Impact structures and events – a Nordic perspective

Abstract

Impact cratering is one of the fundamental processes in the formation of the Earth and our planetary system, as reflected, for example in the surfaces of Mars and the Moon. The Earth has been covered by a comparable number of impact scars, but due to active geological processes, weathering, sea floor spreading etc, the number of preserved and recognized impact craters on the Earth are limited. The study of impact structures is consequently of great importance in our understanding of the formation of the Earth and the planets, and one way we directly, on the Earth, can study planetary geology. The Nordic-Baltic area have about thirty confirmed impact structures which makes it one of the most densely crater-populated terrains on Earth. The high density of identified craters is due to the level of research activity, coupled with a deterministic view of what we look for. In spite of these results, many Nordic structures are poorly understood due to the lack of 3D-geophysical interpretations, isotopeor other dating efforts and better knowledge of the amount of erosion and subsequent tectonic modifications. The Nordic and Baltic impact community is closely collaborating in several impact-related projects and the many researchers (about forty) and PhD students (some seventeen) promise that this level will continue for many more years. The main topics of research include geological, geophysical, and geochemical studies in combination with modeling and impact experiments. Moreover, the Nordic and Baltic crust contains some hundred suspect structures which call for detailed analysis to define their origin. New advanced methods of analyzing geophysical information in combination with detailed geochemical analyses and numerical modeling will be the future basic occupation of the impact scientists of the region. The unique Cretaceous/Tertiary boundary (K-T) occurrences in Denmark form an important source of information in explaining one of the major mass extinctions on Earth.

Rock magnetic and paleomagnetic study of the Keurusselkä impact structure, central Finland

“…Large impact breccia deposits or impact melt, however, were not found, which indicates that Keurusselkä is indeed deeply eroded, and possibly much older compared with the other Finnish impact structures (Dypvik et al. 2008).…”

“…Fennoscandia is statistically one of the most densely crater‐populated parts of the Earth (Henkel and Pesonen 1992; Abels et al. 2002; Dypvik et al. 2008) as most of the craters are exposed.…”

Ordovician Source Rocks and Devonian Oil Expulsion on Bolide Impact at Siljan, Sweden - The Re-Os Story

“…Although the Nordic-Baltic region has about thirty recognized impact structures [8] , none rival the Siljan, either in size (largest in Europe) or intensity of study. Estimates of the pre-erosional size of the Siljan crater vary from 65 to 85 km [9,10] .…”

Meteorite impact craters and possibly impact‐related structures in Estonia

“…Reference to impact cratering as a geological process has finally appeared in textbooks during the last decades, as the popularity of the subject increased dramatically. The increased exposition and publicity have produced a boom in identifying new impact structures (e.g., Earth Impact Database, http://www.passc.net/EarthImpactDatabase/index.html; Dypvik et al. 2008), but also some threats.…”