Microbialites and microbial carbonates, formed during growth of microbes by their calcification and binding of detrital sediment, have become one of the most popular geological topics recently. They occur throughout the entire geological history, and especially flourished during the Meso- to Neoproterozoic, Cambrian–Ordovician, Late Devonian–Early Carboniferous, and Early Triassic. Flourish and decline of microbialites and microbial carbonates are closely related to major geological events, paleoclimate, and paleoceanography. Therefore, studies on these microbial-induced sediments are important with respect to revealing paleoceanographic, paleoclimatic, and paleoecological conditions. They also bear important economic significances due to their complex structures and biogenic origins.
Recently, Dr. CHEN Jitao from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences and his colleague provide review and present new views on current progress and problems in the study of microbialites and microbial carbonates, based on literature investigations and their recent researches. The proposed that microbial carbonates can be classified into two categories: stabilized microbial carbonates (i.e., carbonate microbialites, such as stromatolites and thrombolites) and mobilized microbial carbonates (i.e., microbial carbonate grains, such as oncoids and microbial lumps). Various texture, structures, and morphologies of microbialites and microbial carbonates hamper the systematic description and classification. They also provide a practical classification on various structures of microbialites.
Moreover, complex calcification pathways (mostly extracellular) and diagenetic modifications further obscure the origin of some microbialites and microbial carbonates. Recent findings of abundant sponge spicules in previously identified “microbialites” challenge the traditional views about the origins of these “microbialites” and their implications to reef evolution. On the other hand, microbialites and microbial carbonates are not always flourished in the aftermath of extinction events, which, together with other evidences, suggests that they are affected not only by metazoans but also by other geological factors. Their growth, development, and demise are also closely related to sea-level changes, due to their dependence on water depth, clarity, nutrient, and sunlight. Detailed studies on microbialites and microbial carbonates throughout geological history would certainly help understand causes and effects of major geological events as well as the co-evolution of life and environment.
Related information of this paper: Chen Jitao, Lee Jeong-Hyun, 2014. Current progress on the geological record of microbialites and microbial carbonates. Acta Geologica Sinica (English Edition), 88 (1), 260–275.
Representative photographs of various microbialites and microbial carbonates.
(a) Irregular to domal stromatolite, Cambrian Series 2, Laiwu region, Shandong, China. (b) Thrombolite with irregular, dark-gray microbial clots, Cambrian Series 3, Jinan region, Shandong, China. (c) Dendrolite with bush-like structures, Cambrian Series 3, Jining region, Shandong, China. (d) Leiolite with aphanitic texure, Cambrian Series 3, Laiwu region, Shandong, China, which was firstly recognized by Woo (2009). (e) Microbial laminites with desiccation crack, Cambrian Series 3, Linyi region, Shandong, China. (f) Oncoid with spheroidal shapes and crudely-laminated cortex, Cambrian Series 3, Jinan region, Shandong, China.
Different scales of microbialite structures and morphology.
(a) The four investigation scales of microbialites (modified after Shapiro, 2000). (b) Amended investigation scales of microbial structures and morpholog
(Information Source: Nanging Institute of Geology and paleontology, CAS)
