Banded Iron Travertines at the Ilia Hot Spring (Greece): An interplay of biotic and abiotic factors leading to a modern Banded Iron Formation analogue?
Abstract:A hot spring at Ilia in the Greek Island of Euboea precipitates iron‐rich travertine at an ore‐grade concentration (up to 35.3 wt% Fe). This hydrothermal chemical sediment system deposits bands of iron oxyhydroxides (ferrihydrite), millimetres to centimetres thick, alternating with calcium carbonate‐dominated layers, creating “Banded Iron Travertine” (BIT). The ferrihydrite laminae display a dendritic texture formed of spherical nodules often covering filaments identified as bacterial stalks of Zetaproteobacte… Show more
“…Fossiliferous layers are distributed throughout the whole series, including in some cuirasses (La Madeleine waterfall). The general pattern of the fossiliferous sites is broadly similar to fossiliferous travertine formations, and a few cases of iron travertine deposits are known in Spain 38 , 39 and in Greece, also on ultramafic formations with ferrihydrite encrusted leaves 40 . Figure 3 Middle(?)…”
New Caledonia was, until recently, considered an old continental island harbouring a rich biota with outstanding Gondwanan relicts. However, deep marine sedimentation and tectonic evidence suggest complete submergence of the island during the latest Cretaceous to the Paleocene. Molecular phylogenies provide evidence for some deeply-diverging clades that may predate the Eocene and abundant post-Oligocene colonisation events. Extinction and colonization biases, as well as survival of some groups in refuges on neighbouring paleo-islands, may have obscured biogeographic trends over long time scales. Fossil data are therefore crucial for understanding the history of the New Caledonian biota, but occurrences are sparse and have received only limited attention. Here we describe five exceptional fossil assemblages that provide important new insights into New Caledonia’s terrestrial paleobiota from three key time intervals: prior to the submersion of the island, following re-emergence, and prior to Pleistocene climatic shifts. These will be of major importance for elucidating changes in New Caledonia’s floristic composition over time.
“…Fossiliferous layers are distributed throughout the whole series, including in some cuirasses (La Madeleine waterfall). The general pattern of the fossiliferous sites is broadly similar to fossiliferous travertine formations, and a few cases of iron travertine deposits are known in Spain 38 , 39 and in Greece, also on ultramafic formations with ferrihydrite encrusted leaves 40 . Figure 3 Middle(?)…”
New Caledonia was, until recently, considered an old continental island harbouring a rich biota with outstanding Gondwanan relicts. However, deep marine sedimentation and tectonic evidence suggest complete submergence of the island during the latest Cretaceous to the Paleocene. Molecular phylogenies provide evidence for some deeply-diverging clades that may predate the Eocene and abundant post-Oligocene colonisation events. Extinction and colonization biases, as well as survival of some groups in refuges on neighbouring paleo-islands, may have obscured biogeographic trends over long time scales. Fossil data are therefore crucial for understanding the history of the New Caledonian biota, but occurrences are sparse and have received only limited attention. Here we describe five exceptional fossil assemblages that provide important new insights into New Caledonia’s terrestrial paleobiota from three key time intervals: prior to the submersion of the island, following re-emergence, and prior to Pleistocene climatic shifts. These will be of major importance for elucidating changes in New Caledonia’s floristic composition over time.
“…Α common characteristic of the hot springs in North‐West Euboea is the deposition of thermogenic travertine (Kanellopoulos, 2012, 2013; Kanellopoulos et al, 2017, 2019). Previous studies have described their mineralogical composition, mineral chemistry, and their relationship with the chemical composition of the ambient hot water (Kanellopoulos, 2012; Kanellopoulos et al, 2017, 2018, 2019). Also, the great variety of their facies was presented in detail by Kanellopoulos (2012, 2013).…”
The aim of this study is to identify the biomineralisation processes in hot springs of North-West Euboea Island by assessing the physico-chemical parameters of the hot water, the travertine mineralogical composition and facies, and the cyanobacterial microflora. In the studied area, the main mineral phases are calcite and aragonite, creating laminated and shrub facies of travertine deposits in close association with the cyanobacterial microflora. Microscopic analysis of fresh and cultured field samples shows the presence of 81 taxa of Cyanobacteria belonging to six orders, that is, Oscillatoriales, Synechococcales, Spirulinales, Chroococcales, Nostocales and Chroococcidiopsidales with the main factors controlling biodiversity being temperature, salinity and access to sunlight. No Cyanobacteria species were identified in areas with temperatures over 65 o C. In areas with high salinity (27-37‰), the order Oscillatoriales predominates. On the other hand, in areas with high temperatures (63 o C), fewer orders were observed, usually only Synechococcales and Spirulinales. In areas with lower temperatures (37 o C), larger numbers of Cyanobacteria orders were identified. Additionally, salinity seems to regulate the presence of the Nostocales order. The combined geobiological study revealed the presence of four biomineralisation processes involving calcium carbonate minerals, that is, (i) filamentous Cyanobacteria and extracellular polymeric substances trapping calcium carbonate crystals, (ii) extracellular polymeric substances acting as a template favouring mineral precipitation for crystal nucleation, (iii) formation of calcified Cyanobacteria sheaths and (iv) alteration of calcium carbonate crystals by endolithic Cyanobacteria. The identified biomineralisation processes suggest that the formation of calcium carbonate crystals is due to the metabolic activity of Cyanobacteria, or that the Cyanobacteria favour the deposition or the alteration of already existing crystals. The combination of F I G U R E 1 Geological map NW of Euboea (TF = Telethrio Fault, IF = Ilia Fault, AF = Aedipsos Fault and LFS = Lichades Fault System; modified after Kanellopoulos et al., 2020). The sampling sites Ilios, Casino, EOT and Platania are locations at Aedipsos.
“…The spectacular fossils at McGraths Flat in New South Wales are likewise preserved in goethite with local basalts as the source of iron (McCurry et al 2022). Travertines may also include bands of goethite, ferrihydrite and other oxides (Arana et al 1979) and in some cases these preserve plants and insects (Nel and Blot 1990;Kanellopoulos et al 2019).…”
A Neogene hematite-goethite concretionary ‘ironstone' horizon in laterized fluvial sediments in the Massif du Sud of New Caledonia yields abundant fossil dicotyledonous angiosperm leaves. The leaves are preserved in iron oxide, mainly goethite, which replicates the morphology and anatomy of the leaf tissues and comprises 73% of the matrix. Organic remains are minimal and associated with aluminosilicate clay. Leaf tissues are preserved three-dimensionally in multiple ways including casts/molds, permineralization/petrifaction, and replacement. Although the mesophyll is less well preserved, reflecting its greater susceptibility to decay, cellular details of vascular and epidermal tissues are commonly evident. Analyses of leaves from an analogous modern setting reveal the early encrustation and impregnation of tissues by amorphous iron-oxides and clays in association with a microbial biofilm. We propose a taphonomic model in which the fossil leaves, like their modern counterparts, were permeated by iron oxides due to the high availability of iron derived from weathering of ultramafic basement. In contrast to the iron-rich aluminosilicate coatings that form in relatively iron-poor settings, the unusually high concentration of dissolved iron oxides permitted rapid anatomical preservation.
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