Baltica from the late Precambrian to mid-Palaeozoic times: The gain and loss of a terrane's identity
The old terrane of Baltica occupies the mass of northern Europe eastwards to the Urals and lies mostly to the north of the Trans-European Suture Zone. The core, the East European Craton, is thick and formed of rocks dating back to well over 3 billion yr, and Protobaltica can be identified as forming part of the supercontinent of Rodinia at about 1 billion yr ago. Following Rodinia's break up at about 800 Ma, Protobaltica remained attached to Laurentia until it became the newly independent Baltica at between 570 and 550 Ma, with the inauguration of plate spreading to form the northern part of the Iapetus Ocean. To the south, during the Early Cambrian, Baltica was separated from Gondwana by the relatively narrow Ran Ocean. Baltica remained a separate terrane until its docking, firstly with Avalonia at the very end of the Ordovician (443 Ma), and then with Laurentia during the Silurian in the Scandian part of the Caledonide Orogeny. The terrane was much enlarged in the Vendian to include the areas such as Timan-Pechora now lying to the north as they became accreted to Baltica during the late Precambrian Timanide Orogeny. During the Cambrian and Ordovician, Baltica firstly rotated through more than 120° and then drifted northwards from high to low palaeolatitudes. New maps present Baltica's outline and progressive positioning, its late Precambrian and Lower Palaeozoic history, and the Cambrian, Ordovician and Silurian land, basins and biofacies belts within and around it. Some of the Lower Palaeozoic faunas are reviewed briefly: the oceans surrounding Baltica were so wide during the Early Ordovician that a substantial part of the benthic fauna of trilobites, brachiopods and other phyla were endemic. As those oceans narrowed, so the faunas of Baltica became progressively more similar to those of adjacent terranes. Some plankton distributions augment the palaeomagnetic data in latitudinal positioning.