GEOSCIENCE
NOYAL D JOSE
LSES,BANGALORE
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INDEX
TOPIC
PAGE NO.
1)CRYSTALLOGRAPHY
3
2)ECNOMIC GEOLOGY
 MINERLOGY
 ECNOMIC MINERALS
9
10
18
3)GELOGICAL TIMESCALE
20
4)PETROLIFEROUS BASINS OF INDIA
23
5)ROCKS
36
6)STRATIGRAPHY OF INDIA
43
7)REFERENCE
47
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CRYSTALLOGRAPHY
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What is a crystal?
• A crystal is a periodic arrangement of objects (molecules) repeating in two or three dimensions.
• The repeating unit is a parallelepiped (in 3-D) or a parallelogram (in 2-D).
• A crystal of a typical protein will be half a mm on a side and contain 10molecules.
Symmetry of crystals
Symmetry: An operation of rotation, translation, inversion, mirroring, or some
combination of these that takes an object back into itself.
•The simplest symmetry in a crystal is repetition.
•The repeated motif may have its own symmetry.
Atoms and crystals
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Crystal structure
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3-D Bravais lattices
Some relevant crystal structures
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Simple cubic lattice
Body centered cubic lattice (bcc)
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Miller indices, cubic lattices
Effects of temperature
Crystalline and non-crystalline materials
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Economic Geology
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MINERALOGY
Mineral resources can be divided into two major categories - Metallic and Nonmetallic.
Metallic resources are things like Gold, Silver, Tin, Copper, Lead, Zinc, Iron, Nickel,
Chromium, and Aluminum. Nonmetallic resources are things like sand, gravel, gypsum,
halite,Uranium, dimension stone.
A mineral resource is a volume of rock enriched in one or more useful materials.
Finding and exploiting mineral resources requires the application of the principles of
geologySome minerals are used as they are found in the ground, i.e. they require no
further processing or very little processing.
For example - gemstones, sand, gravel, and salt (halite).
Most minerals must be processed before they are used. For example:
 Iron is the found in abundance in minerals, but the process of extracting iron
from different minerals varies in cost depending on the mineral. It is least costly
to extract the iron from oxide minerals like hematite (Fe2O3), magnetite (Fe3O4),
or limonite [Fe(OH)]. Although iron also occurs in olivines, pyroxenes,
amphiboles, and biotite, the concentration of iron in these minerals is less, and
cost of extraction is increased because strong bonds between iron, silicon, and
oxygen must be broken.
 Aluminum is the third most abundant mineral in the Earth's crust. It occurs in the
most common minerals of the crust - the feldspars (NaAlSi3O8, KalSi3O8, &
CaAl2Si2O8, but the cost of extracting the Aluminum from these minerals is high.
Thus, deposits containing the mineral gibbsite [Al(OH)3], are usually sought. This
explains why recycling of Aluminum cans is cost effective, since the Aluminum in
the cans does not have to be separated from oxygen or silicon.
Because such things as extraction costs, labor costs, and energy costs vary with time
and from country to country, what constitutes an economically viable deposit of minerals
varies considerably in time and place. In general, the higher the concentration of the
substance, the more economical it is to mine. Thus we define an ore as a body of
material from which one or more valuable substances can be extracted economically.
An ore deposit will consist of ore minerals, that contain the valuable substance. Gangue
minerals are minerals that occur in the deposit but do not contain the valuable
substance. Since economics is what controls the grade or concentration of the
substance in a deposit that makes the deposit profitable to mine, different substances
require different concentrations to be profitable. But, the concentration that can be
economically mined changes due to economic conditions such as demand for the
substance and the cost of extraction.
Examples:
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
The copper concentration in copper ore deposits has shown changes throughout
history. From 1880 to about 1960 the grade of copper ore showed a steady
decrease from about 3% to less than 1%, mainly due to increased efficiency of
mining. From about 1960 to 1980 the grade increased to over 1% due to
increasing costs of energy and an abundant supply produced by cheaper labor in
other countries.

Gold prices vary on a daily basis. When gold prices are high, old abandoned
mines reopen, when the price drops, gold mines close. The cost of labor is
currently so high in the U.S. that few gold mines can operate profitably, but in
third world countries where labor costs are lower, gold mines that have ore
concentrations well below those found in the U.S. can operate with a profit. For
every substance we can determine the concentration necessary in a mineral
deposit for profitable mining. By dividing this economical concentration by the
average crustal abundance for that substance, we can determine a value called
the concentration factor. The table below lists average crustal abundances and
concentration factors for some of the important materials that are commonly
sought. For example, Al, which has an average crustal abundance of 8%, has a
concentration factor of 3 to 4. This means that an economic deposit of Aluminum
must contain between 3 and 4 times the average crustal abundance,that is
between 24 and 32% Aluminum, to be economical.
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Note that we will not likely ever run out of a useful substance, since we can always find
deposits of any substance that have lower concentrations than are currently
economical. If the supply of currently economical deposits is reduced, the price will
increase and the concentration factor will increase.
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Origin of Mineral Resources
Mineral deposits can be classified on the basis of the mechanism responsible for
concentrating the valuable substance.
 Magmatic Ore Deposits - substances are concentrated within a body of igneous
rock by magmatic processes like crystal fractionation and crystal
settling.Magmatic process such as partial melting, crystal fractionation, or crystal
settling in a magma chamber can concentrate ore minerals containing valuable
substances by taking elements that were once widely dispersed in low
concentrations in the magma and concentrating them in minerals that separate
from the magma.
Examples:
Pegmatites

Hydrothermal Ore Deposits - Concentration by hot aqueous (water-rich) fluids
flowing through fractures and pore spaces in rocks. Hydrothermal deposits are
produced when groundwater circulates to depth and heats upeither by coming
near a hot igneous body at depth or by circulating to great depth alongthe
geothermal gradient. Such hot water can dissolve valuable substances
throughout a large volume of rock. As the hot water moves into cooler areas of
the crust, the dissolved substances are precipitated from the hot water solution.
If the cooling takes place rapidly, such as might occur in open fractures or upon
reaching a body of cool surface water, then precipitation will take place over a
limited area, resulting in a concentration of the substance attaining a higher
value than was originally present in the rocks through which the water passed.
Examples:
Massive sulfide deposits,Vein deposits, Stratabound ore deposits

Sedimentary Ore Deposits - substances are concentrated by chemical
precipitation from lake or sea water. Although clastic sedimentary processes can
form mineral deposits, the term sedimentary mineral deposit is restricted to
chemical sedimentation, where minerals containing valuable substances are
precipitated directly out of water.
Examples:
Evaporite Deposits,Iron Formations –

Placer Ore Deposits - substances are concentrated by flowing surface waters
either in streams or along coastlines. The velocity of flowing water determines
whether minerals are carried in suspension or deposited. When the velocity of
the water slows, large minerals or minerals with a higher density are deposited.
Heavy minerals like gold, diamond, and magnetite of the same size as a low
density mineral like quartz will be deposited at a higher velocity than the quartz,
thus the heavy minerals will be concentrated in areas where water current
velocity is low. Mineral deposits formed in this way are called placer deposits.
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They occur in any area where current velocity is low, such as in point bar
deposits, between ripple marks, behind submerged bars, or in holes on the
bottom of a stream. The California gold rush in 1849 began when someone
discovered rich placer deposits of gold in streams draining the Sierra Nevada
Mountains. The gold originally formed in hydrothermal veins, but it was eroded
out of the veins and carried in streams where it was deposited in placer deposits.
�

Residual Ore Deposits - substances are concentrated by chemical weathering
processes. During chemical weathering and original body of rock is greatly
reduced in volume by the process of leaching, which removes ions from the
original rock. Elements that are not leached form the rock thus occur in higher
concentration in the residual rock. The most important ore of Aluminum, bauxite,
forms in tropical climates where high temperatures and high water throughput
during chemical weathering produces highly leached lateritic soils rich in both
iron and aluminum. Most bauxite deposits are relatively young because they
form near the surface of the Earth and are easily removed by erosion acting over
long periods of time. In addition, an existing mineral deposit can be turned in to a
more highly concentrated
Mineral Deposits and Plate Tectonics
Because different types of mineral deposits form in different environments, plate
tectonics plays a critical role in the location of different geological environments. The
diagram to the right shows the different mineral deposits that occur in different tectonic
environments.
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Mineral Exploration and Production
Ores are located by evidence of metal enrichment. Geologists look for hints in rocks
exposed near the surface, for example, the enrichment process often results in
discoloration of the soil and rock. When such hints are found, geophysical survey's
involving measuring gravity, magnetism, or radioactivity are conducted. Geochemical
surveys are conducted which analyze the composition of water, sediment, soil, rocks,
and sometimes even plants and trees. Once it is determined that a valuable material
could be present, the deposit is assessed by conducting core drilling to collect
subsurface samples, followed by chemical analysis of the samples to determine the
grade of the ore If the samples show promise of being economic to mine, then plans are
made to determine how it will me mined. If the ore body is within 100 meters from the
surface, open-pit mines, large excavations open to the air.are used to extract the ore
before processing. Open pit mines are less expensive and less dangerous than tunnel
mines, although they do leave large scars on the land surface. If the ore body is deeper,
or narrowly dispersed within the non-ore bearing rock tunneling is necessary to extract
the ore from underground mines. Mine tunnels are linked to a vertical shaft, called and
adit. Ores are removed from the walls of the tunnels by drilling and blasting, with the
excavated ores being hauled to the surface from processing. Underground mines are
both more expensive and dangerous than open pit mines and still leave scares on the
landscape where non-ore bearing rock is discarded as tailings. .
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Economic Minerals
Any mineral that has economic potential (i.e., it makes someone money),is defined as an
economic mineral.
Mineral
Economic Use
bauxite
calcite
dolomite
chalcopyrite
galena
garnet
gypsum
graphite
halite
olivine
diamond
sulfur
fluorite
kaolinite
hematite
limonite
magnetite
malachite
quartz
sphalerite
talc
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aluminum ore
Portland cement, chalk, antacids
vitamins, antacid, garden lime
copper ore
lead ore
gemstones, jewelry, sand paper
sheetrock, plaster, cosmetics
lubricants, pencil lead
table salt
jewelry (mineral peridot)
abrasives, girl's best friends
pharmaceuticals, asphalt, plastics
dental applications, steel flux
clay, pottery, tile, Kaopectate, cosmetics
iron ore
iron ore
iron ore
jewelry, copper ore
electronic applications
zinc ore
lubricant, talcum powder
Global Mineral Needs
Because the processes that form ores operate on geologic time scales, the most
economic mineral resources are essentially non renewable.New deposits cannot be
generated in human timescales. But, as mentioned previously, as the reserves of
materials become depleted it is possible to find other sources that are more costly to
exploit. Furthermore, mineral resources are not evenly distributed. Some countries are
mineral-rich; some are mineral-poor. This is a particular issue for strategic mineral
resources. These strategic metals are those for which economical source do not exist in
the U.S., must be imported from other potentially non-friendly nations, but are needed
for highly specialized applications such as national security, defense, or aerospace
applications. These metals include, Manganese, Cobalt, Platinum, and Chromium, all of
which are stockpiled by the U.S. government in case supplies are cut off. How long
current mineral resources will last depends on consumption rates and reserve
amounts. Some mineral resources will run out soon, for example global resources of
Pb, Zn, and Au? will likely run out in about 30 years. U.S. resources of Pt, Ni, Co, Mn,
Cr less than 1 year. Thus, continued use of scarce minerals will require discovery of
new sources, increase in price to make hard-to-obtain sources more profitable,
increased efficiency, conservation, or recycling, substitution of new materials, or doing
without.
Environmental Issues
Extraction and processing has large environmental impacts in terms of such things as
air quality, surface water quality, groundwater quality, soils, vegetation, and aesthetics.
Acid mine drainage is one example, Sulfide minerals newly exposed to Oxygen and
water near the surface create sulfuric acid. Rainwater falling on the mine tailings
becomes acidified and can create toxic conditions in the runoff. This can mobilize
potentially dangerous heavy metals and kill organisms in the streams draining the
tailings.
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THE GEOLOGICAL TIME SCALE
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The scale of geologic time is vast, currently estimated at nearly 4.6 billion
years. During that time, life evolved into the familiar forms we see today.
These materials are provided to assist in understanding time relationships
and how life on Earth changed through time
What is a fossil?

Remains or evidence of once living organisms, preserved to varying
degrees of completeness, found in geologic deposits in the Earth’s crust
 ! Age must be at least 10,000 years old, younger is considered historic
period
 Preservation may be as original material, partially or completely altered, or
only an impression of the original material
!
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Petroliferous Basins of India
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The sedimentary basins of India have received attention of geoscientists due to increased
activities for petroleum exploration since 1950’s. Sophisticated geophysical technique
together with drilling made it possible to obtain vast amount of subsurface data, and tied
wherever possible with surface geology.
The geoscientific studies by ONGC in the petroliferous basins of India from are summarized in
the present contribution, andtakes into account, the interpretations based on real well data, the
seismic and other geophysical information, multimicrofossil bio-stratigraphy, sedimentology
and geochemistry. More specifically, we deal with,
1. Sedimentary petroliferous basins along the Western margins: viz. Rajasthan, Cambay, Kutch,
Mumbai Offshore and Kerala- Konkan
2. East Coast Basins: Cauvery, Krishna-Godavari, Mahanadi and Bengal basins
3. Northeast Basins: Assam and Assam-Arakan basin
4. Central Indian Basins: Ganga and Purnea basins
Basins in Rajasthan
The western Rajasthan shelf located to the west of Aravalli ranges, possesses three important
basins viz., Jaisalmer, Bikaner-Nagaur and Barmer, stretching over an area of about 1,20,000km.
The Jaisalmer Basin
This is the westernmost is separated from the Bikaner-Nagaur basin (Fig. 2) by the PokaranNachana high to the northwest and from the Barmer basin by the Barmer-DevikotNachana high in the south. A pronounced NW-SE-trendingregional step-faulted Jaisalmer-Mari
high zone, marked by the Kanoi and Ramgarh faults that traverse the centre of the basin and
divides it into the Shahgarh sub-basin, the Miajalar sub-basin and the Kishangarh sub-basin. This
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basin in the northwestern Indian shield extends as far as the Mari region of Pakistan, and is
tectonically related to the Indus Basin from the beginning of the Triassic. The aerial extent
is over 30,000 km2.This basin is controlled by wrench-fault tectonics.
CAMBAY BASIN
The Cambay Basin, the southern continuation of the Barmer-Sanchor Graben is a narrow
elongated (NNW-SSE trending) intra-cratonic rift basin (area 59,000 sq.km), situated between
Saurashtra craton to the west, Aravalli swell on the northeast and Deccan craton to the southeast.
In the south, it extends into Cambay Gulf and ultimately into the Arabian Sea. A large part of the
basin is covered by Quaternary sediments. Cenozoic outcrops are rare and occur only on the
fringes of the basin. The extensional architecture of the basin is defined by three major
Precambrian trends viz., NNW-SSE trend related to Dharwarian orogeny NE-SW trend related to
Aravalli orogeny, and ENE-WSW trend related to Satpura orogeny orogeny, and ENE-WSW
trend rela
THE WESTERN CONTINENTAL OFFSHORE BASINS
The western continental margin (WCM) of India hosts three major basins viz., Kutch, Mumbai
offshore and Kerala – Konkan, out of which the Mumbai offshore is the major
petroliferous basin, with the other two having oil and gas indications. The continental margin is
featured by parallel to sub parallel ridges and intervening depressions. The continental shelf on
the western margin is wide and tapering, 300 km wide off Kutch-Saurashtra in the north,
narrowing down progressively southward to 60 km in Kerala offshore.
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The WCM comprises shelfal horst/graben complex, Kori- Comorin ridge (KCR) and LaxmiLaccadive Ridge (LLR) from east to the west with sediment fill in the basinal depressions
between them. Three basins are recognized in the offshore, which from the north to south are the
Kutch Basin, the Mumbai Offshore Basin, and the Kerala-Konkan basin. A series of ENE-WSW
ridges separate each of these basins
KUTCH (KACHCHH) BASIN
The Kutch basin, located roughly west of the Cambay Basins extending from land to offshore,
exposes classic Jurassic and Cretaceous succession amidst the vast alluvium covered Rann. The
Mesozoic basin, is a south-western continuation of the Rajasthan basins, extending into the
offshore with a wide shelf platform. The northern limit of the basin continues beyond the IndoPakistan border. In south, the basin is contiguous with Mumbai offshore basin. The surface
outcrop mapping and stratigraphy has been worked in detail in Mesozoic-Cenozoic succession
and it has been possible to extend these units in the offshore through excellent biostratigraphic
correlation especially in the Cenozoic. Extensive development of Deccan Trap covers the highest
Mesozoic succession in the outcrops and continues in the subsurface of the Kutch shelf. The
infratrappean succession comprises clastic sediments of Middle Jurassic to Late Cretaceous. In
the Gulf, however, the Late Cretaceous is mainly a carbonate facies.
MUMBAI OFFSHORE BASIN
The Mumbai offshore basin is the most important producer among the Cenozoic hydrocarbon
basins of India, mainly from the carbonate reservoirs stretching between the Deep continental
shelf (DCS) structure in west to shallow waters in the east. The basin is bounded by the Deccan
Trap outcrops to its north and east, Kori-Comorin ridge to its west and Vengurla arch to its south
and covers an area of about 1,48,000 sq km up to 200 m isobath. Tectonically, Mumbai basin has
evolved from a rift basin, with the main rift (Central Graben) and is a continuation of the
Cambay rift to the south with a lateral shift. The basin is dissected by ENE-WSW grabens
forming two additional very large depo-centres, apart from that of the Central graben, one to the
north (Tapti-Daman Low), and one to the south (South Bombay Low). Post Oligocene there has
been a westward tilt in the basin with a Miocene Hinge line developing. Based on the tectonic
evolution, two sequences have been identified within the Cenozoic succession. The Lower
Paleocene sediments deposited as synrift and initiating the Cenozoic sedimentation. The upper
post-rift sedimentary succession of late Paleocene to Recent have been further subdivided into
successions based on unconformities and their magnitude on the basis of excellent biostratigraphic control.
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KERALA – KONKAN BASIN
This basin lying south of Mumbai offshore basin is bounded by Vengurla arch in north and
extends beyond Cape Comorin into the Indian ocean to the south. It covers an area of ~77,000 sq
km up to 200m isobath and dividedinto two subbasins the Konkan basin between Vengurla and
Tellichery arch and Kerala basin between Tellichery and Trivandrum arch. The basement arches
control the architecture and north- south limits of the basin. The northernmost Vangurla arch
separates the shelfal horstgraben complex of this basin from that of Mumbai offshore
basin, and is differentiated into three shallow depressions by transverse basement arches. These
are Konkan depression, Cochin depression and Cape Comorin depression. The Cretaceous-
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Recent sedimentary succession in the basin is divided into two sequences. The lower,
corresponding to rifting and separation of Madagascar from India-Seychelles
(~90-110Ma in early Cretaceous and earliest part of Late Cretaceous) is referred to as the rift
sequence and overlying late Cretaceous to Recent is referred to as the passive margin
sequence. The event of separation of Madagascar (³ 90 Ma) is represented by ‘older’ traps dated
90-110 Ma in the basin representing the rift sequence. The sedimentary succession
(Late Cretaceous and younger) overlying the older traps represent the passive margin setup. The
lowest sequence (late Cretaceous), limited between older and younger basalts
(Deccan trap equivalent) is encountered in wells drilled in offshore. The succession comprises
sand, shale and siltstone deposited in an inter-middle shelf setup.
EAST COAST BASINS
The Jurassic fragmentation of eastern Gondwanaland initiated with the dismembering of
Antarctica and Australia from India and, concomitant formation of NE-SW trending
Mesozoic rift basins on the eastern continental margin of the latter including Assam, Bengal,
Mahanadi, Palar, Krishna- Godavari and Cauvery basins. These evolved from
a composite of rifted graben in late Jurassic, and later formed a part of the divergent passive
margin. Numerous down-to-basin extensional faulting took place in the basin
due to rifting. Active subsidence along these normal faults parallel to Precambrian Eastern Ghat
trend gave rise to horst-graben setting. Several stages of reactivation of synrift extensional faults
are noticeable.
Cauvery Basin
Cauvery Basin, on the east coast of India, extends from Pondicherry in the north to Tuticorin in
the south, stretching into offshore Bay of Bengal and spans over an area of 62,500 sq.km. upto
200 m isobath (Fig. 10). In the exploratory wells in onland and offshore, the sediments range in
age from Oxfordian (late Jurassic) to Recent. Outcrops are patchy. Five major unconformities
late Albian, Turonian, Campanian, Maastrichtian and Miocene are observed inoutcrops, and
excepting the Campanian unconformity, other unconformities are also recorded in the
subsurface. The hiatus at Turonian was probably caused by Marian mantle plume and consequent
mild basin exhumation. At the KTB unconformity, development of continental facies has been
observed in outcrops. During the late Cretaceous, direction of sea floor spreading changed
parallel to Ninety-East ridge. The north ward movement of Indian plate was taken upon the
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Chagos-Laccadive transform on the west and NinetyEast Ridge transform at eastern plate edge.
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Mahanadi Basin
Mahanadi basin is located along northeastern part of east coast of India and extending to the Bay
of Bengal. The area covers roughly 1, 40,000 sq km up to 2500 m iso-bath
in offshore region.
Bengal Basin
The Bengal Basin lies within the state of West Bengal and covers Bangladesh and northern part
of Bay of Bengal. It encompasses an area of 90,700 sq km. It is demarcated by Indian shield in
north and west and Surma Basin to the east. Singhbhum-Chotanagpur massifs with isolated
lower Gondwana as outliers are exposed in the western part (Fig. 13). The Rajmahal Traps are
exposed in the northwestern part. It is a divergent margin basin, resting orthogonally over
intracratonic Damodar graben with Permo-Triassic sediments and Rajmahal Traps. A thick
succession of late Cretaceous and younger succession is deposited over the eroded Gondwanas
with several intervening nondepositional hiatuses. The rift and post-trappean phase of tectonic
development is recognised. During the initial extensional tectonics, continental-fluvial and
lacustrine sediments were deposited in a graben setup. Large amount of basic lava erupted
through the fractures as a consequence of crustal distension accompanying the rifting. The major
eruptive centre was in Rajmahal hills
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NORTHEAST BASINS
Assam and Assam-Arakan Basin
This basin extends over a large area of NE India, Myanmar and Bangladesh, covering an area of
over 0.1 M sq km. The basin in its deepest parts has accumulated more than 15-20 km of
Mesozoic and younger sediments. It has a polycyclic sedimentation history with distinct episodes
of tectono-sedimentary evolution, and with phases of superposing tectonics presenting a complex
picture
Earliest Permo-carboniferous sedimentation record was within intra-cratonic grabens along
Precambrian weak zones with sediments derived from highland as alluvial fans and delta settings
during early Permian. At this time, India was a part of Gondwanaland continent. This was
followed by later rifting, northward movement, and emergence of passive margin setting and
collision of Indian and Eurasian plates leading to rise of Himalayas. During the second phase of
rifting in early Cretaceous preceding the India-Antarctica
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CENTRAL INDIAN BASINS
Ganga Basin
The vast alluvial sediments of Ganga River and its tributaries occur between rugged upland of
Peninsular India and the rising mountain province of Himalaya. This Indo-Gangetic plain
represents a deep (>8 km thick sediments). In this still deepening foreland basin, sediments
range in age from Mesoproterozoic to Recent . The Basin extends from Delhi-Kalka ridge in the
west, to the Monghyr-Saharsa ridge in east, and covers an area of ~ 0.3 M sq km
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Purnea Basin
The Purnea Basin is located in eastern part of Bihar and north Bengal, and bordered in south by
hills of Rajmahal volcanics and to the north by the Siwaliks along sub- Himalayan foothills.
Further, it is bounded by Bhawanipur fault in west and Kishanganj fault zone in east. The
southern limit of the basin, covering ~18000 sq. km. remains undefined in view of its possible
continuity with Bengal basin. The sedimentary package in the basin, comprising Gondwana and
Cenozoic sediments, directly overlies the crystalline basement. The basin located between
northwest Ganga basin and southeastern Bengal basin, shares its geological history with both
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Rocks
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Sedimentary rocks
Rivers are able to carry bits of rock that have been weathered and eroded. These pieces of rock
grind against each other and become rounded. The faster the river water flows, the larger the
pieces of rock it can transport. When a river enters a lake or the sea, it slows down. Its load of
rock fragments fall to the bottom, forming layers of pebbles, sand and mud. These deposited
layers are called sediments.
The layers of sediment build up and are buried one on top of the other. They are compressed,
and their weight squeezes out the water. Eventually (often after millions of years) the pieces of
rock in the sediment become cemented together to form sedimentary rocks.
Example of sedimentary rocks: sandstone (from grains of sand)
limestone (contains the shelly remains of living creatures)
mudstone (from mud)
Sedimentary rocks are found in ancient dried out lakes and seas (which might now be buried
underground). They often contain fossils as a result of moulds, traces and casts of animals and
plants being trapped and preserved when the sediments were laid down.
There are two (2) types of sedimentary rocks, based on their textures:
1. Clastic (also called “Detrital”)-- form from deposition of solid grains; classified based on
grain size: conglomerate, sandstone, and shale
2. Chemical -- form from minerals precipitating out of water and usually involves some sort of
chemical reaction; classified based on mineral content: limestone, dolomite are examples.
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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
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Igneous Rocks
Igneous rocks come from molten rock called magma. The magma rises upwards from the mantle
and, when it cools, solidifies into hard crystalline rock. There are two main types of igneous
rock:
1. The magma comes from deep underground and is forced into the upper layers of the Earth’s
crust. It cools slowly here, and large crystals form. Granite is an example of this type of rock.
2. The magma erupts from a volcano. It cools quickly on the ground and only small crystals
form.
Basalt is an example of this type of igneous rock.
rocks form from molten rock (magma) crystallizing below earth's surface or from
volcanic activity. They commonly form at plate boundaries and are commonly
exposed in mountainous areas. Igneous rocks form from crystallization of magma at
depth (within the earth's crust) or at the surface (from volcanic eruptions)
There are two (2) basic types or forms of igneous rocks
Plutonic rocks= intrusive igneous rocks = igneous rocks that form from cooling
magma at depth
Extrusive igneous rocks= igneous rocks that form from volcanic activity (at or
near surface)
In general:
Plutonic rocks are usually coarse-grained
Extrusive rocks are usuallyfine-grained
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Bowens Reaction Series:
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


Professor Norman L. Bowen summarized results of experiments done early in
the 1900’s on crystallization of granitic magmas.
These experiments showed that there is a definite sequence of minerals that
crystallize as the temperature of magma is lowered:
Start with a collection of molten magma and progressively cool it. Minerals will
crystallize (solidify) in a order.
Bowen’s Reaction Series represents a sequence that has implications for other
types of rocks as well, although it is only used to determine the crystallization
sequence in a molten magma (intrusive igneous rocks).
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Metamorphic Rocks
Movements of the earth can cause rocks of all types (including sedimentary and igneous rocks)
to become buried deep underground. Once they are underground, the rocks are subjected to high
temperatures and/or high pressures. They do not melt, but their crystal structure and appearance
change. Rocks that contain bands of crystals are likely to be metamorphic.
Other examples of metamorphic rock: slate (from mudstone)
marble (from limestone)
Metamorphic rocks can be found by mountain belts (because pressure and heat are involved
when mountains are formed) and near volcanoes
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Agents of Metamorphism
1 Heat
– Very important because heat drives chemical reactions that result in recrystallization
– Increased heat can be caused by
• The intrusion of a magma
• The subduction of rocks to greater depths
2 Pressure
– Increased pressure caused by
• Subduction of rock to greater depths
• Episodes of mountain building
3 Chemically Active Fluids
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Stratigraphy for the Indian Subcontinent
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The word Stratigraphy derived from Latin stratum and the Greek graphia is literally the
description of strata. Stratigraphy remained a descriptive science for nearly one and half
centuries. But as conceived now stratigraphy is a dynamic subject. The time concept in
stratigraphy established on the basis of lithology, biota, radiogenic-isotope, geochronology,
geomagnetic polarity time scale, chemostratigraphy, Earth’s orbital parameters and
cyclestratigraphy is a fundamental to understanding the dynamic evolution of Planet Earth.
Types of Stratigraphy and properties used in these definitions
Stratigraphy
Lithostratigraphy
Biostratigraphy
Magnetostratigraphy
Chemostratigraphy
Chronostratigraphy
Allostratigraphy
Seismic stratigraphy
Sequence stratigraphy
Defined by
Lithology
Fossils
Magnetic polarity
Chemical properties
Absolute ages
Discontinuities
Seismic data
Depositional trends
Status in India
Nearly complete
Done, needs integrated studies
Continuing work on outcrops
Preliminary stage
Preliminary stage
Some work done
continuing work
Needs acceleration in effort
Lithostratigraphic classification of the Paleozoic sequence of the Kashmir Tethys
Himalayan sequences in the Lidder Valley, J & K.
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Lithostratigraphic classification of the Indus Group
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REFERENCES
1) Paolo Fornasini
Department of Physics
University of Trento, Italy
2) Prof. Stephen A. Nelson
Tulane University
3) B. A. Vining and Baker Hughes, UK
4)S. C. Pickering
Schlumberger,
Gatwick, UK
5) John H. Wood, Gary R. Long and David F. Morehouse
Energy Information Administration
6)Prof.Ramasamy,IIT_Madras
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