TY - JOUR
T1 - Pleistocene organic matter modified by the Hiawatha impact, northwest Greenland
AU - Garde, Adam A.
AU - Søndergaard, Anne Sofie
AU - Guvad, Carsten
AU - Dahl-Møller, Jette
AU - Nehrke, Gernot
AU - Sanei, Hamed
AU - Weikusat, Christian
AU - Funder, Svend
AU - Kjær, Kurt H.
AU - Larsen, Nicolaj Krog
N1 - Funding Information:
We sincerely thank Adrian Jones, Timmons Erick-son, two anonymous reviewers, Paula Lindgren, Anna Losiak, and Tod Waight for constructive and precise comments; Nynke Keulen for assistance with SEM imaging; and John Parnell for a Raman spectrograph of Inglefield Land reference graphite. This research was funded by the Carlsberg Foundation (Copenhagen, Denmark) and the Aarhus University Research Foundation (Denmark).
Publisher Copyright:
© 2020 Geological Society of America.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - The 31-km-wide Hiawatha impact crater was recently discovered under the ice sheet in northwest Greenland, but its age remains uncertain. Here we investigate solid organic matter found at the tip of the Hiawatha Glacier to determine its thermal degradation, provenance, and age, and hence a maximum age of the impact. Impactite grains of microbrecchia and shock-melted glass in glaciofluvial sand contain abundant dispersed carbon, and gravel-sized charcoal particles are common on the outwash plain in front of the crater. The organic matter is depleted in the thermally sensitive, labile bio-macromolecule protohydrocarbons. Pebble-sized lumps of lignite collected close to the sand sample consist largely of fragments of conifers such as Pinus or Picea, with greatly expanded cork cells and desiccation cracks which suggest rapid, heat-induced expansion and contraction. Pinus and Picea are today extinct from North Greenland but are known from late Pliocene deposits in the Canadian Arctic Archipelago and early Pleistocene deposits at Kap Kobenhavn in eastern North Greenland. The thermally degraded organic material yields a maximum age for the impact, providing the first firm evidence that the Hiawatha crater is the youngest known large impact structure on Earth.
AB - The 31-km-wide Hiawatha impact crater was recently discovered under the ice sheet in northwest Greenland, but its age remains uncertain. Here we investigate solid organic matter found at the tip of the Hiawatha Glacier to determine its thermal degradation, provenance, and age, and hence a maximum age of the impact. Impactite grains of microbrecchia and shock-melted glass in glaciofluvial sand contain abundant dispersed carbon, and gravel-sized charcoal particles are common on the outwash plain in front of the crater. The organic matter is depleted in the thermally sensitive, labile bio-macromolecule protohydrocarbons. Pebble-sized lumps of lignite collected close to the sand sample consist largely of fragments of conifers such as Pinus or Picea, with greatly expanded cork cells and desiccation cracks which suggest rapid, heat-induced expansion and contraction. Pinus and Picea are today extinct from North Greenland but are known from late Pliocene deposits in the Canadian Arctic Archipelago and early Pleistocene deposits at Kap Kobenhavn in eastern North Greenland. The thermally degraded organic material yields a maximum age for the impact, providing the first firm evidence that the Hiawatha crater is the youngest known large impact structure on Earth.
UR - http://www.scopus.com/inward/record.url?scp=85090563679&partnerID=8YFLogxK
U2 - 10.1130/G47432.1
DO - 10.1130/G47432.1
M3 - Article
AN - SCOPUS:85090563679
SN - 0091-7613
VL - 48
SP - 867
EP - 871
JO - Geology
JF - Geology
IS - 9
ER -