Impactites from the Hiawatha crater, North-West Greenland

• Main Author: Gustafsson, Jacob
• Format: Bachelor Thesis
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2020
• Subjects: Hiawatha; impact crater; Cape York; Baffin Bay; Greenland Ice Sheet; Younger Dryas; meteorite; impactite; organic carbon; conifer; vitrinite reflectance; Ro; cellular texture; chromite; chromium isotope; toasted quartz; ballen quartz; melted carbonate; granular zircon; planar deformation feature; Geology; Geologi; Ballen; Greenland; Baffin; Ice Sheet
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-187412

The recent discovery of the 31-km-wide Hiawatha impact crater has raised unanswered questions about its age, impactor and highly unusual organic carbon component. Previous research suggests a fractionated iron meteorite impactor, a probable maximum 3–2.4 Ma impact age and a possible Younger Dryas impact age. The first objective in this study has been to investigate a possible link between the Cape York meteorites and the Hiawatha impact crater by comparing the chromium isotopic signature in chromite from a Cape York meteorite with the chromium isotopic signature in potential chromite from the Hiawatha impactor. The second objective has been to investigate a possible Hiawatha signature in the Younger Dryas deposits from Baffin Bay. The third objective has been to study the organic carbon component in impactites derived from the Hiawatha impact crater. Heavy mineral grains were separated from glaciofluvial sediment which contains Hiawatha impactite grains. Not a single chromite grain was found and the possible link to the Cape York meteorites could not be tested. The petrographic examination of Younger Dryas marine deposits resulted in absence of impact-related Hiawatha grains. A petrological investigation revealed that organic carbon was likely found in five of six variably shocked impactites derived from the Hiawatha impact crater. The character of the organic carbon varies between the samples and also within individual samples. Vitrinite reflectance measurements of the organic carbon in two impactites yielded low reflectance values compared to charcoalification experiments of wood. Organic particles with different reflectance in the same sample suggest that the particles had different impact histories prior to settling and becoming a rock. Diagnostic conifer cellular texture was found in at least one of the samples. The character of the organic particles in the impactites supports the suggestion in a previous study that the sources of the Hiawatha organic carbon component are unmetamorphosed surficial deposits ...