A major Miocene deepwater mud canopy system: The North Sabah-Pagasa Wedge, northwestern Borneo

Three-dimensional seismic reflection data, well data, and analogues from areas with extensive shale tectonics indicate that the enigmatic deepwater shale nappe or thrust sheet region of northern offshore Sabah, Malaysia, now referred to as the North Sabah-Pagasa Wedge (NSPW), is actually a region of major mobile shale activity characterized by mini-basins and mud pipes, chambers, and volcanoes. A short burst of extensive mud volcano activity produced a submarine mud canopy complex composed of similar to 50 mud volcano centers (each probably composed of multiple mud volcanoes) that cover individual areas of between 4 and 80 km(2). The total area of dense mud canopy development is similar to 1900 km(2). During the middle Miocene, the post-collisional NSPW was composed predominantly of overpressured shales that were loaded by as much as 4 km thickness of clastics in a series of mini-basins. Following mini-basin development, there was a very important phase of mud volcanism, which built extensive mud canopies (coalesced mud flows) and vent complexes. The mud canopies affected deposition of the overlying and interfingering deposits, including late middle to early late Miocene deepwater turbidite sandstones, which are reservoirs in some fields (e.g., Rotan field). The presence of the extensive mud volcanoes indicates very large volumes of gas had to be generated within the NSPW to drive the mud volcanism. The Sabah example is only the second mud canopy system to be described in the literature and is the largest and most complex.

Automated summary

Research on the enigmatic deepwater shale nappe region in northern offshore Sabah, Malaysia has found evidence of major mobile shale activity. This activity has led to the formation of mini-basins, mud pipes, chambers, and volcanoes, including an extensive mud volcano complex consisting of around 50 mud volcano centers. The presence of these mud volcanoes indicates the generation of large volumes of gas within the area.