Quaternary sedimentary cycles in relation to sea level change in Vietnam

Abstract

Vietnam has over 3200 km shoreline which extends from north to south of the country. Sea level changes were principal factors influenced on sedimentary environment and compositions. In Quaternary, cycles of sea level change and tectonic movement were main factor that created Red River delta, Nam Bo plain and Central plain. There are 5 sedimentary cycles corresponding to 5 cycles of sea level change of the Red River delta and Nam Bo plain. Sedimentary cycles were characterized by sedimentary coefficients such as: grain size, clay content, index of cation Fe2+/Fe3+ exchange, pH variation from the start to the end of cycles. They are represented by fluvial terraces, marine terraces, marine notches and peat layers. In central littoral plain, the relationship between sedimentary cycles and sea level is represented by five sandy cycles and distribution of coral terraces in shallow sea. There are 5 generations of ancient shoreline zones, which correlated with glacial and interglacial periods in Vietnamese continental shelf: the shoreline in 30 m water depth is correlated with (Q2 1-2). Up to 60 m water depth is correlated with (Q1 3b‐Q2 1) and 100‐120 m water depth is correlated with Wurm2 glaciation (Q1 3b)(?). In 200‐300 m water depth correlated with Wurm1 glaciation (Q1 3a)(?), at 400‐500 m water depth correlated with Riss glaciation (Q1 2b)(?), at 600‐700 m water depth correlated with Mindel glaciation (Q1 2a)(?), and at 1000‐1500 m water depth correlated with Gunz glaciation (Q1 1)(?). As such Quaternary sea level changes in mainland and continental shelf interacted and quite distinctive form each other by pendulum rule.