Origin of oils in Po Basin, Northern Italy

Abstract The crude oils of the Po Basin are characterized by means of different analytical techniques (capillary GC of the saturated and aromatic hydrocarbons, carbon isotopic composition of the fractions, capillary GC/MS of the steranes and terpanes, V and Ni content). The geochemical data allow to sharply discern three main genetic groups, one in the Pedelpine area (Malossa group) and two in the Pedeapennine area (Cortemaggiore and Cavone groups). Furthermore two other oils are distinguished: one in the Pedealpine area(Gaggiano), slightly different from the Malossa group, and one in the Pedeapennine area (Bagnolo), peculiar for its terpane distribution. Extract of rock samples, from units which show the best source rock characteristics, were also studied in order to establish oil-source rock correlations. The “Riva di Solto” Argilite (Triassic) was found to be the primary source for the Malossa oil group. The “Marnoso Arenacea” (Tertiary) is recognized as the source rock for the Cortemaggiore oil group; the presence of oleanane in both oil and rock extract was a key point for the conclusive evidence for the source of this oil. For the Cavone group a Triassic carbonate, a sulfur rich kerogen is inferred as the probable source rock. The Meride Limestone (Triassic) is the source rock for the Gaggiano oil, whereas for the Bagnolo oil a possible Tertiary origin is suggested. This case history provides another record of the occurrence of oleanane in oils generated by Tertiary source rocks containing organic matter of continental origin.