Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western Australia

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

“…Rare occurrences of carbonate rocks from inferred shallow marine environments are known from early Archean successions, including the 3.45 Ga Warrawoona Group (Hofmann et al, 1999). Their genesis and the sudden appearance of widespread and thick stromatolitic carbonate platforms at about 2.9-2.6 Ga remains, however, unexplained, and the mechanism of biocalcification and carbonate precipitation for the entire Precambrian is still vigorously debated (Altermann and Kazmierczak, 2003;Altermann et al, 2006).…”

“…Schopf et al, 2007;Glikson et al, 2008) and were formed by microbial ecosystems (microbial mats) (e.g. Hofmann et al, 1999;Tice and Lowe, 2004;Allwood et al, 2006), understanding of the genesis of such ancient rocks (3.5 Ga) and their possible relationships to modern living microbial mats and sites of carbonate rock formation, is inadequate (Grotzinger, 1989;Arp et al, 2001;Sumner and Grotzinger, 2004). The process of mineralization in microbial ecosystems in natural environments remains in general, but particularly in the Archean, one of the outstanding enigmas of carbonate rock formation, despite decades of intensive research and debate.…”

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).…”

A case for biotic morphogenesis of coniform stromatolites

“…When vertical growth dominates, coniform structures evolve that reproduce the features of Conophyton, a stromatolite that flourished in certain lowsedimentation environments for much of the Proterozoic [9]. Increasing the dominance of vertical growth produces sharply-peaked conical forms, comparable to coniform stromatolites described from the 3.45 Ga Warrawoona Group, Western Australia [5].…”

“…The biogenicity of stromatolites older than 3.2 Ga 1 is unclear [2,3,4,5]. If they are indeed biotic, they are the oldest morphological evidence for life, now that the identification of 3.3 to 3.5 Ga microfossils [6] has been challenged [7,8].…”