Chapter 18 Tonian–Cryogenian rifting and Cambrian–Early Devonian platformal to foreland basin development outside the Caledonide orogen

Abstract

AbstractDifferent parts of a Tonian–Early Devonian sedimentary succession, covering Proterozoic crystalline basement, occur along the erosional front to the Caledonide orogen, as outliers and coastal strips on land, and as more continuous strata in offshore areas. Rift-related Tonian–Cryogenian siliciclastic sedimentation preceded the break-up of the supercontinent Rodinia, the birth of Baltica and surrounding oceanic realms during the Ediacaran, and a marine transgression across Baltica during the Cambrian. An Ediacaran alkaline and carbonatite intrusive complex in central Sweden formed in connection with the extensional activity. Subsequently, during the Cambrian–Early Devonian, Baltica drifted northwards in the southern hemisphere to the equator, and six different lithofacies associations containing both siliciclastic and carbonate sedimentation were deposited in platformal shelf and Caledonian foreland basin settings. Bentonites in Ordovician and early Silurian successions were coupled to closure of the surrounding oceanic realms. Tectonic processes during the Caledonian orogeny around the margins to Baltica, the distance to different crustal components in this continent and climatic changes steered variations in lithofacies. Resultant fluctuations in sea-level gave rise to hiatuses and palaeo-karsts. Uranium and other metals in kerogen-rich black shales (Cambrian–Early Ordovician), hydrocarbons, stratabound Pb–Zn sulphide deposits in Cambrian (–Ediacaran?) sandstone, and limestone constitute the main resources.