Hydrocarbons of bitumen inclusions in magmatic rocks in north of Khakassia

In this article gas-chromatography-mass spectrometry (GC-MS) method was used to study molecular composition ofsaturated and aromatic hydrocarbons of three samples of bitumen from the north of Khakassia: heavy bitumen from fractured basalts andsolid bitumen from effusive amygdaloidal basalts outcrops in the valley Sokhochul, as well as solid bitumen from dolerite intrusions inthe area Krasnaya Gorka. Saturated hydrocarbons (94.1-95.4 % rel.) predominate in the major part of composition of hydrocarbons inall the studied bitumen. They include alkanes, alkylcyclohexanes, steranes, sesquiterpanes, tri-, tetra- and pentacyclic terpanes. It isshown that n-alkanes predominate in solid bitumen from amygdaloidal basalts, and in others bitumen steranes and terpanes dominate.These features of composition can be attributed to the occurrence of biodegradation processes, which lead to the decrease of n-alkanescontent and increase of polycyclic naphthenes structures. The ratio of isoprenoid and normal alkanes, as well as the composition ofhopanes indicates significant microbial processing of heavy bitumen and higher thermal transformation of solid bitumen. Data on thecomposition of steranes indicate a specific source of original organic matter of Krasnaya Gorka bitumen, which differs from the sourceand conditions of organic matter accumulation of Sokhochun bitumen. The identified aromatic hydrocarbons include mono-, bi-, tri-,tetra-and pentacyclic structures. Features of composition of heavy bitumen are arilisoprenoids; polyphenyls, binaphthalenes of phenylsubstitutednaphthalenes, phenyl-phenanthrenes and pyrenes are present in solid bitumen. By the results of bitumen hydrocarbons study,which are present in magmatic rocks from in the north of Khakassia we can conclude that the bitumen in fractured basalts was notexposed to rigorous thermal stresses and formed a deposit in solidified basaltic magma. Hydrocarbon fluids were present in fissuredbasalt, which was the result of oil deposit overflow from sedimentary rocks. Source rocks that generated the organic matter, which laterbecame the biodegraded heavy bitumen, were deposits accumulated in the photic zone of the euxinic basin. Bitumen occurring in thedolerite intrusions and amygdaloidal basalts had experienced the impact of very high temperatures. This indicates that organic materialwas in contact with the liquid magma, which determined the features of aromatic hydrocarbons of bitumen. Duration of exposure toextreme temperatures in case of bitumen in dolerite intrusions was significantly greater than in amygdaloidal basalts. We can assumethat bitumen was part of the xenoliths trapped by magmatic melt and subjected to contact metamorphism. Time of cooling of the melt atthe surface was smaller and the conversion of organic material into amygdaloidal basalts stopped earlier, as intermediate products ofpyrolysis were formed in the bitumen.

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