| The interaction between deep-water gravity flow and bottom flow is a currently hot topic in deep-water
sedimentary research in the world. This study focuses on the Upper Eocene of the Rovuma Basin in East Africa, utilizing a
comprehensive approach integrating drilling and 3D seismic data to investigate this geological topic. The sedimentary
architectural elements and evolution characteristics under a high-frequency sequence stratigraphic framework is studied to
reconstruct the depositional and evolutionary patterns of the submarine fan under the interaction of gravity and bottom
currents in the Upper Eocene. The results show that: (1) The Upper Eocene submarine fan in the study area develops three
types of sedimentary architectural elements: deep-water channels, overbanks and lobes. The channels can be further divided
into two types: confined deep-water channels and semi-confined unidirectionally migrating channels. (2) The Upper Eocene
third-order sequence can be divided into three fourth-order sequences: Ps1, Ps2 and Ps3. Among them, the Ps1 sequence
develops a confined deep-water channel-lobe complex, the Ps2 sequence develops a semi-confined unidirectionally
migrating channel-lobe complex, and the Ps3 sequence develops a lobe complex. The evolution of these sequences
represents a cyclic evolution process within the third-order sequence under the background of continuous rise in sea level,
changes in seafloor landform filling, attenuation of gravity flow energy, and relative enhancement of bottom currents.
(3) Bottom currents could strip fine-grained materials in gravity flows accumulate on the northern side (downstream side of
the bottom current) of the deepwater depositional system, forming asymmetric overbank / drift deposits with positive
topography. This, thereby, restricts channels and lobes to southward erosion and deposition, resulting in the Eocene
deepwater depositional system and depositional architectural elements that exhibit a unidirectional migration and stacking
pattern on the upcurrent side. It is inferred that bottom currents may enhance the reservoir quality of gravity flow deposits. |
