Morphologies and gas emissions from the Shamakhy-Gobustan mud volcano region, Azerbaijan

Azerbaijan hosts the largest concentration of mud volcanoes on Earth. This widespread phenomenon occurs due to the combination of unique geological peculiarities. Azerbaijan is characterized by high sedimentation rates combined with the deposition of thick organic-rich series. The generation of hydrocarbons at depth resulted in petroleum basin formation. This, combined with the naturally buoyant rapidly buried sediments, created the ideal setting and conditions to generate widespread sedimentary volcanism. Some Azerbaijani mud volcano provinces have been intensively studied. Others (e.g., the Shamakhy - Gobustan region) are less explored. Here I report a multidisciplinary study (i.e. including field mapping and observations, the study of satellite images, CO2 and CH4 flux measurements, and gas sampling from active seepage sites) conducted on six mud volcanoes (Maraza, Gyzmeidan, Gushchu, Melikchobanly, Madrasa, and Shikhzarli) located in the northern Shamakhy-Gobustan region. The surface morphologies feature elongated (Kichik Maraza, Melikchobanly) and pie-shaped (Gizmeydan, Gushchu, Shikhzairli) strutures. One mud volcano (Madrasa) does not display a defined edifice and is positioned on the flank of a laterally extensive fault wall. The surface degassing may occur through randomly distributed scattered pools and gryphons where gas, water, mud and oil, are released. These majority of the emissions are commonly present in the crater area (Kichik Maraza, Gizmeydan, Melikchobanly MVs). The tempo of the eruptive activity can also affect the distribution and presence of active degassing. The structures that have been recently erupting often display limited or no visual gas release features (e.g. pools or well-developed gryphons) since these have been removed during the mud breccia flows (Kichik Maraza, Gushchu, Shikhzairli). Molecular and isotopic analyses of the sampled seeps reveal that most of the gas is methane-dominated with a thermogenic origin. Gas molecular fractionation occurring during the vertical migration from the reservoirs is systematically observed. In addition in some instances it was also observed evidence of secondary microbial methane and biodegradation. An extensive campaign of flux measurements was carried out over the crater and the flanks of the mud volcanoes. Degassing was detected at all the structures, including those that did not display obvious visual seepage. Results shows that the targeted MVs release a significant amount of CO2 and CH4 with maximum emissions of 20.3 and 63.6 tonnes yr-1, accordingly