The Bedrock Geology of West Cork

Principles of Geology

Fundamental to the understanding of geology are these three principles:
Geology does not end at the coast. Despite most geology maps only showing detail for areas of land, the rocks continue onto the continental shelf. The sea covers the edges of the continents, but they are still continental crust. The oceans don't start until the continental shelf ends.
Geology is still happening now. The processes are slow and they are not always visible, but geology is not just a thing of the past. It is about deposition, and erosion, the wearing away of surfaces, the deposition of sediments; plate movements, earthquakes, and volcanoes; all the processes that are happening today. This is known as 'uniformitarianism'. Appreciating this can make geology come very much alive.
Every rock type represents an environment. This is the attraction of geology, that it represents a record of past environments, like a directory or an index. As we can see from the bedrocks of West Cork, even subtle and hardly detectable changes in rock type can be interpreted as being caused by variations in environmental conditions. Thus palaeoecology and palaeoenvironmental studies are relevant, even going back hundreds of millions of years.

Desert Sands and Sinking Sediments

The bedrock of West Cork - as it is at the present time - was originally deposited as sediment in a vast hot and arid desert basin. Dispel from your mind the green damp landscape of West Cork; the roaring Atlantic throwing breakers against the rocky coastline; the cliffs and inlets of the southern and western coasts; and the lakes, rivers, bogs and woodlands. Forget the lush green fields and grazing cows; the farms and cottages; the gardens, mountains and moorlands. Most important of all dismiss the coastline as the recent construction it is, a mere 10 to 12,000 years old. In their place, to the north of Kerry, and also to the west, out off the rocky Atlantic coast, across wide and flat dusty plains and beyond foothills, lay a vast range of mountains. Periodic rainstorms washed out rock, sand and mud from the mountains to the foothills and out, south, onto the plain. And away to the south, beyond where the Celtic Sea now washes over the continental shelf between Cornwall, Ireland and Brittany, lay the coastline where this desert met the sea.

At that time, between about 390 and 300 million years ago, during the mid-Devonian to early Carboniferous periods, this part of the earth’s crust lay at a low latitude, just south of the equator. The environment was probably similar to the North African Atlas Mountains and Sahara desert today.

The Munster basin stretched from Killarney in the north, to somewhere off the south coast, where the boundary of the basin has not yet been found. To the east it extended as far as county Waterford and the Comeragh Mountains, and to the west beyond the present rocky coast. At this time the area of the Munster basin was twice as wide north to south than it is now – subsequent folding and faulting has shortened the land surface. We can, experimentally, undo the faults and folds to find the true ‘flattened’ surface as it was before being deformed. This is known as a palinspastic reconstruction, and is represented by the image above.

NEXT - Rivers Without End - most rivers run down to the sea, but the waters running across the Devonian plains of West Cork 350 million years ago, just ran out of steam - and soaked in or evaporated away.

West Cork Palaeoecology

The Environment of West Cork through Time

Visit the Blogsite at westcorkpalaeo.ie (new tab)

Desert Sands and Sinking Sediments