Posted by: Alan Pitts | September 12, 2011

Folded Lakes Marble

So here it goes. Back to school, back to blogging.

It was just about the very best summer a geology student like myself could hope for. It all began with geology field camp, where geology undergrads go to complete their geologic training and take place in the sacred art and practice of field mapping.  I was lucky enough to attend field camp in Ireland’s beautiful county Galway.

Among some of the strange and wonderful things I saw at camp were:

  •  Charismatic metasedimentary rocks of the Dalradian Super Group,
  •  All sorts of sweet glacial features.
  •  Some amazing igneous structures such as pillows and some pretty famous columnar basalt.
  • The site of the “last stand of the neptunists”, which in terms of last stands was no less thrilling than Thermopylae, The Alamo or Little Bighorn.
  •  World-class Carboniferous marine sedimentary successions in the Clare Basin.
  • Sheep in numbers best quantified with scientific notation.

I also learned all about safely navigating across expansive man-eating bogs and turf harvesting. I learned how a pint of Guinness can be used as a semi-accurate analogy for practically any geologic concept. And I felt the painful, fiery sting of Ireland’s most serious natural threat to a field mapper, the dreaded Stinging Nettle ( as there are no snakes, bears, or poison ivy).

All in all it was a great experience and now that I’m back home I’m planning on synthesizing all the information and  blogging a bit about all the things I saw this summer (with little breaks to write about Virginia geology here and there).

I will start at the beginning of the trip and hope to move through my  stockpile of geology photos more or less as I experienced the geology of the Emerald Isle. Today, I’m featuring some of the most spectacular folded marbles I have ever seen.

Ladies and gentleman, boys and girls, friends of all ages, I give you…  The Lakes Marble Formation.

Photo by Lori W.

Located in the Cur region of Connemara, this marble is part of a Neoproterozoic metasedimentary package of rocks, the Dalradian Super Group which have been folded into an anticlinal structure and mineralogically altered from several stages of mountain building.  The white bands are almost pure calcite and the darker bands contain detrital quartz and other siliclastics, zooming in on one of the pictures will provide a better look and  you can see how the black bands stand “proud” as they are more resistant to weathering.

Here is a geologic map of Ireland, simplified from the official map produced by the GSI that can be found here.  I modified this image to highlight the area of interest. Right away one can see the highlighted area is just about the most complex area on the map, or at least one showing a great deal of lithological variation.

Here is a closer look at the highlighted region. I drew in a green line to show the antiformal shape of the rock units.


The trace of this antiform can be seen in the terrain as well. Here is a google image of the region.

The chain of lakes that arc eastward of Connemara National park basically provide an outline of the Connemara Antiform.  There are several other geologically interesting aspects of this image that I’m intentionally not mentioning as I hope to discuss them in a future blog post.

Here is another green dashed line to drive the point home.

The amazing Dr Martin Feely, our guide to Irish regional geology, hailing from The National University of Ireland, Galway, discussing the mineralogy of the marvelously folded marble. 

This last photo is of the surrounding area, visible are the more resistant quartzite ridges which make up the core of the antiform ( more on that later) and some of my favorite friends from Ireland.  

Some references on the topic:

  • Geoffrey and Shackleton.Structure and stratigraphy of the Dalradian rocks of the Bennabeola area, Connemara, Eire. Geological Society,London, Special Publications 1979, Vol. 8, pp 243-256
  • Leake. The geology of SW Connemara, Ireland: a fold and thrust Dalradian and metagabbroic-gneiss complex. Journal of the Geological Society, London,1986. Vol.143, pp 221-236
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Responses

  1. great rocks. do you have an rss feed for your blog?

  2. Hi Charles, Thanks ! I’ve added an RSS feed button on the right side of the blog which should allow you to subscribe to the feed. Im not all together familiar with RSS feeds and how they work, but I was able to subscribe to my own blog with google reader using the button on the side. Hope that works and thanks for reading !

  3. I used one of you pictures in my slideshow. I didn’t see where you require permission. I would like to use another as well. I believe it is proper for me to ask. I would like you to see how it was used and give my permission, or I will gladly but it down.


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