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Hi there. Thanks f.. by paulocon   (Show all posts)
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kernowclimber
2010-05-06 18:38:38
"Crinoid fossils in Dartry limestone" from kernowclimber Expand pics
Crinoid fossils in Dartry limestone (Expand pics)
Reading the rocks beneath our feet: crinoids
Simon has suggested that a description of a crinoid (mentioned in my recent Benbulben post) could be useful to other walkers who might encounter interesting fossils in the rocks while out and about in our mountains. Iím not a geologist, but mcrtchly is, so I thank him for aiding in this brief description.

Crinoids (also known as sea lilies) have been around for about 530 million years, first appearing in the fossil record of ocean sediments deposited during the Cambrian Period. These delicate creatures related to star fish, sea urchins and star dollars, resembled a flower complete with stalk and root-like parts and formed vast colonies on the floors of warm, shallow seas all over the globe during the Paleozoic Era. Some cast off their stalk and root-like anchor to become free-moving. However, many species of crinoids died out in the mass Permian extinctions, but the few that survived include the ancestors of the present day species which tend to inhabit deeper waters.

The bodies of crinoids are comprised of calcareous (calcium carbonate) plates. When these creatures die and sink to the sea floor, millions of their bodies compact over time to form thick limestone beds, some of which are eventually uplifted to form new land. As crinoid skeletons are made of calcium carbonate they fossilise easily. The stalks are the commonest parts to be fossilised and often look like stone worms when seen lengthwise and may protrude slightly from weathered rock.

Benbulben Mountain is comprised of rocks formed around 320 million years ago in the Carboniferous Period. The land that became Ireland then lay on the southern edge of a continent called Laurentia that straddled the Equator and was subject to repeated periods of inundation by the Tethys Sea. A hard and resistant rock named Dartry limestone forms the upper cliffs and precipices of Benbulben and lies atop softer shales overlying Glencar limestone.

Our fossil find (photographed) was made close to the top of the waterfall on the way up to the Benbulben plateau from Glendarragh Valley and shows fragments of crinoid stalks trapped in Dartry limestone. Benbulben is a good place to look for all sorts of fossils and near the bottom of the waterfall we found a fragment of a giant coral we believe to be Caninophyllum that thrived in the warm Equatorial waters off Laurentia.
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User profile
ewen
ewen 22 hours ago.
Now living furth of Scotland and getting to know the Irish hills. If you come across a Scottish hill Walker with dodgy knees and walking sedately, stop and say hello.

  
Summit Comment
Knockroe: OMG - I forget to check the MV page!
Pepe 22 hours ago.
Decided to make a day out of a Dublin-Waterford drive, despite low-hanging cloud. Knockroe wore a misty white cap as I glanced up from the Sculloge Gap carpark. Planning my attack (so I thought), ...

  
Summit Summary
Bleantasour Mountain: A boggy but short ascent route
Collaborative entry Last edit by: simon3 a day ago.
Go to the forest entrance at S22452 09704. there is room here for a few cars.Walk down the forest track, crossing a ford and follow the track until you can see open ground.Walk south along the edg...

Track
A handy way up two western Monavulaghs.
simon3 a day ago.
Easy access to the ridge.Improved RouteUsing the hard won experience of others and new forest roads we found a relati... walk, Len: 6.5km, Climb: 263m, Area: Bleantasour Mountain, Comeragh Mountains

  
Summit Summary
Milk Hill: Carry on bagging
Collaborative entry Last edit by: simon3 a day ago.
Go to the forest entrance at S22452 09704. there is room here for a few cars.Walk down the forest track, crossing a ford and follow the track until you can see open ground.Walk uphill to the summi...

  
Summit Comment
Seefin: Fine day spoilt by Scramblers
ewen a day ago.
Started at the Coillte gate at 068145 where there is parking for 2 cars. I then followed the forest road around until the first turn off to the left. This takes you along to the fire break/path at...

Forum: General
Local 97
marymac 3 days ago.
An abstract Artist, Charles Shaw, said "Real happiness consists in not what we actually accomplish, but what we think we accomplish." I moved house. So my Local 100 changed. The new list includes ...

  
Summit Comment
Gortrumnagh: Drive or Walk
sandman 2 days ago.
The gravel track at L6133851903 will bring you up to the second quarry workings allowing you to park at L6213651955 and enter the open hillside via a gate just inside the quarry to the left. No si...

  
Track
Hacha Grande by following my nose.
jackill a day ago.
walk, Len: 11.5km, Climb: 636m, Area: Spain, Canary Islands ()

Summit Comment
Derrylahan: Coastal Hill
sandman 2 days ago.
As this hill is located in a field covered in gorse bushes the easiest access is via the adjacent land owner. Parking at L6670259115 i was fortunate to bump in to the farmer whose farm yard is loc...

  
Summit Comment
Ballynew: Coastal Hill
sandman 2 days ago.
Park at L6231659377 opposite a very modern designed house and follow the non tared track and as it turns right go straight up hill thru an old overgrown trail still used by some cattle on there ow...

  
Forum: General
MI: Celebration Ireland's mountain environmen
simon3 5 days ago.
Date: 26-28/05/2017Venue: Cappanalea OETC, Killorgin. Co. KerryTo coincide with National Biodiversity Week, Mountaineering Ireland is hosting a weekend celebration of Irelandís mountain environmen...


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