Abstract

Microscopic morphologic variations of Epiphyton thalli in microbial buildups were examined in order to detail controlling factors on morphology and calcification processes, and their implications for identification of calcified microbes. Microbial carbonate of the Zhangxia Formation (Middle Cambrian), Shandong Province, China comprises thrombolites, stromatolites, and Epiphyton buildups, as well as consortia of microbial and metazoan communities. Epiphyton, a rigid framework of the buildups, is subdivided into four types based on characteristics of the branches. Type 1 consists of ∼75-μm-diameter dendritic rods of dense micrite that form bush-shaped and chambered thalli. Type 2 has ∼80-μm-thick branches characterized by transverse segments. Type 3 consists of thin, ∼50-μm diameter micritic branches that form round thalli. Type 4 is characterized by laterally arrayed, branching tubes that form fan-shaped thalli. All morphologic types have bipartite branched filaments as a basic growth pattern. Bush-shaped thalli are dominant in the inner part of the Epiphyton bioherms, while chambered thalli, which are solitary, connected, and tiered, are common in the outer part. Such physical energy conditions as currents or waves control the density, length, and sheath thickness of the branches and propagation pattern of the thalli. Chamber outlines of Epiphyton thalli resemble those of Renalcis, although internal structures of the branching rods and tubes in the chamber walls are distinct. Thalli become similar to that of Renalcis when calcification and diagenesis remove or obliterate the internal fabric of the chamber wall. Morphologic variations of Epiphyton thalli and subsequent textural changes can result in identification as different groups of calcified microbial taxa.

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