Journal of Stratigraphy and Sedimentology Researches (Nov 2014)
Palynology and paleoecology of Sarcheshmeh and Sanganeh formations at Baghak section (east of Kopeh-Dagh)
Abstract
1-Introduction The Kopeh-Dagh as an inverted basin (Allen et al. 2003) is extended from the east of the Caspian Sea to NE Iran, north Afghanistan and Turkmenistan. Following the closure of palaeo-Tethys in the Middle Triassic and the opening of Neo-Tethys during the early to middle Jurassic, the Kopeh-Dagh basin formed during the early to middle Jurasic. Sedimentation took place continuously from the Jurassic through the Neogene time in the Kopeh-Dagh basin (Afshar-Harb 1979). The first geological study on these strata was done by Amiranian oil company from 1937 to 1938. Many biological and stratigraphical studies had been carried on later on this basin. Kalantari (1969), Seyed-Emami (1980), Seyed-Emami and Aryai (1981), Seyed-Emami et al. (1984, 1994, 1996), Immel et al (1997), Raisossadat and Mousavi-Harami (2000), Raisossadat (2004, 2006) and Mahanipour et al. (2011) are among those who studied the biostratigraphy and sedimentology of the Cretaceous strata of this basin. In this paper we report on palynological and paleoecological data from two mid-Cretaceous formations (Sarcheshmeh and Sanganeh) in Baghak section situated in eastern part of Kopeh-Dagh basin. 2-Materials and Methods Fifteen samples from the Sarcheshmeh and thirty five samples from Sanganeh formation were processed palynologically. The preparation method of Traverse, 2007 was used. Cold hydrochloric (20%) and hydrofluoric (50%) acids were used to dissolve carbonates and silicates. The residue was neutralized and centrifuged in ZnCl2 (specific gravity 1.9), then sieved at 15 um using a nylon mesh, and mounted on microscope slides using liquid Canada balsam. Three slides were made from each sample. The microscope slides were examined under a light microscope and the index dinocysts were photographed and presented in two plates. In order to study palynofacies, in each slide numbers of organic materials including phytoclasts, marine palynomorphs and non-structural organic materials were calculated in five purview and then the percent of each palynological elements were acquired. 3- Discussion, Results and Conclusion All of the 50 rock samples prepared have yielded dinofalgellate cysts. The assemblages recorded include such taxa as: Acomosphaera sp., Achomosphaera neptunii, Batioladinium sp., Bourkidinium granulatum, Cauca parva, Circulodinium sp., Circulodinium brevispinosum, Circulodinium distinctum, Cometodinium sp., Coronifera oceanica, Cribroperidinium sp., Cribroperidinium orthoceras, Florentinia sp., Florentinia cooksoniae, Florentinia mantelii, Glaphyrocysta sp., Gonyaulacysta sp., Gonyaulacysta polythyris, Hystrichosphaeridium sp., Kiokansium sp., Kiokansium polypes, Klithrosphaeridium sp., Muderongia sp., Muderongia tabulate, Odontochitina operculata, Oligosphaeridium complex, Oligosphaeridium poculum, Oligosphaeridium porosum, Oligosphaeridium totum, Paleoperidinium cretaceum, Prolixosphaeridium sp., Prolixosphaeridium parvispinium, Pseudoceratium sp., Pseudoceratium retusum, Pterodinium sp., Spiniferites sp., Spiniferites ramosus, Subtilisphaera sp., Systematophora sp., Tanyosphaeridium sp. (Plate 1-2). Based on the presence of the index dinoflagellate cyst, Odontochitina operculata throughout the entire section, it can be concluded that the first appearance of this species is before the first sample of the Sarcheshmeh Formation (sample 398) and therefore the identified dinoflagellate cysts are a part of the Odontochitina operculata Zone. This palynozone originally erected by Wilson (1984) for Aptian strata in New Zealand and Morgan (1980) suggest the age of Aptian for Odontochitina operculata Zone. The presence of species Gonyaulacysta polythyris, Circulodinium brevispinosum and Florentinia mantelii which are recorded from early Aptian strata in different part of the world such as Australia (Backhouse, 1988), France (Stover, 1996), south of Alpine Italia (Torricelli,2000) and south of Tanzania (Schrank & Mahmoud, 2002) in lower formation reveal the age of Late Barremian to early Aptian for the Sarcheshmeh Formation. The Upper formation contains species Cauca parva with middle Aptian-Lower Albian age (Stover, 1996) and Frorentinia cooksonia with middle Albian age (Williams 1993) found in different regions such as Libya (Uwins & Batten, 1988), United States (Hedlund & Norris, 1986) and west of Australia (Cookson & Eisenack, 1962). This species suggest the age of middle Aptian- middle Albian for the Sanganeh Formation. Statistical analyses of the three main groups of palynological elements (Phytoclasts, Marine palynomorphs and non-structural organic materials) lead to the recognition of five palynofacies in studied section. Studying the recognized palynofacies indicate that the sedimentation rate and oxygen level of the basin were variable but decreasing from Sarcheshmeh to Sanganeh Formation. Based on index dinoflagellates it can be concluded that depositional environment of the Sarcheshmeh and Sanganeh formations ranged from inner to outer neritic environment.
