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Simulating the Grain-Size Distribution of Wisconsinan Age Glaciofluvial Sediments: Applications to Fluid Transport

WEBB, ERIK K., and MARY P. ANDERSON, University of Wisconsin--Madison, Madison, WI

A sedimentary depositional model, SEDSIM, was used to simulate the deposition of glaciofluvial sediments in south-central Wisconsin. These types of deposits are present at or near the surface over much of the northern United States and have a high contamination potential. They also represent relatively recent analogs for ancient braided stream systems.

Sixty sediment samples were used to determine the average sediment properties for a facies assemblage located 8-10 km from the ice margin. A regional depositional system was simulated, using SEDSIM, to determine the range of input values that reproduced our observed average sediment characteristics. Progressively smaller scale models were constructed to produce more detailed estimates of the grain-size distribution. The grain-size estimates from the finest scale model were translated into relative hydraulic conductivity values using the method of Hazen. The resulting conductivities were incorporated into a fluid flow model to illustrate the control that heterogeneity of petrologic properties has on the direction and rate of fluid movement.

This work indicates that a wide range of input parameters will reproduce the bulk sediment properties. Furthermore, small-scale features may not be reproduced under the assumptions incorporated in the current SEDSIM code. Thus, for sedimentary depositional models to be used to predict permeability and porosity distributions, or to interpret paleo-flow conditions, we must determine calibration targets that are more sensitive to flow parameters than bulk grain-size distributions.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)