Palaeo-tsunami in the southern Caribbean: clarity through new geological archives?

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Engel, M, Bruckner, H, Messenzehl, K, Frenzel, P, Wennrich, V, May, SM, Daut, G, Willershauser, T, Scheffers, A, Scheffers, S, Vott, A & Kelletat, D 2010, 'Palaeo-tsunami in the southern Caribbean: clarity through new geological archives?', paper presented to American Geophysical Union, Fall Meeting 2010, San Fransisco, USA, 13-17 December.


A general lack of accounts of palaeo-tsunami deposits in back barrier environments throughout the Caribbean and diverging and conflicting interpretation of onshore coarse-clast deposits and landforms on the Leeward Netherlands Antilles (Bonaire, Curaçao, Aruba) encouraged the investigation of coastal stratigraphies along the coast of Bonaire. This work was conducted in order to (i) identify overwash deposits and reconstruct the regional history of high-energy wave events and (ii) provide a scientific basis for local hazard assessment. Vibracores and push cores at the windward (Playa Grandi, Lagun) and leeward coast (Saliña Tam, Klein Bonaire) were analyzed in terms of sedimentary characteristics, geochemical composition and fossil content. The coring sites in exposure to wave energy, foreshore morphology, sediment budgets, relief gradient and vegetation cover. Accordingly the pattern of subsurface overwash deposits varies significantly from site to site depending on exposure direction. For instance, although a prominent layer of sand and shell debris identified at the Lagun embayment (2000-1700 BP) has a counterpart at the sheltered lagoon of Saliña Tam, it is obviously absent at the northern coast. Along the entire island major layers of extreme wave deposits were radiocarbon dated to around 3300 BP, 2000-1700 BP and >500 BP. Sedimentary characteristics, bedforms and geochemical signatures did not provide unequivocal evidence for either tsunami or hurricane storm surge. However, evidence from the taphonomic characteristics of mollusc shells (articulation, fragmentation, rounding, encrustations, abrasion/dissolution) found within candidate coarse sediment layers and by comparison with the marginal sediment input of recent category 4/5 hurricane storm surges, the deposits were classified as representatives for palaeo-tsunami events.