299-9 From Sediments to Signposts: The Paleoproterozoic Phosphorus Cycle and Early Earth Oxygenation

Session: Geochemical Studies of Sediments (Posters)

Presenting Author:

Author:

Abstract:

The Paleoproterozoic Era was a transformative phase in Earth's history, witnessing profound changes in the atmosphere, biosphere, and lithosphere. Beginning 2.4 billion years ago, the Great Oxidation Event (GOE) marked a pivotal shift in atmospheric oxygen levels and shallow marine environments driven by the rise of cyanobacteria capable of oxygenic photosynthesis. While the GOE is primarily known for establishing an O₂-rich atmosphere, it also fundamentally reshaped the cycling and availability of Phosphorus (P). P is a crucial element for cellular processes: it forms the backbone of genetic material, provides structural integrity to cell membranes, and drives energy metabolism. Without P, life as we know it would not exist. On geological timescales, P imposes the ultimate nutrient limitation. The bioavailability of P regulates the consumption of CO₂, modulates the burial of organic carbon, and influences photosynthetic O₂ production, establishing links between P-cycling and atmospheric and oceanic redox states.

The earliest evidence of P-bearing sedimentary rocks dates back to ~3.5 Ga. However, the sedimentary record is characterized by low [P] until the Paleoproterozoic. The synchronous global emergence of phosphorites marked a shift in the sequestration and cycling of P. This shift has been interpreted as a geochemical response to early-stage oxygenation of the atmosphere-ocean system, indicating an underlying causal mechanism that linked redox with P availability and deposition. However, the mechanisms governing P retention, release, bioavailability, and utilization during the Paleoproterozoic remain poorly constrained. Estimates of P availability during the GOE span several orders of magnitude, with conflicting evidence emerging from biological and geological proxies. Phylogenomic analysis suggests elevated [P] back to 3.6 Ga, while carbonate-associated phosphate records indicate high [P], though only extending back to the Neoarchean. In contrast, P/Fe ratios and bulk shale P provide evidence of significant P limitation until ~1.7 Ga and ~750 Ma, respectively.

To resolve these discrepancies, a multi-proxy investigation of early marine redox states, microbial metabolisms, and nutrient feedback mechanisms is necessary to understand how the earliest phosphorites not only reflected but may also have driven the emergence of oxygen and complex life.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7707

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.