CLAY MINERALOGY FINGERPRINTING OF SEDIMENTS DEPOSITED FROM TROPICAL STORM IRENE IN THE CONNECTICUT RIVER WATERSHED

Tropical Storm Irene caused major flooding and massive sediment transport through the Connecticut River watershed and unprecedented high sediment load through the Connecticut River. Flooding was especially severe in the Deerfield River and associated tributaries where landslides and scour mobilized large volumes of glacial sediment. Deposits from this storm have been found to be finer grained, enriched in potassium and depleted in zirconium relative to underlying sediment.

This study compares the clay mineralogy of known Irene sediment with clays extracted from upland till deposits. The <1 µm size fraction was separated by centrifugation and oriented samples were prepared for X-Ray Diffraction (XRD) analysis using the filter peel method. Samples were analyzed following air dried, ethylene glycol salvation, and heating to 350˚C and 550˚C. Samples of clay-rich Lower Till collected from sites in both the Deerfield and Westfield River watersheds were compared to samples from a sediment core from Keeney Cove, which is located off the Connecticut River near Hartford, CT.

The Keeney Cove core includes pre-Irene, Irene, and post-Irene sediment. Analysis of the Irene layer shows a suite of XRD peaks characterized by a sequence of peaks indicating the presence of chlorite/vermiculite, illite and kaolinite. The intensity of the 14Å peak is lower than that of the 7Å peak. This is distinctly different from both pre and post-Irene samples where the intensity of the 14Å peak is greater than that of the 7Å peak. Peak ratios in the Irene layer are similar to those found in the upland till while the pre- and post- Irene ratios suggest a more weathered source. This supports the idea that during Irene, upland sediment was delivered to the main stem of the Connecticut River and quickly moved through the channel to the sea. This is different from the normal flood where the flooding of the floodplain traps upland sediment preventing it from moving great distances downstream. Downstream sediment comes mainly from more weathered remobilized sediment and thus accounts for the clay mineral differences between the Irene and pre- and post-Irene