Palynofacies analysis and depositional environment of the upper Triassic Kurra Chine Formation: integrated by samples from sarta and Tawke oil fields and outcrop samples from sirwan valley in the kurdistan region, northern Iraq

Palynofacies (PF) analysis was conducted on 34 crushed samples of the Upper Triassic Kurra Chine Formation. These samples were collected from one outcrop sample and two production wells in northern Iraq. A 10μm nylon mesh sieve was used for the concentration of palynomorphs. Four palynofacies types were found in this study. PF1 was characterized primarily by amorphous organic matter (AOM), suggesting a distal suboxic-anoxic depositional environment. PF2 comprised of AOM, along with some Phytoclasts and palynomorphs, indicating a distal dysoxic-oxic shelf depositional environment. PF3 displayed an increasing volume of palynomorphs, signifying a distal dysoxic-anoxic shelf depositional environment. PF4 predominantly consisted of palynomorphs and Phytoclasts, representing a mud-dominated oxic shelf (distal shelf) depositional environment. Kerogen types were identified as type II, which is oil-prone in three palynofacies, and type III which is gas-prone in one palynofacies.


Introduction
This research is running palynofacies for outcrop samples and two subsurface sections.The outcrop section is located 15km far from the southeast of Halabja city.It is located between Boyen and Sazan Villages.It is about 2.4 km from Boyen Village and 4km from Sazan Village.It is located at the border between Iraq and Iran.The selected area's coordinate system in Sirwan Valley is between 35 0 05' 35" N and 46 0 05' 58" E. The Sarta oil field coordinate system is between 43 0 58' 20.399" E 36 0 31' 39.228" N coordination.The Tawke oil field coordinate system is between 42 0 58' 11.1" E 37 0 09' 25.6" N coordination (Figure 1).This Formation constitutes a petroleum system encompassing source, reservoir, and cap rocks, defined by its lithological distribution.Kurra Chine was originally described in the outcrop of the Ora fold in the Amdiya district in Northern Iraq (22).Palynofacies analysis plays a crucial role in petroleum geology by helping determine the origin of organic matter (OM) in sedimentary rocks.It aids in identifying the composition and abundance of different OM types and the deposition of source rocks (21).Palynofacies is a term rooted in paleopalynology, which refers to the classifications of palynomorph assemblage in a body of sediment.It reflects interior environmental settings and is distinct from regional palynoflora (20).( 17) defined palynofacies as distinctive assemblages of particular organic matter present in sediments that are insoluble in acids such as HCl and HF.
The concept and explanations of the Palynofacies were first described by (12).Palynology is a particulate organic matter contained in sediment following the removal of the sediment matrix by HCl and HF (21).Palynofacies can characterize a sedimentary body that contains a distinctive 1300 (2024) 012033 IOP Publishing doi:10.1088/1755-1315/1300/1/012033 2 assemblage of palynological organic matter, thought to reflect a specific environmental condition or characteristic range of hydrocarbon-generating potential (12).Conversely, palynofacies analysis involves the identification of components within organic matter, the assessment of their proportional and overall quantities, and the evaluation of their size and level of preservation.(11).
Previous studies on the palynofacies of the Kurra Chine Formation were conducted by (1).These studies involved the examination of the cutting and core samples in various wells in the Mosul Block.Previous researchers have also described this Formation in the context of sedimentology, petroleum, source rock, reservoir rock, and depositional environments as documented in (2,4,6,7,8).The primary focus of this research is to ascertain the palynofacies types and the depositional environment present in the carbonate rocks of the Kurra Chine Formation located in northern Iraq.This study seeks to address a gap in our understanding of hydrocarbon potentiality and the depositional environment related to the formation.The findings of this study will contribute to our comprehension of how palynofacies play a role in the paleoenvironment of the deposited sediments within the Kurra Chine Formation.

Geological setting
Tawke oil field began oil production in 2007 and has since been connected to a Turkey-Iraq pipeline for oil export to European markets.The current crude oil production in this field stands at approximately 43,000 barrels per day.In contrast, the Sarta field is relatively new compared to the Tawke field, with production commencing at the end of 2020.Presently, it produces around 3,000 barrels per day, but this output has been affected by certain borehole completion issues (6).
Northern Iraq is situated within the Zagros fold belt, a region known for its abundant hydrocarbon resources (16).According to (22), the thickness of the Kurra Chine Formation at its type locality is about 834m.It primarily consists of limestone with dark brown and black colors, featuring varying bedding thicknesses of dolomite and breccia beds.The studied area is located within a high folded zone and is part of the Zagros fold belt.The Shnrwe Anticline in Halabja City is structurally linked to the research outcrop area.Structural analysis of the Sarta well is associated with the Pirmam Anticline in Erbil, while the Tawke Wells structural study is connected with the Tawke Anticline in Zakho.The Taurus-Zagros fold and thrust belt encompasses the Tawke field.The tectonics of the studied area is characterized by the interaction of the Arabian and Eurasian orogeny.Iraq is located in the Northeast of the Arabian Plate that collided with the Iranian Plate, leading to the formation of a foreland basin, representing the Zagros fold belt.The Zagros fold belt is divided into four main zones (figure 1).According to (5), Iraq belongs to the Gondwana Continent beside the Indian and African plates in the Paleozoic Era.From the middle Permian to the Triassic and Jurassic periods rifting and extension formed, leading to the break of the Gondwana continent and the NeoTethys Ocean (3).During this period, Carbonate rocks were the predominant sedimentary rocks, while clastic rocks were formed in the fluvial deltaic depositional environment.The highest thickness of Neotethys reached 4000 km during the Late Triassic (Kurra chine Formation) and Middle Jurassic periods (18).Kurra Chine Formation underlies Baluti Formation and overlies the Galikhana Formation.The lower contact of the Kurra Chine Formation is unconformable whereas its upper contact is conformable (10).

Material and Methodology
Ninety-nine thin-section slides were created from 34 samples obtained from the Kurra Chine Formation.These samples were collected from two subsurface wells and one outcrop situated at various locations in Northern Iraq.Fourteen samples were specifically collected from the Kurra Chine Formation outcrop in Sirwan Valley near Halabja, close to the Iraqi-Iranian border.Additionally, nine samples were taken from the Kurra Chine Formation at the Sarta well (S-2), while eleven samples were obtained from the Tawke well (T-17) within the Kurra Chine Formation (refer to Table 1).
Samples were prepared and analyzed at the laboratory of the Salahaddin University Erbil.Samples procedures commence with the extraction of organic matter in the Kurra Chine samples.Approximately 25 to 50 g of each sample was prepared and standard extraction techniques were followed (13,14,19).The crushed samples underwent a treatment process involving dilute hydrochloric acid (10%) initially, followed by concentrated hydrochloric acid (37%).Subsequently, the samples underwent five washes with distilled water.In the next phase, HF acid (52%) was introduced to the samples, and they were rinsed five times with distilled water until neutral to dissolve carbonate and siliceous contents.The concentration of palynomorphs was then filtered by decantation using a 10µm nylon mesh sieve.Glass slides were prepared, and these slides were examined under a transmitted light microscope with magnifications of 40× to identify and enumerate palynomorphs, Phytoclasts, and amorphous organic matter.

Palynofacies Analysis and Classifications
Palynofacies were initially coined by (12) to encompass all acid-resistant organic materials extracted from sediments or sedimentary rocks through palynological processing techniques.The composition and presence of organic matter (OM) in sedimentary rocks reflect the majority of the variables that have influenced the terrestrial or aquatic environments in which it originated, was transported, and subsequently deposited (9).
As outlined in reference (21), microscopic analysis of palynofacies serves the primary purpose of determining various critical aspects, such as the origin, hydrocarbon-generating potential, and degree of thermal alteration of organic matter (OM).Additionally, it seeks to gauge the relative proportions and preservation states of different components, comprehend the depositional paleoenvironment, and evaluate oxidation-reduction conditions.Within the kerogen assemblage, three main categories of morphological constituents are identified: Palynomorphs: These are organic-walled constituents that persist after maceration using HCl and HF acids.The Kurra Chine Formation exhibits this type in all the studied sections.Phytoclasts: These are fragments of tissues originating from higher plants or fungi.The Kurra Chine Formation has relatively low occurrences of this type, except for one sample in the Tawke section.Amorphous organic matter: This category encompasses structureless material derived from nonfossilizing algae, advanced tissue biodegradation, phytoplankton, bacterially derived amorphous organic matter (AOM), as well as higher plant resins and amorphous products resulting from the diagenesis of macrophyte tissues (as per reference 21).The Kurra Chine Formation exhibits this type in all studied sections, with significant volumes documented (Tables 2, 3, 4).

Result and Discussions
Four main types of palynofacies associated with depositional paleoenvironmental differences in the Kurra Chine Formation have been identified based on quantitative and qualitative variations in kerogen content, along with the distribution of amorphous organic matter compared to Phytoclasts and palynomorphs.The identification of depositional environment and kerogen types was carried out according to the criteria outlined in reference (21), as presented in Table 5 5

.1. Palynofacies type 1 (PF1):
This type of palynofacies is abundant in the Kurra Chine Formation.The determination of these types is based on the relatively high proportion of organically generated amorphous organic matter.It is present in all studied sections (plate 3a).In Sirwan Valley outcrop samples are exhibited in most depths.
In Sarta oil field exhibits a depth of 3720-3740m while in Tawke oil field presents a depth of 4160-4240m.This palynofacies is dominated by 90% AOM and the remains will be palynomorphs and Phytoclasts (Figure 2).It is located at IX on the ternary diagram.Shale was the main lithology of this type of palynofacies.

Palynofacies type 2 (PF2):
This type of palynofacies is less than the previous palynofacies in the Kurra Chine Formation.The determination of these types is based on the relatively high proportion of amorphous organic matter.It is present in all studied sections.In Sirwan Valley outcrop samples are exhibited in depths 100 and 118m.In Sarta oil field exhibits depths of 3690-3700m, 3790-3800m, and 3800-3820m while in Tawke oil field presents at depths of 3870-3880m, 4130-4140m, and 4150-4160m (Figure 3a).This palynofacies is dominated by 70% AOM and the remains will be palynomorphs 15% and Phytoclasts 15% (Figure 2).It is located in VIII on the ternary diagram.Shale was the main lithology of this type of palynofacies.

Palynofacies type 3 (PF3):
This type of palynofacies is abundant in the Sarta and Tawke oil fields in the Kurra Chine Formation.The determination of these types is based on increasing the proportion of palynomorphs.It is presented in three studied sections.In Sirwan Valley outcrop samples are exhibited in depths 6m,12m, and 80m.
In Sarta Oil Field exhibits depths of 3550-3560m, 3640-3650m, and 3790-3800m while in Tawke oil field is present at depths of 4160-4170m and 4530-4540m (Figure 3b).This palynofacy is dominated by 55% AOM and the remains will be palynomorphs at 40% and Phytoclasts at 5% (Figure 2).It is located in VII on the ternary diagram.Shale was the main lithology of this type of palynofacies.

Palynofacies type 4 (PF4):
This type of palynofacies is less abundant in in Kurra Chine Formation.The determination of these types is based on increasing the proportion of palynomorphs and Phytoclasts.It is presented in three studied sections.In Sirwan Valley outcrop samples are exhibited at a depth of 210m.In Sarta oil field is exhibited in depths 3670-3680m while in Tawke oil field is present at depths 4440-4450m.This palynofacies is dominated by 40% AOM in Sirwan Valley samples and 20% AOM in the Sarta and Tawke oil fields.The main component is palynomorphs which is 60 -70% and Phytoclasts 10% (Figure 2 5).PF2 indicates VIII on the ternary diagram.It shows the Distal dysoxic-oxic shelf depositional environment.This is type II oil pron (Table 5).PF3 indicates VII on the ternary diagram.It shows the Distal dysoxic--anoxic shelf depositional environment.This is type II oil pron (Table 5).PF4 indicates V on the ternary diagram.It shows the mud-dominated oxic shelf (distal shelf) depositional environment.This is type III gas pron (Table 5).The Tyson ternary diagram is shown in (Figure 4,5,6).The depositional environment of the Kurra Chine Formation is distal based on the ternary plot (Figure 7).

Figure 1 :
Figure 1: illustrates the location map of the study area including well location and outcrop samples (15).

8 Fig. 2 : 9 Fig. 3a :
Fig. 2: Display the palynofacies types.a,b,c) represent various aspects or types of amorphous organic matter.d,e,f) depict different palynomorphs, which are individual organic particles.g,h, i) depict phytoclasts, which are plant fragments or detritus.

Fig. 3b :
Fig. 3b: The distributions of various components, such as amorphous organic matter, Phytoclasts, and palynomorphs, within the Sarta oil field samples of the Kurra Chine Formation.

Fig. 3c :
Fig. 3c: The distributions of various components, such as amorphous organic matter, Phytoclasts, and palynomorphs, within the Tawke oil field samples of the Kurra Chine Formation.

Fig. 5 :
Fig. 5: The sample distributions of the Sarta oil field.

Fig. 6 :
Fig. 6: The sample distributions of the Tawke oil field.

Fig. 7 :
Fig. 7: The model of the depositional environment of the Kurra Chine Formation of the studied area.

Table 1 .
Palynological samples from each location.

Table 2 .
The distribution of palynodebris and the percentages of different types of organic matter in samples from the Kurra Chine Formation from Sirwan Valley outcrop samples in northern Iraq.

Table 3 .
The distribution of palynodebris and the percentages of different types of organic matter in samples from the Kurra Chine Formation from Sarta oil field in northern Iraq.

Table 4 .
The distribution of palynodebris and the percentages of different types of organic matter in samples from the Kurra Chine Formation from Tawke oil field in northern Iraq.