The preservation potential of some recent stromatolites

Abstract

Stromatolites are laminated organo‐sedimentary structures, generally compared to present day blue‐green algal mats. Their morphology, species composition and overall extent are largely governed by the amount of wetting, although other factors such as competition, predation and desiccation, also contribute. The Trucial Coast mats are essentially intertidal. Stromatolite accretion rates in this area are of the order of 0·2 mm p.a. but lamina growth is far from regular. The area is also characterized by the development of evaporites, especially gypsum which proves to be an important agent of mat destruction. The growth of crystals causes disruption within the upper portions of the stromatolite section with the result that none of the upper intertidal mat forms are preserved. Other agencies of destruction include bacterial decay, desiccation and dehydration, and compaction under burial which may depress and deform the original mat relief. Decay results in the almost total loss of cellular contents, only a few empty sheaths and the pigment surviving into the fossil record. Preservation may be effected via (a) burial or (b) lithification. However, few modern algal mat structures bear any resemblance to fossil stromatolite heads with the exception of those from Shark Bay. From this, one might infer that pene‐contemporaneous lithification is a prerequisite for their preservation.

Origin and significance of lamination in Lower Cretaceous stromatolites and proposal for a quantitative approach

“…Stromat olites partially composed of evaporites (typically sulphates) also occur, as products of syndepositional alteration referred to as 'gypsification' (Rouchy and Monty, 1981;BabeL 2007). Additionally, many examples of stromatolites and other microbial carbonates contain displacive and replacive sulphate laminae, similar to those of Leza coarse-grained stromatolites (Gunatilaka, 1975;Horodyski and Vonder Haar, 1975;Park, 1977;Aref, 1998;Gerdes et al, 2000;Rouchy and Monty, 2000;Ortl, 2010). Similarly, we interpret evaporite laminae of the Leza coarse-grained stromatolites as formed by very early diagenetic intrasedimentary precipitation of evaporite minerals when interstitial waters reached oversaturation.…”

Modern Stromatolites: A Review

“…The studies of such environments (e.g. Kinsman and Park 1976;Park 1976Park ,1977Horodyski et al 1977;Krumbein et al 1977;Campbell and Golubic 1985) show organismal distribution patterns that are consistent with Garrett's model, and confirm an almost absolute dominance of prokaryotes. Similarly, extreme conditions in the non-marine realm are found in thermal springs (Brock 1978;Castenholz 1973;Ward et al 1989), and somewhat less extreme in the Antarctic lakes (Parker et al 1981;Parker and Wharton 1985).…”

“…Therefore, the term 'potential stromatolites' when used for mats and non-lithified stromatolites (Krumbein 1983), may be misleading, because it raises expectations that may not be fulfilled. Preservation potential (see, for example, Park 1977), is a probabilistic measure analogous to life expectancy calculated by insurance companies. Early lithification increases the expectancy of preservation.…”

Shallow Marine Microbial Carbonate Deposits

“…For example, it can survive deeper within a mat than other cyanobacteria and can even function in the transition zone between oxygenated and anoxic zones of a mat (Golubic 1992a). M. chthonoplastes also dominates the mat surfaces in depressions of folded, convoluted mats forming in the intertidal of Abu Dhabi where the ponded water found in these depressions is often Ozdepleted (Park 1977 Fig. 3; Golubic 1991).…”