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1.2. Physical Geography 1.2.1. Geology A. Evolution of the Caspian Sea The Caspian Sea was separated from the Black Sea with which it had formed a single Sarmatian Sea during the Pliocene (in Cenozoic, about 2-3 million years ago). The formation of the Caspian basin was completed in upper Pliocene. At the end of the Pliocene and in Quaternary period, the Caspian body of water was isolated from the world’s oceans by the changed regional movements. After the separation, the global climatic variations affected the regime of the Caspian Basin. B. Geology and geomorphology of The Caspian Basin The main geomorphologic of element of the sea floor is in the south Caspian trough with an uneven floor relief and maximum depth. The western part of the middle Caspian and the entire south Caspian belong to an alpine geosynclinal area. The southern trough of the Caspian with the adjacent lowland, forms a large inter-mountain megadepression bounded by folded mountain formations to the west, south and the east. The south Caspian trough is a region of young tectonic movements and of active mud volcanism not only on dry land, and in the shallows, but also deep within the trough. A so-called granite layer, proper to typically oceanic regions, is absent from a considerable area of the trough. The South Caspian in the geological past was a part of the Tethys Sea, and therefore the floor devoid of the granite layer maybe considered a relic of the sea that ceased to exist in the Cenozoic. C. Stratigraphy of the Southern coastline The Mesozoic range and tertiary foothills of Alborz mountain range south of the coastal plain in Mazandaran province, strike northwest, towards the seashores of Alamdeh-Nowshahr. This reduces the coastal plain in this area. This is the nearest approach of Alborz to the Caspian Sea. They are eroded along old cliff lines of the Caspian Sea and are probably displaced along a flexure line in the narrow coastal plain. In the south of Chaloos, the range is formed by coarse of the Jurassic Formation (Shemshak), Cretaceous limestone, sand tuff and volcanic units (Chaloos Formation), and by upper Cretaceous marl limestone and shale. South of Babol, the coastal range exposes upper Cretaceous-Paleocene marls, which are covered by the marine Caspian Neogene (Vindobonian-Sarmatian), and continental coarse clastic units, in thickness of 2000 to 3000 meters, increasing towards the coasts to more than 4000 meters. This Caspian Neogene foothills zone with cores of upper Cretaceous marls gradually turns east of Talar river to the eastern Mazandaran embayment, striking E-to ENE between the main northern thrust of the Paleozoic range and the south Gorgan uplift. The marine Neogene units change into littoral and continental coarse clastic beds, and give way to exposures of upper Cretaceous marls and Jurassic-Neocomian limestone cores. The south Gorgan uplift of pre-Cambrian metamorphic rocks is covered by a thin, lower Jurassic shale and sandstone and by a massive Jurassic limestone (Lar formation), which form the boundary between Neka valley and the coastal plain. At Neka, the Lar limestone cover of the south-Gorgan uplift plunges under the coastal alluvium but continues in the subsurface as a gravity high (Spur of Neka to Dasht-e-Naz). The upper part of Atrak valley and the hills near Iran-Turkmenistan border north of Hezarcheh contains continental coarse clastic, and red beds of the Neogene. The western plunge of the fold belt has on-lapping Pliocene littoral Caspian deposits and is covered by an extensive Pleistocene loess blanket of up to 30 meters in thickness, which makes an excellent soil for mechanized, dry farming wheat production. Dasht-e-Gorgan, between Gorgan River and Atrak is a flat steppe with less than 30 cm of annual rainfall; covered by loess terraces and partly alkaline soils (Solonchak) which are below the sea level, west of the Gorgan-Tangeli road. The partly marine mud and clay deposits and fossil beach sands cover a sequence of young Neogene marine Caspian strata, which increases in thickness from the east to the west to the Caspian Sea shore to more than 4000 meters (Map 4). 1.2.2. Geomorphology and Landscape The southern part of the Caspian shores is a narrow coastal plain with an average width of about 50 km, created by the “regional regression” of the sea, which probably once extended as far as the foot of the Alborz Mountains. A large number of rivers originate in the northern foothills of Alborz, but they are mainly short rivers (especially on the western side, i.e. Gilan Province) and cover small distances before they enter the sea. Alborz and its associate mountains range form a continuous wall along the north of Iran. This system consists of parallel ranges, increasing in elevation from the north and the south. The geographical territory of the region consists of terrestrial and aquatic ecosystems. The aquatic ecosystems consist of marshes, wetlands and other bodies of water. The terrestrial ecosystem comprises high mountains, foothills and the plain adjacent to the mountains and the hills. The plain has two major parts one of which forms the coastal region and the other forms the plains away from the sea. The coastal strip is a narrow piece of land a few meters, in some places and a few kilometers in other areas. These strips are usually covered by sand dunes (Anzali coastal region) along the sea. The coast is generally flat, except a mountain around Ramsar, which is in the plain adjacent to the sea. The southern coasts of the Caspian Sea have fewer bays than the other coastlines. To the east of the coast, mountains are drawn away from the sea and vast plain of Gorgan exhibits a continuous flat plain, reaching Bandar-e-Turkaman. The eastern coast also possess sandy deserts void of vegetation cover, in which the temperature is usually higher than the other places. From Ramsar to the west, the coastline gets wider because mountains are drawn to the south where the vast Delta of Sefid-rood River expands. This region comprises the coastal plain of the southern coast of Caspian Sea. This coastline is almost 2800 km2 and is formed by alluvial sediments. In the west, the Talesh Mountains approach the Caspian basin; the width of the shore decreases and becomes narrow again. The important coastal features along coastlines include Anzali marshes in the west, Sefid-rood Delta (cape) in the middle and Gorgan bay in the east. This bay is separated from the sea by Miankaleh peninsula. Intensive geological and tectonic investigations reveal vulnerability of all these mountainous areas to the seismic dangers. Existence of active faults in the western and southern regions also adds to the vulnerability of the region to tremor. These regions include Astara fault, Talesh fault and the fault in the southern coast of the Caspian Sea. The narrowest part of Caspian (southern) coastal plain is located between Tonekabon (in the west of the Mazandaran province) and Roodsar (in the east of Gilan province). The coastal plain of the Caspian has beautiful landscape with resort and recreational areas such as Ramsar with fine sand beaches. In the Sefid-rood River Delta and Rasht area on the west, the coastal plain widens to 33 km. This area is densely populated and is covered mostly by rice paddies; tea plantations and citrus orchards are cultivated on the lower foothills. The Anzali lagoon, which is rich in.wildlife resources, is located in this area. The outlet to the Caspian Sea on the sand spit has developed into the Bandar-e-Anzali harbor. A. Sedimentation and Sedimentary features Different types of coastal, deltaic, marshlands and marine sediments exist in the region. The major sedimentary features in the Caspian coastal region are as follow: Coastal Sand Dunes Sand dunes are one of the prominent features along he coastal regions of Mazandaran and Gilan, some as high as 20 meters. These dunes are made of small sandy particles and fragments of shells and are parallel to the seashore. Occasionally these parallel dunes are translocated by wind blows and affect the shorelines. Distribution of these dunes are more prevalent in the eastern part of the coastline. Coastal Sediments These sediments constitute the upper parts of the coastline (Supratidal) and are generally made of uniform sand particles (like Anzali beach), which favor the bathers and swimmers who come to the region for this purpose. Deltatic Sediments These sediments are formed at the river mouth, where they flow into the sea and are distinguished by their triangular shape. Since they are formed in the gentle slope, they are usually made of uniform particles. The most important delta in the Caspian Sea is the Sefid-rood Delta, which forms a vast coastal plain in the southeastern region of the Caspian Sea. Sediments of this delta are carried up to 5 km into the sea. The terrestrial part of this delta forms an asymmetrical delta on which small harbour of Kiashahr is situated. Vast areas of this delta consist of paddy fields. Wetland Sediments These include sediments associated with the Caspian Sea wetlands having an average depth of 5 meters. The two major areas are the Anzali wetland and the Gorgan Bay. The sediments of these areas mainly consist of silt and clay grains associated with high amount of organic matter originating from the lush vegetative growth. Marine Sediments There is a special pattern in the distribution of particles types and depths of sediments in the Caspian Sea. In the Southern Caspian, which is also the deepest part of the sea, silt and clay with some carbonates cover a major part of the deep sea floor. Fine sand on the other hand, covers the shallower parts; where as sand and silty sediments cover the floor of bays and estuaries (map 2). Almost 50 % of the sea floor with depth of more than 50 meters in southern and central parts are covered by fine particles of silt and clay, while in the rest of the sea floor in the shallower parts, sand and silt are prevalent. The carbonate compounds are more or less found in all sediments of middle southern Caspian region. B. Coastal Topography and Erosion The slope of the Southern Caspian Sea varies in different parts of the shoreline. Considering the coastal land slopes from the land towards the sea starting from Astara in the west to Gomishan-tappeh in the east, the beaches can be grouped into three major types:
Most of the beaches with high and moderate slopes are sandy, mixed with coarse or medium gray sand and the waves can easily disperse them. Beaches type 1 and 2 are subject to erosion. Most of these types of beaches are located in the west (Astara to the west or Bandar-e-Anzali), and in the middle parts (east of Sefid-rood estuary to the west of Bandar-e-Gaz) of Caspian coastline. C. Mineral Resources There are two major types of mines present in the Caspian region, sodium sulfate and hydrocarbon. Both reserves are being utilized commercially in some parts. The sodium sulfate mine is in Qara-Boghaz Bay, which is situated, in the central part of the eastern coastline. According to the latest data, the continental shelf’s hydrocarbon resources of the Caspian Sea is one of the largest in the world and it is estimated that there are more than 40 billion barrels of oil under the sea floor. The exploration for offshore oil in Iranian Caspian waters started in 1980 and since then, a number of 16 exploration wells have been drilled in the eastern, middle and western part of the shelf. So far, none of these wells have encountered oil, but a few have shown signs of gas. In the past, sand mining was common throughout the shoreline, but it was prohibited by law due to its environmental hazards, but at present sand mining along the rivers is developing extensively, and adversely affecting both the riverine and the marine ecosystems. |
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