TSUNAMI LAYERS IN THE HUDSON RIVER, NY -HOW MANY SEPARATE EVENTS?

We have now documented three types of tsunami event layers in the Hudson River. All of the tsunami layers are graded, with the finest and lightest sediment at the top. The tops of the layers contain pelagic open-ocean marine microfossils, often with coccoliths on their surfaces. Open ocean microfossils do not occur in typical Hudson River sediments deposited north of New York harbor. The layers contain wood and root fragments. The first layer (1A) is younger than 2498±35 B.P. in age. It contains vesicular aluminosilicate glass with minor Fe. The glass is typically red, white or black. We have found shocked ilmenite grains, micron wide ilmenite needles and aluminosilicate crystals of probable sillimanite. To our knowledge, sillimanite is not found in volcanic glass and may be a unique marker for some impact glass. This event dumped meters of glass bearing sediment. The second layer (1B) is circa 2500^±200 BP in age. The base of this tsunami layer is marked by a sedimentary unconformity, often coinciding with an abrupt change in sediment bulk density. This tsunami layer contains abundant carbon spherules. The spherules are less dense than water and must have been entrained into the layer during a rapid depositional event. The abundance of carbon spherules increases upward in the tsunami layer. This tsunami layer also contains impact ejecta. In core CD01-02, carbon spherules in the tsunami layer contain lonsdaleite, a hexagonal polymorph of diamond that is unique to impact ejecta and meteorites. In other cores, the lower part of the tsunami layer contains shock-deformed minerals: shocked ilmenite and plagioclase feldspar containing chevron-like deformed bands with internal kinks. The third tsunami event layer (2) is newly found and is older than layer 1A. It contains vesicular aluminosilicate glass that is white and black in color with a flat bottom. It also contains mixtures of Mn oxide and calcium carbonate that are black and white in color. In addition, it contains open ocean calcium carbonate fossils with a significant Mg content. We have never found a mixture of the three tsunami event layers at any one stratigraphic level in the 10 cores that we have examined. We require further geochronological and stratigraphic work to sort out the absolute ages and origin of these layers.