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Are there signs of a large Paleocene impact, preserved around Disko Bay, West Greenland? Nuussuaq spherule beds origin by impact instead of volcanic eruption?

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A.P. Jones
A.P. Jones
Research School of Geophysical Sciences, University and Birkbeck College London, Gower Street, London WC1E 6BT, UKadrian.jones@ucl.ac.uk
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A.T. Kearsley
A.T. Kearsley
Department of Mineralogy, Natural History Museum, Cromwell Road, South Kensington, London SW7 5BD, UK
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C.R.L. Friend
C.R.L. Friend
45, Stanway Road, Risinghurst, Headington, Oxford OX3 8HU, UK
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E. Robin
E. Robin
Laboratoire C.E.A./C.N.R.S. des Sciences du Climat et de l'Environnement, 91198 Gifsur-Yvette, France
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A. Beard
A. Beard
Research School of Geophysical Sciences, University and Birkbeck College London, Gower Street, London WC1E 6BT, UK
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A. Tamura
A. Tamura
Research School of Geophysical Sciences, University and Birkbeck College London, Gower Street, London WC1E 6BT, and Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
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S. Trickett
S. Trickett
Research School of Geophysical Sciences, University and Birkbeck College London, Gower Street, London WC1E 6BT, UK
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P. Claeys
P. Claeys
Department of Geology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
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Published:
January 01, 2005

On the Nuussuaq peninsula, Western Greenland sedimentary deposits of glass spherules also contain high Ir, Co, Ni, and Cu anomalies. The iron-rich silicate glass spherules (to ∼3 wt% NiO, ∼35 wt% FeO) are highly circular in cross section. They show surface dissolution, smectite replacement and calcite infilling of vesicles, though many glasses are optically unaltered. They are strikingly heterogeneous, with schlieren outlining counter-flowing convection cells. Their pronounced Fe-Ni correlation is unlike volcanic suites, but is explained by mixing between basaltic melt and an enriched iron-nickel source. Distinctive nickel-spinel (∼7–10 wt% NiO) contains very nickel-rich cores. Occasional glass spherules show compositional gradients toward resorbed silicates, (plagioclase, clinopyroxene); isotropic plagioclase has anomalous texture comparable to impact-melted lunar breccias. Their anomalously high copper and sulfur (to ∼1%) have lead to an explanation as products of fire-fountaining of exotic or picritic Disko lavas; they would be perhaps the only non-impact occurrence of Ni spinel. Since their discovery, better criteria for recognition of spherules ejected from large impacts have been established, and greater variations in meteorite chemistry as potential projectiles have been described. New mineralogical and petrographic textural data for the Nuussuaq spherules suggest they should be reinterpreted as impact ejecta; the highly oxidized Ni-spinel is a very characteristic signature of meteorite impact ejecta. Delicate preservation features rule out substantial sedimentary reworking, and spherule bed thicknesses imply a large source crater. Stratigraphically, the spherule beds are poorly constrained, but nannofossils and magnetostratigraphy place them close to onset of the West Greenland flood lavas (ca. 61–62 Ma). They share many characteristics with massive native iron localities in dykes and lavas up to >100 km away on Disko (Qeqertarsuaq) Island, but their precise relationship remains to be established.

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Contents

GSA Special Papers

Large Meteorite Impacts III

Thomas Kenkmann
Thomas Kenkmann
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Friedrich Hörz
Friedrich Hörz
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Alex Deutsch
Alex Deutsch
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Geological Society of America
Volume
384
ISBN print:
9780813723846
Publication date:
January 01, 2005

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