Development of spit–lagoon complexes in response to Little Ice Age rapid sea-level changes in the central Guilan coast, South Caspian Sea, Iran

The central Guilan coast along the Iranian Caspian coastline is characterized by sandy beaches and the development of spit–lagoon complexes, which are prone to preserve past sea-level fluctuations. The morphology of three spit–lagoon complexes along the central Guilan coast was studied using ground penetrating radar (GPR) and sediment sequences to understand the effects of past sea-level changes on spit–lagoon development. The results showed the prominent role of coastal setting in conditioning the development of spit–lagoon formation in response to sea-level change. When the Caspian Sea experienced a highstand in the Little Ice Age, the coast of central Guilan recorded fluctuations in sedimentation which are reflected, for example, by river avulsion and beach ridge formation depending on physical setting. In the western half of the central Guilan, eastward longshore currents and strong wave action on a W–E coastline coupled with sea-level changes shaped the Anzali spit–lagoon complex; while in the eastern part of the studied area river avulsion and changing the coastline orientation are responsible for development of the Amirkola and Kiashahr spit–lagoon complexes under the same sea-level fluctuations. Although sea-level change has a major role in spit–lagoon development, an increase in the frequency of storms, changes in sediment supply due to more precipitation, and river avulsion are other players in spit–lagoon development in the central Guilan during the Little Ice Age and more recent times.