Linear Dunes (by sarah)
Last Wednesday I had an interesting lecture on the Linear dunes of the Namibia from Charlie Bristow he specialises in modern sedimentary environments. I have always liked sand dunes I really enjoyed all the Applied Sedimentology course I did at Imperial except the petroleum bits and even quiet alot of that I found interesting.
The premise people had been working on was that these huge dunes where left over from the last glacial maxium but this turns out not to be so. There is cool dating techniques you can use on sand that has been sitting in the dark - you get like an exposure date for the last time it saw sunlight as the sunlight 'bleaches' the sand grains and sets the exposure age to zero.
I remembered from before that there where three types of motion on the sand dunes - there are little sort of parasitic dunes moving across the huge great big stonking dunes for a start. It is/was thought that these types of dunes do not appear in the geological record so they where of interests becuase of that but in cutting into the dunes it is now thought that they might look simialar to other types of dunes - dune morphology and how they look inside due to migration (the wind blowing them sideways or back to front or whatever) is actually a bit of a geometric nightmare to get your head around especially when you start looking at how a paloe (old turned into rock) dune bed can be exposed - it could be tilted, cut at a strange angle and all sorts.
Anyway the dunes are younger and would appear to be able to tell us about climate changes that may have occured in the area - this includes looking for 'fossilise' hirax poo but these are rare. There are also fulgurites which are the formation you get when lightning hits sandy substrates which supports the idea of climate change which would have produced vegitation ie it got wetter - it started to rain and plants grew their root sort of stoped the dune sand from being blown about.
I suggested they look for root material which is apparently on the cards.
Sun 26th Oct 2008 10:09 am 
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