Sedimentary Architecture in Meanders of a Submarine Channel: Detailed Study of the Present Congo Turbidite Channel (Zaiango Project)

Abstract

International audienceSinuous deep-water channels are recognized in most large deep-sea fans in the world. They present a particular interest to oil companies, since they are significant hydrocarbon reservoirs in deep offshore environments. The understanding of their geometries and their internal sedimentary architecture is necessary to better characterize reservoir heterogeneity of sinuous submarine channels. Therefore, numerous studies have been undertaken recently to better understand the behavior and sedimentary architecture of deep-water channels. The aim of this paper is to present our results concerning the development of the meandering channel of the present Congo turbidite system (or Zaire turbidite system). The study is based on high-resolution data including multibeam bathymetry, seismic lines, echosounder profiles, high-resolution side-scan sonar images, and gravity cores, collected by IFREMER along the submarine Congo channel between 1994 and 2000, during Guiness and ZaiAngo surveys. The present Congo turbidite channel is a long incised turbidite channel. It is presently active. It has been built gradually by progradation of the distal depositional area. The most distal part of the channel is the youngest part and shows an immature morphology: the channel presents a low incision and a low sinuosity. In contrast, the upper part of the channel has undergone a long evolutionary history. Its pathway is mature and complex, with numerous abandoned meanders visible in the morphology. This paper presents evidence of progressive channel migration and meander development of the Congo channel. It describes and explains the presence of terraces inside the channel. The detailed characterization of channel morphology and migration geometry shows that the evolution of the channel path is very similar to fluvial meandering systems with (1) lateral meander extension or growing, (2) downstream translation of the thalweg, and (3) meander cutoff. Seismic and 3.5 kHz echosounder profiles show that the terraces, which are visible in the seafloor morphology, are not the imprints of incisional processes. Terraces are true depositional units infilling the channel. They are built during and after the lateral migration of the channel. They are composed of (1) point-bar deposits and (2) inner-levee deposits aggrading above the point bar deposits. Point-bar deposits are characterized by low-angle oblique reflectors forming deposits with a sigmoidal shape. They seem very similar to those observed in fluvial systems. The similarity between fluvial and turbidite point bars suggests that the basal part of the turbidity currents flowing in this channel can be considered as very similar to river flow. With the high-resolution dataset collected in a present Congo turbidite channel, we provide a new description of the channel morphology and evolution, at a "reservoir" scale, intermediate between outcrop observations and 2D and 3D seismic data. The detailed interpretation of intrachannel sedimentation, associated with lateral channel mig...

Submarine channel evolution: active channels in fjords, British Columbia, Canada

“…In deep submarine settings, channel systems have been shown to develop extensive lateral accretion packages (LAPs), similar to point bars on the inside of channel bends (e.g. in the Congo fan channel system; Abreu et al 2003;Babonneau et al 2010). The dips of LAPs are reported to be in towards the channel thalweg (Abreu et al 2003).…”

“…Much of the recent research on turbidite channel systems has been spurred by their increasing importance as hydrocarbon reservoirs in deep-water fan settings (Babonneau et al 2010;Mayall et al 2010 and references therein). Textural heterogeneity in such systems, determining porosity and permeability, impacts the successful exploitation of such deep-water resources; the spatial organization and origin of channel system facies is thus also of economic interest (Mayall et al 2006).…”

The possible role of Coriolis forces in structuring large-scale sinuous patterns of submarine channel–levee systems

“…The turbidity currents can be triggered by numerous mechanisms, such as sloping layers of sediment offshore of a large river mouth that become unstable owing to loading, underground gas release or seismic activity [11] or by sediment resuspension by wave action, tides or storms on the continental shelf. The length scales of sinuous channels can be very large (1000 km or more), such as the Zaire Fan system in West Africa [12] or the North Atlantic Mid-Ocean Channel (NAMOC) near eastern Canada [13]. Sinuous channels are usually contained within wide and deep levees.…”

“…The values of Ro W were calculated using the mean channel width and a mean velocity U = 1 m s −1 , representing a typical mean velocity observed or inferred for numerous submarine channel systems [14,26,27] latitudes [25]. By contrast, narrow and highly sinuous submarine channels at low latitudes such as the Zaire [12], Amazon [19] or the Indus Channel [1] all have |Ro W | > 8. The correlation of low peak sinuosity with low Rossby number and high peak sinuosity with high Rossby number supports the hypothesis of Peakall et al [4] that Coriolis forces could be one of the key controls for significantly lower sinuosity at high latitudes.…”

Rapid Adjustment of Submarine Channel Architecture To Changes In Sediment Supply

“…This is especially difficult to do in outcrop and core studies, where shale drapes and erosional surfaces are often interpreted as signs of channel abandonment and reoccupation, but, due to the lack of three-dimensionality and fine-scale age control, it is impossible to verify whether that is indeed the case. The integration of high-resolution bathymetry, high-resolution "chirp" seismic reflection surveys, and core data has provided new insights into the architecture and evolution of submarine channel systems (Pirmez et al, 1997;Gervais, 2002;Babonneau et al, 2002Babonneau et al, , 2004Babonneau et al, , 2010Paull et al, 2011). The absence, however, of three-dimensional (3D) seismic reflection data often hampers the understanding of the 3D complexity of these systems.…”