Organic geochemical evidence for environmental changes since 34,000 yrs BPfrom Lago di Mezzano, central Italy

The composition of organic matter in a 34,000 yr sediment profile from Lago di Mezzano, central Italy, was investigated by bulk organic geochemical me thods and analyses of lipid distributions. High relative amounts of long-ch ain fatty acids, n-alkanols and n-alkanes from the cuticular waxes of terre strial plants in the Late Pleistocene sediments indicate a high relative pr oportion of allochthonous organic matter. In the Holocene sediments higher relative amounts of algal and bacterial lipids are detected which indicate a higher relative contribution of autochthonous organic matter. These resul ts are corroborated by Hydrogen Index (HI) and Oxygen Index (OI) values fro m Rock-Eval pyrolysis which show a good general correlation with the TOC co ntent indicating significant variations of the organic matter composition. Variations of HI and OI observed for different lithozones of the sediment p rofile can be related to environmental and climatic changes throughout the lake history. Both bulk organic geochemical and molecular data point to a g ood overall preservation of the organic matter.