东昆仑南带中元古代晚期—新元古代早期叠层石组合的发现

东昆仑南带加嗡门地区碳酸盐岩地层中发现的中元古代晚期-新元古代早期叠层石组合以大型锥叠层石及其相关的分子Conophyton garganicus var. inkeni,C. cf. ressoti Menchikov, Jacutophyton f. 和Conicodomenia cf. longotenuia等最丰富, 并与Baicalia共生, 故可视之为Conophyton-Baicalia组合.这叠层石组合可以与天山、华北等地蓟县系中部-青白口系中部叠层石组合对比,尤其酷似于天山地区蓟县系的爱尔基干组合和华北蓟县系的闪坡岭叠层石组合,而显著有别于华南地块.它还可以与南乌拉尔、西伯利亚、北美、北非和阿拉斯加半岛等地区的中里菲界上部--上里菲界下部层位中的叠层石组合对比.加嗡门叠层石组合的时限为距今1 300～850 Ma,大致为蓟县纪中期-青白口纪中期或中里菲晚期-晚里菲早期.东昆仑南带存在前寒武纪微地块,当时此微地块的古地理和古环境与天山、华北、西伯利亚和阿拉斯加半岛等地区的前寒武纪地块相似,均位于低纬度区,其上均广泛发育适宜叠层石繁育的温暖陆表海,它们可能共同处于罗迪尼亚超大陆的低纬度大陆边缘部位,与华南地块的不同.这对本区和东昆仑地层和大地构造研究,以及对罗迪尼亚超大陆重建提供了新的古生物约束.

DISCOVERY OF LATE MESOPROTEROZOIC-EARLY NEOPROTEROZOIC STROMATOLITE ASSEMBLAGE IN THE SOUTHERN BELT OF EASTERN KUNLUN

This paper reported, for the first time, a newly discovered Late Mesoproterozoic—Early Neoproterozoic stromatolite assemblage, named the “Jiawengmen stromatolite assemblage”, represented by the Conophyton-Baicalia group in Jiawenmen area, the southern belt of the eastern Kunlun. The stromatolite assemblage was dominated by large-scale conical stromatolites and related elements, i.e., Conophyton garganicus var. inkeni, C. cf. ressoti Menchikov, Jacutophyton f. and Conicodomenia f., which commonly co-existed with elements of the group of Baicalia. This assemblage could be correlated with that of the Middle Jixian System—Middle Qingbaikou System in North and Northwest China, but different from that in South China. It could also be correlated with that in the upper horizon of the Middle Riphean—lower horizon of the Upper Riphean in South Ural Mountains and Siberia of Russia, North Africa, and Alaska Peninsula. These facts suggested that the Jiawengmen stromatolite assemblage probably colonized during 1 300～850 Ma ago. Accordingly, the stromatolite-bearing carbonate rocks were then proposed to correspond to the Middle Jixian System—Middle Qingbaikou System or the upper Middle Riphean—lower Upper Riphean. Our stromatolite data further revealed that a Precambrian microblock, named the Maqen Microblock, likely occurred in the southern belt of the eastern Kunlun. Similar stromatolite assemblages in the Maqen microblok and those blocks that occurred in the North China, Siberia and North Africa pointed to a similar palaeogeographic and palaeoenvironmental condition. These microblok and blocks were likely located at low-latitudes and on the continental margin of the Rodinian supercontinent, where warm epicontinental seas were favorable to widespread colonization of stromatolites during the Late Mesopro—terozoic—Early Neoproterozoic. However, the stromatolite assemblage was quite different from those of South China Block, suggesting different palaeogeographic contexts, probably of different tectonic affinity as well.