The organic geochemistry of rocks from Upper Jurassic deposits foreland of the Indigiro-Zyryansky trough
The work is devoted to geochemical studies on the organic matter of rocks along the section of the Upper Jurassic of the Ilin-Tassky anticlinorium using natural outcrops and core material from the foreland zone, where the Upper Jurassic deposits were thrust over the Cretaceous. There are no materials on organic geochemistry for the Jurassic sediments in contrast to the Cretaceous and Cenozoic, that would allow us to assess their oil source potential. The results of geochemical studies of Jurassic rocks of the allochthon (foreland) will make it possible to predict the oil source properties in the autochthonous area under the Cretaceous deposits of the inner part of the trough. New obtained data on the composition and chemical structure of bitumoids showed that the initial organic matter was of a mixed nature with a predominance of planktonic material capable generating large amount of liquid hydrocarbons. The predominantly aliphatic composition of the hydrocarbon part of the bitumoids was mainly due to the aquagenic nature of the initial material, as indicated by the chromatomass spectrometry data on the distribution of saturated hydrocarbons. At the same time, the shift of the maximum of n-alkanes to the high-molecular-weight region, the noticeable presence of polyarenes, and aromatic character of the carbon skeleton of resins and asphaltenes could be due to the admixture of carbonized residues. In general, the obtained results showed that the geochemical features of the organic matter of the Upper Jurassic deposits of the Indigiro-Zyryansky basin allow them to assess as oil source. The presence of allochthonous bitumoids indicates migration processes that took place within the Jurassic strata. This suggests that oil accumulations can be expected on the Alazeysky uplift in the area of pinch-out of the Jurassic rocks