DEGREE OF PYRITIZATION OF VARYING TISSUE TYPES: A TAPHONOMY EXPERIMENT

While the exact conditions and chemical reactions regarding the formation of pyrite are relatively well understood, the exact conditions behind fossilization via pyritization are not conclusive. Deposits such as Beecher's Trilobite Bed and other Konservat-Lagersätten deposits display exceptional preservation of soft tissues through pyrite replacement.

In this study we aimed to test the preservation potential of varying tissue types in conditions emulating the Eocene London Clay, where fossils are exceptionally preserved via pyritization. We used four different organisms for this study: plant leaves, stems, chitons and polychaetes. Each was buried for six weeks under anoxic conditions and observed three times weekly. At the end of six weeks, the overlying water was removed and samples were left to air dry. Samples were then exhumed and analyzed using light microscopy and SEM/EDS.

Pyrite was not conclusively identified, most likely due to the short experimental period, as well as exhumation methods. Regardless, the different experimental tissues displayed varying stages of mineralization, from complete replacement to little to no mineralization. Chitons displayed full mineralization of soft tissue with exceptional morphological detail preserved. Polychaetes displayed similar soft tissue detail. Plant stems remained mostly unmineralized with mineralization only localized to the nodes. The plant leaves displayed similar patterns of localized mineralization with localized replacement of the leaf stem, and the fleshy portion of the leaf displaying no mineralization. This experiment demonstrates that under the right conditions, soft tissue can be rapidly and exceptionally preserved by mineral replacement. Further experiments are required to further refine specific timing for each individual tissue type, as well as possibly retaining anoxic conditions during the exhumation process.