Submarine mass-transport deposits in the Semantan Formation (Middle-Upper Triassic), central Peninsular Malaysia

Author : Mazlan Madon
Publication : Bulletin of the Geological Society of Malaysia
Page : 15 - 26
Volume Number : 56
Year : 2010

Bulletin of the Geological Society of Malaysia 56, December 2010, pp. 15 – 26


Submarine mass-transport deposits in the Semantan Formation (Middle-Upper Triassic), central Peninsular Malaysia

Mazlan Madon

Petronas Research Sdn Bhd, Lot 3288-3289, Kawasan Institusi Bangi, 43000 Kajang, Malaysia

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Abstract — Relatively fresh exposures of the Semantan Formation along the East-Coast Highway (Lebuhraya Pantai Timur – Fasa 1) between Karak and Kuantan, central Peninsular Malaysia, have given new insights into the sedimentary processes in the Triassic flysch basin that once separated west and east Malaya. An eastward change from distal to proximal facies between Karak and Maran indicates a west-facing, active continental shelf to slope sedimentation. Outcrops between Karak and Temerloh, east of the Late Triassic-Early Jurassic Bentong-Raub collisional suture, are generally characterized by “classical” flysch-like, thinly-bedded sandstone-mudstone facies. Further east of Temerloh towards Maran, and nearer to the paleo-shelf and slope, more sandy and thick-bedded turbidite facies occur. A proximal deep-marine facies association in the Semantan Formation is exposed at the Chenor Junction (Exit 821), kilometre 139 along the highway. South- and north-facing cuts on either sides of the highway reveal large gravity-slide blocks (megaclasts), slumps, debris flow deposits, and associated syn-sedimentary thrust faults and glide surfaces. These features are strongly indicative of large-scale submarine mass-transport processes on the palaeo-slope of the Triassic active margin. The Chenor mass-transport complex is made up of zones of incoherent slump deposits intercalated with well-bedded turbidite/debrite facies. In the lower part of the succession, there are megaclasts of sandstone-mudstone facies, measuring several metres in size, encased in a plastically deformed silty matrix. The megaclasts are highly deformed internally by numerous meso-scale normal faults, probably due to gravitationally-induced extension. Along with other smaller sandstone blocks, these megaclasts are interpreted as slide blocks due to slope failure up-dip. There are other gravity-induced structural features such as rotational slumps, glide surfaces, thrust faults and associated soft-sediment folds. The slump folds and thrusts show vergence to the west, as opposed to the generally eastward tectonic vergence. A few of the well-stratified units show strongly inclined stratal surfaces which may be attributed to lateral accretion of turbidite fan lobes. Several sets of these inclined surfaces are bounded by erosional surfaces which could have resulted from different episodes of turbidity flow. The association of incoherent mass-flow units with the more well-stratified deposits reflects the close spatial and temporal relationship between submarine mass-transport events and turbidity flows on the Triassic active slope and basin plain.

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Keywords: mass-transport deposits, Semantan Formation, turbidites