Occurrence of soft sediment deformation at Dive Agar beach, west coast of India: possible record of the Indian Ocean tsunami (2004)

We describe here a sequence of soft sediment deformation (SSD) structures at Dive Agar beach near Srivardhan in the west coast of India. The ~120-cm-thick sediment package is represented by a basal undeformed sand (layer A) sharply cut by ~30-cm-thick intermixed beach sand and terrigenous sand (layer B1) followed by complex load structures and convolutions (8?C15?cm) within a coarse sandy layer (B2). The layer B2 is scoured by terrigenous sand (layer C1) which is capped with a silty mud layer (C2). The entire sequence (B2?CC1?CC2) is intruded by sand dykes originating from the lower layer B1. This sediment package is further overlain by a heavy mineral reach marine sand (layer D) with liquefactions long axes inclined southward as a result of forceful long-shore drift. The profile ends up with coarse-grained, poorly sorted sand including angular clasts of terrigenous outwash deposits indicating return of distal inundations. Intense deformation (liquefaction) is restricted to the heavy mineral-rich marine and the intermixed sands (layers B2 and D), whereas the terrigenous sand layers show scoured bases with oscillatory and pebbly tops. The presence of complex load structures injecting into the underlying layers, the top-truncated sand dykes, macro-thrust faults, scouring, and inclusion of coral fragments can explain it as a record of tsunami in the west coast. Occurrence of un-decayed consumer plastic material within the deformed layers suggests it as one of the most recent tsunami events (i.e., 2004 IOT), the only reported event after 1945 in the west coast. Alternative marine and terrigenous sands are characteristic of tsunami run-up and backwash deposits, while the dimensions of SSDs may be related to the <2?m magnitude (height) of the 2004 IOT at Dive Agar.