Molybdenum isotope and trace metal signals in an iron-rich Mesoproterozoic ocean: A snapshot from the Vindhyan Basin, India

Abstract

This is a repository copy of Molybdenum isotope and trace metal signals in an iron-rich Mesoproterozoic ocean: A snapshot from the Vindhyan Basin, India.

Restricted Oxygen‐Deficient Basins on the Northern European Epicontinental Shelf Across the Toarcian Carbon Isotope Excursion Interval

“…It is thus worth noting that the δ 15 N records of other T‐CIE profiles located in the shallow shelf settings fall in the Mo‐based diazotrophic range. This N 2 fixation isotope record contradicts the possibility of existing water‐column partial denitrification and/or anammox of marginal marine basins connected to the open ocean ( δ 15 N values traditionally > +3‰; e.g., Ader et al., 2016; Garvin et al., 2009; Gilleaudeau et al., 2020; Stüeken et al., 2016), but is in line with redox‐controlled N biogeochemical cycle in hydrographically restricted environments.…”

“…Biomass preserves this signature in marine sediments. Thus, in ancient sedimentary rocks, δ 15 N values between −4‰ and + 2‰ can be confined to the dominant operation of Mo‐based diazotrophy, while higher δ 15 N values (> + 3‰) evidence water‐column partial denitrification and/or anammox (e.g., Garvin et al., 2009; Gilleaudeau et al., 2020; Stüeken et al., 2016).…”

“…However, the reliable δ 15 N values between +0.3 and + 2.5‰ found in the uppermost tenuicostatum and lower falciferum zones (Figure 4) do not reflect the isotope effect of water‐column partial denitrification and/or anammox (traditionally > + 3‰; cf. Garvin et al., 2009; Gilleaudeau et al., 2020; Stüeken et al., 2016). By contrast, such a N isotope signal is in accordance with Mo‐based diazotrophy likely under N‐limited conditions.…”

“…When entering the T‐CIE, if sedimentary deposition occurs in open marine environments, the extensive seawater deoxygenation (OAE) would partially consume NO 3 − through water‐column denitrification, the most prominent oceanic NO 3 − removal process (Sigman & Fripiat, 2019; Stüeken et al., 2016). Considering that partial denitrification and/or anammox preferentially releases 14 N as the form of N 2 /N 2 O to the atmosphere, resulting in higher δ 15 N values of the residual N pool, organic matter (OM) deposited in open marine environment records such 15 N‐rich seawater signal through assimilation and imparts δ 15 N values ≥3‰ in sediments (e.g., Garvin et al., 2009; Gilleaudeau et al., 2020; Stüeken et al., 2016; Tesdal et al., 2013). This is because a large dissolved marine N reservoir is required to record the isotopic fingerprints of its redox‐driven cycle in co‐deposited sediments (Stüeken et al., 2016).…”

“…Considering that partial denitrification and/or anammox preferentially releases 14 N as the form of N 2 /N 2 O to the atmosphere, resulting in higher δ 15 N values of the residual N pool, organic matter (OM) deposited in open marine environment records such 15 N-rich seawater signal through assimilation and imparts δ 15 N values ≥3‰ in sediments (e.g., Garvin et al, 2009;Gilleaudeau et al, 2020;Stüeken et al, 2016;Tesdal et al, 2013). This is because a large dissolved marine N reservoir is required to record the isotopic fingerprints of its redox-driven cycle in co-deposited sediments (Stüeken et al, 2016).…”