| Popis: |
Leiolites exposed in the Jinzhouwan section of Cambrian Miaolingian in Dalian City, Liaoning Province, North China Platform, were developed in the highstand systems tract of third-order sequence. The macroscopic and microscopic characteristics of leiolites are studied via field and indoor polarizing microscope observations. Macroscopically, leiolites mainly consist of micrites without any special internal structure. Microscopically, in addition to micrite matrix, calcimicrobes (including Girvanella, Subtifloria, Angulocellularia, Renalcis, Tarthina, and Bacinella-like fabric), microclots, benthic ooids, bioclasts, dolomite, and terrigenous debris were observed. Girvanella shows four types of growth habits. Differences in microfabrics and microbial communities within the Miaolingan leiolites may be caused by the different local environmental conditions. The calcimicrobes dominated by calcified sheaths of filamentous cyanobacteria, together with amounts of pyrites and poorly preserved calcified microbes, indicate that the formation of leiolites is related to the calcification induced by microbial metabolic activities and the degradation of organic matter by heterotrophic sulfate-reducing bacteria. The complex calcification in the microbial mats dominated by filamentous cyanobacteria in the study area provides an example for studying the first cyanobacterial calcification episode during Phanerozoic. |
