Abstract

Tràng An area has undergone a series of sea transgressions and regressions corresponding to global glacial and interglacial periods from the Early Pleistocene to the  Late Holocene, especially the Flandrian sea transgression. The alternating sea transgressions and regressions affecting the Ninh Bình area are: Cát Lâm, Bỉm Sơn and Vĩnh Phúc transgresions in Pleistocene, followed by Đống Đa transgression (also calledHải Hưng transgression and corresponding with  Flandrian transgression in countries such as Belgium, Holland, etc.) which reached the maximum in Early-Middle Holocene.. Erosion notches in the limestone mark the Quaternary sea levels at different elevations. The results of C¹⁴ dating of oyster shells in the erosion notches at 2m a.s.l give the age of 4,300 to 6,500 years BP, corresponding with Early-Middle Holocene (Hải Hưng transgression - Flandrian transgression). The caves in Tràng An area are mostly through karst caves and fossil caves formed in four periods: Period 1 lasted from the end of Early Pleistocene to the beginning of Middle Pleistocene with the formation of the oldest caves at 60m a.s.l, such as Trống, Bói, Chợ. Period 2 was in Late Pleistocene with the formation of the caves at 10-15m, 20-30m a.s.l, such as Thung Bình and Mòi. Period 3 was in Early-Middle Holocene with the formation of  the caves at 2-9m a.s.l, such as Vàng, Ông Hay, Ốc, Trâu Bái Đính, Thiên Hà, etc. In period 4 were formed the caves at below 2m, mainly though caves such as Sinh, Seo, Thuốc, Địa Linh, Quy Hậu, etc. Stone implements of ancient people have been found in many caves, such as Ốc, Thiên Hà, Vàng, Ông Hay, Mòi, which were used as shelters during Hải Hưng (Đống Đa)transgression  in Early-Middle Holocene when the seawater submerged the Tràng An area as a whole to the height of 2 to 10m. Some caves like Trống, Bói and Chợ might have been occupied by ancient people in the Late Pleistocene (23,000 years BP).