266 The Neoproterozoic Earth and Life Co-evolution (Posters)

This session aims to enhance discussions and foster interdisciplinary collaborations to advance understanding of the Neoproterozoic Earth and life co-evolution. Contributions from paleontologists, geochemists, sedimentologists, Earth system modelers, and related fields are highly encouraged.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Investigating Nitrogen Cycling Dynamics Preserved in Neoproterozoic (Glacio)marine Sediments: Insights from the Southwestern Unites States

Paper number: 266-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

During the Neoproterozoic, shallow marine settings experienced global glaciations, evolving redox structures, and eukaryotic expansion. Discerning the coevolution of habitability and eukaryotes within these settings depends on understanding nutrient availability. One key limiting nutrient is nitrogen (N), a bioessential element whose speciation varies relative to biologic activity and water column redox. Marine N cycling is reconstructed using sedimentary N isotope values (δ15N); however, the δ15N record remains spatially and temporally limited for the Neoproterozoic. To address this, we present N isotopic values for whole rock (δ15NWR) and kerogen fractions (δ15Nker), organic δ13C values, trace element concentrations, and mineralogical abundances from late Tonian, Cryogenian, and Ediacaran sediments in the southwestern Unites States.

 

Our results show aerobic N cycling persisted for much of the Neoproterozoic. Most Ediacaran, Cryogenian, and Tonian sediments have δ15NWR values around 5- 7‰, similar to average nitrate δ15N in modern seawater. Within the same samples, most δ15Nker values are ~2- 4‰ lower than δ15NWR. During the late Tonian, δ15NWR decreases 2- 4‰, then increases during the Cryogenian. This 2- 4‰ difference is also observed in the δ15Nker fraction and occurs between Tonian- Cryogenian sections in the Death Valley area (Horse Thief Springs and Kingston Peak formations) and the Wasatch Mountains (Big Cottonwood and Mineral Fork formations). Enrichments of redox-sensitive trace metals mostly align with sections of low δ15N. Chemical Index of Alteration values are generally higher during the Tonian and Ediacaran (CIA=65-80) and lower during the Cryogenian (~55-70). C/N ratios of whole rock and kerogen, as well as mineralogy, reflect heterogenous inputs of allochthonous sediment. However, these inputs are shown to have low N concentrations and do not obscure the authigenic δ15N signal. The combined δ15N results and other geochemical proxies describe N cycle conditions where nitrate would have been available in local, partially oxygenated seawater during the Tonian, Cryogenian and Ediacaran. A more anaerobic N cycle developed near the Tonian-Cryogenian transition, perhaps driven by the onset of Sturtian glaciation.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413243

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