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Journal > Journal of Mathematical and Fundamental Sciences > Oligocene Cyclic Sedimentation Deduced from Taphonomic Analysis of Molluscs in Lacustrine Deposits of the Pematang Group, Pesada Well, Central Sumatra Basin

 

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Journal of Mathematical and Fundamental Sciences
Vol 48, No 1 (2016)
Oligocene Cyclic Sedimentation Deduced from Taphonomic Analysis of Molluscs in Lacustrine Deposits of the Pematang Group, Pesada Well, Central Sumatra Basin
Aswan, Aswan ( Department of Geological Engineering, Faculty of Earth Science Technology, Institut Teknologi Bandung (ITB), Jl. Ganesha 10, Bandung, 40132, Indonesia)
Graha, Satia ( Chevron Pacific Indonesia, Rumbai, Riau)
Suryadi, Dodi ( Department of Geological Engineering, Faculty of Earth Science Technology, Institut Teknologi Bandung (ITB), Jl. Ganesha 10, Bandung, 40132, Indonesia)
Wiguna, Taufan ( Department of Geological Engineering, Faculty of Earth Science Technology, Institut Teknologi Bandung (ITB), Jl. Ganesha 10, Bandung, 40132, Indonesia)
Qivayanti, Sri Iman ( Chevron Pacific Indonesia, Rumbai, Riau)
Article Info   ABSTRACT
Published date:
01 Apr 2016
 
The Oligocene cycle of Pesada Well, Central Sumatra Basin, Indonesia is composed of a deepening-upward series of depositional cycles in a lacustrine environment affected by oscillations of the water level. Taphonomic analysis of gastropod molluscs was used to interpret the cycle architecture of the Brown Shale (Pematang Group). Four types of shell concentrations were identified. The early transgressive deposit has a distinct erosion surface at the base, contains concretions, is formed of coarse-grained sediment with abraded and broken shells, and is interpreted as reworked deposits. The late transgressive deposit contains a hiatal concentration formed by continuing lake level rise, with many complete shells preserved in life position. The maximum transgressive deposit has complete shells in life position or that have been transported, as well as juvenile molluscs and broken shells. The early regressive deposit contains alternating shell-rich and shell-poor layers. Since the lacustrine system shows no tectonic effects and also no marine influenced indications, the seven sedimentary cycles identified in the Pesada Well are likely to have been affected by oscillations between monsoonal and dry periods.
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