DIMENSIONAL ANALYSIS OF MUD-RICH SEDIMENTARY DEPOSITS ON CONTINENTAL SHELVES

Dimensional analysis of sedimentary and dynamical parameters associated with modern mud-rich deposits on continental shelves is used to synthesize a diverse set of measurements and information, and to identify common factors that contribute significantly to growth of these deposits. Little effort has been made to determine unifying relationships for the modern deposits, despite the large and growing number of individual field studies that now exist. An analysis based on a simple model that incorporates input, capture, and loss of fine sediment onto continental shelves leads to dimensionless groupings of significant variables that can be applied to specific modern shelf-mud deposits. These dimensionless parameters appear to provide a unifying relationship that links sediment supply, accumulation, and dynamics for the deposits.

Studies over the past three decades document the common occurrence of fine-grained sedimentary deposits on continental shelves, mostly associated with rivers that discharge fine sediment along many coasts around the world. Data from six specific studies of modern mud-rich shelf deposits are used to evaluate the dimensionless numbers that were derived in this analysis. The studies include modern accumulations off the Amazon, Yukon, Eel, Po, Ebro, and Russian Rivers. The author participated in each of these studies over the past two and one-half decades. The data are used to evaluate two of the most significant dimensionless numbers that represent sediment accumulation and properties ("Sedimentation Number") and dynamical processes including sediment supply and bottom shear stress ("Transport Number"). These numbers can be related to the more familiar Shields and Mobility Parameters, but contain additional variables.

The relationship that was defined by the six specific studies was tested with data from two mud deposits off China (off the Huanghe and Changjiang Rivers) that were collected by others. The results suggest that the Sedimentation and Transport dimensionless numbers represent fundamental quantities that describe these types of deposits. Important factors like accumulation rates or sediment supply can be determined from the relationship if the other important parameters that make up the dimensionless numbers are known or can be estimated.