Permeability of Different Types of Cross
Stratification Formed in Unidirectional Flow
Arnold J.H. Reesink
Binghamton University, Department of Geological Sciences
Binghamton, NY, USA
[email protected]
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