Full
YU Jitao,born in 2000,is a Ph.D. candidate. He is mainly engaged in research on deepwater sedimentology,reservoir characterization and modeling. E-mail: yjt_cup@foxmail.com.
Outline
The Eocene submarine fan channel system in the Rovuma Basin,East Africa,constitutes a significant case study for investigating the interaction between deep-water gravity flows and bottom currents. To address key scientific questions concerning the genetic types of individual channels and their distribution following differential reworking by bottom currents,this study systematically examines the genetic classification,spatial distribution,and mechanisms of bottom-current modification of single-channel systems in the lower Eocene strata of the region. Integrated analysis is based on core samples,well logging data,3D seismic datasets,and experimental results. The findings reveal the following: (1)The deep-water channel depositional system comprises four genetically distinct lithofacies—debris flow,turbidity current,bottom-current reworked,and hemipelagic drape deposits—which are further classified into 17 subtypes. Based on the relative abundance of gravity flow-related lithofacies,two primary types of single-channel systems are identified: debris flow-dominated fill channels and high-density turbidity current-dominated fill channels.(2)Debris flow-dominated fill channels are characterized by low width-to-depth ratios,sinuous geometries,and poorly developed levees. In contrast,high-density turbidity current-dominated fill channels exhibit straight to moderately sinuous morphologies,significantly higher width-to-depth ratios,and more pronounced levee development and thickness. Under the influence of bottom currents,both channel types display asymmetric cross-sectional profiles and lateral migration opposite to the direction of bottom-current flow. However,the high-density turbidity current-dominated channels exhibit greater asymmetry and more intense migration behavior.(3)Mechanistically,due to the high shear strength of debris flows,bottom-current reworking occurs primarily through “in-situ winnowing,” resulting in lenticular lithofacies containing internal traction structures. These channels show weak levee-channel asymmetry(average asymmetry index ≈1.35)and limited lateral migration(average migration index ≈0.65). Conversely,high-density turbidity currents,which possess lower shear strength,undergo “bulk reworking” of fine-grained suspended sediments by bottom currents. This process promotes the development of downcurrent-side lateral accretion deposits,leading to enhanced levee-channel asymmetry(average asymmetry index ≈2.5),increased confinement along the northern channel margins,and more pronounced migration against the bottom-current direction(average migration index ≈0.8). This study elucidates the differential response mechanisms of genetically distinct channel types to bottom-current interactions,offering critical insights for high-resolution characterization and targeted exploration of deep-water reservoirs.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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