## 2 Geological Setting of Central Luconia  
The Central Luconia Province is bounded by two main tectonic features in this region, which are the West Baram Line in the east and West Balingian line in the west. These ancient faults are oriented in the NW-SE direction (Figure 1) and the West Baram Line is believed to represent the southern limit of the subduction of the oceanic crust of the Proto-South China Sea [24; 25]. The continental shelf of Luconia-Dangerous Grounds was under thrusted beneath West Borneo [11; 21; 26; 27] and this event induced the uplifting of the older sediments (the deep-water sediments of Rajang Group) during Eocene-Cretaceous. Shortly after that, topography denudation took place during the post-orogenic relaxation phase [2]. This was followed by crustal stretching due to the second rifting phase of the South China Sea in the Oligocene mainly within the northern Luconia [28], while the southern of Luconia underwent crustal shortening. This region was later compressed attributed to the regional subsidence during Upper Miocene and series of uplift during Pliocene [29]. The offshore Sarawak is dominated by thick sedimentary sequence comprises of elastic and carbonate rocks. The rocks are calibrated with seismic signals to correlate with seismic facies (Figure 2). Cycle I is the oldest, dating back to \(\sim\)34 Ma until approximately 23.5 Ma followed by Cycle II sedimentation during Lower Miocene (23.5 Ma to 18.0 Ma). Cycle I and II sediments are comprised of deep marine sediments especially at the base of the cycles, followed by non-marine to coastal plain sediments with shallowing upwards sequence. In the southern section of Central Luconia, patches of limestone growth within Cycle I and II are also common [2]. More marine influence in the sediments is recognized at the beginning of Upper Lower Miocene within Cycle III rocks. At this time, many limestone build-ups begin to grow in the central section of Luconia Province, however, the growth of limestone become more abundant during deposition of Cycle IV and V continues until approximately 8 Ma, before a major event overseeing the demise of Luconia limestone took place. After that, the sedimentations in offshore Sarawak including Central Luconia Province are predominated by siliciclastics sediments due to rapid uplift on the onshore Borneo [30]. The sedimentation of siliciclastic sediments from 8 Ma until the present day is grouped as Cycle VI to VIII. Several prominent unconformities (Figure 2) are recognized in offshore Sarawak including the Central Luconia Province. The base of Cycle I and the underlying sediments (classified as Pre-Cycle I sediments in this paper) is known as Base Oligocene Unconformity (BOU) which marks the transition from isolated blocks of elevated grabens in the Eocene to a more widespread sedimentation in the Oligocene [29] resulted from the collision of Luconia continental block with Borneo mainland. Base Miocene Unconformity (BMU) differentiate the sediments deposited in Cycle I and Cycle II. BMU marks the changing in direction of the South China Sea spreading and the effect of change in the direction is reflected in the facies changes as observed within the offshore Sarawak [2]. Another profound unconformity in Central Luconia and all other basins in the southern South China Sea is Middle Miocene Unconformity (MMU). In Central Luconia context, MMU splits Cycle III and Cycle IV sediments, marking the beginning of widespread limestone deposition in Luconia. Finally, the youngest recognized regional unconformity in Central Luconia is Shallow Regional Unconformity (SRU) or has been recently renamed as Lapan Unconformity in [31] representing a rapid uplift all over Borneo. Figure 2: (**A**) Simplified stratigraphy chart of offshore Sarawak, particularly in Central Luconia Province adapted from [2] showing major seismic facies correlated with the Cycles nomenclature.