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

Abstract

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 ~50 mud volcano centers (each probably composed of multiple mud volcanoes) that cover individual areas of between 4 and 80 km2. The total area of dense mud canopy development is ~1900 km2. 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.

Evolution of Arc‐Continent Collision in the Southeastern Margin of the South China Sea: Insight From the Isugod Basin in Central‐Southern Palawan

“…Morley et al. (2023) have traced the continuity of the external part of the Palawan wedge to the area offshore North Sabah, Borneo. The North Sabah wedge was characterized by the development of a serious of mini‐basins with sediment thickness of 3–4 km (Morley et al., 2023).…”

“…It not only led to the subsidence of the basin to create accommodation space, but also uplifted and exposed the orogenic wedge subaerially to supply sediments (see Section 5.2). Coincidently, Morley et al (2023) also proposed that early stages of the development of the mini-basin offshore Sabah (13-10.5 Ma) were probably related to underthrusting of the Dangerous Grounds crust below the North Sabah and Crocker wedges. We suggest that this might also involve a process of tectonic underplating.…”

“…Morley et al (2023) have traced the continuity of the external part of the Palawan wedge to the area offshore North Sabah, Borneo. The North Sabah wedge was characterized by the development of a serious of mini-basins with sediment thickness of 3-4 km (Morley et al, 2023). These mini-basins were proposed to be subsided by a combination of downbuilding and normal faulting driven by rapid sediment loading on the unstable, overpressured mudstone (equivalent of the Pagasa Formation) within the wedge (Morley, 2024;Morley et al, 2023).…”

Syn‐ and post‐rift lower crustal flow under the Sunda Shelf, southern Vietnam: A role for climatically modulated erosion

“…However, it seems unlikely that this was the cause because the brittle faulting observed on the seismic profiles finished at the DRU variously dated at ca. 12–13 Ma to 16 Ma) (Morley et al, 2022). Instead, we infer that the rapid subsidence in the Middle Miocene reflects the gravitational collapse of the basins, following inversion driven by short‐lived compression during the collision of Borneo and the Dangerous Grounds (Hutchison, 2005).…”

“…The unconformity represents the product of erosion following basin inversion, which is a characteristic of the Sunda Shelf, as well as parts of northern Borneo (Hutchison, 2005). The age of the DRU has been debated with an age of 12–13 Ma proposed by Lunt (2019), postdating the earlier onset of collision in the Dangerous Grounds prior to 16 Ma (Morley et al, 2022).…”