C53C-0334:
Further Investigations of Cosmogenic Ne-21 Exposure Ages of Glacial Boulders Constrained by Local Bedrock Erosion Rates in Ong Valley, Antarctica
Friday, 19 December 2014
Carson Paige Hedberg1, Daniel J Morgan2, Josh Cox1, Greg Balco3, Jaakko Putkonen4 and Theodore Bibby5, (1)Vanderbilt University, Nashville, TN, United States, (2)Vanderbilt University, Earth and Environmental Sciences, Nashville, TN, United States, (3)Berkeley Geochronology Center, Berkeley, CA, United States, (4)University of North Dakota, Harold Hamm School of Geology and Geological Engineering, Grand Forks, ND, United States, (5)University of North Dakota, Grand Forks, ND, United States
Abstract:
A history of glaciation can be tracked by determining the exposure age of boulders found in glacial drifts using the concentration of the cosmogenic nuclide Ne-21. In order to calculate exposure age, the erosion rate and previous exposure must be taken into consideration. In this study, we measured cosmogenic Ne-21 concentrations in quartz from samples of bedrock and samples taken from distinct glacial drifts in Antarctica. We determined the erosion rate using the concentrations of Ne-21 in the bedrock and then used this rate to calculate the exposure ages of the samples taken from the glacial drifts. The samples were collected from the Ong Valley, Antarctica (157.5 East, 83.25 South), an ice-free valley in the Miller Range of the Central Transantarctic Mountains that contains three distinct glacial drifts. We analyzed samples from the oldest and the youngest of these drifts, from moraines from a small alpine glacier to the east of the main valley, and from the surrounding bedrock of the valley walls above the glacial limit. The average erosion rate we calculated was 23 cm/Myrs. The six samples from the oldest glacial drift have an average exposure age of 2.1 Myrs, but have a range of 4.4 Myrs. The exposure age of samples from the middle of the youngest drift on the valley floor average 90.1 kyrs, with a range of 13.4 kyrs. Samples from a lateral moraine of this youngest drift have an average exposure age of 145 kyrs, with a range of 134 kyrs. The 7 samples taken from the alpine glacier east of Ong Valley have an average age of 1.10 Myrs, but a range of 3.87 Myrs. The high variability in ages among samples from the same glacial drift arises from prior exposure and postdepositional movement of the rocks.
