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Extraterrestrial chromite in Middle Ordovician marine limestone at Kinnekulle, southern Sweden - Traces of a major asteroid breakup event

Schmitz, Birger LU and Haggstrom, T (2006) In Meteoritics and Planetary Science 41(3). p.455-466
Abstract
The distribution of sediment-dispersed extraterrestrial chromite grains and other Cr-rich spinels (> 63 mu m) has been studied in Middle Ordovician Orthoceratite Limestone from two quarries at Kinnekulle, southern Sweden. In the Thorsberg quarry, all similar to 3.2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment-dispersed extraterrestrial chromite grains. Typically, 1-3 grains are found per kilogram of limestone. In the nearby Hallekis quarry, the same beds show similarly high concentrations of extraterrestrial chromite grains, but in samples representing the 9 m downward continuation of the section exposed at this site, only 5 such grains were found in a total of 379 kg of limestone.... (More)
The distribution of sediment-dispersed extraterrestrial chromite grains and other Cr-rich spinels (> 63 mu m) has been studied in Middle Ordovician Orthoceratite Limestone from two quarries at Kinnekulle, southern Sweden. In the Thorsberg quarry, all similar to 3.2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment-dispersed extraterrestrial chromite grains. Typically, 1-3 grains are found per kilogram of limestone. In the nearby Hallekis quarry, the same beds show similarly high concentrations of extraterrestrial chromite grains, but in samples representing the 9 m downward continuation of the section exposed at this site, only 5 such grains were found in a total of 379 kg of limestone. The extraterrestrial (equilibrated ordinary chondritic) chromite grains call be readily distinguished by a homogeneous and characteristic major element chemistry, including 2.0-3.5 wt% TiO2 and stable V2O3 concentrations close to 0.7 wt%. Terrestrial Cr-rich spinels have a wide compositional range and co-exist with extraterrestrial chromite in some beds. These grains may be derived, for example, from mafic dykes exposed and weathered at the sea floor. Considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied. Instead, the difference may be primarily related to all increase in the ancient flux or extraterrestrial matter to Earth in connection with the disruption of the L chondrite parent body in the asteroid belt at about this time. The coexistence in some beds of high concentrations of chondritic chromite and terrestrial Cr-rich spinels, however, indicates that redistribution of heavy minerals on the sea floor, related to changes in sea level and sea-floor erosion and currents, must also be considered. (Less)
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organization
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Contribution to journal
publication status
published
subject
in
Meteoritics and Planetary Science
volume
41
issue
3
pages
455 - 466
publisher
Wiley-Blackwell
external identifiers
  • wos:000236603000008
  • scopus:33646131627
ISSN
1086-9379
language
English
LU publication?
yes
id
87abb98d-08aa-4fdc-bc5f-fc76e451ed63 (old id 414353)
alternative location
http://www.ingentaconnect.com/content/arizona/maps/2006/00000041/00000003/art00008
date added to LUP
2016-04-01 16:38:46
date last changed
2020-12-08 01:39:47
@article{87abb98d-08aa-4fdc-bc5f-fc76e451ed63,
  abstract     = {The distribution of sediment-dispersed extraterrestrial chromite grains and other Cr-rich spinels (> 63 mu m) has been studied in Middle Ordovician Orthoceratite Limestone from two quarries at Kinnekulle, southern Sweden. In the Thorsberg quarry, all similar to 3.2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment-dispersed extraterrestrial chromite grains. Typically, 1-3 grains are found per kilogram of limestone. In the nearby Hallekis quarry, the same beds show similarly high concentrations of extraterrestrial chromite grains, but in samples representing the 9 m downward continuation of the section exposed at this site, only 5 such grains were found in a total of 379 kg of limestone. The extraterrestrial (equilibrated ordinary chondritic) chromite grains call be readily distinguished by a homogeneous and characteristic major element chemistry, including 2.0-3.5 wt% TiO2 and stable V2O3 concentrations close to 0.7 wt%. Terrestrial Cr-rich spinels have a wide compositional range and co-exist with extraterrestrial chromite in some beds. These grains may be derived, for example, from mafic dykes exposed and weathered at the sea floor. Considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied. Instead, the difference may be primarily related to all increase in the ancient flux or extraterrestrial matter to Earth in connection with the disruption of the L chondrite parent body in the asteroid belt at about this time. The coexistence in some beds of high concentrations of chondritic chromite and terrestrial Cr-rich spinels, however, indicates that redistribution of heavy minerals on the sea floor, related to changes in sea level and sea-floor erosion and currents, must also be considered.},
  author       = {Schmitz, Birger and Haggstrom, T},
  issn         = {1086-9379},
  language     = {eng},
  number       = {3},
  pages        = {455--466},
  publisher    = {Wiley-Blackwell},
  series       = {Meteoritics and Planetary Science},
  title        = {Extraterrestrial chromite in Middle Ordovician marine limestone at Kinnekulle, southern Sweden - Traces of a major asteroid breakup event},
  url          = {http://www.ingentaconnect.com/content/arizona/maps/2006/00000041/00000003/art00008},
  volume       = {41},
  year         = {2006},
}