Seawater-sediment-basalt interactions: stable isotope (H, O) and elemental fluxes within the Ordovician volcano-sedimentary sequence of Erquy (Brittany, France)

Ocean Temperatures in the Late Ordovician: A Clumped Isotope Study of Brachiopods and Cements

“…These results echo results from previous clumped isotope studies that the seawater δ 18 O has not changed more than ± 1‰ throughout the Phanerozoic era, and that the secular trend seen in the δ 18 O of carbonate fossils is a product of higher temperatures during the early Paleozoic with cooling towards the modern Came et al, 2007;Finnegan et al, 2011;Henkes et al, 2018). The results also agree with results from studies of ophiolites, hydrothermal alteration of the seafloor, and δ 18 O of marine iron oxide which also suggest little change in seawater δ 18 O throughout the Phanerozoic (Galili et al, 2019;Hodel et al, 2018;Lécuyer et al, 1995;Muehlenbachs, 1998;Muehlenbachs et al, 2003).…”

Reconstruction of an Ordovician seafloor volcanohydrothermal system: a case study from the Copper Coast, southeastern Ireland using field, geochemical and fluid inclusion data

“…As stated above, the absence of a relationship between Fe number and host lithology suggests that the composition of the hydrothermal fluid is probably a dominant influence. The Fe/(Fe + Mg) ratio of chlorite (0.33-0.63) is interpreted to reflect the relative proportions of hydrothermal fluid (Fe-rich) and seawater (Mg-rich) present in the system (Lécuyer et al, 1995;Reed, 1997;Teagle and Alt, 2004). Figure 13 illustrates the distribution of chlorite compositions with varying Fe number: Fe-rich chlorite is located preferentially close to magmatic clasts in peperite while Mg-Fe chlorites are located preferentially throughout the sedimentary host rocks further from intrusions.…”