Relative age determination of the Sarki Formation in the northeastern margin of the Arabian plate, revealed by foraminifera and dasycladacean algae
Determinación de la edad relativa de la Formación Sarki en el margen noreste de la placa Arábiga, mediante foraminíferos y algas dasicladáceas
Irfan Sh. Asaad1,*, Muhamed F. Omer1, Sardar M. Balaky2
1 Department of Earth Sciences and Petroleum, College of Science, Salahaddin University-Erbil. Zanko Street, 44002, Erbil Kurdistan Region, Iraq.
2 Department of Petroleum Geosciences, Faculty of Science, Soran University. Soran, Erbil, Iraq.
* Corresponding author: (S. Asaad) This email address is being protected from spambots. You need JavaScript enabled to view it.
How to cite this article:
Asaad, I. Sh., Omer, M. F., & Balaky, S. M. (2026). Relative age determination of the Sarki Formation in the northeastern margin of the Arabian plate: revealed by foraminifera and dasycladacean algae. Boletín de la Sociedad Geológica Mexicana, 78(1), A080825. https://doi.org/10.18268/BSGM2026v78n1A080825
Manuscript received: June 26, 2025. Corrected manuscript received: August 5, 2025. Manuscript accepted: August 8, 2025.
ABSTRACT
The Sarki Formation crops out in several cores and limbs of anticlines in the Western Zagros Fold-Thrust Belt (WZFTB) within the northeastern margin of the Arabian plate. Its precise age is controversial over the past seventy years. A biostratigraphic study of the formation was carried out in the Gulan section of the Asos anticline, within the imbricated zone of the Kurdistan Region, northeastern Iraq, to determine the relative dating of the formation. The Sarki Formation in the studied section is consists of 294 m of medium- to thick-bedded dolomitic limestone and dolomite, interbedded with thin beds of marl and shale in the lower part, and interbedded with medium-bedded limestone in the upper part. Petrographic examination of 80 thin sections from the Sarki Formation revealed several benthonic foraminifera and dasycladacean algal species from the late Triassic to the early Jurassic epochs. The Triasina hantkeni species was identified in the lower part of the Sarki Formation for the first time in the northeastern margin of the Arabian Plate, dates back to a Rhaetian age. Biostratigraphically, the formation is divided into five biozones from oldest to youngest: assemblage zone A, B and C dated to the early, middle and late Rhaetian, respectively, assemblage zone D, assigned to the Hettangian and assemblage zone E, corresponding to the lower to middle Sinemurian. The suggested new age of the Sarki Formation in the studied section is Rhaetian to early-middle Sinemurian.
Keywords: biostratigraphy, Early Liassic, Late Triassic-Early Jurassic, Rhaetian, Sarki Formation, northern Iraq.
RESUMEN
La formación Sarki aflora en núcleos y márgenes de anticlinales en el Cinturón Plegado del Oeste de Zagros (CPOZ) dentro del margen noreste de la placa arábiga. Su edad precisa ha sido causa de controversia durante los últimos setenta años. Un estudio bioestratigráfico de la formación se llevó a cabo en la sección Gulan del anticlinal Asos, dentro de la región imbricada de Kurdistán, noreste de Iraq, con el fin de determinar el fechamiento relativo de esta formación. En la sección estudiada, la formación Sarki consiste de 294 m de caliza dolomítica y dolomita, intercaladas con capas delgadas de marga y lutita en su parte inferior, e intercalada con capas medianas de caliza en su porción superior. El examen petrográfico de 80 láminas delgadas de la formación Sakai revela varias especies de foraminíferos bentónicos y algas dasicladáceas del Triásico tardío al Jurásico temprano. La especie Triasina hantkeni fue identificada en la porción inferior de la formación Sarki por vez primera para el margen noreste de la placa arábiga, indicando una edad correspondiente al Rhaetiano. Con base en la bioestratigrafía, la formación es dividida en cinco biozonas, siendo de más antigua a la más joven: zonas de asociación A, B y C, fechadas para el Rhaetiano temprano, medio y tardío, respectivamente, la zona D de asociación es asignada al Hettangiano y la zona E de asociación, correspondiente al Sinemuriano inferior a medio. La nueva edad asignada para la formación Sarki en la sección estudiada es del Rhaetiano al Sinemuriano temprano a medio.
Palabras clave: bioestratigrafía, Liassico temprano, Triásico tardío-Jurásico temprano, Rhaetiano, formación Sarki, norte de Iraq.
1. Introduction
The Early Jurassic epoch is characterized by relatively scarce fossils contained within due to the mass extinction at the end of the Triassic period (Basov and Kuznetsova, 2000). During the Late Triassic-Early Jurassic, the continuous extension phases between the Arabian and Eurasian plates, initiated the Neo-Tethys Ocean in the northeastern margin of the Arabian plate with several shallow-marine carbonate platforms in northern Iraq (Asaad and Omer, 2020; Balaky et al., 2025). The Sarki Formation is regarded as a significant carbonate unit in northern Iraq (NE margin of the Arabian plate), which was deposited in a shallow marine environment forming several mountainous series of the Iraqi Kurdistan Region. The Sarki Formation was first reported by Wetzel (1952) as cited in Bellen et al. (1959) in its type section in Chia Gara Mountain, south of Amadyia district, northern Iraq. Its thickness reaches 303 m. The lower part is composed mainly of thin-bedded cherty and dolomitic limestone, shale, sugary dolomites, and recrystallization breccias with a thickness of 122 m. While the upper part consisted of 121 m of grey, highly cavernous, and cherty dolomites (Bellen et al., 1959).
The formation is thought to be Early Liassic (Hettangian-Sinemurian) in age depending on its stratigraphic juxtaposition between the underlying Upper Triassic (Rhaetian) Baluti Formation and the overlying Upper Liassic Sehkaniyan Formation (Bellen et al., 1959; Buday, 1980; Jassim et al., 2006). Moreover, Surdashy (1999) mentioned that the Sarki Formation’s age belongs to the Late Rhaetian-Early Jurassic. However, Lunn et al. (2019) suggested that the underlying formation (Baluti Formation) was deposited between the Late Carnian and Early Norian, the Sarki Formation began to form in the Late Triassic period, based on a review of the palynological study and the dolomite used as a marker. Recently, Delizy and Shingaly (2022), and Delizy et al. (2024, 2025) studied the formation’s surface sections in the Rawanduz area, northeastern Iraq. They looked at the depositional setting and diagenetic processes within the formation, but they have not determined its age. They concluded that it was deposited in a peritidal-lagoon, and high-energy shoal environments. The lateral equivalent of the formation in central Iraq is the Butmah Formation. Whereas the Ubaid Formation, its counterpart in the Iraqi Western Desert (Buday, 1980). In neighboring countries, the Sarki Formation is equivalent to the Neryiz Formation in Iran and correlates with the upper portion of the Dolaa Group in central Syria (Jassim et al., 2006).
The limited occurrences of benthonic foraminifera and green algae in the Early Jurassic epoch, along with the severe diagenetic imprint on the carbonate rocks of the Sarki Formation, have complicated biostratigraphic examinations. Identifying several faunas within the newly studied outcrop (Gulan section) in the current study has allowed for biostratigraphic investigation, helping to resolve the controversy regarding its age. The main aim of the current study is to determine the relative age of the Sarki Formation in the Gulan outcrop based on the benthonic foraminifera and green algae.
2. Geological setting
The carbonate rocks of the Sarki Formation are located in the upper part of the Middle Permian-Middle Jurassic Arabian plate tectonostratigraphic megasequence (AP 6) of Sharland et al. (2001). In the Western Zagros Fold-Thrust Belt (WZFTB), running from southeast to northwest, it can be seen in the core and limbs of several anticlines. These include imbricated, high-folded, and thrust zones (Jassim et al., 2006). The studied outcrop (Gulan section) is located 200 m north of Gulan village, 700 m west of Medera village, on the Chami Gulan stream. It is 15 km from Sarkapkan town in the southeast and about 22 km to the northwest of Ranya city, Sulaymaniah Governorate, Kurdistan Region, northeastern Iraq (lat. 36° 23’ 52” N and long. 44° 42’ 31” E; Figures 1a and 1b).
Structurally, it is located on the northeastern limb of the Asos anticline, close to its northeastern plunge in the Imbricated Zone of western ZFTB (Figure 1b). The Asos anticline is characterized by NW-SE trends with double-plunged fold axes and has a length of 91 km and a width of 8 to 10 km (Syan and Omar, 2025). Stratigraphically, the Gulan section includes a stratigraphic succession starting from the Baluti Formation (Upper Triassic), which forms the core of the Asos anticline, followed by Liassic successions (Sarki and Sehkaniyan Formations) that are overlain by the Sargelu Formation (Middle Jurassic), the Naokelekan and Barsarin Formations (Upper Jurassic). The latter lie beneath the Chia Gara Formation (Upper Jurassic-Lower Cretaceous) and further away are composed of carbonate units from the Cretaceous period (Figure 1b).
The total thickness of the Sarki Formation in the Gulan section is about 294 m (Figures 2 and 3a). The lower 38 m are made up of light grey and dark-grey, medium-to thick-bedded dolomitic limestone, partially brecciated and interbedded with thin beds of yellow marl and grey shale, overlain by 23 m of thick-to-massive-bedded grey dolomite. Subsequently, there were 40 m of the medium-to thick-bedded grey dolomitic limestone bearing gastropods with microbial structures (stromatolites) overlain by 6 m of thick dark-grey dolomitic limestone, which in turn is to 13 m of medium-bedded grey dolomites. The following is composed of 55 m of medium-to thick-bedded grey and light-grey dolomitic limestone interbedded with medium-bedded grey limestone, bearing chert nodules and stromatolitic in some intervals. The rest is 119 m of medium-bedded, light-grey, fractured, dolomitic limestone. The nature of the contact of the Sarki Formation in the studied section is gradational with the underlying Baluti Formation taking on the first thick-bedded dolomitic limestone interbedded with dark-grey shale (Asaad et al., 2021) (Figure 3b). Whereas it is conformable with the overlaying Sehkaniyan Formation, taken between the fractured, thin-to medium-bedded light grey dolomitic limestone of the Sarki Formation and thick-to massive-bedded dark grey dolomites of the Sehkaniyan Formation (Delizy and Shingaly, 2022; Figure 3c).
3. Methods and materials
The field work carried out in the selected area included structural and stratigraphic studies to determine a suitable outcrop of the formation. The Gulan section in the northwest limb of the Asos anticline was chosen because it is accessible and shows a complete succession of the Sarki Formation. The lithology of the formation in the studied area was recorded and described in detail. The main lithology is dolomitic limestone and dolomite in addition to thin beds of marl and shale. A total of 80 fresh samples were collected from the carbonate, marl, and shale beds. The samples were collected at every change in lithology or color (random sampling). The upper and lower parts of each sample were marked. In addition, several samples were collected from the lower and upper contacts to define the position and nature of its boundaries with the underlying Upper Triassic Baluti Formation and overlaying Lower Jurassic Sehkaniyan Formation.
A sum of 82 thin sections was prepared from the carbonate rocks of the Sarki Formation at the workshop of Earth Sciences and Petroleum Department in Salahaddin University-Erbil. All thin sections were stained by alizarin red S solution (ARS) following the Friedman (1959) procedure for discriminating between the calcite and dolomite minerals.
The identification of microfossils from the petrographic thin sections was performed using the Carl Zeiss Jena JENALAB POL polarizing microscope. The foraminiferal and green algae identifications were based on BouDagher-Fadel et al. (2001), BouDagher-Fadel and Bosence (2007), Chablais et al. (2010), Gale (2012), Gale et al. (2012a, 2012b), Senowbari-Daryan (2014), Gale and Kelemen (2017), Senowbari-Daryan and Link (2017), and Gale et al. (2018).
4. Results
4.1. FOSSILS
4.1.1. BENTHONIC FORAMINIFERA
The identified benthonic foraminifera fauna within the carbonate rocks of the Sarki Formation in the Gulan section are Aulotortus friedli (Kristan-Tollmann, 1962; Figure 4a), Aulotortus sinuosus (Weynschenk, 1956; Figures 4b and 4c), Aulotortus gaschei (Koehn-Zaninetti, 1969; Figure 4d), Triasina hantkeni (Majzon, 1954; Figure 4e), Ophthalmidium sp. (Figure 4f), Miliolipora tamarae (Gale et al., 2012b; Figure 4g), Duostomina turboidea (Kristan-Tollmann, 1960; Figure 4h), Diplotremina astrofimbriata (Kristan-Tollmann, 1960; Figure 4h), and Pseudonodosaria sp. belong to the Late Triassic epoch. However, the fossils that belong to the Early Jurassic are Siphovalvulina gibraltarensis (BouDagher-Fadel et al. 2001; Figures 5a and 5b), Siphovalvulina colomi (BouDagher-Fadel et al. 2001; Figure 5c), and Trocholina sp.
4.1.2. DASYCLADACEAN GREEN ALGAE
The discriminated green algae fossils in the studied section of the Sarki Formation are Probolocupsis sarmeikensis (Senowbari-Daryan, 2014; Figure 5d), Probolocuspis tenuiparia (Senowbari-Daryan, 2014; Figure 5e) and Salpingoporella triasica (Richter et al., 1999; Figure 5f) that had the Late Triassic epoch. Whereas Palaeodasycladus editerraneus (Pia, 1920; Figure 5g), Thaumatoporella parvovesiculifera (Raineri, 1922; Figure 5h) and Thaumatoporella sp. (Figure 5i) belong to the Early Jurassic epoch.
4.2. BIOSTRATIGRAPHY
The carbonate rocks of the Sarki Formation in the Gulan section contain a few index fossils due to highly diagenetic processes and rare fossil contents in the Early Jurassic after the Triassic-Jurassic mass extinction. However, the biostratigraphic study of the Sarki Formation in the Gulan section was determined based on the benthonic foraminifera and dasycladacean green algae faunas. The following biozones were identified in the studied formation (Figure 6).
4.2.1. ASSEMBLAGE ZONE A
This biozone occupied the lower 52 m of the Sarki Formation in the studied section (Figure 6). It has recorded the first occurrence of Aulotortus sinuosus (Weynschenk, 1956; Anisian-Rhaetian), Aulotortus gaschei (Koehn-Zaninetti, 1969; Anisian-Rhaetian), Miliolipora tamarae (Gale et al., 2012b; Rhaetian), Duostomina turboidea (Kristan-Tollmann, 1960; Norian-Rhaetian), Aulotortus friedli (Kristan-Tollmann, 1962; Carnian-Rhaetian age), Triasina hantkeni (Majzon, 1954; Rhaetian), and Diplotremina astrofimbriata (Kristan-Tollmann, 1960; Anisian-Rhaetian), in addition to Ophthalmidium sp. and Pseudonodosaria sp. The last occurrence of Aulotortus sinuosus (Weynschenk, 1956) and Aulotortus gaschei (Koehn-Zaninetti, 1969) is recorded at the end of this biozone and forms the total range zone. The only green algae species recorded in its total range zone at this biozone is Probolocupsis sarmeikensis (Senowbari-Daryan, 2014). The fossils of this assemblage zone in the studied rocks of the Sarki Formation date back to the early Rhaetian age.
4.2.2. ASSEMBLAGE ZONE B
The total thickness of this biozone is 37.5 m and overlies the assemblage zone A (Figure 6). It ended with the last occurrence of Miliolipora tamarae (Gale et al., 2012b; Rhaetian), Duostomina turboidea (Kristan-Tollmann, 1960; Norian-Rhaetian), while the Aulotortus friedli (Kristan-Tollmann, 1962; Carnian-Rhaetian age), Triasina hantkeni (Majzon, 1954; Rhaetian), and Diplotremina astrofimbriata (Kristan-Tollmann, 1960; Anisian-Rhaetian) continue their range towards the overlain biozone.
The Aulotortus sinuosus (Weynschenk, 1956) and Aulotortus gaschei (Koehn-Zaninetti, 1969) from the lower biozone are made an interval zone with Miliolipora tamarae (Gale et al., 2012b) and Duostomina turboidea (Kristan-Tollmann, 1960). Probolocuspis tenuiparia (Senowbari-Daryan, 2014; Norian-Rhaetian) from green algae has a total range zone in this biozone. Both foraminiferal and algal faunal assemblages of this biozone indicate the Middle Rhaetian age.
4.2.3. ASSEMBLAGE ZONE C
This biozone overlies the assemblage zone B, which is 52 m thick (Figure 6). It is characterized by the last appearance of Aulotortus friedli (Kristan-Tollmann, 1962; Carnian-Rhaetian age), Triasina hantkeni (Majzon, 1954; Rhaetian), and Diplotremina astrofimbriata (Kristan-Tollmann, 1960; Anisian-Rhaetian). The lower and upper limits of this zone are marked by the last appearances of Miliolipora tamarae and Duostomina turboidea at the bottom, and Aulotortus friedli, Triasina hantkeni, and Diplotremina astrofimbriata at the top. The only green algae species reported within this zone is Salpingoporella triasica (Richter et al., 1999); Norian-Rhaetian). This zone’s fossil assemblage dates back to the late Rhaetian age.
4.2.4. ASSEMBLAGE ZONE D
It has a 102.5 m thickness from the middle to upper part of the Sarki Formation in the Gulan section and is overlie biozone C (Figure 6). It has been limited by the total range zone of Siphovalvulina gibraltarensis (BouDagher-Fadel et al., 2001), which aged between the Lowermost Jurassic and Early Middle Jurassic (Gale et al., 2018). BouDagher-Fadel and Bosence (2007) also found it in the Hettangian stage in the Jebel Aziz, Tunisia. It occurs with other foraminifera like Trocholina sp. in addition to the green algae Palaeodasycladus mediterraneus (Pia, 1920) that had Hettangian-Pliensbachian age (Bassoullet et al., 1978). The absence of Siphovalvulina colomi (BouDagher-Fadel et al., 2001) in the carbonate rocks of the Sarki Formation in this biozone suggests the Hettangian age.
4.2.5. ASSEMBLAGE ZONE E
This biozone covers the uppermost part of the Sarki Formation in the studied outcrop and is thicker than 50 m (Figure 6). The only benthonic foraminifera species recorded within this zone is Siphovalvulina colomi (BouDagher-Fadel et al., 2001), which created a total range zone. It had an age range from Sinemurian to Pliensbachian (BouDagher-Fadel and Bosence, 2007). It is associated with Palaeodasycladus mediterraneus (Pia, 1920; Hettangian-Pliensbachian); its first occurrence was in the previous biozone and its last occurrence in this zone of the studied section. Other green algae species that are located at the top of this assemblage zone are Thaumatoporella? parvovesiculifera (Raineri, 1922) and Thaumatoporella sp. The Thaumatoporella? parvovesiculifera had a long age range from Ladinian to Paleocene (De Castro, 2002). The age of this biozone corresponds with the Sinemurian age and exactly to the early-middle Sinemurian as identified in the western Mediterranean by BouDagher-Fadel and Bosence (2007).
5. Discussion
The lower part of the Sarki Formation in the Gulan section comprises assemblage zones A, B and C, which belong to the Rhaetian age (205.7 to 201.4± 0.2 Ma; Cohen et al., 2013). The Triasina hantkeni (Majzon, 1954) species, which occurs within all three of these zones, was identified in many other localities within the Tethyan biostratigraphy, including the western Carpathians and eastern Alps (Gaždzicki et al., 1979), Slovenian Basin (Gale et al., 2012a), Greece (Romano et al., 2008), northwestern Sicily in southern Italy (Todaro et al., 2022), western Turkey (Işintek, 2023), and central Tunisia (Kamoun et al., 1994). The assemblage zone D is located in the middle and the upper part of the Sarki Formation. Its range is limited to the Hettangian period (201.4 ±0.2 to 199.5 ±0.3 Ma according to Cohen et al. (2013)), and its faunas, especially Siphovalvulina gibraltarensis (BouDagher-Fadel et al., 2001), are found in several places in the Tethyan area, including Gibraltar, northeast Spain, Tunisia and Greece (BouDagher-Fadel and Bosence, 2007). While, in the uppermost part of the studied formation, there is an assemblage zone E that had an Early-Middle Sinemurian age (199.5 ± 0.3 to 196.5 ± 0.3 Ma). Its fossils contain particularly Siphovalvulina colomi (BouDagher-Fadel et al., 2001) found over other areas within the Tethyan realm, involves Gibraltar, northeast Spain, Morocco, Tunisia, and Greece (BouDagher-Fadel and Bosence, 2007).
In this study, according to the biostratigraphic analysis of benthonic foraminifera and green algae, it is indicated that the Sarki Formation in the northeastern margin of the Arabian plate was deposited during the late Triassic–early Jurassic period, precisely in the Rhaetian to early-middle Sinemurian age. The current results revise the previously determined age of the Sarki Formation, which was dated back to the Lower Jurassic (Hettangian-Sinemurian) based on lithostratigraphic stratigraphic position between the Late Triassic (Rhaetian) Baluti Formation and Upper Liassic Sehkaniyan Formation, including studies of Bellen et al. (1959), Buday (1980), Jassim et al. (2006), Al-Badry (2012) and Omar et al. (2022), as shown in Table 1. It is relatively concise with results of Lunn et al. (2019) that addressed the Sarki age as Late Norian- Early Jurassic based on the detailed dolomite marker study of the underlying Baluti Formation. In contrast, no indication of the Norian age of the formation was recorded in the current work. The study by Surdashy (1999), based on petrographic thin sections suggested that the Triassic–Jurassic boundary is within the Sarki Formation without proving that all Rhaetian stage deposits are within the Sarki Formation. However, Hanna (2007), based on palynologic floras, showed that the Triassic-Jurassic boundary is unconformable and the age of the formation is Sinemurian-Toarcian. On the other hand, the assemblage zones A, B and C which include several foraminiferal species of the Late Triassic, especially Triasina hantkeni (Majzon, 1954), which is indicative of the Rhaetian age (Gale et al., 2012a) and identified in the present study for the first time in the northern margin of the Arabian plate, confirm that the whole Rhaetian stage was dated within the lower part of the Sarki Formation. The assemblage zone A, which is characterized by including the total range zone of middle-late (Anisian-Rhaetian) foraminifera both Aulotortus sinuosus (Weynschenk, 1956) and Aulotortus gaschei (Koehn-Zaninetti, 1969) are supposed to be early Rhaetian age. While the assemblage zone B belongs to the middle Rhaetian age and characterized by Late Triassic Miliolipora tamarae (Gale et al., 2012b; Rhaetian), Duostomina turboidea (Kristan-Tollmann, 1960; Norian-Rhaetian) which made an interval zone with the previous zone’s foraminifera. The assemblage zone C is assigned as Late Rhaetian and marked by the last occurrence of all Late Triassic faunas within the studied rocks of Sarki Formation. It is overlain by the Hettangian-aged layers in the middle and upper parts of the studied formation, which can be indicated by the presence of Siphovalvulina gibraltarensis (BouDagher-Fadel et al., 2001). Except the uppermost 50 m of the studied succession was deposited within the early-middle Sinemurian based on the presence of Siphovalvulina colomi (BouDagher-Fadel et al., 2001). Depending on the age range of the identified biozones of the Sarki Formation the time span of deposition can be estimated between 205.7 ± 0.2 to 196.5 ± 0.3 Ma.
6. Conclusions
The total thickness of the Sarki Formation in the Gulan section is about 294 m and consists of light-grey and dark-grey, medium- to thick-bedded and thick-bedded dolomitic limestone and dark-grey dolomite interbedded with thin beds of yellow marl and grey shale in the lower part and interbedded with medium-bedded light-grey limestone in the upper part. It includes chert nodules and stromatolites in some intervals.
The identified benthonic foraminiferal fossils include Triasina hantkeni (Majzon, 1954), which is determined for the first time in the northern margin of the Arabian plate, in addition to Aulotortus friedli (Kristan-Tollmann, 1962), Aulotortus sinuosus (Weynschenk, 1956), Aulotortus gaschei (Koehn-Zaninetti, 1969), Miliolipora tamarae (Gale et al., 2012b), Duostomina turboidea (Kristan-Tollmann, 1960), Diplotremina astrofimbriata (Kristan-Tollmann, 1960), Ophthalmidium sp., and Pseudonodosaria sp. that belong to the Late Triassic epoch. However, the species that belong to the Early Jurassic are Siphovalvulina gibraltarensis (BouDagher-Fadel et al. 2001), Siphovalvulina colomi (BouDagher-Fadel et al., 2001), and Trocholina sp. The dasycladacean green algae faunas involve Probolocupsis sarmeikensis (Senowbari-Daryan, 2014), Probolocuspis tenuiparia (Senowbari-Daryan, 2014) and Salpingoporella triasica (Richter et al., 1999) that aged to the Late Triassic epoch. While Palaeodasycladus editerraneus (Pia 1920), Thaumatoporella parvovesiculifera (Raineri, 1922), and Thaumatoporella sp. had an early Jurassic epoch.
The carbonate rocks of the Sarki Formation are divided into five biostratigraphic zones: The Assemblage Zones A, B and C, which occupy the lower 141.5 m of the formation, consist of several Late Triassic fossils, particularly Triasina hantkeni (Majzon, 1954), and belong to the lower, middle, and upper Rhaetian, respectively (205.7 ± 0.2 Ma). Assemblage Zone D covers 102.5 m in the middle to upper part of the studied section, includes several foraminifera and algal faunas, especially Siphovalvulina gibraltarensis (BouDagher-Fadel et al., 2001), and is regarded as the Hettangian stage (205.7 ±0.2 to 199.5 ±0.3 Ma). The top 50 m of the Sarki succession are made up of the Assemblage Zone E and involve Siphovalvulina colomi (BouDagher-Fadel et al., 2001) with other fauna, which is from the lower to middle Sinemurian (199.5 ± 0.3 to 196.5 ± 0.3 Ma).
This study concluded that the relative age of the Sarki Formation in the northeastern margin of the Arabian plate is dated from Rhaetian to early-middle Sinemurian (205.7 ± 0.2 to 196.5 ± 0.3 Ma). This is older than those who previously dated to the studied formation as an early Liassic.
Contributions of authors
Conceptualization: ISA; (2) Data analysis or acquisition: ISA; (4) Drafting of the original manuscript: ISA; (5) Drafting of the revised and edited manuscript: ISA, MFO, SMB; (7) Fieldwork: ISA, MFO, SMB; (8) Interpretation: ISA; (9) Supervision): MFO, SMB.
Financing
The authors did not receive funds from any organization for this study.
Acknowledgments
This paper is derived from a part of the first author’s Ph.D. dissertation conducted at the Department of Earth Sciences and Petroleum, College of Science, Salahaddin University-Erbil. The authors send their appreciation to Mr. Bzhar A. Delizy and Mr. Goran F. Hassan for their assistance during the field work. Many thanks to Prof. Dr. Luka Gale from the Geology department at the University of Ljubljana, Slovenia for his constructive comments related to the paper. The deepest gratitude to Mike Buchanan a board member of International Association for Promoting Geoethics (IAPG), and Assist. Prof. Rozgar Yousif Omar from the English Department at Salahaddin University-Erbil for their invaluable assistance in grammatically reviewing this manuscript.
Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Handling editor
Francisco J. Vega.
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