Evidence for a Tsunamigenic Impact Event in the New York Metropolitan Area Approximately 2300 B.P.

Details Evidence for a Tsunamigenic Impact Event in the New York Metropolitan Area Approximately 2300 B.P. Evidence for a Tsunamigenic Impact Event in the New York Metropolitan Area Approximately 2300 B.P.

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p31a1381c&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P31A-1381

Mathematics

Logic

4564 Tsunamis And Storm Surges, 6022 Impact Phenomena (5420, 8136)

Scientific paper

Oceanic impacts are a growing source of concern for the scientific community. Though the Earth is ~70 percent covered with water, and logic would therefore dictate that ~70 percent of impacts occur in the oceans, scientific investigations have focused on continental events. This is in part due to the difficulties inherent in examining submarine impact structures. Oceanic impacts lack many of the known features of continental events; however, oceanic impacts, unlike their continental counterparts, produce catastrophic tsunami events that may be used to identify them. Recent discoveries point to a tsunami event that affected the New York metropolitan area approximately 2300 years ago (Goodbred et al. 2006). Here it is shown that impact ejecta found in the tsunami deposit layer indicate an oceanic impact as the source of the tsunami. The sharp resolution of the stratigraphic study of the cores suggests that the sediment containing the impact ejecta was deposited in a tsunami-like event, rather than reworking from an older event. Samples were taken from the layer in sediment cores CD01-01, CD01-02, SD30, and VM32-2 from the Hudson River. Layer thickness ranged from approximately half a meter in CD01-02 to four centimeters in VM32-2. Individual ejecta grains were identified through an examination of the tsunami layer samples with optical and electron microscopy, as well compositional analysis via energy dispersive X-ray spectroscopy. Carbon and aluminum silicate impact spherules were found in the samples. Also present in the samples were shock-metamorphosed phases of feldspar, ilmenite, and olivine exhibiting planar deformation features and shock lamellae consistent with studies of known impact ejecta. TEM studies of the spherules revealed the presence of associated hexagonal nanodiamonds, also known as lonsdaleite, which are uniquely related to shock formation. In addition, the New York area lacks the extreme seismic and volcanic activity that might produce similar results, leaving a hypervelocity bolide impact as the most likely source for the tsunami event and associated impact ejecta. As oceanic impacts pose a serious threat to coastal communities around the world, it is necessary to understand both their frequency and effects. It is hoped that this method of identifying an oceanic impact via the ejecta found in tsunami deposits will improve our understanding of submarine impact events. Citations Goodbred, S., Krentz, S. LoCicero, P., Nitsche, F., Carbotte, S., and A. Slagle. Evidence for a newly discovered 2300-year-old tsunami deposit from Long Island, New York. Eos Trans. AGU 87(53), Fall Meet. Suppl., Abstract OS43C-0681

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