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The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.

The source potential and organic maturity of the shales alternating with the reservoir beds in the Lower Pliocene Productive Series -the major oil-bearing unit in the South Caspian Basin -are inadequate to have formed the observed petroleum accumulations. A geochemical study of rocks collected from wells and outcrop localities has been carried out to assess the oil-and gas-generative properties of the Middle Jurassic to Lower Pliocene sediments of the basin. On the whole the section under review is characterized by poor to good organic richness and low hydrogen index, suggesting type 2 and 3 kerogens. Organic-rich sediments are relatively frequent in parts of the Oligocene-Miocene interval. Source-to-oil correlation based on carbon isotope signatures points to a largely epigenetic origin for the oils reservoired in the Lower Pliocene. Isotopically, the oils in these Productive Series reservoirs are best correlated with organic matter contained in the Miocene sediments.

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Mud volcanism is a global phenomenon usually associated with compressional tectonics that favour extrusion of fluid-and clay mineral-rich sediment both on land and offshore. Methane, the dominant gas phase, is emitted at variable rates during and after emplacement of the mud domes. In case of continental mud volcanoes, the gas is directly released into the atmosphere, thereby contributing to global warming. Azerbaijan is one of the countries with one of the highest abundances of mud domes globally. One of the most prominent mud volcanoes, Dashgil, has been chosen for a case study because of its historic record of violent eruptions, continued activity, and well-documented regional geology in the Caucasus orogenic wedge adjacent to the Caspian Sea. Since 2003, gas flux has quantitatively measured at one of the two crater lakes and is characterized by valve-type behaviour and episodically violent degassing. In 2007, the large crater lake was additionally equipped with methane fluxmeters as well as an in situ pore-pressure probe into the conduit. Our data are complemented by regional seismicity, and exhibit the following results: (1) there seems to be a significant correlation between changes in pore pressure in the conduit feeding the main crater lake and the rate of gas escape; (2) changes in gas-flux rate appear to be independent of local seismicity, in particular since no larger EQs have been recorded since 2003; (3) despite discontinuous monitoring owing to technical failures, we observe an overall increase in methane emission with time; (4) nearby earthquake activity (\M4.6) can be correlated with pore-pressure transients recorded by the piezometer, which reach up to 2.4 kPa compared to the pre-seismic value; (5) from time to time, there are strong lake-level fluctuations decoupled from precipitation or evaporation, which are explained by subbottom hydraulic communication between the two crater lakes and adjacent gryphons. The wealth of observations leads us to conclude that monitoring gas flux and pore pressure provides important time series data for both methane emission into the atmosphere and pore pressure as a proxy for co-seismic strain.

This study summarizes the subsidence history and aspects of the geodynamic evolution of the South Caspian Basin based on the integration of geophysical observations, and subsidence and gravity modelling on selected two-dimensional (2D) profiles. This analysis implies the presence of an attenuated ‘oceanic-type’ crust in the northern portion of the South Caspian Basin, demonstrates characteristics of basin subsidence on variable crustal types and describes sediment-fill evolution in several different parts of the basin. Modelling conducted in this study shows that the observed pattern of subsidence and sedimentation in the South Caspian Basin can be explained by a process of thermal subsidence following Jurassic rifting and further enhanced subsidence that resulted from sediment-induced loading in the Late Tertiary, especially after a large-scale base-level fall after 6 Ma.Variation in crustal type is reflected in differences observed in the degree of subsidence and sediment fill in the overlying stratigraphy. The western part of the South Caspian Basin has subsided differently to the eastern part because of this difference in crustal type. This is also confirmed by gravity modelling, which shows that the South Caspian Basin crustal density is compatible with an oceanic composition in the western part of the South Caspian Basin: the crust in the eastern part of the basin, however, is thicker.

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