MESOZOIC TETHYAN RADIOLARITE AGE DETERMINATION, ZAGROS SUTURE ZONE, KURDISTAN, NE IRAQ

A regional belt of Mesozoic Tethyan radiolarites extends along the northeastern Arabian plate's margin. Outcrops of this radiolarite were documented from Hawasina series in Oman, and northeastwards to Pichakun Series of southern Iran, to Kermanshah of northwest Iran passing onto the Qulqula Group of northeast Iraq up until the Kocali Series of Turkey. The age of most of these radiolarite suites was already constrained. It is the purpose of this work to investigate the age of the radiolarite Suites in northeast Iraq using Radiolarian microfossils chronostratigraphy. Patches of the Mesozoic radiolarite suites are exposed at the Zagros suture zone in Kurdistan Region of northeast Iraq and known as the Qulqula Group. It consists of complexly deformed and thick slices of pelagic radiolarian chert and siliceous limestone, radiolarian red claystone and siliceous mudstone, and reddish-green mudstone and limestone. These units were sampled from three areas (Naurabab, Penjween, and Hawraman) located to the south and east of Sulaimani city in Kurdistan, for radiolarian micropaleontological analysis. Radiolaria microfossils identification and age determination is done at specialized laboratories. Results of the radiolarian age constraint show that these sediments range from Bajocian to the end of the Cenomanian.


INTRODUCTION
Radiolarite is oceanic siliceous rocks often developed as tectonostratigraphic suites frequently associated and obducted with ophiolites complexes during convergence between two plates of the oceanic domain.These complicated suites are often cropped out along tectonic suture line between the collided plates in a patchy form.Radiolarites were reported to have been associated with the Zagros Suture Zone from Oman (Hawasina radiolarites) to Iran (Neyris radiolarites, and Kermanshah radiolarites) to Kurdistan of NE Iraq (Qulqula radiolarites) and up into SE Turkey (Fig. 1).These siliceous radiolarian rocks are obducted along with the ophiolites complexes over the Arabian plate margin as a part of a subduction complex during Late Cretaceous Time (Murris, 1980;Berberian and King, 1981;Alavi, 1994;Al-Qayim, 1995).As convergence between the Arabian Plate and Eurasia continued these rocks over-thrust the Arabian margin sediments forming an important part of an intensively tectonized region of the Zagros Suture Zone (Hessami et al., 2001;Alavi, 2004;Ager et al., 2005;Al-Qayim et al., 2012).In Kurdistan NE Iraq, these suites known as the Qulqula Group which were recognized and described for the first time by Bolten (1955 and1958).The Qulqula Group consists of two Formations: Qulqula Radiolarian Formation, which represents the real radiolarite suites, and Qulqula Conglomerate Formation, which represents the tectonic breccias and erosional products of the first (Al-Qayim et al., 2012).The Qulqula Radiolarian Formation which underly the Qulqula Conglomerate Formation consists of a thick succession of bedded chert, shale, mudstone and siliceous limestone (Bolton, 1958;Buday, 1980;Jassim et al., 1984;Jassim and Goff, 2006).The contacts of both formations are hard to be determined due to intensive structural deformation of the outcrop areas.The boundaries are recognized in most cases as tectonic contacts.
The outcrops of the Qulqula radiolarite are distributed in three major areas (Buday and Jassim, 1987), which are: 1) Khwakurk area (KH) at the Iraqi -Turkish -Iranian border junction; 2) Qulqula gorge (Q) at the north of the Qala Diza Town, and 3) Mawat -Halabja area (N) stretched from the northeast, around Nurabab Peniplain, to southwest of the Sulaimani city (Fig. 2).
The age and stratigraphic position of the Qulqula radiolarite, is long considered as a controversial issue because of insufficient studies was done and the complicated stratigraphy due to the intensive deformation of its sequence.Heron and Lees (1943) assigned the folded mass of radiolarian chert of the Nappe zone and shale probably of Jurassic age.Waddington (1955) supposed that the formation is older than Jurassic, but did not make any precise determination.McCarthy (1956), in Buday (1980) suggested a Triassic -Jurassic age of the formation.Bolton (1958) mentioned that the Qulqula Series is of Aptian to Albian age.He admits the Jurassic age of the formation in the Halabja area.Smirnov and Nelidov (1962) reported that the formation is of Triassic age.

METHODS AND MATERIAL
Three master traverses were selected from this area for field examination, stratigraphic measurements, and sampling.These traverses are 1) Nurabab -Surkew, which is located to the northeast of Chwarta town, and extends from Bayanan village to Surkew mountain toe, across the Nurabab plain.2) Kawlos -Kani Manga, which is located in Nalparez subareas to the north and northeast of Said Sadiq town, and extends from Kawlos village to Milakawa mountain toe at southwest of Penjwin town.
3) Halabja -Avroman traverse, which is located in Hawraman subareas to the north and northeast of the Halabja town and extends to the Hawraman mountain and passing by Biyara village (Fig. 3).In addition, several minor reconnaissance traverses are checked to support the regional stratigraphic evaluation.
Detailed field examination of these outcrops was attempted to get the general view of the distribution, description of the traverses and lithological changes in addition to examining vertical and lateral stratigraphic and facial changes (Fig. 4).Samples were collected along the examined traverses in three selected outcrops areas and from each lithologic unit to assist stratigraphic studies.Thin sections were made and studied in the laboratory under binocular and polarizer microscopes for identifying the petrographic features and the important sedimentological characteristics.

LITHOLOGIC UNITS
The lithologic subdivision of the formation was always a problem due to the complexity of its stratigraphy.Several studies reviewed that problem and came up with different views.Bolton (1958) used Qulqula Series instead of the Qulqula Group, and Buday (1980) divided it into two main formations; the Qulqula Radiolarian Formation (QRF) and the Qulqula Conglomerate Formations (QCF).The Czech Geological team (1976) had divided the group into four lithological units using paleontological approach.Jassim and Goff (2006) gave a detailed description of lithologic characters for these four units.Ibrahim (2009) had suggested Five lithologic units for the Qulqula Group in the Sulaimani area.Al-Qayim et al. (2012) examined the different units of the Qulqula Group from Mawat -Penjwin -Hawraman areas as an integral part of the Zagros Suture Zone.They gave detailed description of five lithologic units with interpretation of their lithologic characters and tectonic environments (Fig. 5).Recent and detailed review of these units and their sedimentological and petrographic characters with the interpretation of depositional environments was given by Ameen et al. (2018).A brief review of these units is given below.

Grayish-Green Sheared Shale Unit (GSSU)
is dominated by dark gray-green sheared shale, and marly shale, alternating rhythmically with light gray to beige, up to 30 cm thick, and calcarenitic limestone.The total thickness of this unit is variable due to the erosion but generally range from fifty to eighty meters.

Reddish-Green Mudstone and Limestone Unit (RGMLU)
are characterized by the alternation of red and green marly mudstone and claystone, with thin to medium beds of calcilutite to calcisiltite bioclastic to pelloidal limestone.
The green marly mudstone yields radiolarians whereas the reddish part shows rare planktonic foraminifera occurrences.The thickness of this unit is variable and generally up to twenty meters.

Red Siliceous Mudstone Unit (RSMU)
is represented by a succession of reddish brown to reddish gray, thin to mediumbedded radiolarian mudstone and shale, which is alternating with siliceous shale, and minor limestone and chert.All lithologies of this unit bear radiolarian especially the lower part.It is up to fifty meters thick.

Radiolarian Chert and Siliceous Limestone Unit (RChSLU)
represents the typical cherty unit of the Qulqula radiolarites.It is consisted of thin to medium bedded 2 -12 cm thick radiolarian chert, with silicified fine-grained limestone, and radiolarian-bearing mudstone.Often, the individual radiolarian chert beds are interbedded with paper-thin shale or mudstone.Chert beds occur in varicolored of gray, whitish gray, green, dark gray and reddish maroon color.The thickness of this unit is variable and range between 15 -50 m.

Red Radiolarian Claystone Unit (RRCU)
has reddish brown to maroon color of laminated radiolarian claystone.Thin silicified horizon is often recognized.The true thickness of this unit is variable and cannot be calculated exactly because of the tectonic inter-thrusting and repetition and erosion.However, measurement of the thickness at different areas shows that it, generally, ranges from 80 to150 m.

RADIOLARITE BIOSTRATIGRAPHY
The age of the radiolarite in Iraq, however, has been assigned based on stratigraphic position and still is highly debatable.The discrepancy among the results often resulted from complex stratigraphic sequence due to intensive deformation.McCarthy (1956) in Buday (1980) suggested a Triassic -Jurassic age of the formation.Smirnov and Nelidov (1962) reported that the formation is of Triassic age.Bolton (1958) mentioned that the Qulqula Series is of Aptian to Albian age.He admits the Jurassic age of the formation in the Halabja area The Cretaceous and most probably the Albian -Aptian age of the whole section of the typical Qulqula might be generally accepted (Buday, 1980).The Czech geologists (1976) in Ibrahim (2009) (Aqrawi et al., 2010).
In Iran, the corresponding Coloured Mélange Series of Gansser is considered to be of Upper Cretaceous (post-Aptian) in age (Stocklin, 1968).The sedimentary sequence of Kermanshah Radiolarian trough deposited during the late Triassic -Late Cretaceous time (Ricou et al., 1977;and Braud, 1987).The Kermanshah radiolarite was recently dated using radiolarians biostratigraphy to be of Early Jurassic (Early Pliensbachian) for the oldest ones, up until the Turonian for the youngest (Gharib, 2009;Gharib and DeWever, 2010) Permian age from radiolarite of the Hawasina nappes.In the same nappes (Bechennec et al., 1990) dated it to be of Permian age for the oldest parts, up until the Santonian age for the youngest.

DISCUSSION
The suggested age determination of the different lithologic units which yields radiolarian microfossiols as demonstrated in the chronostratigraphic chart of Figure (7) reveal two important points.The first point is that the examined radiolarian-bearing units have different ages, which range from Bajocian up to the end of the Cenomanian.
The second point is that the development of the sequences shows that there is a geochronological overlapping between these units.This means that these units were developed, in part, simultaneously within a single sedimentary basin framework.The depositional environment of the Qulqula group in general and for each lithological unit in specific is discussed in details by Ameen et al. (2018).They suggest that the Qulqula radiolarite is deposited in a neritic to the pelagic environment of openly see basin sloping down from the Afro-Arabian margin during late Jurassic time.Carbonate ramp represented by a thick succession of neretic limestone.Slope area occupied by calciturbidite sediments.The slope toe receives the hemiplegic and hemi-turbidite sediments of the radiolarian reddish-green mudstone and limestone unit (RGMLU).The proximal abyssal plain especially in the area of no or limited turbidite influx is often covered by the radiolarian limestone or radiolarian chert of unit (RCHSLU), depending on the position of the CCD depth.The distal abyssal plain which is continuously deposited below the CCD depth is occupied by the radiolarian red claystone and mudstone sediments of the RSMU and RRCU units.By applying this depositional model to the different ages of the radiolarian units, one can put the deposition of these units into the following chronological order.The deposition of the limestone and chert of the proximal abyssal plane was the first to be deposited and began by Early Bajocian and continue through up to the Early Aptian.The deposition of the radiolarian red claystone and mudstone units of the distal abyssal plane started at Berriasian time simultaneously with radiolarian chert and limestone of the proximal abyssal plane.
Deposition of the red abyssal sediment occurs either overlaying or adjacent to the proximal abyssal sediments.By the Aptian time the deposition of the radiolarian chert, limestone, red claystone, and the lower member of the red mudstone units were ceased.
The lower slope sediments of the radiolarian reddish-green mudstone and marlstone were begun at the middle of Aptian.This unit and part of the radiolarian red mudstone unit continued to be deposited up to the end of the Cenomanian (Fig. 7).Other units of the Qulqula Group which bear no Radiolaria probably deposited into older times.and belonging to the extension phase of the Neo-Tethys Ocean and were older or at least equivalent to the oldest radiolarian bearing units in age.In the comparison of this age of the Qulqula Radiolarite with the surrounding areas (Fig. 6), it shows deposition in shorter duration.

CONCLUSIONS
The Qulqula Group of Kurdistan Region, northeastern Iraq represents an important segment of the Zagros radiolarite facies.Four lithologic units of the total six units of this group are radiolarian-bearing pelagic facies.Examination of the radiolarian assemblages from these units reveals the occurrence of many well preserved, and ageindexed microfauna.Biostratigraphic analysis of these units indicates that deposition took place during the interval from Middle Jurassic (Bajocian) to early Late Cretaceous (Late Cenomanian).

Fig. 3 :
Fig. 3: Google Landsat image of northeast Iraq with overlaying geological units of Sulaimanyia area by Ma'ala (2008) showing the selected traverses over the study area of the Qulqula radiolarite exposures

Fig. 5 :
Fig. 5: Diagrammatic presentation of the different tectono-stratigraphic classification schemes of the Qulqula Radiolarite by different authors, including the present study subdivision 1. Neritic Succession Limestone Unit (NSLU) is dominated by several thick successions of dark gray, thick bedded bioclastic shelf limestone (individual beds 10 -110 cm thick).Occasionally, it becomes nodular, cherty or marly.The thickness of the unit ranges from 30 to 80 m.

Fig. 6 :
Fig. 6: Diagrammatic presentation of the Zagros radiolarite age at different places from Oman at southeast to Syria at northwest RESULTS For the radiolarian-bearing units of the Qulqula radiolaraites, twenty-two samples have been selected from the three studied traverse.These samples were analyzed at the Hacettepe University Central Campus (Hacettepe üniversitesi merkez kampusu) of Turkey, for radiolarian identification and age determination.Based on the results of this examination, twelve samples including (KN-2, KN-3, KN-4, KN-14, KN-32, KN-59, KN-61, KN-67, KN-95, NP-4, A-15 and A-16) yielded diverse and determinable radiolarian faunas (Table 1; Fig. 7; Plates 1; 2 and 3).As shown in Figure (7) the age of each sample in each unit is determined based on the overlapping of total ranges of the recognized radiolarian species.Biostratigraphic analysis of the radiolarian samples was assisted by referring to the following references: Dumitrica et al. (1997); Jud (1994); Baumgartner et al. (1995), and O'Dogherty (1994) (Fig. 5).The age of the Radiolarian Chert and Siliceous Limestone Unit (RChSLU) is determined based on seven examined samples (KN-95, KN-67, KN-61, KN-59, NP-4, A-15 and A-16) as Bajocian to Early

Fig. 7 : 1 )
Fig. 7: Chronostratigraphy of the analyzed samples using total-ranges occurrences of the identified Radiolarian species in different Qulqula Radiolarite Units also show the occurrence of four main units recognized in the Qulqula, i.e. the Qulqula Unit One (QU.1) of the Tithonian -Cenomanian, Qulqula Unit.2 (QU.2) of Valanginian -Lower Aptian, Qulqula Unit.3 Qulqula Conglomerate Formation which is deposited during Cenomanian Early Senonian.According to the paleotectonic setting of Iraq and the SW margin of the Neo- Tethys, the radiolarite facies were deposited during Middle -Late Triassic (Ladinian -Carnian) age in fault-bounded troughs Robin et al. (2010) et al. (2010), the age of the radiolarite in the Pichakun nappes, which are exposed in the Pichakun Mountains, is in Neyriz area is of Late Triassic to Coniacian.InOman mountains, DeWever et al. (1988) reported