siwaliks and oild bearing tertiary deposits
TRANSCRIPT
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Siwalik Hills
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Siwalik
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SIWALIK GROUP
Its extent in Pakistan, Jammu andKashmir, Himachal Pradesh andUttaranchal.
The name Siwalik was originally given by
Captain P.T. Cautley in the early 19thCentury (1832) to the outermost Sub-Himalayan Ranges.
He discovered the Siwalik fossils in thecourse of digging for the Ganga canal neara Shiva (Siva) at Haridwar (now inUttaranchal) in the Ganga Valley.
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Hence the name Siwalik was given to the
sedimentary rocks entombing the fossils.
Subsequently it was applied to themammal-bearing horizon of the Neogene
continental deposits of the Himalayan
foothills. The Siwalik Hills(sometimes spelled
Shiwalik, Shivalik,or Sivalik) are a sub-
Himalayan mountain range running 1,600km long from the Tista River, Sikkim,
through Nepal and India, into northern
Pakistan.
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Falconer adopted the term in 1835 todesignated the nearly continuous series of
Tertiary formations stretching from theIndus River in the west to Irrawady Riverin Myanmar in the east.
The succession was later sub-dividedthree-fold without their actual extentsbeing defined.
H.B. Medlicott contributed substantially to
understanding of the stratigraphy of theSiwalik Group, particularly between theGanga and the Ravi rivers.
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Besides Pilgrim (1910-1944), who made a
very detailed study of the Siwalik
vertebrate fauna, others who in the earlier
years contributed to out understanding of
the sediments of the Siwalik were E.H.Colbert, G.E. Lewis, R. Lewis, R. Lydekker
and D.N. Wadia.
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The Siwalik Group occurs in Potwar basin
in NW Pakistan and extends along the
Himalayan foothills to Arunachal Pradeshfoothill in the SE, except for a small brake
near Sikkim.
The group is about 7 km thick and rangesfrom Middle Micocene to early (?)
Pleistocene (16.8 to 0.22 Ma) in age.
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The Siwalik hills are relatively low, andrarely exceed 1000 m above MSL with
conformable trends running parallel to theHimalaya.
The strata are folded and have an outcroppattern, more or less bounded by a major
thrust in the north- the Main HimalayanFrontal Thrust (HFT).
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The Siwalik is separated from the Indo-Gangetic plain in the south by the
Main boundary Fault (MBF).The Siwalik outcrops are generally 10-12 km wide and present them selvesas a series of parallel ridges with a
steep scarp towards south.Between the outermost hills in the
south and the one in the interior in the
north are many narrow valleys calledDuns filled up mostly withQuaternary sediments.
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Stratigraphy and sedimentation
The high degree of lateral and vertical
facies variation and poor continunity of
lithological characteristic precludes the
possibility of satisfactory lithostratigraphic
classification of the Siwalik sediments. Pilgrim, based on the work in Potwar (now
in Pakistan), divided the Siwalik into three
units, designating them Upper, Middle andLower based on correlation between
Siwalik fauna and similar fauna of Europe.
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Chronostratigraphic division of the Siwalik Group ( Tndaon et al., 1988)
Geological time scale Classification of
the Siwalik
Group
Standard
European
Equivalent
Age calculated
from reversal
stratigraphy
Continental
equivalent
Pleistocene Upper
Siwalik
Boulder Cong.
Pinjor
Tatrot
Cromerian
Villafranchian
Astian
1.5 to 0.5 m.y.
2.47 m.y.
5.5 m.y.
?
Mid-Late
Villafranchian
Ruscinian-
EarlyVillafranchian
Pliocene Middle
Siwalik
Dhok Pathan
Nagri
Pontian
Sarmatian
8.5 m.y.
10.8 m.y.
Turolian
L. Vellesian
E. Turolian
Miocene Lower
Siwalik
Chinji
Kamlial
14.3 m.y. Oeningian-
Vellesian
Murcee Group Burdigalian 18.3 m.y Pre-Oeningian
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Lithostratigraphy of the Siwalik Group (Kanunakaran & Ranga Rao, 1976)Subgroup Lithology thichness
Upper
Siwalik
B
A
Predominantly massive conglomerate with red and
orange clay as matrix and minor sandstone and
earth buff and brown claystone.
Sandstone, clay and conglomerate alteration.2300 m
Middle
Siwalik
B
A
Massive sandstone with minor conglomerate and
local variegated claystone.
Predominantly medium to coarse grained sandstone
and red clays alternation, soft pebbly with
subordinate claystone, locally thick prism of
conglomerate.
1400 m to
2000 m
Lower
Siwalik
B
A
Alteration of fine to medium grained sporadicallypebbly sandstone. Calcareous cement and
prominent chocolate and maroon claystone in the
middle part.
Red and mauve claystone with intercalations of
medium to dine grained sandstone.
1600 m
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Lower Siwalik
Lower Siwalik is chiefly a multi-storeyed,
multilateral fluvial complex, primarily ofchannel lag and of lateral accretiondeposits.
The mineralogical composition of thegrains reflects denudation forstratigraphically normal metasedimentaryterrain of the crystalline thrust sheet,
yielding metamorphic detritus. Though sedimentary detritus is present, it
deceases considerably upwards in themolasses sequence.
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Middle Siwalik
It consists of sandstone bodies with
interceded siltstone and shale, followed bymudstone, marl and finally pebbly
sandstone and sandy conglomerate.
There are indicative of flood plaindeposits.
The calcareous content in a part of the
sequence has been derived from clast ofthe Tertiary limestone's of the Himalayan
source.
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Upper Siwalik The Upper Siwalik sediments were deposited
under two distinct conditions, one as inner Siwalikvalley fillings and the other as regular river channeland flood plain deposit, to the south of the presentSiwalik Ranges.
This is probably the result of the uplift of the innersector of the Neogene basin towards the end of theZanclian time (Early Pliocene).
An examination of the sedimentary history along a
section in Kangra sub-basin in Himachal Pradesh,based on magnetic polarity studies, revealedepisodic increasing and decreasing rate ofsediment accumulation ranging from 19 cm/100years to 50 cm/1000 years.
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It was believed that the drainage during part of theTertiary and the Siwalik times in the Indo-
Gangetic depression had but one outlet, wherethe Indus now runs into the sea; that this greatriver system drained the whole of the Himalayanregion.
It was called indo-Brahm River by Pascoe andSiwalik by Pilgrim.
Though based on faunal evidence this hypothesiswas challenged but recent geophysical studies
of the bottom configuration of the Indo-Gangeticplain again seem to suggest the possibleexistence of a major river during the later Siwaliktimes flowing due west from the east.
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Fauna from Siwalik
The Siwalik Group is well known for itswealth of vertebrate fauna, though they
are confined to only certain horizons and
only some of them are of biostratigraphicimportance. Of added significance is the
occurrence of hominoids in almost all the
formations.
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Fauna from Middle SiwalikCarnivora : Sivanasua, Crocuta, Lycyaena.
Proboscidae : Deinotherium.Equidae : Hipparion antelopinum
Suidae : Tetraconodon, Propotamochoerus sp.
Anthracotheriidae : Anthracodon, Anthracotherium.
Rhinocerotidae : Brachypotherum,Gaindatherium.
Giraffidae : Vishnutherium, Giraffokeryx, Hydaspitherium.
Bovidae : Gazella, Protragocerus.
Rodentia : Rhizomys,Kanisamys
Primates : Krishnapithecus, Ramapithecus..
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Fauna from Middle SiwalikCarnivora : Crocuta, Agriotherium, Felis
Proboscidae : Trilophodon, Paratetralophodon, Stegodon
Equidae : Cormohipparion, Equus sivalenis.
Suidae : Hippohyus, Sus, Docoryphochoerus.
Anthracotheriidae : Choeromeryx, Hippopotamus, Cervus.
Rhinocerotidae : Rhinoceras, Coelodonta.
Giraffidae : Sivatherum, Camelopardalis..
Bovidae : Tragocerus, Bos, Bison.
Rodentia : Rhizomys,Hystrix, Nesokia.
Primates : Giganthopithecus, Papio.
Equus stenonis (US) St d
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Equus stenonis (US)
Sivatherium(US)
Stegodon(MUS)
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Geological Framework of Nepal Himalaya Nepal occupies the central sector of Himalayan arc. Nearly
one third of the 2400kmlong Himalayan range lies withinNepal. Similar to other parts of the Himalaya, from south to
north, Nepal can be also subdivided into the following five
major tectonic zones.
Gangetic Plain Sub-Himalayan(Siwalik) Zone
Lesser Himalayan Zone
Higher Himalayan Zone
Tibetan-Tethys Himalayan Zone
Each of these zones is characterized by their own lithology,
tectonics, structures and geological history.
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Geological map of Nepal(modified from Dahal, 2006)
These all tectonic zones are separated from each
other by the thrust faults. The southernmost fault,
the Main Frontal Thrust (MFT) separates the Sub-
Himalayan (Siwalik) Zone from Gangetic Plains. The
Main Boundary Thrust (MBT) separates the Lesser
Himalayan Zone from Siwalik. The Main CentralThrust (MCT) separates the Higher Himalayan Zone
from the Lesser Himalayan Zone.
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Geological map of Nepal(modified from Dahal, 2006)
The South Tibetan Detachment System (STDS)
marks the boundary between the Higher Himalayan
Zone and the overlying fossiliferous sequence of the
Tibetan-Tethys Himalayan Zone. The Indo-Tsangpo
Suture Zone is the contact knot between Indian
plate and Tibetan (Eurasian) Plate in terms of platetectonics.
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Chrono-stratigraphical division of Siwalik sediments.
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Lower Siwal ik
The Lower Siwalik consist of irregularly
laminated beds of fine grained greenish
sandstone and siltstone with mudstone.
The alternating mudstone beds are thickly
bedded and are variegated, red, purple, and
brown coloured.
The best exposures of Lower Siwalik are
found in Surainaka, Amlekhgunj, Arun Khola,Barahchhetra and Rato Khola area of Nepal.
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Midd le Siwal ik
The Middle Siwalik are comprised of medium tocoarse grained salt-and-pepper (looks like mixture
of salt and black pepper) sandstones interbeddedwith mudstone (Fig).
This is differentiated from the Lower Siwalik inlacking variegated mudstone and sandstone. In
upper part of the Middle Siwalik, pebbly sandstonebeds are also found.
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Midd le Siwal ik
In Middle Siwalik the sandstone beds have
thickness mostly ranges from 1 m to 45 m. The exposures of Middle Siwalik are found
mainly in Surkhet, Surai Khola, Hetauda, and
Butwal.
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Upper Siwalik
Comprised of conglomerate and boulder beds and
subordinately sand and silt beds. The mudstone beds of the Upper Siwalik are
massive and irregularly bedded and contain many
invertebrate fossils including Brachiopods and
Gastropods.
The upper part of this sequence contains
conglomerate beds, which have mostly boulder and
cobble size rounded to sub-angular fragments ofLesser Himalayan rocks.
In Bardibas, Hetauda, Bhalubang, and Chitwan the
good exposure of Upper Siwalik can be seen.
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Lesser Himalayan Zone
The LHZ is bounded to the north by the MainCentral Thrust (MCT) and to the south by Main
Boundary Thrust (MBT).
MBT can be traced out in whole Nepal Himalayaand it can be also well observed in aerialPhotographs also (Fig).
The rocks of LHZ have been transportedsouthwards in several thrust slices.
.
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Lesser Himalayan Zone
Generally two types of sequences namely autochthonous
and allochthonous can be distinguished in this Zone
throughout the Himalayas.
The both sequences of the Lesser Himalaya mainly have
unfossiliferous, sedimentary, and metasedimentary rocks
such as slate, phyllite, schist, quartzite, limestone, dolomite,
etc, ranging in age from Precambrian to Eocene.
There are also some granitic intrusions in this zone.
.
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