The Scandinavian alum shales - Mid Cambrian to Tremadoc deposition m response to early Caledonian subduction

Early Caledonian deformation and metamorphism apparently influenced the entire Baltoscandian margin,
involving Early Ordovician assembly of thrust sheets and a related uplift history, extending in to the Mid
Ordovician. Metamorphism during this orogenic episode at temperatures of over 700°C and depths of at
least 50 km suggest that subduction started in the Cambrian. Thus, early tectonothermal activity along
the Baltoscandian margin probably occurred simultaneously with deposition of the Alum Shale Formation
on the Baltoscandian platform. This correlation implies a genetic relationship and favours the hypothesis
that the change to anoxic facies in the Mid Cambrian occurred in response to the start of subduction
along the outer margin of Baltica.