34 Geobiology and Astrobiology in Modern and Ancient Environments: From Microbial Interactions to Planetary Exploration
This session welcomes the submission of geobiological and astrobiological studies, including the investigation of microbe-mineral interactions and biogeochemistry in modern and ancient environments.
Wednesday, 20 May 2026
8:00 AM - 10:00 AM
Alvarado B
Carbonate-associated phosphate and the lack of covariation across Paleoproterozoic carbon isotope excursions: Evidence from the Onega Basin (Russia) and Francevillian Basin (Gabon)
Paper number: 34-1
Program: Technical Sessions
Time: 8:05 AM – 8:25 AM
Authors
Abstract
Marine phosphorus availability is hypothesized to regulate primary productivity, organic carbon burial (forg), and the extent of Paleoproterozoic δ13C excursions. Carbonate-associated phosphate (CAP) provides a direct proxy for paleo-marine phosphate levels. This study tests the “nutrient-control” hypothesis by combining new CAP data with δ13Ccarb, δ13Corg, ΔC, TOC, and isotope-mass-balance estimates of forg at stratigraphic resolution across two different Paleoproterozoic successions: the Francevillian FB Formation (LST12 core, Gabon) and the Zaonega Formation (OnZAP cores, Russia). CAP levels are consistently high, exceeding modern carbonate values by more than an order of magnitude. However, nearest-neighbor correlations between CAP and δ13Ccarb, δ13Corg, ΔC, TOC, and forg lack statistical significance. During positive δ13C conditions, ΔC widens and forg increases, whereas negative δ13C conditions display more variable ΔC and low forg, despite high CAP. These patterns remain consistent regardless of δin, carbonate content thresholds, or the choice of pairing window. Globally, CAP data show that the Paleoproterozoic exhibits a unique combination of modest median values and an extended upper range, indicating episodes of high-phosphate pulses rather than persistent high background levels. Overall, the findings suggest that nutrient-carbon-oxygen feedbacks during the Paleoproterozoic heavily depended on the state, with phosphorus setting the upper bound on gross primary productivity. Still, the isotopic signature only appeared when export fluxes were efficient, and preservation conditions promoted long-term sequestration. CAP reflects the biosphere’s latent capacity to oxygenate the planet, not its inevitable translation in the carbon-isotope record.
Geological Society of America Abstracts with Programs. Vol. 58, No. 4
doi: 10.1130/abs/2026RM-410489
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