Types of Micro Mud Volcanoes in Transylvania, Romania
Abstract:Mud volcanoes are one of the world's most dynamic phenomena. They are distributed worldwide in various tectonic settings. Mud volcanoes can be defined as geological structures with a variety of morphological expressions, constructed mainly of mud that originates deep in the sedimentary succession. The occurrence of mud volcanoes is related to recent tectonic activity (particularly compressional); sedimentary or tectonic loading; hydrocarbon generation and the existence of thick, finegrained, soft, plastic sediments deep in the sedimentary succession (Dimitrov, 2002; Kholodov 2002a, b).
The main driving force of mud volcanism is believed to be the abnormally high pore-fluid pressure and secondly the buoyancy pressure (Dimitrov, 2002). The abnormally high pore fluid pressure can be primarily a result of very high sedimentation rates and the fast burial of these sediments. As a result of the fast burial, sediments retain a big amount of water and organic material and they remain undercompacted. Under the weight of the overburden layers they become overpressured compared with the surrounding sediments. This state is accentuated by the decomposition of organic material and gas generation.
According to Dimitrov (2002) “the high water and gas content decreases the bulk density, shear modules and viscosity, making such sediments semi-liquid and able to flow. Such a sequence of low density, under compacted, over pressured mud or shale overlain by thick denser material, is mechanically unstable and frequently finds expression in mud or shale diapirs or in mud volcanoes.” Pore fluid pressure can be intensified by compressional tectonic forces (folding, thrusting, over thrusting) as well (Kholodov 2002a; Dimitrov, 2002).
Hovland and Judd (1988) suggested a model for mud diapirism related to the formation of mud volcanoes. They assumed that the presence of diapirism facilitates the formation of mud volcanoes, as the migration of salt provides pathways for hydrocarbon migration, which is trapped inside the mud above the salt. As the gas rises and expands, it increases the pore pressure and contributes to the upward mobilization of the mud. If the salt is still mobile it can result in tensional faults that serve as pathways for the over pressured mud.
Document Type: Research Article
Publication date: January 1, 2008