Integrated biostratigraphic zonation for the Malay Basin

Azmi Mohd Yakzan and Awalludin Harun and Bahari Md Nasib and Morley, Robert J. (1996) Integrated biostratigraphic zonation for the Malay Basin. Bulletin of the Geological Society of Malaysia, 39. pp. 157-184. ISSN 2637-109X

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Abstract

This study presents an integrated biostratigraphic scheme for the Malay Basin based on the examination of 6 wells by P.R.S.S., and the review of data from ten wells, which were previously studied by service companies. For each of the wells reviewed, foraminiferal, nannofossil and quantitative palynological data was available. This paper demonstrates that through the integration of data from all three biostratigraphic disciplines, and through taking careful account of lithologies, it is possible to make accurate correlations within the Malay Basin which would not be possible using data from a single discipline. All stratigraphic units in the Malay Basin contain abundant palynomorphs, whereas foraminifera and nannofossils predominantly occur in brief marine transgressive intervals. Palynology thus forms the primary tool for correlation, the succession being divided into 16 palynomorph assemblage zones and subzones (termed ‘PR‘ zones). Nine foraminiferal acme zones (termed ‘TR‘ zones), reflecting transgressive intervals, can be characterised on the basis of their foraminiferal content, and association with calcareous nannofossils and palynological zones. Nannofossils occur predominantly in the more distal sections of the transgressive intervals, and are important in placing the whole sequence of biostratigraphic events into a chronostratigraphic framework by reference to the standard scheme of low latitude nannofossil zones. The chronostratigraphic significance of the scheme of seismic groups established by EPMI and widely used in subsurface studies within the Malay Basin has been appraised by reference to the biostratigraphic scheme. It is concluded that, provided a few adjustments are made to seismic picks in some wells, the seismic markers used to differentiate the seismic groups reflect time planes, and that therefore the seismic groups, which mostly have a distinct lithological expression, may be considered as time-rock units. Each seismic group has been characterised on the basis of biostratigraphic data. By reference to a cumulative maximum time-thickness curve, ages have been applied to the palynomorph assemblage zone and seismic group boundaries. Two distinct unconformities are observed in the upper part of the succession; one, dated at about 10.0-10.5 Ma, and termed the Middle Miocene Unconformity, probably relates to a pronounced period of low sea level, whereas the second, dated at 7.8 Ma in the upper Miocene (here termed the Upper Miocene Unconformity), relates to a phase of tectonic inversion.

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