IMPACT OF POST-DEPOSITIONAL FLUIDS ON PALEOCEANOGRAPHIC SIGNATURES OF EDIACARAN DEPOSITS: IMPLICATIONS FOR PALEOCEANOGRAPHIC CONSTRAINTS OF THE CRYOGENIAN-EDIACARAN-CAMBRIAN TRANSITION

• Grant number: 25/08515-7
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: November 01, 2025
• End date: May 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Ricardo Ivan Ferreira da Trindade
• Grantee: Renan Fernandes dos Santos
• Supervisor: Pierre Sansjofre
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Muséum National d'Histoire Naturelle, France
• Associated to the scholarship: 24/04141-2 - Impact of post-depositional fluids on paleoceanographic signatures of Ediacaran deposits: Implications for paleoceanographic constraints of the Cryogenian-Ediacaran-Cambrian transition, BP.PD

Abstract

Complex ecological behaviors emerged during the Ediacaran, making this period's oceanographic and atmospheric conditions critical for developing early multicellular life. Paleoceanographic reconstructions are primarily based on isotopic records, especially the similarity of isotopic signals across different sedimentary basins, which has led to the proposal of global curves. Among the most widely used proxies are 87Sr/86Sr ratios, useful for inferring continental weathering fluxes and atmospheric CO¿ levels (pCO¿), and ¿¹³C values, the key to reconstructing carbon cycle fluctuations over time. However, interpreting the meaning of these isotopic anomalies, particularly distinguishing whether they are global, regional, or diagenetic, remains a significant challenge in Neoproterozoic paleoenvironmental studies. Diagenetic overprinting can modify pristine signals, casting doubt on the validity of global correlations, which may instead reflect local or regional tectonic-thermal histories. A robust approach to address these limitations is to use integrated multiproxy analyses, combining petrographic, mineralogical, and geochemical data to assess the preservation of primary signatures and identify post-depositional alterations. Conventional bulk rock geochemistry, although widely applied, often masks spatial and temporal variations by averaging signals from multiple cementation and replacement phases. In the case of the deposits studied, detailed petrographic and mineralogical analyses have revealed at least four distinct cementation events, pointing to a complex diagenetic history. This complexity may lead to misinterpretations of the original depositional environment. High-resolution techniques are, therefore, essential. Nanoscale Secondary Ion Mass Spectrometry (Nano-SIMS) is an advanced method that enables chemical and isotopic analysis at the nanometer scale, allowing in situ distinction between preserved primary signals and later alterations. When combined with high-resolution petrography and mineralogical data, Nano-SIMS offers a unique opportunity to refine paleoenvironmental interpretations in complex deposits. This project aims to enhance the geochemical analysis of Neoproterozoic carbonate and siliciclastic deposits by identifying preserved primary signatures. A multiproxy approach - integrating geochemical (major and trace elements, ¿¹³C, 87Sr/86Sr in situ), microfacies, and paleontological data - will enable the reconstruction of Ediacaran redox and oceanographic conditions, contributing to a better understanding of the feedback mechanisms between Earth's chemical and biological evolution during one of its most transformative periods. (AU)