Abstract
We constrained the origin and genetic environment of modern iron ooids (sand-sized grains with a core and external cortex of concentric laminae) providing new tools for the interpretation of their fossil counterparts as well as the analogous particles discovered on Mars. Here, we report an exceptional, unique finding of a still active deposit of submillimetric iron ooids, under formation at the seabed at a depth of 80 m over an area characterized by intense hydrothermal activity off Panarea, a volcanic island north of Sicily (Italy). An integrated analysis, carried out by X-ray Powder Diffraction, Environmental Scanning Electron Microscopy, X-ray Fluorescence and Raman spectroscopy reveals that Panarea ooids are deposited at the seafloor as concentric laminae of primary goethite around existing nuclei. The process is rapid, and driven by hydrothermal fluids as iron source. A sub-spherical, laminated structure resulted from constant agitation and by degassing of CO2-dominated fluids through seafloor sediments. Our investigations point the hydrothermal processes as responsible for the generation of the Panarea ooids, which are neither diagenetic nor reworked. The presence of ooids at the seawater-sediments interface, in fact, highlights how their development and growth is still ongoing. The proposed results show a new process responsible for ooids formation and gain a new insight into the genesis of iron ooids deposits that are distributed at global scale in both modern and past sediments.
Highlights
Sorby[14] first proposed the replacement of calcareous ooids as a possible genetic process
This paper accounts for the still ongoing formation of iron ooids in the seabed off the island of Panarea, one of the volcanic islands of the Aeolian Arc (Tyrrhenian Sea, Italy; Fig. 1a), where shallow-water hydrothermal processes associated with intense volcanic degassing have long been documented (e.g.18–21)
The hydrothermal constraints identified for these newly formed iron ooids will enhance the understanding on the genesis and www.nature.com/scientificreports accretion mechanisms of their fossil counterparts that are distributed at global scale throughout the Phanerozoic, and will contribute to provide a possible interpretation of analogous particles recently discovered on Mars
Summary
Sorby[14] first proposed the replacement of calcareous ooids as a possible genetic process. This paper accounts for the still ongoing formation of iron ooids in the seabed off the island of Panarea, one of the volcanic islands of the Aeolian Arc (Tyrrhenian Sea, Italy; Fig. 1a), where shallow-water hydrothermal processes associated with intense volcanic degassing have long been documented (e.g.18–21). To our knowledge, this is the only place in the world where iron ooids are actively forming today. Massive Ba-Pb-Zn-enriched sulphide deposits have recently been found to the northeast of Panarea[30]
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