Abstract:
Following the line of approach enumerated in the tsunami toolkit of Chagué-Goff et al. (2011), ‘Expanding the
proxy toolkit to help identify past events - Lessons from the 2004 Indian Ocean Tsunami and the 2009 South
Pacific Tsunami, Earth Sci. Rev. 107 (1–2), 107–122’, measurements of elemental and mineral magnetic properties
coupled with textural parameters have been used to evaluate the 2004 Indian Ocean Tsunami (IOT)
induced sediments on the Muttukadu backwaters, East Coast of India. To investigate the sediment provenance,
specific Fe, Mn and Pb elemental concentrations were measured in surface sediments and compared with the
previously published pre-tsunami database of backwater/inner continental shelf sediments. We found the enrichment
of Fe and Pb, against depletion of Mn concentration in present tsunami sediments as compared with
pre-tsunami Muttukadu sediments, reflecting the variation of the sediment source area. However, the present
data of Fe and Pb enrichment and Mn depletion correlates well with continental shelf sediments hinting at
sedimentary routes, processes of erosion and wave propagation. The studied tsunami deposits are characterized
by dominant ∼40–85% coarse sand fractions and higher proportion of detrital low and high coercivity Fe-Ti
oxides, such as magnetite, titanomagnetite and hematite, reflected by magnetic concentration (magnetic susceptibility
(χ), anhysteretic remanent magnetization (ARM)) and coercivity-dependent parameters (soft isothermal
remanent magnetization (Soft IRM), Hard IRM, magnetomineralogical S-Ratio and saturation IRM
(SIRM)). So, it can be shown that the random spatial variability and the inverse relationship between magnetic
concentration χ, ARM and SIRM parameters and grain-size ARM/χ, SIRM/χ and ARM/SIRM ratios as diagnostic
criteria for the tsunami impacted the distribution of magnetic parameters in coastal backwater environments.
Contrasting mineral magnetic and geochemical properties together with more sand (mean 65%) when compared
with silt (mean 25%) content in tsunami sediments indicates that the area was affected by high-energy tsunami
waves. The study validates environmental magnetism as a proxy, which is fast and robust for identifying the
tsunami or palaeotsunami deposits.
