Kelletat, D.H.

Abstract:

We present sediment cores from seven coastal geoarchives on Bonaire, southern Caribbean, containing layers of high- energy sedimentation. Tsunami deposition is inferred for some layers based on the presence of allochthonous reefal shells including articulated specimens and a high percentage of angular fragments, planktonic foraminiferal taxa and those from the deeper shelf (below storm wave base), basal unconformities and hiatuses of >1000 a, rip-up clasts, thin depositional sequences comprising basal traction carpets overlain by normally graded sand, a proximal sediment source (littoral) in the lower part of the deposit and a broad mixture (littoral, shelfal, terrestrial) in the upper part, and the lack of deposition during recent hurricane flooding. Several tsunami layers were precisely dated to 3300-3100 cal BP, whereas the record of further candidate tsunamis is more disjunct. Additional tsunami evidence is provided by the largest coastal boulders (up to 150 t; a-axis up to 10 m). 

Abstract:

A sediment record of three alluvial sites along the east- and northeast-oriented shore of Bonaire (Netherlands Antilles) provides evidence for the recurrence of several extraordinary wave impacts during the Holocene. The interpretation of onshore high-energy wave deposits is controversially discussed in recent sedimentary research. However, it represents a powerful tool to evaluate the hazard of tsunami and severe storms where historical documentation is short and/or fragmentary. A facies model was established based on sedimentary and geochemical characteristics as well as the assemblage and state of preservation of shells and shell fragments. Radiocarbon data and the comparison of the facies model with both recent local hurricane deposits and global “tsunami signature types” point to the occurrence of three major wave events around 3300, 2000–1700 and shortly before 500 BP. Since (i) the stratigraphically correlated sand layers fulfill several sedimentary characteristics commonly associated with tsunamis and (ii) modern strong hurricanes left only little or even no sediment in the study areas, they were interpreted as tsunamigenic. However, surges largely exceeding the energy of those accompanying modern hurricanes in the southern Caribbean cannot entirely be ruled out. The results are partially consistent with existing chronologies for Holocene extreme wave events deduced from supralittoral coarse-clast deposits on Aruba, Bonaire and Curaçao as well as overwash sediments from Cayo Sal, Venezuela.