Sunday, October 3, 2010

Steppingley area

My mind continues to be exercised and so I went for a much needed walk this afternoon to clear my head. My choice of location was a local wood, which I enjoyed wandering round in the midst of a strong breeze.
There were fungi everywhere including club fungi. I think that this is Wrinkled Club….

…but I’ve no idea what this species of coral fungus is!

Mammals seen included a male Muntjac, Rabbit and 2 Grey Squirrels.

There are also Fallow Deer around though, these droppings being characteristically pointed at one end and indented at the other.

And this Badger sett was interesting. It looks like the Badger is a bit of an architect!

This area is a part of the Greensand Ridge which means that there is a lot of sandstone around. This nondescript-looking block holds a secret, the two separate parts revealing this:
Any ideas?


Our Geology Recorder, Martin Whiteley, has furnished me with the following information:

"What you've found are ironstone concretions within a block of Woburn Sands Formation sandstone (otherwise known as the Lower Greensand). These concretions are very common and probably form as the loose sand grains start to become compacted and de-watered as they are progressively buried beneath the sea floor after deposition.

Iron-rich fluids pass through the sand grains and locally precipitate into a wide variety of circular and elliptical forms. The iron-rich 'rinds' are usually dark brown or purple in colour and may enclose sand grains that are less well cemented than those elsewhere in the rock. Some concretions closely resemble burrows that were formed by sea floor dwelling animals such as crustaceans when the sandstone was being deposited, and in these cases it seems as if the iron-rich fluids were preferentially deposited in the lining of the old burrows.

The precise reason why iron is deposited in such curious forms is not really known, but variations in the permeability of the enclosing sediment and the chemical composition of the migrating fluids are probably key."

1 comment:

  1. Very interesting! I find a lot of similar nodules on the sandy ridge behind my house. The nodules have a hard crust around loose dry sand - I think they must erode out blocks like the one you found. It was Martin that finally solved the mystery for me. He really is a very helpful chap.

    Full story here if you're interested:

    All the best