Depositional characteristics and evolution of Miocene deep-water channel systems in block A of Lower Congo-Congo Fan Basin, West Africa

Researches on the depositional characteristics, evolution and constraining factors of deep-water channel systems are the key factors to reveal the "source-sink" process at continental margin and make big breakthroughs in deep-water hydrocarbon exploration. Based on the integrated analyses of seismic, well logging and core data, a sequence stratigraphic framework was established for the Miocene in block A of the Lower Congo-Congo Fan Basin, and then the sedimentary characteristics, evolution and constraining factors of the Miocene deep-water channel systems were purposed. The Miocene in the study area was divided into four third-order sequences, including the Lower Miocene (SQ1), the lower part of Middle Miocene (SQ2), the upper part of Middle Miocene (SQ3), and the Upper Miocene (SQ4). The Miocene deep-water channel deposits are dominated by sandstones and include four types of sedimentary units (deep-water channel deposits, levee-overbank, lobes and mass transport deposits). In the SQ1, weakly restricted-unrestricted depositional channels and lobes were formed. In the SQ2, weakly restricted erosional-depositional channels were developed. In the SQ3, erosional channels were dominant. In the SQ4, erosional isolated channels were widely recognized. Tectonic uplift, denudation, glacial climate and sea level change provided abundant sediment supplies for the development of gravity flow deposits. They might lead to the slope change of paleo-geomorphology in the study area, which further affected the strength of gravity flow and controlled the development and evolution of deep-water channel systems. Moreover, salt structures played important roles in redirecting, restricting, blocking, migrating and destroying the deep-water channels.