Palaeogeography and evolution of the Godavari delta, east coast of India during the Holocene: An example of wave-dominated and fan-delta settings

We investigated the Holocene evolution of the Godavari delta along the east coast of India, by analyses of landforms and 11 borehole cores collected from the delta plain during 2010-2013 with 113 14C dates. The Godavari delta covering an area of 5820 km2 is one of the world's largest wave-dominated deltas fringed by a ~ 30 km wide beach-ridge plain. Our analysis of sediment facies and their ages indicated that the Holocene marine sequence thickens seaward from ~ 10 m to more than 50 m and that the local relative sea level rapidly rose from 43.5 m to 7.5 m below the present sea level during 10.9-8.0 cal ky BP followed by a slow rise up to its current level around 5 cal ky BP. Spatio-temporal variations in sediment accumulation rates and palaeo-shorelines for the last 6 ky revealed successive changes of the main depocentre (delta lobe). We recognised six stages of delta evolution with distinct cyclic shifts of delta lobes controlled by avulsions. A linear beach ridge located 12-14 km inland from the present shoreline, which separates the first three lobes from the last three, represents the effect of coastal erosion of past cuspate delta lobes, as does the current linear shoreline of the central part of the delta. Our study documents continuous net progradation during the Holocene on millennial to centennial time scales. However, a considerable decrease of sediment discharge due to dam construction and water diversion since the 1970s has exacerbated coastal erosion, resulting in shrinking of the Godavari delta plain and tipping it into a persistent destruction phase.