Distant ejecta from the Lockne marine-target impact crater, Sweden

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Authors:Sturkell, Erik; Ormo, Jens; Kolvak, Jaak; Wallin, Asa
Author Affiliations:Primary:
Nordic Volcanological Institute, Reykjavik, Iceland
Other:
Universita d'Annunzio, Italy
Tallinn Technical University, Estonia
Stockholm University, Sweden
Volume Title:Meteoritics & Planetary Science
Source:Meteoritics & Planetary Science, 35(5), p.929-936. Publisher: Meteoritical Society, Fayetteville, AR, United States. ISSN: 1086-9379
Publication Date:2000
Note:In English. 31 refs.; illus., incl. geol. sketch map
Summary:The Lockne impact event took place in a Middle Ordovician (455 Ma) epicontinental sea. The impact resulted in an at least 13.5 km wide, concentric crater in the sea floor. Lockne is one of very few locations where parts of an ejecta layer have been preserved outside the crater structure. The ejecta from the Lockne impact rests on progressively higher stratigraphic levels with increasing distance from the crater, hence forming a slightly inclined discontinuity surface in the pre-impact strata. We report on a ∼30 cm thick sandy layer at Hallen, 45 km south of the crater centre. This layer has a fining upward sequence in its lower part, followed by low-angle cross-laminations indicating two opposite current directions. It is rich in quartz grains with planar deformation features and contains numerous, up to 15 cm large, granite clasts from the crystalline basement at the Lockne impact site. The layer is within a sequence dated to the Baltoniodus gerdae conodont subzone. The dating is corroborated by chitinozoans indicating the latest Kukruse time below and the late Idavere above the impact layer. According to the chitinozoans biostratigraphy, some erosion may have occurred because of deposition of the impact layer. The Hallen outcrop, today 45 km from the centre of the Lockne crater, is at present the most distant accessible occurrence of ejecta from the Lockne impact. It is also the most distant location so far found where the resurge of water towards the crater has affected the bottom sediments. A greater crater diameter than hitherto assumed, thus representing greater impact energy, might explain the extent of the ejecta blanket. Fluidisation of ejecta, to be expected at a marine-target impact, might furthermore have facilitated the wide distribution of ejecta.
Sections:Meteorites and tektites
Subjects:Biostratigraphy; Biozones; Carbonate rocks; Chitinozoa; Conodonta; Ejecta; Impact craters; Impact features; Limestone; Microfossils; Middle Ordovician; Ordovician; Paleozoic; Palynomorphs; Range; Sedimentary rocks; Europe; Jamtland Sweden; Scandinavia; Sweden; Western Europe; Baltoniodus gerdae; Central Sweden; Dalby Limestone; Hallen Sweden; Lockne impact event
Coordinates:N624104 N624104 E0141650 E0141650
Abstract Numbers:03M/733
Record ID:2001002810
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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