Regional conditions cause contrasting behaviour in U-isotope fractionation in black shales: Constraints for global ocean palaeo-redox reconstructions
نویسندگان
چکیده
The U-isotope system is a well-established palaeo-redox proxy that potentially constrains the global extent of marine anoxia during average as well extreme redox events throughout Earth's history. A typical archive forms underneath reducing water column and acts an intense U sink organic-rich black shale. However, degree to which shale archives reflect signature not understood because fractionation between U(VI)-bearing seawater U(IV)-bearing shales may vary function local environmental conditions. Here, we present combination elemental concentration datasets, supported by complementary Mo-isotope record, for Furlo sedimentary section in Marche–Umbria, Italy interrogate combined systematics unravel mechanisms controlling factor ambient seawater. We examine deposited before Oceanic Anoxic Event 2 (OAE 2), was one most climatic perturbations Mesozoic Era took place around Cenomanian–Turonian boundary (Late Cretaceous, c. 94 Ma). results this study show OAE controlled different than ratios recorded 2, with both stratigraphic intervals likely influenced Probable changes include increased reduction associated biomass at or above sediment–water interface varying dissolved hydrogen sulphide concentrations sediment. overall confirm are highly complex studies past oceanic conditions, due sensitivity mechanism difficult constrain. propose application ∆238Ushale-seawater 0.6 ± 0.1 ‰ records under locally constant euxinic conditions non-restricted settings.
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ژورنال
عنوان ژورنال: Chemical Geology
سال: 2023
ISSN: ['0009-2541', '1872-6836']
DOI: https://doi.org/10.1016/j.chemgeo.2023.121411