Boreskov

PP‐43CAUSE‐EFFECT RELATIONSHIP OF THE PALEOZOIC REEF‐FORMATIONEVOLUTION AND GEO‐BIOLOGICAL EVENTS IN THE NORTH OF THE URALSAntoshkina A.I.Institute of Geology, Komi Science Centre, Ural Branch, RAS, Syktyvkar, RussiaThe knowledge of processes leading to full transformation or ontogenic degradation ofreef ecosystems is important for correlation of an initiation and disappearance of reef stagesas display of large geo‐biological events. The reef formation history in the North‐uralian seabasin is subdivided into three stages each of which is characterised by different genetic typesof biogenic frameworks.The first longest Caradoc–Early Emsian stage is characterised by development of barrierecological reefs from 100 to 1200 m in thickness in the conditions of various biosphericevents. It was reflected in distribution of various metazoan‐cyanobacterial (metazoa –rugose corals, bryozoans, sphinctozoan sponges, receptaculitids, hydroids) communities inreef ecosystems. Collision of Baltic and Laurentia paleocontinents has increased areas oferosion and, accordingly, mesotrophy of sea waters. Passive rifting and post‐riftingimmersing as result of an activization of the Pechora Plate basement blocks were shown insharp differentiation of deposition settings within carbonate platforms. Global regressions asa result of a climate coolong at formation of glaciers on Gondwana caused an exposition ofthe carbonate platforms and accordingly of reef surfaces erosion. Climate warminggenerated global transgressions which were often accompanied in the beginning byoccurrence of anoxic conditions sometimes fatally influencing on the reef ecosystems. Atinfringement of ocean circulation owing to global fluctuations of a sea level the anoxiaphenomenon had global character and was accompanied by extinction events (theHirnantian, Ireviken, Lau, Klonk, etc. events). However they did not occur an essentialstructural reorganisation of the reef ecosystems in the north of the Urals since pioneercommunities accepted active participation in formation of the biogenic frameworks.During the second Middle Frasnian‐Tournaisian stage many benthic communitiesconstantly tested hydrochemical and biological stresses in system of biospheric processes.Regeneration and active development of the Pechora‐Kolva paleorift zone as a system ofdeeps at the shelf, frequent fluctuations of a sea level, a collling during the Famennian time,extinction events (the Kellwasser and Hangenberg) have led to development only the210