286 BIOSEDIMENTS AND BIOFILMS mound-shaped (Figure 7) The combined attributes of a stromatolite reflect the interaction of physical, chemical, and biological processes (Figure 8) in the environment For example, currents may cause elongation of the stromatolite along the current direction, a feature observed in modern stromatolites in Shark Bay and in Archaean stromatolites of Western Australia When interpreting the morphology of stromatolites, it is difficult to determine what proportion of the physical attributes of a structure can be attributed to environmental influences and how much to purely biological factors The hard, laminated interior of the stromatolite records the depositional history of the stromatolitebuilding process We can look at the nature of the laminations in order to understand the behaviour and character of a stromatolite-building community Lamination within any sedimentary deposit reflects some past cyclicity in the sedimentation processes In the case of stromatolites, lamination reflects cyclic variations in non-biological sedimentation processes, coupled with the variation in microbial activity Lamination may accrete rapidly or slowly, depending on the causes of accretion and cyclicity Table describes four generalized mechanisms observed in modern stromatolites Interpretation of stromatolite-like structures Stromatolite-like structures can form by a variety of abiological mechanisms In order to verify a biologic origin for purported stromatolites, all possible nonbiological origins ought to be considered, including: Mechanical sedimentary processes such as those caused by waves or currents Post-burial deformation of laminar deposits by dewatering processes Tectonic deformation, i.e., folding Soft sediment deformation or slumping, i.e., cohesive downhill movement of a portion of sedimentary layers Chemical precipitation, e.g., from saturated fluids, such as those associated with hot spring environments Figure Physical attributes of Archaean stromatolites Different attributes can be combined; for example, one ‘community’ may comprise spaced domes with higher order curvature and later deformation These basic characteristics can be used to describe and classify stromatolites observed in the field Adapted from Hoffman HJ (2000) Archaean stromatolites as microbial archives In: Riding R and Awramik S (eds.) Microbial Sediments, pp 315 327 Berlin, Heidelberg: Springer Verlag