Taphonomic Degradation and Stable Isotope Carbon-13 Systematics of Soft-Bodied Ediacaran Biota from the Nama Group, Southern Namibia

The terminal Ediacaran Nama Group of southern Namibia preserves a key evolutionary archive of early complex life, yet the biogeochemical processes governing soft-tissue preservation remain intensely debated. This study integrates micro-scale taphonomic characterization with high-resolution stable carbon isotope systematics (δ¹³C_org) of soft-bodied macrofossils, including Ernietta bearingensis and Pteridinium simplex, collected from the Kuibis and Schwarzrand Subgroups. Scanning electron microscopy paired with energy-dispersive X-ray spectroscopy (SEM-EDS) reveals that preservation was mediated by a combination of early-stage aluminosilicate clay templating and localized micro-pyritization along structural wall boundaries. Elemental mapping indicates strong enrichments of potassium, aluminum, and iron along fossilized carbonaceous compressions. Organic carbon isotopic analysis demonstrates a consistent depleted shift in fossil carbonaceous films (δ¹³C_org = -28.4‰ ± 1.2‰) relative to the surrounding sedimentary matrix (δ¹³C_org = -24.1‰ ± 0.8‰). This systematic isotopic depletion of approximately 4.3‰ reflects preferential microbial degradation of labile organic matter via anaerobic pathways, notably organoclastic sulfate reduction, prior to terminal mineral capping. Our findings indicate that Nama-type preservation relied on a fine balance between rapid sediment entombment, microbially induced surface sealing, and localized porewater redox gradients, providing fundamental insights into the biogeochemical windows that captured soft-bodied organisms prior to the Cambrian explosion.