Siwaliks and Oild Bearing Tertiary Deposits

8/10/2019 Siwaliks and Oild Bearing Tertiary Deposits

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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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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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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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Siwaliks and Oild Bearing Tertiary Deposits

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