Complete Late Cretaceous to Palaeogene strata are exposed in the Gamba area, Tibet. The strata contain abundant fossils. An accurate chronostratigraphic classification has been made according to the fossil study. The authors suggest that the Cretaceous-Palaeogene be located between the Zongshan Formation and Jidula Forma-tions and be marked by the disappearance of the benthonic forarninifer Orbitoides-Omphalocyclus assemblageand the first occurrence of the Rotalia-Smoutina-Lockhartiz assemblage. The contact between the strata above and below the boundary are disconformable, with a short exposure surface within it. The Palaeogene sandy con-glomerate directly overlies the Late Cretaceous shelf carbonate rocks. The significant change of the deposits rep-resents a tectonic movement. The northern margin of the Indian continent and the southern margin of Gangdise had both shown the distinct phenomenon of shallow-sea biogeographic provincialism till the latest Cretaceous, and in this period they were separated by a deep-sea basin. At the beginning of the Palaeogene the shallow-sea fauna showed the features of the same biogeographic realm in the area, suggesting that the separation of the two continents by the deep-sea basin had disappeared and the northern and southern biogeographic provinces be-longed to a single remnant sea basin. The transformation of the sediment types and stratigraphic and palaeonto-logical characteristics provide fundamentat data for the study the timing of initiation of the collisionbetween the Indian and Asian plates. According to that it may be inferred that the early continent-continent collision took place at the time (- 65 Ma) of the Cretaceous -Palaeogene. The mid-late Palaeogene carbonate platform un-derwent continued compression and deformation, which further indicates that the continent collision had taken place at the beginning of the Palaeogene. The fracturing and olistostromes are the result of sustained sollison and compression.