AN INVESTIGATION OF POTENTIAL PINGO REMNANTS IN THE SOUTHERN CONNECTICUT VALLEY

We analyzed a group of 42 scattered depressions covering approximately 140,000 m² in the Wintergreen Woods in Wethersfield to test their possible origin as a pingo field. The small ponds are located on the lake bed of former glacial lake Hitchcock and developed in Elmridge fine sandy loam and Berlin silt loam. High-resolution GPS was used to map these features. The resulting map showed no regular distribution or size pattern and the size of the depressions ranged between 150 - 5000 m². We retrieved five piston cores from one of the larger, water filled depressions and established a cross-section through the pond sediments which was combined with the results of two soil cores taken nearby. The sediment cores are approximately 3 - 4.5 m long and consist of massive brown silt overlying pink varved glaciolacustrine clay-rich sediments. XRD analyses show that the lake sediments are similar to sediment from glacial lake Hitchcock. A, yet undated, spruce cone remnant found in one of the cores attests to a minimum age > 10 ka, based on the regional pollen record, which is consistent with the age of similar depressions found within the Connecticut valley. The great depth of these relatively small depressions, their estimated age and similarity to existing pingo fields elsewhere as well as their clastic sediment fill suggests a periglacial origin. Their position on the lake bed of former glacial lake Hitchcock implies the existence of severe permafrost in central Connecticut while most of new England was already deglaciated and the laurentide ice margin was located approximately 200 km to the north.