Paleoenvironmental reconstruction and sequence biostratigraphy of Miocene transgressive–regressive sedimentary succession in the northern JDA, northern Malay Basin

Abstract

The northern sector of the Malay Basin has long been underrepresented, leaving a gap in the understanding of its paleoenvironmental evolution. In addressing this gap, detailed biostratigraphic analysis based on palynology and foraminifera from two wells, i.e., Tj-1 and Tp-1, has been conducted to reconstruct the paleoenvironment during the Miocene age. The factors influencing their distribution were analyzed using a sequence biostratigraphic approach, complemented by environmental parameters such as grain size and organic matter content, supported by seismic and gamma ray logs. The findings reveal significant differences in the faunal distribution of the inner shelf and delta front between the two studied wells. The inner shelf in Tj-1 well is dominated by Asterorotalia pulchella and the accessory species Pseudorotalia schroeteriana. Whereas Tp-1 well, is dominated by Pseudorotalia schroeteriana, but Asterorotalia pulchella is absent. For delta front species, Bigenerina sp. and Reophax sp. are found throughout Tp-1 well. However, in Tj-1 well, the dominant assemblages are Bigenerina sp. and Miliammina sp. during Serravallian to Tortonian, and Cavarotalia annectens from Tortonian to Messinian. Furthermore, our study identifies a major transgressive–regressive (T–R) event during Langhian to Serravallian period, inferred from stratigraphic dating using the standard palynological zonation of Malay Basin (‘PR’ zone) with the age according to VIM (Vietnam–Indonesia–Malaysia) and SEA (Southeast Asia) cycles, which also highlights unconformities. This suggests that tectonic events have led to distinct fauna provinces within the Miocene biostratigraphic assemblages.