any geologists?

[KeenTeen17]

I recently went to Portpatrick, Scotland and I was wondering what sort of rock these cliffs were? The light coloured ones felt like flint but I'm wondering if the massive black ones are basalt or just wet flint. I recently consulted a map of the area showing the geology. It said the area had Silurian sedimentary rocks which certainly fits flint.

Any body any ideas?



Thanks

[caernerch]

basalt?
caernerch

[ChrisJB]

Whilst not totally au fait with the geology of the Portpatrick area it will not be flint as flint is found in much younger Cretaceous rocks. I strongly suspect that the rocks are linked to the Silurian rocks of the Southern Uplands, where a type of resistant sandstone called greywacke often predominates. It forms on the edge of continental shelves in submarine canyons and in the Southern Uplands is heavily deformed. The Southern Uplands mark the line where the Iapetus Ocean closed at the end of the Silurian. Basalt may also be present as a relic of sea-floor eruptions and/or other volcanic rocks from the closure of Iapetus.
Not a definitive answer alas, but some possibilities to muse upon.

Regards, Chris

[KeenTeen17]

Cheers all these ideas are ace. Its quite hard finding the geology of an area I only just went on holiday

[valleyforge]

Hi,

I'm not too familiar with this area either I'm afraid, but I believe the Portpatrick formation itself is charcterized by massive greywacke-sandstones of Ordovician age, which are underlain
by basalt and dolerite lavas.

Check out this link to the 'Geology of Scotland' by Nigel Trewin (my former sedimentary petrology tutor at the University of Aberdeen) and read from page 167 onwards:

The geology of Scotland - Google Books

Nice stretch of the coast though.

[Jaeviatrix]

Looks like a classic basalt to me, the columnar joining behind the chap in the blue shirt is very basalt. Shallow intrusive/extrusive, fine grained, mafic igneous rock. It has mineral veins running through the fractures as well, possibly calcite? The extrusive ones are probably the remains of ancient lavas. Great scenery too. Hooray I still remember something from my first degree!

Flint does not form rocks like these, it forms nodules in calcareous rocks like chalk, and is called "chert" in the north anyway.

Hope all is good

[poschiavanus]

Try the geology map viewer from the BGS: this enables you to click on a location and get information about the solid and drift formations at that location.

Geology of Britain viewer | British Geological Survey (BGS)

[ChrisJB]

Originally Posted by poschiavanus

Try the geology map viewer from the BGS: this enables you to click on a location and get information about the solid and drift formations at that location.

Geology of Britain viewer | British Geological Survey (BGS)

Thanks for that site. Just added it to my 'favourites'. Checking it out, there are a lot of (grey) 'wackes' for sure around Portpatrick and a few dykes (intrusive igneous bodies that cross-cut the country rock). These seem to cut through the Silurian sedimentary rocks and therefore must be younger.

Regards, Chris