Dynamic Controls on the Evolution of a Turbidite System Offshore French Guiana and Implications on Pinch Out Styles and Stratigraphic Traps

The products of the interaction of sediment gravity flow processes with static basin topography are widely described in the literature. Conversely, subtle depositional topography controls on turbidite architecture in unconfined settings are less well-studied but are critical for accurate identification and characterization of stratigraphic traps. On the French Guiana transform margin (Equatorial Atlantic), highly confined channel complexes were deposited in the Late Cretaceous by a single feeder canyon which passed down-dip into an unconfined base-of-slope fan system. Dynamic topography, created by compensational stacking of sand bodies, led to channel shifting and avulsion to distances up to 20 km, due to local confinement, with concomitant variations in sinuosity and patterns of aggradation. Lateral and abrupt pinch-outs with thinning rates above 160 m/km were observed where the channels were confined by the relief of an older fan and to a structural high. Short-scale lateral degradation and thinning of facies provides efficient sealing and fluid trapping. Less confined distal lateral fans thin at relatively lower rates of 35 m/km. Internal up-dip pinch-outs with thinning rates of 40 m/km2 were observed along the mouth of the canyon due to the abrupt decrease in slope gradient and transition from sand bypass to deposition, but the complex interaction of erosion and deposition resulted in reservoir connectivity to upslope thief sands. The identification of stratigraphic traps at seismic scale is challenging but can be constrained by models, data from wells and analogue outcrops to calibrate the lower scale rock properties, reservoir heterogeneity and seal efficiency.