The structure of a perylene-containing fossilized sclerotium is maintained by original silica

Perylene occurs in sediments throughout the world, especially lake sediments. It has been proposed to originate from 4,9-dihydroxyperylene-3,10-quinone contained in the sclerotium of Cenococcum geophilum, a rhizobium present in the catchment areas of the lakes. Although fresh sclerotia consist mainly of Al2O3, fossilized sclerotia in sediments from Lake Biwa, Japan, contain remarkable amounts of perylene and retain their structure without Al. We focussed on the silicon that maintains the structure of the sclerotia and have identified its origin. Microscopic observation and elemental analysis showed that the segment is mostly clear and contains 2 atom% Si, together with 83 atom% C and 15 atom% O. Furthermore, X-ray diffractometry revealed an absence of crystallinity. We conclude that the silicon in the fossil segment of sclerotia is present in a quartz glass-like amorphous form, plays an important role in maintaining the structure of the sclerotium and was present in the original sclerotium rather than being taken up during diagenesis. This fact may be one of the reasons why perylene is well preserved in sediments for long periods.