Evidence of oxygenic phototrophy in ancient phosphatic stromatolites from the Paleoproterozoic Vindhyan and Aravalli Supergroups, India

Abstract

Fossil microbiotas are rare in the early rock record, limiting the type of ecological information extractable from ancient microbialites. In the absence of body fossils, emphasis may instead be given to microbially derived features, such as microbialite growth patterns, microbial mat morphologies, and the presence of fossilized gas bubbles in lithified mats. The metabolic affinity of micro-organisms associated with phosphatization may reveal important clues to the nature and accretion of apatite-rich microbialites. Stromatolites from the 1.6 Ga Chitrakoot Formation (Semri Group, Vindhyan Supergroup) in central India contain abundant fossilized bubbles interspersed within fine-grained in situ-precipitated apatite mats with average δ C indicative of carbon fixation by the Calvin cycle. In addition, the mats hold a synsedimentary fossil biota characteristic of cyanobacterial and rhodophyte morphotypes. Phosphatic oncoid cone-like stromatolites from the Paleoproterozoic Aravalli Supergroup (Jhamarkotra Formation) comprise abundant mineralized bubbles enmeshed within tufted filamentous mat fabrics. Construction of these tufts is considered to be the result of filamentous bacteria gliding within microbial mats, and as fossilized bubbles within pristine mat laminae can be used as a proxy for oxygenic phototrophy, this provides a strong indication for cyanobacterial activity in the Aravalli mounds. We suggest that the activity of oxygenic phototrophs may have been significant for the formation of apatite in both Vindhyan and Aravalli stromatolites, mainly by concentrating phosphate and creating steep diurnal redox gradients within mat pore spaces, promoting apatite precipitation. The presence in the Indian stromatolites of alternating apatite-carbonate lamina may result from local variations in pH and oxygen levels caused by photosynthesis-respiration in the mats. Altogether, this study presents new insights into the ecology of ancient phosphatic stromatolites and warrants further exploration into the role of oxygen-producing biotas in the formation of Paleoproterozoic shallow-basin phosphorites.

Early Archean origin of Photosystem II

“…The earliest widely accepted fossil of a photosynthetic eukaryote is that from a multicellular red algae, Bangiomorpha (Butterfield, ; Knoll, Worndle, & Kah, ), thought to be 1.0 Ga (Gibson et al., ). Recently described multicellular eukaryotic algae fossils have been reported at 1.6 Ga (Bengtson et al., ; Qu, Zhu, Whitehouse, Engdahl, & McLoughlin, ; Sallstedt et al., ) suggesting that the earliest photosynthetic eukaryotes might be older than that, which would be consistent with recent molecular clock analysis (Yang et al., ; Sanchez‐Baracaldo, Raven, Pisani, & Knoll, ).…”

“…On the other hand, A. thaliana 's D1 shares 87.7% sequence identity with that of a unicellular red alga Cyanidioschyzon merolae . Complex multicellular red algae are known to have diverged at least 1.0 Ga ago (Butterfield, ; Gibson et al., ) and recently described fossils could push this date back to 1.6 Ga (Bengtson, Sallstedt, Belivanova, & Whitehouse, ; Sallstedt, Bengtson, Broman, Crill, & Canfield, ). At the other end of this evolutionary line, the three dominant forms of D1 from Gloeobacter violaceous (G4) share on average 79.2% sequence identity with that of C. merolae or 78.5% with that of A. thaliana .…”

Early Archean origin of Photosystem II

“…The earliest widely accepted fossil of a photosynthetic eukaryote is that from a multicellular red algae, Bangiomorpha (Butterfield, 2000;Knoll et al, 2013), thought to be 1.0 Ga (Gibson et al, 2017). Recently described multicellular eukaryotic algae fossils have been reported at 1.6 Ga (Bengtson et al, 2017;Qu et al, 2018;Sallstedt et al, 2018) suggesting that the earliest photosynthetic eukaryotes might be older than that, which would be consistent with recent molecular clock analysis (E. C. Yang et al, 2016;Sánchez-Baracaldo et al, 2017).…”

“…On the other hand, A. thaliana's D1 shares 87.7% sequence identity with that of a unicellular red alga Cyanidioschyzon merolae. Complex multicellular red algae are known to have diverged at least 1.0 Ga ago (Butterfield, 2000;Gibson et al, 2017) and recently described fossils could push this date back to 1.6 Ga (Bengtson et al, 2017;Sallstedt et al, 2018). At the other end of this evolutionary line, the three dominant forms of D1 from Gloeobacter violaceous share on average 79.2% sequence identity with that of C. merolae or 78.5% with that of A.…”

A review of biotic signatures within the Precambrian Vindhyan Supergroup: Implications on evolution of microbial and metazoan life on Earth

“…Bengtson et al (2017) considered these multicellular fossil organisms as the earliest known crown group of eukaryotes. Recently Sallstedt et al (2018) provided the evidence of oxygenic phototrophy developed by the filamentous microorganisms from the same stratigraphic interval.…”