Scientific publications

A study of the mineral composition of dolerite sills in the Onega Basin, along with the distribution patterns of amorphous carbonaceous matter within these intrusions, has revealed several key features of interactions at the interface between mafic melts and carbon-bearing host sedimentary rocks of the Ludicovian Zaonega Formation. The emplacement of mafic melts was accompanied by fluidization of sedimentary rocks, causing the generation of gas- and oil-saturated fluids, and assimilation of the carbonaceous matter by the melts. This is evidenced by peperites in the roof zones of the sills, the development of columnar jointing in the host shungite rocks, formation of carbon-bearing amygdales within quenched margins, and the accumulation of carbonaceous matter in the interstices of dolerites in the central parts of the bodies. Dolerite sills exert a dual effect on the migration of gas- and oil-saturated fluids, acting as a trigger for petroleum generation and as barriers or pathways for hydrocarbon migration. The data suggest that the emplacement of early-stage, medium-Mg dolerite sills (Lebeshchina type), characterized by shallow depths of crystallyzation and peperite-type contacts, could be considered as one of the key factors driving oil and gas generation in the Onega Basin. The nature of the contact zone interaction between the Fe-Ti dolerite sills formed within the 2.00–1.96 Ga age interval and the host carbon-bearing rocks suggest that mafic melts could be emplaced into sedimentary sequences at varying stages of consolidation, where the oil-bearing horizons had not yet undergone lithification. The older Fe-Ti dolerite sills (Shunga type) experienced fluid enrichment of residual melts, accompanied by the precipitation of carbonaceous matter within interstices and as mineral inclusions. In contrast, the second group of Fe-Ti dolerite sills (Maksovo type) is characterized by the formation of columnar jointing within the exogenous contact zone of the host shungite rocks, as well as the presence of carbonaceous matter within amygdales and the groundmass of the quenched margin rocks.