Organic matter composition and maturity of the Callovian (Middle Jurassic) sediments from Lithuania

In both the terrigenous Papilė Formation (Lower Callovian) and shallow- to deepermarine facies of the Papartinė and Skinija formations (Middle and Upper Callovian, respectively), terrestrial organic matter predominates. This is emphasized by the carbon preference values higher than 1 for all samples and in some cases higher than 2, as well as the occurrence of characteristic higher plants biomarkers like cadalene, dehydroabietane, simonellite and retene. Fragments of charcoal found in the samples of the Papilė Formation indicate wildfires that took place in the early Callovian of Lithuania. Unlike the Callovian of Western Europe, in the Middle Callovian of Lithuania there is no evidence of anoxic conditions occurring in the water column. Measured values of huminite reflectance (Rr) for selected samples are in the range of 0.21% to 0.31%, what is characteristic for immature OM. This indicates that investigated deposits during their whole diagenetic history laid nearly on the surface and the thickness of younger cover does not exceed 500 m. This is supported by biomarkers analysis. In the all Callovian samples less thermally stable ββ-hopanes significantly dominated what suggest immature character of the samples.