Bulletin of the Geological Society of Malaysia, Volume 70, November 2020, pp. 39 – 56
Amajida Roslim1,*, Antonino Briguglio2, László Kocsis1, Firdaus Abd. Rahman3, Izaz Fahad Bahrein1, Sulia Goeting2, Hazirah Razak1
1Faculty of Science/ Geology, Universiti Brunei Darussalam, Jalan Tungku Link Gadong, BE1410, Brunei Darussalam
2DI.S.T.A.V. Università degli Studi di Genova, Corso Europa 26, I – 16132 Genova, Italy
3Department of Geosciences, Faculty of Geosciences & Petroleum Engineering, Universiti Teknologi PETRONAS, Malaysia
*Corresponding author email address: nurulamajidaroslim@gmail.com
Abstract: Eleven Neogene outcrops (seven of the Miri Formation and four of the Seria Formation) from Brunei Darussalam are described. Detailed stratigraphic columns are presented with special emphasis on the sedimentary sequences, providing insights into the depositional environments. The rocks are comprised mostly of sandstone, claystone and a mix of both lithologies, and are piled up in cycles of coarsening upward successions, which are here interpreted as parasequences. Most sections are characterized by abundant and diverse sedimentary structures, reworked fossiliferous deposits and organic fragments such as ambers and wood remains. Certain beds are rich in fossils: among the macrofossils, the most common are bivalves, gastropods and followed by fish remains (teeth and otholiths), crustaceans, corals and echninoderms, which are abundant at specific locations. Among the microfossils, the most common are foraminifera, which are mostly dominated by either rotaliids or textulariids; the most common genera are Ammonia, Elphidium and Trochammina. Porcelaneous and planktonic foraminifera are rare. Ostracods are also found. Ichnofossils are quite abundant in all sections but are represented mostly by Ophiomorpha and Thalassinoides. In view of the observations, the sections are interpreted as evidence of shallow-marine conditions, in which wave, fluvial and tidal actions strongly influenced the depositional environment. In a few cases, deposition of sediment seems to reflect the transition from wave-dominated to tide-dominated conditions. Our findings indicate that in such shallow marine deposits, the interpretation of sediment type and sedimentary structures alone cannot indicate one specific sedimentary environment, but such observations should include palaeontological evidence to generate more accurate palaeoenvironmental reconstructions. Lastly, our results are discussed in relation to the sedimentary evolution of the region.
Keywords: Brunei, Neogene, sedimentology, palaeoenvironment
DOI: https://doi.org/10.7186/bgsm70202004
