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The Ultrastructure and Origin of Upper Sinian Cherts on the Southeast Continental Margin of the Yangtze Platform 1
Author(s) -
Haisheng Yi,
Yunfu Zeng,
Wenjie Xia
Publication year - 1994
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.1994.mp7004003.x
Subject(s) - geology , margin (machine learning) , continental margin , paleontology , ultrastructure , geochemistry , anatomy , tectonics , biology , machine learning , computer science
Through microscopic and SEM observations and X‐ray diffraction and energy spectrum analyses, the oldest sponge spicules and radiolarians have been found in bedded cherts and it is proposed that microbial activity of algae and bacteria played an important role in silica precipitation. The microbial activity resulted in the formation of a series of single crystals and crystal aggregates with peculiar shapes. Biogenic single crystals usually occur in spherical, rod, platy, colloidal and granular forms. The most common aggregates are framboidal aggregates composed of dense spherical quartz crystals, which are considered to be of typical bacterial origin. Other aggregates, such as favositic, double‐spherical, chain ‐spherical and coccoid ones, are considered to be probably the result of silicification of algal cells and mainly of primary sedimentary origin. This paper also discusses the ultrastructural features and diagnostic indications of jasper rocks formed in a submarine hydrothermal environment and cherts formed by replacement and diagenetic recrystallisation.