| Microbial Mat Page Microbes are all around us. In terms of numbers they rule the earth, and they manage to live under extreme conditions, such as in hot springs, in polar ice, at depth in rock formations, and in any conceivable environment in between. Of interest for this paper are microbes that colonize, stabilize, and modify the surfaces of sandy and muddy sediments. Microbial mat deposits in carbonates are excluded, although the vast majority of published examples is found in that rock type. Modern microbial mats on sandy sediment surfaces are well documented. The microbial colonization of muddy surfaces, although less known, can be readily observed in modern puddles a few days after a rainstorm. Essentially, for any sedimentary surface there is likely a microbial community that is equipped to thrive there if sedimentation rates are sufficiently small. Some can even prosper in absence of sunlight, or in the harsh and dry conditions of deserts. Considering how many times the "present has been the key to the past", it stands to reason that numerous ancient sand and mud surfaces were colonized by microbial communities. Thus, we may assume that sandstone and mudstone deposits of the geologic record should abound with microbial mat deposits It is at this point that an old geologic truth asserts itself once again: "just because something should have existed does not mean that it has been preserved". Positively proving the former presence of microbial mats in sedimentary rocks of any kind is actually quite a formidable task. Even in modern microbial mat systems, all remnants of the constructing microbiota may be destroyed within the first few hundred years of burial. Furthermore, if one applies strict criteria of biogenicity, such as preserved filaments in live position to published examples of fossil microbial mats (or stromatolites), only a very small portion can actually be shown to have a clearly demonstrable organosedimentary origin. | |
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