河南登封寒武系第三统张夏组核形石与遗迹化石的耦合变化

河南登封关口剖面寒武系第三统张夏组下部碳酸盐岩中发育了大量的微生物成因的核形石和后生动物遗迹化石。在野外和显微镜下对核形石和遗迹化石进行观察,并统计它们在地层中所占比例,表明核形石和遗迹化石存在着耦合关系。下部地层以发育凝块石和形状不规则、纹层不连续、代表一种低能弱搅动水体的Ⅰ型核形石为主,不含遗迹化石,表明此时微生物在海洋生态系统中占主导地位。中部地层则以发育浑圆形、纹层连续的Ⅱ型核形石和遗迹化石Planolites为特征;而且随水体能量的增强,Planolites丰度逐渐升高,核形石丰度逐渐降低;二者的丰度变化说明后生动物的存在对核形石的数量有一定影响,但未破坏核形石的生长条件。上部地层发育大量Thalassinoides和生物扰动构造,缺乏核形石;后生动物对沉积基底进行反复扰动,彻底破坏了原始层理以及微生物造岩的环境,核形石消失。可见,在张夏组沉积时期,微生物与后生动物以及环境之间存在着特殊的相互作用关系。

COUPLING VARIATION OF ONCOIDS AND TRACE FOSSILS IN THE ZHANGXIA FORMATION(CAMBRIAN SERIES 3),DENGFENG,WESTERN HENAN PROVINCE

Abundant microbiogenic oncoids and metazoan trace fossils are widely distributed in the carbonates of the lower part of the Zhangxia Formation(Cambrian Series 3),Dengfeng,Henan.The analysis of field outcrop and microscope observation on oncoids and trace fossils and their corresponding proportions in sediments shows that there is a coupling relationship between them.The lower part of the section is dominated by the development of thrombolites and typeⅠ oncoids and trace fossils are absent.The typeⅠ oncoids have irregular shape and discontinuous lamination,formed in a weak-agitated low energy environment condition.The dominance of microbialites in the sediments indicates that microbes are the main organisms in marine ecosystem at that time.The middle part of the section is characterized by the co-existing of type II oncoids and trace fossils Planolites.The abundance of Planolites increases while type II oncoids reduce gradually with the increase of water energy upward.The change of their abundance shows that the occurrence of metazoan has an impact on the development of oncoids but hasn't destroyed the formation condition of oncoids.Abundant trace fossils Thalassinoides and bioturbated structures occur in the upper part of the section.The repeated reworking of sedimentary substrate by metazoan completely destroyed primary sedimentary fabric and genetic environment of microbialites and led to the disappearance of oncoids in the sediments.Therefore,There are special interactive relations among microbes,metazoan and their environmental conditions during the sedimention of the Zhangxia Formation.