CYCLES IN THE ARCHITECTURE OF THE QUATERNARY ZAIRE TURBIDITE SYSTEM:A POSSIBLE LINK WITH CLIMATE

摘要

The presently active Zaire (Congo) turbidite system reveals a well-organized Quaternary architecture, with depocenters that partly overlap each other in response to avulsion. Based on previous work, more than 76 channels are organized into three individual fans (Northern, Southern, and Axial Fan, from the oldest to the youngest). A statistical analysis of both longitudinal and lateral migration of depocenters was conducted. The longitudinal shifts were studied through the temporal evolution of the channel lengths and the distances to the bifurcation points from a common reference point arbitrarily positioned on the canyon course, up-dip from the most proximal bifurcation point. The number of bifurcation points on a channel was also calculated. These three architectural parameters show a cyclic organization through time, better expressed in the Axial Fan, with cycles of down-fan and up-fan movements reflecting prograding-retrograding cycles. Based on a previous study of the kaolinite /smectite (K /S) ratio in the hemipelagic drape covering the Southern Fan, i.e., contemporaneous with the building of the Axial Fan, the prograding peaks of the Axial cycles are correlated to peaks in K /S, which reflect phases of intense Zaire River water discharge, during warm and humid interglacial periods. These correlations suggest that both the channel lengths and the avulsion process are controlled by climate changes that appear as a major forcing factor throughout the Quaternary. The effects of climate control can be modified by the interplay of other internal and/or external factors. Study of the lateral migration revealed that topographic compensation is the major autogenic control, and that external factors such as tectonic evolution in the drainage basin of the Zaire River or halokinesis at the Angola base of slope can locally play a significant role in the location of depocenters.