فهرست مطالب محمد آفرین

In this research, the effect of monsoon phenomenon on the textural characteristics of the sediments of Iranian coasts of the Oman Sea was investigated. For this purpose, necessary sampling was done from 13 stations based on marine sedimentological standards. According to the amounts of sand, silt and clay in the pre-monsoon and post-monsoon samples, the sedimentary types of sand, clayey sand, sandy clay and clay were identified in the studied stations. Granulometric analysis showed that the amount of sand and clay in pre-monsoon samples of shallow and near-shore stations (Tiss, Desalination, Center of the Bay, Ramin, Beris and Pasabandar) range from 43 to 97 and 0 – 27%, respectively. On the other hand, these values change between 8 – 45% and 54 - 82 % in deep and offshore stations, respectively. The amount of sand and clay in post-monsoon samples of shallow and near-shore stations vary between 68% - 96% and 0% - 13%, respectively. The amount of sand and clay in deep stations and far from the coast in post-monsoon samples fluctuates between 8-22% and 58-86%. The amount of organic matter in sediments varies between 1 and 3% in most of the studied stations and is within the normal range. This amount showed a slight increase in Konarak and Ramin stations due to human pollutants and fine-grained sedimentary texture. The low amount of organic matter in the desalination station can be caused by the inflow of more saline wastewater into the bay environment

The present study aims to evaluate the effect of monsoon seasonal variations on sedimentology and beach profile of the Chabahar Bay. Based on the above data, during the monsoon, Chabahar Bay sedimentary environment is categorized into Tis and desalination plant coasts (sand), Konarak (clay), and mouth of the Chabahar Bay (clayey sand). On the other hand, after monsoon the area is divided into Tis (high sand content), Konarak and mouth of the Bay (high silt content), and desalination plant (the same contents of sand and silt). Data revealed that the high-energy SSE monsoon waves carry small particles to offshore leading to increase the proportion of sand particles in the eastern and central parts of the bay (onshore and offshore Tis and desalination plant coast). However, as is sheltered by a headland, the western part of the bay (onshore and offshore Konarak) is lesser affected by monsoon waves and therefore is covered by finer sediment particles (mostly clay). Longshore currents are likely responsible for fine-grain sedimentation in Konarak as well. After the monsoon, however, wave energy weakening leads to deposition of finer grain sediments and formation of sand bars and berms along coasts Chabahar Bay. This sedimentation/erosion regime causes lack of considerable sedimentation around harbours located in the eastern part of the bay (Shahid Kalantari, Shahid Beheshti, Hafte Tir and Tis), while the Konarak harbor (west of the bay) is faced by a severe sedimentation.

In this study, geochemical and sedimentological assessment was carried out on mudstone and sandstone deposits of Eastern coasts of Chabahar. Fifty samples were taken five sectione of Tiss, Ramin, Lipar, Gorankesh and Garindar estuary and subjected to grain size analysis and chemical analysis using XRF and ICP AES methods. Positive sorting and skewness (with the frequency of fine grain particles) of samples indicate deposition in a low energy environment. Plotting geochemical data of major elements Late Miocene- Pleistocene age 10 mudstone and sandstone samples in east coasts of Chabahar in Makran zone, on siliciclastic rocks classification diagrams, showed that the sandstones are wacky and Mudstones are shale. The mean calculated chemical indexes of alteration (CIA) and weathering (CIW) for siliciclastic sediments, confirm low level weathering of source rocks of this sediments. The average index of combinational variety (ICV) for the studied sediments was 1.57, which indicates that these deposits have a moderate chemical maturity and are derived the first cycle of sediments. Distribution pattern of rare earth elements on spider diagrams shows the enrichment of light rare earth elements (LRRE) relative to heavy rare earth elements (HRRE) in the rocks. High ratios of LILE/HFSE and LRRE/HRRE in the rock samples and similarity of their chemical composition with subduction zone facies, indicates that siliciclastics of Chabahar coasts have formed in a subduction zone. The diagrams of tectonic setting associated with patterns of multivariate charts also shows that the studied rocks have been developed in an active continental margin.

The Chabahar coastal area is located in the Makran sedimentary-structural zone. The basement of the Makran zone consists of an oceanic crust and flysch units which completely overlie by thick sequences of mudstone, sandstone and conglomerate in the Chabahar area. Fifty samples were taken from sections of Tiss, Ramin, Lipar, Gorankash and Gareeandar and were studied by calcimetry, XRF, ICP and XRD. The result of calcimetry analyses shows lime contents of marl samples vary from 9 to 21 percent, and it is better to introduce them as mudstone. Na2O, P2O5 and Fe2O3 contents of the study rocks are lower than the upper continental crust CWI= 88.8 shows arid to semi-arid. Based on geochemical data, mudstones and sandstones of Chabahar coastal area were derived from a quartzose sedimentary source. Geochemical characteristics of the study rocks and using of discrimination diagrams for tectonic setting, based on major and trace elements, suggest that they formed in an active continental margin, This conclusion is logical because the Makran zone is an active subductional continental margin.