DEPTH DISTRIBUTION OF LARGER BENTHIC FORAMINIFERA IN DIFFERENT TROPHIC ENVIRONMENTS: UNLOCKING ENVIRONMENTAL VARIATIONS IN THE PAST

This PhD project has dealt with modern benthic foraminifera of Brunei from the nearshore shallow shelf locality and offshore carbonate atolls as well as fossil benthic foraminifera from an onshore locality. Identification of benthic foraminifera from both modern and fossil localities was done by assessing their taxonomy and systematics within the Indo-Pacific region. The importance of Brunei in the Indo-Pacific region was due to the fact that it is located at the edge of the Coral Triangle, which is the modern marine biodiversity hotspot of today. Benthic foraminifera from Brunei were understudied and recent findings have shown promising results on Brunei’s benthic foraminifera diversity. Within the modern localities, a total of 231 species of benthic foraminifera are found nearshore Brunei and 60 species on the carbonate atolls. There are species of benthic foraminifera from the modern localities which have shown different patterns of distribution as a result of environmental parameters such as substrate type, light intensity and hydrodynamics which change in different trophic conditions. The results revealed the difference in distribution of key species, Operculina ammonoides, Amphisorus hemprichii and Parasorites orbitolitoides from both nearshore Brunei and carbonate atolls. Furthermore, there are also other species of larger benthic foraminifera that have different depth distributions in both nearshore Brunei and carbonate atolls from the family Calcarinidae, Amphisteginidae and Nummulitidae. Smaller benthic foraminifera such as Pseudorotalia and Asterorotalia which are found in the nearshore locality display different depth distributions due to the difference in sediment composition. Therefore, these results can be used to compare benthic foraminifera distribution from different trophic conditions in carbonate and mixed carbonate-siliciclastic environments. A study conducted on fossil locality in the Lumapas area in the Brunei-Muara district observed the presence of larger benthic foraminifera. Geologically, Brunei’s sedimentology is mainly made up of sandstone and clay but only one locality with a limestone bed was found. From the available thin sections, only one species of larger benthic foraminifera was present and identified from the genus Miogypsina and its taxonomy was determined by comparing other conducted studies within the region. Similarly, to Miogypsina, there were different genera of corals identified from the Lumapas limestone bed which have been known to live in turbid water conditions. These results have provided insight of possible palaeoenviornmental conditions in Lumapas. However, more sampling and observation is required to further understand Brunei’s paleoenvironment during the Miocene in a mixed carbonate-siliciclastic condition. Subsequently, other projects have been simultaneously conducted towards the development of understanding the palaeoenvironment of Brunei by assessing modern and fossil localities. A study made on two transects (Muara and Tutong) focused on the sedimentological characterization throughout the core samples with depth whereby both transects have shown different sediment compositions which have been influenced by the river discharging fine sediments from inland towards the marine shelf. Biogenic components were also studied from both transects where benthic foraminifera flourish and it was found that they have different distributional patterns due to varying sediment compositions despite their presence at the same depth in both transects. This led to the building of a taxonomic data of benthic foraminifera within the shelf environment of Brunei in addition to the studies made on benthic foraminifera from reef and wreck sites in the same area. A study was also conducted on fossil localities onshore Brunei for their palaeontological and sedimentological characteristics where fossil foraminifera have been reported. The fossil localities are made up of different environments from shoreface to offshore marine settings where different genera of rotaliids were found. The genera found are Elphidium, Bolivina, Ammonia, Pseudorotalia, Asterorotalia and Operculina which have been known to be associated with muddy to sandy sediments where these rotaliids are also present today in the modern marine waters of Brunei. There is also a study on Palynology that was carried out by using pollen and spores for palaeoenvironment interpretation and although this study does not relate to foraminifera, it has played a role in further understanding the past environment of Brunei during the Neogene. These onshore fossil localities have an origin of a mangrove to marine environmental setting which can also be observed in Brunei today. Therefore, with all these studies integrated together, by studying both modern and fossil localities of Brunei, these results could give the complete representation on the palaeoenvironment of Brunei during the Neogene. Rotaliids have been very important in determining the palaeoenvironment as they have shed a light on how their depth distribution can vary depending on substrate type, light intensity and water movement in different trophic conditions. Having a taxonomic baseline of benthic foraminifera spanning from different marine environments such as the marine shelf, reefs, lagoons, deltas within various depths that consists of different substrate composition in a fully carbonate or mixed siliciclastic condition can be used as a guide for future studies within the region and can be used in unlocking and understanding the environmental variations of Brunei in the past.