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Microbes are well-known for their great diversity and abundance in modern natural environments. They also are believed to provide critical links among higher organisms and their associated environments. However, the low diversity of morphological features and structures of ancient microbes preserved in sediments and rocks make them difficult to identify and classify. This difficulty greatly hinders the investigation of geomicrobes throughout Earth history. Thus, most previous paleontological studies have focused on faunal and floral fossils. Here, geomicrobial functional groups (GFGs), or a collection of microbes featured in specific ecological, physiological or biogeochemical functions, are suggested to provide a way to overcome the difficulties of ancient microbe investigations. GFGs are known for their great diversity in ecological, physiological and biogeochemical functions. In addition, GFGs may be preserved as the biogeochemical, mineralogical and sedimentological records in sediments and rocks. We reviewed the functions, origins and identification diagnostics of some important GFGs involved in the elemental cycles of carbon, sulfur, nitrogen and iron. GFGs were further discussed with respect to their significant impacts on paleoclimate, sulfur chemistry of ancient seawater, nutritional status of geological environments, and the deposition of Precambrian banded iron formations. [ABSTRACT FROM AUTHOR]

The article explores the use of the geobiological approach in the assessment of Chinese carbonate source rocks. A series of paleoecological and biogeochemical parameters were employed to represented organic carbon (OC). It notes that clastic rocks based on geobiological parameters are qualified source rocks, while good source rocks from carbonates have low total organic carbon (TOC) values. It also notes the broad range of habitat types for carbonate source rocks in the Yangtze platform.