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Mud Volcanoes of Azerbaijan - Windows to the Subsurface

Berner, Ulrich 1; Scheeder, Georg 1; Kus, Jolanta 1; Movsumova, Ulviyya 2
1 Petroleum and Coal Geochemistry, Fed. Inst. of Geosciences and Natural Resources, Hannover, Germany.
2 Geology Institute of the Azerbaijan National Academy of Sciences, Baku, Azerbaijan.

Mud volcanoes are prominent geological features of Azerbaijan. Tectonic forces control their occurrences in regions with over-pressured subsurface sediments as mud volcanoes are closely linked to fault systems. The mud of volcano cones contains numerous ejected rock fragments, which we use to identify the depths from which the mud has been transported.

Organic geochemical, organic petrographical and mircopalaeontological investigations have been performed on selected samples of 19 mud volcanoes. The amounts of extractable hydrocarbons in relation to organic carbon contents indicate that most of the sediment samples are impregnated by migrated hydrocarbons. Hydrogen and oxygen indices derived from RockEval pyrolyses indicate that the organic matter of the sediments consist mostly of mixtures of Type II and III kerogens.

All extracted hydrocarbons have been affected by secondary alterations that most likely involved biodegradation as the normal alkanes have been removed to a large extend. Despite of biodegardation, environmental and maturity sensitive biomarkers could be identified. C27- to C29-sterane isomers suggest a dominance of aquatic organic matter. An influence of diatoms on the sterane distribution seems plausible although, an admixture of land plant material can also not be excluded. Homohopane isomerization ratios as well as the ratio of trisnorneohopane over trisnorhopane suggest that the extracted hydrocarbons come from a coalification range which spreads from immature to mature although, maximum maturity does not reach the peak of oil generation. C29-sterane isomerisation ratios support this finding.

Vitrinite reflectance measurements on the rock ejecta indicate a similar range of maturities as suggested from biomarker analyses. However, the data indicate again that most of the investigated rocks have been impregnated by allochthonous hydrocarbons as biomarker maturities may slightly depart from the measured reflectance values.

We estimated from published maturity/depth conversion that the mud volcanoes along a SSW-NNE transect from the Kura Basin to the Apsheron Peninsula produce their mud from a depth range between 4000 and 5500 m corresponding to a maturity range of 0.5 to 0.65% vitrinite reflectance. However, no specific regional maturity or depth trends could be identified.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009