Mass transport complex in east Sumba: a reference from world-class outcrop at Watuparunu coast – Mio-Pliocene gravity slumps
Proceedings, Indonesian Petroleum Association Forty-Third Annual Convention & Exhibition, September 2019
Awang Harun Satyana, Aries B. Nugroho, Cipi Armandita, Ferry Yustiana
Watuparunu Coast in Southeast Sumba Island, Indonesia is composed of coastal cliff demonstrating excellent – world-class outcrop of deep-water mass transport complex (MTC) with complicated deformation related to gravity slumps. Seismic data (2D and particularly 3D) have recently enabled large MTC’s of Recent to ancient deep-water basin to be described in considerable detail. However, the exposures of MTC’s are scarce therefore, outcrop reference to examine seismic interpretation are seldom available. MTC outcrop of Watuparunu Coast recently accessible, could provide the reference. MTC is subaqueous mass flow or landslide deposits that move downslope due to gravity sliding. It is important to study MTC’s since these mass movement processes represent significant threats to the security of continental slope and deep-marine engineered installations, including deep-water exploration and development; geo-hazards for tsunamis to coastal communities; release of methane to atmosphere from frozen gas hydrates originally stored in slope areas but released upon MTC; the roles of MTC in deep-water petroleum system. MTC’s characterized the geology of East Sumba in Mio-Pliocene time. Within the period, East Sumba subsided to the north and east as response to the uplift of the Masu Mountains to the south and opening of the Savu Basin to the east. This caused gravity sliding from high to low areas. Volcano-clastic rocks eroded from the Masu Mountains and pelagic marls and chalks of Kananggar Formation were deposited and moved downslope forming slides, slumps, or debris flow and they continued into the Savu Basin. Around 1 km long and 20-50 m high of the coastal cliff outcrop show the MTC at Watuparunu Coast. Slump structures dominate the MTC, forming very tight fold and thrust system. The top of the MTC is irregular erosional surface, its bottom is not exposed but it is considered as planar detachment surface where all faults ramp to. Internal facies consisting of: rotated blocks, pressured ridges, folded and thrusted blocks, and chaotic facies. This is the first publication and study of Watuparunu outcrop complex as MTC. This excellent outcrop provide reference to study slump structures of MTC’s which globally comprise up to 70% of the entire slope and deep-water stratigraphy. Exploring and developing petroleum in deep-water area should aware these deposits for the sake of engineering aspects and petroleum system. MTC’s may act as both lateral and top seals for underlying hydrocarbon reservoirs and could create MTC-related stratigraphic traps.
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