Abstract

Tsunami deposits related to the 1929 Grand Banks earthquake and washover deposits related to the 1991 Halloween storm differ in their sedimentary characteristics and positions on the landscape. Regarding sedimentary characteristics, the tsunami deposits are composed of one to three subunits of massive to fining-upward, very coarse- to fine-grained sand, whereas the storm deposits consist of interbedded and laminated coarse-, medium-, and fine-grained sand, exhibiting delta foreset stratification and subhorizontal, planar stratification with channels. Regarding landscape position, the tsunami deposits occur up to 343 m inland, including landward of tidal ponds, and up to 6 m above mean sea level, as well as 3 m above the barrier-beach bars and related dunes; the wash-over deposits occur up to 94 m inland, immediately landward of barrier-beach bars and in adjacent tidal ponds, and up to 1.2 m above mean sea level but no higher than the barrier-beach bars. These observations compared with those from other studies form the basis of proposed criteria for distinguishing paleotsunami from paleostorm deposits in the geologic record. If paleotsunami deposits can be identified with confidence, they will contribute to assessment of tsunami and seismic hazards along the coast of eastern North America and elsewhere.

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