Evidence of Late Holocene shoreline progradation in the coast of Kerala, South India obtained from OSL dating of palaeo-beach ridges

• Beach ridges are located at the west coast of Kerala, south India.
• Ridge formation is between 5 and 3 ka in central Kerala.
• Primary sedimentary structures in beach ridges identify the wave-built facies.
• The height and age of sediment units at the wave-built to aeolian facies boundary show past sea level.
• Sea level was between 3.5 and 4.5 m above MSL and the shoreline was ~ 3 km inland at ~ 4 ka.

The luminescence chronology of beach ridges in the central part of Kerala along the west coast of India has been made for the first time in order to reconstruct past sea-level highstands and coastline progradation. Transitional boundaries between shoreface to foreshore and foreshore to dune (aeolian) environments were used as marker horizons for determining the palaeo-shoreline as well as sea-level indicators. The study presents the results of optically-stimulated luminescence (OSL) dating of sand samples collected from wave- and wind-built horizons derived from quartz using single aliquot regenerative dose (SAR) protocol. The OSL ages from most of the sites are consistent with each other, indicating a stage of coastline progradation between 3 and 5 ka and widespread beach ridge formation all along the west coast of Kerala during this period. The OSL ages of transition levels together with the elevation measured using differential global positioning system (DGPS) indicates that the sea level was between 3.5 and 4.5 m above present MSL during the Late Holocene period. It may also imply the emergence of the coast due to neo-tectonic activity as the sea-level curve for the east coast from reported ages indicates a mean elevation between 1.5 and 2.5 m. The ages are discussed in the light of reported events, such as sea-level changes, coastal geomorphology, hydrological variations and neo-tectonics.