Abstract The sedimentological and ichnological data of the Mila Group in the Alborz Basin, northern Iran indicate that the appearance of exotic facies and resurgence of microbialites resulted from the development of extraordinary palaeoceanographic conditions with widespread environmental stress and enhanced precipitation of CaCO 3 . Inhospitable environmental conditions in the Mila Group platform led to a considerable reduction in ichnodiversity, bioturbation intensity and depth and size of burrows, which led to periods of dominating calcimicrobe ecology. The development of exotic or anachronistic facies started around the Cambrian Stage 4–Wuliuan boundary, probably simultaneous with the SPICE event, whereas the Furongian exotic facies period probably took place simultaneous with the HERB event. Biotic and physico-chemical changes in the ocean during these events may have led as well to the virtual absence of the mixed layer and infaunal ecospace utilization in the deposits of the Mila Group. Nevertheless, the local presence of metazoan-microbial build-ups that established between the two suggested exotic facies developments indicates that these periods started at the Cambrian Stage 4–Wuliuan boundary interval, but a fluctuation of abnormal palaeoceanographic conditions and ambient normal marine conditions took place during the Miaolingian and Furongian in the Alborz Basin as a representative of the northern Gondwanan margin.

Abstract The lower Paleozoic succession of central Europe exposed in the Bohemian Massif is a classic area of geology with a long-standing tradition of research dating back to the eighteenth century. The Ordovician rocks form parts of sections in several units that sit on the Cadomian basement. These sedimentary and volcano-sedimentary fills of partial depressions in the basement are relics of the system of rift basins in the Gondwanan margin reflecting the rifting of the Rheic Ocean. The Ordovician sections are related to the subsidence period during the extensional regime accompanied by volcanism. They are underlain by Neoproterozoic or Cambrian rocks and continue up usually without breaks. After closure of the Rheic Ocean owing to the Gondwana–Laurussia collision, the Ordovician successions were incorporated into the Variscan Orogen belt and preserved in denudation relics such as the Bohemian Massif and its units. Ordovician strata with Gondwanan shelf affinities can be traced along the Variscans from Spain to central Europe, and are reflected in the regional stratigraphic scale based mainly on the succession in the Prague Basin. The Ordovician fill of this accumulation centre, together with relics of another preserved in the Schwarzburg Anticline, represents the main exposures in the Bohemian Massif. The individual features of the Ordovician successions, such as facies developments, fossil associations and volcanism, make them model areas both for understanding the palaeogeographic and geotectonic evolution of the peri-Gondwanan margin and a stratigraphic standard for a cool-water regime.

Abstract The Cambrian was originally defined as a rock interval with a trilobite-dominated fauna that overlay a presumed biologically barren Precambrian epoch. Work to formally define the Cambrian base arose after the discovery of Precambrian macrofossils in South Australia. The Working Group on the Precambrian–Cambrian Boundary (set up in 1972) promoted an emphasis on an extended pre-trilobitic interval with mineralized skeletal elements (small shelly fossils or early skeletal fossils). The study of early skeletal fossils made the Ulakhan-Sulugur (Siberia) and Meishucun (South China) sections candidates for the basal Cambrian Global Stratotype Section and Point (GSSP), but difficulties in correlation and the taxonomy of early skeletal fossils did not allow the selection of a reliably correlative horizon. Bilaterian ichnofaunas below the first diverse early skeletal fossils suggested the definition of a Cambrian base GSSP below the early skeletal fossils. Work on the thick, stratigraphically continuous and fairly unifacial sections in the Burin Peninsula, southeastern Newfoundland led in 1992 to an ichnofossil-defined GSSP at Fortune Head. Despite arguments for a revision and redefinition of the lower boundary of the Cambrian System, the best definition of the basal Cambrian GSSP is at Fortune Head and does not rely on the Treptichnus/Trichophycus pedum (abbreviated below as T. pedum ) first appearance datum, but rather on the base of the T. pedum Assemblage Zone at the highest occurrence of Ediacaran taxa and in the lower range of T. pedum .

Abstract The Cambrian (c. 545-488 Ma) is probably the most poorly studied and least documented of all Phanerozoic systems in Central Europe. Cambrian deposits in Central Europe are generally of limited extent, often largely covered by vegetation and slightly to strongly metamorphosed so that data on depositional environments and palaeogeographic history are very limited. Regional differences in the tectonic and resulting sedimentary history as well as faunal characteristics indicate a melange of plates and terranes in a configuration that differs extremely from their original spatial distribution. Despite considerable interest in the Cambrian on a global scale following recognition of the ‘Cambrian Explosion’, and various areas with peculiar regional and faunal aspects (e.g. Burgess Shale, Chengjiang, Kaili), there has been a lack of detailed and general research on the Cambrian of Central Europe during the last two decades. Relevant studies have concentrated on a few areas such as Lusatia, the Holy Cross Mountains, or the Barrandian area in Bohemia. The most relevant surface exposures are found in Bohemia, the Franconian Forest area in Bavaria, in western Thuringia, in the Lusatia area in Saxony, the Holy Cross Mountains of southern Poland, and in the Brabant Massif of Belgium (Fig. 4.1 ). These outcrops are of relatively limited extent, but some yield important fossil assemblages. In addition, Cambrian strata are known from a number of drillholes such as in the Delitzsch-Torgau-Doberlug Syncline of NW Saxony, Upper Silesia, and a large area in north and east Poland, which is part of the East European Platform. Our