Perylene as an indicator of conifer fossil wood degradation by wood-degrading fungi

Abstract

The occurrence of perylene in Middle Jurassic fossil wood and Miocene xylites from Poland is described, along with its correlation with unsubstituted polycyclic aromatic hydrocarbons (PAHs) as well as cellulose content. Both Middle Jurassic and Miocene wood remnants were of relatively low maturity [ca. 0.2–0.3% vitrinite reflectance (Rr)], had excellent preservation of biomarkers and biomolecules and, in the case of the Middle Jurassic fossil wood samples, generally good preservation of anatomical structures due to early diagenetic mineralisation. The results from 42 Middle Jurassic and 8 Miocene (most taxonomically defined) fossil wood fragments demonstrated a negative correlation between the concentration of perylene and those of generally typical conifer biomarkers (e.g. cadalene, dehydroabietane, simonellite and retene). In addition, good correlation (R2 0.81) was observed between the ratio of perylene to the above conifer biomarkers and the ratio of PAHs (phenanthrene and fluoranthene and pyrene) to the conifer biomarkers. This implies that the high concentration of perylene in fossil wood indicate its extensive degradation during decay, transport and early diagenesis. We defined a conifer wood degradation index as: CWDI=perylene/(perylene+cadalene+retene+simonellite+dehydroabietane),CWDI=perylene/(perylene+cadalene+retene+simonellite+dehydroabietane), and observed a wide range of values (0.001 for less degraded wood to 0.95 for highly degraded samples). Anatomical wood preservation was associated with CWDI values. In most of the samples characterised by poorly preserved anatomy, high CWDI values were observed, while anatomically well-preserved samples generally had lower CWDI values. We determined similar δ13C values for perylene from the fossil wood samples (−26.4% to −27.8%), whereas the values for the conifer biomarkers were slightly higher and varied from −25.6% to −26.6%. In contrast, pyrene was depleted in 13C (−27.5% to −28.2%). The carbon isotope values of perylene are consistent with an origin from wood-degrading fungi.