GEOLOGICAL EVOLUTION OF THE SEFIDRUD DELTA, SOUTHERN CASPIAN SEA, IRAN

The Sefidrud delta is a large, wave-dominated clastic sediment prism associated with wide beach ridges, coastal dunes, lagoonal and related sediments in the southern Caspian Sea, Iran. It has been formed by the River Sefidrud which has a drainage area of 61300 km² covering nearly whole tectonically active Albroz mountain ranges and partly central Iran. This river is the largest sediment source of the Caspian Sea compared to drainage area, water and sediment discharge with 5.2 million ton a year. At present, surface of subaerial delta plain and coastal length of the delta are 1405 km⁵ and 91 km respectively. Progradation is about 65 km, despite active delta lobe has prograded 5 km in the last 500 years. The receiving basin, southern Caspian Sea is highly energetic because of regional geography, therefore coastal deposits included the Sefidrud delta are composed of wave-dominated clastic facies. In addition, Caspian Sea has a regular, long-time water fluctuation with 400-450 years of period. The marine terraces of Gilan-Anzali coastal plain at 50 m, 20 m and 0 m (present water surface elevation of Caspian Sea is -26 m bsl) and fluvial terraces at 150 m prove the long-term sea-level oscillation in late Plesitocene. Therefore, the Sefidrud delta has been developed during repetitive transgressive and regressive coastal conditions. Indeed, the Sefidrud delta is a unique example of sediment accumulation under joint and complex effects of active tectonism, high volume of sediment input, long-term water-level oscillation and high wave energy. This study aims to explain evolution of the Sefidrud delta based on geology, facies analysis and core logs.