Early Post-Burial Deformation of Turbidite Channel Sands in the Deep Gulf of Mexico

Perus, Marine¹, Patrice Imbert² (1) Total Exploration and Production, Pau, France (2) TOTAL CSTJF, 64000 Pau, France

Sand injection is now commonly observed in sedimentary series, both at the outcrop and on reflection seismic. Injection is usually part of the larger-scale liquefaction or fluidization of a parent sandbody. Characterization of the parent sandbody is commonly difficult at the outcrop for need of good and extensive enough exposures. Three-dimensional seismic imaging of turbidite channels in the deep Gulf of Mexico provides insights into large-scale remobilization of thick packages of sediment, thanks to the combination of a strong reflector at the top of the initial channel-fill and a fair internal reflectivity of the deformed overlying series.

Where undeformed, the channel-fill sand is about 100 m thick. The main features observed in the deformed zones range from gently tilted blocks to sunken rafts. Individual rafts can exceed 1 km in width or length, and reach 100 m in thickness.

As a consequence, sand appears to be reshaped into knolls and diapirs, much like salt structures in areas of moderate halokinesis. Extensional features in the axial part of the channel are associated with compressional structures laterally, large scale sand blades (wing-like) playing the role of sand injections lining a thrust plane. In some instances, wedging in the deformed cover of the sand indicates progressive deformation rather than one single “explosion” of the sand.

The areal relationship between deformed and undeformed areas seems to indicate that deformation occurs through fluidization of the sand by pulses of upward migration of compaction fluids, vertically channelled by successive sandbodies.