Clay minerals of Shiranish Formation in, Erbil, Duhok northern Iraq

In the Upper Cretaceous of northern Iraq (upper Campanian-Maastrichtian), the Shiranish Formation is examined for clay minerals using X-ray diffraction in the Duhok (Sandor section) and Erbil cities (Lailuk section). In the marl section of the Shiranish Formation, the layers of chlorite, illite, kaolinite, palygorskite, and a mixed layer of montmorillonite-chlorite strata were discovered to have formed antigenically. The variation in minerals indicates the Cretaceous’ changing climate. Palygorskite is a result of leaching processes that are more successful due to variations in the parent rocks. The transition of palygorskite from montmorillonite and illite can occasionally be impacted by post-depositional diagenetic processes. Because of the warm conditions that supply the eroded clastic materials from earlier successions of Cretaceous in the area, chlorite, mixed-layers, and illite may have predominated over kaolinite. The variation in source rocks and drainage conditions is reflected in the variation of clay minerals in the investigated sequence, which could improve leaching rate processes.


Introduction
Shiranish Formation close to the village of Shiranish Islam, northeast of Zakho, from the High Folded Zone of Iraqi Kurdistan had been first defined by Henson (1940, in Bellen et al., 1959).This formation is the base of a series of regressive -transgressive in the Upper Cretaceous (Campanian and Maastrichtian) (Dunnington, 1958).In the Lailuk section, the Shiranish Formation overlays the Bekhme Formation with non-conformable.The upper contact of the formation is nonconformable with the Paleogene deposited and taken at the base of the sandstone or siltstone bed of the Kolosh Formation, while the lower contact of the formation is conformable with the Bekhme Formation, distinguished by a very thick limestone bed for the Bekhme Formation and the marly limestone bed Shiranish.This recovery has a thickness of 190 meters.Much of authors have studied the clay minerals of the Shiranish Formation, such as study of)El-Anbaawy and Sadek,1979) studied the clay minerals in the Shiranish Formation connected with faunal content and microfacies fabric to recognize of depositional environment in this formation, cleared the montmorillonite with a low abundance of kaolinite in the upper unit of the Shiranish Formation may reflect the shallow marine conditions of normal salinity.(Al-Haj and Al-Juboury,2018) cleared the transformation of palygorskite from precursor illite or montmorillonite in the Shiranish Formation, and the illite appeared as white flakes.(Al-Dulaimi et al, 2023) recognize the chlorite over illite and observed differences in paleoclimatic and paleoenvironmental conditions during deposition and the source of rocks from which these clay minerals were derived.The Study area is located in northern Iraq, including in the governorates of Erbil a Duhok  1).The aim of this study is to determine the variation and spatial distribution of clay minerals in the Shiranish Formation.

3-Field work and Methodology
This study's goals were associated with field, lab, and office work.The two rock sections that were studied in the northern parts of Iraq (the Lailuk section was in the Mergasur area, Erbil city; and the Sandor section was on the southern limb of the Bekhair Anticline, Duhok city) were sampled in the field, and part of the laboratory work was completed in the physics department at the Basrah University and the other part in the sedimentology department at the Marine Sciences Centre of the University of Basrah.During the fieldwork noticed the clay fraction in the marl layers, which are characterized by a dark gray color in the Erbil city (Figure 3), and a blue color in the Duhok city (Figure 4).Five samples were chosen, two from Erbil and three from Duhok-were selected for X-ray diffraction examination in order to identify clay mineral.All five samples are marle.The bulk sample approach is used to evaluate the components of rocks, while the methods of Carpenter (1971), Grim (1968), Millot (1970), and Thoraz (1975) are followed for studying clay minerals.The five samples are grinding to get powder, distilled water is added to the powder and then some drops of H2O2 (30%) are dropped to discard organic matter from clay minerals (Folk, 1974).Using a 0.063 mm wet sieve, take a specific weight from the sample.After washing with distilled water and then again until the mixture was suspended, the carbonate was eliminated by treating with 17% acetic acid.After waiting four hours and six minutes, a certain amount of clay is extracted by shaking the sample into a 1000 ml cylinder at a depth of five centimetres.Each sample was developed on many slides (Grim, 1968;Carrol, 1970;Thorez, 1976).

4-Result
Clay minerals investigated in the upper Cretaceous (Campanian-Maastrichtian) from the Duhok and Erbil cities contained chlorite (41-51%), montmorillonite-chlorite mixed layers (14-24), illite (10-16%), kaolinite (10-14%), and palygorskite (2-5%).The first three types are relatively more common in the studied Shiranish Formation.The chlorite presence is highest in the lower part of the Lailuk section and in the central part of the Sandor section.The large values of Mixed layers of clay minerals were found in the lower part of the Sandor section, while the lower values of these layers were found in the middle parts of the Lailuk section.Kaolinite mineral has a detrital origin and has a high presence in the upper parts of the Sandor and Lailuk sections.On the other hand, the authigenic Illite is found in the middle and lower parts of the Sandor and Lailuk sections.Shiranish Formation had various clay minerals origins between terrigenous (detrital) like kaolinite may supplied during regressive period from the continental or authigenic such as palygorskite, chlorite, and illite, while the diagenetic as mixed layers.

5-Discussion
The idea that some of clay minerals in sediments are of detrital origin is supported by the fact that clay minerals are frequently chemically inert in deep waters and have not changed much in the weathering zone, and the diagenesis may result in the emergence of clay minerals.Berner (1971) came to the conclusion that a negligible fraction was based on the distribution of clay minerals in oceans.These conditions reportedly existed at the time the Shiranish Formation was deposited in northern Iraq.The formation result of the marine transgressive depositional character of the Shiranish Formation is a result of the early Maastrichtian transgression over the foreland basins on the passive borders of the Arabian Plate.The Shiranish Formation was formed in a maritime environment, which may have facilitated the authigenic deposition of clay minerals like palygorskite as shown in the figure (4-A).The highest percentage of clay minerals in the Shiranish Formation are chlorite and chlorite-montmorillonite minerals, which may have attributed to diagenetic processes due to the increase in the iron ion percentage (Al-Jafar and Al-Jaberi, 2021).The precursor illite and montmorillonite can be changed to make palygorskite, this result agrees with that found in (Al-Jaberi and Salim ,2022).Additionally, In the marine upper Cretaceous Shiranish Formation, where the authigenic palygorskite minerals.These conditions existed at the time the Shiranish Formation was laid down.The preponderance of warm temperatures aids in the preservation of these minerals as well as the input.The dominance of chlorite, mixed layers, and illite over kaolinite in the studied area could be attributed to the erosion of terrigenous elements from previous Cretaceous successions.In the marine upper Cretaceous Shiranish Formation, where the authigenic minerals formed and were sustained, authigenic illite predominated, with minor levels of palygorskite.Authigenic feldspar is where illite comes from.The transportation marine cyclone is where kaolinite first appeared.The majority of the clay minerals were initially created by dust storms and precipitated as clays in marine environment

6-Conclusions
The Shiranish Formations in northern Iraq are composed of authigenic, diagenetic, and terrigenous (detrital) minerals.Kaolinite mineral has a detrital origin because it does not form in marine conditions.Chlorite, Illite, and palygorskite are of authigenic origin.The presence of these types of clay minerals in the Shiranish Formation is an indicator of a deep marine environment in the warm climate

Figure 1 :Figure 2 :
Figure 1: Location of the study area

Figure 4 :
Figure 4: Blue marl in the middle part of Sandor section in Duhok region

Figure 4 :
Figure 4: A, B, and C typical x-ray diffraction for samples taken from the Shiranish Formation marl