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Thursday, 16 December 2010

Photos of the "striations" in the Avenue

Thanks to Robert for alerting me to these pics:

http://www.flickr.com/photos/pauljcripps/3587361988/in/set-72057594060375863/

http://www.flickr.com/photos/pauljcripps/3587362620/in/set-72057594060375863/

They are copyright reserved, so I can't show them here, but they do seem to show some smallish grooves at the bedrock - regolith interface.  I assume they run straight downslope -- I wonder if they owe more to surface solution processes than to periglacial processes?  Difficult to say without examining them in detail.

5 comments:

Robert Langdon said...

The immediate question that sprang to my mind when I look at these glacial stripes is - why here?

The entire area - if you believe current theories - was totally covered in forest for about 4,000 years.

Consequently, over that period of time every square inch would have had some form of growth. Tree roots would destroy any stripes over a period of time, unless very deep in the soil - these stripes are only 18 inches below he ground. Therefore, any kind of tree would have cut through these stripes leaving - broken chalk - and this is found all over Salisbury plain at this depth.

The only logical conclusion is that something stop the foliage growing over The Avenue and Stonehenge Bottom.

I know of two things that would do this - Ice or Water.

Get another proof for my second edition - thanks guys!

RJL

BRIAN JOHN said...

They are not glacial stripes, Robert. They MAY be periglacial, but I'm increasingly coming to the view that they are solutional in origin -- showing up a very irregular grooved surface on the solid chalk, beneath the broken chalk in the regolith.

Why would tree roots destroy these rock surface irregularities? It is just as likely that the irregularities are themselves a product of tree growth and enhanced biological processes to go with the normal solutional processes on a chalk surface. If the pollen evidence shows a well-wooded landscape, then that is what we have to accept.

I wouldn't mind betting that much of Salisbury Plain is underlain by these chalk surface irregularities. There is no reason whatsoever to assume that they are restricted to the Avenue, Stonehenge and Bluehenge -- that's just where a lot of digging happens to have been done by archaeologists.

Where you conjure your "proof" from, goodness knows....

Robert Langdon said...

Nice idea, may get away with the pine but not the Birch, Hazel,Oak and Elm!

http://hellis.biz/tree_root_systems.aspx

One tree would destroy the entire chalk foundation in a complete circle of the tree using its height as the radius - in a forest trees are every 3-4 metres - so one spot will have at least 3-4 trees cutting root grooves.

In the Avenue - nothing but Ice Age stripes.

The Car Park 100m away was excavated in 1966 and a large tree hole was found that was 2.5m wide and cut into the chalk to a depth of 0.7m - they did not find any glacial evidence.

Consequently, I think i'll stick with my proof until we find any evidence of these stripes above the suspected waterline or Mesolithic tree holes in the dry valleys.

RJL

BRIAN JOHN said...

I don't know what you are talking about here, Robert. Are you trying to prove that there were no trees in certain areas where people have assumed trees to have been present? Trees do not "destroy chalk foundations" -- their root systems sit in the regolith, and some deeper roots probably help to break up the rock - regolith interface, and then, when they die, the roots rot away.

I have seen bits and pieces of old roots in all sorts of geological situations, above and beneath the solid rock - loose debris junction.

I think you are putting up a nonsensical Aunt Sally here, just in order to knock her down. None of this stuff about trees, and their presence or absence, proves anything at all.

Anonymous said...

These make me think of the Cart Tracks in Malta, which are currently thought to result from early human carts or sleds cutting through soft ground down to soft bedrock, which later hardened up.