## 1 Introduction  
The Central Luconia Province encompasses a geological province famous for its prolific hydrocarbon exploration, located in the offshore of North Sarawak, Malaysia (Figure 1) within vicinity of the South China Sea. Central Luconia is dominated by Middle to Upper Miocene limestone reservoirs with varying thickness from several hundreds of meters to over one kilometer in places at depths ranging from 750 to 2500 m from present day sea level [1]. The orientation of the build-ups is not consistent throughout the province [2] (Figure 1C). This region is subdivided into numbers of regional lows and highs that are partitioned into localized extensional horsts and grabens trending systematically in SSW- NNE and WSW-ENE compressional structures [3]. In the southern part, the majority of the carbonate build-ups are oriented in NNE-SSW and turning to NE-SW at the transition from the southern region to the central region. The orientation of platforms in the central part is mostly in E-W direction, while the platforms in the northern part are oriented in NW-SE, with a few in NE-SW directions. The inconsistency in the limestone build-ups orientation is pre-evaluated to reflect the basement topography and structure underneath the sedimentary deposition. The Luconia Block (crystalline basement of Central Luconia and its surrounding provinces) that host this sedimentary basin had underwent a prolong tectonic history, but the precise chronology of events or location of the main structural features remains uncertain. [4; 5] suggested the suturing of Luconia-Dangerous Grounds Block/Microcontinent with South East Asia had resulted in the cessation of palaeo-Pacific subduction in Late Cretaceous. Meanwhile, [6] proposed the deformation to be resulted by the Late Cretaceous or Paleocene collision of Luconia and Sundaland, which brings palaeo-Pacific subduction east to the Mesozoic granite (basement) to a rest. However, the role of Luconia -Dangerous Grounds block in the palaeo-Pacific subduction was brought to less attention when [7; 8; 9] suggested that the palaeo-Pacific subduction zone retreated from South East Asia during Cretaceous as response to slab rollback, back-arc rifting and eventual Proto-South China Sea seafloor spreading. Luconia continental shelf has been envisaged as a large Cathaysia-derived continental fragment that presently occupies much of the southern margin of the  
Figure 1: (**A**) Locality map showing the offshore Sarawak and coverage of the Air-FTG® survey. (**B**) Airborne-gravity survey under MyGeoid Project by the government of Malaysia ([PERSON] et al., 2017). (**C**) Survey area for Air-FTG® conducted by Bell Geospace and utilized in this study. Top carbonate map for Cycle IV-V limestone is overlaid with the survey area, the seismic profiles and exploration wells. Only three regional seismic lines are presented in this paper (labelled as Line 1014, 1004 and 1008). All datasets presented in (**C**) are courtesy of Malaysian Petroleum Management (MPM), PETRONAS. South China Sea [10]. It could be drifted from the southern China Mainland, rifted, and finally collided with Sarawak mainland [10; 11; 12]. As such, the subsurface structure for Luconia and the surrounding provinces remain conjectural. Several geophysical studies have been conducted to interpret the shallow and deep subsurface structure and geometry of the sediments' deposition in this area, focusing on the interpretation of seismic data [1; 3; 13; 14; 15; 16; 17; 18; 19; 20; 21], gravity, and magnetic data [22; 23; 22]. A study by [1] exposed the potential depth for the basement in Central Luconia (offshore Sarawak) to be shallower than initially perceived. The depth to the top of basement along a E-W seismic transect (location has not been revealed) was interpreted at 10,000 km to 12,000 km but free air-gravity-magnetic modelling reveal potential depth of the top basement at 5500 km to 10,500 km. Wide wavelength ranges of gravity and magnetic data provide critical clues to both deep and shallow structural framework.