Ordovician of Kazakhstan

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 is critically discussed and revaluated. The archipelago model is considered as 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 in less degree to the Australian sector of Gondwana, while biogeographical connections with Siberia and Baltica were negligible. During the Sandbian to Katian, a loose cluster of Kazakh microcontinents and island arcs became a major biodiversity hotspot and species pump located in 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.