New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland
An unconformable sedimentary succession deposited between c. 2130–1848 Ma on Archaean gneisses of the foreland of the Palaeoproterozoic Ketilidian orogen includes a layer with coarse sand-sized silicate spherules. The layer is c. 1 m thick and consists mainly of coarse diagenetic dolomite. In additi...
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ftoberlincollege:oai:digitalcommons.oberlin.edu:faculty_schol-4367 2023-05-15T16:27:34+02:00 New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland Chadwick, Brian Claeys, Philippe Simonson, Bruce M. 2001-03-01T08:00:00Z https://digitalcommons.oberlin.edu/faculty_schol/3368 https://doi.org/10.1144/jgs.158.2.331 English eng Digital Commons at Oberlin https://digitalcommons.oberlin.edu/faculty_schol/3368 https://dx.doi.org/10.1144/jgs.158.2.331 Faculty & Staff Scholarship Palaeoproterozoic South Greenland Spherules Impacts Ejecta Geology text 2001 ftoberlincollege https://doi.org/10.1144/jgs.158.2.331 2022-11-26T18:28:15Z An unconformable sedimentary succession deposited between c. 2130–1848 Ma on Archaean gneisses of the foreland of the Palaeoproterozoic Ketilidian orogen includes a layer with coarse sand-sized silicate spherules. The layer is c. 1 m thick and consists mainly of coarse diagenetic dolomite. In addition to c. 18% spherules, the layer also contains 3% well-sorted, very fine quartzose sand and 6% larger intraclasts of chert and carbonate. The spherules were previously interpreted as microfossils (Vallenia sp.) because of their spheroidal shapes and inclusions of carbonaceous matter. The spherules are reinterpreted as replaced impact ejecta because they have shapes typical of splash-form microtektites, some contain possible examples of replaced skeletal spinel crystals, perlitic cracks and devitrification spherulites, and non-spherical particles with shapes and textures of typical glassy and scoriaceous volcanic ash are absent. The carbonaceous matter is attributed to hydrocarbons that migrated into the spherule layer from elsewhere in the sedimentary succession. The spherules were reworked after deposition, probably as a result of turbidity currents or storm- or impact-induced waves. Analysis of one spherule-bearing sample revealed only 0.02 ppb iridium, a value comparable with low iridium abundances in distal layers of other terrestrial impact ejecta. The spherules in South Greenland are the first distal impact ejecta recognized in mid-Precambrian strata. They represent a major impact because their aggregate thickness exceeds the thickest spherule accumulations reported from the Cretaceous-Tertiary boundary layer. Given their loosely constrained age and the implied scale of the impact, the Ketilidian spherules could be distal ejecta from either the Vredefort, South Africa, (c. 2025 Ma) or Sudbury, Canada, (c. 1850 Ma) impacts. Text Greenland Digital Commons at Oberlin (Oberlin College) Canada Greenland Journal of the Geological Society 158 2 331 340 |
institution |
Open Polar |
collection |
Digital Commons at Oberlin (Oberlin College) |
op_collection_id |
ftoberlincollege |
language |
English |
topic |
Palaeoproterozoic South Greenland Spherules Impacts Ejecta Geology |
spellingShingle |
Palaeoproterozoic South Greenland Spherules Impacts Ejecta Geology Chadwick, Brian Claeys, Philippe Simonson, Bruce M. New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
topic_facet |
Palaeoproterozoic South Greenland Spherules Impacts Ejecta Geology |
description |
An unconformable sedimentary succession deposited between c. 2130–1848 Ma on Archaean gneisses of the foreland of the Palaeoproterozoic Ketilidian orogen includes a layer with coarse sand-sized silicate spherules. The layer is c. 1 m thick and consists mainly of coarse diagenetic dolomite. In addition to c. 18% spherules, the layer also contains 3% well-sorted, very fine quartzose sand and 6% larger intraclasts of chert and carbonate. The spherules were previously interpreted as microfossils (Vallenia sp.) because of their spheroidal shapes and inclusions of carbonaceous matter. The spherules are reinterpreted as replaced impact ejecta because they have shapes typical of splash-form microtektites, some contain possible examples of replaced skeletal spinel crystals, perlitic cracks and devitrification spherulites, and non-spherical particles with shapes and textures of typical glassy and scoriaceous volcanic ash are absent. The carbonaceous matter is attributed to hydrocarbons that migrated into the spherule layer from elsewhere in the sedimentary succession. The spherules were reworked after deposition, probably as a result of turbidity currents or storm- or impact-induced waves. Analysis of one spherule-bearing sample revealed only 0.02 ppb iridium, a value comparable with low iridium abundances in distal layers of other terrestrial impact ejecta. The spherules in South Greenland are the first distal impact ejecta recognized in mid-Precambrian strata. They represent a major impact because their aggregate thickness exceeds the thickest spherule accumulations reported from the Cretaceous-Tertiary boundary layer. Given their loosely constrained age and the implied scale of the impact, the Ketilidian spherules could be distal ejecta from either the Vredefort, South Africa, (c. 2025 Ma) or Sudbury, Canada, (c. 1850 Ma) impacts. |
format |
Text |
author |
Chadwick, Brian Claeys, Philippe Simonson, Bruce M. |
author_facet |
Chadwick, Brian Claeys, Philippe Simonson, Bruce M. |
author_sort |
Chadwick, Brian |
title |
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
title_short |
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
title_full |
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
title_fullStr |
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
title_full_unstemmed |
New evidence for a large Palaeoproterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland |
title_sort |
new evidence for a large palaeoproterozoic impact: spherules in a dolomite layer in the ketilidian orogen, south greenland |
publisher |
Digital Commons at Oberlin |
publishDate |
2001 |
url |
https://digitalcommons.oberlin.edu/faculty_schol/3368 https://doi.org/10.1144/jgs.158.2.331 |
geographic |
Canada Greenland |
geographic_facet |
Canada Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
Faculty & Staff Scholarship |
op_relation |
https://digitalcommons.oberlin.edu/faculty_schol/3368 https://dx.doi.org/10.1144/jgs.158.2.331 |
op_doi |
https://doi.org/10.1144/jgs.158.2.331 |
container_title |
Journal of the Geological Society |
container_volume |
158 |
container_issue |
2 |
container_start_page |
331 |
op_container_end_page |
340 |
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1766016972844171264 |