Permeability of Different Types of Cross Stratification Formed in Unidirectional Flow
Arnold J.H. Reesink
Binghamton University, Department of Geological Sciences Binghamton, NY, USA
The permeability of various types of cross stratified deposits formed in unidirectional flow is investigated quantitatively. Cross stratification formed by bedforms in unidirectional flow is the most common sedimentary structure in river channel deposits, and is common in deposits from other depositional environments. The grain-size sorting that allows cross strata to be recognized is determined by three main factors: (1) pre-sorted sediment that arrives at the lee side of the dune, related to superimposed bedforms and longer-term variations in water flow and sediment transport; (2) sorting due to differential deposition of sediment on the lee side and associated grain flows, and; (3) movement of sediment on the lee side by the water currents in the lee-side flow separation zone (Reesink and Bridge, 2007). The relative importance of these factors depends on flow and sediment transport, and results in many different types of cross stratification. The influence of this large variety of cross stratification types on permeability is not generally appreciated. This quantitative investigation of the variation in permeability of different types of cross strata will identify the range in permeability values associated with cross stratified sediment. Cross strata with a large range in grain sizes are expected to have a higher degree of permeability anisotropy.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid