PALEOECOLOGICAL AND PALEOZOOGEOGRAPHICAL ANALYSIS OF ORDOVICIAN HELIOLITOID CORALS OF MONGOLIA

Abstract

During the Middle-Late Ordovician, Mongolian heliolitoids increased their sizes, diversity of colony shapes, and longevity. Their biotopes, restricted to the sublittoral zone, were more uniform than those of the Tabulata and Rugosa. The maximum reef-building activity of heliolitoids occurred in the first Ralf of the Middle Ashgill (peak of transgression). In the Middle-Late Ordovician, the Mongolian sea basin was situated in the tropical and, partly, in subtropical zones of the Northern Hemisphere within the Siberian-Canadian Paleozoogeographical Region and constituted a single province with the seas of the Altai-Sayan Region and Siberia.