TO WHAT EXTENT ARE CATASTROPHIC AND ENVIRONMENTAL EVENTS USEFUL STRATIGRAPHIC MARKERS FOR DATING THE HUDSON RIVER: THE IMPACT OF MANGANESE CYCLING, THE PEEKSKILL METEORITE AND ZEBRA MUSSELS?

Given the difficulty in dating the Hudson River through radiocarbon dating, this paper studies the efficacy of using significant environmental events as stratigraphic markers. The environmental impacts of manganese cycles, zebra mussels, and/or the Peekskill meteorite were observed in Hudson River cores CDO2-29, LWB1-8, LWB3-44, and LWB4-5. The manganese cycles are a yearly occurrence, during which the Mn content is higher in the spring than it is in the fall. Using an ITRAX XRF scan we identified where the peaks in Mn were to determine the years along the core. We found that for core LWB3-44 sediments at 7.4 cm were deposited in 1992, for LWB4-5 1992 was 9.6 cm. Manganese peaks allows researchers to quickly date along the core, within 1 year in the last 65 years. Along with determining the correlation of Mn derived dates with two environmental events, we will check the inferred dates, against the proven method of Cs dating.

The Peekskill meteorite landed on October 9^th, 1992. We found a core (LWB4-5) that was taken within 0.75 km of the projected track of the meteorite over the Hudson River, with the highest magnetic susceptibilities we observed in a Hudson core. Core LWB4-5 had a high magnetic susceptibility reading at 11cm that occurred around 1991. The high magnetic susceptibilities continue down to 31 cm depth, the location of a possible large fragment of the Peekskill meteorite. Using an event that only affects the already deposited sediments is useful in areas that are difficult to date, although it does not offer detail beyond an inferred boundary date. Conversely, we hypothesized that the zebra mussel invasion of the Hudson in 1991/1992 would change the composition of Hudson River sediments deposited afterwards. Papers have stated that after the zebra mussel invasion, the overall population of diatoms and photosynthetic microplankton decreased, we can also assume that this would lead to a decrease in organic matter content, calcium carbonate and biogenic silica. Organic matter content and CaCO₃ was found using LOI and a coulometer. The paper hoped to find a significant decrease in both indicators after 1992. While this was not the case, work on the biogenic silica content of the sediments at the 1991/1992 interface is in progress and will be reported at the meeting.