HR: 17:05h
AN: T24A-04    [Abstracts]
TI: A multi-proxy approach to tsunami deposit characterization: searching wetlands and lagoons at the Mexican Pacific coast for a record of tsunami inundations
AU: * Ramirez-Herrera, M
EM: mtramirez@berkeley.edu
AF: University of California Berkeley, Department of Geography, 107 McCone Hall, Berkeley, CA 94720-4740, United States
AU: Cundy, A
AF: School of the Environment, University of Brighton, Lewes Road, Brighton, BN2 4GJ, United Kingdom
AU: Kostoglodov, V
AF: Instituto de Geofisica, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Coyoacan, Mexico, D.F., 04510, Mexico
AU: Carranza-Edwards, A
AF: Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico, D.F., 04510, Mexico
AU: Morales, E
AF: Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico, D.F., 04510, Mexico
AU: Metcalfe, S
AF: School of Geography University of Nottingham, Nottingham, Nottingham, NG7 2RD, United Kingdom
AB: It is extremely important to integrate historic accounts with geologic evidence of past tsunamis to fully understand hazards to the highly populated Mexican coast. We aim to complete a record of tsunami events using a multi- proxy approach to identify tsunami deposits recovered from marsh lagoonal sediments on the Guerrero coast of Mexico. Core samples from nine study sites on tropical wetlands show distinct stratigraphic changes with depth, indicating clear rapid change in depositional environments over time. Core sequences recovered include evidence of land level changes and three probable tsunamis based on stratigraphic, granulometric, geochemical, and microfossil analysis (diatoms and pollen) of marsh sediments. Radiocarbon data indicate that the sediment units cored are up to ca. 6161+/- 53 yr BP. A probable tsunami event and coseismic subsidence dates back at 3800 yr BP. Discrete sand units fining up show sharp erosional contacts at the base, medium to poor sorting, fine to coarse sand, with clay/mud rip-up clasts. However, traces of these apparent tsunami deposits are not extensive over a large area and we could not correlate them from one site to another. We hypothesize that the distribution and preservation of tsunami deposits in these tropical lagoonal marshes and wetlands might be controlled by mangrove vegetation fringing coastal lagoons and estuaries. Recent observations after the 2004 Indian Ocean tsunami showed that mangroves may dissipate tsunami energy and result in flumed-shape sediment deposition. If this is the case, finding tsunami deposits over extensive areas in mangrove marshes and wetlands would prove very challenging.
DE: 3022 Marine sediments: processes and transport
DE: 4217 Coastal processes
DE: 4564 Tsunamis and storm surges
DE: 7221 Paleoseismology (8036)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly