Perception vs. Reality in Deep-Water Exploration
The common perception in exploration is that deep-water sands are predominantly a product of low- and high-density turbidity currents, and that submarine-fan models with channel/levee and lobe elements are the norm. The reality, however, is that deep-water systems are extremely complex and variable in terms of depositional processes and sand- body geometries. For example, the Bouma Sequence, composed of Ta, Tb, Tc, Td, and Te divisions, is believed to be the product of a turbidity current. However, recent core and outcrop studies show that the complete and partial Bouma sequences also can be explained by processes other than turbidity currents, such as sandy debris flows (i.e., "Ta") and bottom-current rewo king (i.e., "Tb, Tc and Td"). Massive sands are interpreted routinely as high- density turbidites, but the reality is that the term "high-density turbidity current" commonly refers to sandy debris flow in terms of flow rheology and sediment-support mechanism. Deep-water sequences in the North Sea, Norwegian Sea, Offshore Gabon, Offshore Nigeria, Gulf of Mexico, and the Ouachita Mountains are generally considered to be turbidite-rich submarine fans. However, the reality is that these sequences are composed predominantly of sandy slumps and debris flows, not turbidites. Fan models are attractive to explorationists because of their predictable sheet-like geometries; however, these simplistic conceptual models are obsolete because they defy reality. Although he turbidite paradigm is alive and well for now in the minds of many sedimentologists and sequence stratigraphers, the turbidites themselves that form the foundation for fan models are becoming an endangered facies!
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California