During the one day excursion we will visit different localities in the Siljan impact crater. This crater is the largest impact crater in Europe (ca. 65 km in diameter) and was formed about 377 million years ago. It is a complex impact structure, i.e. has a central uplift. The target rocks are composed of granite with a sedimentary cover (mainly limestone). During the excursion we will visit three geological localities: Vidablick, Solberga quarry and Styggforsen.

Vidablick is the first stop and located at the southern part of the crater. Here we can get a nice overview of the whole structure, which is today deeply eroded but still with a clear crater morphology.

Next stop is Styggforsen, located on the eastern side of the structure. This locality is situated in a beautiful old forest by a waterfall and a stream. Processes during the last Ice Age have carved out a canyon in the ground, which enables us to view spectacular outcrops of vertically displaced sedimentary rocks at the border with the central uplift. The central uplift is composed of heavily brecciated (fragmented) granite.

The last geological stop is Solberga quarry, also on the eastern side of the ring. This is a limestone quarry with large scale rock exposure for easy exploration. After impact, a hydrothermal system was generated in the crater, and evidence for this can be seen as hydrothermally precipitated mineral veins of fluorite and calcite with occasional sulphides in fractures of the limestone in the Solberga quarry. In addition to the hydrothermal veins, Solberga also offers a number of other geologically interesting features including fossils and oil seeping out of the limestone. The oil is probably generated locally due to impact heating. The Siljan impact structure was drilled by initiative of Thomas Gold in 1986 in order to investigate possible abiotic oil formation. Abiotic oil formation is a disputed theory that has recently got new attention.