Outcrop at the northern coast of Skälö. Approach via road from Västrum to the
northern part of Skälo. Walk behind the eastern side of the bridge. Be careful, wet rocks are slippery!
In the area around Skälö basic volcanites are intercalated within the felsic metasediments of
the Västervik Formation. They mainly strike NW-SE concordant to the surrounding rocks. At this location
the rocks are black colored, dense and fine-grained with visible layering and flow fabric. Numerous bubbles,
some of them filled with secondary minerals, are striking (cf. fig. 4.17a-d). According to Reifferscheidt (1996),
the main components of this basic rock are hornblende, biotite, quartz, ores and plagioclase. It has been discussed
whether they should be interpreted as sills or flows. Following criteria point to basic flows:
A contact zone with apophyses can only be found at one side of these rocks, the footwall. The rocks show
an asymmetric zonation with bubbles of different sizes (cf. fig. 4.17b-c). This can be ascribed to degassing
processes under different pressure conditions, that depend on the closeness to the surface. The closer to
the surface the bigger the bubbles are developed. This matter of fact can also be used as identification of
the hanging walls and footwalls. It is also possible to count several sequenced flows on this criteria. In
his studies Kresten (1972) assigned these rocks to the first generation of basic magmatism.
Kresten, P., 1972. Der basische Magmatismus und seine Stellung in der geologischen Entwicklung des
Västervik-Gebietes, Südostschweden, GFF, 94, 91-109.