Sedimentação Do Congo

Journal of Sedimentary Research, 2010, v. 80, 852–866

Research Article

DOI: 10.2110/jsr.2010.078

SEDIMENTARY ARCHITECTURE IN MEANDERS OF A SUBMARINE CHANNEL: DETAILED STUDY OF THE

PRESENT CONGO TURBIDITE CHANNEL (ZAIANGO PROJECT)

N. BABONNEAU,1

B. SAVOYE,*2

M. CREMER,3

AND M. BEZ4

1

Universite´ de Brest, CNRS UMR 6538 Domaines Oce´aniques, IUEM, Place Nicolas Copernic, 29280 Plouzane´, France

2

IFREMER, GM-LES, BP70, 29280 Plouzane´, France

3

Universite´ Bordeaux I, CNRS UMR 5805 EPOC, Avenue des Faculte´s, 33405 Talence, France

4

TOTAL, CSTJF, Avenue Larribau, 64000 Pau, France

e-mail: [e-mail]

ABSTRACT: Sinuous 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 migration, also provides new data for

interpretation of flow dynamics in submarine meandering channels.

INTRODUCTION

Meandering deep-water channels have been observed at the surfaces of

most of large deep-sea fans in the world: the Amazon Fan (Damuth et al.

1983; Flood and Damuth 1987; Pirmez and Flood 1995), the Mississippi

Fan (Kastens and Shor 1986; Pickering et al. 1986), the Bengal Fan

(Hu¨ bscher et al. 1997; Schwenk et al. 2003), the Indus Fan (Kenyon et al.

1995; Kolla and Coumes 1987), the Nile Fan (Loncke et al. 2002), and the

Rhoˆ ne Fan (Droz and Bellaiche 1985; Torres et al. 1997). Submarine

meandering channels present a particular interest to oil companies, since

they are significant hydrocarbon reservoirs in deep offshore environ-ments. The understanding of their geometries and their internal

sedimentary architecture is necessary to better characterize reservoir

heterogeneity. Therefore, numerous works have recently been carried out

by both industrial and academic researchers to understand the behavior

and sedimentary architecture of sinuous deep-water channels, including

different