西藏岗巴察且拉剖面白垩系孢粉组合

PALYNOLOGICAL ASSEMBLAGES FROM THE CRETACEOUS SUCCESSION AT CHAQIELA,GAMBA COUNTY,XIZANG

雅鲁藏布江以南的藏南特提斯喜玛拉雅白垩系一直备受关注,但迄今仍缺乏有关白垩纪孢粉组合序列的系统报导。本文详细研究报导了岗巴察且拉这一代表性剖面的孢粉化石。根据重要孢粉类群的分布和发生情况,从下部的门卡敦组向上经岗巴东山组、察且拉组和岗巴村口组共计产出2个孢粉组合及3个亚组合,由下向上依次为Microcachryidites antarcticus-Crybelosporites带和Gabonisporis-Crybelosporites pannuceus带。前者还可进一步的细分为3个亚带,自下而上分别为:Cicatricosisporites-Crybelosporites stylosus亚带、Cyclosporites hughesii亚带和Crybelosporites striatus亚带。根据孢粉类群的分布和发育特征以及沟鞭藻等化石,Microcachryidites antarcticus-Crybelosporites带的时代被推定为早白垩世Berriasian期—Albian期,Gabonisporis-Crybelosporites pannuceus带时代则为Cenomanian期至Coniacian期甚至Santonian期。前者的3个亚带的时代则分别为Berriasian期—Barremian期(Cicatricosisporites-Crybelosporites stylosus亚带)、Aptian期(Cyclosporites hughesii亚带)和Albian期(Crybelosporites striatus亚带)。上述组合可以与印度南部Cauvery等盆地孢粉组合很好的对比,与同期的澳大利亚组合则在早期(Microcachryidites antarcticus-Crybelosporites带)相似、后期具有差异。

So far, little is known about the Cretaceous palynofloras in the Himalayan Tethys, south to the Yarlung Zangbo Suture in southern Xizang, no matter to say a good, continuous palynological sequence. The present paper reports our recent re- search on pollen and spores from a typical section of the Cretaceous in this area at Chaqiela near the town of Gamba. All the four lithological units of the section, i. e. the Menkadun, Gamba Dongshan, Chaqiela and Gamba Cunkou formations in ascending order, are palynoferous. Two pollen and spore zones and three subzones are founded according to the occurrences of key taxa through the sequence as （in ascending order） Microcachryidites antarcticus-Crybelosporites Zone and Gabonisporis- Crybelosporites pannuceus Zone. The former can be further subdivided into Cicatricosisporites-Cry- belosporites stylosus , Cyclosporites hughesii and,Crybelosporites striatus subzones. Integrated stratigraphic analysis of the pollen and spore constituents and dinoflagellate cysts in association suggest an Early Cretaceous or Berriasian-Albian age for the Microcachryidites antarcticus-Crybelosporites Zone and a Late Cretaceous or Cenomanian to Coniacian but possibly to Santonian age for the Gabonisporis-Crybelosporites pannuceus Zone. The three subzones of the lower pollen and spore zone are of Berriasian--Barremian （the Cicatricosisporites-Crybelosporites stylosus Subzone）, Aptian （the Cyclosporites hughesii Subzone） and Albian （the Crybelosporites striatus Subzone） in age. These Cretaceous palynoassemblages recovered from southern Xizang are well correlated with the southern Indian records such as from the Cauvery Basin. The palynofloras are also comparable to the Australian ones in the earlier stage or for the Mi- crocachryidites antarcticus-Crybelosporites Zone, but after that they show clearer differentiations.