Holocene evolution and Anthropocene destruction of the Krishna Delta on the east coast of India: Delta lobe shifts, human impacts, and sea-level history

The Holocene evolution of the Krishna Delta was inferred using landform characteristics and 11 sediment cores with 59 Accelerator Mass Spectrometry ¹⁴C dates. The landform assemblages in a 5880 km² area of the Krishna Delta indicate an upper (landward) river-built fluvial plain and a lower (seaward) marine-built beach-ridge plain. Holocene sediment unconformably overlying a Pleistocene basement consists of 11 sedimentary facies, mainly shallowing-upward and deltaic succession. Sea level indicators such as the basal mangrove peat layers above the Pleistocene basement and the foreshore sediments indicate that the sea level rose from −9 m to −3 m during 8.3–6.3 cal ky BP, and stabilised at the present level around 5 cal ky BP. The 3539 km² area of the Krishna Delta beach-ridge plain developed in five major stages during the last 6 cal ky, with distinct lateral and seaward migration of delta lobes (depocentre shifts). Delta progradation accelerated in the last 500 years, forming an out-building lobate delta. However, predominant erosion along the sediment-starved coast during the past five decades, due to impoundment of riverine inputs at the burgeoning upstream dams, has pushed the Krishna Delta into a persistent destruction phase.