Evidence for late Holocene highstands in Central Guilan–East Mazanderan, South Caspian coast, Iran

The Iranian Caspian coast in the central Guilan and east Mazanderan were investigated using the analysis of samples retrieved from outcrops, cores and through geophysical campaign. The analysis of particle size, organic matter, calcium carbonate, and fossil content as well as radiometric dating extends the Caspian Sea-level records through the latest Holocene, ca. 2500 years. Ground-penetrating radar provides information about the internal stratigraphy of exposures along the central Guilan coast. Lagoonal sediments that contained Caspian mollusc shells have been dated at 2500, 900 and 500 BP. Their dated horizons are located at altitudes of −22, −24 and −25 m, respectively, which indicate higher sea-levels during the late Holocene. The internal architecture and morphology of the coastal areas demonstrate spit–lagoon development through littoral drift on the central Guilan and east Mazanderan coasts. These structures also indicate lagoon formation due to rapid sea-level rise. A wide shallow lagoon in the central Guilan (Sefidrud) area was formed due to the last sea-level rise (500 BP). This lagoon then dried up as the result of falling sea-level and infilled due to diversion of the Sefidrud course. These coastal developments show three highstands during the last 2500 years.