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Sedimentological analysis of resurge deposits at the Lockne and Tvären craters: Clues to flow dynamics
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
2007 (English)In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 42, no 11, 1929-1943 p.Article in journal (Refereed) Published
Abstract [en]

The Lockne and Tvaren craters formed about 455 million years ago in an epicontinental sea where seawater and mainly limestones covered a crystalline basement. The target water depth for Tvaren (apparent basement crater diameter D = 2 km) was probably not over 150 in, and for Lockne (D = 7.5 km) recent best-fit numerical simulations suggest the target water depth of 500-700 m. Lockne has crystalline ejecta that partly cover an outer crater (14 km diameter) apparent in the target sediments. Tvaren is eroded with only the crater infill preserved. We have line-logged cores through the resurge deposits within the craters in order to analyze the resurge flow. The focus was clast lithology, frequencies, and size sorting. We divide the resurge into ""resurge proper,"" with water and debris shooting into the crater and ultimately rising into a central water plume, ""anti-resurge,"" with flow outward from the collapsing plume, and ""oscillating resurge"" (not covered by the line-logging due to methodological reasons), with decreasing flow in diverse directions. At Lockne, the deposit of the resurge proper is coarse and moderately sorted, whereas the anti-resurge deposit is fining upwards and better sorted. The Tvaren crater has a smoothly fining-up section deposited by the resurge proper and may lack anti-resurge deposits. At Lockne, the content of crystalline relative to limestone clasts generally decreases upwards, which is the opposite of Tvaren. This may be a consequence of factors such as crater size (i.e., complex versus simple) and the relative target water depth. The mean grain size (i.e., the mean-phi value per meter, (p) and standard deviation, i.e., size sorting (sigma) for both craters, can be expressed by the equation sigma = 0.60 phi - 1.25.

Place, publisher, year, edition, pages
2007. Vol. 42, no 11, 1929-1943 p.
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-55244DOI: 10.1111/j.1945-5100.2007.tb00551.xISI: 000253937700008OAI: diva2:402420
authorCount :3Available from: 2011-03-08 Created: 2011-03-07 Last updated: 2011-03-08Bibliographically approved

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