Stromatolite morphogenesis—progress and problems

Abstract

Stromatolites are laminated, lithified, sedimentary growth structures that accrete away from a point or limited surface of attachment. They are commonly, but not necessarily, of microbial origin and calcareous composition. Although familiar to geologists, they remain enigmatic as to origin and uncertain as to their full potential for historical geology.We summarize here the results of collective inquiry and discussion concerning central problems of stromatolite morphogenesis. We focus on relations between microstructure, laminar details, and gross morphology of ancient, probably biogenic, stromatolites and on the microbial composition and laminar characteristics of analogous modern microbial mats and sedimentary structures produced by them.The basic microstructure-determining unit of the modern stromatolite analog of biogenic origin is the mat-building community of organisms and particularly its dominant species, operating within a particular ecological setting. Biological factors dominate at the laminar and sublaminar level. Gross morphology probably reflects a balance between ecological processes and microbial activity.Nomenclatural clarity and stratigraphic utility turn on a proper understanding of morphogenesis. Although stromatolites will continue to function as stratigraphic and paleoecologic indicators, the reasons behind and limits to their applicability will remain obscure while morphogenetic processes remain uncertain. Finally, we outline some problems whose resolution could reduce that uncertainty.

Fossil evidence of Archaean life

“…83-84 structures (e.g. Walter 1976;Awramik, in Semikhatov et al 1979;Buick et al 1981), others focusing solely on the sedimentological morphology of such structures (e.g. Semikhatov et al 1979, excluding Awramik;Grotzinger & Knoll 1999), and still others searching for a middle ground (Hofmann 1973, pp.…”

A fresh look at the fossil evidence for early Archaean cellular life

“…Stromatolites are macroscopically layered structures comprising wrinkled surfaces, domes, cones and columns (figure 3a,b) that accrete upwards from a point or surface of initiation and have been defined in terms of either requiring (Krumbein & Werner 1983) or not requiring (Semikhatov et al 1979) microbial mediation. In table 1 we adopt the non-genetic term 'stromatoloid' and make no assumptions about the presence or absence of microbial mats.…”

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

“…Clearly visible in examples as old as 3.5 billion years (Hofmann et al, 1999;Allwood et al, 2006), lamination distinguishes stromatolites from other microbial carbonates such as dendrolites, thrombolites and leiolites (Riding, 2011). The shape, continuity, and stacking oflaminae are important in stromatolite description and classification (Hofmann, 1969(Hofmann, , 1973Monty, 1976;Semikhatov et al, 1979;Grey, 1989;Grotzinger and Knoll, 1999), in cluding the definition of stromatolite morphotypes (Maslov, 1960;Vologdin, 1962;Walter, 1972;Semikhatov and Raaben, 2000). Stromat olite lamination has been examined for periodicity (e.g.…”