74 Chapter 4

Fig. 4.10. Composite Lower Palaeozoic stratigraphy of Iran. After Setudehnia, 1975; floodingsurfaces after Sharland et al., 2001.

2008a) (Fig. 4.8). The formation also occurs in Syria,for example as the basal 13 m of the sectionpenetrated at the Khanasser-1 well (Best et al.,1993; Barazangi et al., 1993). Equivalent units inIran are the Zaigun and Lalun Formations (Fig.4.10) (Davoudzadeh et al., 1986).

Mid-Cambrian marine transgression across thenorthern part of the Arabian Plate (Konert et al.,2001) led to widespread deposition of a limestoneunit (Fig. 4.12) within the otherwise siliciclastic-dominated Cambro-Ordovician succession. Thisunit is known as the Burj Formation in Jordan(Andrews et al., 1991) (Fig. 4.13; Plate 4.4) andalso in Syria, where it is 225 m thick at wellKhanasser-1 (Best et al., 1993). In Turkey, it isreferred to as the Koruk Formation (Janvier et al.,1984; Dean et al., 1997) (Figs. 4.8, 4.9). In Iran,

the carbonates are assigned to the Mila Formation(Setudehnia, 1975; Ghavidel-Syooki, 1997) (Fig.4.10). There is a strong velocity contrast betweenthese carbonates and the over- and underlyingsiliciclastics; the carbonate unit thus forms aseismic marker (e.g. in Syria: Best et al., 1993). Asimilar reflector has been recognised in seismicsections from the Western Desert in Iraq (e.g. Al-Haba et al., 1994) and can be tied to the BurjFormation in the Risha-2 well, Jordan (Jassim,2006c). The carbonates may be very thin or absentin the Southwestern Desert of Iraq. Similarly, inJordan and western Iraq, the formation thinssouthwards from about 200 m in the Risha/Rutbaharea to 60 m in the southern part of Wadi Sirhan(Andrews et al., 1991; Jassim, 2006c). Furthersouth, the facies pass into marine siliciclastics

ShaleShale interbedded with sandstoneShale with rare siltConglomerate

Shale with thin siltstone layersMicaceous sandstone, laminated and ripple marked shale with micaceous sandstoneMicaceous sandstones interbeddedwith micaceous shales

Thick-bedded to massivelimestones interbedded withshales rich in trilobites

Shale with salt pseudomorphs

Dolomite with shale intercalations

SandstoneShale with occasional sandstone

Sandstone strongly cross-beddedand friable

Massive sandstone, somelaminated and occasionallycross-bedded

Thin bedded and laminated sandstoneLaminated sandstone with intercalations

Micaceous sandstone interbeddedwith shale

AG

EF

OR

MA

TIO

NM

EM

BE

RT

HIC

KN

ES

S (

m)

LIT

HO

LO

GY

OR

DO

VIC

IAN

Zard

Kuh

LATE

CA

MB

RIA

NIle

beyk

Low

erU

pper

295

900

MID

DLE-

LATE

CAM

BRIA

NM

ila 1055

8523

5

EAR

LY C

AM

BR

IAN

Lalu

n

3000

CB

A82

0

InfracambrianZaigun

Formation

L E G E N D

IRAN

ARABIANPENINSULA

Kuh-e Dinar

Kopet Dagh Foldbelt

Zagros Thrust Belt

Kavir Fault

Ozbak KuhKuh-e Gergh

Golpayegan

TaknarTang-e Ilebeyk

Zenjan

Soltanieh Mila Kuh

ShirgeshtTabas

Nay

band

Fau

ltLu

t Blo

ck

Kah

urak

Fau

lt

Caspian Sea

200 km0O10

O40

O30

O20

Cm30

Cm20

SE

QU

EN

CE

ST

RA

TIG

RA

PH

Y

Shale

Siltstone

Sandstone

Conglomerate

Limestone

Dolomite

D E S C R I P T I O N

75Precambrian and Palaeozoic

within the continental deposits of the AbuKhusheiba Formation (Powell, 1989). In SaudiArabia, these coastal siliciclastics are recorded asthe “spoor” zone of the Saq Formation withSkolithos (Powers et al., 1966; Helal, 1968; Al-Laboun, 1986; McGillivray and Husseini, 1992).They onlap the margins of areas uplifted duringthe Amar collision.

The carbonates comprise tidal flat to lagoonaland occasional oolitic shoal facies (Powell, 1989;Andrews et al., 1991) (see Plate 4.12, page 83). InSE Turkey (and probably also in northern Iraq),the Koruk carbonates are succeeded diachronouslyby deep-water facies of the Sosink/SeydisehirFormations (Figs 4.8, 4.9). The carbonate shelf wasdrowned in early Middle Cambrian time in theAmanos Mountains, and in the latest MiddleCambrian in the Zap Valley in SE Turkey (Dean etal., 1997) (Fig. 4.8). The thickness of the carbonatesthus increases from 100 m in the Amanos region,to 240 m in the Mardin area, to over 400 m at

Fig. 4.11. Map of Iraq showing the thickness ofMegasequence AP2. Interpretation is basedmainly on gravity-magnetic data with very littlewell or outcrop control. Simplified after Jassim,2006c.

Plate 4.2. Dashed white line indicates onlap ofpebbly sandstones of the Lower Cambrian SalibFormation (basal AP2) and other LowerPalaeozoic rocks onto peneplaned Precambrianbasement. Location: near Aqaba, southernJordan, at the road junction with Wadi Rum.Photo by A. Aqrawi. Plate 4.3 (above). Pebbly arkosic sandstones of

the Lower Cambrian Salib Formation at WadiNumaira, Dead Sea — Aqaba road, southernJordan. Photo by A. Aqrawi.

36°

32°

36°

40°

32°

44° 48°

40° 44° 48°

I R A N

I R A Q

S A U D IA R A B I A

K U W A I T

500 m

1000 m

3000 m

S Y R I A

0 100 200km.

Hakkari close to the Iraqi border (Cater andTunbridge, 1992; Dean et al., 1997).

Jassim (2006c) suggested that the Burj/KorukFormation is approximately 400 m thick innorthern Iraq and 200 m thick in the WesternDesert. However, he proposed that the Cambrianis absent in Central and Southern Iraq due to onlapover the uplifted Rayn anticlines of the Ar Raynand Eastern Arabian terranes. It is absent fromthe Burgan High in Kuwait (based on data in Khan,1989) (Fig. 4.12).

Siliciclastic-dominated deposition was re-established in the Late Cambrian, with the fluvialsandstones of the Umm Ishrin/Ajram Formationsin Jordan (Powell, 1989; Andrews et al., 1991;Makhlouf and Abed, 1991; Amireh et al. 1994;Beydoun et al., 1994) (Figs 4.3, 4.5), the Quweira

148 Chapter 6

over a wide area. Two regional-scale “dolomiteplumes” have been identified: the first on the borderbetween Saudi Arabia and Kuwait, and the secondoffshore Saudi Arabia (Fig. 6.10).

This stratigraphically discordant dolomite islocally associated with breccias due to dissolutionof the Hith and Arab Formation anhydrites.Dolomite is present in the Tuwaiq Mountain,Hanifa, Jubaila, Arab, Hith and Sulaiy Formations(Fig. 6.11). It is best-developed in the HanifaFormation. The dolomite shows enhanced porositiesand permeabilities compared to host limestones(Broomhall and Allan, 1987).

Fluid inclusion data from the dolomites indicatethat precipitating fluids were both hot (temperaturesbetween 102 and 155°C) and saline (at least sixtimes seawater salinity — values of 225,000 to249,000 ppm NaCl equivalent were recorded) (Fig.6.10) (Broomhall and Allen, 1987). Both replaciveand saddle dolomites are present. They show similaroxygen isotope ratios suggesting that they werederived from the same parent fluid, although thewestern salient dolomites have a lower temperature,more positive δ18O signature suggesting that theywere precipitated slightly earlier and at shallowerdepths. Fluid inclusions indicate that oil migrationtook place at the same time as dolomitisation. Thereis abundant evidence of dead heavy oil in the poresystems. This may be due to failure of seal integritydue to dolomitisation (Broomhall and Allan, 1987).

Stratigraphically concordant non- fabric-

preserving dolomites and stratigaphically-discordant baroque dolomite also occur in the Arab-D carbonate reservoir in the Ghawar field, some500 km to the south of the Gotnia Basin. Thesedolomites precipitated at temperatures of 85–114°Cfrom pore waters with a salinity of 195,000 – 230,000ppm NaCl equivalent (Cantrell et al., 2004).Stratigraphically discordant dolomitisation ofMiddle Jurasic rocks has also been reported to occurin Lebanon, where it is attributed topenecontemporaneous igneous activity (Nader andSwennen, 2004).

The dolomitisation of Middle Jurassic carbonates,and also perhaps of overlying intervals (in theQamchuqa and Shiranish Formations and theAsmari/Kirkuk Group) thus appears to be largelyhydrothermal in character (e.g. Al-Aasm et al.,2009). The movement of dolomitising fluids mayhave been associated with the onset of Late Neogenecompression in the Gotnia Basin, which causedrupturing of Jurassic and deeper evaporite sealsand therefore permitted the large-scale mobilizationof overpressured Mg-rich formation waters.Broomhall and Allan (1987) interpreted thedolomites to have been formed by brines migratingfrom the Gotnia Basin as a result of burial.

Naokelekan FormationThe Naokelekan Formation was first described fromoutcrops in NE Iraqi Kurdistan. It is a highlycondensed formation, 9 to 34 m thick (typically less

Fig. 6.10. Distribution of stratigraphically discordant dolomite bodies in northern Saudi Arabia,together with temperature and salinity data from fluid inclusion studies. After Broomhall andAllan, 1987.

Kuwait

Gotnia Salt Basin

Arabian Shelf

Stratigraphically-Discordant Dolomite

Iran

227,000-4.6/-4.6102

225,000-6.1/-6.1110

223,000-7.6/-7.7126

236,000-6.8/-6.2111

249,000-9.2/-8.6134

232,000-8.3/-8.2131

236,000-8.8/-8.5136235,000

8.2/-8.0155

50km.0

-8.5/-8.4

-4.9/-4.2

-8.5/-8.7

∂18O ofReplacivedolomite

∂18O ofSaddle

dolomitein 0/00 PDB

Salinites (black) in ppm

Temperatures (red) in °C

149Middle to Upper Jurassic

than 20 m). The formation can be divided into threeunits at its type locality (see Fig. 6.3 for location)(Dunnington et al., 1959):

(i) an upper 3 m of laminated argillaceouslimestones;

(ii) a middle 4 m of “Mottled Limestone Beds”,comprising hard, calcite-veined limestones whichcontain ammonites indicating a “probable earlyKimmeridgian” age (Dunnington et al., 1959);

(iii) a lower 7 m, referred to as the “Coal Horizon”,which comprises thin-bedded bituminous limestonesand dolomites with beds of bituminous calcareousshale. The unit has slump structures and weathersinto nodular “phacoids”. Its top is dated as lateOxfordian on the basis of possible identifications ofthe ammonite Reineckia at Naokelekan in IraqiKurdistan; the nearby occurrence of Choffatia atKurrek suggests a Callovian age for its base(Dunnington et al., 1959).

The formation conformably overlies the SargeluFormation (Jassim and Buday, 2006d); the uppercontact with the Barsarin Formation is oftenmarked by a ferruginous horizon, e.g. in the northThrust Zone (Hamza and Isaac, 1971, in Jassimand Buday, 2006d). Kaddouri (1986) noted a 1.4 mthick pisolitic limestone at this horizon.

The Naokelekan Formation contains a mainlydeepwater fauna (Dunnington et al., 1959). Budayand Suk (1978) in Kaddouri (1986) and Jassim andBuday (2006d), noted that at Halabja and elsewherein Sulaimaniya Province in Iraqi Kurdistan,deeper-water fauna are present includingProtoglobigerina sp., Cadosina sp. and theCallovian–Oxfordian belemnite Hibolitessemihastatus. Shallower-water microfossils alsooccur such as Kurnubia palastinensis Henson,Ammobaculites sp., Textularidae sp., Nautiloculinaoolithica, and the algae Cladocoropsis,Thaumatoporella sp. and Cayeuxia doerflesiana.Indeterminate dascycladaceans together with thestromatoporoid Shuqraia “heybroeki” (now zuffardi)also occur, indicating a Callovian–Kimmeridgianage (Buday and Suk, 1978, in Kaddouri, 1986).

Basinal Najmah FormationAn equivalent of the Naokelekan Formation is theinformally-defined “basinal Najmah Formation” inwells in central and southern Iraq and also inKuwait. This unit includes basinal organic-richlimestones with shelf and slope carbonates (Goff,2005). Other examples of the “basinal NajmahFormation” occur between Awasil and Makhul,

Plate 6.8. Field photographs of the Upper Jurassic Surmeh Formation at the Mungasht anticline onthe eastern margin of the Gotnia Basin in the Iranian Zagros. Bituminous dolomite units are darkbrown in the field and contrast with the intercalated pale grey, tightly cemented limestone units.Bitumen-filled vugs (bottom right) are frequently 5-10 cm in diameter. Photos by J. Goff.

276 Chapter 8

Al-Rawi et al. (1992) renamed the Upper FarsFormation the Injana Formation, and defined a typelocality at Injana along the main Baghdad–Kirkukroad on the NE limb of Jebel Hamrin South (Plate8.31). A supplementary type section occurs in wellGilabat-1 (Al-Rawi et al., 1992). The formation is620 m thick at Injana and consists of alternatingred, brown and grey marls, siltstones, andsandstones with seams of gypsum; fossils includegastropods and bivalves. In the Jambur and

reported from the Jeribe Limestone underlying theLower Fars by Prazak (1978).

Upper Fars FormationThis formation comprises varicoloured marls andsiltstones with beds of sandstones and grits.Occasional beds of freshwater limestones (withostracods and charophytes), lacustrine clays andbentonites also occur (Plate 8.30). The formationis typically 600 to 800 m thick (Fig. 8.34) and forms“badlands” topography (Plate 8.31). Buday (1980)and Al-Rawi et al (1992) reported that the formationreaches 2000 m in thickness but this may be anoverestimate because of probable inclusion of theoverlying Lower Bakhtiari Formation where thisis composed mostly of mudstones.

Plate 8.31. Upper Fars Formation “badlands”topography, Injana, Jebel Hamrin South. Viewfrom a gypsum ridge at the top of the LowerFars. Photo by M. Tucker.

Plate 8.32. Conglomerates and sandstones of theLower Bakhtiari Formation cropping out in theKhanzad hills, about 15 km north of Erbil, IraqiKurdistan. Photo by A. Aqrawi.

Plate 8.30. Middle-Upper Fars Formation.Lacustrine clays, limestones and bentonite.Injana, Jebel Hamrin South. Photo by M.Tucker.

MIDDLEMIOCENE Fat’ha Formation

PLIOCENE Mukdadiya Formation

LA

TE

M

IO

CE

NE

150m

0m

50m

250m

200m

100m

400m

300m

500m

450m

600m

550m

350m

Up

pe

r F

ars

/

Inja

na

Fo

rma

tio

n

Limestone

Pebbly sandstone

Marl

Sandstone

Siltstone

Anhydrite

Fig. 8.34. Stratigraphic column for the UpperFars (Injana) Formation at its type locality atJebel Hamrin. After Al-Rawi et al., 1992.

277Cenozoic

Makhul-Khanuqah areas, rare freshwaterlimestones containing ostracods and charophytesoccur. An oyster limestone was recorded 60 m abovethe base of the formation at Jebel Pulkhana (Al-Naquib, 1960).

The formation is assumed to be of early lateMiocene age based on its stratigraphic positionbelow the uppermost Miocene Lower BakhtiariFormation. It is interpreted here to have beendeposited in an estuarine to lacustrine environment.

Lower Bakhtiari FormationThis formation (Plate 8.32) was depositedsynchronously with the growth of major anticlinesand thus varies in thickness and facies. It wasoriginally included in the “Kurd Series” by Pascoe(1922) but was later reassigned to the LowerBakhtiari Formation in the Tertiary part of theIraq Lexicon (van Bellen, 1959). Al-Rawi et al. (1992)renamed the Lower Bakhtiari Formation theMukdadiya Formation, whose type section (Fig.8.35) is on the NE flank of Jebel Hamrin. Here,the formation is 1411 m thick here and comprisessandstones, pebbly sandstones, grey mudstones andsiltstones with stacked “fining up cycles”.

ThicknessDunnington (1958) published an isopach map ofnorthern Iraq (Fig.8.36) for the combined UpperFars and Bakhtiari Formations using estimatedthicknesses for synclinal areas. He noted that themajor anticlines grew during deposition of theBakhtiari and considered that “a true isopachshould reveal closures of attenuation over everyrising structure but that unfortunately theinformation which would be required for such amap is not accessible”. He noted that it is difficultto estimate the thickness of the BakhtiariFormation because thickness measurements canbe made only on the flanks of anticlines “wheredepositional and some erosional attenuation isknown to have occurred”.

His final isopach map (Dunnington, 1968) wascreated after “arbitrary elimination of crestalattenuation”. He emphasised the shallowing of thebasin to the NW so that “the synclinal thicknessesin the vicinity of the NW plunge of Kirkuk wereonly of the order of 5000 ft (1525m)”. He noted thatthe original thickness of the “Passive Group”comprising all units above the middle part of theLower Fars was between 6000 and 13,000 ft (1830-3960 m) prior to rapid late Pliocene – earlyPleistocene uplift and erosion. The maximumrecorded thickness of the Lower BakhtiariFormation in Iraq is 2050 m (van Bellen et al.,1959)although the location of this section was not given.

On the NE flank of the Kirkuk anticline, Pascoe(1922) noted that the thickness of the Lower StageKurd Series (equivalent to the Upper Fars andLower Bakhtiari) exceeds 7000 ft (2000 m), and that

Fig. 8.35. Stratigraphic column for the LowerBakhtiari (Mukdadiya) Formation at its typelocality at Jebel Hamrin. After Al-Rawi et al.,1992.

the thickness of the combined Lower and UpperBakhtiari Series “must exceed 12,000 ft (3500 m)”.

StratigraphyPascoe (1922) informally recognised five units inthe “Kurd Series” in the Kifri area. The lower unit(Lower Stage Unit: a) can be correlated with theUpper Fars Formation. The succeeding units (b)and (c) in the Lower Stage correspond to the LowerBakhtiari Formation.

In unit (b), Pascoe (1922) recorded the presenceof thick, massive sandstone beds which wererelatively soft, friable and frequently currentbedded, and sometimes full of “root-like concretions”.He noted that the sandstone intervals increase inthickness upwards in the middle of the unit, andthat the sandstones become pebbly in the samedirection and contain thin conglomerates. Heobserved that the unit “produces topographyconsisting of ridge after ridge rapidly alternatingwith deep, narrow, straight, simple valleys”.

LT. MIOCENE Injana Formation

LATEPLIOCENE Bai Hassan Formation

LA

TE

MIO

CE

NE

- E

AR

LY

PL

IOC

EN

E

500m

400m

200m

300m

0m

100m

1000m

900m

700m

800m

600m

1200m

1300m

1100m

Lo

we

r B

ak

hti

ari

/M

uk

da

diy

a F

orm

ati

on

Sandstone

Marl and mudstone

Pebbly sandstone

Conglomerate