Sequence stratigraphy and biostratigraphy of the prolific late Eocene ...

Sequence stratigraphy and biostratigraphy of the prolific late Eocene, Oligocene and early Miocene carbonates from Zagros foldthrust belt in Kurdistan region Fadhil A. Ameen Lawa & Ala A. Ghafur

Arabian Journal of Geosciences ISSN 1866-7511 Arab J Geosci DOI 10.1007/s12517-015-1817-4

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Author's personal copy Arab J Geosci DOI 10.1007/s12517-015-1817-4

ORIGINAL PAPER

Sequence stratigraphy and biostratigraphy of the prolific late Eocene, Oligocene and early Miocene carbonates from Zagros fold-thrust belt in Kurdistan region Fadhil A. Ameen Lawa & Ala A. Ghafur

Received: 13 October 2014 / Accepted: 20 January 2015 # Saudi Society for Geosciences 2015

Abstract The Late Eocene-Oligocene-Early Miocene sequences of the Kurdistan foreland basin, considered as an important shallow, thick oil and gas reservoir in Kurdistan region/N-Iraq. Several diverse larger foraminifera (Alveolina, Orbitolites, Assilina, Archaias, Austrotrillina, Miogypsinoide, Nummulites, Operculina, Borelies, and Lepdicyclina) with important stratigraphic, paleo-ecological, and palaeobiogeographical implications are described with respect to its position in the Neo-Tethys basin. The biozonation, using large benthonic foraminifera, leads to the reconstruction of the chronostratigraphic framework. For that purpose, more than 367 samples from six wells and twelve outcrops, from different tectonic domains, within Zagros fold-thrust belt were analyzed. Almost four sequence boundaries (SB) segmented the depositional sequences into three third-order sequences. The lower most sequence boundary was estimated to be of Bartonian age (37 Ma) that represents by more than 5-m conglomerates between the molasses facies of the Gercus and carbonates of the Pila Spi Formations. The second sequence boundary, known as Zagros Major Hiatus, was estimated to be of the age 34 Ma and was placed at the top of karstfied carbonates of the Pila Spi Formation (Pribonian), directly below the Fatha Formation (Burdigalian-Langhian) almost manifesting the boundary between Tectonomegasequence AP10 and AP11. The third one is almost between the Rupelian and the Chattian (28 Ma) within Kirkuk Group. The last recorded one of Aquitanian age (21 Ma) was placed between the Kirkuk

F. A. Ameen Lawa (*) Department of Geology, University of Sulaimani, Sulaymaniyah, Iraq e-mail: [email protected] A. A. Ghafur Natural Resources Engineering and Management Petroleum Engineering, University of Kurdistan-Hawler, Arbil, Iraq e-mail: [email protected]

Group and Jeribe or Euphrates Formations. The three thirdorder depositional sequences were recognized from deepening and shallowing trends in the depositional facies, stacking patterns, and sequence boundary features. The first third-order represents the Late Eocene sequence (Pila Spi-shelf facies latterly change to Avanah-Jaddala Formations-depocenter facies), the second one represents the Rupelian-Chattian-Early Aquitanian third order in which each of the lower cycle of the Kirkuk Group (Rupelian) and the upper sequence of the Kirkuk Group (Chattian-Early Aquitanian) represents a fourth-order sequence. The last third order manifests by the Late Aquitanian-Early Burdigalian sequence of the Euphrates shelf facies that is changed laterally to Serikagni depocenter facies and mostly change upwards to Jeribe Formation. The lateral and vertical facial changes point to the increasing of the sequence thicknesses from the high folded thrust zone towards the low folded thrust zone and across the transversal Khanqain fault. The carbonate depositional ramp mostly segmented into isolated highs (occasionally separated from the palaeo-shorelines), that are either due to the influence of the thrust propagation deformational front or reactivation of the deep cited faults. Keywords Kirkuk Group . Kurdistan region . Neo-Tethys . Biozonation . Large benthic foraminifera . 3rd order . Sequence boundar type oney

Introduction The discovery of extractable oil and gas from the main limestone of the Kirkuk Oil Field has been a primary focus of attention, and it is the subject of numerous studies. This work concentrates on the Late Eocene, Oligocene, and Early Miocene of the new area within the high and low folded thrust zones, north and north east of Kirkuk embayment, namely

Author's personal copy Arab J Geosci

It consists of the Avanah and Jaddala Formations of the Eocene age and those nine Oligocene formations of the Kirkuk Group (that occur in the Kirkuk structure Bellen 1956; Bellen et al. 1959 and Al-Naqib 1960). The Aquitanian Euphrates-Dhiban and Jeribe Formations also acts as important reservoirs either solely or within the studied sequences (main limestone). The Middle Miocene evaporite of the Fatha Formation (Burdigalian-Langhian age) acts as a cap rock for the reservoirs in the northern part of Iraq including the

within Sulaimani district. In Kurdistan region, the Zagros mountain belts show progressive changes from N-S trend to NW-SE and then to E-W, almost subdivided in to five different parallel structural domains, from SW to NE: (1) the Mesopotamia zone, (2) the low folded thrust zone BLFTZ,^ (3) the high folded thrust zone BHFTZ,^ (4) the Imbricated Zone, and (5) the Zagros suture zone (Fig. 1). The term Bmain limestone^ is an informal term introduced to indicate the first main oil pay zone of the Kirkuk Oil Field.

Zagros Suture Zone

High Folded Thrust Zone Low Folded Thrust Zone 15 13

1

2 3

6

4 10

7

5

12

8

11 2

14 Well no

Khanaqin Fault

5 section no

No

Sections

9

14

Latitude East

Longitude North

Main limestone formations

1 2 3 4 5

Sagrma Zinana Hazar Kani Aj Dagh Awa Spi

Pila Spi- Avanah- Kirkuk Group- Fatha Avanah- Kirkuk Group- Euphrates- Jeribe- Fatha Avanah-Kirkuk Group-Euphrates-Jeribe-Fatha Avanah- Kirkuk Group- Euphrates- Jeribe- Fatha Avanah- Jaddala- Kirkuk Group- Euphrates- JeribeFatha Pila Spi- Avanah- Kirkuk Group- Fatha Pila Spi- Avanah- Jaddala- Kirkuk Group- Fatha Avanah- Kirkuk Group- Fatha Jaddala- Basal Anhydrite- Euphrates- Dhiban- JeribeFatha Avanah- Jaddala- Kirkuk Group- Jeribe- Fatha

6 7 8 9

Bamu Bellula Sharwl Dra Chai-Surkh 9

10

Kurda Meer 1

11

Sarqala

12 13

Pulkhana 5 Kor Mor 2

14

Qumer 1

Avanah- Jaddala- KirkukGroup- Euphrates- DihbanJeribe- Fatha Jaddala- Euphrates- Dhiban- Jeribe- Fatha Avanah- Jaddala- Kirkuk Group- Euphrates- JeribeFatha Avanah- Jaddala- Euphrates- Dhiban- Jeribe- Fatha

15

Swerawa 1

Pila Spi- Fatha

Fig. 1 Geological map of the studied sections and wells from Zagros fold-thrust belt. Kurdistan region (Modified from Ibrahim, 2009)


studied area (Fig. 1). The first exploration well was drilled in 1902 in the Chia Surkh oil field; 90 km southeast of Sulaimani city is considered as one of the pioneer oil explorations in Middle East and Kurdistan region. The general stratigraphy and ramp concept of the Kirkuk oil field carbonates were established by Henson (1950a). He described the Kirkuk productive limestone as a reef complex. The term Breef complex^ is applied to an aggregate of reef limestone with associated calcareous rocks, in which the back reef, reef, and fore-reef (basin ward) can be differentiated by petrographic and micropaleontological criteria. He also considered the integration zone between the ramp-complex and basin ward sediments to be favorable for the generation, migration, and accumulation of oil, where the features of primary and secondary porosity and cementation in fore-reef limestones, if porous, may act as carrier beds and reservoirs. Bellen (1956) described the stratigraphy as the main limestone and indicated that three separate reef Bcycles^ can be identified as Lower (Shurau, Sheikh Alas, and Palani Formations), Middle (Bajawan, Baba, and Tarjil Formations), and Upper (Anah, Azkand, and Bnot known^ Formations) cycles; based on their relative stratigraphic positions, these sequences show lateral facie variations with back reef, reef, and basinal facies. The Bnot known^ was named BIbrahim Formation^ in 1959 by Bellen et al. as a basinal facie equivalent of the Anah and Azkand Formations for the upper Oligocene cycle. Ditmar et al. (1971) revised Bellen’s classification based on three cycles and instead divided the Oligocene sedimentary cycle into two subcycles, the Lower and Upper cycles. The lower cycle comprises the Sheikh Alas, Shurau, Palani, and Tarjil Formations, and the upper cycle consists of the Anah, Azkand, Baba, Bajawan, and Ibrahim Formations. Lawa et al. (2000) studied the stratigraphy and hydrogeology of the Sulaimania area and drew a geological map of the area under consideration and indicated that an Oligocene sequence may be present near the boundary between the high and low folded thrust zones. Al-Banna (2008) studied the OligoceneMiocene boundary in northern Iraq and revised the previously assigned upper subcycle of the Late Oligocene age (Chattian) by Bellen et al. (1959) into the period of the Early Miocene age (Early Aquitanian). The Fatha (Lower Fars) Formation is overlain by the second main detritus sequence of the MiocenePliocene age, constituted by the Injana (Upper Fars) Formation and lower and upper Bakhtiari Formations. This work tries to identify the main shallow large and benthonic foraminiferal zones and correlated with the international and regional standards. Accordingly, new biostratigraphy and chronostratigraphic frameworks for the studied units were proposed. The identification of the sequence boundary nature, types, and causes, in addition to the maximum flooding surfaces, for the studied sections was correlated with regional data sets from Arabian platform and Lorestan and Dezful embayments. Accordingly, the causes of lateral and facial

changes of those prolific carbonates, with special attention to the palaeo-configuration of the depositional basins, were clarified.

Materials and methodology The re-established chronostratigraphic frameworks for the studied units were based on shallow large and benthonic foraminiferal zonations. To achieve these work goals, eight outcrop and seven well data have been selected and utilized to identify sediment composition, fossil content, strata geometries, primary factors controlling carbonate factories, and type of platform configuration for the Late Eocene to Early Miocene. More than 367 rock samples from the studied sections were collected for foraminiferal studies and examined earlier for planktonic, benthonic, and large foraminifera. The samples for foraminiferal analyses, 200–500 g each, were dried and disintegrated in a solution of sodium carbonate using classical cooking methods. At least 300 foraminiferal tests were picked, except for the samples where foraminifera were exceedingly rare. In addition to that, there are more than 320 thin sections for microfacie analysis. The micro faunal slides are clarified by scanning electron microscope (SEM) and housed in the Cardiff University. The orientation of foraminiferal sections is random because the indurate carbonate rocks do not allow specimens to be freed from their encasing sediment. Cahuzac and Poignant (1997) and Serra-Kiel et al. (1998) were the primary references for the shallow benthic zonations. Based on extensive field works and integration of the lithostratigraphic key surfaces, facie distribution and depositional environments were utilized to evaluate the influence of the global sea level changes in the depositional styles.

Geological setting The study area covers two structural domains within the Zagros fold-thrust belt. The first one is represented by the southern periphery of the high folded thrust zone BHFTZ,^ and the second one is located within the low folded thrust zone BLFTZ^. The main studied structures from the high folded zone are as follows: (1) Baranan (Swerawa well)Darbandikhan-Bamu mountain range and (2) BazianSagrma-Qaradagh-Gulan mountain range, whereas the low folded thrust zone structures are as follows: (1) SangawAjdagh and Sharwal Dra anticlines in the south of the Sulaimani area. The studied wells are (1) Pulkhana well no. 5 (from Pulkhana structure), (2) Chia Surkh well no. 9 (from Chia Surkh north dome), (3) Kurda Meer (from Kurda Meer structure), (4) Qumer well (from Qumer structure), (5) Sarqala well (from Sarqala structure), and (6) Kor Mor well from Kor Mor structures (Figs. 1 and 2). It is


Fig. 2 Geological setting of the left bank of Sirwan River area, eastern side of Khanaqin Fault (redraw after Youkhanna and Hradecky 1977)

worthy to mention that all the wells are located within the low folded thrust zone except Swerawa well from the high folded thrust zone. The studied sections are from Kurdistan foreland basin which is a part of major Zagros basin that extends from Turkey, northeastern Syria, and Kurdistan region, through northwestern Iran and continues into southeastern Iran. This foreland basin developed with the disappearance of Neo-Tethys as suturing began in the northwest and migrated southeast during the Middle to Late Eocene (Lawa et al. 2013). The suturing was accompanied by crustal thickening and movement along the initially passive margin of the Arabian Plate and is related to the spreading movements in the Red Sea-Gulf of Aden (Hemplton 1987). A basement fault separated the former structures from each other by a transversal deep fault and called Khanaqin Fault. Those structures on the left bank of Sirwan river show similarities with Lorestan zone of Iranian Zagros foldthrust belt, while those structures on the right bank of Sirwan river (Khanaqin Fault) are considered as a part of Kirkuk embayment within the low folded thrust zone. The Darbandi Bazian-Sagrma-Qaradagh-Gulan anticline series

trends NW-SE and extends for more than 75 km in length and 2–3 km in width, manifesting the boundary between the high and low folded thrust zone. The high folded thrust zone structures are representing rectilinear sinuous elongate asymmetrical anticlines with prominent Zagros trend that changes from N-S in the left bank of Sirwan river to NW-SE in the right bank of Sirwan river. The bracheyasymmetrical doubly plunging anticlines are prominent structures with Late Eocene carbonate carapace of Pila Spi Formation and clastic-dominated Fars sequence on the limbs, almost without (or very rare) evaporite facies and Paleocene Kolosh Formation in their cores. The Baranan back thrust fault also predicted from seismic profile runs semi-parallel to Tanjero valley delimited the northern boundary of the studied area. The anticlines of the low folded thrust zone are relatively more broad and with thick Eocene-Oligocene carbonates in their cores, that is sealed by thick evaporite of Fatha Formation, as the case in Qumer, Shakal, Sarqala, Chia Surkh, Sharwal Dra, Kor Mor, Taza, Pulkhana, and Kurda Meer anticlines (Figs. 1 and 2).


3rd order and MFS

Sea level changes (0)Shallow-------------------Deep(200)

Last Transgresssion

LFTZ

Dominates facies Lagoonal Evaporites

Gap

Lower Fars/ Clastics dominates

HFTZ

Age Middle Miocene

1. The Late Eocene sequence: represented by the Pila Spi Formation in the high folded thrust which changes to Avanah and Pila Spi Formations across high/low boundary that in turn develops southwest towards the Jaddala and Avanah Formations in Kirkuk embayment (Fig. 2). Conglomerate layer separates between late Eocene and

Fourth 3rdorder TST/Hst

Lagoonal Carbonates

Serikagni-

Thin EuphratesJeribe+gap

Gap

Early-Middle Miocene

S.B.T.1

MFS

Third 3rd order TST/Hst Second 3rd order TST/Hst First 3rd order TST/Hst

Inner –Middle Ramp Outer Ramp Lagonal to open marine

Baab-bajwan Shekh Alas=Tarjil Jaddala-Avanah

Avanah-/Pila Spi

Thin AnahAzkand+ Gap Gap

Gap Gap Pila Spi

Oligocene-Early Miocene

SBT I or 2

M-Late Eocene Bartonain -Pribonian

Fig. 3 Third-order depositional systems, maximum flooding surfaces, and sequence boundaries in the studied sequences

H/LFTZ boundary

The late Eocene-Early Miocene carbonate reservoir maximum thickness is about 600 m in Bamo-Bellula sections and Chia Surkh wells (Fig. 2). The total thickness of the studied time package shows sudden facies and thickness changes across the high/low folded thrust boundary from 200 m in the northeastern (NE) limb of the Sagrma structure to more than 400 m in the southwestern (SW) limb of the same structure with remarkable appearance of Kirkuk Group and or Early Miocene Euphrates and Jeribe Formations. A same situation was recorded from Bamo, Belulla, Drabandikhan, and Qaradagh structures

with another diagnostic increase of the studied sequence to 650 m across Khanqain Fault (Figs. 1 and 2). From the low towards high folded thrust zone, the whole studied carbonate sequences show decreasing thickness and shallower facie nature (Fig. 3). This work categorized them as follows:

Lower Fars

Stratigraphy

MFS

SBT I or 2

MFS

S.B.T.1


Oligocene carbonates in the low folded zone (Plate 1, Figs. 7 and 8). 2. The Oligocene-Early Aquitanian of the Kirkuk Group in the High folded thrust zone (HFTZ) is sparsely recorded and mostly absent. Almost a conglomerate bed of variable thickness called the Basal Fars Conglomerate (BFC) is

located between the Late Eocene (Pila Spi Formation) and Early Miocene (Fatha Formation) (Plate 1, Fig. 2). The implication of the possible partial presence of Kirkuk Group members in the high folded thrust zone will certainly increase the potential for hydrocarbons in the studied area. The Kirkuk Group about 10–20 m thick in

Plate 1 Outcrop photos of 1–2: Pila Spi formation in Darbanikhan area; 3–4: Avanah formation in Bamu structure; 5: Jaddala formation in Bellula Gorge area; 6: Sheikh Alas formation in Bellula Gorge area, 7–8: Conglomerate layer separate between late Eocene and Oligocene carbonates Basal Fars Conglomerate (Zagros major Hiatus)


Sagrma-Gulan sections, while on the left bank of (Sirwan River) Khanaqin Fault and change to 70 m thick in Belulla structure. Not only that, but it shows a progressive increase in thickness towards Kirkuk embayment. In the low folded thrust zone, the Kirkuk Group is almost recognized as a set of nine formations (Shurau, Sheikh Alas, Palani, Baba, Bajawan, Tarjil, Anah, Azkand, and Ibrahim Formations) in one incomplete stratigraphic package. The absence of certain formations of the Kirkuk Group may reflect the palaeo-configuration of the basin (Majid and Veizer 1986). 3. The Aquitanian carbonates are mostly reported with Euphrates, Serikagni, Dhiban anhydrites, and/or Jeribe Formations; also, they show a progressive increase in thickness and deeper facie type from the high towards low folded thrust zones. The characteristic features of each lithostratigraphic unit are described as follows as three depositional sequences: (1) Late Eocene (Bartonian-Pribonian) sequence, (2) Oligocene-Early Aquitanian sequence, and (3) Miocene (Middle Aquitanain-Burdigalain) sequence (Fig. 3). 1. Late Eocene (Bartonian-Pribonian) sequence This sequence is about 100–400 m thick and represented by Pila Spi, Avanah (partially and upper part of the Jaddala Formations. Pila Spi Formation: This unit is composed of well bedded, highly fractured dolomite and chalky limestone, almost recognized in the high folded zone and close to the low folded thrust zone. It was described first by Bolton (1956) from Darbandikhan structure. The red silicilastics of the Gercus Formation (Middle Eocene) unconformably underly the Pila Spi Formation with a 5–15-m thick conglomerate between them and marks the base of the studied sequence. The Fatha Formation (Middle Miocene) overlies the karstfied and vugy carbonates of Pila Spi Formation unconformably without Oligocene and Early Miocene sequences and consist the Basal Fars conglomerate by Bellen et al. (1959). This sequence is a boundary of type one and indicates Zagros major hiatus at the top of the Tectonic megasequence Arabian Plate AP10 (Lawa 2004; Lawa et al. 2013) (Plate 1, Figs. 1 and 2). Avanah Formation: Usually, Avanah Formation consists of carbonates, marly limestone, and marl rich with large foraminifera such as Alveolinides, Nummulites, and Orbitolites. This Alveolinide carbonate unit is not recorded from most parts of the high fold-thrust zone but shows first appearance close to the boundary with the low folded thrust zone. Usually, they are overlaid by Pila Spi Formation from the SW limbs of the Sagrma, Bamo, and Bellula and change latterly to Avanah formation, in Aj Dagh anticline (Plate 1, Figs. 3 and 4). In this study,

these forams indicate Middle Eocene to Early Late Eocene age; based on shallow benthonic zones SBZ.21 and SBZ. 22 as the case in Aj Dagh anticline, the presence of this unit was recorded in this structure for the first time. The intercalation of Avanah formation (mostly with the upper part) of the Jaddala formation was delineated in the low folded zone from several oil wells (Kurda Meer, Qumer and Kor Mor), in addition to outcrops in Aj Dagh and Bellula structures. Jaddala Formation: this formation represents the offshore facies of the late Lower Eocene-Upper Eocene in the western and central areas of Iraq and Kirkuk embayment. In its type locality, it consists of marly and chalky limestone and marls with occasional thin intercalations of shoal limestone (Avanah limestone tongues) (Bellen et al. 1959). The diagnostic Eocene planktonic foraminifera facies show shallowing upwards towards ramp facies of the Avanah Formation and acts as an oil reservoir in certain oil fields in Kurdistan region. Such intercalation is recorded from the wells drilled in the studied areas: in Kurda Meer, Sarqala, Kor Mor, and Chia Surkh structures (Plate 1, Fig. 5). Accordingly, the Late Eocene lateral facial changes starts from the lagoonal Pila Spi Formation in the HFTZ, then change to neritic shoalinner ramp facies of the Avanah Formation and finally to the deep marine facies of Jaddala Formation (mostly upper parts) from the low folded thrust zone BLFTZ,^ that is towards the depocenter. 2. Oligocene-Early Aquitanian sequence (Kirkuk Group) Based on lithostratigraphic changes, this group is subdivided into two sequences: the lower one is the Repulian sequence and the upper one is the ChattianEarly Aquitanian sequence. (A) The Lower sequence: this sequence comprised mainly of the ramp Sheikh Alas and Shurau Formations. Sheikh Alas Formation: the Sheikh Alas Formation is characterized by buff, brownish gray to pinkish brown, dolomitize, porous, and locally recrystallized Nummulitic limestone. It was defined by Bellen (1956) from an outcrop in the north dome of the Qara Chauq structure; it represents the fore-reef facies of the lower Oligocene cycle. In the type locality, this unit contains only rare, poorly preserved Nummulites fichteli (Bellen et al. 1959), while in the Kirkuk area, Nummulites intermedius, Nummulites incrassatus, Operculina cf. complanata, and Rotalia viennoti are common, in addition to Nummulites fichteli and Nummulites vascus which are recorded by Ghafur (2012) in southern Kurdistan. Majid and Veizer (1986) suggested that the lower part


Fig. 4 Chronostratigraphic section for Megasequence AP10 and AP11, derived from (Sharland et al. 2001)

Author's personal copy Arab J Geosci Fig. 5 Sequence stratigraphy of exposed formations in Core of Aj Dagh Anticline. SBT1 is sequence boundary type 1, mfs is maximum flooding surface, HST is highstand system tract, and TST is transgressive system tract

of this formation was deposited in a fore slope environment, whereas the upper part represents a lagoonal environment, without any explanation why these two different facies occur next to each other. This unit was recorded from Belulla section, Kurda Meer, and Sarqala wells (Plate 1, Fig. 6). Shurau Formation: the Shurau Formation consists of two parts, a lower porous coralline limestone and upper gray and dense limestone that were first defined by Bellen (1956) in well K-109 in the Kirkuk structure. Fossils in the type locality are relatively rare. In the Kirkuk area, the lower part of the Formation was deposited in the reef and the top in a tidal flat environment (Majid and Veizer 1986).

However, in the west of Iraq, the formation was deposited in the reef and partly in the back reef environment (Jassim et al., 1984). In the study area, it represents the inner-mid ramp facies of the lower Oligocene cycle. This unit has been recorded from oil wells within Kirkuk embayment. (B) The upper sequence: The upper sequence comprises the ramp system of Baba, Bajawan, Azkand, and Anah Formations and the basinal Trjil and Ibrahim Formations. These formations pass both vertically and horizontally into each other. Baba Formation: the Baba Formation consists of porous, dolomitized fossiliferous limestone (Bellen 1959)

Author's personal copy

Sea level

Depositional sequence

System tract

Formations

Fig. 6 Sequence stratigraphy of exposed formations in Bellula Gorge area. SBT1 is sequence boundary type 1, HST is highstand system tract, and TST is transgressive system tract

Microfacies

Arab J Geosci

Sheikh Alas

Kirkuk Group

Deep

shallow

SBT I CB

HST/ TST

Could be HST or TST

NR-1

SBT I

Jaddala

Fine

PK

TST

Coarse

defined by Bellen (1956) from well Kirkuk-109. Ctyroky and Karim (1971) studied the outcrops of this formation in the Anah area (west of Iraq) and identified the following fauna: Rotalia viennoti, Lepidocyclina cf. elephantiana, L. cf. dilatata, L.cf.morgani, Archaias sp., Triloculina sp., Quinqueloculina sp., Robulus sp., peneroplis sp., praerhapydionina sp. (?), Spiroclypeus cf. marginatus, ostracods, gastropods, Spirorbis sp. (?), Chlamys sp. (?), corals, and fish teeth. This fauna indicates a Middle Oligocene age. However, Bellen et al. (1959) dated the upper part of the formation in the Anah area as early Late Oligocene. Based on the fauna, the formation was deposited in a fore-reef environment along both the northeast and southwest margins of the Oligocene basin (Majid and Veizer 1986). Bajawan Formation: Bellen (1956) defined the Bajawan Formation from well Kirkuk-109. It consists of the alternation of tight miliolid limestone with more porous, partially dolomitized coralline algalramp limestone, with relatively abundant coral fragments and thin argillaceous limestone beds (Bellen et al. 1959). The total thickness is about 40 m. Based on the fossil content and the amount of porosity, this formation was subdivided to two parts as follows: (A) The upper dense unit: this consists of dense miliolid limestone which is partly chalky or dolomitized. Its upper part is mostly brecciated; therefore, it looks like

the basal conglomerate of the overlying Fatha Formation. (B) The lower porous unit: this consists of alternation of two types of rocks, one being similar to that of the dense unit of Bajwan with a moderately higher degree of recrystallization, dolomitization, and porosity and the second consisting of a porous and vuggy dolomitic limestone. Two faunal zones were identified within Bajawan Formation (Bellen et al. 1959): a lower Delicata Zone characterized by Praerhapydionina delicata and an upper Kirkukensis Zone characterized by Archais kirkukensis, indicating that the formation is probably of Late Oligocene age. Ditmar et al. (1971) claimed that there is no age difference between the Bajawan and Baba and Anah and Azkand Formations and that these four formations belong to one sequence. The bottom part of the Bajawan Formation was deposited in a ramp and partly inner ramp environment; the upper part was deposited on mud flats (Majid and Veizer 1986). It is also recorded in Aj Dagh and Bamu structures (Plate 2, Figs. 1 and 2). Tarjil Formation: this Formation was defined by Bellen (1956) from well Kirkuk-85. It is composed of slightly dolomitized globigerina marly limestone; it is rich in foraminifera Nummulites intermedius and Lepidocyclina (Bellen et al. 1959). According to Jassim and Goff (2006), these fossils indicate an outer shelf depositional environment, in addition to Nummulites intermedius

Author's personal copy Arab J Geosci Plate 2 Outcrop photos of 1–2: Bajawan formation in Aj Dagh structure; 3–4: Azkand formation in Sharwal Dra structure; 5: Anah formation in Aj Dagh structure; 6: Jeribe formation in Aj Dagh structure; 7–8: Fatha formation in Aj Dagh and Bamu structures

appearing to be restricted to the Early Oligocene age. While Majid and Veizer (1986) found that the lower part of the Tarjil Formation in the Kirkuk region was deposited in an open marine and the top in a toe of slope environment. Jassim and Goff (2006) recorded that the Tarjil Formation crops out in Qara Chauq area and consists of 20 m of hard, yellowish gray limestone overlain by thick-bedded limestone with fossils including Nummulites sp., Lepidocyclina sp., Rhapydionina sp., Rotalia viennoti, Lenticulina sp., gastropods, echinoids, algae, bryozoans, and bivalves. In this work, the basinal facies of the Tarjili Formation was delineated from Kor Mor well in Kirkuk embayments. Kharajyani (2013) mentioned that the upper part of

this unit involves a mixing fauna of planktonic, benthonic, and large benthonic foraminiferas. We think it is a mixed content of the conglomertic horizon at the boundary between the lower and upper Oligocene cycles. Azkand Formation: the unit is about 100 m thick; mostly consists of massive, dolomitic, and recrystallized limestone; and is of high porosity (Bellen et al. 1959), which was defined by Bellen (1956) in the Azkand area of Qara Chauq structure. The recorded fossils include Heterostegina cf. assilinoides and Miogypsinoides complanata in the upper part and Lepidocyclina spp. in the lower part (Bellen et al. 1959); the presence of Heterostegina cf. assilinoides indicates a Late Oligocene (Chattian) age (Plate 2, Figs. 3 and 4). In this


work, it was recorded in Sharwal Dra structure and Kurda Meer wells. Anah Formation: Bellen in 1956 also defined the Anah Formation from the Euphrates valley about 15 km west of Al-Nahiyah village near Anah. It is composed of gray, brecciated, detrital, recrystallized, and coralline limestone, massive in the lower part and becoming thinner bedded upwards (Bellen et al. 1959). Jassim and Goff (2006) pointed out that the formation is mostly a ramp deposit, alternating with inner ramp, miliolid facies. Ctyroky and Karim (1971) reported the following fossils from the Euphrates valley section: Subterranopyllum thomasi, Archaias kirkukensis, Austrotrillina howchini, Rotalia viennoti, Robulus sp., Bolivina sp., Textularina sp., Trioculina cf. gibba, Quinqueloculina sp., P e n e ro p l i s t h o m a s i , P. e v o l u t u s , O p e rc u l i n a cf.complanata, Lepidocyclina sp., Miogypsinoides complanata, Miliolids, Hydrobia sp., Scaphander sp., Acteonia sp., Nassa sp., Natica sp., Mitra sp., Cerithium sp., Pyramidella sp. Juv., Tympanotomus margaritaceus, Oliva sp., Chlamys sp., Euchilus sp. Juv., bryozoa remains indet, Heliastrea defrancei, and fish bones. According to Ctyroky and Karim (1971), the presence of Miogypsinoides complanata indicates a latest Oligocene age. These formation were recorded in Sagrma, Aj Dagh, Bamu structures in addition to Kor Mor wells (Plate 2, Fig. 5). Ibrahim Formation: the Ibrahim Formation consists of globigerina marly limestone with traces of pyrite and occasional glauconitic. It shows slight dolomitization (Bellen et al. 1959) which was first defined by Bellen (1956) from well Ibrahim-1, in the Sheikh Ibrahim structure of the low folded thrust zone, northwest of Mosul. The thickness of the formation at its type section is about 56 m (Buday 1980). This unit was deposited in a basinal environment and represents the basinal equivalent of the upper Oligocene cycle which was recorded in Sharwal Dra structure and Kor Mor wells. 3. Miocene (Late Aquitanian-Burdigalian) sequence: This sequence, manifested by the last marine transgressions of neoetheys basin, is indicated by the deeper facies of Serikagni Formation that change laterally into shallower facies of Euphrates and changes into two more restricted shallower lagoonal facies of the Jeribe and Dhiban Formations. Euphrates Formation: generally, it is composed of interbreeding of limestone and marly limestone, first bed is 2 m thick composed of limestone of fragmentary type, followed by a 5-m sequence, in which the pebbles of the conglomerate are cemented by argillaceous limestone materials. Borelis melo melo was zone recorded from this

unit (Al Hasimi and Amer 1985). This unit has been registered from Kurda Meer, Sarqla, and Kor Mor wells with an average thickness less than 12 m. Dhiban anhydrite Formation: this unit represents semirestricted lagoonal facies, comprised mainly of anhydrite and dolomitic limestone. Occasionally, it is recorded between Euphrates and Jeribe Formations, usually of variable thickness ranging between few meters up to 60 m. It is about 40 m thick in Qumer well no. 1 and Chia Surkh wells (8, 9, 10, and 11). It is not recorded in the outcrops of the study area and surrounding areas; instead of that, about a 1-m conglomerate was detected between the Euphrates and Jeribe Formations from Sarqala well. Jeribe Formation: it is mostly composed of limestone (Oolitic limestone) and dolomitic limestone, well bedded, stromatolitic, and gastropods rich. The thickness is about 1–2 m, recognized from Aj Dagh anticline, occasionally abundant clastics influx, giving rise to thin parallel laminated arenaceous dolostones. Borelis melo kurdica zone was recoded from this outcrop unit and wells in the low folded thrust zone by Ctyroky and Karim (1971) and Lawa (1986). The total thickness is about 70 m. This unit was recorded from outcrops in Aj Dagh, Gulan, and Qaradagh structures in addition to subsurface sections (in Kurda Meer, Sarqala, Kor Mor, Taza, and Chia Surkh wells) with variable thickness and acts as a potential reservoir (Plate 2, Fig. 6). Fatha (Fatha) Formation: this unit is considered as seal rock in the whole studied area and occasionally a reservoir (especially the lower transitional unit) as well as acts as a detachment surface for the overlying units (Lawa et al. 2013). The lower part is composed of alternating gypsum, limestone, and calcareous claystone. The upper part consists of about seven cycles of similar character: alternating horizons of calcareous, sometimes silty, claystones; fossiliferous, sometimes oolitic, limestone; and sandstones. The minimum thickness of individual cycle is about 30 m while the maximum thickness reaches 800 m. The remarkable reduction in evaporite/clastic ratio is associated with thickness reduction from the low (750 m thick in Chia Surkh wells) towards the high foldthrust zone (125 m in Swerea well) (Stevanovitic et al. 2003). It is present in most of localities: Sagrma, Aj Dagh, Bamu, and Bellula and in several wells such as Kurda Meer, Sarqla, Pulkhana, and Kor Mor (Plate 2, Figs. 7 and 8).

Biozonation A moderately diverse larger foraminiferal fauna from the late Eocene to Early Miocene formations with important stratigraphic, palaeo-ecological and palaeo-biogeographical

Author's personal copy Arab J Geosci Fig. 7 Sequence stratigraphy of exposed formations in Sagrma area. SBT1 is sequence boundary type 1, mfs is maximum flooding surface, HST is high stand system tract, and TST is transgressive system tract (Ajdagh section)

implications are described with respect to its position in the Neo-Tethys Sea (Bassi et al. 2007). The fauna is dominated by hyaline-perforated and porcellaneous forams, including Amphistegina, Archaias, Austrotrillina, Miogypsinoides, Neoplanorbulinella, Nummulites, Operculina, Assilina, Lepidocyclina, and Spiroclypeus. The palaeo-environmental setting of the Kirkuk Group is interpreted as a shallow inner ramp setting characterized by Archaias spp. and Austrotrillina spp., the deeper part of the inner ramp with Nummulites spp. Fig. 8 Sequence stratigraphy of exposed formations in Hazar Kani Village. SBT1 is sequence boundary type 1, mfs is maximum flooding surface, HST is highstand system tract, LST is lowstand system tract, and TST is transgressive system tract (Ajdagh section)

1–2. The shallow part of the middle ramp with Spiroclypeus spp., Miogypsinoids spp., and Operculina spp. 2–3. A deeper part of middle ramp setting dominated by coralline rhodoliths along with Lepidocyclinids spp. The presence of Archaias hensoni (Smout and Eames 1958) shows that members much more diverse in the middle-eastern associations of shallow-water larger


porcellaneous foraminifera are also present in the northwestern parts of the Tethys realm and reveal a corresponding diversity gradient among larger foraminiferal faunas in the Zagros Tethyan realm, which are related to a decrease in temperature. Youhanna (1983) and Al-Eisa (1992) also revised the previously assigned upper biozone of the Late Oligocene, which was suggested by Bellen (1956) and Bellen et al. (1959) into the Early Miocene age using the planktonic foraminifera genus Globigerinoides in the Kirkuk area. Abid and Sayyab (1989) re-studied the foraminifera of the Anah Formation, aiming to solve some of the taxonomic and chronology problems concerning this formation; various genera and species were identified to ascertain that the age of this formation, which is Late Oligocene-Early Miocene age. Grabowski and Liu (2010) used Sr87/Sr86 ratios to re-establish a new chronostratigraphic framework for the studied interval and conclude that Sr isotope ages of anhydrites from the Fatha Formation from many wells give consistent ages of middle to late Burdigalian (15.6–18.5 Ma). The platform carbonates of the Jeribe Formation are early to middle Burdigalian in age (18.5–19.6 Ma). The basin-filling evaporites of the Dhiban Formation were deposited from earliest Burdigalian through late Aquitanian (19.6–21.3 Ma). The Euphrates and Serikagni Formations are still older, deposited in the early Aquitanian to late Chattian (21.8–24.3 Ma). Lawa (1986) recoded the following species and genera from outcrops and wells in northern Iraq within Fatha successions: Ammonia sp.; Rotalia spp.; Miogypsina sp.; Miogypsina globulina (Micheloii); Ammonia eccarri (linnne); Ammonia spp; Ammonia beccarri var parkinsoniana (de orbigney); Elphidium sp.; Valvulina sp.; Textularia sp.; Pyrgo sp.; Elphidium incertium; Ammonina acuta; Rotalia umbonata Leroy; Epnoides sp; Noionella sp; Peneroplis sp., Peneroplis farsensis Henson; Quinquloculina elongata; Quinquloculina graciles, Triloculina sp.; Spiroloculina spp., Clavulinds sp.; Sulcocythrealla; Actinothyeris, and Cytherata therea. The following pelecypods are recorded: Ostrea (Ostrea latimarginata and Ostrea sub angulat); Clausinella persica; and Chalmys, Cardium among mollusk group. Typical gastropod genera are Acteonina, Turritella, Tricolia, and Littorina. However, the Table 1 This study’s biozones of Late Eocene to Early Miocene age

predominate fossils in the lower part are Mililolides (Quinquiloculina sp. and Spiroloculina sp.) and Peneroplis farsensis. Such assemblages indicate the BurdigalinaLanghian age for the Fatha Formation. The selected sections are characterized by being rich in fossils; mostly benthic foraminifera, occasional planktonic foraminifera, and macro fossils including pelecypods, gastropods, echinoids fragments, red algae, and coral bioherms are also present. Index fossils of Benthic Large Foraminifera (BLF) have been used for the purpose of determining the age of the studied units, because of their precise time indication boundaries, wide geographical distribution, and abundance in the selected sections. The biozones in this study are two Eocene biozones Alveolina biozone (AL) and Discocyclina biozone (DI) and three Oligocene-Early Miocene (Early Aquitanain) zones Nummulites fichteli biozone (NF), Praerhapydionina delicata biozone (PD), and Austrotrillina howchini biozone (AH). The last two zones of the Late Aquitanian-Early Burdigalian age are Borelis melo melo from Miocene; the main properties of each zone are clarified in Table 1. 1. Alveolina biozone (AL): this biozone recorded only in the Avanah Formation of the Bamu section at the western limb of the Bamu anticline and close from the Iranian border and can be correlated with Eocene part of the Asmari formation, in addition to Kurda Meer well, when it shows an interfingering with the upper part of Jaddala formation. This zone is defined by the total range of Alveolina elliptic and Alveolina oblonga (Table 2; Plate 3, Figs. 1 and 2). The last occurrence of Alveolinides marks the top of this zone, which also has a predominance of both porcellaneous and hyaline larger benthic foraminifera such as Nummulites, Asterigerina, and Orbitolites with minor components of miliolids, Biloculina; Triloculina; Quinqueloculina, and Spirolina. The characteristic feature of this zone is the extinction of Alveolinids, which can be correlated with the upper boundary of the Shallow Benthic Zone 17 (SBZ.17) in the zonations of Serra-Kiel et al. (1998) (Table 2).

Age Cenozoic

Miocene

Langhian

Formation

Biozones

Fatha (Lower Fars)

A. beccari (AB)

Burdigalian Aquitanian

Oligocene L. Eocene

Chattian Repulian Pribonian Bartonian

Remarks

O. marginata (OM) Jeribe-Dhiban EuphratesAnah-Azkand-Ibrahim Bajawan-Baba-Tarjil Sheikh Alas-Shurau Pila SpiAvanah-Jaddala(U.Parts)

Borelis melo kurdica (BMK) Borelis melo melo (BMM) Austrotrillina howchini (AH) Praerhaypidionina delicata (PD) Nummulites fitchteli (NF) Discocyclina (DI), Alveolina (AL)

Bartonian Priabonian SBZ 22B

SBZ 22A

SBZ 21

SBZ 20

SBZ 19

SBZ 17 Praerhapydionina delicata (PD)

SBZ 23

Nummulites fichteli (NF)

Chattian

Borelis melo melo (BMM)

Borelis melo kurdica (BMC)

SBZ 18

BMC

BMM

AH

PD

NF

DI

AL

This study SBZ

SB Zones

Austrotrillina howchini (AH)

Age

E. Burdigalian

Epoch

Aquitanian

Miocene

SBZ 24

Discocyclina (DI)

Rupelian

Oligocene

SBZ 25

Alveolina (AL)

Eocene


Arab J Geosci

Table 2 This study’s biozones are correlated to global shallow benthic zones BSBZ^ of Cahuzac and Poignant (1997) and Serra-Kiel et al. (1998)

Author's personal copy Arab J Geosci Plate 3 Photomicrographs and outcrop photos of the studied areas biozones; 1–2: Alviolina; 3– 4 Discocyclinina; 5: Nummulites Fichtelli; 6: Praerhapydionina delicate

According to Hottinger (1960), Drobne (1977), and Nebelsick et al. (2000), the association of Alveolinids, Mummulitids, Asterigerinids, and small Miliolids define the rocks of late Eocene age. Behnam (1979) recorded this zone from the Bamo and Belula sections too. 2. Discocyclina biozone (DI): the Discocyclina biozone is recorded from the Avanah Formation at three localities, in the southwestern limb of the Aj Dagh Anticline at the Awa Spi locality, while at the northeastern limb and at the core of the Aj Dagh Anticline, it is absent. It is also present in the Bamu Gorge locality at the western limb of the Bamu Anticline and in the Bellula Gorge locality (Tables 3, 4 and 5). The DI biozone is defined by the occurrence of the Discocyclinids without Alveolinids (Table 2; Plate 3, Figs. 3 and 4). The top of the biozone is defined by the last occurrence of Discocyclinids. The Discocyclina is associated with Nummulites and Asterigerina and with minor components of miliolids, Biloculina, Triloculina; Quinqueloculina; Spirolina; Orbitolites; Operculina; Actinocyclina sp., and

Pellatispira sp. The later confirms the Late Eocene age for this biozone, because of its short age range which is located at the end of the Late Eocene (Sartorio and Venturini 1988; Serra-Kiel et al. 1998). The characteristic of the upper boundary of Discocyclina biozone is the extinction of Discocyclinids, and this can be correlated with the upper boundary of Shallow Benthic Zone 20 in the zonations of Serra-Kiel et al. (1998) (Table 2). The larger foraminifera of the upper part of the Dammam Formation include assemblages of Discocyclina; Nummulites and Pellatispira are confirmed as being of the Late Eocene age (Bokhary et al., 2008). 3. Nummulites fichteli biozone (NF): this biozone defines the Sheikh Alas Formation and is present in the Bellula Gorge locality on the western limb of the Bamu Anticline (Table 5) representing the total range (first and last occurrence) of Nummulites fichteli (see Table 2; Plate 3, Fig. 5); this is associated with Nummulites vascus. The lower boundary of this biozone indicates the first appearance of Oligocene strata (Kirkuk Group), and the upper

BS.17

BS.8

BS.7

BS.6

BS.5

BS.4

BS.3

BS.2

BS.1 DI

Bajawan

L.Oligocene

PD

BS.21

AL

Avanah

Middle-Late Eocene Formation sample no. Faunal zone

Anah BS.23

BS.22

BS.20

BS.19

BS.18

BS.16

BS.15

BS.14

BS.13

BS.12

BS.11

BS.10

BS.9 AH

Gastropods Echinoids

Red algae

Textularia sp.

Asterigerina sp.

Operculina sp.

Discocyclina sp.

Nummulites sp.

Orbitolites sp.

Alveolina sp.

Quinqueloculina sp.

Triloculina sp.

Biloculina sp.

Archaias kirkukensis

Praerhapydionina delicata

Dendritina rangi

Spirolina sp.

Peneroplis evolutus Peneroplis thomasi

Peneroplis sp.

A. howchini

A. paucialveolata

Austrotrillina sp.

miliolids sp.

Age

E.Mio


Arab J Geosci

Table 3 Distribution chart of the Middle Eocene-Early Miocene benthic foraminiferal biozones from Bamu gorge locality

DI

Avanah

Late Eocene Jaddala Bajawan

L. Oligocene

AH

Anah

Jeribi

E.Miocene

DS.15

DS.14

DS.13

DS.12

DS.11

DS.10

DS.9

Unconformity

DS.8

AW.19

Palaeosol

AW.18

AW.17

AW.16

AW.15

AW.14

AW.13

AW.12

AW.11

AW.10

AW.9

AW.8

AW.7

AW.6

AW.5

AW.4

AW.3

AW.2

AW.1

Echinoids

Bivalves

Red algae

Borelis melo curdica

PK forams

Textularia sp.

Pellatispira sp.

Orbitolites complanatus

Discocyclinid sp.

Heterostegina sp.

Operculina sp.

Amshistegina sp.

Asterigerina sp.

Nummulite sp.

Quinquiloculina sp.

Triloculina sp.

Biliculina sp.



Dendritina rangi

Spirolina sp.

Peneroplis thomasi

Peneroplis evolutus

Peneroplis sp.

Austrotrillina howchini

Austrotrillina paucialveolata

Austrotrillina sp.

miliolids sp.

sample no.

Faunal zone

Formation

Age


Table 4 Distribution chart of Eocene-Miocene benthic foraminiferal biozones in the Awa Spi locality


BL.68 BL.67 BL.66 BL.65 BL.64 BL.63 BL.62 BL.61 BL.60 BL.59 BL.58 BL.57 BL.56 BL.55 BL.54 BL.53 BL.52 BL.51 BL.50 BL.49 BL.48 BL.47 BL.46 BL.45 BL.44 BL.43 BL.42 BL.41 BL.40 BL.39 BL.38 BL.37 BL.36 BL.35 BL.34 BL.33 BL.32 BL.31 BL.30 BL.29 BL.28 BL.27 BL.26 BL.25 BL.24 BL.23 BL.22 BL.21 BL.12 BL.11 BL.10 BL.9 BL.8 BL.7 BL.6 BL.5 BL.4 BL.3 BL.2 BL.1

Echinoids

Bivalves

Red algae

solitary coral

Colonial coral

PK forams

Pellatispira sp.

Asterigerina sp.

Actinocyclina sp.

Discocyclina sp.

Nummulites sp.

Nummulites fichteli

Nummulites vascus

Textularia sp.

miliolids sp.

sample no.

Faunal zone NF DI

Formation Shiekh Alas Jaddala Avanah

Late Eocene

Early Oligocene

Age

Table 5 Distribution chart of the Eocene-Miocene benthic foraminiferal biozones in the Bellula locality


boundary is in the Chattian, which may correlate with the shallow benthic zones SBZ 21, SBZ 22A, and SBZ 22B, which were described by Cahuzac and Poignant (1997); Sirel (2003), and Gedik (2008) (Table 2). The NF biozone is similar to the Nummulites zone which was described by Bellen (1956); Bellen et al. (1959), and Majid and Veizer (1986) as one of the zones of the Kirkuk Group of the Early Oligocene which extends to the middle Oligocene age in the Kirkuk area. In the north-central Zagros Basin in Iran, Hakimzaheh and Seyrafian (2008); Laursen et al. (2009), and Seyrafian et al. (2011) used benthic foraminifera to determine the age of the Asmari Formation, and they recorded the Nummulites vascus-Nummulites fichteli zone as being of Early Oligocene (Rupelian) age. However, Lackpour et al. (2008) studied the Asmari limestone of Iran and reported that the Nummulites fichteliintermedius and Nummulites vascus belong in the Lower to Middle Oligocene. Mukhopadhyay (2003) studied the foraminiferal assemblage from the Eocene-Oligocene boundary of the Cambay Basin in India; the first appearance of Nummulites fichtelli has been correlated with the lower boundary of SBZ 21 of Serra-Kiel et al. (1998). Other records of Nummulites fichteli from India have been reported as being from the Early Oligocene age by Sengupta (2000, 2002). Drooger and Laagland (1986) considered this zone of Early Oligocene age; these commonly consist of Nummulites fichteli and Nummulites vascus. 4 . P r a e rh a p y d i o n i n a d e l i c a t a b i o z o n e ( P D ) : a Praerhapydionina delicata zone defines the Bajawan Formation, and it is present in three localities of the Aj Dagh Anticline: Zinana, Hazar Kani, and the core of the Aj Dagh Anticline as well as in the Bamu Gorge section in the Bamu Anticline (Tables 3, 6, 7 and 8). This biozone is characterized by the occurrence of Praerhapydionina delicata (see Table 2). The upper boundary is represented by last occurrence of Praerhapydionina delicata (Plate 3, Fig. 6 and Plate 4, Fig. 1). The typically associated porcellaneous benthic foraminifera are miliolids, Peneroplis sp., Peneroplis evolutus, Peneroplis thomasi, Austrotrillina sp., Austrotrillina ?paucialveolata/ asmariensis, Dendritina rangi, Archaias kirkukensis, Biloculina, Triloculina, Quinqueloculina, and rare Spirolina. According to Henson (1950a), Adams (1970), and Abid and Sayyab (1989), the age of Praerhapydionina delicata is limited to the Oligocene period (Early and Late Oligocene). However, Praerhapydionina delicata was identified by Lackpour et al. (2008) in the lower part of the Asmari Formation as being of the Middle Oligocene age. Praerhapydionina delicata, as a biozone, was first described by Bellen (1956) and Bellen et al. (1959) in the Kirkuk area as one of the two biozones of the Bajawan Formation

(kirkukensis and delicata) of Middle Oligocene age. A similar biozone is also reported by Behnam (1979) in the Khanaqin area, in the northeast of Iraq. In this study, the PD biozone is limited only to the Late Oligocene age. Furthermore, one of the associated fossils in this zone is Dendritina rangi, which starts to appear from the Late Oligocene age (Henson 1950b), thus confirming that the age limit of this biozone is the Late Oligocene. So this biozone could correlate with the shallow benthic zones SBZ 22B and SBZ 23, according to Cahuzac and Poignant (1997). 5. Austrotrillina howchini biozone (AH): this biozone defines the Anah Formation and is present in most of the sections in the study area in the Sagrma Anticline, in all of the localities of the Aj Dagh Anticline, and in the Bamu Anticline. It is absent only in the Bellula Gorge and Sharwal Dra localities (Tables 3, 4, 6, 7, 8, and 9). The biozone is characterized by the occurrence of the Austrotrillina howchini (see Table 2 and Plate 4, Figs. 2 and 3). The lower boundary of this biozone is represented by the first occurrence of Austrotrillina howchini and associated by porcelaneous miliolids, Austrotrillina sp., Austrotrillina ?paucialveolata/asmariensis, Peneroplis sp., Peneroplis evolutus, Peneroplis thomasi, Dendritina rangi, and Archaias kirkukensis. Minor components of Spirolina, Biloculina, Triloculina, and Quinqueloculina are also present. Smout and Eames (1958) studied the Asmari Formation in Iran and found that the middle of the Asmari Limestone contains Austrotrillina howchini, which directly underlies beds of the Burdigalian age in normal succession; they assessed the age of this fauna as Aquitanian, because it is definitely more closely related to a Burdigalian than to an Oligocene fauna. According to Adams (1968, 1970), the first appearance of Austrotrillina howchini is in the Early Miocene (Aquitanian). As a result, this biozone can be correlated with the shallow benthic zone SBZ 24 according to Cahuzac and Poignant’s zonation (1997). This study reveals that the age of the Kirkuk Group in the northeast of Iraq corresponds to the Oligocene (Rupelian-Chattian) and Early Miocene (Aquitanian) stages (Table 2). This study emphasized that the upper part of the Kirkuk Group, Anah, Azkand, and Ibrahim Formations, were deposited in the Late Oligocene and extended to the Early Miocene (Aquitanian) age. Accordingly, the Kirkuk Group is composed of ramp setting, in few localities evolved to shelfal, shelf margin, and basinal limestones divided into many lithostratigraphic units which are not readily correlated without an age framework. Lawa et al. (2000) and Stevanovic et al. (2003) recorded the Oligocene horizon in Aj Dagh and Sagrma area from outcrops in the low folded thrust zone and close from the high folded thrust


Echinoids

Bivalves

Gastropods


Textulaia sp.


Discocyclina sp.

Quinquiloculina sp.

Triloculina sp.

Biloculina sp.



Dendritina rangi

Spirolina sp.

Peneroplis thomasi

Peneroplis evolutus

Peneroplis sp.

Austrotrillina asmerensis



Austrotrillina sp.

miliolids sp.

Sample number

Faunal zone

Formation

Age

Table 6 Distribution chart of the Eocene-Miocene benthic foraminiferal biozones in the Zinana locality

Jeribi

E. Miocene

Z.34 BMC

Z.33 Z.32 Z.31

Annah

Z.30 Z.29 AH Z.28 Z.27 Z.26 Z.25 Z.24 Z.23 Z.21 Z.20 Z.19 Bajawan

Late Oligocene

Z.22

PD

Z.18 Z.17 Z.16 Z.15 Z.14 Z.13 Z.12 Z.11 Z.10 Z.9 Z.7

Avanah

Late eocene

Z.8 Z.6 DI

Z.5 Z.4 Z.3 Z.2 Z.1

zone during their mapping of that field. Khanqa et al. (2009) considered the conglomeritic sequence between

the Pila Spi and Fatha Formation, which is known as Basal Fars conglomerates, to be equivalent in part to the

Avanah

Late Eocene Bajawan

Late Oligocene Anah BMC

Jeribi

Early Miocene

CA.30

CA.29

CA.33

CA.32

CA.31

CA.28

CA.27

AH CA.26

CA.25

CA.24

CA.23

CA.22

CA.21

PD CA.20

CA.19

CA.18

CA.17

CA.16

CA.15

CA.14

CA.13

CA.12

CA.11

CA.10

CA.9

CA.8

CA.7

CA.6

CA.5

CA.4

CA.3

CA.2

CA.1

Echinoids

Bivalves

Gastropods

Red algae

solitary coral

Colonial coral


Borelis melo melo

Textularia sp.

Asterigerina sp.

Amshistegina sp.


Operculina sp.

Nummulite sp.

Nummulite fichteli

Rotalia sp.

Triloculina sp.

Spirolina sp.



Dendritina rangi

Peneroplis evolutus Peneroplis thomasi

Peneroplis sp.



Austrotrillina sp.

miliolids sp.

sample number

Faunal zone

Formation

Age


Table 7 Distribution chart of the Eocene-Miocene benthic foraminiferal biozones in the core of the Aj Dagh locality


Echinoids

Bivalves

Gastropods

Colonial coral

Rotalia sp.

Quinqueloculina sp.

Triloculina sp.



Dendritina rangi

Spirolina sp.

Peneroplis thomasi

Peneroplis evolutus

Peneroplis sp.


A. paucialveolata/asmariensis

Austrotrillina sp.

miliolids sp.

sample number

Faunal zone

Formation Jeribi Annah

E.Miocene

Age

Table 8 Distribution chart of the Eocene-Miocene benthic foraminiferal biozones in the Hazar Kani locality

AS10 AS.9 AH AS.8

Bajawan

L. Oligocene

AS.7 PD AS.6 AS.5

Avanah

L.Eocene

Unconformity

AS.4 AS.3 AS.2 AS.1

Palani and Euphrates Formations, or Anah and Ibrahim, or Asmari formation. Such statement contradictional with all previous studies and the possibility of the mixing of four formations in one single bed does not coincide with lithostratigraphic principles. Therefore, our study of that sequence and the lower part of the Fatha Formation emphasize the presence of Ostrea lataimaragina, Ostrea subanagluta, Ammonia beccarii, and Peneroplis thomsis zones (Plate 4, Fig. 6) and point precisely to the middle Miocene Burdigalian-Langhian age for the Fatha formation. The conglomerate constituents that is studied by Khanqa et al. (2009) mostly point to the mixing of the seasonal flooded Basara River with the deposits of this conglomerates (Plate 1, Fig. 2). 6. Borelis melo melo biozone (BMM): this biozone appears above the Kirkuk group and almost indicates the lagoonal facies of the Euphrates formation which is recorded from several oil wells such as Chia Surkh, Kurda Meer, Sraqla, and Kor Mor, but there is no record from any outcrops in the area. The most common benthonic foraminifera are Borelis melo melo, Ammonia beccarii, Ammonia sp., Rotalia umbonta, Elphidium, Miogypsina sp., Peneroplis farsensis, Quinquloculina akanaraina,

Quinquloculina spp, Spiroloculina spp., Tricloculina sp., Ostracaods, Bryozoa, Gastropods, and shell debris of echinoids. The dolomitic limestone zone of this unit acts as an excellent reservoir in several wells such as Kurda Meer.1, Chia Surkh.2, and Sarqala well and bout 40 m thick (Table 2; Plate 4, Fig. 4). Almost the Dihban anhydrite facies lead to mass extinction of this zone or truncated occasionally from the overlying Euphrates formation by unconformity surface as the case in Kurda Meer well. Latterly, this zone may change to deeper facies of the Serkagnai formation which show an increase of the planktonic foraminiferal rich facies which are not well identified in this work but recognized in Sarqala well.1. 7. Borelis melo curdica biozone (BMC): this biozone is recognized in Jeribe formation from several oil wells and outcrops in the low folded zone and mostly disappeared in the majority of the high folded zone. The common foraminiferals are Amphestigina sp., Ammonia beccari, Quinquloculina, Spiroloculina; Borelis melo melo, borelis melo curdica, Peneroplis farsesnsis, and Peneoplis eveloutus; mostly shallow habitat turtilleds, gastropods, and stromatolitic limestone facies are predominated in the high/low folded zone boundary and mostly indicated

Author's personal copy Arab J Geosci Plate 4 Photomicrographs and outcrop photos of the studied areas biozones; 1 Praerhapydionina delicate; 2–3 Austrotrillina howchini; 4 Borelis melo melo; 5 Borelis melo kurdica; 6 Ammonia beccari

the paleoshore line of the Early to Middle Miocene basin, in Kurda Meer.1, Taza.2, Sarqala, Kor Mor, and Chai Surkh wells. This zone is about 50 m average in thickness. In the studied outcrops from Aj Dagh, Qupey Qaradagh, and Gulan structures, they are almost less than 10 m in thickness (Table 2; Plate 4, Fig. 5). They mostly act as good dolostone and dolomitic limestone reservoir for oil and condensate gas in the low folded thrust zone, as it is recognized from Chia Surlh, Kurda Meer, and Kor Mor fields (Table 9).

Sequence stratigraphy To understand the patterns of deposition, an attempt was made to identify and date sequence boundaries and to tie the facies within sequences to specific system tracts based on basic ideas by Vial et al. (1977) and Possamentier et al. (1988). Almost four sequence boundaries (SB) segmented the depositional

sequences into three third-order sequences. The lower most sequence boundary was estimated to be of Bartonian age (37 Ma) and represent by more than 5-m conglomerates between the molasses facies of the Gercus and carbonates of the Pila Spi Formations. The second sequence, known as Zagros Major Hiatus, was estimated to be 34 Ma age and was placed at the top of karstfied carbonates of the Pila Spi Formation (Pribonian), directly below the Fatha formation (BurdigalianLanghian) (Plate 1, Figs. 1 and 2) almost manifesting the boundary between Tectonomegasequence AP10 and AP11. According to Sharland et al. (2001, 2004) and Aqrawi et al. (2010), the Late Eocene sequence of the studied main carbonates are related to the upper most part of the Tectonomegasequence AP10 and manifest boundary with the Tectonomegasequence (TMS) AP11 (Fig. 4). This boundary is dated as 34 Ma and marks the first continent-continent collision between the Arabian Plate and Eurasia along the Zagros suture. Lawa et al. (2013). The collision and uplift in the Zagros caused a southwestward shift in facie belts,


Echinoids

Bivalves

Gastropods

solitary coral


Quinqueloculina sp.

Triloculina sp.


Dendritina rangi

Spirolina sp.

Peneroplis thomasi

Peneroplis evolutus

Peneroplis sp.


A. paucialveolata/asmariensis

Austrotrillina sp.

miliolids sp.

sample no.

Faunal zone

Formation

SG.32 Fatha

M. Miocene

Age

Table 9 Distribution chart of the Eocene-Miocene benthic foraminiferal biozones in the Sagrma locality

SG.31 SG.30

Anah

E. Mocene

SG.29 SG.28 AH SG.27 SG.26 SG.25 SG.24 SG.23 SG.22 SG.21 SG.20 SG.19 SG.18 SG.17 SG.16

SG.14 Avanah

Late Eocene

SG.15

SG..13 SG..12 SG.11 SG.10 SG.9 SG..8 SG.7 SG.6 SG.5 SG.4 SG.3 SG.2 SG.1

marking the onset of the final closure of Neo-Tethys (Beydoun 1991; Goff et al. 1995). In SW limb of Sagrma anticline (H/LFTZ boundary) near to the edge of the Oligocene and Miocene basin, only 4.5 m of Early Aquitanian succession was recorded. The third one is almost

between the Rupelian and the Chattian (28 Ma) within Kirkuk Group. The last recorded one of the Aquitanian age (21 Ma) was placed between the Kirkuk Group and Jeribe or Euphrates Formations. The Late Eocene sequence transgressive surface reaches the maximum flooding surface (MFS) Pg.20, while


the Oligocene sequence contains MFS Pg. 30–50, where the basin is affected by the compressions along Zagros margin. The Ng10 maximum flooding surface records coincide with the planktonic condensed section within the Serikagni Formation (Aquitanian age). The Eocene sedimentation terminated due to a regional eustatic sea level fall which led to non-deposition and erosion across the Arabian Plate (Jones and Racey 1994; Goff et al. 1995; Ellis et al. 1996). The Supra-Dammam Unconformity marks a sequence boundary type one (SBT I) between Tectonomegasequence AP10 and AP11. In the Kurdistan foreland basin, the duration of this break shows a progressive decrease from the Zagros suture towards the Arabian Platform (Lawa et al. 2013). Ranjbaran et al. 2007 subdivided the Asmari formation from Gachsaran area into four third-order depositional sequences, which is laid down in the southern side edge Neo-Tethys Ocean (Zagros area). Taking in consideration the above proposed framework, the whole studied sequences are grouped into three third-order depositional sequences determined from shallowing and deepening trend of depositional facies and changes in the stacking pattern, also based on the determination of the sequence boundaries as well as, the maximum flooding surface indications. 1. The Late Eocene third-order sequence in the high folded thrust zone underlies by sequence boundary of type one were the deltaic facies of the Gercus Formation separated by thick conglomerate horizon from the lagoonal facies of the Pila Spi Formation and terminated by the top of TMS AP10 in the upper part of Pila Spi Formation which is truncated by sequence boundary type one with subaerial exposure that extends for more than 14 Ma. The Late Eocene succession (Avanah Formation) is composed of mid ramp skeletal packstone (NR-2) and inner ramp peloidal grainstone (PG), and the bioclasts are an indicator of changing the relative sea level from relatively deeper marine to shallow marine carbonates (Fig. 5). This relative sea level change can be recognized twice. As a result, a shallowing upward (coarsening upward) sequence is generated. During the regression and a highstand system tract, the rate of sediment supply is more than the rate of accommodation space creation. The last transgression Pg20 starts with a retrogradational stacking pattern of tidal flat and shallow marine facies change to aggradational stacking pattern that is characterized by well-bedded dolostones and chalky carbonates of the Pila Spi Formation, almost manifesting highstand system tracts (HST). Towards the H/LFTZ boundary, the accommodation space increases and the transgressive system tract (TST) manifests by the abundance of Alveolina associated with Nummulite grainstone facies. The aggradational stacking pattern of the succeeding highstand system tract also combined with the abundance

of the Discocyclina and milioids with a remarkable decrease in the Alveolinds and increase of the Orbitolites large foraminifera with green calcareous algae. In the low folded thrust zone, the boundary between Jaddala and Avanah seems to be without interruptions and mostly gradational as the case in the Kurda Meer and Belulla structures. At the border between high and low folded zones, the Late Eocene sequence transgressive system tracts are associated with large perforated and hyaline foraminifera. The maximum flooding surface related to the last bed of the planktonic rich foraminifera and showed variation to early highstand system tract, which is associated with increase of carbonate bed and large imperforated foraminifera and green calcareous algae with Orbitolites and Alveolina. Towards the low folded thrust zone, the late Eocene accommodation space shows significant expansions, and accordingly, the planktonic foraminifera-rich marl and marly limestone facies of the Jaddala Formation point the maximum flooding surfaces and reach the early stage of the highstand system tracts during late Eocene, while the late highstand system tract (late HST) predicated from the Alveolinds-Orbitolites bearing limestone of the Avanah Formation. In a certain case, the Avanah Formation overlies by Late Oligocene sequence, in the Kurda Meer, Aj Dagh, and Bamu structures, with the presence of conglomerate layer between them such as the case in Aj Dagh structure (Plate 1, Figs. 7 and 8) or directly overlie by Euphrates Formation with more gap in time span duration as the case in Qumer well. Bou Dagher (2008) and Grabowski and Liu (2010) found that the Oligocene Kirkuk Group has two sets of progradational shelf to shelf margin limestone that pass laterally into basinal globigerina limestones and the tops of the shelf sequences were sub-aerially exposed and eroded with prograding upward steepening shelf margins. 2. The Kirkuk Group successions comprise of two fourthorder depositional sequences within one third-order sequence. In correlation with other studies, they also coincide with the first sequence of Megasequence AP11 between Pg30 and Ng10 (Sharland et al. 2001, 2004; AlBanna 2008; Al-Juboury and McCann 2008; Aqrawi et al. 2010; Lawa et al. 2013) and has been defined by different hierarchical cycles, some of which are bounded by major sequence boundaries (Fig. 4). The Oligocene sequences were developed after a long period of subaerial exposure and erosion in which the lower contact was unconformable; it is called the SupraDammam Unconformity (Al-Husseini 2008) and developed a sequence boundary type one (SBT I) (Lawa 2004; Al-Qayim 2006). The Kirkuk Group successions were deposited on a shallow water ramp, where the sea level behavior may have played a significant role in defining


the sedimentology, thickness, lateral extent, and sequence stratigraphy of this succession. The Oligocene super sequences were incorporated into one third-order depositional sequence that totally disappears in the northern part of the HFTZ and appears just in a narrow strip close to the H/LFTZ boundary. The Kirkuk Group shows two significant variations in thickness and facie nature, the first one from NE to SW across the H/ LFTZ boundary and the second direction almost from West to East and that is across Khanaqin fault (Sirwan river) (Figs. 1 and 2). 2-A. The Repulian fourth-order cycle represent by Sheikh Alas and Shurau Formations that are recorded only from few outcrops in low folded zone such as the case of Bellula section; the new cycle of early Oligocene, Sheik Alas formation, was followed by the basinal Jaddala formation with the contact between these two formations which is unconformable with the presence of a short break between them and may form a sequence boundary type I. The Kirkuk Group has only an Early Oligocene Sheikh Alas Formation in this locality which is composed of a thick-bedded mid ramp (NR-1 and CB) of microfacies in which the stacking pattern of microfacies could be attributed to the product of deposition within either highstand system tract (HST) or transgressive system tract (TST) (Fig. 6). The Kirkuk Group succession is followed by the Early Miocene Fatha Formation occurring unconformably which makes a sequence boundary type I. The approximate break time between them is about 7 Ma. 2-B. The upper third-order sequence of Chattian to Early Aquitanian in age and represented by Baba, Bajawan, Anah, Azkand, Tarjil, and Ibrahim Formations, reflecting a progressive increase of the accommodation spaces and deepening facies from inner ramp (Bajawan and Anah Formations) to mid ramp then to the outer ramp (Baba-Azkand Formation) and finally to the deep open marine facies (Ibrahim Formation). Anah Formation sediments were deposited and point to the Early Miocene (early Aquitanian) age in the study area. It comprises medium- to thick-bedded skeletal packstone (SP-2) and represents shallow water inner ramp deposit (Fig. 7), almost points to a very short-term TST that onlaps on the hinterland periphery. The approximate break between the Late Eocene Avanah Formation and the Early Aquitanian Anah Formation in the high folded zone may reach 10 Ma called Zagros Major Hiatus (Lawa et al. 2013). Towards the low folded

zone, the Bajawan Formation is dominated by skeletal grainstone (SP-3) which is commonly interbedded with peloidal skeletal packstone/ grainstone (MP-2) and coral bioherm (CB). In the upper part of the unit, the main lithology is skeletal packstone (SP-1) of the Anah Formation. It could represent highstand system tract (HST) due to an overall shallowing upward (coarsening upward) trend. Therefore, the shallowing upward trend was formed due to a draw down in relative sea level (NE flank of Aj Dagh, Awa Spi area). Sequence boundary of type one mostly formed by an abrupt fall in relative sea level (Van Wagoner et al. 1990) between Avanah and the overlying Bajawan Formations; this is followed by a lowstand system tract. It comprises a lowstand wedge, which is made up of fluvial deposits within incised valleys that can be recognized by the presence of thick (2–3 m) conglomerate layer. This layer separates the Late Eocene Avanah Formation from the Bajawan Formation of the Kirkuk Group (Fig. 8). Accordingly, inner rampmid ramp facies are recorded close from the H/ LFTZ boundary (as the case in Aj Dagh and sagrma sections) and shows an increase of deeper facies towards the Kirkuk embayment depocenter (i.e., Sarqala and Kor Mor wells). In Qumer and Taza wells in addition to Sharwal Dra structure, there are the deeper marine facies of Ibrahim Formation composed of rich planktonic foraminifera with basinal facies. The Oligocene accommodation space is wider and shows aggradational stacking pattern of ramp facies extending for a long time and can be split into two fourth-order sequences easily, occasionally separated by hard ground surface can be detected sparsely. However, about 200 m thick of Oligocene successions pointing to Ng10 may extend into Ng20 that is of early Miocene Aquitanian age. 3. The last third-order of the late Aquitanian-Burdigalian age and represented by the Serikagni, Euphrates, Dhiban, and Jeribe Formations almost manifests the last marine transgression in the Neotethyan sea in Kurdistan region and characterized the planktonic deep wackestone facies of the Serikagni formation that is equivalent to the Ng20 maximum flooding surface recorded by Sharland et al. (2001, 2004) and Al-Husseini (2008). Almost the Serikagni and Euphrates facies comprise the first fourthorder cycle, while the Dhiban and Jeribe Formation point to the second fourth-order with the last studied third order. Aqrawi et al. (2010) mentioned that towards the end of the Oligocene, the basin system become restricted probably due to tectonic movements along the Zagros margin and


progradational infill by Oligocene-Aquitanian deposits. Such significant regressions lead to the deposition either of Basal Anhydrite, which is not recognized in any outcrops or studied wells in this area. Instead of that, thin conglomeritic horizon was detected in the case in Awa Spi and Hazar Kani sections and Kurda Meer well. This might be correlatable with Hamrin Formation as coated by Al-Banna et al. (2002). Above such conglomerates, the new transgression was straitened and represented by the retrogradational stacking parasequences of open marine organic rich facies which were flourished, especially in the basin near the depocenter, while thin marginal facies of the Euphrates are onlapping on the Oligocene or Late Eocene carbonates, respectively. The deep marine rich in planktonic foraminiferal wackestone and mudstone facies represent by planktonic zone of Serikagni formation, almost shows lateral changes to carbonates, equivalent facies of the Euphrates Formation, is characterized by predominance of miliolides and soritoides such as Borelis melo melo recorded from Kurda Meer, Sarqala, Kor Mor and Chia Surkh wells. The Euphrates’ stacking pattern occasionally terminated by sudden changes in sea level leading to either deposition of the Dhiban anhydrites or a conglomerate horizon, as the case in Sarqala well. The Jeribe Burdigalian facies manifested by shallower facies, rich in gastropods, echinoids, and porcellaneous index foraminifera, Borelis melo kurdica, and pointed to the shallowing upwards from Aquitanian into the Burdigalian age. Almost no Dihban Anhydrite was detected in the studied wells mostly pointing to the tectonic interruptions, occasionally during the Burdigalian age and manifested by the presence of conglomeratic horizon between Euphrates and Jeribe Formations. 4. The thin Jeribe facies in the basin margin (about 2 m in Aj Dagh and 5 m in Gulan structure) (Plate 2, Fig. 6) show an increase to more than 50 m in Chai Surkh well. The porous open marine carbonates of Jeribe Formation mostly recognized as low energy mudstone and wackestone that changes upwards into packstone and grainstone with some wave and current action with clastics inputs and replaced the proper carbonates sequences into crosslaminated arenaceous carbonates as the case in Aj Dagh sections and Kurda Meer wells (Plate 2, Fig. 6). The whole studied section is terminated by sequence boundary type one with major Zagros hiatuses between Pila Spi and Fatha Formations in the basin periphery and between Jeribe and Fatha Formations in the depocenter and characterized by the deposition of cyclic alternations of thick evaporite sequence of 125 m in Swerawa well (in HFTZ) that increases to more than 750 m thick in Chia Surkh, Kurda Meer, and Qumer wells with remarkable facial changes. Information about all formations with their facie type and their occurrence is in

Table 10; correlations of outcrops in the shape of fence diagram are in Fig. 9.

Discussions The Kurdistan Foreland basin generated in the late Cretaceous and developed during the Paleogene shows progressive migration of the depocenter for about 60 km towards SW (Lawa 2004; Lawa et al. 2013). In the Iranian Zagros segment, this migration is recorded by Saura et al. (2011) with different rates ranging between 6 mm a-1 and 2.4 mm a-1 during the late Palaeocene-earliest Eocene associated with coeval subsidence rate. The product of this tectonic activities leads to the development of patchy reef on the platform with inner ramp facies onlap on the hinterland and outer ramp-deep marine facies downlap on the depocenter in the Kirkuk embayment during the Oligocene. The relatively uplifted segment associated with the thrust and on the flanks of the fault-propagated fault. The facie variations and thickness change manifest the whole Oligocene and early most Miocene sequences. During the Early Miocene, the ramp-predominated facies all change to lagoonal carbonates and occasionally splitted by the Dhiban evaporite. Such conditions are similar to those in Dezful embayment and Lorestan zone (Kavoosi and Sherkati 2007). Such model more coincides with the left bank facie association in the studied area. On the bank of the Sirwan river that is in Lorestan continuation to Kurdistan region, the recorded sequence of the Eocene-Oligocene-Early Miocene shows great lithological, microfacie, and sequence evolutions similarly to Asmari formation rather than to those in the right bank (Kirkuk embayment) as case we can recognized more than 600 m carbonates overlies the Paleocene Kolosh (equivalent to Pebdah Formation) with minor interruption. This similarity to the Asmari group recorded by Van Buchem et al. (2010) and Laurence et al. (2009). Accordingly the Oligocene marine and early Miocene Basinal facies show progressive shallowing upwards facies within a major depression mainly within Kirkuk embayments. The carbonate platform developed through the high and low fold-thrust zone have been subjected to compression tectonic stress that leads to the decrease of the accommodation space towards the hinterlands and to the development of the patchy reef on the palaeo-highs above the fold-propagated fault-thrust sheets. Accordingly, the Oligocene platform shows reduced thickness on the flanks of the folds with reefal facies at the rising substrates that is dissected by transversal deep-seated fault consisting of horst features. The sea level change can influence the ramp setting facies and cause the patchy and discontinuous developments of the reefal facies in the dissected platform inside the reefal system; such type of settings are known from foreland basin setting in the Oligocene-Miocene of the Mediterranean region too. The high subsidence rates from the advancing Orogenic wedge will generate onlap onto

Author's personal copy Arab J Geosci Table 10 The study area formations with their facies type, age, and their occurrence Formation

Facies

Age

Recorded from

Fatha Jeribe

Alternating cycle Shallow marine

Burdigalain-Langhian Burdigalian

Dhiban Euphrates

Anhydrites Lagoonal

Aquitanian Aquitanain

Anah Azkand Ibrahim Bajawan Baba

Inner ramp Outer ramp Globigerina Inner ramp Outer ramp

E.Aquitanain-Chattian E.Aquitanain-Chattian E.Aquitanain-Chattian Chattian Chattian

All sections and wells Aj Dagh, Gulan, Qaradagh, Chia Surkh, Kurda Meer, Sarqala, Taza, Kor Mor, Pulkhana, Qumer Sarqala, Qumer, Chia Surkh, Pulkhana Kurda Meer, Sarqala, Chia Surkh, Kor Mor, Pulkhana, Qumer Aj Dagh, Sagrma, Bamu, Kor Mor Sharwal Dra, Kurda Meer Sharwal Dra, Kor Mor Aj Dagh, Bamu Kirkuk embayments

Tarjil Sheikh Alas Shurau Pila Spi Avanah

Globigerina Coral-algae Outer ramp Mlioiolids Alveolindis Orbitolina limestone

Chattian Repulian Repulian Pribonian PribonianBartonian

Kor Mor Belulla, Kurda Meer, Sarqala Kirkuk embayments Sagrma, Bamo, Swerawa AjDagh,Sagrma,Bamu, Bellula, Kurda Meer, Sarqala, Qumer

Avanah-Jaddala Jaddala

Alveolina-planktonic marly limestone Planktonic foraminifera

Pribonian-BartonaianBaratonin

Aj Dagh, Bellula, Kudra Meer, Kor Mor, Qumer Bellula, Kurda Meer, Sarqala, Kor Mor, Chia Surkh, Pulkhana.

the foreland basin, and downlap in axial setting largely has ramp profile. The late Eocene basin was created after the

Fig. 9 Fence diagram of the studied outcrops

filling of the Kurdistan foreland basin by the molasses facies of the Gercus facies in the basin margin and coeval deep facie


planktonic rich marl of the Jaddala facies towards the depocenter. Accordingly, the depositional sequence of Late Eocene almost underlain by SBT1 conglomerate horizons about 5 m thick below the Pila Spi Formation in the high folded thrust zone that may change to 250-m conglomerates (Lawa 2004). Such horizon may change to sequence boundary of type SBT2 manifested by the hard ground surface between Jaddala and Avanah Formations, as the case in Kurda Meer well. The basin fill is classified into 12 lithofacies facies that are associated and analyzed as facie maps, defining shallow marine littoral, lagoonal, inner, middle, outer ramp, and basinal facies as environments of deposition. Stacking patterns and the lateral translations of conditions, together with strata geometries and terminations, delineate three base levels and controlled the third-order depositional sequences within the Late Eocene, Oligocene, and Early Miocene time spans. Recently, (Ehrenberg et al. 2007) there has been a result of Sr stratigraphy of Asmari Formation throughout the Dezful Embayment. Following the late Eocene, an elaborate system of banks of coral-algal facies and larger foraminifera is established in the studied part of the Tethyan carbonate platform in low folded thrust zone of the Arabian platform. In the studied area, such condition can be recognized and with predomination of Alveolinides and Orbitolina and Soritoides abundant fauna of inner ramp and shoal depositional facies then shows shallowing upwards towards more lagoonal and miliolids facies of Pila Spi Formartion towards the basin periphery during Late Eocene. While towards the depocenter, the Avanah outer ramp facies gainstone and Discocyclindis occupy the outer portions of the platforms and show lateral changes to deep marine facies of the Jaddala Formation as planktonic wackestone and mudstone facies. The sea level changes show rapid fluctuations at the late Eocene-Oligocene boundary that is indicated by conglomerate horizon between the Avanah Formation and the Late Oligocene super sequence in the outer most portion of the Oligocene basin (Plate 1, Figs. 7 and 8). Another notable sea level drawdown was recognized in the Aquitanian time between the Anah and Jeribe Formations. The last rapid regression was extended to the Burdigalian age where the Basal Fars Conglomerates spread in most part of the Tethyan sea (Plate 1, Fig. 2).

&

&

&

&

Conclusions &

As for moving towards depocenter BSW^ from high folded thrust zone (HFTZ) to low folded thrust zone (LFTZ) of the Late Eocene-Early Miocene basin, the deeper facies start to appear and increased both in accommodation space and facies variability and points to the restriction of the Neo-Tethys Sea. Four main sequence boundaries of type one was detected at Late Eocene; between Late Eocene and Oligocene; between Oligocene

&

&

and Miocene and even within Oligocene succession close to the L/HFTZ boundaries. The biozones identified are composed of two late Eocene biozones: Alveolina biozone (AL) and Discocyclina biozone (DI) with three biozones from the OligoceneEarly Miocene of Kirkuk Group: Nummulites fichteli biozone (NF), Praerhapydionina delicata biozone (PD), and Austrotrillina howchini biozone (AH), in addition to two early Miocene biozones: Borelis melo melo biozone (BMM) and Borelis melo Curdica biozone (BMC). Nummulites-rich Avanah Formation from Late Eocene was incorrectly described as Sheikh Alas Formation of Early Oligocene by several authors. These Nummulitesrich layers contain Pellatispira sp. which is the index fossil for the latest Late Eocene age. Three depositional super sequences were identified: (1) The Late Eocene sequence in high folded thrust zone represent the lagoonal facies of the Pila Spi Formation that changes laterally into Avanah zone, then to AvanahJaddala towards Kirkuk embayments. (2) The Kirkuk Group sequence extends from Repulian to Early Aquitanian, and (3) the last sequence is EuphratesSerikagni-Jeribe-Dhiban Formations extending in age from Late Aquitanian-Early Burdigalian age. The Oligocene Kirkuk group shows a progressive change from inner ramp then to outer ramp and then to deep planktonic rich basin facies; such pattern complicated in the studied area by continuous migration of the deformational front and the influence of the transversal faults like Khanaqin fault, Basra valley, and Little Zab river fault. The late Aquitanian transgression was dominated by the deep marine facies of Euphrates Formation or Serikagni Formation and manifests the last Planktonic zone in NeoTethys basin. The overlying evaporite of the Dihban Formation manifests the progradational stacking pattern and regression of the Neotethyan Sea. Such regression and decrease of the accommodation space are also characterized by SBT2 between Euphrates and Jeribe Formations; there was no accommodation space for Dhiban anhydrites to be accumulated in that basin. Accordingly, isolated basins were developed, and patchy Jeribe Formation can be recorded in the studied area with a remarkable increase towards the Kirkuk embayment. The Kirkuk Group comprises two fourth-order sequences within one third-order sequence, in which the first fourthorder sequence is located at Rupelian and composed of the Sheikh Alas and Shurau Formations. The second fourthorder is found in Chattian-Early Aquitanian and consists of the Bajawan, Baba, Tarjil, Anah, Azkand, and Ibrahim Formations. Khanaqin Basement Fault splits the studied area into two parts and leads to developing two different depositional


sequences with different thicknesses on each side of the fault, most probably the left bank. Oligocene facies show similarity to Asmari group of Lorestan zone rather than Kirkuk Group.

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