Subsurface reflections of prograded paleoscarps in avis Island, North Andaman, India

Prominent subsurface reflections from two GPR transect marked four lithological anomalies below Avis Island coral reefs. These scarps dip 5-10° towards sea and they consist of sands with more than 30-40% heavy mineral concentrations that produce distinct subsurface reflections that make possible to locate the buried erosional scarps. Heavy minerals are considered as the indicators of erosion as well as a proxy for sediment transport of extreme wave events. Heavy minerals including magnetite have higher magnetic susceptibility values: L1a:°644.6; °L1b:°556.8, L2a: 584.2 and L2b: 612×10-5°SI units to the background magnetic susceptibility of 5-10×10-5°SI units for quartz-rich sands suggest severe reworking process during an extreme wave event. The two profiles (L1 and L2) with four paleoscarps: L1a at a distance of 10 m from the shore, L2a approximately 15 m from the shore, L2b around 30 m from the shore and L1b nearly 35 m from the shore and the corresponding age of the dated coral above the paleoscarps increases towards land exhibiting progradation sequence. These subsurface reflections of paleoscarps were found at a depth of 1-1.5 m below the ground surface beneath the reported age of coral reefs suggesting that these coral reefs and the paleoscarps are found due to the same event.