Analysis of the Younger Dryas Impact Layer
We have uncovered a thin layer of magnetic grains and microspherules, carbon spherules, and glass-like carbon at nine sites across North America, a site in Belgium, and throughout the rims of 16 Carolina Bays. It is consistent with the ejecta layer from an impact event and has been dated to 12.9 ka...
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ftcdlib:qt03q2r98x 2023-05-15T16:41:37+02:00 Analysis of the Younger Dryas Impact Layer Firestone, Richard B. 2010-04-14 application/pdf http://www.escholarship.org/uc/item/03q2r98x english eng eScholarship, University of California qt03q2r98x http://www.escholarship.org/uc/item/03q2r98x public Firestone, Richard B.(2010). Analysis of the Younger Dryas Impact Layer. Lawrence Berkeley National Laboratory. Lawrence Berkeley National Laboratory: Lawrence Berkeley National Laboratory. Retrieved from: http://www.escholarship.org/uc/item/03q2r98x Physics Life Sciences Earth Sciences Chemical Sciences impact ejecta layer impact crater methods of elemental analysis magnetic grain and microspherule analysis analysis of carbon spherules and glass-like carbon article 2010 ftcdlib 2018-01-26T23:52:49Z We have uncovered a thin layer of magnetic grains and microspherules, carbon spherules, and glass-like carbon at nine sites across North America, a site in Belgium, and throughout the rims of 16 Carolina Bays. It is consistent with the ejecta layer from an impact event and has been dated to 12.9 ka BP coinciding with the onset of Younger Dryas (YD) cooling and widespread megafaunal extinctions in North America. At many locations the impact layer is directly below a black mat marking the sudden disappearance of the megafauna and Clovis people. The distribution pattern of the Younger Dryas boundary (YDB) ejecta layer is consistent with an impact near the Great Lakes that deposited terrestrial-like ejecta near the impact site and unusual, titanium-rich projectile-like ejecta further away. High water content associated with the ejecta, up to 28 at. percent hydrogen (H), suggests the impact occurred over the Laurentide Ice Sheet. YDB microspherules and magnetic grains are highly enriched in TiO2. Magnetic grains from several sites are enriched in iridium (Ir), up to 117 ppb. The TiO2/FeO, K/Th, TiO2/Zr, Al2O3/FeO+MgO, CaO/Al2O3, REE/ chondrite, FeO/MnO ratios and SiO2, Na2O, K2O, Cr2O3, Ni, Co, U, Th and other trace element abundances are inconsistent with all terrestrial and extraterrestrial (ET) sources except for KREEP, a lunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), and other incompatible elements including U and Th. Normal Fe, Ti, and 238U/235U isotopic abundances were found in the magnetic grains, but 234U was enriched over equilibrium values by 50 percent in Murray Springs and by 130 percent in Belgium. 40K abundance is enriched by up to 100 percent in YDB sediments and Clovis chert artifacts. Highly vesicular carbon spherules containing nanodiamonds, glass-like carbon, charcoal and soot found in large quantities in the YDB layer are consistent with an impact followed by intense burning. Four holes in the Great Lakes, some deeper than Death Valley, are proposed as possible craters produced by the airburst breakup of a loosely aggregated projectile. Article in Journal/Newspaper Ice Sheet University of California: eScholarship |
institution |
Open Polar |
collection |
University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
English |
topic |
Physics Life Sciences Earth Sciences Chemical Sciences impact ejecta layer impact crater methods of elemental analysis magnetic grain and microspherule analysis analysis of carbon spherules and glass-like carbon |
spellingShingle |
Physics Life Sciences Earth Sciences Chemical Sciences impact ejecta layer impact crater methods of elemental analysis magnetic grain and microspherule analysis analysis of carbon spherules and glass-like carbon Firestone, Richard B. Analysis of the Younger Dryas Impact Layer |
topic_facet |
Physics Life Sciences Earth Sciences Chemical Sciences impact ejecta layer impact crater methods of elemental analysis magnetic grain and microspherule analysis analysis of carbon spherules and glass-like carbon |
description |
We have uncovered a thin layer of magnetic grains and microspherules, carbon spherules, and glass-like carbon at nine sites across North America, a site in Belgium, and throughout the rims of 16 Carolina Bays. It is consistent with the ejecta layer from an impact event and has been dated to 12.9 ka BP coinciding with the onset of Younger Dryas (YD) cooling and widespread megafaunal extinctions in North America. At many locations the impact layer is directly below a black mat marking the sudden disappearance of the megafauna and Clovis people. The distribution pattern of the Younger Dryas boundary (YDB) ejecta layer is consistent with an impact near the Great Lakes that deposited terrestrial-like ejecta near the impact site and unusual, titanium-rich projectile-like ejecta further away. High water content associated with the ejecta, up to 28 at. percent hydrogen (H), suggests the impact occurred over the Laurentide Ice Sheet. YDB microspherules and magnetic grains are highly enriched in TiO2. Magnetic grains from several sites are enriched in iridium (Ir), up to 117 ppb. The TiO2/FeO, K/Th, TiO2/Zr, Al2O3/FeO+MgO, CaO/Al2O3, REE/ chondrite, FeO/MnO ratios and SiO2, Na2O, K2O, Cr2O3, Ni, Co, U, Th and other trace element abundances are inconsistent with all terrestrial and extraterrestrial (ET) sources except for KREEP, a lunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), and other incompatible elements including U and Th. Normal Fe, Ti, and 238U/235U isotopic abundances were found in the magnetic grains, but 234U was enriched over equilibrium values by 50 percent in Murray Springs and by 130 percent in Belgium. 40K abundance is enriched by up to 100 percent in YDB sediments and Clovis chert artifacts. Highly vesicular carbon spherules containing nanodiamonds, glass-like carbon, charcoal and soot found in large quantities in the YDB layer are consistent with an impact followed by intense burning. Four holes in the Great Lakes, some deeper than Death Valley, are proposed as possible craters produced by the airburst breakup of a loosely aggregated projectile. |
format |
Article in Journal/Newspaper |
author |
Firestone, Richard B. |
author_facet |
Firestone, Richard B. |
author_sort |
Firestone, Richard B. |
title |
Analysis of the Younger Dryas Impact Layer |
title_short |
Analysis of the Younger Dryas Impact Layer |
title_full |
Analysis of the Younger Dryas Impact Layer |
title_fullStr |
Analysis of the Younger Dryas Impact Layer |
title_full_unstemmed |
Analysis of the Younger Dryas Impact Layer |
title_sort |
analysis of the younger dryas impact layer |
publisher |
eScholarship, University of California |
publishDate |
2010 |
url |
http://www.escholarship.org/uc/item/03q2r98x |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
Firestone, Richard B.(2010). Analysis of the Younger Dryas Impact Layer. Lawrence Berkeley National Laboratory. Lawrence Berkeley National Laboratory: Lawrence Berkeley National Laboratory. Retrieved from: http://www.escholarship.org/uc/item/03q2r98x |
op_relation |
qt03q2r98x http://www.escholarship.org/uc/item/03q2r98x |
op_rights |
public |
_version_ |
1766032077246955520 |