Chapter Three Classification of Structures Left by Microbial Mats in Their Host Sediments

We view the structures and features described in this atlas as sedimentary structures, albeit of a complex organo-physico-chemical origin. Just like their physical sedimentary structure counterparts (e.g., Pettijohn and Potter, 1964), they can be of great assistance in unravelling depositional palaeoenvironments inferred for ancient rock successions. Pettijohn and Potter (1964) included stromatolites in their well known classification of primary physical sedimentary structures, under their class 2E structures, as positive growth features upon bedding planes (Noffke et al., 2001a). The combination of microbial construction, accretion of detrital grains, and biochemical precipitation implicit in stromatolite formation (e.g., Walter, 1976) was originally thought to be endemic to carbonate-forming settings (e.g., Awramik, 1984; Walter et al., 1992; Altermann, 2004). There is a growing recognition, however, that surficial microbial communities interacted with physical agents of erosion, sedimentation and even deformation (Noffke et al., 2001a) in ancient clastic sedimentary settings (e.g., Schieber, 1986, 1998a, 1999, 2004; Hagadorn et al., 1999; Gehling, 1999; Pflüger, 1999). A large array of modern examples of resultant features, both microbial and clastic-sedimentary has been presented in Chapter 2 of this book.