نشریه رخساره های رسوبی
سال ششم شماره 1 (پیاپی 10، تابستان 1392)

Petrographic characteristics of carbonate rocks such as mineralogy، texture، crystal size، porosity، fracturing، dissolution and degree of cementation play major roles in karstification. In order to investigate the effects of these factors on carbonate rock units in Shotori Mountains، stratigraphic intervals including Esfandiar، Jamal and Shotori Formations have been studied. Due to the effect of purity of limestone on development of karst، the percentages of insoluble residues in some samples and hydrochemical data of springs have been analyzed. In the studied region، remarkable thickness of limestones، proper lithology and suitable tectonic situation are important factors for karstification، whereas climatic condition is the main prohibiting element. However several karstic features، including karrens، dry valleys، karst springs، dissolution pit and cave were observed in the studied area، but the results of this study revealed that further wet climatic condition is necessary for evolution of karst in this region.

For interpretation of source of sediments، paleoclimatic conditions and tectonic setting of marine sediments in Makran region، Chabahar، fifteen samples from five cores from Oman continental shelf sediments have been analyzed. Analyses of major elements revealed that the dominant source may have been from felsic and intermediate rocks. The positive correlation of Al2O3 with K2O and CaO، and abundance of Al2O3 suggest that these elements are primarily controlled by the dominant clay minerals. Based on major element geochemistry، the climatic conditions is warm and arid and Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values of sediments show that chemical alteration may have done by leaching. However، a value of ICV is indicative of recycled sediment. The quartz–toleitic rocks are likely to be the main source for sediments، which are common in back arc zone of Makran subduction. This sediment is product of long washed recycled sediments after several uplifting stages in active Makran subduction zone.

Despite the majority of Quaternary deposits consist of alluvial sediments، an important proportion of deposits (in active tectonic zones) are formed as tufa and travertine. The studied travertine in this research (from seven measured sections) are located in three neighboring provinces (Qazvin، Hamedan and Kurdistan)، situated in the Central Iran and Sanandaj-Sirjan structural zones. Petrographic studies show distinct lamination، microscopic and macroscopic porosity (5-10%) in the samples. Most studied samples are biosparite; plant and algae debris present in some sections. SEM analysis shows mosaic and equant calcite crystals، grows in pore spaces. XRD analysis indicates low-magnesium calcite is present in all studied sections; some clay minerals and quartz are present in few sections. Geochemical analysis (XRF method) indicates that the average CaO and SiO2 in samples are 52. 98% and 1. 98% respectively; Si mainly occurs as quartz veins and sandstone clasts. MgO (0. 062%)، Al2O3 (0. 47%، as clay minerals) and Fe2O3 (0. 41%، as iron oxide) are also exists. Based on the cement type، meteoric and vadose diagenetic environments were recognized.

Ruteh Formation is composed of dark bioclastic limestone and marl layers in the Baghdarreh section، Soltanieh Mountains (northwest Iran). It is about 43 meters in thick. Ruteh Formation is Murghabian in age based on foraminifers’ assemblages. Carbonate layers contain Zoophycos، Chondrites، Planolites and Rhizocorallium trace fossils، which Zoophycos is the main and abundant among other rare trace fossil. Microfacies analysis (10 identified microfacies) shows sediments of Ruteh Formation deposited in three facies belts including inner، middle and outer homoclinal carbonate ramp. Zoophycos only present in the outer ramp to open marine microfacies with anaerobic and low tolerances conditions، below storm weather base. Where the depth increased، size of Zoophycos and its burrow diameter increases which fellowed by development of bioturbation. Ruteh Formation’s Zoophycos have no lobate structure and it formed in organic bearing carbonate sediments.

The Qom Formation deposits in the Bijegan area، northeast of Delijan، are Rupelian-Chattian in age، with a thickness of 162 meters. It consists of sandy limestone، thin to medium and thick bedded and massive limestone. It is disconformably overlain the Lower Red Formation. The upper boundary is covered by alluvium. 8 carbonate microfacies related to semi- restricted lagoon and open marine (slope) environments identified. Based on 120 thin section studied، microfacies analysis and field observation the Qom Formation in the study area deposited on an open shelf setting.

In this paper، the calcareous nannofossils at the contact between Aitamir and Abderaz Formations in Dobaradar and Hammam Qaleh sections in the east and Qalehzoo and Sheykh sections in the west Kopet Dagh basin، for consideration of biostratigraphy and paleaoecology، were studied. On the basis of paleontological studies، 22 genera and 33 species in Dobaradar section، 25 genera and 37 species in Hammam Qaleh section، 9 genera and 13 species in Qalehzoo section and 17 genera and 22 species in Sheykh section، were detected، photographed and counted and the biozonation of studied regions have been determined. On the basis of these biozones، the age of the boundary between Aitamir and Abderaz formations in the Dobaradar and Hammam Qaleh sections is Late Santonian and the age of this boundary in Qalehzoo and Sheykh sections is Early Campanian. The increases in abundance from east to west and paleoecological interpretation show that the depth of the Kopet Dagh basin increased from east to west. Based on reduced diversity and abundance of species in the west، it can be stated that environmental conditions in the east were better for living calcareous nannoplanktons than west Kopet Dagh.

Abtalkh Formation has been chosen for microbiostratigraphy and paleoecology studies in the Qareh Sou section (south flank of Kalat-e-Naderi syncline، NE Iran). The measured thickness of Abtalkh Formation in this section is 1410m and consists mainly of marl and marly limestone. This study led to identification of 15 genus and 40 species of planktonic foraminifera in 5 biozones. Based on these fossils، the age of Abtalkh Formation in the Qareh Sou section is lowermost early Campanian to late Campanian. In addition، using the population variations of planktonic/benthonic foraminifera and epifaunal/infaunal benthonic foraminifera ratio، paleoecology conditions were determined. Based on these data، this formation is divided into 4 parts (P1، P2، P3، P4). During deposition of P1 and P3 sea level and food supply were high but the amount of oxygen was low; while during deposition of P2 and P4، sea level and food supply were low but the amount of oxygen and environmental energy was high.

The studied section exposes in Chehel Kaman synclinal entrance in east of Kopet-Dagh basin. A small collection of fossil pteropods، referred to as Limacinidea superfamily، is reported from the lowermost portion of Middle Eocene sediments of Khangiran Formation. This is the first record of fossil pteropods from this formation. This research was led to identification of 3 species from 2 pteropod genera. On the basis of these Pteropods، the age of these sediments are Lutetian. These planktonic gastropods occurrence have paleoecological importance because pteropods dispersion is affected by environmental factors such as water temperature، salinity، depth and oxygen content. Based on these pteropods and calculation of the depth on the basis of planktonic and benthic foraminifera، it can be interpreted that the palaeo depth was about ~500 m for the sediments containing pteropod. Their presence along with foraminifera in the Khangiran Formation indicates deposition in an open sea basin above aragonite compensation depth.