Late Cretaceous To Early Paleogene Foraminiferal Biozones In The Xishan Section,Gamba,Tibet

The Late Cretaceous – early Paleogene lager benthic foraminifera in the eastern Neo-Tethyan Ocean of south Tibet still remain poorly known.This investigation of Upper Cretaceous and lower Paleogene sedimentary successions from Gamba of south Tibet provides the high resolution foraminiferal biozonation description from the shallow water limestones in south Tibet,which will fill the research gap of the foraminiferal evolution in Gamba of south Tibet.Based on the section at Gamba,we divide the successions into thirteen biozones(TLK1-2 and TP1-11):(1)TLK1,a Coniacian-Maastrichtian,outer neritic setting,dominated by keeled planktonic foraminifera,such Globotruncan;(2)TLK2,a latest Maastrichtian,forereef environment with benthic assemblages dominated by Lepidorbitoides,Orbitoides and Omphalocyclus;(3)TP1-4,a Danian-Thanetian,backreef or shallow reefal environment,dominated by small rotaliids and miliolids,such as Lockhartia and Daviesina,where firstly observed the Nummlitid Ranikothalia;(4)TP5-11,a late Paleocene-early Eocene,shallow reefal warm environment with benthic assemblages,dominated by Alveolina and Assilina.Many LBF forms such as Assilina in eastern Tethys(Tibet)appear about 1Ma later than in the western Tethys,revealing their gradual eastward migration.The biostratigraphy sequence of late Cretaceous-early Paleogene larger benthic foraminifera in eastern Tethys were re-established in this thesis.A clear link was also established between the SBZs in the eastern Tethys and those in western Tethysb.Based on the forminifera biostratigraphy,the Paleocene-Eocene boundary in shallow warm water environments were identified in this study.