Foraminiferal evidence of submarine sediment transport and deposition by backwash during the 2004 Indian Ocean tsunami |
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| Authors: | Daisuke Sugawara Koji Minoura Naoki Nemoto Shinji Tsukawaki Kazuhisa Goto and Fumihiko Imamura |
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| Institution: | Institute of Geology and Paleontology, Graduate School of Science, Tohoku University, Aoba-ku, Aramaki, Sendai 980-8578, Japan (email: ),;Graduate School of Science and Technology, Hirosaki University, Bunkyo-cho, Hirosaki 036-8561, Japan,;Division of Eco-Technology, Institute of Nature and Environmental Technology, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan, and;Disaster Control Research Center, Graduate School of Engineering, Tohoku University, Aoba-ku, Aramaki, Sendai 980-8579, Japan |
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| Abstract: | Micropaleontological analysis of nearshore to offshore sediments recovered from the southwestern coast of Thailand was performed to clarify the submarine processes of sediment transport and deposition during the 2004 Indian Ocean tsunami. The distribution pattern of benthic foraminifers showed seaward migration after the tsunami event. Agglutinated foraminifers, which are characteristic of an intertidal brackish environment, were identified in the post-tsunami samples from foreshore to offshore zones. These suggest that sediments originally distributed in foreshore to nearshore zones were transported offshore due to the tsunami backwash. On the other hand, the distribution pattern of planktonic and benthic species living in offshore zones showed slight evidence of landward migration by the tsunami. This suggests that landward redistribution of sediments by the tsunami run-up did not occur in the offshore seafloor of the study area. Our results and a review of previous studies provide an interpretation of submarine sedimentation by tsunamis. It is possible that tsunami backwashes induce sediment flows that transport a large amount of coastal materials seaward. Thus, traces of paleotsunami backwashes can be identified in offshore sedimentary environments as the accumulation of allochthonous materials. This can be recognized as changes in benthic foraminiferal assemblages. |
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| Keywords: | backwash foraminifer sediment flow 2004 Indian Ocean tsunami 2004 Sumatra–Andaman earthquake |
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