Investigation of active tectonic impact on geomorphological changes of the Iranian coast of Makran (Case study: Chabahar)

The study area is located in the north of the Oman Sea and southeast of Iran in Sistan and Baluchestan province. The Makran Trench is the physiographic expression of a subduction zone along the northeastern margin of the Oman Sea adjacent to the southwestern coast of Baluchestan of Pakistan and the southeastern coast of Iran. Numerous geomorphological landscapes such as cliffs, Omega and U-shaped bays, erosion columns, various faults and so on have been formed in a beautiful and unique way in the region. In this region the oceanic crust of the Indian Ocean Plate is being subducted beneath the continental crust of the Makran Plate. Makran is one of the largest accretionary wedges on the globe. The study area between latitudes 25 ̊ to 25̊ and 45̍ north and longitude 56 ̊, 45̍ lengths up to 61̊, 52̍ north of the Sea of Oman and the north-eastern Sistan-Baluchestan province is located. The study area is located in the external part, the structure of the Makran coastal land area larger than the selected range. In the Makran region, the Arabian Plate subducts beneath the Eurasian Plate at ~4 cm/yr. This subduction is associated with an accretionary wedge of sediments which has developed since the Cenozoic To the west, the Makran Trench is connected by the Minab Fault system to the Zagros fold and thrust belt. The Makran accretionary complex is characterized by a number of features associated with escaping water and methane. Mud volcanoes are found onshore in both Iran and Pakistan, and cold seeps exist offshore for example Tang Mud volcano. The formation of an island (Zalzala Jazeera) after the 2013 Baluchestan earthquakes is thought to be the result of a mud volcano. Extreme coastal inundation associated with the 2004 Indian Ocean and 1945 Makran tsunamigenic–earthquakes highlight the risk of Tsunamis to coastlines of the northern Oman Sea (Vaziri et al., 2019).

In this research have been used the methods of Office and library studies, Field Studies (photographed and documented in structural geology features, 85 thin sections and 62 washed samples that were collected in the study areas), Laboratory studies [Thin sections were stained using Alizarin Red S (Dickson, 1966) and were studied using standard petrographic microscope techniques. Carbonate rocks were classified according to Dunham’s carbonate classification (1962), and siliciclastic rocks were classified using Folk’s classification (1980). At this point, a set of 85 samples, 62 thin sections were studied to determine the lithofacies. In each of the thin, skeletal and non-skeletal components were identified and the percentage of each constituent grains major and minor chart using comparative Flugel (2010), respectively. As well as 23 samples of sediments were paleontological studies. On the basis of petrographic studies classification of carbonate rocks by Dunham’s method and nomination of microfacies by Flugel’s classification was done and three basic microfacies have been identified. Based on the identification of different lithofacies and interpretation of their depositional environments. We applied the concepts that were developed by many workers to determine sequence boundaries, depositional sequences and system tracts] and Data analysis, interpretation and conclusions: The initial processing by computer skills such as Excel and final processing using software was computed. Sea level positions were interpreted for the Pleistocene interval based on lithofacies variations with the sequence stratigraphic framework established in this study.

The rock types are siltstone, sandstone, conglomerate and lumachelle and limestone. Strata of the Makran Formation are subdivided into two major carbonate lithofacies and two siliciclastic lithofacies. Based on skeletal grains and the amounts of micrite, the sediments deposited in the lithofacies of the sandy packstone to siltstone lithofacies were deposited in relatively deep water, below fair-weather wave base under low-energy environmental (Open-Marine) conditions. The presence bioclastic debris of stenohaline indicate that sandy grainstone were deposited in an upper shoreface setting. Plotting the interpreted relative water depths vs. Stratigraphic position for each occurrence of each subfacies shows a predictable stacking pattern that formed coarsening upward cycles. These meter-scale shallowing-upward cycles in the Pleistocene interval formed in response to sea level fluctuations coupled with subsidence due to both sediment loading and tectonic movements. Because of terrigenous influx, siliciclastic sandstone and siltstone were deposited in the dominantly carbonate-producing area, formed a mixed siliciclastic-carbonate sequence. At times when the siliciclastic point sources were shifted far to the south carbonate deposition reestablished itself in southeastern Iran.

Makran is a constant competition between tectonic processes and erosion processes, shaping the geomorphological changes of the region (such as erosion columns, folds, cliffs, bad land, Omega bays, sand dunes, dissolution cavities, taphoni cavities, coastal falls and so on). The presence of several mud volcano in Makran accretionary complex with special features in the coastal areas of Iran and Pakistan shows the effect of active tectonics on the geomorphology of the study area. Due to the increase in sediment thickness from west to east, increase in subduction rate of Makran zone, coastal uplift and faulting of coastal barracks and the entry of destructive sediments and the direction of old flow in sedimentary structures, it seems that the origin of clastic grains in the north It is a study that reduces the amount of detrital particles and creates conditions for the sedimentation of carbonates. Therefore, the coastal sedimentary model is proposed for Pleistocene sediments that have been deposited under dual conditions in terms of sedimentary environment energy. These geomorphological changes are caused by regional sea level changes, sedimentation process, the tectonic process caused by subduction of oceanic and continental plates, relative sea level changes and evidence-based climate change due to evidence-based glacial and interglacial periods.