TECTONIC EVOLUTION OF SOUTHWEST MARGIN OF NORTH CHINA IN EARLY PALAEOZOIC AND ITS' SEDIMENTARY RESPONSE: A CASE STUDY OF THE DUANJIAXIA PROFILE

According to the depositional characteristics of the early Paleozoic in the southwest margin of North China, we believe that the sedimentary response could well reflect the environment changes caused by tectonic transformation in this region. Basin evolution of the region has gone through two tectonic periods:a passive continental margin in Sinian-Middle Ordovician and an active continental margin in Late Ordovician-Silurian. The Zoulang passive continental marginal basin and the HeLan basin were formed in the former period under clastic flat and Shallow carbonate shelf environments, and the Zoulang back-arc basin was formed in the later period. The area began to strongly subside when the Zoulang back-arc basin was formed in Late Ordovician-Silurian. Slumping and turbidite deposits have been found on the deep-water slope.. Owing to the influence of the Caledonian Movement, the deep water environment changed into the shallow carbonate environment again when the sea level dropped in Later Ordovician.