The South Swedish Dome: a key structure for identification of peneplains and conclusions on Phanerozoic tectonics of an ancient shield

Abstract

The relationships between different denudation surfaces/peneplains formed across crystalline basement rocks give valuable information to the tectonic development of ancient shields. The denudation surfaces can be identified by the aid of their landforms, tilt and remnant weathering mantles in relation to cover rocks. Three types of denudation surfaces are identified across south Sweden (1) a tilted flat plain, (2) a tilted hilly surface with relative relief below 150 m and (3) stepped horizontal plains with residual hills. All three types of denudation surfaces are peneplains, denudation surfaces graded to specific base levels. The re-exposed parts of the inclined flat sub-Cambrian peneplain (SCP) extend as a landscape feature from below cover rocks in the north and east and reaches up on the highest summits of the South Swedish Uplands. The SCP (the exact unconformity) is encountered again below Cambrian covers outside the west coast. Thus south Sweden is a geological dome, the South Swedish Dome (SSD), in relation to the Cambrian cover. The southern and western low flanks of the exposed part of the dome are instead characterized by a hilly peneplain, the inclined sub-Cretaceous denudation surface, with remnants of thick, kaolinitic, clayey saprolites. This sub-Cretaceous peneplain is cut off at a distinct level in the south and west by the almost horizontal South Småland Peneplain, a never covered, epigene, peneplain. The uplift history of the SSD aids to the understanding on the development of late Tertiary drainage systems of the Baltic Basin by the Eridano River.

Keywords:

• Denudation surface
• peneplain
• relief differentiation
• saprolite
• remnants of cover rocks
• uplift
• tectonics

Acknowledgments

Karna Lidmar-Bergström thanks her late husband, Jan Bergström, for daily discussions during the time in Lund on the contact of the Precambrian basement surface and the cover rocks (Jurassic and Cretaceous) and for the many joint excursions in Halland, Skåne and Blekinge. Jan’s knowledge of the possible provenance of erratic boulders was of utmost value during field trips. During his stay at the Geological Survey in Lund, Jan made many of the map sheets with Cretaceous sedimentary rocks and there was a mutual benefit between Karna and her husband on the relationships between the basement surface and its cover rocks. Grants from the Science Council during the years 1982–2005 were the economic base for the work by Karna after finishing of her thesis in1982 as well as economic salary support from the Deparment of Physical Geography at the University of Stockholm (1994–2004) and the Faculty of Natural Sciences at the University of Stockholm (1995–2001). During several years Mats and Karna worked together on saprolites in southern Sweden and Siv Olsson, Department of Quaternary Geology, Lund, made all our X-rays of the sampled saprolites and joined us during several field trips.