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The Östersund/Lake Storsjön area is herein divided into a western and eastern part, with the Upper Ordovician Kyrkås Quartzite Formation cropping out to the east and northeast (Fig. 1⇓). A detailed analysis of this formation is presented from Nifsåsen Quarry (701350/144325, Swedish National Grid), 5.5 km NNE of Östersund, with comparisons to the successions at the nearby Ljusberg, Rannåsen and Storhögen quarries (Fig. 1⇓). Nifsåsen Quarry exposes a 90 m thick succession of siliciclastic sedimentary rocks previously not described. The Kyrkås Quartzite Formation represents Late Ordovician deposition, and may contain almost the entire Hirnantian interval.
This paper uses sedimentological analysis to interpret the depositional environments and their evolution for the Kyrkås Quartzite Formation, and provides an understanding of the Late Ordovician–Early Silurian environmental development in the Caledonian foreland basin. Comparisons with coeval deposits (the Ede Quartzite Formation) in the western part of the area, where eustatic sea-level changes have been recorded (Dahlqvist & Calner, in press), are also made.
2.a. Palaeogeography and geological setting
During the latest Ordovician times the Baltic craton was situated at southern …