The Role of Cyanobacteria In the Microfabric Heterogeneity of Cambrian Leiolite, North China
Author:
Mei Mingxiang12, Riaz Muhammad345, Koeshidayatullah Ardiansyah6, Liu Ziliang34, Ahmed Mohamed S.7, Fathy Douaa8
Affiliation:
1. 1 School of Earth Sciences and Natural Resources, China University of Geosciences, Beijing 100083, China 2. 2 State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China 3. 3 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu-610059, China 4. 4 College of Energy Resources, Chengdu University of Technology, Chengdu-610059, China 5. 5 Hydrocarbon Development Institute of Pakistan, Islamabad, Pakistan 6. 6 Department of Geosciences, College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia 7. 7 Geology and Geophysics Department, College of Science, King Saud University 2455, Riyadh 11451, Saudi Arabia 8. 8 Geology Department, Faculty of Science, Minia University 61519, Egypt
Abstract
ABSTRACT
Based on their mesostructures, carbonate microbialites are divided into four major groups: laminated stromatolite, clotted thrombolites, structureless leiolites, and dendritic dendrolite. Among the various types of microbialites, leiolites, also known as “cryptomicrobial deposits,” are uncommon in the stratigraphic records. This is exacerbated by leiolites relatively structureless and aphanitic structure, making their identification and characterization more challenging. Previous studies have revealed that leiolites have contrasting fabrics at different scale, heterogeneous microscopic fabrics and structureless mesoscopic to macroscopic fabrics. While it is widely assumed that cyanobacteria play a significant role in the formation of carbonate microbialites in marine environments, the origin and controlling mechanisms of variations in leiolites microstructures and macrostructures remain enigmatic. In the central part of the North China Platform, two excellent exposures of massive, structureless Cambrian bioherms (Furongian) dominated by leiolites were observed (Qijayu section). The Qijayu-section leiolites offer a unique opportunity to investigate the role of cyanobacterial input in governing the formation and textural heterogeneities of such microbialites. In addition, the significance of the Furongian leiolites stems from their association with a period of global development of microbial-dominated carbonate platforms. Our findings suggest that these Furongian leiolites developed during the forced-regressive systems tract. At the microscopic level, these Furongian leiolites exhibit a high degree of heterogeneity which is controlled by the presence of various types of cyanobacteria (Hedstroemia, Subtifioria, Girvanella), sponge mummy, and benthic ooids. The Hedstroemia, Subtifioria and Girvanella excreted extracellular polymeric substances that form multiple biofilms in cyanobacterial microbial mats where Furongian leiolites grew. The role of cyanobacteria in the microscale heterogeneity of Cambrian leiolites is evident, and this provides new insights into the development of microbial-dominated carbonate platforms in similar settings elsewhere. As a result, this study provides not only a reference example for global correlation but also some solid clues for further understanding the growth style of leiolites in the geologic record.
Publisher
Society for Sedimentary Geology
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