| Title | An example of the Middle to Late Devonian marine nitrogen cycle from mudstones of the Horn River Group, Northwest Territories, Canada |
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| Author | LaGrange, M T ;
Li, K; Li, L; Kabanov, P; Konhauser, K O; Harris, B S; Biddle,
S K; Terlaky, V; Gingras, M |
| Source | Palaeogeography, Palaeoclimatology, Palaeoecology vol. 618, 111512, 2023 p. 1-12, https://doi.org/10.1016/j.palaeo.2023.111512 |
| Image |  |
| Year | 2023 |
| Alt Series | Natural Resources Canada, Contribution Series 20220353 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; digital; on-line |
| File format | pdf |
| Province | Northwest Territories; Yukon |
| NTS | 96D; 106; 116A; 96E; 96L; 96M; 116B; 116G; 116H; 116I; 116J; 116O; 116P; 97B; 97C; 107A; 107B; 107C; 107D; 117A; 117D |
| Lat/Long WENS | -140.0000 -125.0000 70.0000 64.0000 |
| Subjects | paleontology; stratigraphy; mudstones; organic deposits; shales; black shales; nitrogen; marine deposits; marine environments; Horn River Group; Devonian |
| Illustrations | stratigraphic columns; location maps; bar graphs |
| Program | GEM-GeoNorth: Geo-mapping for Energy and Minerals GEM Program Coordination |
| Released | 2023 03 14 |
| Abstract | The Middle to Late Devonian was characterized by the widespread deposition of organic-rich mudstone units and successive biotic crises and anoxic events in the marine realm, the cause of which remains
debated and requires constraints from associated marine conditions. This study provides an example of the marine nitrogen cycle throughout the late Eifelian to middle Frasnian anoxic pulses. We present new and previously published organic whole-rock
N (d15Nbulk) and carbon (d13Corg) isotopic datasets from organic-rich mudstone units of the Horn River Group (Canol and Hare Indian Formations) and overlying Imperial Formation in the Central Mackenzie Valley, Northwest Territories, Canada. In the
ConocoPhillips Mirror Lake N-20 core, d13Corg ranges from - 31.0 per mil to - 24.3 per mil with d15Nbulk from - 3.8 per mil to +1.9 per mil, whereas the Husky Little Bear N-09 core is characterized by d13Corg from - 31.0 per mil to - 27.2 per mil and
d15Nbulk from - 2.0 per mil to +5.9 per mil. The N isotopic signatures near 0 per mil and a lack of d15Nbulk - d13Corg relationship are characteristic of N2 fixation by primary producers. Regular oscillations in d15Nbulk are interpreted as the
product of episodic, mild oxygenation events. Together, our d13Corg and d15Nbulk results suggest that locally, N2 fixation was the dominant source of N for primary producers in the late Eifelian to middle Frasnian, despite fluctuations in d13Corg and
global marine paleoredox. These findings contribute to our understanding of the nitrogen speciation and bioavailability associated with anoxic events, biotic crises, and widespread organic carbon burial in the Eifelian to Frasnian oceans. |
| Summary | (Plain Language Summary, not published)
The Middle to Late Devonian was characterized by the widespread deposition of organic-rich mudstone units and successive biotic crises and anoxic events
in the marine realm, the cause of which remains debated and requires constraints from associated marine conditions. This study aims to understand trends in primary producer type and biological productivity throughout the late Eifelian to middle
Frasnian anoxic pulses. We present new and previously published organic carbon (d13Corg) and whole rock N (d15Nbulk) isotopic datasets from organic-rich mudstone units of the Horn River Group (Canol and Hare Indian Formations) and overlying Imperial
Formation in the Central Mackenzie Valley, Northwest Territories, Canada. Presented here results on carbon and nitrogen stable isotopes suggest that locally, diazotrophs were dominant in the late Eifelian to middle Frasnian in this paleo-basin,
despite fluctuations in marine paleoredox, and that the growth rate of primary producers varied throughout the late Givetian to middle Frasnian. These findings contribute to our understanding of the ecological patterns associated with anoxic events,
biotic crises, and widespread organic carbon burial in the Eifelian to Frasnian oceans. |
| GEOSCAN ID | 330889 |
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