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Facies distribution of post- impact sediments in the Ordovician Lockne and Tvären impact craters: Indications for unique impact-generated environments
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology. (Paleontologigruppen)
2007 (English)In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 42, no 11, 1971-1984 p.Article in journal (Refereed) Published
Abstract [en]

The Lockne and Tvaren craters formed in the Late Ordovician Baltoscandian epicontinental sea. Both craters demonstrate similarities concerning near-synchronous age, target seabed, and succeeding resurge deposits; however, the water depths at the impact sites and the sizes of the craters were not alike. The post-impact sedimentary succession of carbonates, i.e., the Dalby Limestone, deposited on top of the resurge sediments in the two craters, is nevertheless similar. At least three main facies of the Dalby Limestone were established in the Lockne crater, depending on sea-floor topography, location with respect to the crater, and local water currents. The dominating nodular argillaceous facies, showing low values of inorganic carbon (IC), was distributed foremost in the deeper and quiet areas of the crater floor and depressions. At the crater rim, consisting of crushed crystalline basement ejecta, a rim facies with a reef-like fauna was established, most certainly due to topographical highs and substrate-derived nutrients. Between these facies are occurrences of a relatively thick-bedded calcilutite rich in cephalopods (cephalopod facies). In Tvaren, the lower part of the succession consists of an analogous argillaceous facies, also showing similar low IC values as in Lockne, followed by calcareous mudstones with an increase of IC. Occasionally biocalcarenites with a distinctive fauna occur in the Tvaren succession, probably originating as detritus from a facies developed on the rim. They are evident as peaks in IC and lows in organic carbon (Corg). The fauna in these biocalcarenites corresponds very well with those of erratic boulders derived from Tvaren; moreover, they correspond to the rim facies of Lockne except for the inclusion of photosynthesizing algae, indicating shallower water at Tvaren than Lockne. Consequently, we suggest equivalent distribution patterns for the carbonates of the Dalby Limestone in Lockne and Tvaren.

Place, publisher, year, edition, pages
2007. Vol. 42, no 11, 1971-1984 p.
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-12757DOI: 10.1111/j.1945-5100.2007.tb00554.xISI: 000253937700011OAI: oai:DiVA.org:uu-12757DiVA: diva2:40526
Available from: 2008-05-19 Created: 2008-05-19 Last updated: 2010-05-07Bibliographically approved
In thesis
1. Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters: The Aftermath of the Lockne and Tvären Events
Open this publication in new window or tab >>Late Ordovician Faunal Distribution and Ecospace Partitioning in Marine Impact Craters: The Aftermath of the Lockne and Tvären Events
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the Middle to Late Ordovician a boost of marine biodiversity occurred which is regarded as the most rapid diversity in Earth’s history, and termed the Great Ordovician Biodiversification Event. This time is also unique in that at least four marine meteorite craters with a good record of post-impact sediments are preserved in Baltoscandia. Catastrophic impacts can serve as constructive events and produce wide-ranging environments providing new ecological niches for a diverse biota to occupy. Additionally, they generate distinctive patterns of biological destruction and recovery. This, and the study of distribution and ecospace utilisation of Late Ordovician faunas, has been analysed in two almost contemporary (around 455 million years ago) meteorite craters (Lockne and Tvären, Sweden). Within the confined space of the impact craters environments varied from shallow and reef-like to over 200 m in depth and from well oxygenated to hypoxic. These types of environments favored colonization of different individual groups. In Tvären rhynchonelliformean brachiopod assemblages from the shallow crater rim include a range of morphotypes, not established elsewhere in the crater. Within the crater depression rhynchonelliformean brachiopods were not established until the upper third of the remaining crater fill. Colonization of post-impact faunas varies dependent on topography, depth and susbstrate within the impact craters. This is recognised for scolecodonts in Tvären and for gastropod-like mollusks, linguliform and craniiform brachiopods in both of the craters, as they inhabit a wide range of ecospace. A succession of different taxa is observed from the deepest part of each crater and upwards towards inferably more shallow, higher energy, water settings. The development of new community types and narrowly-defined niches in the craters helped further drive both α and β biodiversity during a critical phase of the Great Ordovician Biodiversification Event.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 45 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 685
impact crater, Lockne, Tvären, ecospace, the Great Ordovician Biodiversification Event
National Category
Natural Sciences
urn:nbn:se:uu:diva-109605 (URN)978-91-554-7639-7 (ISBN)
Public defence
2009-12-04, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Available from: 2009-11-09 Created: 2009-10-20 Last updated: 2009-11-12

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