NJG82-3-02
2002
The Mesoproterozoic sub-Heddal unconformity, Sauland, Telemark, south Norway.
82
3
pp. 139-152.
82-92394-03-8

In the Sauland area, the Vindeggen group, which corresponds to the northern part of the traditional Seljord group, is overlain unconformably by the Lifjell gro up (southern part of the traditional Seljord group ), whereas the Heddal gro up unconformably over Iies both of these groups. The subHeddal unconformity transects progressively older rocks when moving from south to north. In the south, the 1145 Ma old Skogsåa porphyry of the Heddal group Iies either directly on the Lifjell orthoquartzite or is separated from it by a thin layer of epiclastic muscovite schist. At Heksfjellet, the unconformity transects the basal Heksfjellet conglomerates of the Lifjell gro up. Here the Heddal gro up starts with a c. l m thick cobbly mica schist, which passes upwards via an acid volcanic detritus zone into the Skogsåa porphyry. Farther to the north, in the Moltelia area, the unconformity joins and even intersects the sub-Lifjell unconformity. The muscovite schist and the Skogsåa porphyry Iie on the rugged, karst-like, palaeoweathered surface developed on the uppermost Vindeggen orthoquartzite, indicating that the Lifjell Gro up was eroded before deposition of the Heddal gro up. Consequently, the Vindeggen-Lifjell/Heddal contact is a distinct stratigraphic unconformity. Recent age determinations place the age of the unconformity to be between 1150 Ma and 1145 Ma.

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