JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2018 | Volume:33 | Issue:4 (69) |Papers Count:7

Tufa is the non- marine carbonates that formed from cold to low temperature freshwater at low depth and low energy flow conditions. Abgarm’s tufa is a typical kind of these deposits. Field and microscopic studies led to recognize of seven allochthonous and autochthonous lithofacies. The presence of dense plant covering river margins, increasing use of dissolve CO2 in water and providing chemical conditions due to turbulence are factors that are important in the formation of tufa. Based on concentrations of dissolved ions, the type of Abgarm water is Ca- Mg- HCO3. Based on ions ratio, the water with primary meteoric origin is affected by passing through dolomitic limestone and evaporite of the Mozduran and Shurijeh formations. The high concentrations of these ions caused the carbonate to be trapped between algae filamentous and formed a kind of active tufa. The presence of gastropod species show a dominance wet climatic conditions when these deposits formed. At the next step, decreasing rainfall and increasing temperature and evaporation, caused the death of two gastropods species (Melanopsis praemorsa and Galba truncatula) in the studied area. Isotopic analysis of oxygen and carbon show the effects of meteoric waters and Mozduran aquifer limestone formation in isotopic compositions of tufa in Abgarm area.

The Shotori Mountains, with an area of about 2500 Km2 are located in west Tabas. Carbonate formations outcrops are about 53% and include Gamal, Shotori and Esfandiar formations. Sequence stratigraphy and difference hydrostratigraphy leaded to forming three karstic aquifers entitled Gamal, Shotori and Esfandiar. Almost all springs in this studied area emerge from these karst formations. So that annual discharge these karst springs is about 83% of total annual discharge in the studied area. The higher extend, thick layer and more purity of the limestone in Esfandiar formation in comparison with the Gamal and Shotori formations lead to the higher degree of karstification in this formation so that the main springs emerging from this formation. In addition to the effect of stratigraphy on quantity, it has a significant effect on the quality of the discharging water from the springs in the area. Springs which discharge form Esfandiar formation with volcanic and Qala Dokhtar formation basement have higher quality than Esfandiar with Baghamshah basement. The electrical conductivity of the first group of springs is below 500 mS/ cm whereas it fluctuates between 700 to 1800 mS/ cm in the second group.

Various types of non-tectonic fractures are considered in carbonate-evaporite Kangan and Dalan formations in central Persian Gulf in this study. Mud cracks have small sizes and low frequencies and have been formed in shallow water coastal (tidal and intertidal) environments exposed alternatively. Presence of syneresis and desiccation cracks show salinity change or dewatering. These fractures also have no major effect on reservoir properties such as the mud cracks but have higher frequency and show their original depositional environment. These fractures formed in sabkha environments. A lot of water has been released during gypsum-anhydrite transformations in these formations. In the case of low permeability, the rock can’t pass the fluid and so hydraulic fractures have been formed due to the mineral phase change. These fractures formed in burial diagenesis in tidal facies with high evaporation. Stylolite related fractures are vertical, perpendicular to the layering and stylolite surface. These fractures are also related to burial diagenesis, filled and prevent fluid flow in the studied formations. Loading fractures are vertical and have been filled by anhydrite in most cases. These fractures could enhance the permeability if they are open. Results show that except the last group, all detected fractures act as local fluid barriers in Kangan and Dalan formations in central Persian Gulf area.

Micropalaeontological study based on planktonic foraminifera in the Cenomanian - Turonian succession of the Holul section, located in the Lurestan geological province (west of the Kermanshah City), resulted in distinction of Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica biozones. Whiteinella archaeocretacea biozone globally defines the Cenomanian - Turonian transition. Detection of this biozone in the Holul section could be a clue for continuous sedimentation of the Cenomanian - Turonian transition in the studied stratigraphic section. Elongated chambers planktonic foraminifera such as Muricohedbergella simplex are relatively common during time span of Whiteinella archaeocretacea biozone in the Holul stratigraphic section. Results of the isotopical analysis in the studied section indicates an increasing - decreasing trend from the top of Rotalipora cushmani to the base of Helvetoglobotruncana helvetica biozones including two positive shifts before and after Whiteinella archaeocretacea biozone that can be correlated with carbon isotope peaks of OAE2 in the Neotethys Basin.

Type section of Pabdeh Formation (Late Paleocene- Early Oligocene) is located in the Gurpi anticline, Zagros, Khouzestan Province. Lithologically Pabdeh Formation consists of purple and white to yellowish marl, marly limestone and thin- to thick- bedded limestone, rich in pelagic foraminiferas. Pabdeh Formation conformably overlies Gurpi Formation and is conformably overlained by Asmari Formation. Petrographic studies, description and microfacies analysis specially hemipelagic, pelagic and calciturbidite facies of Paleocene to Lower Oligocene indicate that Pabdeh Formation was deposited in a deep marine basin. Field observations, facies studies and sequence studies resulted in identification of stratal key surfaces of sequence stratigraphy such as sequence boundary, maximum flooding surface, transgressive surface, system tracts and 9 depositional sequences. Sequence P1, P2 and LST, FSST of sequence P3 are of Paleocene in age, based on identification of planktonic foraminifera, TST, HST and FRWST of sequence P3 and sequences P4, P6, P7 and P8 were deposited during Eocene, and sequence P9 suggest an age of Upper Eocene- Lower Oligocene. All sequences begin with SB2 and except of sequence P3 and P4 , SB2 and Ts surfaces coincide with each other. Deepest mfs is belongs to the sequence P3; due to the remarkable abundance of glauconite minerals. Relative sea- level curves in most sequences, except for sequences P3, P8 and P9 exactly correlate with standard global sea level curves. The role of synsedimentary tectonic activities and sea-level oscilations, probably, are responsible for deposition of sequences P3, P8 and P9.

Introduction: The Kopet-Dagh sedimentary basin is located in north-east Iran, southern Turkmenistan and Afghanistan and is composed of Mesozoic and Cenozoic sedimentary successions. Fifteen formations have been introduced in the Kopet-Dagh Basin. The Cretaceous formations include Shurijeh, Zard, Tirgan, Sarcheshmeh, Sanganeh, Aitamir, Abderaz, Abtalkh, Neyzar and Kalat (Afshar-Harb 1994). Aitamir Formation is one of the main rock units in the Kopet-Dagh basin. This paper presents the biostratigraphic data obtained based on nannofossils from the upper part of the Aitamir Formation. In order to study calcareous nannofossils a stratigraphic section was chosen in northwest Kopet-Dagh. The measured section is located about 35 km west of Maraveh Tappeh city and near Cherli village at 37 50' N latitude and 55 31' E longitude. Based on foraminifera assemblage, Kalantari (1969) suggested Cenomanian age for the Aitamir Formation. Thereafter, Seyed-Emami (1980), Seyed-Emami and Aryai (1981), Seyed-Emami et al. (1984), Immel et al. (1997), Mosavinia et al. (2007) and Mosavinia and Wilmsen (2011), based on ammonites, reported a late Albian-middle Cenomanian age for this formation. Moreover, Moradi Salimi (2012), and Raisossadat et al. (2013) in the center and west of Kopet-Dagh, Sharifi et al. (2012) and Garmabi and Mosavinia (2012) in the east of Kopet-Dagh discussed the ammonite contents and paleobiogeography of ammonites in the Aitamir Formation. The calcareous nanoplanktons of the formation have been studied by Susani (2005), Mousazadeh (2005), Moheghy et al. (2014) and Mousavi et al. (2016a, b). In the measured section, the formation conformably overlies the Sanganeh Formation and underlies the Abderaz Formation. The lower sandstone member is 711 m, consists of glauconitic coarse to fine grained sandstones with some intercalation of silty sandstones while the upper shale member is 359 m, composed of green to greenish grey, grey shales and marlstone that changes to limestone beds of Abderaz Formation at the top. A total of 100 samples were collected from the section with a thickness of 1070 m. The preservation and abundance of calcareous nannofossils in the lower sandstone member of the Aitamir Formation is very rare and poor but in the upper shale member it is good and the most abundant nannofossils belong to this member.Thirty-five (35) samples were collected from the shale member and used for calcareous nannofossil studies. For detailed calcareous nannofossil examination, simple smear slides were prepared using standard procedures. Smear slides were made from the fresh surface of raw sediment samples. Prepared slides were studied by using a polarized microscope and photographed by a digital camera. Corel draw and Photoshop softwares were used for drawing charts and figures.Discussion and Conclusion: The standard Upper Cretaceous calcareous nannofossil biozonation Sissingh (1977) (the CC zones), which was modified by Perch-Nielsen (1985) and UC biozonation of Burnett (1998) were used. This scheme largely resulted from the examination of potential stage-boundary sections. Both biozonations were applied to the data on the range-charts.The biostratigraphic studies of the shale member of the Aitamir Formation resulted to the identification of 23 genera and 32 species of calcareous nannofossils are as follows; Amphizygus megalosa, Broinsonia enormis, Calcicalathina alta, Corollithion kennedy, Cyclagelosphaera margerelii, Eiffellithus turriseiffelii, Eprolithus floralis, Gartnerago segmentatum, Haqius circumradiatus, Icrorhabdulus belgicus, Lithraphidites carniolensis, Manivitella pemmatoidea, Marthasterites furcatus, Microrhabdulus decorates, Prediscophaera intercisa, Prediscosphaera columnata, Quadrum gartneri, Radiolithus planus, Retecapsa angustiforata, Retecapsa crenulata, Rhagodiscus angustus, Rhagodiscus splendens, Stoverius achylosus, Tranolithus orionatus, Tranolithus phacelosus, Watznaueria barnesiae, Watznaueria biporta, Watznaueria fossacincta, Zeugrhabdotus fibuliformis, Zeughrabdotus diplogrammus, Zeugrhabdotus embergeri, Zeugrhabdotus xenotus.The following biozones are suggested based on Sissingh (1977) and Burnett (1998). According to the first occurrence and last occurrence of index species and fossil assemblages, three biozones of Sissingh (1977) Eiffellithus turriseiffelii Zone (CC9), Microrhabdulus decorates Zone (CC10) and Quadrum gartneri Zone (CC11) equivalent to biozones UC0-UC7 of Burnett (1998) are suggested. The identified nannofossils zones, could confirm a Late Albian to Early Turonian age for the shale member at the Cherli section in the north western Kopet-Dagh. The determined age is nearly equal with the age obtained by foraminifera (Motamedalshariati et al. 2012). The age of the uppermost part of the Aitamir and the lowest part of Abderaz formations is the Early Turonian. Therefore, it appears that the contact between the Aitamir and Abderaz formations conform and sedimentation was continuous. In the boundary, lithology transitionally changes from shale in the uppermost part of the Aitamir Formation to limestone in the lowest part of the Abderaz Formation. However, more studies are required on this boundary in the western part of the basin.