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Tuesday, 19 August 2014

That pink Saunton erratic




Luckily those Geocache people have been hunting for the Saunton pink erratic lately, and so there are a few nice photos on the web.  Here are three of them -- click to enlarge. 

According to Natural England, the erratic weighs about 12 tonnes and is deemed to have come from western Scotland.......

4 comments:

Dave Maynard said...

That erratic appears to be bedded underneath stratified sandstone, or it an optical illusion? Is it more likely just to have been wedged under there.

Dave

BRIAN JOHN said...

Quite right, Dave and Kostas. Sandrock is widespread in SW England and in Wales -- this is a Pleistocene deposit, originating in sand dunes for the most part, in coastal locations, and then concreted or cemented, sometimes because of the presence of iron or calcium carbonate in the environment. The presence of land snails etc in the sand can also provide a source for the cement. It looks like rock, and is indeed rock, but take it from me that it is very recent!

Constantinos Ragazas said...

Brian,

Thanks for explaining how that pick erratic got to be wedged under that coastal cliff sandrock. This was my original small curiosity in my earlier post.

You write, ”this [sandrock] is a Pleistocene deposit, originating in sand dunes for the most part, in coastal locations, and then concreted or cemented,”

So we have the glacial deposit of the pink erratic on a coastal rock platform; followed by the deep dune burial of the pink erratic (and other rocks); followed by the cementing of the sand dunes; followed by coastal erosion of the sandrock cliff through wave action to expose the pink erratic wedged in the cliff.

Makes sense. If that sandrock coastal cliff can be dated to a latter time than the glacial transport of the pink erratic. And the coastal rock platform where the pink erratic rests can be dated to yet an earlier time than both the glacier transport of the pink erratic and the sandrock formation where the pink erratic is wedged in.

The cliff sandrock shows clear near horizontal layers. Is this consistent with the cementing of sand dunes along the coast?

Question. Is this the only scenario possible here that can explain the pink erratic wedged in that coastal sandrock cliff?

Kostas

BRIAN JOHN said...

The sandrock is very common. In places it appears to be beach sand, with grains affected by wave action -- and in other cases it seems to be aeolian, and presumably accumulated in sand dunes. Bedding patterns vary somewhat, as you would expect. Cementing happens whatever the details of bedding may be.