GEOLOGY
ASSIGNMENT-1
BY:
JEET VISHNOI
Chapter -1
ROCK
Rrock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.
The Earth's outer solid layer, the lithosphere, is made of rock
Types of Rocks
Igneous rocks
Metamorphic rocks
SEDIMENTARY ROCKS
Sedimentary Rocks
These processes form the sedimentary rocks:
Erosion --broken down and worn away wind and water (erosion).
Transportation - These little bits of our earth are washed downstream where
Deposition - they settle to the bottom of the rivers, lakes, and oceans Layer after layer of
eroded earth is deposited on top of each.
Lithification - These layers are pressed down more and more through time, until the
bottom layers slowly turn into rock
There are two type of sedimentary rocks:
1) Clastic sedimentary rock
2) Non clastic sedimentary rock
Clastic sedimentary rock
The classification of clastic sedimentary rocks is based on the particle types found in the rock.
Some types of clastic sedimentary rocks are composed of weathered rock material like gravel,
sand, silt, and clay.
Name of Rock
Fragment Type
Breccia
Coarse Fragments of Angular Gravel and Rocks
Conglomerate
Coarse Fragments of Rounded Gravel and Rocks
Sandstone
Sand Sized Particles that are 90 % Quartz
Arkose
Sandstone composed of 25 % Feldspar Grains
Shale
Clay Particles
Siltstone
Silt Particles
Mudstone
Mixture of Clay and Silt
Limestone
Mixture of Shells, Coral, and Other Marine
Skeletons
These are some samples of clastic sedimentary rocks
Non Clastic Sedimentary rocks
The remaining types of sedimentary rocks are created either from chemical precipitation and
crystallization, or by the lithification of organic matter. We identify these sedimentary rocks as
being non clastic.
Some non clastic sedimentary rocks and their precipitate type are given below:
Name of Rock
Precipitate Type
Halite
Sodium and Chlorine
Gypsum
Calcium, Sulfur, and Oxygen
Silcretes
Silica
Ferricretes
Iron
Limestone
Calcium Carbonate
Dolomite
Calcium Magnesium Carbonate
These are some samples of non clastic sedimentary rocks
Igneous rocks
Igneous rocks are called fire rocks and are formed either underground or above ground.
Underground, they are formed when the melted rock, called magma, deep within the earth
becomes trapped in small pockets. Cooling of magma a and lava results in igneous rocks.
Lava When magma appears above the earth.
Characteristics of Magma
Types of Magma
Types of magma are determined by chemical composition of the magma.
Three general types are recognized, but we will look at other types later in the course:
Basaltic magma -- SiO2 45-55 wt%, high in Fe, Mg, Ca, low in K, Na, T-1000 to 1200oC
Andesitic magma --SiO2 55-65 wt%, intermediate. in Fe, Mg, Ca, Na, K T- 800 to 1000oC
Rhyolitic magma -- SiO2 65-75%, low in Fe, Mg, Ca, high in K, Na T -650 to 800oC.
Gases present In magma



Mostly H2O (water vapor) with some CO2 (carbon dioxide)
Minor amounts of Sulfur, Chlorine, and Fluorine gases
The amount of gas in a magma is also related to the chemical composition of the
magma. Rhyolitic magmas usually have higher dissolved gas contents than basaltic
magmas .
Magma type and Rock formed
Magma
Type
Solidified
Rock
Chemical Composition
Temperature
Viscosity
Gas Content
Basaltic
Basalt
45-55 SiO2 %, high in Fe,
Mg, Ca, low in K, Na
1000 - 1200 oC
10 - 103 PaS
Low
Andesitic
Andesite
55-65
SiO2
%,
intermediate in Fe, Mg,
Ca, Na, K
800 - 1000 oC
103 - 105 PaS
Intermediate
Rhyolitic
Rhyolite
65-75 SiO2 %, low in Fe,
Mg, Ca, high in K, Na.
650 - 800 oC
105 - 109 PaS
High
Volcanoes
Two types of volcano ar there:
1) Explosive and
2) Non explosive
1) Explosive Eruption
Favored by high gas content and high viscosity (Andestic and Rhyolitic magmas)
Tephra and Pyroclastic Rocks
Average Particle
Size (mm)
Unconsolidated Material (Tephra)
Pyroclastic Rock
>64
Bombs (liquid on ejection) or Blocks
(solid on ejection)
Agglomerate
Lapilli (mostly gas bubbles)
2 - 64
<2
Lapilli Tuff
pumice stone
Ash
Ash Tuff
Non explosive eruptions
Favored by low gas content and low viscosity magmas ( basaltic to andestic magmas)
Shield Volcanoes
A shield volcano is characterized by gentle upper slopes (about 5o) and somewhat steeper
lower slopes (about 10o).It is thin lava.
Strato volcanoes
Have steeper slopes than shields, with slopes of 6 - 10o low on the flanks to 30o near
the summit.Steep slope near the summit result from thick, short viscous lava flows that
don't
travel far from the vent.
Cinder cones
Volcanic dome
Classification of rocks on their mode of occurrence
Structures associated with Igneous rocks
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts
discordantly across:


planar wall rock structures, such as bedding or foliation
massive rock formations, like igneous/magmatic intrusions and salt diapirs.
Dikes can therefore be either intrusive or sedimentary in origin.
Radiating dykes
Arcuate dykes /ring dyke
A ring dike or ring dyke in geology refers to an intrusive igneous body. Their chemistry,
petrology and field appearance precisely match those of dikes or sill, but their concentric or
radial geometric distribution around a centre of volcanic activity indicates their subvolcanic
origins.
Radiating dykes
A dike swarm or dyke swarm is a large geological structure consisting of a major group of
parallel, linear, or radially oriented dikes intruded within continental crust. They consist of
several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive
event and are magmatic and stratigraphic. Such dike swarms may form a large igneous province
and are the roots of a volcanic province.
Sill
a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds
of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term
sill is synonymous with concordant intrusive sheet. This means that the sill does not cut across
preexisting rocks, in contrast to dikes, discordant intrusive sheets which do cut across older
rocks. Sills are fed by dikes, except in unusual locations where they form in nearly vertical beds
attached directly to a magma source.
Sill
Laccolith
A laccolith is a sheet intrusion (or concordant pluton) that has been injected between two layers
of sedimentary rock. The pressure of the magma is high enough that the overlying strata are
forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base.
Lopolith
A lopolith is a large igneous intrusion which is lenticular in shape with a depressed central
region. Lopoliths are generally concordant with the intruded strata with dike or funnel-shaped
feeder bodies below the body.
Batholiths and Stock
A batholith (from Greek bathos, depth + lithos, rock) is a large emplacement of igneous
intrusive (also called plutonic) rock that forms from cooled magma deep in the Earth's crust.
Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite,
quartz monzonite, or diorite
CLASSSIFICATION OF IGNEOUS ROCKS
Sialic (or granitic or felsic)
silicon and aluminum (SiAl) dominated ,Light coloured.
Characteristic of continental rust Forms a stiff (viscous) lava or magma
Rock types include: Granite
Intermediate (or andesitic) Intermediate in composition between sialic and mafic Rock
types include: Andesite (aphanitic), Diorite (phaneritic)
Mafic (or basaltic)
Contains abundant ferromagnesian minerals (magnesium and iron silicates) Usually dark
in color (dark gray to black) Characteristic of Earth's oceanic crust, Hawaiian volcanoes
Forms a runny (low viscosity) lava include: Basalt (aphanitic)
Ultramafic
Almost entirely magnesium and iron silicates (ferromagnesian minerals)
Rarely observed on the Earth's surface .Believed to be major constituent of Earth's mantle
Rock types include: Peridotite (phaneritic) ,dominated by olivine - the birthstone is Peridot,
which gives its name to Peridotite
CLASSSIFICATION OF IGNEOUS ROCKS
METAMORPHIC ROCKS
Rocks which were once igneous or sedimentary rocks but morphosed under T and P The
rocks are under tons and tons of pressure, which fosters heat build up, and this causes
them to change. If you exam metamorphic rock samples closely, you'll discover how
flattened some of the grains in the rock are.
Agents of Metamorphism and The Type of Metamorphism
Changes occur because of:
Heat ,Pressure ,Chemical fluids
Rocks adjust to become more stable under new, higher temperatures and pressures.
Heat:There are several sources of heat for metamorphism.
Geothermal gradient
Regional Metamorphism
Contact Metamorphism
2 ) Pressure
>> Burial Pressure.
>>Regional Metamorphism.
>>Tectonic pressures
>> Regional Metamorphism.
>>Dynamic Metamorphism
Rocks formed along fault zones are called mylonites.
3 Chemical Fluids
>>hydrothermal solution
>> Black smokers
How do rocks change?
Metamorphism causes changes in:
1. Texture
2. Mineralogy
Texture
The processes of compaction and recrystallization change the texture of rocks during
metamorphism.
1. Compaction

The grains move closer together.

The rock becomes more dense.

Porosity is reduced.

Example: clay to shale to slate
2.Recrystallization
Metamorphic Textures
1. Foliation is a broad term referring to the alignment of sheet-like minerals.
Types of foliation:
Schistosity
Slaty cleavage –
Phyllitic structure Gneissic banding –
Lineation refers to the alignment of elongated, rod-like minerals such as amphibole,
pyroxene, tourmaline, kyanite, etc.
2. Non-foliated or granular metamorphic rocks are those which are composed of
equidimensional grains such as quartz or calcite. There is no preferred orientation.
The grains form a mosaic.
Examples: quartzite derived from the metamorphism of quartz sandstone,
and marble derived from the metamorphism of limestone or dolostone.
Grade of Metamorphism
1.Prograde metamorphism
Prograde metamorphism involves the change of mineral assemblages with increasing
temperature and (usually) pressure conditions. These are solid state dehydration reactions, and
involve the loss of volatiles such as water or carbon dioxide. Prograde metamorphism results in
rock characteristic of the maximum pressure and temperature experienced. Metamorphic rocks
usually do not undergo further change when they are brought back to the surface.
2,Retrograde metamorphism
Retrograde metamorphism involves the reconstitution of a rock via revolatisation under
decreasing temperatures (and usually pressures), allowing the mineral assemblages formed in
prograde metamorphism to revert to those more stable at less extreme conditions. This is a
relatively uncommon process, because volatiles must be present.
Minerals orientation becomes in the direction of stress applied.
Type of metamorphism
1. Dynamic/Cataclastic metamorphism
Dynamic metamorphism is associated with zones of high to moderate strain such as
faultzones. Cataclasis, crushing and grinding of rocks into angular fragments, occurs in
dynamic metamorphic zones, giving cataclastic texture.
The textures of dynamic metamorphic zones are dependent on the depth at which they
were formed, as the temperature and confining pressure determine the deformation
mechanisms which predominate. Within depths less than 5 km, dynamic metamorphism
is not often produced because the confining pressure is too low to produce frictional heat.
Instead, a zone of breccia or cataclasite is formed, with the rock milled and broken into
random fragments. This generally forms a mélange. At depth, the angular breccias transit
into a ductile shear texture and into mylonite zones.
2. Contact metamorphism
Contact metamorphism occurs typically around intrusive igneous rocks as a result of the
temperature increase caused by the intrusion of magma into cooler country rock. The area
surrounding the intrusion where the contact metamorphism effects are present is called
the metamorphic aureole. Contact metamorphic rocks are usually known as hornfels.
Rocks formed by contact metamorphism may not present signs of strong deformation and
are often fine-grained.
3. Regional metamorphism
Regional or Barrovian metamorphism covers large areas of continental crust typically
associated with mountain ranges, particularly subduction zones or the roots of previously
eroded mountains. Conditions producing widespread regionally metamorphosed rocks
occur during an orogenic event. The collision of two continental plates or island arcs with
continental plates produce the extreme compressional forces required for the
metamorphic changes typical of regional metamorphism
SO. WE CAN CONCLUDE THE ROCK CYCLE:
CHAPTER -2
PETROGRAPHY
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. The mineral
content and the textural relationships within the rock are described in detail. Petrographic
descriptions start with the field notes at the outcrop and include megascopic description of hand
specimens. However, the most important tool for the petrographer is the petrographic
microscope. The detailed analysis of minerals by optical mineralogy in thin section and the
micro-texture and structure are critical to understanding the origin of the rock. Electron
microprobe analysis of individual grains as well as whole rock chemical analysis by atomic
absorption or X-ray fluorescence are used in a modern petrographic lab. Individual mineral
grains from a rock sample may also be analyzed by X-ray diffraction when optical means are
insufficient. Analysis of microscopic fluid inclusions within mineral grains with a heating stage
on a petrographic microscope provides clues to the temperature and pressure conditions existent
during the mineral formation.
Methods of investigation
Macroscopic characters
The macroscopic characters of rocks, those visible in hand-specimens without the aid of the
microscope, are very varied and difficult to describe accurately and fully. The geologist in
the field depends principally on them and on a few rough chemical and physical tests; and
to the practical engineer, architect and quarry-master they are all-important. Although
frequently insufficient in themselves to determine the true nature of a rock, they usually
serve for a preliminary classification, and often give all the information needed.
There are some tools which are used in Macroscopic characters:
 With a small bottle of acid to test for carbonate of lime.
 a knife to ascertain the hardness of rocks and minerals.
 pocket lens to magnify their structure
 Other simple tools include the blowpipe to test the fusibility of detached crystals, the
goniometer, the magnet, the magnifying glass and the specific gravity balance
It is easy to see that a sandstone or grit consists of more or less rounded, water-worn sand grains
and if it contains dull, weathered particles of feldspar, shining scales of mica or small crystals of
calcite these also rarely escape observation. Shales and clay rocks generally are soft, fine
grained, often laminated and not infrequently contain minute organisms or fragments of plants.
Limestones are easily marked with a knife-blade, effervesce readily with weak cold acid and
often contain entire or broken shells or other fossils. The crystalline nature of a granite or basalt
is obvious at a glance, and while the former contains white or pink feldspar, clear vitreous quartz
and glancing flakes of mica, the other shows yellow-green olivine, black augite, and gray
stratiated plagioclase.
Microscopic characteristics
When dealing with unfamiliar types or with rocks so fine grained that their component minerals
cannot be determined with the aid of a hand lens, a microscope is used. Characteristics observed
under the microscope include colour, colour variation under plane polarised light (pleochroism,
produced by the lower Nicol prism, or more recently polarising films), fracture characteristics of
the grains, refractive index (in comparison to the mounting adhesive, typically Canada Balsam),
and optical symmetry (birefringent or isotropic).
Separation of components
eparation of the ingredients of a crushed rock powder to obtain pure samples for analysis is a
common approach. It may be performed with a powerful, adjustable-strength electromagnet. A
weak magnetic field attracts magnetite, then haematite and other iron ores. Silicates that contain
iron follow in definite order—biotite, enstatite, augite, hornblende, garnet, and similar ferromagnesian minerals are successively abstracted. Finally, only the colorless, non-magnetic
compounds, such as muscovite, calcite, quartz, and feldspar remain. Chemical methods also are
useful.
Methods of separation by specific gravity have a still wider application. The simplest of these is
levigation—treatment by a current of water. Fluids are used that do not attack most rock-forming
minerals, but have a high specific gravity. Solutions of potassium mercuric iodide (sp. gr. 3.196),
cadmium borotungstate (sp. gr. 3.30), methylene iodide (sp. gr. 3.32), bromoform (sp. gr. 2.86),
or acetylene bromide (sp. gr. 3.00) are the principal fluids employed. They may be diluted (with
water, benzene, etc.) or concentrated by evaporation.
Chemical analysis
chemical research methods of are of great practical importance. Crushed and separated powders,
obtained by the processes above, may be analyzed to determine chemical composition of
minerals in the rock qualitatively or quantitatively. Chemical testing, and microscopic
examination of minute grains is an elegant and valuable means of discriminating between
mineral components of fine-grained rocks.
Thus, the presence of apatite in rock-sections is established by covering a bare rock-section with
ammonium molybdate solution. A turbid yellow precipitate forms over the crystals of the
mineral in question (indicating the presence of phosphates). Many silicates are insoluble in acids
and cannot be tested in this way, but others are partly dissolved, leaving a film of gelatinous
silica that can be stained with coloring matters, such as the aniline dyes (nepheline, analcite,
zeolites, etc.).
Complete chemical analysis of rocks are also widely used and important, especially in describing
new species. Rock analysis has of late years (largely under the influence of the chemical
laboratory of the United States Geological Survey) reached a high pitch of refinement and
complexity. As many as twenty or twenty-five components may be determined, but for practical
purposes a knowledge of the relative proportions of silica, alumina, ferrous and ferric oxides,
magnesia, lime, potash, soda and water carry us a long way in determining a rock's position in
the conventional classifications.
A chemical analysis is usually sufficient to indicate whether a rock is igneous or sedimentary,
and in either case to accurately show what subdivision of these classes it belongs to. In the case
of metamorphic rocks it often establishes whether the original mass was a sediment or of
volcanic origin.
Specific gravity
Specific gravity of rocks is determined by means of a balance and pycnometer. It is greatest in
rocks with the most magnesia, iron, and heavy metals—least in rocks rich in alkalis, silica, and
water. It diminishes with weathering and, generally, highly crystalline rocks have higher specific
gravity than wholly or partly vitreous rocks of the same chemical composition. The specific
gravity of the commoner rocks ranges from about 2.5 to 3.2.
The broad explanation of rocks and textures and composition has been given in the previous
chapter and in this chapter I explain about grains and their microscopic view.
Diagenesis
Refers to processes that lithify sediments or make them into a solid sedimentary rock. It may
occur at or very near surface, but more commonly occurs after sediments are buried.
Diagenetic Processes
1. Weathering and Erosion- from pre-existing rocks
2. Transportation- movement from one place to another (by wind, water, or ice material is then
deposited.
3. Compaction -- due to pressure; fine-grained sediments undergo more compaction than coarse
sediments
4. Cementation -- precipitation of minerals around sediments (commonly quartz or calcite are
precipitated)
5. Recrystallization -- due to pressure, temperature changes
6. Lithification -- squeezing out of fluid to make final solid rock
There are two types of grains after diagenesis:
1. Sorting - terms referring to the range of particle sizes in clastic rocks (well- or poorly-sorted)
2. Roundness - degree of smoothness of particle edges and sphericity. (Well-rounded and
angular)
Durham’s classification of carbonate rocks
Some basic structure are there which can be identified by macroscopic view
. Ripple marks - undulations on a sand surface produced by wind or water (asymmetrical or
symmetrical)
2. Cross-bedding - inclined layering produced in sand by ripples or dunes at an angle to the
horizontal
3. Mudcracks (desiccation cracks) - polygonal pattern of cracks produced on the surface of mud
as it dries.
4. Raindrop imprints - circular pits produced by the impacts of rain on soft mud
5. Graded bedding - progression of grain sizes from coarser at the bottom to finer on top (or
vice-versa)
6. Flute marks - scoop-shaped depressions preserved on the bottom surface of muddy beds. Good
indicator of top and bottom of bed.
7. Tool marks - ridges or discontinuous marks with a preferred orientation on bottom surfaces of
beds. Indicates current direction.
8. Tracks-footprints of organics, dinosaur footprints. Trails are caused as organism crawls
through mud or sediment. Burrows - excavations made by organisms in soft sediment commonly
filled with different sediment
9. Stromatolites-mound-like structures formed when sediment is trapped by blue-green algae.
Characteristic of limestones. Oldest life form on Earth.
10. Stylolites-pressure solution cracks formed as pressure squeezes solution through fractures in
carbonates.
By the sorting and roundness we can identified the diagenesis degree of the sedimentary
Igneous Rock Classification Lab
Igneous Rock Classification
Identification of Igneous rocks is based on two main characteristics
Texture – the appearance of the rock due to the rate of magma cooling.
Composition – the type of minerals found in the rock (mineral composition).
Textures of igneous rocks
Intrusive rocks (Textural terms)
phaneritic texture – crystals are visible and form a mosaic of interlocking mineral aggregates
(less than 1 cm)
porphyritic texture – crystals can be separated into two distinct visible sizes. There can be
small grains or large grains, but crystals appear in 2-distinct sizes.
Vesicular texture- sponge like appearance, texture contains numerous cavities or holes.
Pyroclastic texture – textures created by rapidly cooling lava that is “hurled” through the air
picking up fragments(tuffaceous texture) .
Igneous Rock Composition
mineral composition = mineral assemblages= chemistry The mineral is either ferromagnesian
(dark colored) or felsic (light colored).
ferromagnesian (mafic) :minerals rich in Fe, Mg – creates a dark colored rocks
Pyroxene (Augite)
Amphibole (hornblende)
Mica - Biotite
COMMON ROCK-FORMING MINERALS
Nesosilicates
Olivine (Mg,Fe)2SiO4 I, m 2MgO SiO2
Garnet
3MgO Al2O3 3SiO2
"Red" garnets (Mg,Fe,Mn)3Al2Si3O12 i, M
"Green" garnets Ca3(Cr,Al,Fe3+)2Si3O12 m
Zircon ZrSiO4 i, s, m
Alumino-silicate Al2SiO5 M
Andalusite M
Sillimanite M
Kyanite
Staurolite FeAl9O6(SiO4)4(O,OH)2 M
Titanite (Sphene) CaTiSiO5 i, m
Sorosilicates
Epidote Ca2(Al,Fe)Al2O(SiO4)(Si2O7)(OH) m
Cyclosilicates
Beryl Be3Al2(Si6O18) i
Tourmaline (Na,Ca)(Li,Mg,Al)(Al,Fe,Mn)6 i, m
(BO3)3Si6O18(OH)4
Name And Composition
QUARTZ-SiO2 H 7, vitreous, colourless, crystalline, conchoidal fracture no cleavage
FELDSPAR
ORTHOCLASE - KAlSi3O8
H 6 distinct cleavages subvireous, even fracture
PLAGIOCLASE - NaAlSi3O--CaAl2Si2O H6 distinct cleavages subvitreous even fracture
MICA
MUSCOVITE - KAl3Si3O10(OH)2 platey, H 2 book, asterism
BIOTITE - K(Mg ,Fe)3AlSi3O10(OH)2 platey, H2 book, asterism black
colourless
FERROMAGNESIAN MINERALS
HORNBLENDE - Ca2Na(Mg,Fe)4(Al,Fe,Ti)3Si6O22(O,H)2 greenish black
PYROXENE
Ca(Mg,Fe,Al)
(Si,Al)2O6
greenish
black
H
OLIVINE - (Fe,Mg)2SiO4 green
CALCITE - CaCO3, H 3, even fracture, gives CO2 to acid
GYPSUM - CaSO4.2H2O H 2
HALITE - NaCl
H5.5-6
5.5-6.
CHAPTER-3
MINERAL
What is a Mineral?
Minerals are the major solid constituents of the earth
Hard to define but substances having the stated properties are termed as minerals.
1.Naturally occurring
2. Inorganic
3. Solid
4. Definite chemical composition
5. Orderly internal crystal structure
Define physical properties? What are these ?
Can you name some?
Polymorphs Two minerals having
similar chemical composition
But different crystal structure
Different crystalline structures, or how the atoms and molecules are arranged, result in different
minerals.
e.g. diamond and graphite. (atomic diagram if possible.)
Both minerals are composed of carbon (C), the same chemical composition.
Physical Properties
1.Color and Some Related Properties of Minerals
Minerals are colored because certain wavelengths of light are absorbed, and the mineral
color then results from the combination of those wavelength which reach the eye.
If light is not absorbed, the mineral is colorless in reflected or refracted light
black fall wave-of light are absorbed.
2.- Hardness Resistance to scratching or abrasion.
A. Moh's Hardness Scale
-a listing of minerals with increasing relative hardness 1-10-
1. talc
6. feldspar
2. gypsum
7. quartz
3. calcite
8. topaz
4. fluorite
9. corundum
5. apatite
10.diamond
-the following can be assigned a hardness in this scaleglass = 5.5; knife = 5.5; steel file = 6-7; fingernail = 2.5; penny = 3
-the hardness of a mineral can differ slightly in the direction of scratching--kyanite
between a hardness of 5 to 7, and calcite between 2 and 3
3. Tenacity
--the cohesiveness of a mineral, or the resistance a mineral offers to breaking, crushing,
bending or tearing-1. brittle--if a mineral powders easily
2. malleable--if a mineral can be hammered into sheets
3. sectile--if a mineral can be cut into thin shavings with a knife
4. ductile--if a mineral can be drawn into wire
5. flexible--if a mineral is bent but does not resume the original shape
6. elastic--if a mineral bends and resumes the original shape
4.Streak
--is the color of the powder from the mineral on a porcelain plate (streak plate)---since most minerals are softer than porcelain (8 hardness on Moh's Scale), their powder will
remain after scratching it on the streak plate
5. Luster
--is the general appearance of the surface of a mineral in reflected light--minerals can have a
metallic luster
non metallic luster sub metallic luster
some specific types of non metallic luster are:
1. Vitreous -resembles glass--quartz crystals
2. Resinous -resembles a resin--sulfur and sphalerite
3. Pearly -pearl-like and present on mineral surfaces paralleling cleavage planes--talc
4. Greasy-appears to be covered by oil or grease--massive quartz
5. Silky-silk or satin-like--satin spar gypsum
6. Adamantine-brilliant looking minerals which have a high index of refraction—
diamond.
6.Taste Nerve ending reaction in the tongue to different chemicals e.g halite
7.Cleavage Breakage of a mineral along planes of weakness in the crystal structure
-breakage is along atomic planes.
cleavage is consistent with crystal symmetry and may be one to multi-directional from one
mineral to another.
--micas
=
one
direction
of
-feldspars,
pyroxenes
and
amphiboles
=
two
directions
--calcite and dolomite = three directions of cleavage (rhombohedral)
of
cleavage
cleavage
-cleavage may be of various qualities as perfect, good, fair or poor but the same
cleavage quality and quantity will be present in all specimens of the same mineral
-the presence of cleavage in a mineral is often observed by reflecting light off a fresh
surface and observing a stair like arrangement of thin parallel layers
8.Parting
-breakage of minerals along planes of structural weakness such as twinning planes
-unlike cleavage, parting is not shown by all specimens of the same mineral but
only those which are twinned or formed under special pressure conditions
C. Fracture
Breakage of a mineral, not along planes of weakness in the crystral structure.
Properties and Causes of Fracture
Fracturing may at times follow cleavage planes,
Does not produce a new face that is flat, nor will that surface be a potential crystal face
except by random chance.
A fracture will be irregular, usually showing frequent changes in its direction.
Fractures are not reproducible either within the same crystal, or between crystal specimens.
Fracture will simply follow the path of greatest local weakness that relieves the stress causing
it as it progresses through the mass of the crystal.
There are six (6) generally accepted types of fracture.
These are:
a). Subconchoidal Fracture - Is similar to conchoidal fracture,
only it is not as curved. It may often appear as warped, nearly flat, planes.
e.g. Euxenite is an example of both subconchoidal and conchoidal fracture.
b).Uneven Fracture - produces surfaces that are not smooth or curved, but instead have a rough
or somewhat ragged appearance. E.g. Gummite is a good example of uneven fracture.
c).Earthy Fracture - produces a surface that has a texture similar to that of clay.
It is usually found in minerals that are composed of extremely small microcrystals or are very
weak in their physical structure. It may be thought of as being like uneven fracture, but on a
much smaller reference scale. This Coconinoite is an excellent example of earthy fracture.
d.Splintery Fracture - occurs in fibrous or acicular minerals that are relatively stronger along
one axis than they are along the others. This produces fragments that are usually longer along
that dimension than they are in cross-section. e.g.Coproskiodowskite is a good example of a
splintery fracture.
e.Conchoidal Fracture - produces a smoothly curved that is characteristic of broken obsidian,
commonly called natural glass.
It is sometimes described as a 'clamshell' fracture due to the curved, hollow, clamshell shaped
fractures it produces.
E.g. Melanocerite shows many excellent examples of conchoidal fracture
D. Specific Gravity
-a number that expresses a ratio between a substance and the weight of an equal volume of water
at 4 degrees C--the number is the same for that of the density without units -specific gravity
(S.G.)
depends on
(1) the kind of atoms comprising a mineral (atomic weight)
(2) the packing of the atoms (close packing or loosely packed)
-S.G. can be measured with a Jolly Balance which determines the weight of a mineral in air and
the loss of weight in water--the S.G. number is then obtained by dividinweight in air by the loss
of weight in water
Significance and conclusion
Minerals are the building blocks of rocks.
They grow or breakdown by chemical reactions
Thus provide information for interpreting the changes
that have occurred in the earth through out the history.
>> Important commercially. (muscovite)
ORE MINERALS
An ore is a type of rock that contains minerals with important elements including metals. The
ores are extracted through mining; these are then refined to extract the valuable element(s).
The grade or concentration of an ore mineral, or metal, as well as its form of occurrence, will
directly affect the costs associated with mining the ore. The cost of extraction must thus be
weighed against the metal value contained in the rock to determine what ore can be processed
and what ore is of too low a grade to be worth mining. Metal ores are generally oxides, sulfides,
silicates, or "native" metals (such as native copper) that are not commonly concentrated in the
Earth’s crust or "noble" metals (not usually forming compounds) such as gold. The ores must be
processed to extract the metals of interest from the waste rock and from the ore minerals. Ore
bodies are formed by a variety of geological processes. The process of ore formation is called or
genesis.
Extraction
The basic extraction of ore deposits follows the steps below;
1. Prospecting or exploration to find and then define the extent and value of ore where it is
located ("ore body")
2. Conduct resource estimation to mathematically estimate the size and grade of the deposit
3. Conduct a pre-feasibility study to determine the theoretical economics of the ore deposit.
This identifies, early on, whether further investment in estimation and engineering studies
is warranted and identifies key risks and areas for further work.
4. Conduct a feasibility study to evaluate the financial viability, technical and financial risks
and robustness of the project and make a decision as whether to develop or walk away
from a proposed mine project. This includes mine planning to evaluate the economically
recoverable portion of the deposit, the metallurgy and ore recoverability, marketability
and payability of the ore concentrates, engineering, milling and infrastructure costs,
finance and equity requirements and a cradle to grave analysis of the possible mine, from
the initial excavation all the way through to reclamation.
5. Development to create access to an ore body and building of mine plant and equipment
6. The operation of the mine in an active sense
7. Reclamation to make land where a mine had been suitable for future use
SOME ORE MINERALS
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
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Argentite: Ag2S for production of silver
Barite: BaSO4
Bauxite Al(OH)3 and AlOOH, dryed to Al2O3 for production of aluminium
Beryl: Be3Al2(SiO3)6
Bornite: Cu5FeS4
Cassiterite: SnO2
Chalcocite: Cu2S for production of copper
Chalcopyrite: CuFeS2
Chromite: (Fe, Mg)Cr2O4 for production of chromium
Cinnabar: HgS for production of mercury
Cobaltite: (Co, Fe)AsS
Columbite-Tantalite or Coltan: (Fe, Mn)(Nb, Ta)2O6
Galena: PbS
Gold: Au, typically associated with quartz or as placer deposits
Hematite: Fe2O3
Ilmenite: FeTiO3
Magnetite: Fe3O4
Molybdenite: MoS2
Pentlandite:(Fe, Ni)9S8
Pyrolusite:MnO2
Scheelite: CaWO4
Sphalerite: ZnS
Uraninite (pitchblende): UO2 for production of metallic uranium
Wolframite: (Fe, Mn)WO4
INDUSTRIAL MINERALS
Abrasives, natural - Diamonds, garnets (almandine, pyrope and andradite), corundum (emery).
Barite - A major use for barite is as a weight increasing additive for drilling oil and gas wells.
Calcite - A major source for this mineral is limestone. It has been used for the manufacture of
cement, application to agricultural lands for pH control, as a building material, and crushed for
gravel.
Clays - Used in the manufacture of bricks, tiles and as a filler for paper etc.
Attapulgite
Ball
Bentonite
Calcium
Common
*Minerals
Fire
Clay Hectorite*
Kaolinite*
Bentonite Meerschaum
Clay Palygorskite*
Clay Refractory
Clay
Saponite*
Sepiolite*
Shale
Sodium Bentonite
Feldspars - Used in manufacture of glass, ceramics and enamels. Includes orthoclase,
microcline, and albite (member of the plagioclase series).
Gemstones - The most valuable total gemstone production is diamond; corundum varieties, ruby
and sapphire; beryl varieties emerald, aquamarine, and kunzite. Many other semiprecious
gemstones are mined for decorative and jewelry use.
Gypsum - A major source for Portland cement, plaster of Paris, a soil conditioner, and an
important component in drywall.
Perlite - Used in lightweight aggregates.
Soda Ash (sodium carbonate) - Primary production from trona, nahcolite and brines.
Zeolites - The primary natural production of zeolites include the minerals chabazite,
clinoptilolite, and mordenite.
Miscellaneous mineral production - wollastonite, vermiculite, talc, pyrophyllite, graphite,
kyanite, andalusite, muscovite, and phlogopite.
Fossils
Fossils (from Latin fossus, literally "having been dug up") are the preserved remains or traces of
animals (also known as zoolites), plants, and other organisms from the remote past. The totality
of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossilcontaining) rock formations and sedimentary layers (strata) is known as the fossil record.
Like extant organisms, fossils vary in size from microscopic, such as single bacterial cells[4] only
one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and
weighing many tons. A fossil normally preserves only a portion of the deceased organism,
usually that portion that was partially mineralized during life, such as the bones and teeth of
vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Preservation of soft
tissues is rare in the fossil record. Fossils may also consist of the marks left behind by the
organism while it was alive, such as the footprint or feces (coprolites) of a reptile. These types of
fossil are called trace fossils (or ichnofossils), as opposed to body fossils. Finally, past life leaves
some markers that cannot be seen but can be detected in the form of biochemical signals; these
are known as chemofossils or biomarkers.
CHAPTER-4
Stratigraphy
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The study of strata (layers) of rocks with an eye toward interpreting the geologic
history of the region
Closely tied to dating methods
Uses a variety of methods - fossils, stable isotopes, paleomagnetic, sedimentary
cycles - to correlate and distinguish layers.
Very important for oil exploration and mining.
Collection of Stratigraphic Data
Stratigraphic Procedures
Out crop procedures
Selection of sections to be measuredGood exposure
Spacing between sections
Amount of stratigraphic column
Degree of exposure or cover
Structural simplicity
Accessibility
Type area or stratotype
Standard for correlation
Well exposed section if subsurface should be accessible via a record of well cuttings etc.
Complete as possible
Include upper and the lower contacts of units
Continuous and un faulted
Fresh exposures
Description of measured section
Thickness- formation & members
Stratigraphic relations
Lithology
Stratification
Internal structure
Weathering behavior
Paleontology
Measuring Horizontal strata


Accurate measures of elevation
Methods
A) hand level
B) Jake stick or Jacob’s staff- slope encountered
Stratigraphic Principles
Principle of stratigraphic superposition
Oldest rocks are on the bottom
Youngest rocks are on the top
Dead Horse Point, UT
Principle of original lateral continuity:
Sedimentary layers don’t just stop suddenly
They extend horizontally until they taper out
Graybull, WY
Principle of unconformities
Some stratigraphic sections are incomplete
Any place where there is missing time is called an unconformity
Unconformities normally happen either through erosion or non-deposition
The Great Unconformity,Grand Canyon, AZ
Disconformity
Nonconformity
Stratigraphic Thinking
One
possible
interpretation
Chapter-5
CRYSTALLOGRAPHY
CRYSTALLOGRAPHY is the study of crystals. It is a division of the entire study of
mineralogy.
1) Geometrical Crystallography
2) Physical Crystallography
3) Chemical Crystallography.
A CRYSTAL is a regular polyhedral form, bounded by smooth faces, which is assumed by a
chemical compound, due to the action of its interatomic forces, when passing, under suitable
conditions, from the state of a liquid or gas to that of a solid.
During the process of crystallization, crystals assume various geometric shapes dependent on the
ordering of their atomic structure and the physical and chemical conditions under which they
grow.These forms may be subdivided, using geometry, into six systems :
•
(1) CUBIC
•
(2) TETRAGONAL
•
(3) ORTHORHOMBIC
•
(4) HEXAGONAL
•
(5) MONOCLINIC
•
(6) TRICLINIC
Before we continue some factors should be clear to the reader:

Crystal is a polyhedral form bounded with geometrical faces
o Forms – arrangement of certain faces in a crystal
o Faces – rectangular, triangle, square, trapezium, rhambus


Interfacial angle – Angle between any two adjacent faces
o It is measured by a) Contact goniometer, optical goniometer,
goniometer
Axes - Reference line

Axial ratio

Parameter – face in relationship to axes Relative to intercepts by crystal faces
o 1/a, 1/3b, 1/2c
1:1/3:1/2 0:2:3
Holohedral forms : Normal class Maximum possible symmetries
Hemihedral forms :half of numer of faces of normal class +ve & -ve forms
Normal class Octahedron 8 ---- >Tetrahedron 4 faces
Hemimorphic forms
:Half of the numbers of faces of hemihedral forms
Tourmaline, Zincite
Enantiomorphic forms :Right and left handed mirror image forms with Identical
mathematical relationships one form is no interchanged Right handed quartz – Left
handed quartz . Quartz with trigonal trapezohedron dipyramid R and L sides.
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Theodolite
length of axes constant -Law of constancy if axial ratios.
Fundamental forms
o Closed form : Fully enclosed Octahedron (111)
o Open forms :Pinacoids and Prisms.
Planes of Symmetry
Any two dimensional surface that, when passed through the center of the crystal, divides it into
two symmetrical parts that are MIRROR IMAGES is a PLANE OF SYMMETRY.
A cube has 9 planes of symmetry, 3 of one set and 6 of another.
In the left figure the planes of symmetry are parallel to the faces of the cube form, in the right
figure the planes of symmetry join the opposite cube edges.
Axes of Symmetry
Any line through the center of the crystal around which the crystal may be rotated so that after a
definite angular revolution the crystal form appears the same as before is termed an axis of
symmetry. Depending on the amount or degrees of rotation necessary, four types of axes of
symmetry are possible when you are considering crystallography:
When rotation repeats form every 60 degrees, then we have six fold or HEXAGONAL
SYMMETRY.
When rotation repeats form every 90 degrees, then we have fourfold or TETRAGONAL
SYMMETRY.
When rotation repeats form every 120 degrees, then we have threefold or TRIGONAL
SYMMETRY.
When rotation repeats form every 180 degrees, then we have twofold or BINARY
SYMMETRY.
CENTER OF SYMMETRY
Most crystals have a center of symmetry, even though they may not possess either planes of
symmetry or axes of symmetric .Triclinic crystals usually only have a center of symmetry. If you
can pass an imaginary line from the surface of a crystal face through the center of the crystal (the
axial cross) and it intersects a similar point on a face equidistance from the center, then the
crystal has a center of symmetry.
Note: The crystal face arrangement symmetry of any given crystal is simply an expression of
the internal atomic structure. The relative size of a given face is of no importance, only the
angular relationship or position to other given crystal faces.
THE SHAPES OF CRYSTALS ARE EXPLAINED BELOW:
(1) CUBIC (aka ISOMETRIC)
The three crystallographic axes a1, a2, a3 (or a, b, c) are all equal in length and intersect at
right angles (90 degrees) to each other.
(2) TETRAGONAL
Three axes, all at right angles, two of which are equal in length (a and b) and one (c)
which is different in length (shorter or longer).
Note: If c was equal in length to a or b, then we would be in the cubic system.
(3) ORTHORHOMBIC
Three axes, all at right angles, and all three of different lengths.
Note: If any axis was of equal length to any other, then we would be in the tetragonal system!
4) HEXAGONAL
Four axes! Three of the axes fall in the same plane and intersect at the axial cross at 120 degrees
between the positive ends. These 3 axes, labeled a1, a2, and a3, are the same length. The fourth
axis, termed c, may be longer or shorter than the a axes set. The c axis also passes through the
intersection of the a axes set at right angle to the plane formed by the a set.
(5) MONOCLINIC
Three axes, all unequal in length, two of which (a and c) intersect at an oblique angle (not 90
degrees), the third axis (b) is perpendicular to the other two axes.
Note: If a and c crossed at 90 degrees, then we would be in the orthorhombic system!
(6) TRICLINIC
The three axes are all unequal in length and intersect at three different angles (any angle but 90
degrees).
Note: If any two axes crossed at 90 degrees, then we would be describing a monoclinic crystal.
Chapter-6
petroliferous basins
Sedimentary basins refers to a geographical feature exhibiting subsidence and consequent
infilling by sedimentation. On burial they are subjected to increasing pressure and begin the
process of lithification. The sedimentary basins of India occupy an area of 3.14 million sq. km.
of which 3,20,000 sq. km. is in the offshore up to 200m isobaths. There are total 26 sedimentary
basins out of which 13 are important for Hydrocarbon reserves.
Basin classification Category- I is the petroliferous basins with proved hydrocarbon reserves and
where commercial production has already started. These basins are:
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Assam shelf
Bombay offshore
Cambay
Cauvery
Tripura
Krishna-Godavari
Category – II comprises basins with occurrence of hydrocarbons but from which no commercial
production has been obtained yet . Category – III comprises basins with no significant oil & gas
shows but which on Geological considerations are considered to be prospective. Category – IV
comprises uncertain prospects. It includes the basins which bear an analogy with hydrocarbon
producing basins in the world.
Assam–Arakan Basin :
Assam–Arakan Basin It includes Assam, Nagaland, Arunachal Pradesh, Manipur, Mizoram and
Tripura. The Assam shelf has an extent of 40,000 sq.km. and includes the Shillong Plateau, the
Garo, Khasi, Jaintia, Mikir Hills and the upper Assam valley.
Tectonic History
The Assam-Arakan sedimentary Basin is a shelf–slope–basinal system. The shelf part of the
basin spreads over the Brahmaputra valley and the Dhansiri valley, the latter lying between the
Mikir hills and the Naga foothills. From the Digboi, the shelf runs westward to the southern
slope of the Shillong plateau. The shelf-to-basinal slope, i.e., the hinge zone lies below the Naga
schuppen belt. The basinal (geosynclinal) part is occupied by the Cachar, Tripura, Mizoram and
Manipur
fold
belts.
The shelf part rests on Precambrian granitic basement, whereas the basinal part lies on
transitional to oceanic crust. The area within the Upper Assam shelf, having high petroleum
potential, measures approximately 56000 sq km and contains about 7000m thick sediments of
mostly Tertiary period, and the area in the basinal part with moderate to high hydrocarbon
potential measures about 60,000 sq km and contains more than 10,000m thick sediments of
mostly
Tertiary
period.
The major structural elements of the Assam–Arakan Basin and the salient features of each
element
are
briefly
described
as
following.
Upper Assam Shelf
1. Southerly to southeasterly moving thrust sheets of younger (Miocene to Plio-Pleistocene)
sedimentary rocks in the Assam Himalayan foothills.
2. The Himalayan Foredeep zone north of the Brahmaputra river lies in the northern
periphery of the foredeep is overridden by the southerly moving thrust sheets of younger
sedimentary rocks.
3. The Brahmaputra-Arch, running along the southeastern side of the Brahmaputra river in
Upper Assam.
4. The southeastern slope of the Upper Assam Shelf, southeast of the Brahmaputra arch,
having local structural highs and lows, upto the Naga thrust, and extending 8 to 10 km
beneath the Naga schuppen belt . This element contains most of the oil fields of the
Upper Assam Shelf.
5. The Shillong Plateau and Mikir hills Uplift, composed mostly of Precambrian granitic
and metamorphic rocks. The southern slope of the Shillong Plateau exposes Gondwana,
Cretaceous and Tertiary rocks.
Shelf–To–Basinal Slope To Basinal Area
1. The Naga Schuppen Zone,occurring between the Naga and the Disang thrusts. In this
shelf–slope–basinal architecture, the hinge zone, at and across which the Upper
Cretaceous-Eocene shelf facies changes over to basinal facies, is envisaged to lie below
the Naga schuppen belt. The Kharsang, Digboi and Champang oil fields are located in
this element.
2. The Assam – Arakan Fold Belt This fold belt may be divided into two zones bounded
by prominent thrusts, viz, (i) the Naga fold zone, lying in between the Disang and Tapu
thrusts and having exposures of Disang shales and Barail sediments, and (ii) the central
flysch zone, lying between the Tapu thrust and Changrang – Zunki thrust and having
exposures of mainly Disang shales.
3. The Zunki schuppen belt, containing mostly older Disang shales (Upper Cretaceous) &
occurring between the Zunki and Moya thrusts.
4. The Ophiolite Complex, occurring in between the Moya and the Eastern thrust. Disang
shales, occurring in association with ophiolites, are somewhat metamorphosed here.
5. The Naga Metamorphic Complex, east of the Eastern thrust. The metamorphic complex
occurs mostly to the east of the Indo-Myanmar international border.
Stratigraphy:.
Sedimentary sequences ranging in age from Late Mesozoic to Cenozoic are exposed in the
Assam-Arakan Basin. The sequences can be divided into shelf facies and basinal (geosynclinal)
facies. The shelf facies occur in Garo hills, Khasi-Jaintia hills, parts of North Cachar hills and
Mikir hills, and below the alluvial cover in Upper Assam, Bengal and Bangladesh. The basinal
facies occur in the Patkai range, Naga Hills, parts of North Cachar hills, Manipur, Surma valley,
Tripura, Chittagong hills of Bangladesh and Chin hills of Myanmar (Burma). The generalized
stratigraphic succession
Geological History
The Assam-Arakan basin witnessed two major phases of tectonic development. It developed as
a composite shelf-slope-basinal system under a passive margin setup during the period from
Early Cretaceous to the close of Oligocene. During the post- Oligocene time, however, different
parts of the mega basin witnessed different evolutionary trends, mostly under compressive
tectonic
forces.
During Middle to Late Cretaceous, when the Indian plate was moving northward, a number of
horst and graben features developed on the granitic crust in the southern slope of the Shillong
Plateau and Dhansiri valley. In these grabens, a sequence of sandstones, shales and subordinate
limestone towards top, assigned to the Khasi Group, was deposited in the southern slope of the
Shillong Plateau, and a sequence of sandstone and shale, assigned to the Dergaon Group, was
deposited in the Dhansiri valley. Presence of pelagic fauna indicates that these sediments were
deposited in shallow shelf to open marine conditions during Maestrichtian to Early Paleocene
time. During this time, the basinal area to the east and southeast witnessed deposition of Lower
Disang shales, radiolarian cherts and subordinate limestones in the distal deeper part of a
marginal downwarp, i.e., tilted broad shelf adjacent to ocean basin. The limestones with
negligible
impurities
were,
perhaps,
deposited
on
sea
mounds.
The Indo-Burmese trench system that developed during the oblique subduction of the Indian
plate below the Burmese plate became the locus of deposition of Upper Disang shales under
deep marine conditions. The formation of the trench system was, possibly, initiated in the
northeastern part and gradually progressed southward. The closing of the trench system was also
initiated in the northeast and then gradually progressed southward. The Andaman trench, which
has been receiving mostly argillaceous sediments since, possibly, Upper Cretaceous-Paleocene,
is
the
southward
extension
of
the
Indo
–
Burmese
trench
system.
During Paleocene, there was a marine transgression on the southern edge of the Shillong Plateau,
depositing sediments of the Therria Formation consisting of limestone, sandstone and shale. The
Lakadang Formation (Early Eocene) comprising limestone and coal bearing sandstones was
deposited in shallow marine to lagoonal conditions, while the overlying Tura Sandstone
Formation (Early Eocene) was deposited under fluvio-deltaic environment. The Tura Formation
is extensively developed in the Upper Assam Shelf and is oil bearing in Borholla, Champang and
Nahorkatiya
oil
fields.
During Eocene to Oligocene, due to the rise of the peripheral arc system (rise of the basement
ridge) consequent upon the active oblique subduction of the Indian plate, the intervening sea
became progressively narrower southward. During this period, the Assam Shelf was being
evolved in a passive margin tectonic setting and under shallow marine to brackish water
sedimentation
conditions.
Following the deposition of the Tura Sandstone, there was a wide spread marine transgression in
which the Sylhet Limestone (Middle Eocene) was deposited almost all over the Upper Assam
Shelf. Towards the close of Middle Eocene, limestone deposition ceased because of an increase
in the influx of finer clastics in the shelf. These clastics, making the lower part of the Kopili
Formation, were deposited in open marine conditions during Late Eocene, when marine
transgression was waning out. Further increase in the clastic influx in the stable shelf during Late
Eocene to Early Oligocene resulted in marine regression with the deposition of the upper part of
the Kopili Formation, consisting of shales, siltstone and subordinate sandstones, in shallow
marine to pro-delta environments. In the North Bank of the Brahmaputra river, however,
environmental conditions were deltaic with the deposition of sandstones with minor shales and
siltstones.
East of the hinge zone, i.e., in the basinal area, Upper Disang shales, which are lateral facies
equivalent of the Sylhet and Kopili formations, were deposited in deep water basinal conditions.
During shallowing of the sea in the basinal area, the succeeding sediments of the Barail Group
were deposited under environments ranging from moderately deep marine to deltaic.
Following completion of collision and subduction of the oceanic part of the Indian plate during
Late Oligocene (to Early Miocene?) when the continental part of the Indian plate seems to have
come close to Tibetan and Myanmar (Burmese) plates, there was upliftment and erosion all over
the shelf and in a major part of the basinal area. This event was followed by a pronounced south
to southeastward tilt of the basin, mostly the geosynclinal part, which was, perhaps, caused by
subduction related tectonic loading. This foredeep was the site of deposition of the Surma Group
of sediments under shallow marine (lower part) to brackish water (upper part) environments.
Continued indentation by the Indian plate caused westward propagation of tectonic forces, which
in turn caused development of a decollement thrust at the base of the Upper Disang shales, and a
number of synthetic thrust faults. These lateral tectonic movements were accompanied by
upliftment and total withdrawal of the sea, heralding the onset of continental sedimentation (the
Tipam Sandstone Formation) on the Assam Shelf as well as on the earlier basinal area. Presence
of radiolarian chert and ophiolite fragments in the lower part of the Tipam Sandstone in many of
the Dhansiri Valley and Upper Assam wells suggest that a certain fraction of the sediments
making the lower part of the Tipam Formation came from the rising Barail Range towards east
(Barail sediments in the Barail Range are reported to contain volcanogenic particles) or from the
Ophiolite
belt.
Towards the end of the Tipam Sandstone deposition, there developed a series of N-S to NE-SW
trending compressive structures in the basinal area. During the growth of these structures, the
Girujan Clay Formation was deposited in the synclinal lows (structural basins) in Cachar area as
indicated by seismic and well data from the Katakhal syncline of Cachar area where the Girujan
Clay Formation is named as the Govindpur Formation. The Girujan Formation in the eastern &
northeastern parts of the shelf also was deposited in structural lows. The most prominent
structural depression was formed in Kumchai – Manabhum area in front of the Mishmi uplift,
where the Girujan Clay Formation attains a thickness of about 2300m.
The development of the frontal foredeep in front of the rising Himalaya, during Mio-Pliocene
and later times, due to tectonic loading by thrust slices was filled with coarser sediments. During
this time, sedimentation in the Surma basin (including Sylhet trough) and the Kohima
synclinorium took place in intermontane basins, depositing the arenaceous Lower Dupitila
sediments over a post–Girujan unconformity and the argillaceous Upper Dupitilas over a postLower Dupitila unconformity. During Pleistocene time, there was the last major folding
movement and further upliftment of the Barail Range, the Central Disang uplift, the Mishmi
Hills and the Himalaya. The Dihing boulder conglomerates, shed by the rising mountains were
deposited at the feet/toes of the rising mountains. The Dhekiajuli Formation, consisting of mostly
soft sandstones, was deposited at the mountain fronts in the Upper Assam Shelf and in areas now
overridden by younger Naga thrust.
Petroleum
System:.
All the oil and gas fields, discovered till date in the Upper Assam shelf, are situated mostly on
the southeastern slope of the Brahmaputra arch, and almost all the major oil fields like
Nahorkatiya, Lakwa, Lakhmani, Geleki, Dikom Kathaloni etc. lie in a belt bordering the Naga
thrust. In the Dhansiri valley also, oil fields like the Borholla and Khoraghat and Nambar lie in
the same belt. In the Naga Schuppen belt, oil accumulations in the Lakshmijan and the
Champang oil fields occur in that zone of the shelf which is overridden by the Naga thrust. In the
Digboi and Kharsang oil fields, oil occurs in Tipam Sandstone and Girujan Clay formations,
respectively,
overlying
the
Naga
thrust.
Source Rock and Hydrocarbon Generation
The important source rock sequences occur within the argillaceous Kopili Formation and in the
Coal-Shale Unit of the Barail Group. The average TOC of shales within the Sylhet Formation is
about 0.60%, in the Kopili Formation, about 2.5% and in the Barail Coal-Shale Unit, about 3.8%.
The average TOC ranges of different formations (shale samples) are as follows:
Formation
Average TOC Range
Remarks
Barail (shales)
2.5% to 4.5%
Excellent source potential
Kopili (shales)
1% to 3%
Excellent source potential
Sylhet Limestone
~ 0.61%
Poor source potential
Basal Sandstone
~ 0.62%
Poor source potential
Organic matter richness of shales increases towards the Naga thrust. In both Kopilis and Barails, the
organic matter is terrestrial type-III with varying contributions of Type-II.
Barail Coal-Shale Unit in the Schuppen belt also form important source rock sequence. In the Naga
fold belt, in addition to above, Disang shales also possess excellent source rock characteristics with
TOC
around
4%
and
VRo
varying
from
0.69%
to
1.94%.
Geochemical analysis of exposed sediments from the Schuppen belt show a TOC range of 0.641.20% for Barail shales. The dominant organic matter type is structured terrestrial. Presence of
amorphous (upto 60%) and extractable organic matter (upto 55%) indicates a fairly good liquid
hydrocarbon generating potential. Organic matter is mainly humic and sapropelic. TAI of 2.6 to
2.75 and VRo of 0.57 to 0.67% show that the sediments are thermally mature and within oil
window. In the subthrust, the source sequences occur at greater depths and, therefore, should be in a
higher state of thermal maturity. It is expected that the source sequences within the Kopili and
Barail formations in the subthrust would be at the peak oil generating state.
Cap Rock and Entrapment
There are three well developed regional cap rocks within the Tertiary sedimentary succession, the
lower one, occurring in the Upper Eocene is the argillaceous Kopili Formation, the middle one is
the Barail Coal-Shale Unit and the upper one, overlying the Tipam Sandstone is the Girujan Clay.
Most of the oil accumulations, discovered till date in the Upper Paleocene-Lower Eocene,
Oligocene (Barail) and Miocene (Tipam Sandstone) reservoirs, occur in structural combination
(fold + fault) traps developed by compressive forces during Mio- Pliocene and later times. Most of
these hydrocarbon traps, particularly those developed in post- Barail sediments, orient parallel to
the Naga thrust. Faults associated with these traps in the southeasterly sloping shelf zone in the
Brahmaputra and Dhansiri valleys have NE-SW to NNE-SSW orientation. Most of the prominent
faults continue upward into post-Tipam sediments, and the rest die out in the lower part of the
Tipam Formation. Some of the prominent faults, particularly those near the Naga thrust, are reverse
faults, e.g., one at the northeastern flank of the Geleki structure, another at the northern flank of the
Rudrasagar structure. It may be mentioned that oil, generated in the Kopili and Barail source beds,
accumulated in post-Barail sediments by vertical migration through such prominent faults. Oil
within the Kopili Formation (composed predominantly of shales with subordinate sandstone) occurs
in strati-structural combination traps, as in the Geleki field. Oil within the Girujan Clay Formation
as in the Kumchai and Kharsang fields also occurs in combination traps, but here the control of
lithology on accumulation is more than that of structure. In the Borholla field of the Dhansiri valley
and Champang field of the neighbouring schuppen belt, oil reserves occur in structurally controlled
subtle trap in fractured basement rocks. Oil accumulations within the Bokabil Formation (Middle
Miocene) in the Khoraghat and Nambar fields of the Dhansiri valley, occur in structural
combination traps.
Hydrocarbon Potential
The Brahmaputra Valley part of the Upper Assam Shelf south of latitude 27° 30', where active
exploration for hydrocarbons has been continuing for about half a century, seems to have reached
the middle stage of exploration maturity. But, the Dhansiri Valley shelf, areas north of Lat. 27° 30'
and the Naga Schuppen belt are still in the early stage of exploration maturity. In the North Cachar
area, exploration by deep drilling is yet to be initiated. Whatsoever, in view of what has been
narrated on Upper Assam and Nagaland oil fields, and source, reservoir and cap rocks, and
entrapment mechanism, the Brahmaputra valley still holds a large quantity of ‘yet-to-find’ oil, and
Tinsukia – Sadiya area which partly falls in the Mishmi Depression; the Dhansiri valley and the
Schuppen belt possess high hydrocarbon potential worth pursuing intensive exploration. The
prognosticated resource base of the Upper Assam shelf and the Naga schuppen belt is roughly 3180
MMt, of which about 27% has been converted into inplace geological reserves. It is envisaged that
the undiscovered oil would continue to be found in structural, strati- structural and subtle traps in
areas mostly bordering the Naga thrust and in the Naga Schuppen belt.
THE CAMBAY BASIN :
THE CAMBAY BASIN The Cambay Basin occupies an area of approximately 56,000 sq.km. The
Cambay Basin can be divided into six tectonic blocks : Sanchor block ,Tharad block ,AhmedabadMehsana block ,Tarapur block, Broach block ,Narmada block .The Cambay Shale is the main
source rock in this basin.
eographic Location of the basin
The Cambay rift Basin, a rich Petroleum Province of India, is a narrow, elongated rift graben,
extending from Surat in the south to Sanchor in the north. In the north, the basin narrows, but
tectonically continues beyond Sanchor to pass into the Barmer Basin of Rajasthan. On the southern
side, the basin merges with the Bombay Offshore Basin in the Arabian Sea. The basin is roughly
limited by latitudes 21˚ 00' and 25˚ 00' N and longitudes 71˚ 30' and 73˚ 30' E. (FIG: 1, Index Map)
Category of the basin
Proved
Area
The
total
area
of
the
basin
is
about
53,500
sq.
km.
Age of the Basin & Sediment-thickness
The evolution of the Cambay basin began following the extensive outpour of Deccan Basalts
(Deccan Trap) during late cretaceous covering large tracts of western and central India. It’s a
narrow half graben trending roughly NNW-SSE filled with Tertiary sedimentswithrifting due to
extensional tectonics. Seismic and drilled well data indicate a thickness of about 8 km of Tertiary
sediments
resting
over
the
Deccan
volcanics.
Major Discoveries, Total Seismic coverage, 2D/3D and exploratory wells drilled
A total of 12,937 gravity and magnetic stations were measured by the ONGC in the entire Cambay
Basin. The Bouguer anomaly map has helped in identification of the major structural highs and
lows in the basin. The magnetic anomaly map also depicts the broad structural configuration of the
basin. A total of more than 30,688 LKM of conventional data has been acquired.
The total volume of seismic reflection data acquired from the Cambay Basin is of the order of
104113 LKM (2D) and 7895 sq. km (3D). (Fig: 2, Showing Density of Seismic coverage)
In 1958, ONGC drilled its first exploratory well on Lunej structure near Cambay. This turned out to
be a discovery well, which produced oil and gas. The discovery of oil in Ankleshwar structure in
1960 gave boost to the exploration in the Cambay Basin. More than 2318 exploratory wells have
been drilled in Cambay Basin. Out of 244 prospects drilled, 97 are oil and gas bearing.
tectonic History
:.
Type of Basin
Intracratonic rift graben.
Different Tectonic Zones with in the Basin
The Cambay rift valley is bounded by well demarcated basin margin step faults. Based on the
cross trends the basin has been divided into five tectonic blocks. From north to south, the blocks
are:



Sanchor – Tharad
Mehsana – Ahmedabad
Cambay – Tarapur


Jambusar – Broach
Narmada Block.(FIG 4: Tectonic Map of the Basin)
Basin Evolution:.
The Early Tertiary sediments ranging in age from Paleocene to Early Eocene represent syn-rift
stage of deposition that was controlled by faults and basement highs in an expanding rift system.
These sediments are characterised by an assortment of illsorted, high energy trap derived
materials. Subsidence of the basin resulted in the accumulation of a thick sequence of euxinic
black shales with subordinate coarser clastics. The Middle Eocene witnessed a regressive phase
with oscillating conditions of deposition and development of deltaic sequences in the entire
basin. There was a regional southward tilt of the entire rift basin during Late Eocene and it is
marked by a regional marine transgression extending far to the north upto Sanchor basin.
Oligocene – Lower Miocene marks another phase of tectonic activity with extensive deposition
of coarser clastic sediments in the central and southern blocks.
Generalized Statrigraphy :.


Standard stratigraphic table. (Fig 5: Generalized Stratigraphy of Cambay Basin)
Sedimentation survey and Depositional environment in different location zones
The formation of the Cambay Basin began following the extensive outpour of Deccan basalts
(Deccan Trap) during late Cretaceous covering large tracts of western and central India. The
NW-SE Dharwarian tectonic trends got rejuvenated creating a narrow rift graben extending from
the Arabian sea south of Hazira to beyond Tharad in the north. Gradually, the rift valley
expanded with time.
During Paleocene, the basin continued to remain as a shallow depression, receiving deposition
of fanglomerate, trap conglomerate, trapwacke and claystone facies, especially, at the basin
margin under a fluvio–swampy regime. The end of deposition of the Olpad Formation is marked
by a prominent unconformity. At places a gradational contact with the overlying Cambay Shale
has also been noticed.
During Early Eocene, a conspicuous and widespread transgression resulted in the deposition of
a thick, dark grey, fissile pyritiferous shale sequence, known as the Cambay Shale. This shale
sequence has been divided into Older and Younger Cambay Shale with an unconformity in
between. In the following period, relative subsidence of the basin continued leading to the
accumulation of the Younger Cambay Shale. The end of Cambay Shale deposition is again
marked by the development of a widespread unconformity that is present throughout the basin.
Subsequently, there was a strong tectonic activity that resulted in the development of the
Mehsana Horst and other structural highs associated with basement faults.
Middle Eocene is marked by a regressive phase in the basin and this led to the development of
the Kalol/ Vaso delta system in the north and the Hazad delta system in the south. Hazad and
Kalol/ Vaso deltaic sands are holding large accumulations of oil.
Major transgression during Late Eocene-Early Oligocene was responsible for the deposition of
the Tarapur Shale over large area in the North Cambay Basin. The end of this sequence is
marked by a regressive phase leading to deposition of claystone, sandstone, and shale
alternations and a limestone unit of the Dadhar Formation.
The end of the Paleogene witnessed a major tectonic activity in the basin resulting in the
development of a widespread unconformity.
During Miocene The depocenters continued to subside resulting in the deposition of enormous
thickness of Miocene sediments as the Babaguru, Kand and Jhagadia formations.
Pliocene was a period of both low and high strands of the sea level, allowing the deposition of
sand and shale.
During Pleistocene to Recent, the sedimentation was mainly of fluvial type represented by
characteristic deposits of coarse sands, gravel, clays and kankar followed by finer sands and
clays, comprising Gujarat Alluvium.
Throughout the geological history, except during early syn– rift stage , the North Cambay Basin
received major clastic inputs from north and northeast, fed by the Proto–Sabarmati and Proto–
Mahi rivers. Similarly, the Proto–Narmada river system was active in the south, supplying
sediments from provenance, lying to the east.
Petroleum System :.
Source Rock
Thick Cambay Shale has been the main hydrocarbon source rock in the Cambay Basin. In the
northern part of the Ahmedabad-Mehsana Block, coal, which is well developed within the deltaic
sequence in Kalol, Sobhasan and Mehsana fields, is also inferred to be an important hydrocarbon
source rock. The total organic carbon and maturation studies suggest that shales of the
Ankleshwar/Kalol formations also are organically rich, thermally mature and have generated oil
and gas in commercial quantities. The same is true for the Tarapur Shale. Shales within the
Miocene section in the Broach depression might have also acted as source rocks.
Reservoir Rock
There are a number of the reservoirs within the trapwacke sequence of the Olpad Formation.
These consist of sand size basalt fragments. Besides this, localized sandstone reservoirs within
the Cambay Shale as in the Unawa, Linch, Mandhali, Mehsana, Sobhasan, fields, etc are also
present.
Trap Rock
The most significant factor that controlled the accumulation of hydrocarbons in the Olpad
Formation is the favorable lithological change with structural support and short distance
migration. The lithological heterogeneity gave rise to permeability barriers, which facilitated
entrapment of hydrocarbons. The associated unconformity also helped in the development of
secondary porosity.
Transgressive shales within deltaic sequences provided a good cap rock. (Fig 6: Generalized
Tectono Stratigraphy Map Showing Source rock, Reservoir Rock, and Oil and Gas Occurrences.)

Timing of migration & Trap formation: The peak of oil generation and migration is
understood to have taken place during Early to Middle Miocene.
Petroleum Plays : Structural Highs and fault closures & Stratigraphic traps (pinchouts /
wedgeouts, lenticular sands, oolitic sands, weathered trap) in Paleocene to Miocene sequences
have
been
proved
as
important
plays
of
Cambay
Basin.
Paleocene – Early Eocene Play :


Formations : Olpad Formation/ Lower Cambay Shale.
Reservoir Rocks : Sand size basalt fragments & localized sandstone. Unconformities
within the Cambay Shale and between the Olpad Formation and the Cambay Shale have
played a positive role in the generation of secondary porosities. The Olpad Formation is
characterised by the development of piedmont deposits against fault scarps and fan delta
complexes.
Middle Eocene Play :


Formations : Upper Tharad Formation
Reservoir Rocks : In Southern part, Hazad delta sands of Mid to Late Eocene & in the
Northern part the deltaic sequence is made up of alternations of sandstone and shale
associated with coal. Plays are also developed in many paleo-delta sequences of Middle
Eocene both in northern and southern Cambay In the Northern Cambay Basin, two delta
systems have been recognised.
Late Eocene – Oligocene Play :


Formations : Trapur Shale, Dadhar Formation.
Reservoir Rocks : This sequence is observed to possess good reservoir facies in the
entire Gulf of Cambay. North of the Mahi river, a thick deltaic sequence, developed
during Oligo–Miocene, has prograded upto south Tapti area.
Miocene Play :

Formations : Deodar : Formation (LR. Miocene), Dhima Formation (Mid Miocene),
Antrol Formation (UP. Miocene) The Mahi River delta sequence extends further
westward to Cambay area where Miocene rocks are hydrocarbon bearing.
CAUVERY BASIN :
CAUVERY BASIN The Cauvery Basin, situated 160 to 460 km south of Chennai city,
encompasses an area of 25,000 sq. km. falls in Indian territorial waters. The basin is subdivided into
six sub-basin:- Ariyalur Pondicherry sub-basin. Tranquebar sub-basin Thannjavur sub-basin
Nagapatinam sub-basin Ramnad Palk Bay sub-basin Mannar sub-basin
Basin Introduction :.
The Cauvery Basin extending Extends along the East Coast of India, bounded by 08º - 12º 5’ North Latitude , 78º - 800 East Longitude has been under hydrocarbon exploration
since late nineteen fifties. Application of CDP seismic in 1984 considerably increased the pace
of exploration resulting in the discovery of several small oil and gas fields. The first deep well
for exploration was drilled in 1964.
The Cauvery Basin covers an area of 1.5 lakh sq.km comprising onland (25,000 sq.km) and
shallow offshore areas (30,000 sq km). In addition, there is about 95,000 sq km of deep-water
offshore areas in the Cauvery Basin. Most of the offshore and onland basinal area is covered by
gravity, magnetic and CDP Seismic surveys. Geological map for the outcrop terrain shows the
exposed formations.
Category and Basin Type:
Cauvery basin is a pericratonic rift basin and comes under category first. (Basins with
established to commercial production.)
Basin Age & Sediment Thickness



Result of Gondwanaland fragmentation during drifting of India- Srilanka landmass
system away from Antarctica/ Australia plate in Late Jurassic/ Early Cretaceous.
The basin is endowed with five to six kilometers of sediments ranging in age from Late
Jurassic to Recent (mainly thick shale, sandstone & minor limestone).
Prognosticated resources : 700 MMT (430 MMT: onland areas and 270 MMT: offshore)
eology :.
The Geological history of the Cauvery Basin began with the rejuvenation of rifting, i.e., creation
of a new rift basin during Late Jurassic and Early Cretaceous times




Exploration efforts still young in Cauvery Offshore-confined mainly to land and close to
coast.
Cretaceous fan model (New discovery in CY-OS-2) promising for future exploration.
Discovery by RIL (Dhirubhai-35) has opened a new corridor for exploration in Cauvery
deep water
Big size subtle features seen on GXT-DGH long offset lines at deeper levels
Sedimentation
History
and
Despositional
Environment
Evolution of the Cauvery Basin is understood to have taken place through three distinct stages-
Late Jurassic-Early Cretaceous Rift Stage.





Initiation of rifting have begun during the Late Jurassic/Early Cretaceous.
Rift stage sediments (Shivganga and Therani formations) of Upper Gondwana affinity are
known from exposures.
These were deposited in fluvial environments.
The Kallakudi Limestone , younger to the Shivganga Formation, may represent an
episode of basinal deepening and paucity of clastic supply.
In the subsurface, the Andimadam Formation, overlain by the Sattapadi Shale, appears to
mark the peak of this transgressive episode during Cenomanian.
Late Cretaceous





Initiation of rifting have begun during the Late Jurassic/Early Cretaceous.
Rift stage sediments (Shivganga and Therani formations) of Upper Gondwana affinity are
known from exposures.
These were deposited in fluvial environments.
The Kallakudi Limestone , younger to the Shivganga Formation, may represent an
episode of basinal deepening and paucity of clastic supply.
In the subsurface, the Andimadam Formation, overlain by the Sattapadi Shale, appears to
mark the peak of this transgressive episode during Cenomanian.
Post Cretaceous





Towards the end of the Cretaceous, the basin experienced a phase of upliftment and
erosion and a gradual basinward tilt of the shelf.
The Tertiary sequence was deposited in a general prograding environment with gradual
subsidence of the shelf.
This sequence can be subdivided into two groups, the Nagore and Narimanam. The
Nagore Group is well developed in the south, whereas the Narimanam Group attains its
full development north of Karaikal High.
The Kallakudi Limestone , younger to the Shivganga Formation, may represent an
episode of basinal deepening and paucity of clastic supply.
– By this time, Tertiary deltaic environment appears to have considerably progressed
eastwards.
Tectonic History :.
The Cauvery Basin is an intra-cratonic rift basin, divided into a number of sub-parallel horsts and
grabens, trending in a general NE-SW direction. The basin came into being as a result of
fragmentation of the Gondwana land during drifting of India-SriLanka landmass system away from
Antarctica/Australia continental plate in Late Jurassic / Early Cretaceous. The initial rifting caused
the formation of NE-SW horst-graben features. Subsequent drifting and rotation caused the
development of NW-SE cross faults.
eneralized Stratigraphy :.
The stratigraphy is worked out from outcrop geology and sub-surface information gathered from
seismic and drilling data.






Precambrian:
Precambrian cratonic rocks comprising granites and gneisses are exposed all along the
western margin of the basin.
Late Jurassic-Early Cretaceous:
Overlying the Cratonic basement along the margin of the basin are exposures of
sedimentary rocks of Gondwanic affinity identified as the Shivganga Beds and Therani
Formation. The Therani Formation contains index Gondwana plant fossils (Ptilophyllum
acutifolium). These rocks are feldspathic, gritty and kaolinitic.
Early Cretaceous:
The rocks of the Uttatur Group is made up of Kalakundi, Karai Shale and Maruvathur
Clay formations in the outcrops and the Andimadam, Sattapadi and Bhuvanagiri
formations in the sub-surface. These formations overlie the older Gondwana rocks and
basement granites and gneisses.
Andimadam Formation:
In the subsurface, the formation is developed in grabens, namely, the Ramnad, Tanjore,
Tranquebar and Ariyalur Pondicherry grabens. The lower boundary of the formation is
marked by Archaean Basement rocks, while the upper boundary is defined by an
argillaceous section. It comprises pale grey, fine to coarse grained, micaceous sandstone
and micaceous silty shale.
Sattapadi Shale:
This formation is widely distributed in the basin.It is absent in the southeastern part of the
basin. The Andimadam Formation marks its lower boundary and an arenaceous facies of
the Bhuvanagiri Formation marks its upper contact. It comprises mainly silty shale and
thin calcareous sandstone. The environment of deposition is inferred to be marine. The
age assigned is Albian-Cenomanian. This is one of the important source sequences for
HC generation.
Bhuvanagiri Formation:
The formation is developed mostly in the northern and central parts of the basin. The
formation is predominantly sandstone with minor claystone and shale. A CenomanianTuronian age can be assigned to this formation. It is inferred to have been deposited in
middle shelf to upper bathyal environment.











Palk Bay Formation:
The occurrence of this formation is restricted to the Palk Bay. The lithology is
dominantly calcareous sandstone with a few bands of sandy claystone. The depositional
environment is inferred to be shallow marine in a fan delta setting.
Late Cretaceous:
The sediments in the outcrops are classified under two groups, namely, the Trichinopoly
and Ariyalur groups. The Trichinopoly and Ariyalur groups in outcrops consist of
Sandstones and Limestone formations.
Kudavasal Shale Formation:
It is present all along the eastern part of the basin. The formation consists of
shale/calcareous silty shale with occasional calcareous sandstone bands.
Nannilam Formation:
It is conformably overlain and underlain by the Porto-Novo and Kudavasal formations
respectively. The formation consists of alternations of shale, calcareous silty shales and
occasional calcareous sandstones. The formation age ranges from Santonian to
Campanion.
Porto-Novo Shale:
Predominantly developed in the northern part of the Ariyalur-Pondicherry Sub-basin,
west of Karaikal Ridge and Palk Bay Sub-basin. It is predominantly argillaceous with
minor siltstone. The age of the formation is Campanion to Maastrichtian.
Komarakshi Shale:
The formation has developed towards the eastern part of the basin. It unconformably
overlies the Bhuvanagiri/ Palk Bay Formation and underlies the Karaikal/Kamalapuram
formations. The formation consists mainly of calcareous silty shale. The age of the
formation is Coniacian to Maastrichtian.
Tertiary:
A complete sequence of Tertiary sediments is encountered in the sub-surface. The
exposed rocks are represented by the Niniyur Formation of Paleocene age and the
Cuddalore Sandstone of Mio-Pliocene age. The sub-surface section of Tertiary rocks is
considerably thick and has been classified into two groups, the lower part is named as the
Nagaur Group and the upper part, as the Narimanam Group.
Nagore Group:
The formations of this group overlie the Ariyalur Group. The base and top of the group is
marked by pronounced unconformities. The four formations recognized in this group are
described below.
Kamalapuram Formation:
The Porto-Novo---Komarakshi Shale unconformably underlies the formation, whereas
the overlying Karaikal Shale has conformable contact. It consists of alternations of shaly
sandstones and shales.
Karaikal Shale:
The formation conformably overlies the Kamalapuram Formation. The formation
comprises shales, which are occasionally calcareous/pyritic. The age of the formation
ranges from Paleocene to Eocene.
Pandanallur Formation:
It has a restricted areal extension. It consists of claystone sandstone, deposited in middle
shelf environment. Age of the formation is Lower Eocene.










Tiruppundi Formation:
The formation is present in Pondicherry offshore, Nagapattinam Sub-basin, and south of
Palk Bay Sub-basin. The formation comprises limestone, siltstone and sandstone. It is of
Middle Eocene to Early Miocene age.
Narimanam Group:
The youngest sedimentary sequence comprising sandstone, clay/claystone and limestone
which are well recognized with distinct character is designated as a Group. This group
comprises eight formations.
Niravi Formation:
The formation unconformably overlies the Tiruppundi Formation/Karaikal Shale. The
formation consists of grey coloured, fine to medium grained, calcareous sandstone with
occasional pyrite and garnet.
Kovilkalappal Formation:
It occurs in Tanjore and Nagapattinam Sub-basins and overlies the Niravi Formation, and
underlies the Shiyali Claystone. It is argillaceous in nature with a dominant presence of
limestone.
Shiyali Claystone Formation:
: It is observed to occur in Madanam and Karaikal area. The age of the formation ranges
from Oligocene to Lower Miocene.
Vanjiyur Sandstone Formation:
The formation has limited areal extent. It is predominantly arenaceous in character and
comprises dark grey, calcareous sandstone and siltstone.
Tirutaraipundi Sandstone Formation:
The formation is present in the southern part of the Nagapattinam Sub-basin towards Palk
Bay. It comprises mainly sandstones with minor limestone.
Madanam Limestone Formation:
The formation is unconformably underlain by the Tirutaraipundi Sandstone and Vanjiyur
Sandstone. It comprises mainly limestone with minor silty clays.
Vedaranniyam Limestone Formation:
The formation occurs only in the southeastern part of the basin. It consists of
predominantly coral limestone and minor grainstone.
Tittacheri Formation:
The formation is present in a large part of the basin. It grades into the Cuddalore
Sandstone Formation near the outcrops. This consists of unconsolidated gravely
sandstone and earthy clays.The age of the formation is Lower Miocene to Pliocene.
Petroleum System :.
Petroleum System and Generalized Stratigraphy
Prognosticated Resources/Proved Reserve

The Cauvery Basin is an established hydrocarbon province with a resource base of 700
MMT.

430 MMT for onland areas and 270 MMT in the offshore.
Proven / Expected Play Types


TStructural and combination traps in Early Cretaceous to Paleocene sequences.
Stratigraphic traps such as pinch-outs / wedge-outs and lenticular sand bodies in Early to
Late Cretaceous sequences.
Source
Sattapadi shale within Cretaceous– main source Kudavasal Shale within
Cretaceous Basal part of Kamalapuram Fm (Paleocene).
Reservoir
Andimadam, Bhuvanagiri & Nannilam Formations within Cretaceous
Kamlapuram and Niravi Formations within Paleocene Precambrian Fractured
Basement.
Cap Rock
Sattapadi shale within Cretaceous Post unconformity shales like Kudavasal and
Kamlapuram.
Entrapment Structural/ Stratigraphic, Combination traps.
BOMBAY OFFSHORE BASIN :
BOMBAY OFFSHORE BASIN It lies in region of Western continental shelf of India and forms an
important hydrocarbon bearing province. It is extending from Saurashtra Coast in the North to
Vengurla arch near Goa in the South covering an area of about 1,20,000 sq.km. up to 200 m
isobaths. Tectonically the basin can be subdivided into Surat depression, Bombay High platform,
Ratnagiri block, Shelf margin basin and the Shelf-edge basement arc. Bombay Offshore Basin is
producing nearly 70% oil and gas of India’s total hydrocarbon production
Geographic Location of the basin
Mumbai Offshore basin is located on the western continental shelf of India between Saurashtra
basin in NNW and Kerela Konkan in the south.
Category of the basin
The basin falls under the category I, which implies that the basin has proven commercial
productivity.
Area
It covers an area of about 116,000 km2 from coast to 200 m isobath.
Age of the Basin & Sediment-thickness
The age of the basin ranges from late Cretaceous to Holocene with thick sedimentary fill ranging
from 1100-5000 m. Though possibility of occurrence of Mesozoic synrift sequences in the deepwater basin have been indicated by the recently acquired seismic data by GXT, it needs to be
further ascertained by future studies.
Exploration history
Exploration in the Mumbai Offshore Basin started in the early sixties when regional geophysical
surveys were conducted by the Russian seismic ship. The first oil discovery in this basin was
made in the Miocene limestone reservoir of Mumbai High field in February 1974. Subsequent
intensification in exploration and development activities in this basin have resulted in several
significant discoveries including oil and gas fields like Heera,Panna, Bassein, Neelam,Mukta,
Ratna,Soth tapti, Mid Tapti etc.In addition number of marginal fields like B-55, B-173A, B119/121, D-1 and D-18 have been put on production in the last decade.
Recent Discoveries (2007-08)
Block/Prospect
Discovery
Formation
Operator
B-55-5
Gas
Mukta
ONGCL
B-12-11
Gas
Daman
ONGCL
D-1-14
Oil
Ratnagiri
ONGCL
B-172-9
Gas
Panna
ONGCL
BNP-2
Gas
S1 Pay
ONGCL
Tectonic History :.
Type of Basin
Mumbai offshore is a pericratonic rift basin situated on western continental margin of India.
Towards NNE it continues into the onland Cambay basin. It is bounded in the northwest by
Saurashtra peninsula, north by Diu Arch. Its southern limit is marked by east west trending
Vengurla Arch to the South of Ratnagiri and to the east by Indian craton.
Different Tectonic Zones with in the Basin
Five distinct structural provinces with different tectonic and stratigraphic events can be identified
within the basin viz. Surat Depression (Tapti-Daman Block) in the north, Panna-Bassein-Heera
Block in the east central part, Ratnagiri in the southern part, Mumbai High-/Platform-Deep
Continental Shelf (DCS) in the mid western side and Shelf Margin adjoing DCS and the Ratnagiri
Shelf.
Surat Depression
It forms the southward extension of the Cambay Basin and to the west it is separated from
Saurashtra Basin by Diu Arch. An arm of this Depression extends far south into Panna-Bassein-
Heera block (Central Graben) and further south into Ratnagiri block (Vijayadurg Graben). A ‘high’
feature interrupts the north-south continuity of these grabens. A few small-scale grabens radiating
from these diastamise and circumscribe horsts in Ratnagiri block. The Surat Depression has
numerous structural features of different origins like basement-controlled anticlines, differential
compaction over sand bodies encompassed by shale, inversions and growth fault related roll over
features.
Panna-Bassein-Heera Block
This block located east of Mumbai High/Platform and south of Surat Depression has three distinct
N-S to NW-SE trending tectonic units which lose their identity in Miocene. The western block is a
composite high block dissected by a number of small grabens. The Central graben is a syn
sedimentary sink during Paleogene and Early Neogene. The eastern block is a gentle eastward
rising homocline.
Ratnagiri Block
It is the southward continuation of the Panna-Bassein-Heera block. This block is differentiated into
four distinct tectonic units by three sets of NNW-SSE trending enechelon fault systems. The
western block is termed ‘Shrivardhan Horst’ and to its east is ‘Vijayadurg Graben’ which is also a
syn sedimentary sink during Paleogene and Early Neogene. There is a general southward
shallowing of this graben. Adjoining this is ‘Ratnagiri Composite Block’ with a number of ‘highs’
and lows’ and further east, like in the northern block, there is a gradual easterly rising homocline
called ‘Jaygad Homocline’.
Mumbai Platform
It is bounded by Shelf Margin to its west and south and by Saurashtra Basin and Surat Depression
to its north. Mumbai Platform includes Mumbai high and DCS area. The intervening area between
these two is gentle homoclinal rise with a few structural ‘highs’ of different origins. Major part of
the Mumbai High area remained positive almost up to Late Oligocene missing much of the
sedimentation activity. In comparison to other blocks in the basin, Mumbai block remained
relatively stable which probably helped in the deposition of uniform carbonate-shale alternations
over Mumbai High during Early Miocene and early part of Middle Miocene, which later
accommodated huge accumulations of hydrocarbons making Mumbai High, a Giant Field.
Shelf Margin
Its northern boundary with Saurashtra Basin is indistinct and to its west lies Deep Sea Basin with
the western boundary marked by part of a regional ridge ‘Kori High’. Except for the deposition of
thin carbonates during Eocene, possibly due to paucity of clastic supply into the basin during this
period, the block essentially remained a clastic depocenter throughout Oligocene and Neogene
times. During post Eocene times the block experienced continuous sinking with varied intensity to
accommodate the enormous clastic material that was being brought into Surat Depression by proto
Narmada and Tapti river systems and getting dispersed westward into this block.
Generalized Statrigraphy :.

Mumbai Offshore Basin
Basin Introduction :.
Geographic Location of the basin
Mumbai Offshore basin is located on the western continental shelf of India between Saurashtra
basin in NNW and Kerela Konkan in the south.
Category of the basin
The basin falls under the category I, which implies that the basin has proven commercial
productivity.
Area
It covers an area of about 116,000 km2 from coast to 200 m isobath.
Age of the Basin & Sediment-thickness
The age of the basin ranges from late Cretaceous to Holocene with thick sedimentary fill ranging
from 1100-5000 m. Though possibility of occurrence of Mesozoic synrift sequences in the deepwater basin have been indicated by the recently acquired seismic data by GXT, it needs to be
further ascertained by future studies.
Exploration history
Exploration in the Mumbai Offshore Basin started in the early sixties when regional geophysical
surveys were conducted by the Russian seismic ship. The first oil discovery in this basin was
made in the Miocene limestone reservoir of Mumbai High field in February 1974. Subsequent
intensification in exploration and development activities in this basin have resulted in several
significant discoveries including oil and gas fields like Heera,Panna, Bassein, Neelam,Mukta,
Ratna,Soth tapti, Mid Tapti etc.In addition number of marginal fields like B-55, B-173A, B119/121, D-1 and D-18 have been put on production in the last decade.
Recent Discoveries (2007-08)
Block/Prospect
Discovery
Formation
Operator
B-55-5
Gas
Mukta
ONGCL
B-12-11
Gas
Daman
ONGCL
D-1-14
Oil
Ratnagiri
ONGCL
B-172-9
Gas
Panna
ONGCL
BNP-2
Gas
S1 Pay
ONGCL
Tectonic History :.
Type of Basin
Mumbai offshore is a pericratonic rift basin situated on western continental margin of India.
Towards NNE it continues into the onland Cambay basin. It is bounded in the northwest by
Saurashtra peninsula, north by Diu Arch. Its southern limit is marked by east west trending
Vengurla Arch to the South of Ratnagiri and to the east by Indian craton.
Different Tectonic Zones with in the Basin
Five distinct structural provinces with different tectonic and stratigraphic events can be identified
within the basin viz. Surat Depression (Tapti-Daman Block) in the north, Panna-Bassein-Heera
Block in the east central part, Ratnagiri in the southern part, Mumbai High-/Platform-Deep
Continental Shelf (DCS) in the mid western side and Shelf Margin adjoing DCS and the
Ratnagiri Shelf.
Surat Depression
It forms the southward extension of the Cambay Basin and to the west it is separated from
Saurashtra Basin by Diu Arch. An arm of this Depression extends far south into Panna-BasseinHeera block (Central Graben) and further south into Ratnagiri block (Vijayadurg Graben). A
‘high’ feature interrupts the north-south continuity of these grabens. A few small-scale grabens
radiating from these diastamise and circumscribe horsts in Ratnagiri block. The Surat Depression
has numerous structural features of different origins like basement-controlled anticlines,
differential compaction over sand bodies encompassed by shale, inversions and growth fault
related roll over features.
Panna-Bassein-Heera Block
This block located east of Mumbai High/Platform and south of Surat Depression has three
distinct N-S to NW-SE trending tectonic units which lose their identity in Miocene. The western
block is a composite high block dissected by a number of small grabens. The Central graben is a
syn sedimentary sink during Paleogene and Early Neogene. The eastern block is a gentle
eastward rising homocline.
Ratnagiri Block
It is the southward continuation of the Panna-Bassein-Heera block. This block is differentiated
into four distinct tectonic units by three sets of NNW-SSE trending enechelon fault systems. The
western block is termed ‘Shrivardhan Horst’ and to its east is ‘Vijayadurg Graben’ which is also
a syn sedimentary sink during Paleogene and Early Neogene. There is a general southward
shallowing of this graben. Adjoining this is ‘Ratnagiri Composite Block’ with a number of
‘highs’ and lows’ and further east, like in the northern block, there is a gradual easterly rising
homocline called ‘Jaygad Homocline’.
Mumbai Platform
It is bounded by Shelf Margin to its west and south and by Saurashtra Basin and Surat
Depression to its north. Mumbai Platform includes Mumbai high and DCS area. The intervening
area between these two is gentle homoclinal rise with a few structural ‘highs’ of different origins.
Major part of the Mumbai High area remained positive almost up to Late Oligocene missing
much of the sedimentation activity. In comparison to other blocks in the basin, Mumbai block
remained relatively stable which probably helped in the deposition of uniform carbonate-shale
alternations over Mumbai High during Early Miocene and early part of Middle Miocene, which
later accommodated huge accumulations of hydrocarbons making Mumbai High, a Giant Field.
Shelf Margin
Its northern boundary with Saurashtra Basin is indistinct and to its west lies Deep Sea Basin with
the western boundary marked by part of a regional ridge ‘Kori High’. Except for the deposition
of thin carbonates during Eocene, possibly due to paucity of clastic supply into the basin during
this period, the block essentially remained a clastic depocenter throughout Oligocene and
Neogene times. During post Eocene times the block experienced continuous sinking with varied
intensity to accommodate the enormous clastic material that was being brought into Surat
Depression by proto Narmada and Tapti river systems and getting dispersed westward into this
block.
Generalized Statrigraphy :.
Sedimentation History and Depositional Environment
This phase signifies the early syn-rift stage & is represented by trap-derived
clastics contributed by the then existing paleo-highs essentially in continental
to fluvial environment in its lower part (Panna Formation). It is overlain by
grey to dark grey shales with subordinate sands possibly representing the first
marine transgression into the basin. Presence of carbonaceous shale and coal
at a few places suggest localized restricted conditions.
Late
PaleoceneEarly Eocene
Main clastic depocenters like Surat Depression and the contiguous
southward lows like Central Graben (Panna Bassien block) and Vijayadurg
Graben (Ratnagiri Block) received these sediments in considerable thickness
aided by syn-sedimentary activity of the bounding faults. A few localized
depressions in Mumbai Platform and over some other horst blocks also
received these sediments. Panna Formation is wide spread in the basin except
over the crestal parts of prominent paleo-highs like Mumbai High, Heera etc.
Its thickness varies from almost nil to hundreds of meters in deep sinks.
Shelf Margin block, though under deep marine realm seem to have received
lesser quantities of sediments which were either derived from the Diu Arch
(?) or from localized provenances. The facies developed in this block are
mainly claystone, argillaceous and carbonates with some amount of pelagic
fauna.
Carbonate facies (Devgarh Formation) development is observed towards the
southern edge of Mumbai High in the form of muddy foraminiferal- algal
banks; Deep Continental Shelf area and isolated off-shelf carbonate build-ups
at a few places in Shelf Margin and Ratnagiri.
The syn-rift stage of Late Paleocene-Early Eocene period got terminated with
a basin wide regression and development of an unconformity
After a period of peneplanation, the basin witnessed a major transgression.
Extensive carbonate sedimentation occurred in the shallow shelf area of
Mumbai Platform, Panna-Bassein-Heera block and Ratnagiri block
(Bassein Formation). However the period witnessed essentially clastic
sedimentation in Surat Depression (Belapur and Diu formations) with
occasional carbonate bands and a few sand stringers and argillaceous
Middle –Late carbonates and shales in Central and Vijayadurg Grabens (Panna-BasseinHeera block and Ratnagiri block). Shelf margin was generally starved of
Eocene
clastics with deposition of minor claystone and carbonates of mixed middle
shelf to bathyal origin ( Belapur Formation)
Bassein Formation also indicates a wide range of environments – restricted
platform, shelf lagoon with isolated shoals in Bassein area to open carbonate
shelf in DCS and Ratnagiri and finally deep water carbonates in Shelf
Margin area. It also formed wedge outs against the rising flanks of Mumbai
Early
Oligocene
High and Heera, which can be considered as potential exploration targets.
During this period, Surat Depression experienced the maximum subsidenceaccumulating thick under compacted claystone relating to the prograding
delta from northeast (Mahuva Formation). The Mumbai platform
experienced generally shallower water depths and shale interbeds within
limestone becoming more frequent. In Shelf Margin area thinner carbonates
are deposited under relatively deeper conditions.
End of Early Oligocene also witnessed initiation of the westerly tilt of the
basin.
Close of Early Oligocene is marked by a minor period of non-deposition
except in Shelf Margin area. A few brief spells of transgression followed by
continuous eustatic rise in sea level up to Early Miocene marked this period.
Crestal part of Mumbai High that hitherto remained a positive area also got
submerged during this period.
Surat Depression witnessed reduced subsidence resulting in a regressive
coastline. A package consisting of sand bodies deposited in distributary
channels, coastal bars, tidal deltas and other transitional environments
encased in marginal marine normally pressured silty and carbonaceous shale
overlying over pressured prodelta clay stone of Early Oligocene. (Daman
Formation) The reservoir facies within this Formation have assumed great
importance as they have been found to host significant amounts of
hydrocarbons.
There was faster subsidence in Shelf Margin to accommodate the increased
Lat Oligocene sediment load supplied by the westward prograding delta system. The finer
clastics reaching the Shelf Margin block were mainly deposited in the
depression between Kori High and the carbonate platform. (Alibag
Formation)
Southward Close of Early Oligocene is marked by a minor period of nondeposition except in Shelf Margin area. A few brief spells of transgression
followed by continuous eustatic rise in sea level up to Early Miocene marked
this period. Crestal part of Mumbai High that hitherto remained a positive
area also got submerged during this period.
Earl
Southward from Surat Depression, clays got dispersed over Panna-BasseinHeera block, including the crestal areas and the northern part of Ratnagiri
block as well as Bombay Platform. While in Mumbai High-DCS area and
southern part of Ratnagiri, the unit is termed as Panvel Formation, in PannaBassein-Heera and northern part of Ratnagiri, the unit is named as Alibag
Formation.)
It was a period of eustatic rise in sea level punctuated by a brief spell. The
finer clastics entering into Surat Depression got mostly dispersed westward
Miocene
Middle
Miocene
Middle
MioceneHolocene
into Saurashtra basin and Shelf Margin area. Limited quantity of clastics got
dispersed southward and entered Mumbai platform at its southeast and also
up to Heera area. In response to the rising sea level, the delta being formed in
Surat Depression in Late Oligocene shifted eastward.
Bassein and the area to its south that experienced shoaling conditions during
Eocene was the site for fine clastic deposition during Early Miocene.
Mumbai High and its western part (DCS) underwent fairly thick carbonate
sedimentation. In fact the major reservoir of Mumbai High that hosts major
part of the Country’s hydrocarbon reserves belongs to this unit. While over
the Mumbai High area the facies are low energy, very fine grained to clayey
carbonate reservoirs, the DCS area represents high-energy bio-clastic
grainstone facies along with minor mudstone and wackestone.
The sea level continued to rise during this period. Clastic supply also
continued into the basin. However much of the clastic material got dispersed
westward into Saurashtra and Shelf Margin areas. Considerable quantity of
clastics got dispersed southward also covering the entire Panna-Bassein area
and also the Mumbai High and its immediate surroundings to the west and
south. This clastic unit over Mumbai High includes sheet like sand, which
has also been found to be hydrocarbon bearing. Carbonate sedimentation
continued in Ratnagiri and DCS areas. Toward the later part of Middle
Miocene, clastic deposition almost came to a halt in Mumbai High and other
areas and consequently carbonates got deposited over many areas. Uppermost
part of the Middle Miocene Limestone in Heera field has been found to be
hydrocarbon bearing. Close of Middle Miocene was marked by a very
pronounced unconformity.
Post Middle Miocene witnessed a major transgression covering the entire
basin coupled with spectacular increase in clastic supply. The earlier initiated
westerly tilt of the basin also became more pronounced. All these events
brought the carbonate sedimentation to a total halt. The increased clastic
supply also resulted in a significant progradation of Miocene shelf at places
up to 80 km (Chinchni Formation)
Petroleum System :.
Source Rock
There are three major depocenters in the basin viz. Surat Depression in the north, Shelf Margin
in the west and Central and Vijayadurg Grabens in the south.
Source Rock
Blocks
Surat
Depression
Character
Comments
The bounding faults of this tectonic
Shallow
protected
shelf
facies
unit have been continuously active
consisting of organic rich shales
accommodating huge pile of sediments
(Panna Formation- Paleocene to early
that are being brought by the
eocene & Belapur Formation- Middle
Narmada/Tapti fluvial systems
Eocene)
The enclosure provided by the Diu
3-11% organic carbon and the
Arch and Mumbai High could have
kerogene type is mixed Type II and
prevented free open marine circulation
Type III.
and coupled with optimum subsidence
appears to have helped in preservation
Expected oil window is around 3000 m
of organic matter.
Several layers of shale/claystone in a
few wells are reported to have requisite Possible reasons for the exploration
TOC and have reached the oil window setbacks could be the speculative
Shelf
(Panna
Formation
&
Belapur nature of reservoir rocks and
Formation)
hydrocarbon expulsion pressure did not
Margin
exceed the ambient hyper pressure
The oil window from the available within the formation inhibiting primary
geochemical data appears to be migration .
between 2900m and 3850m.
It is widely perceived that the Central
Graben in Panna-Bassein Heera
block and Vijayadurg Graben in
The finer clastics entering into Surat Ratnagiri block had contributed to
Depression through Narmada /Tapti huge hydrocarbon accumulations in
systems have been getting partially many major structural features like
Central and dispersed southward and entering these Panna, Bassein, Heera, South Heera,
Vijaydurg two prominent lows that appear to be etc. lying on the western horst block
an arm of the Depression extending to suggesting
a
major
westward
grabens
the south. Syn depositional sinking of hydrocarbon migration. However
these two lows accommodating the discovery of Neelam field within
huge clastic influx from north is Central Graben indicated hydrocarbon
evident from the seismic data.
opportunities within the graben itself
provided better reservoir facies
coupled with proper entrapment
condition is available.
Reservoir Rock
Mumbai offshore basin has been blessed with both clastic and carbonate reservoir facies in
almost total Tertiary Section ranging from Paleocene to Middle Miocene.
Reservoir
Age
Lithology/Location
Comments
Middle
Miocene
The uppermost part has been found to
be hydrocarbon bearing at a few places
Carbonate sections at Ratnagiri,
A sheet like sand deposited over
Mumbai high & Diu (Ratnagiri &
Mumbai High (S1) is also proved to be
Bandra formations)
gas bearing in commercial quantity in
Mumbai High
Lower
Miocene
Deposited under cyclic sedimentation
with each cycle represented by
lagoonal, algal mound, foraminiferal
Represented by a thick pile of
mound and coastal marsh facies
carbonates hosting huge quantity of oil
The porosity is mainly intergranular,
and gas over Mumbai High (Bombay,
intragranular, moldic, vuggy and
Ratnagiri)
micro-fissures and the solution cavities
interconnected
by
micro-fissures
provided excellent permeability.
Sands in the central and mid-eastern
Deposited under prograding delta
part of Surat depression i.e. TaptiOligo– Early
conditions
Daman area, Daman formation.
Miocene
Carbonates adjoining Mumbai High(
Proved to be excellent reservoirs
Panvel formation )
E.Oligocene
clastics
of
Surat
depression(Mahuva
Formation)
Eocene and
Deposition of thicker carbonate facies
Early
over the horst blocks in Panna- BaseinOligocene
Heera and Ratnagiri blocks (Bassein,
Mukta & Heera formations).
Proven hydrocarbon bearing reservoirs
in
Tapti
area.
Gradual increase of sea level, shielding
from the clastic onslaught from the
northern
part
of
the
basin.
The intervening regressive phases have
aided in developing good porosity in
these rocks making them excellent
reservoir levels in the basin.
Paleocene
Coarser clastic facies developed within
The clastics of Panna formation are
the upper marine shale sequence in
proved to be excellent reservoirs in the
areas of Mumbai High, Panna and
Sw flank of Panna –Basin platform.
Ratnagiri (Panna Formation)
Cap Rocks
Shale encompassing the coarser clastic facies in the Paleocene section, widespread transgressive
shale overlying the Middle Eocene Bassein Formation, alternation of shale and tight limestone
over early Oligocene Mukta Formation, widespread intervening shale layers within Early
Miocene Mumbai formation over Mumbai High and in DCS area, post Middle Miocene
clay/claystone of Chinchini Formation over parts of Heera etc. had provided effective seal for the
underlying
hydrocarbon
accumulations
in
the
Mumbai
offshore
basin.
Entrapment
As mentioned earlier, Mumbai offshore basin has been endowed with a wide variety of
entrapment situations like- structural closures with independent four way closures of very large,
large, medium and small sizes, fault closures and faulted closures with effective fault sealing,
strati-structural features like Paleogene wedges against rising flanks of paleohighs, mud mounds,
carbonate build-ups, unconformity controlled traps, Paleogene and Neogene carbonate wedges
against the rising Eastern and Jaygad Homoclines. Mumbai Offshore Basin Introduction
Tectonic History Generalized Stratigraphy Petroleum System Petroleum Plays
Petroleum Plays :.
Major Identified play types
1.
2.
3.
4.
5.
6.
7.
8.
Paleogene Synrift clastics(Paleocene-Lr. Eocene, Panna Fm)
Eocene Carbonate Platform (Bassein formation)
Lr.Oligocene Carbonate plays (Mukta and Heera formations)
Oligocene-Lr. Miocene deltaic Play (Mahuva &Daman formations)
Up. Oligocene carbonates ( Panvel and Ratna formations)
Lr. Miocene carbonate (L-III and L-IV reservoirs, Bombay / Ratnagiri formation)
Lr-Mid. Miocene clastics(S1 sands),
Mid. Miocene carbonate (L-I and L-II reservoirs, Bandra Formation)
1. Paleogene Synrift clastics(Paleocene-Lr. Eocene, Panna Fm)





Area : Western and southeastern flank of Mumbai High,western flank of central
graben,Heera-Panna Block
Reservoir rock: sandstone
Depositional environment: Continental (parallic) to coastal
Trap: structural /stratistructural(updip pinch outs)
Source rocks: Paleocene-Eocene (Panna Formation)
Commercial production from few wells of Heera Field. Areas SW of Bassein Field containing B80, B-23A prospects and prospect D-33 in DCS have been identified for pre-development studies
along with younger pays. In addition commercial flow has been observed in prospects like B-34,
B-59,
B-127,
Panna
East
wells
etc.
2. Eocene Carbonate Platform(Bassein Formation)





Area: Heera-Panna Composite Block, part of MH-DCS block (NW and SW flank of
Mumbai High), Ratnagiri
Reservoir rock: Limestone
Depositional environment: shallow shelf /Shelf-lagoon carbonates
Trap: structural /stratistructural(wedge outs)/diagenetic traps(?)
Source rocks: Paleocene-Eocene (Panna Formation)
Commecial production from several medium sized and marginal Fields






Mukta-Panna
Bassein
Heera
Neelam
B-55
B-173A
South Heera
In addition several prospects in Heera-Panna Composite block and BH-DCS block has been
tested
hydrocarbon
in
commercial
quantities.
Areas identified for development/pre-development studies:




NW of Mumbai High
SW of Mumbai High
West and SW of Bassein
Bassein East
3. LR. Oligocene Carbonates (MUKTA AND HEERA FORMATIONS)





Area: Heera -Panna composite block, MH-DCS platform
Reservoir rock: limestone
Trap: structural
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: Heera,panna,neelam,Basseim,B-55,D-18 etc
4. Oligocene - LR. Miocene Distal Deltaic-Coastal Play (DAMAN AND MAHUVA
FORMATIONS)







Area: Tapti-daman Block
Reservoir rock: Sandstone
Depositional environment: Deltaic to coastal
Trap: Structural /stratistructural
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: South Tapti/Mid Tapti
Areas identified for development/pre-development studies: C-series structures, North
Tapti,
5. Up. Oligocene carbonates ( Panvel and Ratnagiri formations)






Area: MH-DCS Block
Reservoir rock: limestone
Trap: structural
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: B-121/119
Tested commercial potential from wells located in the MH-DCS Blocks Area identified
for Dev/pre-development studies: B-46, B-48 (NW of Mumbai High), B-192, B-45, and
WO-24 etc
6. Lr. Miocene carbonate (L-III and L-IV reservoirs)






Area: Mumbai High
Reservoir rock: limestone
Trap: structural
Depositional environment/facies: Deposited under cyclic sedimentation with each cycle
represented by lagoonal, algal mound, foraminiferal mound and coastal marsh facies
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: Mumbai High, D-1 Prospects identified for development WO-24, B-45 along with
other pays
7. Lr-Mid. Miocene clastics(S1 sands)





Area: Mumbai High and adjoining area
Reservoir rock: sandstone/siltstone
Trap: strati-structural
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: Mumbai High, recent discovery on BNP prospect
8. Mid. Miocene carbonate (L-I and L-II, Bandra Formation)





Area: Mumbai High, DCS and adjoining area (L-I and L-II)
Reservoir rock: Limestone
Trap: structural
Source rocks: Paleocene-Eocene (Panna Formation)
Fields: Mumbai High,Heera,D-1
KRISHNA GODAVARI BASIN :
KRISHNA GODAVARI BASIN It an area of about 15,000 sq. km. of on land and the East- coast of
India , West and North western limits are demarcated by Archaean outcrops. The basin is divided
into six sub-basins. Mandapeta Sub-basin West Godavari sub-basin East Godavari sub-basin
Krishna sub-basin Nizamapatnam sub-basin K.G.Offshore sub-basin.
K.G. Basin is called the Middle-East of India as it has got such considerable amount of reserve
that if properly utilized can serve the energy needs of not only the whole of India that also will
make us more energy efficient so that we can even export crude and oil products to other nations.
Basin Introduction :.
Extensive deltaic plain formed by two large east coast rivers, Krishna and Godavari in the state of
Andhra Pradesh and the adjoining areas of Bay of Bengal in which these rivers discharge their
water is known as Krishna Godavari Basin. The Krishna Godavari Basin is a proven petroliferous
basin of continental margin located on the east coast of India .Its onland part covers an area of
15000 sq. km and the offshore part covers an area of 25,000 sq. km up to 1000 m isobath. The basin
contains about 5 km thick sediments with several cycles of deposition, ranging in age from Late
Carboniferous to Pleistocene.
The major geomorphologic units of the Krishna Godavari basin are Upland plains, Coastal
plains, Recent Flood and Delta Plains.
The climate is hot and humid with temperature reaching up to 42 degree symbol is to be inserted
C during summer. The mean day temperature varies between 35 C and 40 C during summer and
25 C and 30 C during winter.
Geological/ Geophysical Surveys
ONGC has carried out detailed geological mapping in the area covering 4220 sq. km since 1959.
Geological map of Krishna Godavari Basin.
Gravity-Magnetic surveys, in onland part have been carried out by ONGC over an area of 19,200
sq. km. In offshore area, M/s. Prakla Seismos and GSI acquired the gravity-magnetic data for
ONGC. Composite Bouguer gravity and composite magnetic anomaly map
Seismic Coverage
Conventional single fold surveys were initiated in 1965 and upto 1973 about 2,690 line km of
data was acquired. CDP surveys commenced in 1973 and so far about 34,642 Line Km. data with
foldage varying from 6 to 48 have been acquired. ONGC has also carried out 2,325 Sq. Km. 3D
seismic in onland area.
In offshore area, the first surveys of regional nature were carried out during 1964-65. These
surveys were followed by multifold 2D / 3D seismic surveys, in shallow to deep waters and
transition zone. As on 1st April 2005,(Figures of year 07-08 are to be taken instead of 2005 )
more than 74,753 Line Km. 2D and 26,508 Sq. Km. 3D seismic surveys have been carried out.
Additionally, during 1972-74, 2,028 km. Refraction data was acquired to study the basement
configuration and also shallow reflectors.
More than 225 prospects have been probed by drilling of more than 557 exploratory wells.
Hydrocarbon accumulations have been proven in 75 of these prospects (22 oil & 53 gas).
Notable oil discoveries are Kaikalur, Vadali, Mori, Bantumilli, Lingala, Suryaraopeta,
Gopavaram, Kesanapalli, and Kesanapalli West. The gas discoveries are Adavipalem,
Elamanchili, Enugupalli, Narsapur, Razole, Tatipaka-Kadali, Pasarlapudi, Mandapeta,
Chintalapalli. Nandigama, Endamuru, Penumadam, Ponnamanda, Achanta, Mullikipalle,
Magatapalli, Gokarnapuram, Kesavadasapalem, Lakshamaneshwaram, Rangapuram and
Sirikattapalli.
In onshore, so far 141 prospects have been probed by 375 exploratory wells by ONGC, out of
which 11 oil & gas pools and 31 gas pools have been discovered and most of them are on
production. In offshore ,Sso far more than 84 prospects have been probed by 182 exploratory
wells . Hydrocarbon accumulations have been proved in 33 of these prospects (11 oil & gas and
22 gas prospects). About nineteen discoveries have been made by Pvt./JV companies so far in
NELP blocks (Fifteen Dhirubhai discoveries by RIL in blocks KG-DWN-98/3 and KG-OSN2001/2, three discoveries by Cairn Energy Pty. Ltd. (CEIL) in block KG-DWN-98/2 within MioPliocene, 3 discovery by ONGC in the block KG-DWN-98/2 within Plio-Pleistocene sandstone
of Godavari formation and one discovery by GSPC in block KG-OSN-2001/3 within Lower
Cretaceous). To check the above the shallow and a deepwater discoveries.
Tectonic History :
Krishna Godavari Basin is a Continental passive margin pericratonic basin. The basin came into
existence following rifting along eastern continental margin of Indian Craton in early Mesozoic.
The down to the basement faults which define the series of horst and grabens cascading down
towards the ocean are aligned NE-SW along Precambrian Eastern Ghat trend.
The geological history comprises of following stages:
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Rift Stage:The basin got initiated through rift / syn-rift tectonics between Permo-Triassic
to Early Cretaceous and is essentially characterized by lagoonal to fluvial to occasionally
brackish water sediments. The northeastern part of the present onland basin was part of
an intra cratonic rift set up till Jurassic that constituted the southeastern extension of NWSE trending continental rift valley slopping northward. The basin has been initiated
through rifting during Permo-Triassic period.
Syn Rift Stage: The early stage synrift sediments were deposited during early subsidence
by tectonic fault systems. Basin subsidence continued along basement bound fault system
accommodating synrift sediments of late Jurassic to early Cretaceous.
Drift Stage:Rift to drift transition is marked by a southerly/ southeasterly tilt of the basin
leading to widespread marine transgression during Cretaceous and deposition of marine
shale sequence followed by onset of overall regressive phase during Late Cretaceous,
represented by a deltaic sequence comprising Tirupati Sandstone with dominant
arenaceous facies. During Maastrichtian-Danian, the basin experienced major volcanic
activity (Razole Volcanism) covering 1600 sq. km. area and having span of 5.5 million
years.
Late Drift Stage:Initial soft collision between the Indian and Eurasian Plates and
initiation of Matsyapuri-Palakollu fault appears to have greatly influenced the Paleogene
and younger tectonic regiment and the consequent sedimentation pattern.
Sediment induced Neogene tectonics: Increased gradients for the river systems and
increased sediment load coupled with significant sea level falls during Neogene had
triggered sediment induced tectonics in the shelf and slope parts of the basin creating
highly prospective exploration locales. Some of the recent very significant discoveries in
these settings had opened new hydrocarbon opportunities in the Krishna-Godavari basin
and necessitated re-estimation of its hydrocarbon resource potential.
The five major tectonic elements of the basin are- Krishna Graben, Bapatla Horst, West
Godavari Sub basin, Tanuku Horst and East Godavari sub basin.
Generalized Statrigraphy
In the northwestern and western margins of the basin, out crops of Achaean crystallines and
sediments ranging in age from Late Permian to Pliocene are present. However, major part of the
basin is covered by alluvium/sea. The geological map of the basin shows the details of outcrop
belt.
The outcrop and sub-crop lithologic information has been gathered from a large numbers of
wells drilled in the shelfal area and onland.
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The stratigraphy has been worked out.
Litho - Stratigraphy Nomenclature
Depositional Environment
Four distinct depositional systems have been recognized in Krishna Godavari basin. These are Godavari delta system, Masulipatnam shelf slope system and Nizampatinam shelf –slope system
and Krishna delta system.
The maximum thickness of the sediments in Krishna Godavari basin is around 5000 m.
Controlling factor of the thick pile of sediments is presence of long linear Gondwana rift valley.
Palaeontological evidences suggest a period of slow sedimentation and subsidence but changes
in water depth during deposition.
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Tertiary Play : Principal Depositional Elements from Shelfal Staging Area to Basin-Plain
Krishna Godavari Basin - Depositional Model of the Shallow Offshore
Seismic section showing spread of Pliocene Channel- Levee complexes and Overbank
deposits
Petroleum System :.
Krishna-Godavari basin is a proven petroliferous basin with commercial hydrocarbon
accumulations in the oldest Permo-Triassic Mandapeta Sandstone onland to the youngest
Pleistocene channel levee complexes in deep water offshore. The basin has been endowed with
four petroleum systems, which can be classified broadly into two categories viz. Pre-Trappean
and Post-Trappean in view of their distinct tectonic and sedimentary characteristics. Seismic
imaging of Pre-Trappean section poses problems in terms of data quality.
Source rich areas at different stratigraphic levels
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Hydrocarbon Generation Centres in Cretaceous.
Hydrocarbon Generation Centres in Paleocene.
Hydrocarbon Generation Centres in Eocene.
Pre -Trappean Petroleum System
Permo-Triassic
Kommugudem-Mandapeta-Red
This is the oldest known petroleum system in the basin.
Bed
Petroleum
System
Kommugudem Formation is the main source rock for this system. It belongs to
Artinskian (Upper Early Permian) age. This coal-shale unit is more than 900
Source Rock m thick in the type well Kommugudem-1.It has a good source rock potential
with rich organic matter with TOC ranging between 0.5 to 3% and vitrinite
reflectance in the deeper part of the basin is in the range of1.0 to 1.3.
Generation threshold occurred during Cretaceous.
Mandapeta Sandstone of Permo-Triassic age is the principal reservoir rock for
Reservoir
this system. It may be noted that these sandstones are in general tight and need
Rock
frac jobs for exploitation. However, porous and permeable patches are also
present and chasing them seismically is a major exploration challenge.
Tight layers within Mandapeta Sandstone and the overlying argillaceous Red
Cap Rock
Bed act as effective seals.
Entrapment is essentially structural in nature. As mentioned earlier, seismic
Entrapment mapping of pre-trappean section has serious problems due to the presence of a
good seismic energy reflector in the form of Basalt above this system affecting
the seismic data quality.
Late Jurassic-Cretaceous Raghavapuram-Gollapalli-Tirupati-Razole Petroleum System
Source Rock Raghavapuram Shale of Lower Cretaceous age is considered as the principal
Reservoir
Rock
source rock not only for this system but also for the onland part of the basin.
Maximum thickness up to 1100 m is recorded in the subsurface. The sequence
comprises essentially carbonaceous shale with intervening sands possibly
representing brief regressive phases in an otherwise major transgressive phase.
The organic matter is dominantly of Type III and III B. The maturity level
varies between catagenetic to inadequately matured in different parts of the
basin. TOC is recorded up to 2.4%. It has the proclivity for generation of both
oil and gas.
Lenticular sands within Raghavapuram Shale possibly representing
intervening regressive phases are one of the potential exploration targets;
though mapping them seismically poses some challenges as mentioned above.
A recent major find in its time equivalent (?) in shallow offshore part of the
basin opened up some very exciting exploration opportunities in this sequence.
Recent exploratory efforts in deep offshore also indicated prospectivity in
Cretaceous sequence
Sands within Gollapalli Formation of Late Jurassic-Early Cretaceous in
Mandapeta-Endamuru area and its time equivalent Kanukollu Formation in
Lingala-Kaikalur area are another potential target in this petroleum system.
A northeast southwest trending corridor of Upper Cretaceous Tirupati
Sandstone, product of a regressive phase, between southeastern side of Tanuku
Horst and MTP fault is emerging as another important target.
Raghavapuram Shale acts as effective seal for both Gollapalli reservoirs and
the sands within Raghavapuram Shale. Shale intercalations within Tirupati
Formation appear to act as seal for the accumulations within the Formation.
Cap Rock
Razole Formation (Deccan Basalt) acts as a regional cap for the pre-trappean
hydrocarbon accumulations. It is of interest to note that occasional occurrence
of hydrocarbons is noticed within Razole Formation itself, indicating its
reservoir potential also.
Entrapment While the entrapment style is essentially structural, accumulations in
Raghavapuram Shale have strati-structural element in their entrapment.
Post-Trappean Petroleum System:
Palakollu-Pasarlapudi Petroleum System
It is the most prolific system in the onland part of the basin contributing major part of the onland
hydrocarbon production. It has an abnormally pressured source sequence and a reservoir
sequence with more than normal pressures.
The Paleocene Palakollu Shale is the source sequence. It is deposited in
Source Rock considerable thickness in the area to the south of MTP fault with a ENE-WSW
alignment paralleling the fault. It shows fair to god source rock potential with
proclivity to generate mainly gaseous hydrocarbons. TOC ranges between 0.6
to >5% and is dominantly humic type, rich in inertinite and about 10-20%
contribution is from Type II organic matter. Subsidence history of Palakollu
Shale suggests generation threshold to be around Middle Eocene.
Sand layers within source rich Palakollu Shale are found to be potential
reservoir rocks, though most often with very limited accumulations.
Reservoir
Associated high pressures also do not make them attractive targets.
Rock
Pasarlapudi Formation of Lower to Middle Eocene is the principal producing
sequence onland with many potential reservoir levels.
Laterally persistent shales within Pasarlapudi Formation have been found to
act as effective seals for the accumulations within Pasarlapudi Formation.
Cap Rock
Palakollu Shale encompassing the occasional sands within the Formation also
acts as seal for them.
Though structural entrapment is the dominant element for Pasarlapudi
Entrapment
Formation, strati-structural element also appears to be occasionally present.
Vadaparru Shale –Matsyapuri / Ravva Formation-Godavari Clay Petroleum System
Discovery of medium sized fields with liquid hydrocarbon in the Coastal Tract, significant
discovery of Ravva Field in the shallow offshore and some very exciting mega discoveries in
deep offshore parts of the basin have made this youngest petroleum system, a very important
one.
: Vadaparru Shale is the principal source sequence. Average TOC for this
sequence is about 4%. Organic matter is in the early phase of maturation in the
coastal part and increases basin ward. Organic matter is of Type III and has
potential to generate both oil and gas. Generation threshold for this sequence
is around Lower Miocene.
Source Rock
An interesting recent observation regarding the source sequence is that some
major gas accumulations in both shallow and deep offshore are found to be of
biogenic origin also. This observation throws some interesting challenges in
terms of exploration strategies to be adopted especially for the offshore part of
the basin.
Sands within Matsyapuri and Ravva Formation and also the sands within
Vadaparru Shale are important potential levels and are known to house
significant hydrocarbon accumulations in the basin. Recent discoveries in the
Reservoir
channel- levee complexes in intra slope terrace/basin setting within Godavari
Rock
Clay of Pliocene-Pleistocene has opened up hitherto unexplored frontiers of
the basin for exploration.
Shales within Matsyapuri and Ravva Formations, Vadaparru Shale and
Cap Rock
Godavari Clay act as effective seals.
Though structural element plays dominant role for hydrocarbon accumulations
Entrapment in this system, role of strati-structural element is noticed. Clear understanding
of sediment induced tectonics and precise mapping techniques for reservoir
facies can yield very rich dividends especially in the younger sequences.
Krishna-Godavari Basin endowed with such effective petroleum systems
ranging from Permo-Triassic to Pleistocene offer very exciting exploration
challenges with matching rewards especially in deep water areas.
Hydrocarbon Potential :.
The Krishna Godavari Basin is an established hydrocarbon province with a resource base of
1130 MMT, of which, 555 MMT are assessed for the offshore region (upto 200 m isobath .
Several oil and gas fields are located both in onland and offshore parts of the basin. The
entrapments are to be expected from Permo-Triassic to Pliocene sediments. The Tertiary
hydrocarbon entrapments are so far observed only in offshore part of the basin while Paleogene
to Permo-Triassic entrapments are discovered in East Godavari and West Godavari sub-basins in
the onland part.
The reservoir facies of Permo-Triassic occur within the well identified source facies at the
bottom and overlying Cretaceous argillaceous facies, which act as source as well as cap. In view
of the fact that hydrocarbon indications are observed in well KB-4B-1, drilled in the north
western part of offshore basin, and also, in well KG-1-B-1, indication of gas with higher
hydrocarbon and oil stains in ditch samples collected from Late Paleozoic sediments, imparts the
older sequence a fair degree of importance. These older sediments can also be expected to be
present upto Krishna island area around the coastal part. The occurrence of gas fields like
Mandapeta and Endamuru and indications of hydrocarbons in offshore areas point to the fair
potential of this sequence.
The Cretaceous and Early Tertiary accumulations of hydrocarbons are present in several fields
e.g., Kaikalur, Bantumilli, Lingala, Narsapur, Razole Chintalapalli etc. both in East as well as
West Godavari Sub-Basins. The Cretaceous sequence in offshore wells, like well KB-1B, has
also indicated presence of hydrocarbons during drilling. Suitable source and reservoir facies are
also reported in this well. The hydrocarbon generation centers in Cretaceous are shown in Figure
10. In view of this, the Cretaceous holds good potential for accumulation of hydrocarbons where
some twenty commercial accumulations have been discovered so far.
A number of gas fields are producing from Paleocene reservoirs, particularly in East Godavari
Sub-Basin. The Tatipaka, Pasarlapudi, Kadali and Manepalli are the fields located onland, while,
GS-8 is occurring in the offshore part of the basin. The hydrocarbon generation centers in
Paleocene indicate fair to rich organic content on the basinal side. The indications of gas and its
pressure in this sequence justify good potential for Paleocene in the basin. Ten pools of
hydrocarbon have already been discovered in this age group.
The Eocene accumulation of gas is observed in Elamanchili, Tatipaka, and Pasarlapudi etc. Mori
prospect is oil producer. These oil fields including GS-38 in offshore area indicate good
hydrocarbon potential in Eocene sequence. Hydrocarbon generation centers in Eocene. Reefal
limestone and associated shelf sediments of Eocene age form another category of hydrocarbon
plays, in the lower deltaic areas of Godavari river and shallow waters of Masulipatnam Bay.
Drape folds on tilted narrow fault block may have the potential for both oil and gas entrapment.
Eight hydrocarbon pools have already been discovered.
The Mio-Pliocene sequence in offshore part is promising. The commercial hydrocarbon
accumulation in Ravva field is well known. The prospects GS-38, G-1 and G-2 are also
hydrocarbon bearing in Mio-Pliocene strata. As many as fourteen commercial finds have come
from this sequence.