## 4 Differences in Basin Architecture and Sedimentary Evolution
### Reformed Delta Basins  
The reformed delta basin is a passive continental margin basin with a ring structure belt after highly constructive delta reformation since the Miocene. It not only has a large sedimentary thickness; however, its own strata can form independent tectonic--sedimentary characteristics; and it has also reformed the original basin architecture.  
Figure 5: Two-dimensional seismic section BB\({}^{\prime}\) of Angoche Basin (see the location in Figure 1). Vertically, the development and distribution range of rift sequences are narrow, and the thickness of depression sequences is large. Horizontally, it displays the characteristics of a “narrow continental shelf and steep continental slope”.  
Taking the Rovuma Basin as an example, this type of basin has the obvious characteristics of \"vertical stratification and horizontal zoning\" (Figure 7). Vertically, it includes three sets of sequences, namely the lower rift sequences, the middle depression sequences, and the upper reformed delta sequences. The seismic reflection and sedimentary filling characteristics of the first two sequences are basically the same as those of the faulted depression basins. Since the Miocene, highly constructive deltas have developed in the upper part, and four ring structural belts, namely, the growth fault belt, plastic diapir belt, thrust fold belt, and foredeep gentle slope belt, are formed from onshore to offshore. Among them, the growth fault belt develops large-scale sand bodies in delta front subfacies, while the plastic diapir belt, the thrust fold belt, and the foredeep gentle slope belt are mainly gravity flow-induced collapse bodies, waterways, and submarine fans.  
Since the Oligocene, with the decrease in global sea level, the supply of deposit sources in the continental shelf area has been sufficient, and the delta front sand bodies have gradually thickened. Moreover, the highly constructive progradation toward the sea led to an increase in the stratum slope. After the sedimentary sand bodies fall off vertically  
Figure 6: Two-dimensional seismic section CC\({}^{\prime}\) of Coriole Basin (the location is shown in Figure 1). Both the rift sequences and depression sequences are well developed, and the thickness in the depocenter is relatively large.  
Figure 7: Two-dimensional seismic section DD\({}^{\prime}\) of Rovuma Basin (the location is shown in Figure 1). Vertically, it includes three sets of sequences, namely the lower rift sequences, the middle depression sequences, and the upper reformed delta sequences. Laterally, four tectonic zones are developed.  
under the action of gravity, they expand downward along the slope. With the continuous progradation of the delta sand bodies, an inner ring growth fault belt can be formed on the foredeep facies belt, where the delta sand bodies are highly developed. Due to the increase in slope towards the sea, the sand bodies undergo gravity-sliding along the mudstone of the lower front delta. If the slope is large enough, the sand bodies will collapse and be transported in block form to the foot of the slope. During the transportation process, the uneven compaction of the lower mudstone forms a plastic diapir belt. Other sand bodies continue to move downward under the influence of gravity, forming thrust fold belts after the kinetic energy decreases [14; 27]. A small amount of sand bodies are not captured by the thrust fold belt and deposited in the delta front gentle slope belt.