Comparison On Deep Water Deposition Of West Africa Passive Margin Basins-Case Studies Of Niger Delta Basin And Lower Congo Basin

Deepwater deposition in West Africa passive margin basins plays an important role in hydrocarbon resources.At the same time,deepwater deposition are different in different basins,such as Niger Delta Basin and Lower Congo Basin.Well understanding these differences of sedimentary characteristics in these two basins is key to hydrocarbon exploration and development.Based on basin reports and field reports from IHS and C&C database and published references,characteristics of deepwater depositional systems,including depositonal characteristics,controls,sedimentary model,between the two basins have been analyzed and studied for Niger Delta Basin and Lower Congo Basin.Since Quaternary,deepwater depositions in Lower Congo Basin are characterized by single-source sediment supply,large-scale channel-submarine fan system in abyssal plain and long-distance transportation.However,they are characterized by multi-source sediment supply,medium or small channel-fan system on slope,near-distance transportation in Niger Delta basin.Furthermore,erosive powder of gravity flow channels is increasing since Miocene rather than stable depositional channels in Niger Delta basin.Taking into consideration of size,sedimentary features and distribution of deepwater systems in the two basins,the differences between Niger Delta Basin and the Lower Congo Basin can be summarized as follow.Firstly,single source Lower Congo Basin contrast with multi sources Niger Delta Basin deep water systems.Secondly,controls on deep water systems of shale structure dominating slope may not be the same with that of salt structure.Thirdly,limited sediment supply and steeper continental shelf resulted together in shorting of delta in Lower Congo basin and restricting of transportation of sediments into canyons to basin floor fans.Therefore,there are multi-source sediment supplies from migrating river mouth in Niger Delta basin rather than single-source(canyon-)sediment supply in Lower Congo basin.The key controls for deepwater deposition come form tectonic evolution,structure development and sources influx regime.