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GEOLOGY ON ICE: Gauging the Age of Ice Ages in New York State

How do scientists determine the age or timing in which the glaciers retreated from New York State during the last Ice Age?

For several decades, geologists working in New York State have been searching for clues to accurately understand the timing of the most recent Ice Age (New York has likely had 20 + glaciations). However, chronologic data used to understand the time and location of retreating glacial margins has been elusive or, at least, not readily available. In the past, organic materials such as bone, wood or peat was radiocarbon dated and provided some crude ideas of timing. However, recent advances in radiocarbon dating are helping scientists by providing more precise data to constrain the timing of deglaciation (see also publication: New AMS Radiocarbon Dates from Late Pleistocene Mastodons and Mammoths in New York State, USA).

Scientists use a variety of techniques to understand the Ice Ages. One technique involves examining elevation models of the landscape to determine locations where the glaciers stopped. Such locations often build a ridge perpendicular to the direction of glacier movement known as a moraine. Long Island and Cape Cod are big moraines; most moraines are smaller and more subtle. Geologists who specialize in the study of landforms created by glaciers (geomorphologists) can recognize the topographic patterns of moraines.

Of particular importance are locations where a modern lake formed near or behind a former moraine (ice margin). These are important because the lake that forms acts like a trap and time capsule. As soon as the lake forms it begins to collect sediment, typically from rain runoff from nearby areas that are higher. In this sediment is material such as twigs, leaves, insects and pollen.

Geologists and other scientists brave the cold of winter time and go out on the ice of the frozen lake and collect cores of the layers of sediment that have accumulated in the lake since it formed. The goal is to find a leaf or twig that washed into the lake after the glacier melted. These materials can then be dated. The current dating techniques (i.e., AMS- radiocarbon dating) provide dates within a decade or so of when that lake formed, and thus, indicate when the glacier left that location.

METHOD:

Geologists from the NYSGS in the State Museum ventured out in January 2013 to Lawson Lake in southwestern Albany County to core the bottom sediments of the lake. Weathering biting winds with a windchill of -5 degrees Fahrenheit, they collected two sediment cores for a total depth of 14 meters using a Livingstone Coring device and also completed a ground penetrating radar (GPR) survey to measure the basin depth and layers of sediment.

Once collected, the cores were brought back to the Geological Sciences Sediment laboratory in the NYSM and cut in half, described, photographed and broken up into 10 cm intervals for sieve analyses. Using a number 45 sieve, geologists carefully sifted out the ancient muds looking for organic remnants, such as plants, sticks, seeds and insects.

Once rinsed, geologists picked out several specimens of terrestrial wood and plants and sent them off to have radiocarbon dating performed.

 

Treasures extracted from the Lawson Lake Core:
Pieces of wood twigs from a conifer tree, plant seeds, pine needles, and insects.

 

twig seed needle insect


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