SEA LEVEL-RELATED COASTAL CHANGES IN EASTERN AND SOUTHEASTERN SRI LANKA

The 2004 Indian Ocean Tsunami devastated Southeast Asia and Sri Lanka in particular. Following the 2004 event, worldwide tsunami scientists recognized the need for identifying stratigraphic signatures of paleo-tsunami events in the area and to develop a regional tsunami chronology. This project carried out detailed down core sediment profiling at 1 cm resolution to recognize the signatures of paleo-coastal environmental change, to differentiate them from the regional record of tsunami deposits. This provides valuable information on both coastal hazards and climate change in Sri Lanka and the northern Indian Ocean.

XRF, visible reflectance, magnetic susceptibility and grain size analysis was employed to extract suitable paleo-environmental proxies from sediment derived from the tropical Precambrian crystalline terrain. Sites in eastern and southeastern Sri Lanka provide ideal locations for this study due to high rate of progradation and thus inflated sediment sections. Approximately 100 m of core were extracted along landward transects from nine lagoons, two swales, and one back barrier marsh along the prograding coastline. Bulk organic matter, wood, mollusk shells, and inorganic carbonate were used for AMS ¹⁴C dating.

The results suggest that key periods of transition in the coastal environment occurred in the mid-Holocene between 5200 years ago and 2500 years ago. Results indicate a sea level high-stand between 5200-4900 yrs BP subsequent to a short sea level low-stand. Gradual infilling of Kirinda estuary and Okanda lagoons initiated after sea level stabilization around 4900 yrs BP. Proxy evidence suggests the onset of a sea level regression after around 4500 yrs BP. These sea level variations correlate with reported events in regional records. Beach ridge development started after around 4900 yrs BP and intensified after around 2500 yrs BP.