Geology of the Hølonda-Hulsjøen area, Trondheim region.

Abstract

The geology of the area south of Trondheim is described. A new stratigraphical division of the Early Palaeozoic is proposed and its structure outlined. The entire Early Palaeozoic sedimentary and volcanic complex has been divided into four seperate groups, differing in lithology and separated by conspicuous layers of synorogenic conglomerates: 1) The oldest Støren Group (presumably of Tremadocian age), 2) The Krokstad Group (largely of Arenigian, Llanvirnian and Llandeilian age ), 3) The lower Sandå Group (of Caradocian and perhaps partly of Ashgillian age), 4) The youngest Upper Sandå Group (presumably of Silurian age). The total thickness of the Ordovician-Silurian sequence overlying the Støren volcanic complex is about 800 m. The overall structure is interpreted at a series of closely packed tight to isoclinal folds accompanied by sharing and stretching phenomena, which are grouped into extensive anticlinorial and synclinorial belts.