1. INTRODUCTION

Sedimentary basins are region of prolonged subsidence of the earth’s Surface. In that region

there are accumulation of sediment either actively or inactively. The driving Mechanism of

subsidence are related to the process within earths which are the relatively rigidly, cooled

thermal boundary layer of the earth’s known as Lithosphere. Lithosphere is composed of number

of plates which are in Motion with respect to each other. Sedimentary basins exist as motion of

plate tectonics. There are two type of lithosphere

Continental lithosphere; this is a plate which is able to store elastic stresses over long time

referred as elastic lithosphere. It has strength profile with depth and thin and denser.

Oceanic lithosphere; these are thick and light hence lack low strength layer, its strength

increases with depth to brittle-ductile transition in upper mantle

Relative motion produces deformation, vulcanicity, and seismicity and concentrated along their

boundaries. These boundaries are classified into

Divergent boundaries mid ocean ridge spreading center of the ocean basin

Convergent boundaries associated with large amount of shortening such as continental

collision

Transform boundaries associated with strike-slip deformation

Plate tectonic has the premise that deformation is concentrated along plate boundaries, the

continental lithosphere deform far from plate boundaries and appear to behave at geological time

scale.

Formative mechanism of sedimentary basin fall into small number of categories. These

categories are

Isostatic consequences of changes in crustal/lithospheric thickness

Loading of the lithospheres causes a deflection or flexural deformation

Viscous flow of the mantle causes non- permanent subsidence/uplift

Tanzanian basin are classified into inland basin, coastal basin, shallow water basin and deep

offshore basin. During the field we conducted coastal basin analysis which categorized into

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Tanga basin, Ruvu basin and Mandawa basin. Tanga basin is analyzed from basement, Karoo,

Jurassic and cretaceous and at Ruvu basin we analyzed lithologies from cretaceous and Jurassic

and ruvu river as the boundary between Tanga basin and Ruvu basin. Lastly Mandawa basin

which categorized into groups and formation. Rufiji River as the boundary between Mandawa

basin and Ruvu basin. Coastal basin formed pemian to peasic.

Figure 1. Tanzania Basins

1.2 Location

Coastal basin is the basin which is found at the coastal of Tanzania and it separated by Indian

Ocean an East and metamorphic basement in west. It start from Somalia basin to Ruvuma basin

in south Tanzania. It extends from Tanga region in Northern part and Lindi/Mtwara in southern

part and at central it cross Coast region. Dar es Salaam platform is one of the basin found in

Tanzania.

1.3 Accessibility

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Coastal basin is not well accessible by buses but it will be easy to reach the location of outcrop

once land cruiser car is used and in some area it is required to walk in order to reach the place

where outcrop is located. Mostly of the field site can be easily accessed by walk traverse and

that will make to hit the targeted location.

1.4 METHODOLOGY

These are methods involved in our field work in order to gather information during our field

route in all three basins through the equipment’s used to collect data during the basin analysis

based on structure and stratigraphic sequence of surface lithology. The methods that were used

during the field works were;

Data collected through tools such as

Compass

GPS and hand lens

Magnetic compass,

Geological hummer and sample bags

Field note book

Pen and digital camera

Description

Geological Compass –specifically for structural measurement of strike, dip and dip

direction of the outcrop exposed. Basically, geologists uses geological compass to

measure orientation of geological structures, as they map in the field to analyze (and

document) the geometry of bedding planes, joints and / or metamorphic foliation and

lineation. The type of compass used during mapping was known as Brunton compass and

suunto compass.

Global Positioning System (GPS), for taking coordinate of the area in Universal

Transversal Mercator (UTM) format. Used to know the locality of lithologies in specific

basin

Geological hammer for splitting and breaking rocks. In field geology, they are used to

obtain a fresh surface of a rock in order to determine its composition, nature, mineralogy,

history and also to estimate of rock strength. Geological hammer also, they are employed

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to break rocks with the aim of revealing fossils inside. Geologist's hammers sometimes

used for scale in a photograph. Fresh surface of a rock from the fields, can be easily

obtained in order to determine its mineralogical composition, nature, and history and field

estimation of the rocks strength. In fossil collecting, and mineral collecting. They are

employed to break rocks with the aim of revealing fossils inside.

Hydrochloric acid (HCL) for testing the presence of carbonate in a particular lithology’s

Color pencils, trace papers used for cross section and stratigraphy map construction to

analyses lithologies information

Field notebook It is of a great significance in the field, we used for booking every piece

of information we came across with along the way. We recorded details about

mineralogy, degree of weathering and specific coordinates of outcrops as well as

geological features like joints, sedimentary structures and so forth.

Hand lens

This came into application whenever we wanted to magnify a rock sample for a closer

and precise investigation of mineral composition of the specimens and the true colour.

Sample bag

This was used for carrying different rock samples from the field area for the purposes of

doing further analysis or observations of those samples.

Magnetic pencils

These were used to taste rocks with iron contents or magnetic properties. Example

Hematite and magnetite

Marker pens

Marker pens were used for labeling samples before they are put into the sample bags.

Marker pens were of different colors such as red, blue and black.

Field camera was used for taking photographs of lithologies and strucuters observed as

well as video clips of all interesting features and outcrops which will be used in the field

report attachment

Safety clothing were used for ensuring one’s safety or safety involved. They included

hard boots, preferably jeans, helmets, reflectors and safety goggles.

Tape measure was used during the field for measuring estimation of lithology length

and size

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1.5 Objectives of field study

Objectives of field study in Tanga, Ruvu and Mandawa basin are the following

To study sequence stratigraphy of coastal basin

To know the lithologies which are dominant

To understand petroleum system of coastal basin

To understand well and enable to differentiate or indicate observable petro physical

parameters

To analyze the rock lithologies found in term of color, grains size,

To study the paleontology of coastal basin and its depositions environments

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CHAPTER TWO

2 GEOLOGICAL SETTING OF COASTAL BASIN

Geological setting of coastal basin of Tanzania is associated with tectonic activity. Broadly, the

major features are the northeasterly trending Selous / Ruvu rift basins separated from a north-

south string of embayment collectively termed the Jurassic Rift Basins. A Tertiary sag basin

dominates the offshore Coastal Basin making underlying structure inherited from offshore

extensions of the rift basins. Basin configuration reflects the interaction of structural elements

derived firstly from rifting and secondly from major basement lineaments which fan from

southwest to northwest and may be related to thermal doming in the early Jurassic between

Madagascar and Tanzania.

The main tectonic series which have influenced the structural evolution of the sedimentary

basins of Tanzania are as follows:

Extensional rifting beginning in the late Carboniferous and extending through the Permo-

Triassic into the early Jurassic.

Early Jurassic thermal doming between Tanzania and Madagascar leading to enhanced

differential subsidence of the Jurassic Rift Basins on the eastern flank of the Masasi

Basement Spur.

Bajocian onset of sea-floor spreading in the Somalia Basin along the northern arm of a

rift-rift-transform triple junction resulting in the southward movement of Madagascar

along the transform (Davie Fracture Zone) thereby abandoning the Selous/Ruvu rift as a

failed arm.

Cessation of sea-floor spreading in the Somalia Basin in the late Cretaceous and

lithospheric cooling causing major subsidence in eastern Tanzania.

Development of the Modern Rift Basins in the late Tertiary related to a period of major

thermal doming, uplift and erosion in East Africa accompanied by extensional faulting

and subsidence in the offshore area and the formation of the Tertiary sag basin.

The stratigraphic evolution of the sedimentary basins of Tanzania is described below in terms of

four stages in continental rifting, namely pre-rift, syn-rift, transitional and post-rift:

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Pre-rift Gondwanaland was made up of a series of stable cratonic nuclei separated by

zones of structural weakness later to develop into the rift zones which fragmented the

supercontinent. Basement in the area of the Tanzanian coastal basins comprises high

grade metamorphics, mainly gneisses, of the Mozambique orogenic belt.

Syn-rift sedimentation began in the late Carboniferous and continued throughout the

Permo-Triassic into the early Jurassic during which time the major Karoo basins rifting

and fault movement initiated erosion and generated fluvial systems which deposited

sequences and fining-upward megacycles of coarse proximal, high and low energy

fluvial, floodplain, deltaic and lacustrine deposits with occasional marine incursions.

Each megacycle corresponds broadly to the Permian and Triassic (Rufiji / Tanga Series).

Transitional stage during the early Jurassic encompassed the last pulses of major rifting;

it is particularly associated with differential subsidence leading to the formation of a

series of semi-enclosed basins around the flanks of the Masasi Basement Spur and the

Dar-es-Salaam Platform. A widespread transgression resulted in the development of

restricted marine conditions in the subsidizing basins leading to the possible extensive

deposition of evaporites - the Nondwa formation found in the Mandawa basin. On the

flanks of the basins, continental conditions persisted with Lower Jurassic sediments

(Ngerengere Beds) demonstrating similar lithofacies to the underlying megacycles in the

Older Karoo, particularly the widespread distribution of fluvial sandstones.

Post-rift stage lasted from the Middle Jurassic to the Recent. It began in the Bajocian

with the onset of sea-floor spreading in the Somalia Basin which stranded the Ruvu

Selous rift as a failed arm of a triple junction. This event is marked by a regional

unconformity and the start of a major marine incursion which transgressed a basin

topography inherited from earlier rifting. Renewed conditions of restricted circulation

may have resulted in the widespread accumulation of the Makarawe shale - a potentially

good oil-prone source rock. By the Bathonian, the open marine transgression had reached

the boundaries of the rift basins depositing limestones (Amboni, Kidugallo and Mtumbei)

over much of the area.

Callovian extends onwards the coastal basins of Tanzania evolved as a passive continental

margin on a subsiding, northeasterly tilting substratum on which sedimentation was controlled

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by intermittent tectonic activity and changes in sea-level. In the deeper parts of Ruvu Basin and

Rufiji Trough, the mid-Jurassic transgression continued into the late Jurassic depositing

argillaceous sediments of the Bagamoyo formation which forms an effective regional seal in

these areas. Elsewhere, the late Jurassic and early Cretaceous is a regressive phase with the

accumulation of thick continental, deltaic and marginal marine deposits of the predominantly

sandy Kipatimu Beds. A regional mid-Cretaceous unconformity and the deposition of platform

carbonates mark the end of the regressive phase and the onset of a major marine transgression in

the late Cretaceous. Local regressive sedimentation persists in the Cenomanian but generally the

Upper Cretaceous comprises shelf and slope clay stones of the Ruaruke formation. Subsidence

continued into the Paleocene in the coastal and offshore areas, although regression set in as

sedimentation rates began to exceed subsidence and remained until the present. Several phases of

uplift occurred in the late Tertiary resulting in regional unconformities at the base of the Middle

Eocene and at the base of the Miocene. Middle Eocene, Neogene and recent sediments are

strongly regressive and comprise continental, deltaic and marine facies.

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CHAPTER THREE

3.0 Geology and Structures

3.1 Geology

In the field study area we uncounted different lithology’s and structures which indicated that the

basin geology or rock and deformation are differently. Geology of both three basins starting from

Tanga, Ruvu and Mandawa basins are influenced with tectonic activities which lead to formation

of different structures. Mostly dominants rock from the basements are metamorphic rock and at

basins we met with sedimentary rocks.

3.1.2 Lithology

These are observed outcrop/rock from the field site. Those outcrop were firstly described in

terms of name of rocks, grain size, color, hardness, angularity, sphericity, visible porosity,

sorting, carbonate contents and hydrocarbon elements. Through these details the rocks were

named accordingly. The following below are Lithological name as it arranged according to the

basins

TANGA BASIN

Mostly dominant lithology in Tanga basin is whitish fine grained dolomitic marble, which

reacted with hydrochloric acid with strike 359 and 021NE at 0494747E, 9495852N at Mbuta

quarry at basement.

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Figure 2. Dolomitic marble of Tanga basement

Sandstone which clastic sedimentary rock which varied in size from fine, medium to course.

Some of those sandstone were calcareous and sand limestone and non-calcareous sandstone.

Dominant minerals are quartz, k-feldspar, mica and iron. Calcareous sandstone found at

0505055E, 9442039N and non-calcareous sandstone found at 0509669E, 9456991N. The

difference between calcareous and non-calcareous is on reactivity or response to hydrochloric

acid reaction, calcareous respond to acid while non calcareous does not. Sand limestone is a

sandstone with many sand. Also there were interbedded layers of mudstone and siltstone and

claystones observed.

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Figure 3; Calcareous Sandstone of Lower Karoo

Shale lithology with plant imprints observed at 0489900E, 9450102N which is black in color,

hard, very compacted with hematite, muscovite minerals, poor porosity with finely grained. It is

layered in thin laminated beds with 186 strike 010SE Dip amount. Outcrops was also

encountered in shallow drilled well Kakindu 1 sample.

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Figure 4; Black shale of Kakindu River

Limestone outcrop found in massive layer with fine grained, whitish to grey in color with calcite

mineral, react with hydrochloric acid. Also limestone with different size of grains observed

which termed as oolitic limestone(less than 1 cm) at 0505050E, 9441993N and pizolitic

limestone (greater than 1 cm) at 0504976E, 9442045N with bivalves, echinoids and sponge.

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Figure 5. Limestone of Kiomon Quarry

RUVU BASIN

Gneiss with whitish and black color with foliation is observed at the basement. This lithology

formed a sharp contact with Jurassic sediments at Mkwizu quarry. This metamorphic rock

dominated with hornblende minerals is found at 0429531E, 9296105N and at Kikumbi cha

Mkulu where inferred contact between limestone and gneiss observed windward side

Sandstone which is calcite whitish grey found with course to medium grains. Since contains

calcite minerals it react with hydrochloric acid which is massively and thick bedded at

04118881E, 9249619N with strike 273 and dip 011SE and fine thin layers of sandstone at

0443848E, 9297429N,

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Figure 6; Calcareous sandstone of Kigudalo

Fossiliferous limestone which is grey in color with fine grains is dominant in different location.

Those limestone are massive bedded and some locality are thick with fossils like pectin,

gastropods, echinoids, bivalves and coral at 0418484E, 9267486N. Also oolitic limestone with

many fossil content found at 0426792E, 9284502N and pizolitic limestone at 0411764E,

9249657N. Some layers of mudstone, clay stone and siltstone are found but were not well

exposed at the surface but we observed through drainage and at gullies like at 0433268E,

9265826N

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Figure 7. Fossiferous Limestone of Tonga Hill

MANDAWA BASIN

Chemical sedimentary rock observed at Mandawa basin as gysum, carbonates and salt dome and

Pindilo shale’s which showed salt dispirism due buoyance effect of salt. Pindilo shales are

blackish in color which is very light and found at 0534516E, 8952191N. Gypsum at 0542050E,

8970501N. This is common in Pindilo group at Nondwa formation

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Figure 8; Pindilo shale of Makangaga Quarry and gypsum

Most limestone is dominated in this basin but the difference between this limestone and

limestone from Tanga, Ruvu basin is in the content of fossils. Fossil content in Mandawa is

higher and some fossils dominated in one location which lead naming rock by using the

dominant fossils like Numulitic limestone at 0552463E, 8973486N and gastropods, sponge

fossils present. Coral reef limestone 0514517E, 9056019N and other limestone like oolites with

coral fossils and bioclastic limestone at 0489470E, 9055729N with strike 201 dip 007.

Limestone found at Mandawa group in Mtumbei formation, Mavuji group in Mitole, Narwehe

Kihuluhulu formation

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Figure 9; Nummulitic Limestone with other fossils like bivalves

Ammonitic sandstone found at Mandawa basin with fine to medium grain but yellowish in

colour due to oxidizing environment at 0533434E, 9032093N. Massive and thick bedded

sandstone with fine grains found at 0543393E, 8978992N. Sandstone lithology act as a member

in Mtumbei, Kipatimu, Mitole, Narwehe Kihuruhuru and Nangurukuru formation.

Claystone intercalated at 0493683E, 9057284N with sandstone and observed at contact with

limestone 514311E, 9056227N b.ut this reacted with hydrochloric acid. Fossilized claystone with

belemnites and ammonids which intercalated with sandstone at 0539532E, 8989290N. These

lithologies some intercalated with mudstone, siltstone and claystone. Some interbedded with

other lithologies.

3.2 Structures

Different structures observed within those lithologies. These structures associated with human

activities and others are naturally occurred or we can term those structures as primary structures

and secondary structures. Primary structures are those structures formed during deposition of

sediments while secondary structures are those associated or formed after deposition. These

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structures has got its usual meaning in geology or petroleum geology. We can use those symbols

to know something during our basin analysis. During the field routes we countered a lot of

structures which are the following bellow

Bedding Primary layering in a sedimentary rock, formed during deposition, manifested by

changes in texture, color, and/or composition; may be emphasized in outcrop by the presence of

parting

Bedding plane a distinct surface of contact between two sedimentary rock layers. It

represents mechanical zones of weakness and they form when there is a compositional or

textural difference is exist between two beds. It has been observed in all basins but

mostly in Tanga basin at 0489900E, 9450102N

Plants imprints these are remains of plant which left on the surface of beds. These are

good indicators of deposition environment and area for hydrocarbon exploration. These

plants imprints are secondary depositional structure. Found at 0490026E, 9450043N

Joints A fracture in rock along which there has been no displacement. Joints are

associated with tectonic activities and joint may result a fault formation. Fractures are

observed in all three basin due to human and tectonic activities

Cross beds are surfaces within a bed that are oblique to the overall bounding surfaces of

the bed. Cross beds are observed in all basin especially in Tanga basin at Ndoyo bridge,

kidugalo in Ruvu basin and Ngole in Mandawa Basin

Figure 10; Cross beds

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Fault is a discrete fracture between blocks of rock that have been displaced relative to

each other, in a direction parallel to the fracture plane.It has been observed at 0431076E,

9297461N

Figure 11; Fault and joints structures

A fracture or fracture zone in rock along which movement has occurred.

Burrows the traces of worms or other burrowing organisms that live in unconsolidated

sediment. They stand out because of slight textural and color contrasts with the burrowed

rock.

Ripple marks Ridges and valleys on the surface of a bed formed as a consequence of

fluid flow. If the current flows back and forth, as along a beach, the ripples are

symmetric, but if they form in a uniformly flowing current, they are asymmetric. The

crests of symmetric ripples tend to be pointed, whereas the troughs tend to be smooth

curves. Thus, symmetric ripples are good facing indicators. Asymmetric ripples are not

good facing indicators, but do provide current directions.

Graded beds display progressive fining of clast/grain size from the base to the top, and

are a consequence of deposition from turbidity flows.

Pinch out

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Figure 12; Pinch out structures at River Mringi bridge

Contact any surface between two geologic units.

Unconformity If there is an interruption in sedimentation, such that there is a measurable

gap in time between the base of the sedimentary unit and what lies beneath it

Fold A bend or flexure in a rock unit or series of rock units that has been caused by

crustal movements. Fold structure is encountered at 0534516 E, 8952191N.

Figure 13; one of the observed fold structure

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Flute casts Asymmetric troughs formed by vortices (mini tornadoes) within the fluid that

dig into the unconsolidated substrate. The troughs are deeper at the upstream end, where

the vortex was stronger. They get shallower and wider at the downstream end, because

the vortex dies out. Flute casts can be used as facing indicators. Found at 0531378 E,

9033810 N

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CHAPTER FOUR

4 STRATIGRAPHY OF EACH BASIN

4.1 TANGA BASIN

Tanga basin has two main boulder faults which are Karoo fault and Cenozoic fault both of which

tend from North East (NE) to South West (SW) where fault divided into two group. Synthetic

faul which lie in the same direction of boulder fault is the one, and the secondly is the ant-

synthetic fault which lies in different direction to the boulder fault. And due to fault then lead to

sediments to be deposited on footwall while some at hangingwall.

Basement composed of dolomitic marble, quarzite, and gneiss at footwall of Karoo that

encounter at Kijenge village where Mbuta abandoned quary found which consist of massive

bedded dolomitic marble of high fracture paraller to bedding plane while other are perpendicular

to the bedding plane of about 10cm to 15cm. Tanga basin mainly based on Karoo age which

mainly due to rifting that pocced upto drift during jurrassic period.

Karoo divided into three part which are lower karoo, middle karoo and upper karoo.

Lower Karoo consist of coarse to medium grains size and some of fine grain size. At

Umba river there are various litology encounter of coarse grain in texture with some

amount of quartz and soft wall which cuted by water, also boulder which are elongated

and round in shape of yellow brown colour termed as conglomeratic sandstone and

arkosic sandstones that contain feldspar with gneiss boulder. Also in other place there is

reddish brown to dark grey for weathered sample due to iron content as also quartz and

feldspar observed which probabbly carbonecious shale, sandstone, and the interbedded of

shale and sandstone layer

Middle Karoo start from transition of gradual change in lithology for convolution shape

with some lithic sand which are hard compose of calcite and mud with implits. Middle of

karoo at pangarawe abandoned quarry consist of fissile of fine grained laminated which

are black ion colour with water ring structuers, also cross cutting and paraller cutting

beds are found the lithology was carbonecious shale of moderate to high weathered. For

Kakindu river channel consist of dark gray of fine grain size contain calcite mineral of

strike 140°/ dip 18°/ dip direction 50° (NE) which was shale containing plant imprints, at

0489605E/ 9450319N/ Altitude of 124m.

Upper Karoo divide into lower division of upper and upper division of upper

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Lower division of upper Karoo is the period when difting occur as intercalated of fine

to medium grain size. At Ndoyo bridge 0511341E/ 9459964N there was fine grain

material to medium with lithic and massive bed of 55° strike05° dip/145° dip direction

wich composed of sandstone bed. At a coordinate 0510761E/ 9459048N there was ripple

mark of fine to medium grain where claystone found inlarger content than sandstone

Figure 14; fine sandstone outcrop

Upper division of upper Karoo is the one contain very coarse reddish brown colour

sandstone. Near Ngole bridge of 0509454E,9450761N there is arkosic with silica at

highly deformed area which consist of massive sandstone bed, and shale. Also ther was a

major continous fault and rollover truncation

Jurrassic period where the ocean start to open during drifting like Amboni kast as marine

environment contains calcareous in form of limestone which mainly contains oolites and

pisiolitic properties as silica structures with mineals like quartz, calcite and aragonite as light and

grey colour obtained. Ambani bridge is the jurasic where transition from upper karoo as

calcareous sandstone and massiv bedding with some fault due to drifting. For Amboni quarry

there is fine to medium grainsize with some silica contents of massive bedded limestones and at

Kimoni lithology found are mud limestone and limestone.

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Figure 15. ZB limestone

4.2 RUVU BASIN

In ruvu basin drifting is the main process where water overstep Karoo whith maga ccoss

bedding. This basin composed of basement, jurrassic, Karoo, and cretaceous period, where

jurassic divided into three categories which are lower jurrassic, middle jurrassic and upper

jurrassic while cretaceous divided into lower cretaceous and upper cretaceous.

Basement in ruvu basin dominated by gneiss, dolomitic marble, and quarzite which are ductile

materials while basin are of brittle material. Basement make contact with middle jurassic when

overstep karoo at Mkwazu quarry, Kikumbi cha nkuru, and Tonga hills 1,2 and 3.

For jurassic divided into three categories which are lower jurrassic, middle jurrassic and upper

jurrassic

Lower jurrassic is mainly composed of medium to coarse grain. At kidugalo various

lithology observed like calcareous sandstone, congomeratic sandstone, and siltstone. Also

graded bedded of bed which are of fining upward and of coarse upward. Cross bedding

layer of sandstone found and soft sediment structures which are less compacted of

sandstone with compacted layer which is hard. Oolitic limestone found due to ooids and

cross stratification.

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Figure 16; Oolitic limestone of Kidugalo

Middle jurrassic mainly composed of sandlimestone, siltstone, and shale as at Msolwa

quarry where there is quartz, mafic grains, calcite, and feldspar with bedded layer of

about . Also coraliferrous limestone and bilvalvia as fossilferous limestone observed as

the grain size of the rocks ranged from fine to medium size. As the middle jurassic

overlay the Basement.

Upper jurasic is mainly composed of marine environments. At Pera there is intercaleted

between upper jurasic and lower cretaceous, where the grainsize are of fine which are

light brown of calcite, illite and smertite mineral. Also mainly place of upper jurasic

composed of coral species, bilvalvia as imprints and boulder of siltstone between

claystone, so the litology are calcareous siltstone and calcareous claystone

And cretaceous divided into two parts which are lower cretaceous and upper cretaceous.

Lower cretaceous is the period where regration took place as it compose of medium to

coarse grain size. In Mwetemo abandoned quarry composed of red, light, brown, yellow

and black coroul while quartz and feldspar observed and lithology obtained are

congomeratic sandstone.

Upper cretaceous is of the transgration period composed of fine to medium grain size at

region scale. At pera abandoned quarry where light green, and redishbrown to pink/red??

colour and minerals like feldspar, k-feldspar, and calcite as it fizz when reacting with

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hydrochloric acid, and lithology observed are calcareous siltstone, calcareous sandstone,

siltstones and mudstone.

4.3 MANDAWA BASIN

It has been classifield into groups and formation. There are five groups such as

PINDIRO GROUP

Oldest group with one observed formation which is Nondwa formation which dominated with

evaporates. It has been formed during triasic and comprises Claystone, gypsum, carbonates and

salt and black shales termed as Pindilo Shales. Salt diapirism occured due to bouyance effect

MANDAWA GROUP

It has three observed formation with different members in each formation. These formation are

the following

Mtumbei formation it is formed during mid jurasic and has limestone member which varies

from down with oolitic limestone and up with bioclastic limestone and sand limestone with

calcite minerals. It is fine grained limestone which fizzy when reacted with greyish in color.sand

limestone also reacted with hydrocloric acid

Kipatimu formation is the formation formed during upper Jurassic with two members such as

lower kipatimu with fine grained sandstone and intercalation of claystone. And at upper

kipatimu with course grained sandstone, claystone and kaolinite.

MAVUJI GROUP

Mitole formation it is upper crateous kimedian to belycian with two members. Lower Mitole

has oolitic limestone with fossils such as bivalves and Upper Mitole is dominated with sandstone

lithology which is finely grained

Nalwehe formation dominated with limeston on top or at lower elevation and sanstone lithology

at upper height. Both has fossil contents such as corals and bivalves.

Kihuluhulu formation is formation with dominant reef limestone, calcareous limestone and fine

grained sanstone with some fossils such as ammonites, belemnites.

KILWA GROUP

Nangurukuru formation is the formation formed during santonian to missipian at Upper

crateceous dominated with fine greyish claystone which is bloke and calcareous and some

calcareous sandstone and structures like flute carst, joints and fossils. Also limmonitic yellowish

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sandstone observed and it is yellow in color due to environment depostion wwhich led to iron

presence. Neretic erchno facies used to distringuish Nangurukuru claystone and Kivinje

claystone.

Kivinje formation it is dominated with fine grained greyish claystone which is covered with

mudstone on top of it. It does not react with hydrochloric acid and is highly tectonically

desturbed. In geological time scale is found formed during paleocene to lower miocene

Masoko Formation it is mid eocene formation with whitish nummulitic limestone which react

with acid. Found to have many fossils like corals, bivalves, gastropods and Nummulites thats

why it is termed as nummulitic limestone

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CHAPTER FIVE

5.0 PETROLEUM SYSTEM RELATION TO BASIN

Petroleum systerm it compises reservoir, seal( cap rock), source rock, trap as the elements of

sedimentary basin. The process involved are maturation and migration that related to events

about space for accomodation and timing in case of geological time.

The source rock should compose organic matter in the shale or limestone.

The reservoir rock must be porous enough for hydrocarbon to be preserved which is due

to diagnesis for primary porosity while secondary porosity due to chemical reaction

example

sandstone. Also reservoir must be permeable enough. But for the case of claystone have

high porosity but no interconected pore while sandstone have low porosity but high

interconected pores because of the way sediments compacted.

Migration of hdrocarbon is the process of oil/gas to shift from one place to another which

can be primary migration as the hydrocarbon from the source to the reservoir and

secondary migration is about from the resrvoir to the caprock. The good caprock can be

salt and anhydrite/claystone due to more plastic formation.

Trap is the element which can be of structure, stratigraphic or combination. As structural

trap is due to tectonic activities example fold to make anticline, and fault for deposition.

While stratigraphic is about cyncline like salt domes.

5.1 Tanga basin

In Tanga basin the source rock found at middle karoo where at Kakindu River composed of shale

which contain plants remain. The reservoir due to migration can be at lower division of upper

karoo which consist of sandstones while cap rock can be at upper division of upper karoo, and

the seal can be jurasic period at Amboni which consist limestone.

5.2 Ruvu basin

For Ruvu basin the source rock can be at middle jurasic which compose of most of fossils, the

reservoir rock can be lower cretaceous due to composition of medium to coarse grain size while

trap can be at upper cretaceous.

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5.3 Mandawa basin

Since Mandawa basin is dominated with sandstone, limestone and intercalation of mudstone and

clay stone it is very potential in hydrocarbon exploration due to being a good source rock and

good reservoir. Also there are many fossils content in different formation like Mtumbei, Mitole,

Kihuruhulu and Nangurukuru formation.

On comparison of those basin Mandawa basin seem to be potential because there are some

drilled exploration well which shows high percentage of hydrocarbon richness and some

formation characters relates for example Songosongo relates to Mtumbei. Tanga basin is very

potential due to observed lithology characters such as porosity, permeability and source rock and

reservoir rock. Ruvu basin follows and does not have much fossils content as Mandawa or Tanga

basins

5.4 Paleontology

Is the study of remains of living things such as plants and animals who lived in ancient time.

These fossils become deposited when sediments deposits of after the sediments become

deposited. In petroleum it can be used to study the area and correlate to petroleum system.

During the field work we counted a lot of fossils in all basin but its content differs. Such

countered fossils are important for deposition environment, direction of fossils, maturity of

hydrocarbon, indication of reservoir, age of the rock, dominant fossils presents. Mostly fossils

found in Tanga basin are plant imprints on a shale which used to indicates as fluvial deposition

environment, coals, gastropods, Bivalves, burrows, pizolite and oolites and at Ruvu basin are

coal, gastropods, Bivalves, belemnites, corals, pectens, and at Mandawa basin the same fossils

observed but others found fossils are nummulitesa t 0552463E, 8973486N ammonites, reef

corals, skoliptus and thallathinoids, trace fossils and neretic facies at 0531378E, 9033810N.

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CHAPTER SIX

FIELD EXECUTION AND RECOMMENDATION

6.1 Field execution

There are shallow bore which were drilled by TPDC and others are in process of drilling. So we

visited there for more study and explanation about stratigraphic of the drilled well and the aim of

the drilling. Their main aim is to know the karoo beds stratigraphy in order to correlate and to

test source rock. Drilling operation was done by STAMICO and the sample which obtained were

analyzed preliminarily and then properly packed and sent to Dar es salaam where they stored and

other analyzed in the Laboratry.

6.2 Recommendation

Basin analysis and sequence stratigraphy field is very interesting and enjoyable field for the

students who took petroleum because it bring understanding of mostly basin lithologies and

structures and leaves them with many question which will them to do their final year research or

a scientific research about basin and hydrocarbon potentiality. Also it bring the students

awareness about deposition information and petroleum system in general. But this field has some

difficulties to accomplish it effectively and when it will be once again conducted needs some

improvements. These are

Transport facilities such will have the student to reach all desired localities

Increase number of equipment so that it will be easy to study many things for example

magnetometer and gravimeter

Communication or information should be sent early as possible to the local administrative

Enough fund or finance to the students which will help them to do field work effectively

Lastly more expose to other related basin like Ruvuma basin, Malagalasi basin so that

they can observe the difference which exist and make other basin to be more potential

and other not

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CHAPTER SEVEN

7.0 CONCLUSION

Coastal basins are result of tectonic activity which lead to rock fragmentation due to rifting and

drifting extension. The sediments become deposited at the low land area through water bodies

like fluvial during Karoo rifting, marine during Jurassic and transition and terrestrial. These lead

to formation of clastic, bioclastic and chemical sedimentary rock. Metamorphic rock acted the

source of sediments in coastal basins. Observed lithologies are good source rock and reservoir

and their petrophyisical parameters are indication of good location for oil and gas investigation,

also fossils which are seen like bivalves, gastropods, sponge, reef coral, are the good indicators.

These gives an evidence and and attraction for more detailed investigation of oil and gas

Field work based on investigation and observation of surface outcrop were conducted from Tanga basin

in north upto ruvu basin and Mandawa basin. Exposure are along quarry, roads, rairway cut, river stream

which based on lithological and paleontological differences where by tectonic and stratigraphical frame

work obtained.

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