Photosynthesis-Induced Biofilm Calcification and Calcium Concentrations in Phanerozoic Oceans

Abstract

Photosynthetic carbon assimilation is commonly invoked as the cause of calcium carbonate precipitation in cyanobacterial biofilms that results in the formation of calcareous stromatolites. However, biofilm calcification patterns in recent lakes and simulation of photosynthetically induced rise in calcium carbonate supersaturation demonstrate that this mechanism applies only in settings low in dissolved inorganic carbon and high in calcium. Taking into account paleo-partial pressure curves for carbon dioxide, we show that Phanerozoic oceans sustaining calcified cyanobacteria must have had considerably higher calcium concentrations than oceans of today. In turn, the enigmatic lack of calcified cyanobacteria in stromatolite-bearing Precambrian sequences can now be explained as a result of high dissolved inorganic carbon concentrations.

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

“…They also cast a new light on the rock-building potential of microbiota in the formation of the Archean carbonate platforms and stromatolitic reefs (Grotzinger, 1989). In the light of our observations it is difficult to accept statements claiming a negligible role for calcified cyanobacteria in Precambrian seas (Arp et al, 2001). The abundant cyanobacterial mats in the Nauga Formation and consequently in the entire Transvaal Supergroup stromatolitic carbonates, suggest mass production of fine-grained calcium carbonate by benthic coccoid cyanobacteria in the Neoarchean.…”

“…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.…”

Facula, Faculae

“…For example, the absence of microfossils in Archean stromatolites has been used to question their biogenicity (e.g., Grotzinger and Rothman 1996). Alternatively, the varying abundance of microfossils has often been related to variations of environmental conditions triggering or hindering fossilization (e.g., Arp et al 2001). It is thus important to understand processes of fossilization in order to identify the main factors controlling the formation of microfossils and better read the paleontological record.…”

A case for biotic morphogenesis of coniform stromatolites

“…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].…”

“…As a result, attention has been focussed on how biotic stromatolites might be distinguished from abiotic accretions such as tufa, speleothems, and calcrete [10]. Several Proterozoic stromatolite forms grew in environments of lowsedimentation and their formation seems to have been due to the growth of a BMC, containing photosynthetic bacteria, and accretion of calcium carbonate in the resulting biofilm [1,3,9]. For forms which lack evidence of detrital material being trapped or bound by the BMC we propose a model for stromatolite morphogenesis which involves two processes only:…”