Morphology, sedimentology and biology of mud volcanoes on the Moroccan continental margin.

摘要

Detailed geophysical investigations and seafloor ground-truthing carried out in 1999 on several seafloor features exhibiting extrusive-type structures, which were previously thought to represent subjacent salt structures, have been conclusively identified as mud volcanoes. These mud volcanoes reflect the position of deep fault structures, which are associated with the local transpressive stress regime, and serve as conduits for fluid and gas flow responsible for the observed mud volcanism.; Three regions of mud volcanism and diapirism were identified (the Western Moroccan Field (WMF), Middle Moroccan Field (MMF) and Eastern Moroccan Field (EMF)). In the WMF the diapiric structures are represented by long, sinuous ridges on the seafloor. Sedimentary basins have formed adjacent to these ridges. In the MMF, sidescan data, grab samples and gravity core samples confirm the existence of two mud volcanoes, (Yuma and Ginsburg). Methane hydrate (clathrate) was recovered from Ginsburg. In the EMF, gravity core samples confirm the existence of three mud volcanoes (Kidd, Adamastor, TTR) and seismic and sidescan sonar data suggest that there are at least nine other mud volcanoes with associated diapirs and coral reef structures. Mud volcanoes and the presence of methane hydrates had not been identified in this region prior to this study.; One mechanism for development of these structures involves the migration, from depths exceeding 1 km, of thermogenically produced methane-rich fluids along existing faults and fractures. Movement of the Gibraltar Arc, which is responsible for olistostrome development, plus deep crustal faulting related to the past and present.