Abstract The Kasimovian Stage is the lower stage of the Upper Pennsylvanian Subsystem, in which a series of considerable biotic and abiotic events happened and changed the Earth. The Variscan orogeny and the Late Paleozoic Glaciation are two major events that caused geographical isolation of marine faunas and difficulties for a global correlation of biostratigraphy. Regional timescales of the Kasimovian across major continents are reviewed here. A global correlation of the Kasimovian is tentatively established based on a detailed review of major fossil groups such as conodonts, fusulines and some macrofossils. The index taxon for the base of the Kasimovian Stage has not been selected. The conodont species Swadelina subexcelsa , Idiognathodus heckeli , I. turbatus and I. sagittalis have good potential. Among them, I . heckeli is considered the best marker for the base of the Kasimovian Stage because it can mark a bioevent in a wide geographical range, and more importantly, it has a clear taxonomic definition within a phylogenetic lineage. The fusuline Montiparus might be regarded as an auxiliary marker to define the base of the Kasimovian based on its wider distribution. Other proxies, i.e. isotopic dating and strontium, carbon and oxygen isotopic stratigraphy throughout the Kasimovian, are also reviewed. The Global Boundary Stratotype Section and Point (GSSP) candidates for the Kasimovian Stage include the Naqing section, South China, the Usolka section, South Urals and the Afanasievo section, Moscow Basin. The Naqing section is regarded as the most appropriate GSSP candidate in terms of its complete sedimentary succession, well-recorded conodont lineages and well-studied bio-, chemo- and cyclo-stratigraphy.

Abstract A comprehensive review of the current state of research on Kazakh Ordovician litho-, bio- and chronostratigraphy is presented. An Ordovician lithostratigraphic framework applied to eight Kazakh first-order tectonic units is outlined and its correlation with the International Chronostratigraphic Scale is given. Presently used criteria for definition of the Kazakh Ordovician regional stages are critically discussed and revaluated. The archipelago model is considered as the most appropriate for reconstruction of the relative position of inferred Kazakh volcanic island arcs and microcontinents in the Ordovician Period. A biogeographical assessment of Kazakh Ordovician benthic faunas suggests strongest affinity to the contemporaneous faunas of Tarim, South and North China and to a lesser degree to the Australian sector of Gondwana, while biogeographical connections with Siberia and Baltica are negligible. During the Sandbian to Katian, a loose cluster of Kazakh microcontinents and island arcs became a major biodiversity hotspot and species pump located at low latitudes on both sides of the equator. Radiolarian cherts from accretionary complexes preserved an almost complete record of biogenic sedimentation for at least 30 Ma from the Furongian to Darriwilian, providing a unique opportunity to study biotas and environments in Ordovician oceans.