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Morphology and features of Cambrian oncoids and responses to palaeogeography of the North China Platform
- Source :
- Journal of Palaeogeography, Vol 9, Iss 1, Pp 1-18 (2020)
- Publication Year :
- 2020
- Publisher :
- SpringerOpen, 2020.
-
Abstract
- 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.
- Subjects :
- 010506 paleontology
Outcrop
Terrigenous sediment
Miaolingian series
Geochemistry
Girvanella
Morphological classification
010502 geochemistry & geophysics
01 natural sciences
Carbon and oxygen isotopes
Sedimentary depositional environment
chemistry.chemical_compound
North China
Microbial mat
chemistry
lcsh:Paleontology
Facies
Carbonate
lcsh:QE701-760
Geology
0105 earth and related environmental sciences
Oncolite
Subjects
Details
- Language :
- English
- ISSN :
- 25244507
- Volume :
- 9
- Issue :
- 1
- Database :
- OpenAIRE
- Journal :
- Journal of Palaeogeography
- Accession number :
- edsair.doi.dedup.....5317f0b59b73bac370ea794bfe9ba426