## 4 Differences in Basin Architecture and Sedimentary Evolution
### Rifted Basins  
Rifted basins exhibit a \"lower-rift and upper-depression\" architecture, characterized by a basin architecture with thicker underlying rift sequences and thin overlying depression sequences. Taking the Obbia Basin as an example (Figure 4), its overall characteristics are vertical stratification and horizontal zoning. There is a significant difference between the two sets of sequences (lower-rift and upper-depression) in the vertical direction: the underlying Karoo-Jurassic rift sequences are widely developed, with a thickness of over 3500 m; the extensional faults control the formation of alternated horst-graben structural features. The seismic reflection quality in the middle-lower parts of the rift sequences is generally poor, the basement reflection is not clear, and the \"hill-shaped\" seismic reflection characteristics above the upper horst-style fault block belong to carbonate sedimentary formation. Drilling reveals that the upper part is a continental fluvial-delta-lacustrine sedimentary system [9]. The depression sequences overlying the rift sequences have obvious \"wedge-shaped\" characteristics, with underdeveloped faults and a regional angular uncontorformity contact with the underlying strata. The maximum total sedimentary thickness is less than 4000 m. The seismic reflection characteristics at the stratigraphic boundary are obvious: the seismic reflections in the lower part of the depression sequences exhibit weak amplitude and near-blank reflection architecture, and the major deposits during the transgression period are fine-grained sediments in deeper water. From the continental slope to the abyssal plain, multiple sets of small wedge-shaped seismic reflection architectures are developed in the middle and upper strata; the thickness from near-shore to far-shore changes from thinner to thicker, and the amplitude changes from stronger to weaker, belonging to the small delta-deepwater gravity flow sedimentary system.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multicolumn{2}{c}{**Hydrocarbon**} & \multirow{2}{*}{**Sedimentary Filling**} & \multirow{2}{*}{**Typical Basin**} \\ \cline{2-2} \cline{4-5}  & & **Vertical** & & & \\ \hline \multirow{2}{*}{Rifted type} & Lower rift and upper depression & Wide continental shelf and gentle continental slope & Mainly rift sequences (thickness \textgreater{} 3500 m), with thickness \textless{} 4000 m during the depression period & Obbia and Morondava \\  & & & & depression period \\ \hline \multirow{2}{*}{Depressed type} & \multirow{2}{*}{Mainly depression} & Narrow continental shelf and steep & Underdeveloped rift sequences and depression sequences \textgreater{} 4000 m & Angoche \\  & & continental slope & sequences \textgreater{} 4000 m & \\ \hline \multirow{2}{*}{Faulted depression type} & Lower rift and upper depression & Wide continental shelf and gentle continental slope & Rift sequences \textgreater{} 3500 m, depression sequences \textgreater{} 4000 m & Coriole and Zambezi \\  & & & & depression stage are \\ \hline \multirow{2}{*}{Reformed delta type} & Lower rift, middle depression, and upper convolution structure & Developing zonal structural belts from onshore to offshore & Do. Since the Miocene, a high constructive delta (thickness \textgreater{} 4000 m) has developed in the upper part & Rovuma and Juba \\  & & & & developed in the upper part \\ \hline \hline \end{tabular}
\end{table}
Table 1: Attributes of passive continental marginal basins in the sea region of East Africa.