Modern Iron Ooids of Hydrothermal Origin as a Proxy for Ancient Deposits

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 CO 2 -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.

Fluid‐driven Hydrovolcanic Activity along Fracture Zones and near Seamounts: Evidence from Deep‐sea Fe‐rich Spherules, Central Indian Ocean Basin

“…Harrison and Peterson (1965) suggested the role of hydrothermal exhalations and the release of CO 2 resulting in a change in temperature and pressure, thereby affecting the pH of the water column and enhancing the formation the Fe-rich mineral phase in deep -sea sediments. This process was used to explain the unusual abundance of iron in the East Pacific Rise (Goldberg and Arrhenius, 1958), in-situ origin of a magnetic mineral near abyssal hills in the Indian Ocean (Harrison and Peterson, 1965), the Amorphous Goethite Facies of the Red Sea metalliferous sediments (Bischoff, 1969), microscopic amorphous iron-manganese oxide precipitates (0.5 to 25 µm) in the sediment columns near the Mendocino and Murray FZ (von der Borch and Rex, 1970) and formation of modern iron spherules in Panarea volcanic island of Aeolian Arc (Bella et al, 2019). Later, Peckover et al (1973), Sheridan and Wohletz (1981), Wohletz andMcQueen, (1984b), andWohletz et al (1995) experimentally demonstrated that during hydrovolcanic eruptions a mechanism that resembles FCI takes place.…”

Depositional Conditions of Cretaceous Ironstones Deposit in the Chulym-Yenisey Basin (Western Siberia)

“…Alternately, the presence of iron was linked to the transfer from the ancient river system and precipitation in the zone of mixing of acidic river waters with alkaline sea waters. A few researchers [6,[74][75][76][77] considered the ironstone deposits as a product of low-temperature seeps with mobilization of iron-saturated fluids into the ancient seabed, as described in modern sediments. Therefore, depositional conditions of continental ironstones of the Chulym-Yenisey depression, which is contemporaneous with the West Siberian iron ore basin, remain unexplored.…”

Ooidal ironstones in the Meso-Cenozoic sequences in western Siberia: assessment of formation processes and relationship with regional and global earth processes

“…6 and 7). Absence of pyrite framboids as well as the mineralogical assemblage dominated by goethite ooids with early diagenetic illite-smectite and lepidocrocite cement indicates oxic depositional conditions (Aller et al 1986;Kimberley 1994;Heikoop et al 1996;Sturesson et al 2000;Di Bella et al 2019) for the Maastrichtian and Paleocene intervals (Figs. 6 and 7; see also Rudmin et al 2019).…”