Shamsuddin Jirin

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W.M. Khairul W. Sulaiman

Shahriza Salwani M Shah

Siti Syareena M Ali

Petronas (Malaysia)

M Fauzi B A Kadir

Norshida Mohsin

Petronas (Malaysia)

M. Rapi B. Som

Petronas (Malaysia)

Robert J. Morley

Royal Holloway University of London

M. Rapi M. Som

Petronas (Malaysia)

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Petronas (Malaysia)

Royal Holloway University of London

United States Virgin Islands Department of Health

Public Health England

Monash University

Kiel University

University of Bath

James Cook University

Australian Research Council

Universidad de Granada

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Abstract: Labuan Outcrop Revisited: New Findings on Belait Formation Facies Evolution (Geology Paper 21)

M. Rapi B. Som M Fauzi B A Kadir Siti Syareena M Ali Shamsuddin Jirin W.M. Khairul W. Sulaiman

Outcrop

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The Sequence Biostratigraphy and Chronostratigraphy of The Malay Basin

Robert J. Morley Shamsuddin Jirin

Through a comprehensive review of biostratigraphic data from the Malay Basin, in relation to seismic data, it is demonstrated that a large proportion of the microfossil assemblage variation seen in the basin is driven by sequence stratigraphic processes. Sequence biostratigraphic signals fall into two types: 1) signals relating to sea and lake level change, such as abundance and diversity acmes of foraminifera and nannofossils, and acmes of mangrove pollen and lacustrine algae, and 2) palynomorph assemblage changes reflecting climate change, which would have paralleled changes in sea level. Biostratigraphic signals for each systems tract can be distinguished. The maximum flooding surface, separating the transgressive systems tract from the highstand, is generally marked by a foraminiferal (and sometimes nannofossil) abundance and diversity acme, whereas the highstand is generally characterised by pollen signals suggesting a warm and wet climate. The transgressive systems tract is invariably marked by an acme of mangrove (Rhizophora type) pollen, and the transgressive surface by an increase in abundance of marine microfossils. The lowstand is usually characterised by an acme of cool and/or seasonal climate pollen, although some for some lowstands the climate was cool but wet, and these are generally characterised by acmes of pollen from an unusual type of peat swamp. Lacustrine algal signals need to be used differently is sequence interpretation depending on the strength of marine influence. The succession has been divided into 21 sequences based on biostratigraphic signals alone. Fourteen of these are within seismic groups D-M. Sequences within seismic groups A-H can each be independently dated using mainly nannofossils which occur at the maximum flood, but for sequences within seismic groups I – M there are no reliable Malay Basin microfossil occurrences for which the age has been accurately established. However, within groups I through M, terrestrially derived palynomorphs are abundant, and by correlating using palynological zones into the West Natuna Basin, where good nannofossil control is available to the base of the Arang Formation at the base of the Early Miocene (tying the 'PR' Malay Basin palynological zones of Azmi et al (1996) into the West Natuna 'P' zones of Morley et al (2003), the succession can be accurately dated down to base Group J. The age for Groups K through to M is proposed by sequence correlation with the West Natuna Barat and Gabus Formations, for which the age has been proposed using climate signals alone, through comparison with the global oxygen isotope curve. The study indicates that the age of the Group J/K boundary (previously ~21.4 Ma) is underestimated, and that this boundary should coincide closely with base Early Miocene at 23.09 Ma.

Chronostratigraphy

Malay

Sequence (biology)

10.3997/2214-4609-pdb.256.p12

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Labuan Outcrop Revisited: New Findings on Belait formation Facies Evolution

M. Rapi M. Som M Fauzi B A Kadir Siti Syareena M Ali Shamsuddin Jirin W.M. Khairul W. Sulaiman

The sedimentary successions of the Belait formation exposed across the northern side of the Labuan Island has been studied by various workers such as Hazebroek, 1993; Levell, 1983, 1987; Tate, 1994. Based on his work, Mazlan Madon (1994, 1997) concluded that the basal Belait Formation was deposited in fluvial system developed over an eroded Temburong landscape in an overall transgressive regime. Facies development in the basal Belait reflects a quick change transition from fluvial systems (braided to meandering) to shallow marine successions represented by coarsening-upward offshore shales to shoreface sandstones. The presence of two (2) new outcrops provide the opportunity to further study the lateral continuity and vertical facies succession within the Belait Formation. A total of nine (9) outcrop sites including two (2) new locations were studied and logged and 142 samples were taken and analysed for biostratigraphic information. Results showed that the fluvial succession within the Belait Formation is not presence above the Temburong Formation at the new outcrop and replaced by coastal plain, fresh/brackish water estuarine successions. The fluvial succession thickened away from the new outcrop in the direction of Layang-layangan in the west and Tg. Kubong to the east. Furthermore, the fluvial succession in Tg. Kubong is also thinner than previously reported (Mazlan, 1994). Rapid change form fluvial to estuarine environment was observed based on biostratigraphic data. Interms of vertical facies development, we proposed that there are two (2) incised valleys developed where the fluvial succession was deposited and rapidly overlain by brackish water fluvial-estuarine deposits. The new outcrop area is interpreted as an interfluve and appears to be where the center of the anticline is located. The relatively thin fluvial to shallow marine transition above the sequence boundary, implying rapid deepening due to the steepening depositional surface, coupled with rising sea level and uplifting in the new outcrop area. This finding will help us in understanding the relationship between sea level, tectonic activity and vertical/laterar\l facies development.

Outcrop

10.3997/2214-4609-pdb.251.21

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