Eleven sediment samples from different geological layers and four fossils from the South of Sweden were collected and estimated to be 80 million years old (approximately late of Cretaceous period). The samples were analyzed for polychlorinated dibenzo-p dioxins (PCDD/Fs) to investigate whether these samples are likely to contain dioxins from a natural formation. For over thirty years, the scientific community has discussed the possibility of a natural formation of dioxins. Several hypothesis have been put forward, but often rejected by the evidence of a source of anthropogenic pollution in the samples. In order to answer this issue, two types of analyses have been performed : high resolution gas chromatography-high resolution mass spectrometry (HRGC/HRMS) and elemental analyzer-isotopic ratio mass spectrometry (EA-IRMS). HRGC/HRMS provides information about the source of dioxins comparing the distribution of all PCDD/Fs to experimental isotopic patterns from past publications. δ13C of organic carbon gives information about the nature of carbon present in soils and can be helpful to trace paleoclimates.