Abstract
Modern marine hydrothermal vents occur in a wide variety of tectonic settings and are characterized by seafloor emission of fluids rich in dissolved chemicals and rapid mineral precipitation. Some hydrothermal systems vent only low-temperature Fe-rich fluids, which precipitate deposits dominated by iron oxyhydroxides, in places together with Mn-oxyhydroxides and amorphous silica. While a proportion of this mineralization is abiogenic, most is the result of the metabolic activities of benthic, Fe-oxidizing bacteria (FeOB), principally belonging to the Zetaproteobacteria. These micro-organisms secrete micrometer-scale stalks, sheaths, and tubes with a variety of morphologies, composed largely of ferrihydrite that act as sacrificial structures, preventing encrustation of the cells that produce them. Cultivated marine FeOB generally require neutral pH and microaerobic conditions to grow. Here, we describe the morphology and mineralogy of filamentous microstructures from a late Paleoproterozoic (1.74Ga) jasper (Fe-oxide-silica) deposit from the Jerome area of the Verde mining district in central Arizona, USA, that resemble the branching tubes formed by some modern marine FeOB. On the basis of this comparison, we interpret the Jerome area filaments as having formed by FeOB on the deep seafloor, at the interface of weakly oxygenated seawater and low-temperature Fe-rich hydrothermal fluids. We compare the Jerome area filaments with other purported examples of Precambrian FeOB and discuss the implications of their presence for existing redox models of Paleoproterozoic oceans during the "Boring Billion."
Highlights
In the decades since their first discovery in 1977, marine hydrothermal vents have been reported from all of the world's oceans in a wide variety of tectonic settings where a heat source is present, including at more than 400 sites on mid-ocean ridges, fore-and back- arc spreading centers, arc volcanoes, and intra-plate volcanoes and seamounts (e.g., Beaulieu et al, 2013; Corliss et al, 1979; Fouquet et al, 2010; Karl et al, 1988; Pedersen et al, 2010; Petersen et al, 2019)
The weak Energy Dispersive Spectrometer (EDS) carbon signal we found in one of the FIB-TEM sections (Figure S2) is not spatially associated with a well-defined filament, and its origin could have several explanations, including being contemporaneous to filament formation, or a later contamination related to diagenesis or metamorphism
We suggest that the Verde Central jasper (VCJ) filaments were formed by cells that oxidized reduced iron from vent fluids as an energy source, with iron oxyhydroxides being a product from this reaction
Summary
In the decades since their first discovery in 1977, marine hydrothermal vents have been reported from all of the world's oceans in a wide variety of tectonic settings where a heat source is present, including at more than 400 sites on mid-ocean ridges, fore-and back- arc spreading centers, arc volcanoes, and intra-plate volcanoes and seamounts (e.g., Beaulieu et al, 2013; Corliss et al, 1979; Fouquet et al, 2010; Karl et al, 1988; Pedersen et al, 2010; Petersen et al, 2019). Relative to jaspers from the United Verde and Copper Chief horizons (Figure 2b), the VCJ samples display mostly higher REE abundances, with strong enrichments in the heavy rare earth elements (HREE) and very low ratios of light rare earth elements (LREE) to HREE (LaSN/YbSN = 0.005–0.058; Table 1).
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