EARLY CAMBRIAN BIOCONSTRUCTIONS IN THE ZAVKHAN BASIN OF WESTERN MONGOLIA

The Neoproterozoic-Cambrian succession in the Zavkhan Basin of western Mongolia preserves early Cambrian bioconstructions of Nemakit-Daldyni an to Botomian age. As elsewhere (Siberia, Morocco), the Nemakit-Daldy nian bioconstructions in the upper Tsagaan Gloom Formation to lower Ba yan Gol Formation interval were purely calcimicrobial. Spectacular cal cimicrobial 'patch reefs' of presumed Tommotian age are present in the lower Bayan Gol Formation. In contrast, late Atdabanian-early Botomia n bioconstructions are varied and well developed in the upper Salaany Gol Formation including, in addition to calcimicrobial bioherms, Gordo nophyton-Razumovskia crusts, radiocyathan-archaeocyathan bioherms and thickets of the ramose archaeocyath Cambrocyathellus. These latter Zav khan Basin buildups show some ecological and sedimentological features in common with coeval bioconstructions in South Australia, which also developed under a tectonically active regime.