Nitrogen Isotopes in Kukersite and Black Shale Implying Ordovician-Silurian Seawater Redox Conditions

Abstract

For the first time data on nitrogen isotopes from the Ordovician-Silurian sedimentary rocks of the Baltic Basin are reported. Supplementary samples come from several regions worldwide. The data reveal the existence of different primary bioproductivity pathways in the Ordovician-Silurian. During the formation of black shale surface waters were oxygen-poor and maintained N 2 -fixing primary production indicated by δ 15 N -0.3‰ on average. The average δ 15 N of kukersite oil shale is +7.4‰. The positive δ 15 N values are in accordance with the formation of kukersite in oxic waters, showing that Gloeocapsomorpha prisca was a nitrate-using not N 2 -fixing cyanobacteriumlike organism. The black shale samples from the deep shelf suggest that seawater, including the photic zone, often suffered from deficiency of oxygen.

Lipid biomarker and stable isotopic profiles through Early-Middle Ordovician carbonates from Spitsbergen, Norway

“…Elevated 2α-methylhopanes combined with low (ranging from -2 to +4‰ but averaging -1 to +1‰ for normal marine salinity facies) δ 15 N total values are in general agreement with a stratified and nutrient (nitrate)-limited aquatic environment favouring diazotrophic bacteria. Nitrogen isotope values reported here are similar to those reported in another Early Ordovician section (Azmy et al, 2015) and fixed nitrogen limitation has been commonly associated with Late Ordovician shelf and basinal settings (e.g., LaPorte et al, 2009;Kiipli & Kiipli, 2013;Luo et al, 2016). The more organic-rich strata of the lower Olenidsletta Member yield δ 15 N total signatures which are slightly 15 N-depleted by about 1‰ (mostly within the 0 to -1‰ range in Figure 3D) relative to organic-lean rocks.…”

Environmental conditions and microbial community structure during the Great Ordovician Biodiversification Event; a multi-disciplinary study from the Canning Basin, Western Australia

“…Nitrogen isotopes of G. prisca-rich sedimentary rocks, including samples from the Goldwyer Formation, have been reported previously (Kiipli and Kiipli, 2013) which exhibited average δ 15 N values of +7.4‰. Relative to the atmospheric N2 source (0‰), denitrification in the water column leads to a much larger isotopic fractionation (~20‰) than microbial nitrogen fixation (<3‰) (Luo et al, 2016).…”

“…Relative to the atmospheric N2 source (0‰), denitrification in the water column leads to a much larger isotopic fractionation (~20‰) than microbial nitrogen fixation (<3‰) (Luo et al, 2016). These results indicate that denitrification occurred when G. prisca was abundant, suggesting G. prisca was a nitrate A C C E P T E D M A N U S C R I P T 21 using not N2-fixing microorganism (Kiipli and Kiipli, 2013). Cyanobacteria and aerobic methanotrophs have the ability to fix atmospheric nitrogen, thus providing a potential nitrogen source for G. prisca.…”

Depositional framework of the East Baltic Tremadocian black shale revisited

“…Both those groups contain species capable of fixing N 2 . The dominance of nitrogen-fixing primary production pathways during the accumulation of Tremadocian black shales in Estonia has been lately proposed by Kiipli & Kiipli (2013) based on low d 15 N values. Blumenberg & Wiese (2012) suggested that high bioavailable P loading versus bioavailable N could have been the main trigger of black shale formation in shallow seas during late phases of Cenomanian/Turonian ocean anoxic event.…”