Asphalt volcanism investigated in the deep southern Gulf of Mexico, Campeche-Sigsbee Salt Province

After the discovery of an approximately 1 km² area of ​​solidified asphalt on a seamount (knoll) in the southern Gulf of Mexico, scientists defined the term asphalt volcanism for the process of formation because of the numerous other signs of eruptive deposition on the seafloor. They named the structure Chapopote, after the word asphalt in the Aztec language. Subsequent visual examinations of the seafloor revealed extensive surface deposits of solidified asphalt and light crude oil seeping from locations along the rim of a crater-like structure at 2,900 m water depth. Large areas of the asphalt deposits were colonized by vestimentifera tubeworms, bacterial mats, and other biological communities. Further seafloor mapping showed that most of these knolls have crater-like areas associated with seepage. During recent expeditions, the crater structures of Mictlan Knoll and Tsanyao Yang Knoll were mapped in high resolution, sampled in detail and visually examined with MARUM ROV QUEST4000. Although large areas are also covered with lava-like asphalt sheets, the asphalt seems not to be flown at higher temperatures. Extrusion of heavy liquid oil in form of whips or sheets were observed at several locations which indicate a slow consolidation of the liquid oil to form firm asphalt. After extrusion, chemical and physical changes in the asphalt generate increasing viscosity gradients both along the flow path and between the flow’s surface and core. This allows the asphalt to form pāhoehoe lava-like shapes and to support dense chemosynthetic communities over timescales of hundreds of years.