A SEDIMENT RECORD FROM A KETTLE BOG ON THE LAKE ESCARPMENT MORAINE, WESTERN NEW YORK

The Lake Escarpment Moraine is a recessional moraine in western New York (WNY) that formed as the Laurentide Ice Sheet (LIS) retreated from its Last Glacial Maximum position. There are few direct constraints on the timing of formation of this moraine, but correlation with other features suggests an age of ~16.9 ka. Recent work has hypothesized that a major readvance of the LIS overran this moraine from ~13 – 13.3 cal kyr BP. Here, we address this by analyzing a sediment record from a kettle bog on the Lake Escarpment Moraine. First, we collected a 6.8-m-long core from Little Protection Bog (42.621012, -78.463551) using a Livingstone piston corer to extract the post-glacial sediments, and a Geoprobe percussion corer to extend our record to the stiff, basal minerogenic sediments. We created a radiocarbon-based age-depth model using eight macrofossils. In addition, we measured loss-on-ignition and magnetic susceptibility to characterize the depositional environment. Finally, we calculated bulk density in the hypothesized interval of re-advance to look for signs of possible over-compaction from glacial overriding. The Geoprobe collected laminated sands and gravel. The Livingstone cores show a transition from wet gray clay to gray gyttja. Above the gray gyttja is crudely laminated brown/red gyttja, which underlies a fibrous peat. The base of the brown gyttja is ~13.8 cal kyr BP, however, there are inorganic lacustrine sediments beneath this lowest date; our age-model estimates lacustrine sedimentation began ~15.4 cal kyr BP. There is a 40% increase in organic matter around 13.8 cal kyr BP, which occurs during the Allerød period. The organic content continues to rise slowly until 10.8 cal kyr BP where it reaches 80%. The slow rise may be attributed to the cold Younger Dryas. Our data suggest that the glacier retreated prior to 13.8 cal kyr BP and does not support a readvance from 13 – 13.3 cal kyr BP. There is continuous deposition of lacustrine sediments and no over-compaction of the sediment through the hypothesized glacial overriding interval. The contact between lacustrine silt and fibrous peat dates 7.6 cal kyr BP, marking the time when the lake likely filled with sediment and lateral encroachment of vegetation around the perimeter shifted the lake to a bog.