STRATIGRAPHIC AND LITHOLOGIC CONTROLS ON POOL FORMATION IN A NORTHERN PEATLAND USING GROUND PENETRATING RADAR

Stratigraphic and lithologic controls on the processes leading to pool formation were examined in Caribou Bog, a 2200-hectare peatland in central Maine. Ground penetrating radar (GPR) studies indicate a close correlation between the location of pools within the bog and subsurface stratigraphy and lithology. GPR surveying along several pools and loosely consolidated Sphagnum filled wet depressions precisely defined peat thickness, an underlying organic-rich lake sediment interface, the glaciomarine interface, and elevated till surfaces. A maximum investigation depth of 10 m was achieved in this peatland. Direct verification of peat and lake sediment thickness, as well as sampling of the glaciomarine and till deposits, constrained the GPR interpretation. Abrupt thinning of lake sediment and glaciomarine clay, combined with the presence of elevated till surfaces, such that peat rests directly on till in some places, correlates with pool location. The geophysical data suggest that pools develop as primary features during peatland formation. In contrast GPR surveys along loosely consolidated Sphagnum filled wet depressions define a continuous sequence of underlying lake sediment and glaciomarine deposits with no presence of elevated till surfaces, suggesting a different formation as compared to pools. The presence of these features within the peatland may suggest later development after peatland formation (secondary features) resulting from changes in water table, peat accumulation and/or climatic controls.