Late Ordovician – early Silurian transgressive sedimentation in the Jämtland basin, central Swedish Caledonides

Abstract

Abstract The sedimentary facies of the Kyrkås Quartzite Formation, Ede Quartzite Formation, and Rönnöfors Conglomerate from the meta‐sedimentary sequences of the Lower Allochthon of Jämtland, central Swedish Caledonides are described and interpreted. The biostratigraphical correlation, which includes new graptolite evidence from the Kyrkås Quartzite, indicates that the transgressive sedimentation represented by these coarse clastic units was initiated in late Ordovician times. Debris flow conglomerates of the Rönnöfors Conglomerate, and slumping in the Kyrkås Quartzite, indicate basement uplift and instability in the Jämtland basin. A local metamorphic source contributed much of the matrix and clasts of the Rönnöfors Conglomerate, but both the Kyrkås and Ede formations were derived from sedimentary source areas. Palaeocurrents that flowed from the west, and the probably wide inshore platform areas of carbonate mud flats fringing Baltica towards the east, mean that much of the coarse clastic sediment for the Kyrkås and Ede formations may have been derived from longshore transport, e.g., from late Precambrian or Cambrian sandstones. Cherns, L. & Karis, L., 1995: Late Ordovician – early Silurian transgressive sedimentation in the Jämtland basin, central Swedish Caledonides. GFF, Vol. 117 (Pt. 1, March), pp. 23–30. Stockholm. ISSN 1103–5897.