Affiliation:
1. Geological Survey of Finland Kuopio Finland
2. Department of Geology University of Tartu Tartu Estonia
3. Loop and Line Oy Kirkkonummi Finland
4. Solid Earth Geophysics Laboratory, Physics Department University of Helsinki Helsinki Finland
Abstract
AbstractThe Summanen structure is located in Central Finland and is one of Finland's 12 known meteorite impact structures. In 2017, the discovery of Summanen was based on numerous shatter cone boulders with planar deformation features (PDFs) and a circular electromagnetic anomaly, which is 2.6 km in diameter. The site was revisited in 2020 and 2022, and shatter cone‐bearing outcrops were discovered. PDFs and feather features were identified in samples from these outcrops. A total of 38 PDF sets in 27 quartz grains resulted in rational crystallographic orientations concentrating on {104}, {103}, {102}, and {112}, implying shock pressures of 2–20 GPa. Gravity measurements were taken, and the electrical conductivity of the structure was studied. The gravimetric results revealed a circular negative anomaly of about 4 km in diameter, with an amplitude of −3.5 mGal. Excluding the gravitational effect of water and Quaternary sediments reduces the anomaly to −1.6 mGal. A bowl‐shaped conductive layer, likely containing relict saline water in the impact‐fractured bedrock, was identified to a depth of 240 m. Topographic and bathymetric data were combined to determine the impact's effect and interpret the level of erosion. Cobbles of sedimentary sand‐ and siltstones were found on the coastline of Lake Summanen. Based on their similarity to those found in the Söderfjärden impact crater with a Cambrian age, it is likely that these rocks and post‐impact infill are also of a similar age.
Subject
Space and Planetary Science,Geophysics
Reference34 articles.
1. Interactive Inversion Algorithm and Apparent Resistivity Versus Depth (ARD) Plot in Multifrequency Depth Soundings;Aittoniemi K.;Acta Polytechnica Scandinavica Applied Physics Series,1987
2. Anttila P. Ahokas H. Front K. Heikkinen E. Hinkkanen H. Johansson E. Paulamäki S. et al.1999.Final Disposal of Spent Nuclear Fuel in Finnish Bedrock—Kivetty Site Report. Posiva Oy Posiva Report 99‐09.202pp.
3. New Evidence for Impact from the Suvasvesi South Structure, Central East Finland
4. Iso-Naakkima, a circular structure filled with Neoproterozoic sediments, Pieksämäki, southeastern Finland