In-situ carbonate U-Pb dating and high-resolution stable-isotope analysis of fluvial stromatolites

Fluvial stromatolites are widespread in upper Paleocene–Eocene successions of the South Pyrenean Foreland Basin (SPFB, Spain) yet their geochronological and paleoenvironmental potential remains largely unexplored. Recently documented stromatolites from the Escanilla Formation provide a unique opportunity to investigate continental environmental change across the Middle Eocene Climatic Optimum (MECO), a prolonged global warming event that is well constrained in marine archives but remains poorly dated and resolved in terrestrial records.

Although existing magnetostratigraphic frameworks provide broad temporal control, in-situ U–Pb dating of fluvial stromatolites using LA-MC-ICPMS yields absolute age constraints that refine the stratigraphic placement of the MECO within the Escanilla Formation and improve chronologic resolution across the SPFB. These age anchors allow direct integration of continental sedimentary records with global climate archives.

High-resolution stable-isotope analyses (δ¹³C and δ¹⁸O) performed using SIMS across individual stromatolite growth bands capture seasonal variability in hydrological and thermal conditions. Variations in δ¹⁸O are interpreted to reflect changes in water temperature and/or evaporative conditions, while δ¹³C variability records shift in dissolved inorganic carbon sources and microbial activity within fluvial systems. Together, these data provide insight into seasonality, hydrology, and climate sensitivity of continental environments during a major Eocene warming event.

This study demonstrates that fluvial stromatolites represent robust, datable continental archives capable of resolving both absolute timing and high-frequency environmental variability during past greenhouse climate perturbations.