The Silurian succession of the Oslo Region.

Abstract

he marine Silurian succession of the Oslo Region displays agreat variety of mixed clastic and carbonate lithofacies. Maximumthicknesses (< 650 m) and most complete successions are seen in thecentral parts of the region in the Ringerrike and Asker districts.Existing numerical stratigraphical units are based on a mixture offaunal and lithological criteria and are often diachronous. We hereinpropose the replacement of this scheme throughout the region by aseries of formal lithostratigraphical units and use existing such unitswhere possible. In these terms the entire marine succession comprisestwo groups and eleven formations, all of which are defined anddescribed in this paper. Our new information on the age relationshipsand depositional environments of these units permits a new appraisal ofthe paleogeographical evolution of the Oslo Region and adjacent sectorsof the Caledonides during the Llandovery and Wenlock. Our work hasrestricted itself to the marine Silurian succession; the transition tothe overlying red bed deposits of the Ringerike Group occured in thelate Wenlock in the Ringerike district. In order to present a completereview of Silurian deposits of the Oslo Region we also give a briefdescription of the red bed sequence.