Paleoclimate change during the Neogene period in Vietnam: Sedimentological evidences from the Hoanh Bo basin (Quang Ninh province, Northeastern Vietnam)

The Hoanh Bo Basin is filled with Neogene continental sediments which were subdivided into the Dong Ho, Tieu Giao and undivided Quaternary formations. The Dong Ho formation, two main sedimentary systems were recognized, namely alluvial and lacustrine with the main amount of lacustrine sediments, while there are also 2 main sedimentary systems, namely alluvial and fluvial with the main amount of fluvial sediments in the Tieu Giao Formation. Keeping track ofthe bottom formation of the basin and comparing characteristics of materials, the change of plant world from the lowest strata to the upper one in vertical profile during the Neogene period represents that the evolution of Neogene climate is the gradual transmutation from semi-dry and hot, even dry and hot into wet tropical condition.