F Yousefi Moghadam; M Allameh; S.M Hosseininezhad; L Bakhshandeh
Abstract
Ab-deraz Formation is one of the Lithostratigraphic units of upper cretaceous the age of which is determined as touronian-santonian in Kopet-Dagh sedimentary basin located in northeast Iran. Its major lithology in Sanganeh section contains Marl, Marly limestone, and gray shales and light green shale ...
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Ab-deraz Formation is one of the Lithostratigraphic units of upper cretaceous the age of which is determined as touronian-santonian in Kopet-Dagh sedimentary basin located in northeast Iran. Its major lithology in Sanganeh section contains Marl, Marly limestone, and gray shales and light green shale along with three band of chalky limestones. This Formation thickness in Sanganeh section is measured as 530 meter out of which 41 samples were systematically taken. In order to interpret the Paleoenvironment and Sequence stratigraphy, this Formation in Sanganeh section was analyzed by using palynological facies and conformity of Osracodas and Dinoflagellates. Having examined the frequency ratio (abundance) of two groups of Ostracoda (Platycopids to Podocopids), it was observed that the most abundant oceanic dissolved oxygen is seen in Marly layers near Calcareous band of chalky limestones and the least abundant is seen in layers far from those bands. In addition, based on the abundance of Genus, such as Paracypris, Brachycthere, and Bairdia mostly seen near Calcareous band of chalky limestones and Ostracoda with ornamented Carapce and thicker layers such as Veenia, Pterygocythereis seen in Marly layers near chalky limestones, it can be stated that it is shallower near Calcareous band of chalky limestones and moving toward Marly and shale layers, it becomes deeper. Analyzing 82 Palynological slides resulted in identification of three Palynofaies of V, IV, II, in this Formation. The results obtained from statistical studies of palynological factors including AOM to Marine palynomorph ratio, abundance of Foraminifera test lining, and peridinioid/Gonyaulacoid ratio for determining the amount of oxygen in the environment indicate that often there were low levels of oxygen in this Formation, however, there were times when oxic condition was dominant. Also in order to Relative sea level changes by Palynological facies, two factors were used first one being dinocysts of specific inner neritic to outer neritic ratio and chorate/ proximate, proximochorate and cavate cysts (C/PPC) ratio. Studies in which Ostracoda were used confirm the results obtained from palynological studies and show that sediments of Ab-deraz Formation are deposited on each other in an open marine and change from Inner neritic to outer neritic in disoxic to suboxic environment.
L. Fateh Bahari; M.H. Mahmoudi Gharaei; A. Mahboubi; R. Moussavi-Harami
Abstract
Ab-Deraz Formation (Turonian to Santonian) is a marly - Carbonates sequence consists of three marl-chalky limestones intervals. This formation widely crops out in Kopet-Dagh Basin in NE of Iran. Chalk and calcareous marl couplets show decimeter to meter scale cycles. Carbonate content of chalky beds ...
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Ab-Deraz Formation (Turonian to Santonian) is a marly - Carbonates sequence consists of three marl-chalky limestones intervals. This formation widely crops out in Kopet-Dagh Basin in NE of Iran. Chalk and calcareous marl couplets show decimeter to meter scale cycles. Carbonate content of chalky beds are 80-95% in rhythmic couplets, and about 65-80% in calcareous marly beds. The Ab-Deraz Formation is studied in tow Hamam-Ghale and Padeha outcrops, and also in well No.56 of Khangiran. Three dominate frequency of sediments are identified based on gamma ray log, which are related to three type of Milankovitch cycles including the long eccentricity (413 ka), eccentricity (100 ka) and precession (21-23 ka) cycles. Biostratigraphic age determination based on foraminifera is comparable with orbital chronology calculated by on eeccentricity cycles counting. These cycles are also correlated with carbonate contents in studied sections.
