LATE QUATERNARY EVOLUTION OF THE FRENCH-GUIANA CONTINENTAL-SHELF - EVIDENCE FROM 3.5-KHZ DATA

Twelve seismic profiles (3.5 kHz) accounting for more than 1850 line k ilometres over a 36,000 km(2) area were examined to evaluate the seism ic stratigraphic framework of the French Guiana continental shelf. The high density of seismic data favoured a high-resolution seismic strat igraphy interpretation. Acoustic reflectors in the seismic profiles we re related to sedimentological properties. The various acoustic reflec tors observed in the area can be attributed to: (1) a substratum S whi ch covers the entire area, (2) a formation A, which consists of sedime nts deposited in channels of fluvial origin, (3) a formation B, which is composed of coral clasts, and (4) two high sea-level sedimentary pr isms C and D, which correspond to a near modern sea level, and are Hol ocene in age.The extent of these formations is controlled by the speci fic morphology of the acoustic substratum, which is asymmetrical on ei ther sides of the shore-normal line extending northeast from Kourou. T he influence of Amazon discharge is controlled by this feature.