Stratigraphic Significance of Larger Benthic Foraminifera in Miocene Carbonates from Nam Con Son Basin, Vietnam

Larger benthic foraminifera (LBF) in Southeast Asia developed prosperously in the Neogene. So, they play a meaningful role in defining the stratigraphy and depositional environment of carbonate formations. Many studies from a lot of localities in this region have been published to present their prevalence, diversity and their significance. However, they remain poorly published in Vietnam even though they are recorded abundantly in the Miocene carbonate deposits in the Tertiary basins on the Vietnam continental shelf, especially in the Nam Con Son Basin, in the southeast. This paper presents the first review on LBF in Miocene carbonate sediments and their stratigraphic range in the Nam Con Son Basin. As a result, a stratigraphic framework for the Miocene LBF of the basin, ranging from Te5 to Tg letter stages, is established. This may be used to identify the geological age and to support the correlation of carbonate deposits in this area. In general, their evolution demonstrates the development of carbonate formations in the basin, which are connected to the opening of the South China Sea; foraminifers follow the main evolutionary lineages of the Indo-Pacific province but have distinctive characteristics. In the Early Miocene, LBF appeared sparsely in Te5, then became frequent in lower Tf1. In the Middle Miocene, they presented their diversity and abundance in the fauna of Miogypsina, Lepidocyclina (Nephrolepidina), Cycloclypeus and Katacycloclypeus. In the Late Miocene, some of them were recorded in the carbonate formations in the high structures in the southeast of the basin.