Geomicrobiology Group, Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, 72076 Tuebingen, Germany.
Nat Commun. 2013;4:1741. doi: 10.1038/ncomms2770.
During deposition of Precambrian iron formation, the combined sedimentation of ferrihydrite and phytoplankton biomass should have facilitated Fe(III) reduction during diagenesis. However, the only evidence for this reaction in iron formations is the iron and carbon isotope values preserved in the authigenic ferrous iron-containing minerals. Here we show experimentally that spheroidal siderite, which is preserved in many iron formation and could have been precursor to rhombohedral or massive siderite, forms by reacting ferrihydrite with glucose (a proxy for microbial biomass) at pressure and temperature conditions typical of diagenesis (170 °C and 1.2 kbar). Depending on the abundance of siderite, we found that it is also possible to draw conclusions about the Fe(III):C ratio of the initial ferrihydrite-biomass sediment. Our results suggest that spherical to rhombohedral siderite structures in deep-water, Fe-oxide iron formation can be used as a biosignature for photoferrotrophy, whereas massive siderite reflects high cyanobacterial biomass loading in highly productive shallow-waters.
在元古代铁矿形成期间，水铁矿和浮游植物生物量的共同沉积应该有利于成岩过程中的 Fe(III)还原。然而，在铁矿中，唯一能证明这种反应存在的证据是自生含亚铁铁矿物中保存的铁和碳同位素值。在这里，我们通过实验证明，在许多铁矿中保存的、可能是菱铁矿或块状菱铁矿前身的球形菱铁矿是由水铁矿与葡萄糖（微生物生物量的一种替代物）在成岩条件（170°C 和 1.2kbar）下反应形成的。根据菱铁矿的丰度，我们发现还可以根据初始水铁矿-生物量沉积物的 Fe(III):C 比值得出结论。我们的结果表明，深海、氧化铁铁矿中的球形至菱铁矿结构可作为光亚铁营养生物的生物特征，而块状菱铁矿则反映了高生产力浅水中高蓝藻生物量负荷。
