Lithological control on the state of preservation of fossil seed coats of water plants

In this study 1 Eocene wood sample and 25 fossil Eocene seed coats of water plants from 6 different localities on the south coast of England are analyzed using scanning electron and light microscopy, in addition to Curie-point pyrolysis-GC(-MS) and solid state 13C NMR, in order to characterize their morphological and chemical alteration in relation to different lithologies. Results from the translucent inner seed coat layers, tegmens, reveal that these tissues consist of aliphatic type biomacromolecules similar to cutan. The tegmens remain morphologically and chemically unaltered. By contrast, the results from the outer seed coat layers, testae, show that these are composed of polyphenolic macromolecules derived from lignin-celluloses. The testae are, on average, morphologically best preserved in fine-grained sediments, whereas best chemical preservation is observed in testae from coarse-grained sediments. Testae associated with pyrite in blue or green fine-grained sediments show poor quality chemical preservation, whereas those from dark brown and grey clays with pyrite show chemical preservation more similar to that of testae from coarse-grained sediments. These results show that diagenetic alteration of organic matter is not only determined by burial history but can also be greatly influenced by differences in lithology.