چكيده لاتين :
Introduction:
Kopeh-Dagh sedimentary basin is located in NE of Iran and is mainly composed of Mesozoic and Cenozoic sedimentary rocks (35? 30?-38? 15? N, 54? 00?-61? 31?E)(Afshar-Harb 1994). The Sarcheshmeh Formation is one of the lower Cretaceous strata in Kopeh-Dagh. In this investigation, the mentioned Formation is investigated in two stratigraphic sections which are as follow: 1) Jooragh village which is located between 59? 10?7? E and 36? 58?16? N geographical coordinates with 950 m elevatuion, in 65 km far from Mashhad city in the Mashhad-Quchan road in the east of Chenaran township. 2) Sheikh village which is located between 37? 32?48? N and 57?31?22? E geographical coordinates with 1125 m elevatuion, in 20 km far from Bojnourd city.
Matherial & Method
The main porpose of this research in determination and analysis of the existed palynofacies according to the changed percentage of 3 main groups of palynological elements (AOM, Phytoclasts, Marine Palynomorph). Relative analysis of the sedimentary environment are according to the palynofacies and the existed index dinoflagellates for environment and also evaluation of Oxygen and its changes in different parts and as well the determination of sedimentation rate in the Sracheshmeh Formation in the east and west of Koept-Dagh sedimentary basin.
The material used, inclues 35 outcrop sample collected from shale and marly shale layer throughout the Sarcheshme Formation in Jorgh section and collected 41 sample from Sheikh section. Laboratory maceration procedures of Travers (2007) were used to prepare sample. These procedures include chemical treatment of 15-20 gr of each sample with cold HCL (20%) and HF (37%) acids were used to dissolve carbonate and silicates. No oxidants or Alkalis were used, because such treatments can be affect the natural colors of palynomorphs and phytoclast. The residue was neutralized centrifuged in Zncl2 (specific gravity 1.9), then sieved 10 um using a nylon mesh, and mounted on microscope slides using liquid Canada balsam. Palynofacies analyses were also performed on these microscope slides. A total of 300 organic particles per sample were counted, classified, and proportionally calculated.
Discussion & Conclusions
Palynostratigraphy
Totally, 33 specious and 25 genera of dinoflagellates are determined from the Sarcheshmeh Formation in the Joragh section as well 31 specious and 28 genera from the Sheikh village. AOMe important dinoflagellates are as follow:
Achomosphaera neptunii, Achomosphaera ramulifera, Apteodinium sp. Apteodinium thellium, Batiacasphaera sp. Bourkidinium granulatum, Cassiculosphaeridia reticulate, Cerbia tabulata, Circulodinium distinctum, Cliestosphaeridium sp., Cometodinium sp., Cribroperidinium orthoceras, Cribroperidinium sp., Cyclonephelium distinctum, Dingodinium albertii, Florentinia cooksonia, Florentinia deanei, Florentinia mantelli, Hystrichosphaeridium atlasiense, Kleithriasphaeridium eoinodes, Kiokansium polypes, Muderongia pariata, Muderongia tomaszowensis, Odontochitina operculata, Oligosphaeridium asterigerum, Oligosphaeridium complex, Oligosphaeridium pocolum, Oligosphaeridium prosum, Oligosphaeridium sp., Oligosphaeridium totum, Paleoperidinium cretaceum, Pterospermella sp., Prolixosphaeridium parvispinium, Pseudoceratium pelliferum, Pseudoceratium retusum, Spiniferites ramosus, Subtilisphaera sp., Subtilisphaera perlucida, Systematophora sp., Tanyosphaeridium sp., Tenua hystrix.
Between determined ones, Achomosphaera neptuniind, Cerbia tabulate and Subtilisphaera are reported from the late Aptian from different parts of the world (Davey and Verdier 1974). Cyclonephelium distictum, Oligosphaeridium compelex, Kiokansium polypes and Odontochitina are reported from the Aptian of Canada (Kimyai 2000). Also, Cassiculosphaeridia reticulate, Cerbia tabulata Oligosphaeridium complex are reprted from the early Aptian of Australia, France and south of Alp (Stover 1996). AOMe specious such as Achomosphaera neptunii, Cyclonephelium brevispinosum Oligosphaeridium pocolum , Pseudoceratium retusum are reported from different parts of the world till the late Aptian (Skupien 2003). According to the determined dinoflagellates in 2 stratigraphic sections and their compression with biozones in different parts of the world, the Aptian age is assigned for 2 sections. By the way, the age of the mention formation is assigned to Aptian according to the determined foraminifera by Kalantari (Afshar-Harb 1994).
Palynofacies
For each sample relative proportions of these groups were determined and plotted on Tysonʹs ternary diagram. In palynological facies investigations, 4 palynological facies are determined in two section: Type I: Highly proximal shelf or basin, Type II: Marginal basin, Type IV: Shelf to basin transition and Type VI: Proximal suboxic-anoxic shelf. According to the determined palynological facies, the sedimentary environment of the Sarcheshmeh Formation in the base of the Joragh section is a low-mid depth which is going lower toward the upper parts and has a few deeper to the end of the section. This trend is exactly the same for the Sheikh Village section in the west of Kopet-Dagh basin. But, the existence of palynological facies type VI in the upper part of the Formation can be a sign for coming out later in this part in comparison with Joragh section.
Palynologically productive samples contain spore, pollen grains, dinoflagellate cysts (Marine palynomorph), foraminiferal test linings, acritarchs, wood debris (plant tissue or phytoclast debris) and Amorphous Organic Matters (AOM). To determine more accurate environment ,Factors affecting the degree of organic materials are factors maintaining protect organic materials (Lability) and ratio of marine Palynomorphs to translate AOM, marine Palynomorphs to opaque AOM and also opaque AOM to translate AOM. Evaluation and Comparative Study show quantity of oxygen, sedimentaion rate and paleoenvironment energy rate. Review and determine the percentage of three main elements palynologicy and it also reviews factors protect organic materials shows low-oxygen condition with low sedimentation rate. The samples of Sarcheshmeh Formation (Anjirbolagh section) based on the type of dinoflagellate cysts recognize that the environment based on sedimentary environment is variable of the inner neritic to outer neritic.
Key words: Palynofacies, Palaeoenvironment, Sarcheshmeh Formation, Aptian, Joragh section, Sheikh section, Kopeh-Dagh
