藏南江孜所金混杂堆积中灰岩块体里的浮游有孔虫

PLANKTIC FORAMINIFERA FROM THE LIMESTONE BLOCKS IN SUOJIN,GYANGZE,SOUTHERN TIBET

通过对藏南江孜所金北剖面混杂堆积中灰岩块体的分析,在2块样品中发现了丰富的浮游有孔虫化石。样品SJ-28含5属12种或未定种,包括Contusotruncana fornicata,C.patelliformis,C.plummerae,Globotruncana arca,G.falsostuarti,G.linneiana,G.ventricosa,Globotruncanita atlantica,Gl.sp.,Gl.stuartiformis,Pseudotextularia nuttalli和Muricohedbergellasp.等,指示的地层时代为晚白垩世中坎潘期至晚坎潘期。样品SJ-18发现5属9种或未定种,主要有Contusotruncana fornicata,C.patelliformis,C.plummerae,Globigerinelloides sp.,Globotruncana arca,G.falsostuarti,Globotruncanitasp.,Gl.stuartiformis和Muricohedbergellasp.等种,指示的时代为晚白垩世中坎潘期至马斯特里赫特期。因此,这些产有孔虫灰岩块体的形成时代应为中坎潘期至马斯特里赫特期,这为探讨该地区混杂堆积的形成时代提供了新的化石证据。上述有孔虫组合的主要面貌特征是化石丰度较高,分异度中等,全部由浮游有孔虫组成,未见底栖有孔虫,反映了远洋深海的沉积环境,可与附近床得剖面和勇拉剖面出露的床得组红层中所产的有孔虫动物群进行对比。这些灰岩块体的沉积环境可能与江孜地区的床得组红层相当。

Two limestone blocks from the Mélange at the Suojinbei section contain rich planktic foraminifera.A diverse foraminiferal fauna of 12species from 5genera has been recovered from sample SJ-28,including Contusotruncana fornicata,C.patelliformis,C.plummerae,Globotruncana arca,G.falsostuarti,G.linneiana,G.ventricosa,Globotruncanita atlantica,Gl.sp.,Gl.stuartiformis,Pseudotextularia nuttalli and Muricohedbergella sp.This planktic assemblage was dated as early to late Campanian.A relative younger assemblage ranging from middle Campanian to Maastrichtian was recovered from sample SJ-18,including 9species in 5genera:Contusotruncana fornicata,C.patelliformis,C.plummerae,Globigerinelloides sp.,Globotruncana arca,G.falsostuarti,Globotruncanita sp.,Gl.stuartiformis and Muricohedbergellasp.The planktic foraminifera indicates a age of the middle Campanian to Maastrichtian for the limestone blocks at the Suojinbei section.It provides new fossil evidence for discussing the age constraint of the Mélange in the Gyangze area.The assemblages are characterized by the high abundance and middle diversity of the planktic forms with the absence of benthic forms,which indicate a deep-sea sedimentary environment.The assemblages can be correlated with the contemporaneous faunas found in red beds of the Chuangde Formation at the Chuangde section and the Yongla section of the Gyangze area which suggests a similar depositional environment between the limestone blocks and the red beds in the Gyangze area.