Premium
Organic and mineral imprints in fossil photosynthetic mats of an E ast A ntarctic lake
Author(s) -
Lepot K.,
Compère P.,
Gérard E.,
Namsaraev Z.,
Verleyen E.,
Tavernier I.,
Hodgson D. A.,
Vyverman W.,
Gilbert B.,
Wilmotte A.,
Javaux E. J.
Publication year - 2014
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12096
Subject(s) - microbial mat , cyanobacteria , fossilization , autotroph , phototroph , murchison meteorite , chemistry , photosynthesis , botany , environmental chemistry , geology , biology , astrobiology , paleontology , bacteria , meteorite , linguistics , philosophy , chondrite
Lacustrine microbial mats in A ntarctic ice‐free oases are considered modern analogues of early microbial ecosystems as their primary production is generally dominated by cyanobacteria, the heterotrophic food chain typically truncated due to extreme environmental conditions, and they are geographically isolated. To better understand early fossilization and mineralization processes in this context, we studied the microstructure and chemistry of organo‐mineral associations in a suite of sediments 50–4530 cal. years old from a lake in S karvsnes, L ützow H olm B ay, E ast A ntarctica. First, we report an exceptional preservation of fossil autotrophs and their biomolecules on millennial timescales. The pigment scytonemin is preserved inside cyanobacterial sheaths. As non‐pigmented sheaths are also preserved, scytonemin likely played little role in the preservation of sheath polysaccharides, which have been cross‐linked by ether bonds. Coccoids preserved thylakoids and autofluorescence of pigments such as carotenoids. This exceptional preservation of autotrophs in the fossil mats argues for limited biodegradation during and after deposition. Moreover, cell‐shaped aggregates preserved sulfur‐rich nanoglobules, supporting fossilization of instable intracellular byproducts of chemotrophic or phototrophic S ‐oxidizers. Second, we report a diversity of micro‐ to nanostructured CaCO 3 precipitates intimately associated with extracellular polymeric substances, cyanobacteria, and/or other prokaryotes. Micro‐peloids T ype 1 display features that distinguish them from known carbonates crystallized in inorganic conditions: (i) Type 1 A are often filled with globular nanocarbonates and/or surrounded by a fibrous fringe, (ii) Type 1 B are empty and display ovoid to wrinkled fringes of nanocrystallites that can be radially oriented (fibrous or triangular) or multilayered, and (iii) all show small‐size variations. Type 2 rounded carbonates 1–2 μm in diameter occurring inside autofluorescent spheres interpreted as coccoidal bacteria may represent fossils of intracellular calcification. These organo‐mineral associations support organically driven nanocarbonate crystallization and stabilization, hence providing potential markers for microbial calcification in ancient rocks.