FN Archimer Export Format
PT J
TI Mechanistic Morphogenesis of Organo-Sedimentary Structures Growing Under Geochemically Stressed Conditions: Keystone to Proving the Biogenicity of Some Archaean Stromatolites?
BT 
AF Hickman-Lewis, Keyron
   Gautret, Pascale
   Arbaret, Laurent
   Sorieul, Stéphanie
   De Wit, Rutger
   Foucher, Frédéric
   Cavalazzi, Barbara
   Westall, Frances
AS 1:1,2;2:3;3:3;4:4;5:5;6:1;7:2,6;8:1;
FF 1:;2:;3:;4:;5:;6:;7:;8:;
C1 CNRS Centre de Biophysique Moléculaire, 45071 Orléans, France
   Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Bologna, I-40126 Bologna, Italy
   Université d’Orléans, CNRS, BRGM, ISTO, Institut des Sciences de la Terre, 45071 Orléans, France
   Université de Bordeaux, CNRS, IN2P3, CENBG, 33175 Gradignan, France
   MARBEC, Université de Montpellier, CNRS, IRD, Ifremer, 34095 Montpellier, France
   Department of Geology, University of Johannesburg, Auckland Park 2006, Johannesburg, South Africa
C2 CNRS, FRANCE
   UNIV BOLOGNA, ITALY
   UNIV ORLEANS, FRANCE
   UNIV BORDEAUX, FRANCE
   CNRS, FRANCE
   UNIV JOHANNESBURG, SOUTH AFRICA
UM MARBEC
IN WOS Cotutelle UMR
   DOAJ
   copubli-france
   copubli-europe
   copubli-univ-france
   copubli-int-hors-europe
   copubli-sud
TC 15
UR https://archimer.ifremer.fr/doc/00512/62323/66580.pdf
LA English
DT Article
DE ;microbial mat;stromatolite;anoxygenic photosynthesis;X-ray micro-scale computed tomography;Archaean;early life;Dresser Formation;Middle Marker horizon
AB Morphologically diverse organo-sedimentary structures (including microbial mats and stromatolites) provide a palaeobiological record through more than three billion years of Earth history. Since understanding much of the Archaean fossil record is contingent upon proving the biogenicity of such structures, mechanistic interpretations of well-preserved fossil microbialites can reinforce our understanding of their biogeochemistry and distinguish unambiguous biological characteristics in these structures, which represent some of the earliest records of life. Mechanistic morphogenetic understanding relies upon the analysis of geomicrobiological experiments. Herein, we report morphological-biogeochemical comparisons between micromorphologies observed in growth experiments using photosynthetic mats built by the cyanobacterium Coleofasciculus chthonoplastes (formerly Microcoleus) and green anoxygenic phototrophic Chloroflexus spp. (i.e., Coleofasciculus–Chloroflexus mats), and Precambrian organo-sedimentary structures, demonstrating parallels between them. In elevated ambient concentrations of Cu (toxic to Coleofasciculus), Coleofasciculus–Chloroflexus mats respond by forming centimetre-scale pinnacle-like structures (supra-lamina complexities) associated with large quantities of EPS at their surfaces. µPIXE mapping shows that Cu and other metals become concentrated within surficial sheath-EPS-Chloroflexus-rich layers, producing density-differential micromorphologies with distinct fabric orientations that are detectable using X-ray computed micro-tomography (X-ray µCT). Similar micromorphologies are also detectable in stromatolites from the 3.481 Ga Dresser Formation (Pilbara, Western Australia). The cause and response link between the presence of toxic elements (geochemical stress) and the development of multi-layered topographical complexities in organo-sedimentary structures may thus be considered an indicator of biogenicity, being an indisputably biological and predictable morphogenetic response reflecting, in this case, the differential responses of Coleofasciculus and Chloroflexus to Cu. Growth models for microbialite morphogenesis rely upon linking morphology to intrinsic (biological) and extrinsic (environmental) influences. Since the pinnacles of Coleofasciculus–Chloroflexus mats have an unambiguously biological origin linked to extrinsic geochemistry, we suggest that similar micromorphologies observed in ancient organo-sedimentary structures are indicative of biogenesis. An identical Coleofasciculus–Chloroflexus community subjected to salinity stress also produced supra-lamina complexities (tufts) but did not produce identifiable micromorphologies in three dimensions since salinity seems not to negatively impact either organism, and therefore cannot be used as a morphogenetic tool for the interpretation of density-homogeneous micro-tufted mats—for example, those of the 3.472 Ga Middle Marker horizon. Thus, although correlative microscopy is the keystone to confirming the biogenicity of certain Precambrian stromatolites, it remains crucial to separately interrogate each putative trace of ancient life, ideally using three-dimensional analyses, to determine, where possible, palaeoenvironmental influences on morphologies. Widespread volcanism and hydrothermal effusion into the early oceans likely concentrated toxic elements in early biomes. Morphological diversity in fossil microbialites could, therefore, reflect either (or both of) differential exposure to ambient fluids enriched in toxic elements and/or changing ecosystem structure and tolerance to elements through evolutionary time—for example, after incorporation into enzymes. Proof of biogenicity by deducing morphogenesis (i.e., a process preserved in the fossil record) overcomes many of the shortcomings inherent to the proof of biogenicity by descriptions of morphology alone. 
PY 2019
PD AUG
SO Geosciences
SN 2076-3263
PU MDPI AG
VL 9
IS 8
UT 000482981000025
DI 10.3390/geosciences9080359
ID 62323
ER

EF