(named for the Isle of Thanet in the county of Kent, Great Britain), the second stage from the bottom of the Paleogene system (period).
The Thanetian stage was distinguished by the French geologist E. Renevier in 1873. It is represented in the stratotype by greensands with mollusks. In the Paris Basin, the Thanetian stage is composed of sands and, less frequently, marls. In its upper parts there are freshwater fauna and lignites. The Thanetian stage lies atop the Montian stage and is overlain by the Ypresian stage. In the USSR, the Thanetian stage corresponds approximately to the Kacha stage in the Crimea, which is represented by aleurite marls with mollusks, foraminifers, and other fossils.