CHAPTER ONE
INTRODUCTION
1.1 LOCATION AND ACCESSIBILITY OF THE AREA.
The area mapped is situated in Dengi and Bashar in Kanan and WaseLocal Government Area of Plateau
state and forms part of federal survey of Nigeria Bashar sheet 192 (1:100,000). The area covers
approximately 800km². Accessibility is difficult as there are no major roads in the area. Minor roads are
the Dengi – Jarmai, Jarmai – Bashar. The main settlements in the area are Jarmai, Bashar, Gudus, Gama
and Yuli. The area has a network of footpaths and river channels which are seasonal. The study area is
within N 9˚022'06.7" to N 9°019'53.3" and E 10°05'53.3" E 10°07'18.5"
FIQURE 1.1 Map showing Dengi and its environs.
1.2 TOPOGRAPHY/ RELIEF
The area is more or less flat in terms of its relief with some few gentle slops and hills, since the area
forms part of the upper Benue trough which is a basin with depositional process taking place make the
area flat or leveled. The area have an altitude within 300m to 400m with streams and river channels.
1.3 VEGETATION
The vegetation here is prominently made up of sparsely distributed trees, herbs, shrubs, and grasses. The
tress helps control the activities of erosion. The area like any other parts of northern Nigeria is
characterized by two distinct (dry and rainy) seasons. The area lies within the Sudan savanna vegetation,
which is characterized by grasses, thorny bushes, and open forest.
1.4 DRIANAGE PATTERN
The drainage pattern in the study area is mainly dendritic, the rivers takes their source from the high
elevated portion of the area and spread out in all directions. Most of the rivers dry up during the dry
season. The drainage pattern is influence by the structural pattern in the study area.
1.5 LAND USE
The lands are mainly use for farming activities and the major crops produced are cassava and maize
others include rice, millet, groundnut etc. The land is used mainly for farming, ranching of cattle and
hunting.
CHAPTER TWO
GENERAL GEOLOGY
2.1 GEOLOGY OF THE UPPER BENUE TROUGH
The Upper Benue Trough is made up of two arms, the Gongola Arm and the Yola Arm (although some
authors have sub-divided the Upper Benue Trough to include a third central Lau-Gombe sub-basin, e.g.
Akande et al., 1998).
In both arms of the basin, the Albian Bima Sandstone lies unconformably on the Precambian Basement.
This formation was deposited under continental conditions (fluvial, deltaic, lacustrine) and is made up of
coarse to medium grained sandstones, intercalated with carbonaceous clays, shale, and mudstones. The
Bima Sandstone was subdivided by Carter et al. (1963) into a Lower, Middle and Upper Bima.
The Yolde Formation lies conformably on the Bima Sandstone. This formation of Cenomanian age
represents the beginning of marine incursion into this part of the Benue Trough. The Yolde Formation
was deposited under a transitional/coastal marine environment and is made up of sandstone limestone,
shale, clays and mudstones. In the Gongola Arm, the laterally equivalents Gongila and Pindiga
Formations and the possibly younger Fika Shale lie conformably on the Yolde Formation. These
formations represent full marine incursion into the Upper Benue during the Turonian – Santonian times.
Lithologically, these formations are characterized by the gray to dark/blue carbonaceous shale and
limestone, intercalating with pale coloured limestone, shale and minor sandstones. The Gombe formation
lies on the Pindiga formation while the Keri Keri formation which is the youngest lies on the Gombe
formation. (nuhu George et el)
2.1 THE GEOLOGY OF THE AREA MAPPED
The area mapped comprises of a transitional basement environment to a sedimentary environment. The
mapping exercise lasted for two (2). The different stations visited within those days with their GPS
coordinate and Altitude are outline below;
DAY ONE
STATION GPS CO-ORDINATE ALTITUDE (meters)
1 (few km from dengi) N 09 22 48.5 E 10 00 21.3 397
2 N 09 22 83.5 E
3a (River Jiamia) N 09 22 10.8 E 10 04 51.6 322
3b N 09 22 14.2 E 10 04 54.1 336
4 (Bashar) N 09 18 30.4 E 10 09 21.4 359
5 N 09 18 39.7 E 10 09 24.6 363
6 N 09 19 10.1 E 10 09 22.2 391
7 N 09 18 59.5 E 10 08 53.4 273
DAY 2
STATION GPS CO-ORDINATE ALTITUDE (meters)
1 N 09 18 59.6 E 10 08 53.1 337
1B (Bashar) N 09 19 00 E 10 08 55.6 369
2 (Bashar) N 09 18 56.6 E 10 08 53.3 375
3 N 09 18 50.3 E 10 08 51.8 374
4 N 09 19 85.8 E 10 08 53.8 373
5 N 09 19 50.7 E 10 08 59.0 384
THE BASEMENT MIGMATITE GNEISS
Occurs as massif boulders and have undergone regional metamorphism. The rock contain light and dark
bands foliation. The Dark bands contains ferromagnesian minerals while the light bands contains felsic
minerals. The foliation on the gneiss is gneissocity which shows the area is of high grade metamorphism.
The rocks here have gone beyond gneissocity to migmatization but without ptimmatic folds which is the
evidence of it. Mine composition: orthoclase feldspar, quartz and mafic minerals. The rock is also
pegmatitic in composition with large crystals of quatz and feldspar.
Figure ; Pegmatite composition in Migmatite
THE GOMBE FORMATION
The Gombe formation is a heterogneouse sequence within the upper Benue Trough of shale, sandstone
and clay, it consists of rapidly alternating thin bed of silty shale, fine to medium grained sandstone with
some intercalated flaggy ironstone regaraded as estuarine to deltaic deposition (Carter et al 1963)
THE PINDIGA FORMATION
In an ideal situation the pindiga under layer the gombe formation. The pindiga is similar lithology with
the Gombe formation with some variation in the shale and sandstone characteristics.
Sandstone
Sandstone are rocks composed primarily of sand-size grains, usually particles of mineral, rock, or organic
material that have been reduced to "sand" size by weathering. The sandstone covers most parts of the
study area, some of the sandstones are highly weathered. The color ranges from brown-dark, brown,
reddish-brown to buff red. For the Pindiga Sandstone, it is fine grained, has a fissile nature (not
indurated). The Gombe Sandstone is coarser grained and some of the Gombe sandstone are highly
ferrogenized. Some of the Gombe Sandstone have been highly baked and the beds tilted due to extreme
tectonic activities. Mineral Composition; High quartz content, feldspars and Ferromagnesian. Gombe
Sandstone has more iron content than the Pindiga Sandstone.
Shale
Shale is a laminated or fissile clastic sedimentary rock. It is a fine-grained rock made made of compressed
mud and clay. They occur in playas rivers basins and oceans and can be easily divided into thin layers.
Some of the shale lie vertically in the area, due to intense tectonism affecting the beds. The shale appears
grey in colour. The Pindiga and GombeShales were encountered, in term of differences, The Pindiga
Shale is more dark coloured than Gombe Shale. Mineral Composition;Composed predominantly of silt
and clay minerals, quartz grains. Other minerals include; Feldspar, carbonate minerals, Iron oxides.
Siltstone
A siltstone is a lithified, non-fissile mudrock. In order for a rock to be named a siltstone, it must contain
over 50% silt-sized material. Silt is any particle smaller than sand, 1/16 of a millimeter, and larger than
clay, 1/256 of millimeter. Depositional Environment of siltstone are; Flood plain, Delta, or Mid-
continental Shelf. It is reddish brown in colour and is found within the area interbedded with Mudstone in
Gombe formation and interbedded with Sandstone in Pindiga Formation. Mineral Composition;
Siltstone has a mixture of micas, feldspar, quartz and clay minerals.
Mudstone
Mudstone is made up of tiny clay particles (less than 0.05mm) that can't be seen with the naked eye.
These tiny particles are deposited in quiet low-energy environments like tidal flats, lakes, and the deep
sea. It is found interbedded with Siltstone in Gombe Formation forming the distal bar sand of the
sequence. The mudstone together with the siltstone is motted as they show different colors due to intense
heat affecting them.Mineral Composition;Generally, contain clay minerals, other minerals such as
quartz, feldspar, mica and iron oxide can be found.
SEDIMENTARY STRUCTURES
Bedding and Lamination
Stratification of bedding is produced by changes in the pattern of sedimentation usually due to change in
composition and grain size.
Trough Crossbedding
Trough Crossbedding is characterised by curved planar erosional surfaces. It can be used to measure
paleocurrent direction. The structure were identified on Gombe Sandstone.
Figure : crossbedding on the Gombe sanstone.
Ripple marks
Ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation
by water(current or waves) or wind. Ripple marks were observed in Gombe sandstone.
Bioturbation
Bioturbation is the reworking of sediments by animals or plants. They are common in the study area on
Gombe Formation. The importance of the structures lies on the information they give on the depositional
history of the environment and the evidence of life in sediments since body fossils were not preserved in
the whole area.
Veins
Veins are distinct sheet-like body of crystals minerals within a rock. It was encountered on migmatite-
gneiss within the area at some few meters away from Dengi.
CHAPTER THREE
STRATIGRAPHY/ EVOLUTION OF THE MAPPED AREA
The study area is within the Gongola arm of the Upper Benue trough. The Albian Bima Sandstone lies
unconformably on the Precambian Basement. The Yolde Formation lies conformably on the Bima
Sandstone This formation of Cenomanian age represents the beginning of marine incursion into this part
of the Benue Trough. The Pindiga Formations and the possibly younger Fika Shale lie conformably on
the Yolde Formation. The Gombe formation is overlaying the Pindiga Formation and the Keri-Keri
formation is overlaying the Gombe. The Keri–Keri Formation is made up of whitish grey sandstones,
siltstones, and clay stones with the clay stones dominating the lithology in most places
FIG 2: Stratigraphic successions in the Upper Benue Trough (Gongola Arm)
Lau-Gombe sub-baisn, eg. Akande et al., 1998).
The continental Bima Group comprises the oldest sediments in the Upper Benue Trough which directly
overlie the crystalline basement rocks. This formation is diachronous and probably of Albian–Turonian
age. It is a poorly sorted, medium to coarse-grained, thick to massive – bedded, and cross – stratified
feldspathic sandstone with variable colors; from brown, reddish brown, grey to white.
The Pindiga Formation outcrops over an area extending from the extreme north-eastern part of the area
mapped. It is exposed along the Bashar-Jarmai road, where it consists of alternating silty shale and thin
fine-grained sandstone beds that are reddish brown in colour. The Pindiga Formation can be seen lying
upon the basement; also, it lies conformably on top of the Yolde Formation. The Pindiga formation can be
seen directly below the Gombe in the SW and NE on the map of the study area.
The Gombe Formation has a marked angular unconformity between it and the Kerri-Kerri Formation and
is made up of three major lithofacies which may prove recognizable as separate members. At the base, the
Gombe Formation consists of rapidly alternating thin beds of silty shales, sometimes with plant remains
and fine to medium grain sandstones with some intercalated thin flaggy ironstones. Bioturbation is
common in this facies, mainly horizontal feeding burrows of Thalassinoides type. This lithofacies is
repeated in the Gombe Inlier above few tens of meters of strata belonging to the bedded facies
CHAPTER FOUR
ECONOMIC GEOLOGY OF THE AREA.
Economic geology of an area are those valuable minerals of the earth that can be mined and sold for
profit. Some of the economic minerals that are associated with the area as a result of the geology of the
area are outline below;
SANDSTONE
Sandstones are economically important as major reservoirs for both petroleum and water, as building
materials, and as valuable sources of metallic ores. Most significantly, they are the single most useful
sedimentary rock type for deciphering Earth history. Sandstone was a popular building material from
ancient times. It is relatively soft, making it easy to carve. It has been widely used around the world in
constructing temples, homes, and other buildings.
SHALE
a. It is a source material in the ceramics industry to make brick, tile and pottery.
b. Shale is crushed and heated with limestone to make cement for the construction industry
c. The petroleum industry uses fracking to extract oil and natural gas from oil shale.
d. can serve as source rock in the formation of hydrocarbon.
SILTSTONE
a. It is rarely mining for use as a construction material or manufacturing feedstock.
b. The pore spaces of siltstone serve as good aquifer. It is rarely porous enough or extensive enough to
serve as an oil or gas reservoir.
c. Its main use is as a low-quality fill when better materials are not locally available.
MIGMATITE GNESIS
a. are use in construction purpose as aggregates, dimension stone, cement manufacturing and tailing
material.
b. may host mineral deposits associated with partial melting.
CHAPTER FIVE
SUMMARY AND RECOMMENDATIONS
SUMMARY
The study Areas covered during the geologic field work are Dengi, Jarmai in Kanam LGA and Bashar In
Wase LGA which is within the Bashar Sheet 192. The area under study predominantly composed of the
Migmatite which is the basement complex, Sedimentary Formations like Bima Formation overlaying the
Basement, Pindiga Formation overlaying the Yolde formation though we were not able to map the area
where there is the exposure of the Yolde formation. and then Gombe overlaying the Yolde This
sequenced Stratification is typical of the Gongola Arm of the Benue Trough. Rock types identified
Includes Migmatite, Mudstone, Siltstone, Sandstone, Shales etc.
At the course of our mapping we saw some structures like ripple mark, lamination, bedding, trough, mud
crack etc. these structure helps us to be able to established the geology of that location and the tectonic
force that have acted on the area. The Economic of these minerals, rocks goes a long way to see how one
can benefit from these minerals not just an individual but also the society at large.
RECOMMENDATIONS
1. Students should be more expose to all three geological environment (igneous, metamorphic and
sedimentary) field work quite early.
2. The school and the government should develop a financial scheme to help fund the field work to
ease the pressure on the students.
