tajjal area

7/25/2019 tajjal area

1/9

GEOLOGY OF THEAREA

CHAPTER 2

2.1 Introduction:-

Geological and structural know how of the area is very important while doingseismic interpretation. Main reason behind grasping the knowledge aboutthe geology of the area is that sometimes dierent lithologies can produce

similar seismic signatures and sometimes similar lithologies can producequite dierent seismic signatures.

o be prepared to deal with such complexities, an interpreter must haveknowledge of the geology and its stratication, unconformities and ma!orstructures of the study area.

2.2 Regional Settine:-

akistan acquired its structural and stratigraphic features from tectonic eventsassociated with plate movements that occurred from late "aleo#oic time to

present. $rom "ermian through middle %urassic time, the area known todayas &ndus 'asin was located in the southern hemisphere. ()emal et al, *++aigham and Mallick, ///0.

1ccording to )a#mi and %an (*++20, the geology of "akistan is divided into tworegions, which are given below3

S GondawanianDomain S TethyanDomain

he southern part of "akistan belongs to Gondawanian 4omain and is sustained

by &ndo5 "akistan crustal plate, our 6tudy area of Ta!!al also lie in this part of"akistan.

2.3 Bain o! Pa"itan:-

he basins and their subdivision include the following3

1. &ndus 'asin

a. 7pper &ndus 'asin8 Potwar Sub-basin8 Kohat Sub-Basin

b. Middle &ndus 'asin

c. 9ower &ndus 'asin

2. 'aluchistan 'asin

3. )akar )horasan 'asin ("ishin 'asin0:adri, *++; Structural #one o! Bain:-


2/9

CHAPTER 2

GEOLOGY OF THEAREA

6tratigraphy of "akistan is discussed in context of 'asins- largest 'asin of

"akistan is &ndus 'asin. &n Table .* main structural #ones of this basin are

discussed. Geological


3/9

?

CHAPTER 2

GEOLOGY OF THEAREA

(

2.4 Stratigra&)*:-

1ccording to $ig .? early siliclastics were deposited on the top of an extensivecarbonate "latform (Ahilton 9imestone0 that underwent massive and

regionally extensive environmental collapse in )immeridgian5Dxfordiantimes as a result of renewed rifting between the &ndian and 1frican plates

and subsequent drowning. The late %urassic drowned 7nconformity and the9ower Goru condensed section is therefore used to Eatten the regiona

seismic sections on Eattening sections on this hori#on removes the younger

structural relationships in a near depositional form. The prospective sandprone sequences in the 9ower Goru play $airway consist of alternate

sandstone shale paralics deposited in deltaic marine strand plain and barrierbar shore face to oshore setting on a ramp. &nformally, these units are

named as 9ower Goru members F1F, F'F, FAF to F4F intervals. Thesesedimentary packages were deposited on the top of vast and extensive

ramp built by the 6ember and F1F and low5 stand deposition. 1 gradual andlong5 term base level rise (?rd order eustatic or tectonic5 eustatic sea level

rise0, punctuated by high frequency @rth and ; th order relative sea leve

Euctuations, and an active northerly to long shore drift and tidal eect(wave5and tide5dominated system0 led to the deposition of aggradational towesterly prograding wedges that rarely reached the shelf margin position of

ramp built by the 6ember and F1F low stand5 ramp. The areas close to

structural highs works with the westward facies related shale5out of theprograding sand wedges to provide stratigraphic traps.

$igure . Geographic 'oundaries of Ta!!al 1rea


4/9

@

CHAPTER 2

GEOLOGY OF THEAREA

S+I $AI( LST, $B

$igure .? 6tratigraphy of the Ta!!al 1rea.

2.5 $aor For.ation O! T)e Area /Taiial0:ollowing are the ma!or formations which encounter in the T1%%19 1rea.

1 CHILTO( LI$ESTO(E

he Ahiltan limestone is typically a massive, thick bedded, dark limestone, but

shows colour and texture variations within one section and in dierent areas.

The colour varies from black, dark grey, grey, light grey, brownish grey

bluish grey to occasionally white. "isolitic limestone beds are present locally

The texture varies from ne5grained, sub5lithographic to oolitic, reefoid and

6helly. &n the 1xial 'elt, the limestone gives a fetid smell.

Faleacene RANiKOTFM.

P ARK FM.

HI

ua

!G

LOWER

CRETACIOUS

i"

36

i

JiK#

UPPER GORU MB.T

9imestone6hale6andstone

6hale and6andstone

Mia rl4arkcolor 9%mestone

*D" INTERVAL

C" INTERVAL

"B" INTERVAL

"A" INTERVAL

SEMBARM. JURASSIC C HILT AN LIMESTONE

nr5Lyt!Afcg..fNag $T%$..,

9 OO .*.*r>&n%urvn%'

rv rSrf H t I

1

rv r*w rv rw iS/ rv rv rv


5/9

CHAPTER 2

GEOLOGY OF THEAREA

The Ahiltan limestone is widely distributed in the 6ulaiman )irther "rovinceand 1xial belt, forming prominent high mountains like )oh5e5Maran, )oh5e56iah, Ahilian, Murdar Ghar, Takatu, )halifat and ardah. The Ahiltanlimestone, where developed, overlies the 6hirinab formation conformably.

The upper contact with the Ma#ar 4rik formation is gradational. =o fossilsare found and on the basis of stratigraphic position age given is Middle%urassic (6hah, *+220.Dn the basis of lithology Goru $ormation is divided intwo parts P 9ower Goru P 7pper Goru

8 LO4ER GOR+

he lower Goru is main reservoir rock within the area. The lower Goru hori#onas a general ; divisions based on predominant lithologies (Gilbert )illing etal0.

The 'asal 6and units are(

O )ower Sha#eO Midd#e sand unit *whi+h has a ,ood reser"oir otentia#O /er Sha#eO /er Sand

8 +PPER GOR+

he upper Goru sequence of middle to late cretaceous unformable overlies thelower Goru formation which consists of mainly marl and calcareousclaystone occasionally with inerbeds of silt and limestone (Gilbert )illing etal0.

he Goru $ormation is widely distributed in the )irther and 6ulaiman "rovinceThe lower contact with the 6embar formation is conformable and is verylocally reported unconformable. The upper contact is transitional with the"arh 9imestone. The Goru formation may be correlated with the 9umshiwa$ormation of the )ohat5"otwar "rovince. The formation contains foraminifersand bivalves and age given is Qarly Aretaceous (6hah, *+220.

8 5+(GA( FOR$ATIO(


6/9

GEOLOGY OF THEAREA

CHAPTER 2

B

8 Rilliams (*+;+0 dened the formation as 4ungan $ormation. The

formation dominantly consists of nodular to massive limestone with

subordinate shale, marl, and sandstone and limestone conglomerate

9imestone is dominant in most of the places and is dark grey to brown

and creamy white. The shale is dark blue grey, brown and olive and theshale becomes dominant in the southern 6ulaiman Sange. The 4ungan

formation is mainly developed in the 6ulaiman "rovince and parts of the

Aalcareous one of the 1xial 'elt. The formation unconformably overlies

the $ort Munro formation in the :uetta and >arnai region and in the

north5eastern 6ulaiman "rovince it unconformably overlies the "ab

sandstone, Rhile the upper contact with the Gha#i! formation is

conformable. The formation is richly fossiliferious. The fossils recorded are

foraminifers, gastropods, bivalves and algae. $oraminifers are dominant

and on the basis of these fossils age given to this formation is QarlyQocene age (6hah, *+220.RA(I6OT GRO+P

lanford (*2B0 was the rst to give the name Sanikot group.Uredenberg(*+/+a0 subdivided the Sanikot group into 9ower Sanikot (sandstone0 and7pper Sanikot (limestone0. Dne division of Sanikot group suggests that itcomprise of three formations which are )hadro formation, consists of olive,yellowish brown sandstone and shale with inter5beds of limestone. )eepingascending stratigraphy order, 1bove )hadro formation is 'ara formation(9ower Sanikot sandstone0 consists of variegated sandstone and shale. 1nd

the upper one is the 9akhra formation (7pper Sanikot limestone0 consists ofgrey limestone, grey to brown sandstone and shale. Uarious authors havegiven it dierent divisions. 'elow are explained the three formations as partof the Sanikot group with details (6hah, *+220.

8 6HA5RO FOR$ATIO(

he basal part of the formation is comprised of dark colored limestone withshale, followed by olive, grey to green, soft, ferruginous, medium grainedfossiliferous sandstone an olive, grey to brown gypsiferous shale with inter5beds of fossiliferous limestone. 1 number of basaltic lava Eows are also

present. The volcanic contain dark green and black basalt inter5bedded withmudstone, clay stone and sandstone. The formation is widely distributed in)irther fold belt and its thickness varies at dierent localities..&ts lowecontact is unconformable with Moro formation and "ab 6andstone, while itsupper contact is conformable with 'ara and 4ungan formations in various


7/9

GEOLOGY OF THEAREA

CHAPTER 2

2

parts of )irther56ulaiman fold belt.

)hadro formation may be correlated with the lower part of the Sakhshan$ormation of Ahagai and Sas )oh area. $ossils reported from the formationinclude Aorbula Globigerina pseudobulloides and G. triloculinoides and so

many others. 1nd age given to the formation is Qarly "aleocene ()a#mi and1bbasi, //0

8 BARA FOR$ATIO(

his rock unit consists of soft sandstone, shale and clay, at some places it isrichly coloured and variegated with brown and red colors. The sandstone isne to coarse grained, soft, poorly sorted and cross bedded. 6ome of theshale are highly carbonaceous and has been developed into high economiccoal deposits at 9akhra, 6onda and Thar. $erruginous nodules and minorvolcanic fragments are also found. This formation is widely distributed in

)irther fold belt. The lower contact with the khadro formation isconformable, in the 'ara 4ome, and in Sahman 4horo it overlies a *+ mthick sequence of 4eccan trap basalt (Gingerich et al. *+2+0. 1nd the uppercontact with the 9akhra formation is conformable, and where the 9akhraformation is missing, it has upper unconformable contact with the Qocene9aki formation. The formation is fossiliferous. it has yielded some bonefragments of crocodiles and turtles and some dicotyledonous leaves, andcalcareous algae. 6o basis on these fossils age given is Middle "aleocene()a#mi and 1bbasi, //0

1 LA6HRA FOR$ATIO(he formation consists dominantly of limestone with minor sandstone and

shale. 6howing that the Euvial sandstone of 'ara formation passes upsectioninto marine sequence of 9akhra $ormation. The limestone is grey, thin tothick bedded, nodular, brecciated, sandy, and argillaceous at dierentplaces and fossiliferous.The sandstone is grey to brown in color, ne tocoarse grained, thin to thick bedded, ferruginous and fossiliferious. Theshale is grey, weathers yellow brown and at some places grades into claystone. 9akhra $ormations is widely distributed in )irther "rovince. 1nd has

thickness in the range of @/ and @/ at dierent places.This rock unit ischaracteri#ed by a rich fossils that includes corals, mollucs and echinoidsDn the basis of fauna Uredenberg (*+B0 divided the $ormation (his upperSanikot0 into two biostratigraphic #one. The lowest < basal hori#on (one *0is characteri#ed by gastropods and is free from foraminifera (ka#mi and1bbasi, //0.


8/9

GEOLOGY OF THEAREA

CHAPTER 2

2.6 Source Roc":-

he 6embar has been identied as the primary source rock for much of theGreater &ndus 'asin, there are other known and potential source rocks. Sockunits containing known or potential source rocks include the 6alt Sange

$ormation FQocambrianF shales, "ermian 4andot and Tredian $ormationsTriassic Rulgai $ormation, %urassic 4atta $ormation, "aleocene "atala$ormation, Qocene Gha#i! $ormation, and lower Miocene shales. Df all thepossible source rocks in the &ndus 'asin, however, the 6embar is the mostlikely source for the largest portion of the produced oil and gas in the &ndusforeland.

he 9ower Aretaceous 6embar $ormation consists mainly of shale withsubordinate amounts of siltstone and sandstone. The 6embar was depositedover most of the Greater &ndus 'asin in marine environments and ranges in

thickness from / to more than B/ m.2.7 Reer7oir:-

roductive reservoirs in the 6embar5Goru


9/9

GEOLOGY OF THEAREA

CHAPTER 2

+

plates. The tilted fault traps in the 9ower &ndus 'asin are a product ofextension related to rifting and the formation of horst and graben structures.

The temporal relationships among trap formation and hydrocarbongeneration, expulsion, migration, and entrapment are variable throughout

the Greater &ndus 'asin. &n the foreland portion, formation of structural trapspre5date hydrocarbon generation, especially in the 9ower &ndus 'asin. &n theMiddle and 7pper &ndus 'asins, traps may also have formed prior tohydrocarbon generation, although the temporal relationships between trapformation and hydrocarbon generation are not as distinct as in the 9ower&ndus 'asin. The structural deformation in the foldbelt region is generallycontemporaneous with hydrocarbon generation, suggesting that some of thehydrocarbons generated from the 6embar probably leaked to the surfaceprior to trap formation.

2.9

Seal:-The known seals in the system are composed of shales that are inter5beddedwith and overlying the reservoirs. &n producing elds, thin shale beds ofvariable thickness are eective seals. 1dditional seals that may be eectiveinclude impermeable seals above truncation traps, faults, and updip facieschanges.1 GOR+ FOR$ATIO(

The Goru formation consists of inter5bedded sandstone, shale and siltstoneThe limestone is grained, thin bedded, light to medium grey in colour (6hah,*+220.

tajjal area

Documents