Cerium anomaly in a marine carbonatite could be used as an indicator of redox condition in the paleosea-water.The bottom sea water of the Angola Basin and the Brazil Basin(South Atlantic Ocean) was anoxic during Cretaceous period.At about 58×106-54×106 a BP,the sea water of the South Atlantic Ocean became oxidized condition which was similar to that of the modern Atlantic Ocean.This paper presents a new cerium redox thermodynamic equation which could explain the long-standing problems,such as the different characteristics of the cerium anomalies in the sea water and river water and why there are positive cerium anomalies in the surface sea water.etc. Investigation reveals that at 58×106-54×106a BP,the plates of Africa and South America were separated from each other thoroughly and the unified Atlantic Ocean took shape.We suggest that the Alpine and Himalayan movements were in synchronism.