The Influence of Flow Rheology from the Architecture of Deep-Water Depositional Systems

Donald R. Lowe
Geol. & Env. Sciences, Stanford University, Stanford, CA

The rheology of submarine mass flows and mass movements plays a key role in controlling the large- and small-scale surface morphology and internal architecture of the resulting deep-water depositional systems. Turbulent flows, including turbidity currents and some watery slurry flows, have the ability to erode, transport, and deposit individual particles based on their hydraulic properties. As a result, deep-water systems dominated by sedimentation from such flows show the development of complex morphological architectural elements including channels, bars, levees, crevasses, splays, lobes or distal splays, and broad out-of-channel areas. In contrast, more viscous and cohesion-dominated slurry flows and debris flows are generally laminar during their depositional stages or dominated by thick laminar near-bed layers and generally show minimal ability to scour and fractionate transported particles. Depositional systems dominated by these flow types tend to be lobe-like accumulations with flat or irregular surfaces that show poor development of channels, levees, and other organized features of turbulence-dominated systems. Where periods of deposition from turbidity currents alternate with intervals of debris-flow activity, the debris flows often bury and obliterate the complex surface architecture of the preceding turbidity-current phase of sedimentation, effectively resetting the surface system. Initial flows of the ensuing turbidity-current stage are forced to follow courses determined by debris-flow deposit surface morphology. The resulting turbidity-current deposits may show architectural features and sediment distributions that differ from those of more mature constructional turbidite systems, making predictive modeling of the deposits and reservoir sands difficult.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas