Stratigraphy and structure of the southeastern part of Piramagroon anticline
Published in: Bulletin of the Mineral Research and Exploration
http://bulletin.mta.gov.trBull. Min. Res. Exp. (2017) 154:27-39
Kamal Haji KARIM and Polla Azad KHANAQA
The Piramagroon anticline (or Piramagrun mountain) elongates directly to northwest of Sulaimani city, Kurdistan Region, NE-Iraq. The Southeastern part of the anticline contains two other anticlines (Harmetool and Yakhyian anticlines with their complementary synclines) at southwest and northwest respectively with many other smaller ones. In the present study, the southeastern part has been studied stratigraphically and structurally and the previous studies are critically reviewed. For the first time, the stratigraphy of the anticline has been differentiated and the Kometan, Gulneri and Dokan, Balambo and Sarmord Formations are plotted on the geological map and srtatographic column accurately. The thickness of the Gulneri Formation is 2-4m and the nannofossils analysis showed that its age is Late Cenomanian-Early Turonain. Lithology and bedding styles of the Dokan and Upper part of the Balambo Formation is very similar to Kometan Formation and they can be differentiated by fossils. The outcrop of the Gulneri Formation is helpful for differentiation since it is soft and can be recognized in the field easily. The structure of the anticline is relatively complex as it consists mainly of asymmetrical anticlines with southwest vergen and in some place the anticlines are deformed by reverse fault of asymmetry changed to recumbent fold. The anticlines are shaped by detachments of on the Gulneri and Sarmord formations and other older soft rocks. The resulted anticlines have style of multi-detachment fold or multi-detachment faulted fold.
Key words: Gulneri Formation, Dokan (Dukan) Formation, Kometan Formation, Balambo Formation, Nanno fossil analysis, stratigraphy of Kurdistan
The Piramagroon anticline is one of the largest anticlines of Kurdistan Region, NE-Iraq and has the length, width and elevation of about 45, 6 and 2.4 kms respectively. It is located between Sulaimani city, from southeast, and Surdash town, from northwest. Qamchuqa (or Balambo), Kometan Shiranish and Tanjero Formations are exposed on and around the anticline while its core is occupied by Jurassic rocks. The present study is concerned with its southeastern part which is equal to half of the surface area of the anticline. This part is located between Zewy valley at the northwest and Sarchinar town at the southeast. This part consists f many anticlines, the largest one is called Harmetool anticline (locally, it is famous as Harmetool mountain) which previously called Sulaimani Anticline by Ma,ala (2008) and Al-Hakari (2011). Other anticlines are Sherkuzh and Yakhyiana (Al-Hakari, op.cit) which are located at north and south of the previous anticline respectively with more than four other smaller anticlines (Fig. 1).
The present study is focused on the stratigraphy and structure of the southeastern part of Piramagroon anticline and the study is based on geologic mapping and structural analysis in addition to stratigraphic differentiation by nannofossils. The present study is try to add more useful data and geologic facts to previous studies such as Aziz et al. (1999) (Fig.1), Ma, ala (2008) and Al-Hakari, (2011) (Fig.3).
Fig.(1) the geological map of the studied area shows two strike slip faults (Aziz et al, 1999).
Stratigraphy of the area
The stratigraphy of the southeastern part of Piramagroon anticline is very important due to three points. The first is that the area is zone of facies change between Qamchuqa and Balambo formations (Ameen, 2008). In this area, the thick and massive dolomitic limestone (competent beds) of the former formation, from the west, changes to well bedded and marly limestone (incompetent) of latter formation. Therefore, the phrase “Qamchuqa/Balambo transition or QBT” is used for the equivalent of Qamchuqa Formation in the transition zone. The second is that the structurally, transitional zone from competent to incompetent beds which reflect different deformational patterns that are the combination of the two end members. The third is that the boundary of the Balambo Formation (or Qamchuqa) with Kometan Formation is well exposed in the area.
The boundary and nearby strata must contain either the rocks of Cenomanian- Turonian ages or the events (unconformities) that occurred during the latter ages. Many authors (Sharland et al., 2001; Al Hussaini and Matthews, 2008, Al-Qayim et al., 2012, and Lawa and Gharib, 2009) have cited major unconformity in this boundary. Lawa et al. (2011 in Hakari, 2011) have cited that during the early Turonian, the Qulqula Radiolarian and Main igneous complexes were uplifted and acted as Hinterland for Kurdistan Foreland basin.
In the opinion of the present author, if the above intense tectonic activities, during the Early Turonian, are true, they must have left clear signature in the form either of conglomerate or erosional surface. According to Buday (1980) and Jassim and Goff (2006), there is another important events in the Cenomanian-Turonian age during which Qulqula conglomerate Formation had deposited at the top of Qulqula Radiolarian Formation. This deposition is recently referred to by Ibrahim, 2009 and Al-Qayim et al (2012).
The nanofossils analysis of the boundary between QBT and Kometan Formation showed that the Gulneri and Dokan Formation are exist in the area (Fig.3 and4). This result agree with the conclusion of the Taha and Karim (2009) who refused the unconformities that previously established below and above the Gulneri Formation and mentioned that the formation consist of marl and marly limestone without black shale. It is agree too with the results of Baziany (2006) and Bazizny and Karim (2007) whom refused the existence of Qulqula Conglomerate Formation and concluded that it either belongs to conglomerate of Tanjero Formation or conglomerate of Red Bed Series. Karim et al. (2013) found both formations on the Azmir and Goizha anticlines and prepared a detail map of the area to the north and east of Sulaimani city which show the outcrops of the two formations.
Previously, Aziz et al. (1999), Ma,ala (2008) and Al-Hakari, (2011) mapped the south eastern part of Piramagroon anticline and indicated Qamchuqa, Kometan, Shiranish and Tanjero formations on the crest, upper and lower limbs of the anticline respectively (Fig.1 and 2 ). The above authors have not recognized the Gulneri and Dokan Formations. Al-Hakari (2011) in his correlation chart of the area around Sulaimani City indicated by correlation chart that the Dokan and Gulneri formation did not exist on the anticline. Fig.(3) Location and Geological map of the studied area modified from Karim (2011). The Dokan and Gulneri Formations are located between outcrops of Kometan and Balambo Formation. The equivalent of Gulneri and Dokan Formations are locate between Balambo and Kometan Formations
The Gulneri Formation was first described by Lancaster Jones (1957) in Bellen et al.(1959) near the Dokan Dam site, in the High Folded Zone, where it consists of about 2 m of black, bituminous, finely laminated, calcareous shale with some glauconite and collophane at the lower part. The age of the formation is Early Turonian (Bellen et al., 1959).
The high bitumen content and dwarfed fossils indicate that the Gulneri Formation was deposited in a euxinic environment (Jassim and Buday in Jassim and Goff, 2006). The formation is separated by unconformities with both the overlying and the underlying Kometan and Dokan formations, respectively (Buday, 1980).
In the present study, it was found that it consists mainly of well bedded marly limestone and occasionally laminated and oil impregnated and no shale found in the studied sections. This result of lithology is agree with what concluded by Taha and Karim (2009) who reused the previous lithology (black shale) of Gulneri Formation at type section near Dokan dam site. At the site they discussed in detail that the lithology of formation is marl and marly limestone and the little existed black shale is diagenetic deposition of insoluble residue by pressure solution. They further added that there is no unconformity at the top and bottom of the formation and existed pebbles are ball and pillow like structure formed by pressure.
Therefore, the result of the present study doesn’t aid the presence of the Turonain unconformity in Kurdistan that mentioned by above authors. In the studied area, the upper part of Balambo Formation, Dokan and Kometan formations are very similar in lithology and bedding patterns (Fig.5). They can be separated by foraminifera study and the fortunately the Gulneri Formation can be identified in the field which appear as a covered dark ribbon between white limestones of Kometan and Balambo Formations. The thickness of Gulneri Formation is about 2-4 m. Between Dokan and Surdash towns, it is located between Dokan and Kometan Formation and consist of dolomitic limestone without marl and marly limestone but it has thin beds and due to this thinness, the Gulneri Formation is highly deformed a such as in Tabeen Gore where Karim ( 2014) showed a photo of the formation to prove, its existence. It worth to mention that Lawa et al. (2013) mentioned that Dokan and Gulneri formation are not present (an unconformity with duration of 4.7 m.y) in the Tabeen Gorge 4km to the southeast of Surdash village.
Fig.(5)Southwestern side of the Nadoor valley shows the minor folding and stratigraphic differentiations. It can be seen that one bed (below Gulneri Formation) represents, lithologically, the Dokan formation that has the thickness of 50 cm.
Nannofossils analysis of Gulneri Formation
In the studied area, the outcrops of Gulneri Formation are mostly covered and getting fresh sample is difficult. Therefore, for obtaining fresh sample six 1m deep holes are excavated on the outcrop of the formation with the students (Fig.7 and 8). The six samples are sending to Romania for nannofossils analysis and age determination. The below report is prepared by Dr Ramona Balc ([email protected]) for the samples which gave Thus, the age of the entire interval is Late Cenomanian-Early Turonian.
Sample No. 1 to No.5, Fig. (6, 7 and 8)
The age of the studied samples is given by the presence of Corrolithion kennedyi and Quadrum intermedium. The first mentioned species was identified only in one sample (sample 5). Thus, this level falls in UC3d Nannofossil Subzone (Burnett, 1998), being Late Cenomanian in age. The top of this subzone is defined by the last occurrence (LO) of C. kennedyi. Next level (sample 4 – sample 3) cover the Uc3d – UC5b Nannofossil Subzones, the bioevent marking the base of the UC5b being the first occurrence (FO) of Quadrum intermedium. The age of the above mentioned interval is Late Cenomanian. The last level (samples 2 and 1) falls in UC5c Nannofossil Subzone, the base of this subzone being defined by the FO of Q. intermedium. The age of this subzone is Late Cenomanian-Early Turonian.
Fig.(6) The five samples of the Gulneri Formation which are sent to Romania For Nannofossil analysis. The sample are taken I m below surface and they consist of marly limestone some which are oil imprignated
Fig.(7) Species of the result of the nannofossils analysis which give the age of Late Cenomanian-Early Turonian. Species are:1. Broinsonia enormis (Sample 1); 2. Corrolithion kennedyi (Sample 5); 3. Cylindralithus sp. (Sample 5); 4. Cylindralithus nudus (Sample 5); 5. Discorhabdus ignotus (Sample 5); 6. Eprolithus floralis (Sample 2); 7. Eiffelithus turriseiffelii (Sample 2); 8. Helenea chiastia (Sample 5); 9. Helicolithus trabeculatus (Sample 5);
Fig.(8) Prediscosphaera cretacea (Sample 1); 11. Quadrum intermedium (Sample 3); 12. Rhagodiscus achlyostaurion (Sample 5); 13. Rhagodiscus asper (Sample 4); 14. Retecapsa crenulata (Sample 3); 15. Tranolithus orionatus (Sample 5); 16-17. Watznaueria barnesiae (Sample 2); 18. Watznaueria ovate (Sample 1); 19. Zeugrhabdotus diplogrammus (Sample 4); 20. Zeugrhabdotus embergeri (Sample 3).
Structure of the area
Due to the accurate analysis of the stratigraphy of the studied area in the above sections, the structure analysis was possible in more accurate manner than previous studies.
Strike slip and reverse faults
Aziz et al (1999) have recorded two strike slip faults and called them Sulaimani-Sitak and Chaqchaq strike slip faults. The second one intersects with Chaqchaq strike slip fault beneath western part of Sulaimani city (Fig.1).
The main anticlines in the studied area are two which are named Piramagroon and Sulaimani (Harmetool anticline in the present study)Anticlines by Ma,ala, (2008) and both of them are recently mapped by Al-Hakari, (2011) and he found two other strike slip faults in the area to the west of the Sulaimani-Sitak fault (Fig.2). Fieldwork (by present author) in the area of these four faults (at the west and northwest of the Sulaimani city) has not found evidence for occurrence of them. The geological mapping of the area showed no shifting (opposite movement) of the structures (axes of anticlines and synclines) and stratigraphic units (formations) of the area (Fig.3). In the area two reverse faults are observed which has the displacement less than 20m, one of the cut the southwestern limb of the Piramagroon Anticline and observed inside the Yakhyian valley (Fig. 9). This fault may be anticline break through fault due to fact that the anticline is detachment fold and this type of fault is common in this type of fold. Another reverse fault is seen on the northeastern limb of Harmetool anticline near the mouth of the Nadoor valley (Fig.10).
Type of anticlines
Ma,ala, (2008) and Al-Hakari (2011) has indicated all the main anticlines as southwest vergent asymmetrical anticlines. In the present study it was observed that the above indications are true for the Balambo-Qamchuqa Formation. In some cases the anticlines are reversely faulted which may be belong to anticline breakthrough fault. However, the folds inside Kometan Formation are more or less behaved differently. In addition to asymmetrical anticlines, Kometan Formation contains box and recumbent anticlines (Fig. 11). The later author assigned the anticlines in the studied area as fault propagation folds but the result of the present study concludes that it is detachment fold. The proof for detachment fold is discussed in detail in the north of Sulaimni city by Karim and Ahmad (2014) during the study of Azmir-Goizha anticline. The detachments of the anticlines were occurred on the Gulneri and Sarmord formations and other older soft rocks. The resulted anticlines are in style of multi-detachment fold or multi-detachment faulted fold. Al-Hakari (2011) mentioned that the cores of the anticlines in the studied area occupied by Qamchuqa Formation but the present study showed that Balambo and Sarmord Formations exist in the core (Fig. 2, 9 and 12).
This anticline is located inside the western part of Sulaimani city and geomorphologically consists of three low hills such as UN and Farouk hills (Fig.16). The plotting of its axis indicates that this anticline, most possibly, is an independent anticline. Previously this anticline is assigned as southeastern part of Harmetool anticline by Ma,ala (2008), Al-Hakari (2011) (Fig.13) and Aziz et al, (1999). The elongation of the axis of Sulaimani anticline coincides with the Sherkuzh anticline (Fig.14). Al-Hakari (2011) had indicated two strike slip faults that cut this anticline (Fig.2). In this study one small strike slip fault was found that strikes nearly east-west (Fig.15)
Fig.(13) The geological cross section (Fig.3.49) shows that the anticline is a fault propagation fold uplifted through the reverse slipping of the hanging wall of the blind foreland vergent listric thrust fault associated with the hinterland-vergent-fault. To keep step with the surrounding structure in the area the detachment surface was considered to be Lower Jurassic and Upper Triassic formations
1-The equivalents of the Dokan and Gulneri Formations are found in the studied area for the first time.
2-The age of the Gulneri Formation is Late Cenomanian-Early Turonain
3-A new and updated geological map is drawn of the area on which all the formations are differentiated.
4-The most realistic structural analysis of the area is shown on which new folds and fault is recorded for the first time.
5- The folds of the area consist of detachment anticlines and synclines and detachment was occurred on marls of the Gulneri, Sarmord Formation and other older rocks.
6- The main faults are reverse faults
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