Preservation of Fossil Seeds From a 10th Century AD Cess Pit at Coppergate, York

Abstract

Fossilization processes were investigated in terrestrial archaeological deposits, focusing on the preservation of sub-fossil seeds from a 10th century cess pit at Coppergate in York. Flash pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) revealed that the bulk of the assemblage comprises well-preserved organic remains, exemplified by blackberry (Rubus fruticosus) endocarps which retain a near-pristine ligno-cellulose composition. Crab apple (Malus sylvestris) pips are unique in combining an organic seed coat with an embryo which has been phosphatized. Endosperm tissue, nutrient spheres in the cotyledons and, in one specimen, the cotyledon cell walls are replicated in calcium phosphate. Casts of the sclerotic tests cells were also observed in one specimen. The crab apple seed coats have an unusual composition, interpreted as a tannin-cellulose complex. Precipitation of early diagenetic minerals among these organically preserved fossils appears to be restricted to seeds with permeable coats through which ions were transported from pore waters.