## 4 Seismic Sequence Stratigraphy
### Sequence Stratigraphy Interpretation  
Based on the seismic reflection termination geometries interpreted in 2D sections, seismic facies can be interpreted by integrating 2D with the derived 3D map-view of the depositional system [48; 49; 50; 51; 52]. Three depositional sequences (DS.1, DS.2, and DS.3) with related system tracts were identified in this examination. Sequence boundaries constrain such sequences (SBs), defined depending on the following principles: (1) The high-frequency reflections (stratigraphic discontinuities) and basal erosional patterns noticed on the 2D seismic section, (2) the presence of map-view trunk fluvial deposits supplied by countless carved branch valleys situated on related interfluves and exhibiting dendritic canyons in time-slice view [7], and (3) the existence of over-consolidated horizons during subaerial display is expected to result in the development of soil evaluated by geotechnical well soil properties [53]. On average, deposition sequence thickness is around 20 m and infrequently comes up to 40 m.  
Traditionally, sequences that include a basic sedimentary fill reveal basal valley-bound fluvial layers and are superimposed by estuarine, and subsequently deposit marine and/or periodic concave-up multi-stacked channel deposits. Fluvial deposits of the low stand (convex-up horizontally deposited layers and single or bidirectional down-lap seismic faces) are usually superimposed (SBs) and covered by transgressive surfaces. These deposits are followed by estuarine sediments that are mud-pronounced and correspond to transgressive system tracts (TST) (restricted horizontally continuous seismic facies). The maximum flooding surface (MFS) covers the fundamental TST and is then overlapped with a high stand system tract of open marine mudstone deposits. The seismic nature of the seismic facies at the top of the high stand shows a rise in contrast in acoustic impedance, possibly reflecting the late phase of the high stand systems tract (HST). However, a detailed explanation of the studied succession, which started from the seafloor to approximately \(-507\) ms, is presented, with three primary seismic stratigraphic sequences and their associated systems tract. From bottom to top, the SB-3 represents the horizon as unconformity separating, unit 3 from unit 2. The surface was identified based on the generated synthetic seismogram of Inas-8, Melor-2, and Melor-1 wells, and the seismic facies' variations of this unit, as shown in Figure 12. This event was interpreted on the largest peak between two intense trough amplitude events representing an interface between unit 3 and unit 2. This unit is extended from the time of \(-400\) to \(-490\) ms. In terms of the system tract, unit 3 has been divided into only two cycles. This unit's base was formed during the regression phase, while the sea level was prograding seaward, resulting in a High Stand System Tract (HST) cycle. The HST is represented by the coarsening upward of the gamma-ray. The other cycle in unit 3 is labeled as TST, which forms the top part of this unit. The top of this cycle is marked as a Maximum Flooding surface (MFS) in Figure 12B,C, that caused a retrograding stacking pattern of TST. This cycle yield after the sea level occupied the Malay basin during the connection with the China sea resulted in a TST. Horizon 2 represents the SB2 surface that bounded at the top of unit 2. This horizon was picked based on the gamma-ray record on Melor-2, the generated synthetic seismogram of Melor-1 well, and the seismic facies' variations of unit 2 (Figure 13). Figure 12: (**A**) A regional seismic cross-section of unit 3, (**B**) a detailed explanation of the sequence boundaries of unit 3, systems tract, and faults, and (**C**) the 3D visualization of unit 3 with system tract, parasequences, and parasequences set. This event was interpreted based on the zero-crossing below a strong trough amplitude event, representing an interface between unit 2 and unit 1.