J. A. MacGregor, K. H. Kjaer, N. K. Larsen, T. Binder, A. A. Bjork, O. Eisen, M. A. Fahnestock, S. Funder, A. A. Garde, H. Haack, V. Helm, M. Houmark-Nielsen, K. K. Kjeldsen, S. A. Khan, H. Machguth, Iain McDonald, Mathieu Morlighem, J. Mouginot, J. D. Paden, T. E. Waight & 2 others
A rarely considered element of Arctic system change in the Pleistocene
is the possibility and consequences of any large high-latitude impact.
We report the discovery of a large impact crater hidden beneath Hiawatha
Glacier in northwest Greenland. From airborne radar surveys, we identify
a 31-kilometer-wide, circular bedrock depression beneath up to a
kilometer of ice. This depression has an elevated rim that cross-cuts
tributary subglacial channels and a subdued central uplift that appears
to be actively eroding. From ground investigations of the deglaciated
foreland, we identify overprinted structures within Precambrian bedrock
along the ice margin that strike tangent to the subglacial rim.
Glaciofluvial sediment from the largest river draining the crater
contains shocked quartz and other impact-related grains. Geochemical
analysis of this sediment indicates that the impactor was a fractionated
iron asteroid, which must have been more than a kilometer wide to
produce the identified crater. Radiostratigraphy of the ice in the
crater shows that the Holocene ice is continuous and conformable, but
all deeper and older ice appears to be debris-rich or heavily disturbed.
The age of this impact crater is presently unknown, but from our
geological and geophysical evidence, we conclude that it is unlikely to
predate the Pleistocene inception of the Greenland Ice Sheet.
|Journal||American Geophysical Union, Fall Meeting 2018|
|Publication status||E-pub ahead of print - 2019|