title: Experimental diagenesis of organo-mineral structures formed by microaerophilic Fe(II)-oxidizing bacteria.
abstract: Twisted stalks are organo-mineral structures produced by some microaerophilic Fe(II)-oxidizing bacteria at O2 concentrations as low as 3 μM. The presence of these structures in rocks having experienced a diagenetic history could indicate microbial Fe(II)-oxidizing activity as well as localized abundance of oxygen at the time of sediment deposition. Here we use spectroscopy and analytical microscopy to evaluate if--and what kind of--transformations occur in twisted stalks through experimental diagenesis. Unique mineral textures appear on stalks as temperature and pressure conditions increase. Haematite and magnetite form from ferrihydrite at 170 °C-120 MPa. Yet the twisted morphology of the stalks, and the organic matrix, mainly composed of long-chain saturated aliphatic compounds, are preserved at 250 °C-140 MPa. Our results suggest that iron minerals might play a role in maintaining the structural and chemical integrity of stalks under diagenetic conditions and provide spectroscopic signatures for the search of ancient life in the rock record.
authors.affiliation: Center for Applied Geoscience, Eberhard Karls University Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.
authors.forename: Aude
authors.initials: A
authors.lastname: Picard
authors.affiliation: Center for Applied Geoscience, Eberhard Karls University Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kappler
authors.affiliation: Center for Applied Geoscience, Eberhard Karls University Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Schmid
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
authors.forename: Luca
authors.initials: L
authors.lastname: Quaroni
authors.affiliation: Center for Applied Geoscience, Eberhard Karls University Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Obst
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D007501:Iron / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D017348:Microscopy, Electron, Scanning Transmission; D008903:Minerals / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011312:Pressure; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D008903:Minerals; C000499:ferric oxide; C092844:ferric oxyhydroxide; D007501:Iron; D010100:Oxygen