Morphology and features of Cambrian oncoids and responses to palaeogeography of the North China Platform  

作　　者：En-Zhao Xiao Ming-Xiang Mei Shu Jiang Tehseen Zafar 

机构地区：[1] School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China [2] Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education and Faculty of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China [3] Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China [4] Institute of Geology,University of the Punjab,Lahore 54590,Pakistan

出　　处：《Journal of Palaeogeography》2020年第2期150-167,共18页古地理学报（英文版）

基　　金：National Natural Science Foundation of China (Nos. 41472090 and 40472065)。

摘　　要：The Cambrian strata in the North China Platform are fully exposed. A wide variety of carbonate oncoids with different shapes occur in the Xuzhuang and Zhangxia formations(Miaolingian Series) from six Cambrian sections in the study area. A comprehensive study involving outcrop description, microscopic observation, scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDX), X-ray diffraction(XRD), and carbon and oxygen isotope analysis is conducted to determine the facies, morphology, internal structure, and geochemical properties of the oncoids. The oncoids are divided into six types based on their morphology and internal structure.Microscopic and ultrastructural observations reveal typical microbial fossils(Girvanella) and microbially-related sediments(framboidal pyrite), indicating the biogenicity of the oncoids. Additionally, the XRD and carbon and oxygen isotope analysis results suggest that the formational environments of these oncoids are different due to terrestrial influences. Statistical data on the oncoids from the six sections show that there are obvious differences in the types of oncoids and the proportions of different varieties in each section. The spatial differences in the oncoid morphologies are associated with different palaeogeographic settings. The rough oncoid growth patterns developed in nearshore environments were influenced by terrigenous debris and steep terrain, whereas the delicate oncoid growth patterns developed in offshore environments were less affected by terrestrial factors and were featured by more stable depositional processes related to microbial mats.

关 键 词：Morphological classification Microbial m at Girvonello Carbon and oxygen isotopes Miaolingian series North China 

分 类 号：Q915[天文地球—古生物学与地层学] P534.41[生物学—古生物学]