VARIATIONS IN CLAY MINERALOGY AS A PROXY FOR LATE PLEISTOCENE TO HOLOCENE CLIMATE CHANGE AT KAMPOOSA BOG, STOCKBRIDGE MASSACHUSETTS

Kampoosa Bog is a calcareous fen located near the town of Stockbridge in western Massachusetts. The bog lies within a 4.7km² watershed with 160m of relief, and is underlain by Paleozoic metamorphic rocks of the Stockbridge and Walloomsic formations. Rocks in these units include phyllites, schists and marble. Much of the bedrock is covered with a layer of glacial till deposited during the last glaciation. A radiocarbon date of 13,110 B.P. obtained near the bottom of the bog indicates continuous sedimentation since the retreat of continental ice. A 14m core was collected from the bog during the summer of 2003, using a modified Livingston Corer. Samples were split from the core at 5cm intervals and the <1µm size fraction was separated by centrifugation and used to prepare oriented samples for clay mineral analysis by the vacuum filtration method. Samples were x-rayed air-dried and after treatment with ethylene glycol and heating to 375°C.

Illite is present in all core samples while chlorite is present in most. These are detrital minerals derived directly from the erosion of the till and bedrock. Varying amounts of kaolinite, smectite and vermiculite also occur and were derived from weathering and soil formation processes. Kaolinite is most abundant in the lower 6m of the core while smectite occurs in several distinct zones. All clays were transported to the bog by small tributary streams.

Loss on ignition (LOI) data, show high organic carbon accumulation after the Mid Holocene thermal maximum. This represents the upper 7m of the Kampoosa core. Clays in the upper part of this section are poorly preserved with only illite present above the 5m depth. Clays are better preserved in the 5-7m zone with smectite present in a distinct 20cm thick zone centered at the 6.1m depth. LOI is low during the Younger Dryas and the clay assemblage is dominated by illite, chlorite and kaolinite. Below this depth, LOI remains low, but there are distinct variations in clay mineralogy with at least two zones where smectite is present. These smectite zones may represent relatively warm wet periods when weathering reactions within the watershed produced smectite. Radiocarbon dates suggest that these warm wet periods may correspond to the Allerod and Bolling chronozones.