BigH
Geotechnical
- Dec 1, 2002
- 6,012
G'day mates and colleagues,
Ran into a very interesting geological layering yesterday on site. Thought you might find it somewhat interesting.
Our resident "professorial" geologist writes:
"Good observation. What is in the photo is one of the most typical physical structure you can find in clastic fine-grained sediments, especially when the original (horizontal) bedding is steepened and the erosion makes the beds interface visible.
The lower bed consisted of a mostly clayey sediment which underwent a process of shrinkage by drying. This made the "polygonal soil" structure. The surficial fissures (arranged in pseudo-hexagonal figures) were filled by the upper bed and remained in relief as a cast. Then, the bed containing the physical structure on top was partially eroded in modern times when the sedimentary rocks were put in their current place and deformed up to a sub-vertical geometry. Then, the bed above it preserved the structure at its bottom and exposed it to us.
This is a present-day structure.
The ones in Howard's photo are fossil. There are many other interesting physical structures in Rogun rocks, like for instance ripple marks."
Ran into a very interesting geological layering yesterday on site. Thought you might find it somewhat interesting.
Our resident "professorial" geologist writes:
"Good observation. What is in the photo is one of the most typical physical structure you can find in clastic fine-grained sediments, especially when the original (horizontal) bedding is steepened and the erosion makes the beds interface visible.
The lower bed consisted of a mostly clayey sediment which underwent a process of shrinkage by drying. This made the "polygonal soil" structure. The surficial fissures (arranged in pseudo-hexagonal figures) were filled by the upper bed and remained in relief as a cast. Then, the bed containing the physical structure on top was partially eroded in modern times when the sedimentary rocks were put in their current place and deformed up to a sub-vertical geometry. Then, the bed above it preserved the structure at its bottom and exposed it to us.
This is a present-day structure.
The ones in Howard's photo are fossil. There are many other interesting physical structures in Rogun rocks, like for instance ripple marks."
