none 10.2110/palo.2005.P05-077R Society for Sedimentary Geology Society for Sedimentary Geology 860 23701291 46058 2026052723314448000 10.2110 2026-05-28T03:33:59Z 2006-10-14T04:56:59Z 39 PALAIOS 1938-5323 0883-1351 10 2006 10 01 2006 10 01 2006 21 5 FIONA BROCK 1 Research Laboratory for Archaeology and the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, UK; R. JOHN PARKES 2 School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK; DEREK E.G. BRIGGS 3 Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109, USA derek.briggs@yale.edu Abstract Laboratory experiments on microbial decay were used to investigate the conditions required for pyritization of decaying twigs, as it provides an important source of data on the anatomy of fossil plants. Plane (Platanus acerifolia) was chosen as the experimental taxon, because this genus is preserved in pyrite in the Eocene London Clay. Experiments were designed to develop sulfate reduction under marine conditions, and each contained estuarine sediment with added iron oxide (1%) with a layer of pH-buffered artificial seawater medium above, which had a labile organic-matter source (yeast extract) and an inoculum of anaerobic, sulfate-reducing bacteria. Twigs (5) were pressed into the sediment and the systems incubated with a loose lid, in air at 15°C for up to 12 weeks. These conditions were varied to reflect those thought to promote pyrite formation in the natural environment (high concentrations of reactive iron and bioavailable organic matter, local concentration of decaying material, concurrent high concentrations of sulfide and iron, and oxidation of iron sulfides), plus variations in incubation time, anoxia, pH, and sulfate supply. Changes in the chemistry of the decay systems were monitored with oxygen and pH microelectrodes, and concentrations of sulfate, sulfide, ferrous iron, and sedimentary solid-phase sulfide pools were analyzed at the end of each experiment. All systems rapidly developed bacterial sulfate reduction, dissolved iron, and iron sulfides. In only 2 out of 18 reference systems were areas of some twigs pyritized, however, although this did occur rapidly (5.4 weeks). No twigs in the modified systems were pyritized despite up to a 240% increase in solid-phase iron sulfides, the presence of diffusion gradients of ferrous iron and sulfide, the focus of sulfate reduction on the twigs, and pyrite formation in the sediment. Neither slightly oxidizing nor completely anoxic conditions enhanced pyritization. These results suggest that conditions that promote formation of sedimentary pyrite differ considerably from those that facilitate pyritization of twigs. Pyritization can occur rapidly in conditions common in marine sediments with intense microbial activity, but the process is rather random and may be controlled by the nucleation of pyrite on decaying tissue rather than factors controlling pyrite formation. 10 2006 10 01 2006 10 01 2006 499 506 10.2110/palo.2005.P05-077R https://pubs.geoscienceworld.org/palaios/article/21/5/499/145850/EXPERIMENTAL-PYRITE-FORMATION-ASSOCIATED-WITH https://pubs.geoscienceworld.org/sepm/palaios/article-pdf/21/5/499/2841437/i0883-1351-21-5-499.pdf https://pubs.geoscienceworld.org/sepm/palaios/article-pdf/21/5/499/2841437/i0883-1351-21-5-499.pdf http://palaios.geoscienceworld.org/cgi/doi/10.2110/palo.2005.P05-077R Chemical Geology Allen 182 461 2002 10.1016/S0009-2541(01)00334-5 Role of diffusion-precipitation reactions in authigenic pyritization Allen 243 1995 Geochemical Transformations of Sedimentary Sulfur Geochimica et Cosmochimica Acta Aller 44 1955 1980 10.1016/0016-7037(80)90195-7 Quantifying solute distributions in the bioturbated zone of marine sediments by defining an average microenvironment Palaeontology Allison 31 1079 1988 Taphonomy of the Eocene London Clay biota Bartels 309 1998 The Fossils of the Hünsrück Slate: Marine Life in the Devonian Chemical Geology Benning 167 25 2000 10.1016/S0009-2541(99)00198-9 Reaction pathways in the Fe-S system below 100°C Economic Geology Berner 64 383 1969 10.2113/gsecongeo.64.4.383 The synthesis of framboidal pyrite American Journal of Science Berner 268 1 1970 10.2475/ajs.268.1.1 Sedimentary pyrite formation Geochimica et Cosmochimica Acta Berner 48 605 1984 10.1016/0016-7037(84)90089-9 Sedimentary pyrite formation: An update Bowerbank 1840 A history of the fossil fruits and seeds of the London Clay Palaios Briggs 10 539 1995 10.2307/3515093 Experimental taphonomy Annual Review of Earth and Planetary Sciences Briggs 31 275 2003 10.1146/annurev.earth.31.100901.144746 The role of decay and mineralization in the preservation of soft-bodied fossils Geology Briggs 19 1221 1991 10.1130/0091-7613(1991)019<1221:POSBFB>2.3.CO;2 Pyritization of soft-bodied fossils: Beecher's Trilobite Bed, Upper Ordovician, New York State American Journal of Science Briggs 296 633 1996 10.2475/ajs.296.6.633 Controls on the pyritization of exceptionally preserved fossils: An analysis of the Lower Devonian Hünsrück Slate of Germany Geochimica et Cosmochimica Acta Butler 64 2665 2000 10.1016/S0016-7037(00)00387-2 Framboidal pyrite formation via the oxidation of iron (II) monosulphide by hydrogen sulphide Geochimica et Cosmochimica Acta Canfield 53 619 1989 10.1016/0016-7037(89)90005-7 Reactive iron in marine sediments Deep-Sea Research Canfield 36 121 1989 10.1016/0198-0149(89)90022-8 Sulfate reduction and oxic respiration in marine sediments: Implications for organic carbon preservation in euxinic environments Canfield 337 1991 Taphonomy: Releasing the Data Locked in the Fossil Record American Journal of Science Canfield 292 659 1992 10.2475/ajs.292.9.659 The reactivity of sedimentary iron minerals toward sulfide A survey of findings in the light of recent botanical observations Chandler 151 1964 The Lower Tertiary floras of southern England. 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