Palynofacies and microfacies of Kalat Formation at Chehel-Kaman Valley section (north east Khorasan Razavi)

The Kopet-Dagh Basin formed on the southern margin of the Eurasian Plate since the Jurassic up to the Tertiary. The Kopet-Dagh Basin marks the northern boundary of the Alpine-Himalayan Orogeny in northeastern Iran and also corresponds to the morphological boundary between Turkmenistan and Iran. The Kopet-Dagh Basin is an intracontinental basin and its topography dies out toward southeast in the Afghanistan, indicating a tectonically stable part of the basin. Kalat Formation (Late Cretaceous) is one of carbonate unit in the Kopet-Dagh sedimentary basin (Afshar-Harb, 1994). So far, various studies have been done on this formation, but for the first time, the microfacies and palynofacies of the Kalat Formation have been carried out simultaneously.
In order to study Kalat Formation, one section is measured in the Chehel-Kaman valley. Kalat Formation in this section is located about 163 km from Mashhad with a geographic coordinates of 36° 28ʹ 8ʺ North and 60° 23ʹ 42.4ʺ East and is 310 meters thick and consists of shale and limestone alternation. In order to study palynofacies and microfacies in Chehel-Kaman section (310 m shale and limestone), 36 samples of limestone and 22 samples of shale have been studied. The description of the limestone textures follows the Dunham (1962) classification and shales Tyson charts (1993). Study of limestone thin sections led to identification of three sedimentary facies, A, B, C, including barrier, restricted lagoon and tidal flat that are composed of 12 subfacies. These facies can be classified in two group, carbonates and hybrid. Studying of shale led to identify two facies, A and B. Facies A is equivalent to type I Palynofacies and facies B is equivalent to type II Palynofacies. Shale facies A shows semi restricted lagoon into tidal flat and shale facies B shows deeper semi restricted lagoon to shoal and open marine environment. In the basis of microfacies and palynofacies studies, we can say that Kalat Formation has been deposited in a homoclinal carbonate ramp (Flugle, 2010).
Because the palynofacies and paleo-sedimentary environments of the shale parts of Kalat Formation were based on palynomorphs (dinoflagellates), 52 species of 36 genera of dinoflagellates were identified. In addition to dinoflagellates, spores and bisaccate pollen grains, fungal spores and foraminiferal test linings are also observed.
The palynological parameters of the shale facies of this formation indicate that the lability factor in this section is less than one. Decreasing this factor indicates an increasing the amount of oxygen in the sedimentary environment. Therefore, it is possible that semi-oxygenated conditions dominate during the time of the deposition of these facies. However, according to the numbers obtained, the oxygen content in type palynofacies (A) is more than type (B). On the other hand, the ratio of AOM trans to dark AOM indicates that despite the presence of oxygen, the amount of this element is not high (the number obtained is greater than one), which indicates low oxygen conditions in the parts of shale at the time of sedimentation. However, the amount of oxygen in type palynofacies (A) is more than type (B) (Boulter & Riddick, 1986).
To determine more precisely the amount of oxygen and sedimentation rate from a complementary factor (transparent and dark AOM ratio to marine palynomorphs), the best conservation degree of marine palynomorphs (especially dinoflagellates) is in high oxygen saturation and sedimentation rhythms.
If the low sedimentation rate and the low oxygen content transmitted are of the palynomorphs to the transparent AOM, and in the opposite case, palynomorphs into a dark AOM. According to the measurement of the percentage of transparent AOM percent to marine palynomorph along the stratigraphic column, this is high which indicates low oxygen conditions, and the ratio of the percentage of dark AOM to marine marine palynomorph is low, which indicates low oxygen conditions and high sedimentation rate for palynofacies of the Kalat Formation. Of course, the numbers indicate higher oxygen content and higher precipitation rates for type palynofacies (A) than type (B) (Bombardier & Gorin, 2000).
The ratio of the equal dark palynomaceral to the blade - shaped dark, along with the labilatory factor, expresses the amount of energy governing the environment. Blade - shaped dark palynomaceral can travel a long distance due to high flotation, and are abundant in remote areas. According to the results obtained from the study of palynological slides, the equal dark palynomaceral is also greater than the blade, indicating the close proximity to the coast of the shale parts of the Kalat Formation and the resulting numbers indicate the shallowness of the type Palynofacies (A) than type (B), Kleithriasphaeridium truncatum. The presence of species Cannosphaeropsis utinensis Oligosphaeridium buciniferum and Spiniferites ramosus is an open sea. The abundance of the above examples in Palynofacies type (B) is likely to be related to open sea environment for this facies (Chiaghanam et al., 2013).
On the other hand, species like Alterbidinium varium, Andalusiella dubia, Andalusiella gabonensis, Andalusiella polymorpha, Circulodinium distinctum, Cerodinium diebelii, Godavariella venkatachalae, Palaeocystodinium bulliforme, Phelodinium kozlowskii and Palaeocystodinium lidiae show shallow conditions. The palynological factors and the presence of the above species, as well as the presence of spores and bisaccate pollen in Palynofacies type (A), are indicative of the shallow conditions of these deposits.