Bulletin of the Geological Society of Malaysia, Volume 69, May 2020, pp. 11 – 26
Malaysian Continental Shelf Project, National Security Council, Malaysia
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Abstract: Sand injectites are common in the turbidite sequences of the West Crocker Formation (Eocene-Oligocene) but their occurrences have never been reported. This paper describes sand injectites and related deformational structures from outcrops of West Crocker around Kota Kinabalu, Sabah. The injectites range in scale from millimetres to metres, occurring in the interbedded sandstone-mudstone facies. They are usually found in thickly-bedded massive sandstone facies that comprise mainly Bouma Ta/Tb divisions. This facies type is characterized by dewatering features such as dish and pipe structures and represents parts of the sedimentary system that are prone to overpressure buildup. The injectites are thought to have been formed by the sudden release of overpressure in the water-charged turbiditic sediment at shallow burial depths, possibly triggered by seismic shock or gravitationally induced failure/slumping up-dip of the depositional site. The injectites occur in various forms, including dykes, sills and pipes; the latter representing major conduits for vertical fluid movement and sediment remobilization through the turbidite sequences. The common occurrence of injectites in the West Crocker Formation suggests that they may also be present in the Neogene deepwater sequences offshore West Sabah. Outcrop studies on these features may help predict their presence and distribution in the subsurface and assess their possible impact on reservoir distribution, heterogeneity and connectivity.
Keywords: Sand injectites, turbidites, overpressure, West Crocker Formation, Sabah