plots.
SCATTER PLOT OF MPSI VS OPI
Chart 9: scatter plot of maximum projection sphericity index versus oblate
index (dobkins and folk 1970)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
-15 -10 -5 0 5 10 15
RIVERRIVER
BEACH BEACH
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Chart 10 sneed and folk form diagram
Table 4.34 sphericity form diagram counts all pebbles.
Sneed & Folk classes
Count Percent
Compact 7 7.78
Compact-Platy 3 3.33
Compact-Bladed 18 20.00
Compact-Elongate 13 14.44
Platy 1 1.11
Bladed 26 28.89
Elongate 19 21.11
Very-Platy 0 0.00
Very-Bladed 2 2.22
Very-Elongate 1 1.11
SLI
00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.90.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1.0BLOCK
RODSLAB
C
VP VE
P B E
CBCP CE
VB
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4.5 Discussion
The area under study is a sedimentary terrain. While sedimentary environment
are parts of the earth surface physically, chemically and biologically distinct
from its adjacent areas. This work has emphasised thoroughly that a lot of
processes come into play in the sedimentary environment. The depositional
process is a product of the environment, which in turn is controlled by: Climate
Geography Tectonic setting Sediment supply. Although earlier works have
already modelled these processes categorizing them into three basically distinct
processes; physical chemical and biological.
Sedimentary grains are formed when the rocks at the Earth's surface are slowly
broken up physically by exposure to wind and frost, and decomposed
(chemically) by rainwater or biological action. These processes are collectively
termed weathering. Once a rock has been broken up by weathering, the small
rock fragments and individual mineral grains can be eroded from their place of
origin by water, wind or glaciers and transported to be deposited elsewhere as
roughly horizontal layers of sediment.
The resulting sediment reflects the original rock types that were weathered, the
efficiency of erosion and transport, the extents of chemical and physical
degradation of the sediment grains during transport, and the conditions under
which the grains were deposited from the transporting water, wind or ice. For
example, sand-sized grains of quartz are one of the main constituents of
sandstone, but those grains may have been transported by water in a river,
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carried by waves on a sea-shore, or blown around in hot desert sandstorms (to
give just three possibilities).
In this study work, we distinguish which of the many possibilities was the most
likely to have perpetuated the sedimentary deposit at Use Ikot Amama and the
Agali sandstone of the Benin formation not the less.
Some of the identified beds boosted intercalation of both fine and coarse
grained sandstone indicating either a deltaic or sudden change in the channel
velocity allowing for fine grained sediments to settle.
As earlier noted in the study that the coarse poorly sorted grains indicated a
fluvial environment and also that the particle are channel bed load, the presence
of the high occurrence of the pebbles in the study area conclude the fact that is a
fluvial environment. The observable paraconglomerates and the
orthoconglomerated in the field give the idea of the channel velocity. The
paraconglomerates with indicates high matrix shows a low stream velocity
allowing for the settlement of matrix.
The primary purpose of this study is to understand the facie characterisation of
various outcrop sections at Use Ikot Amama. This means, that the study
described each bed characteristics in terms of texture, geometry, grain to matrix
ratio, and lithological resemblance and repetition so as to track back to the
environment of deposition, the conditions under which the grains were
deposited from the transporting water.
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The field observation shows that the bed consists of fine grain sand, coarse
grain sand, paraconglomerats, orthoconlomerates, breccia and the lithological
sections shows some repetitive geological patterns.
The laboratory analysis revealed more in the characterisation most precisely the
pebble mophometry describing the pebble shape using the elongation ratio, the
oblate prolate index. The mean values of Flatness ratio for the pebbles is 0.69,
Elongation ratio is 0.52, M.P.S.I. is 1.04(river), Oblate Prolate index is
2.14(river). The bivariate plot of M.P.S.I. vs OP Index (Dobkins and Folk,
1970) is based on the proposition that the 0.66 sphericity (M.P.S.I) line best
separate beach and river pebbles while values less than 0.66 are typical of
beachs, higher values above 0.66 suggest fluvial origin. An OP index value
greater than -1.5 generally indicates fluvial conditions. The bivariate plot of
Roundness vs. Elongation ratio (after Same, 1966) show that roundness has the
greatest influence in determination of the depositional environment of the
pebbles i.e the lower the roundness, the higher the probability that the
depositional environment would be fluvial(Olugbemiro and Nwajide, 1997). It
is important to note that roundness alone is not particularly indicative of
depositional environment, rather the extent of abrasion that the grains or pebbles
have undergone, it reflect overall transport history(Lewis and McConchie,
1994) and does not necessarily reflect the distance grains have travelled from
their source. Sphericity is more reliable than roundness because it illustrates the
departure of the body from equidimensionality.
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OP index expresses the relationship of the change in form of pebbles ( platy,
elongate and compact) with environment. The plot of M.P.S.I vs OP index is
more diagnostic for environmental discrimination of pebbles than the plot of
same, 1966 (Roundness vs Elongation ratio). Moreover, with prolong transport,
sphericity and op index become increasingly divergent for fluvial and beaches
and thus provide better discrimination (Dobkins and Folk, 1970). The bivariate
plot of Coefficient of Flatness vs M.P.S.I. show that over 97% of the pebbles
are of fluvial origin.
According to Dobkins and Folk (1970) and Gale (1990), certain form classes
occur much more frequently in one environment than they do in another. Thus,
the three shape classes that are most diagnostic of beach action are platy, very
platy and very bladed. While bladed and platy predominate in high energy
beaches, bladed are most common on low energy beaches. On the other hand,
compact, compact bladed, and compact elongate are most indicative of fluvial
action. While beach pebbles plot toward the left and bottom parts of the
sphericity form diagram, fluvial pebbles plot near the upper part. The sphericity
form diagram of the pebbles sets from Sandstone also point to fluvial origin
(7.6% are compact, 14.4% compact elongate, 20.0% compact bladed, 21.11%
are elongate and 28.89% are bladed).
As for grain size distribution, the mean grain size in a deposit is largely a
function of energy of the processes controlling transport and deposition i.e
particles are segregated according to their hydrodynamic behaviour, which
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depends on size, specific gravity and shape. In contrast, the degree of sorting
grains in a deposit is a function of the persistence and stability of energy
condition except where constrained by availability of grains that can be
deposited in the environment (Olugbemiro and Nwajide, 1997).
From the sieve analysis various parameters were calculated with include the
mean, median, degree of sorting, skewness and kurtosis. Most of the sample
gave a result revealed poor sorted when correlated to the deduced observation
from the field it scores a pass mark. The approach used the size and shape of the
grains in the sediment or sedimentary rock sample acquired to reveal quite a lot
about the origin of the sediment.
Because a vigorous river transports much larger grains than a gentle current in a
lake, so the modal size of the grains which is the 1 grain size gives an
indication that strong currents could have transported and deposited the grains.
In other words, the grain size depends on the energy of the environment in
which the sediment was deposited. The general shape of the grains will tell you
about the nature of the transporting medium.
The degree of sorting in sediment is another useful method that was used in
distinguishing the different types of depositional situation. Sorting is a measure
of the range of grain sizes present in a sediment or sedimentary rock. Poorly-
sorted sediment as in the case of the studied sediments has a wide range of grain
sizes as a result of rapid deposition, such as occurs during a storm. On the other
hand, well-sorted sediment has a narrow range of grain sizes, and is the result of
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extensive reworking of sediment by wind action in deserts, or wave action on
beaches and in shallow shelf seas.
Also, the coarse grained particles show that the sediments were of bed load i.e.
they were carried along the channel beds.
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CHAPTER FIVE
5.1 summary and conclusions
Detailed sedimentological and lithofacies analyses show that the sediments
deposited at the study area Use Ikot Amama were likely deposited by two
sedimentary environment, the fluvial and the deltaic. A typical sequence begins
with accumulation of coarse fluvial channel and/or tidally influenced fluvial
channel deposits. The study of the pebble morphometry and grain size
distribution has shown that Sandstone is likely a product of fluvial deposition
though certain sieve analysis suggest near marine condition. This is in line with
the earlier conclusions of fluvial or fluvial deltaic.
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5.3 recommendations
The outcrop logging that was done is the field was able to provide a vague
model as a result of the analogue tools and methods. Further work should be
carried out using modern tool precisely the laser scanners and digital remote
photographic tools to get a clearer, more detail and information from any
lithology model.
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APPENDIX A
Abbreviations and symbols
B= bladedC= compact
CB= compact bladed
CE= compact elongated
CP= compact platy
E= elongated
L= location
S= section
U= unit
VB= very bladed
VE= very elongated
VP= very platy
MPS = Maximum projection sphericity index
DRI= Disc-Rod Index
OPI = Oblate-Prolate Index
IE = Elongation index = weight of aggregate in the sieve = total weight of aggregateL= long
I= intermediate
S= short
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APPENDIX B
Formula
Elongation ratio=
,
Flatness ratio =
Maximum projection sphericity index (MPS) = Disc-Rod Index (DRI) =
Oblate-Prolate Index (OPI) = []
Graphic mean =
Median = 50
Graphic standard deviation (1) = + Inclusive graphic skewness (SKI) =
+
Graphic kurtosis (KG) =
Degree of sorting =
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APPENDIX C
Verbal limits folk (1974)
SORTING INTERPRETATION
4.00
SKEWNESS INTERPRETAION
-1.0 Very Negatively skewed
-0.3 - (-0.1) Negatively skewed
-0.1 - 0.1 Symmetrical
0.1 - 0.3 Positively skewed
0.3-1.0 Very positively skewed
KURTOSIS INTERPRETAION
3.00 Extremely lepto kurtic
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MEAN INTERPRETAION
-1.00-0.00 Very coarse sand
0.00-1.00 Coarse sand
1.00-2.00 Medium sand
2.00-3.00 Fine sand
3.00-4.00 Very fine sand
4.00-5.00 Coarse silt
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APPENDIX D
Sand sorting classification based on standard deviation
Standard deviation sorting environment
4.00 Extremely poorly sorted Mainly geofluvial
settings
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Appendix E
The Sneed & Folk (1958) diagram