This map incorporates a large amount of data and may initially take a while to load. Read the following as you wait for it to load.
This interactive map is built in layers which can individually be switched on and off. The map can be zoomed in and out by use of the + and – buttons in the top left, or by the use of a mouse wheel.
The measure icon (under the '+' and '-') will activate when clicked. Left click to start a line of measuring, double click to stop that line of measuring; and click again on the icon to turn off measuring. Lengths are displayed in metric units.
The legend for all layers is found by moving the mouse pointer over the icon in the top right. The map is displayed within it's own frame and can be moved by dragging with the mouse left button.
Clicking anywhere on the map will raise a popup box that describes the layers active at that point.
When the map first opens all base layers are switched on. The roads, waterways, and contours (at 50 m intervals) are dependent upon zoom level - the contours will black out the map if displayed when zoomed out, the roads cover the map with a red network. At these zoom levels these layers just obstruct. The roads are principally to enable locations to be found and routes to be followed on the map.
Try zooming in to somewhere you know well. Switch the road and contours layers on, and the waterways. Then zoom on in - this map will allow zooming in very close. Trace the course of a road you know and try to identify the points where the road crosses from one formation to another, or crosses a fault. Are there features on the ground at these points that could relate to the structure you can see on the map?
A word of warning. The upfolding into anticlines and downfolding into synclines has indirectly given rise to the ridges and valleys in West Cork, and also to the peninsulas reaching out into the ocean - this can all be seen from the map. But be very careful about attributing a hill to an upfold of rock or a valley to a downfold - this is by no means always the case. Indeed some of the most noticeable hills in the area are in fact on the axis of a downfold - a syncline. Have a look at Mount Gabriel (location 1 on the map), there in the middle of the Mizen peninsula - easy enough to find with contours and geological lineworks switched on. However, as a contrast, have a look at the Ruagagh valley heading east from Drimoleague (location 2)and past Three Lakes through Clashnacrona gorge (location 3). This valley appears to follow the line of the Dunmanus - Drimoleague fault, which may, as a line of weakness, have contributed to the forming of the valley, by drainage following a more easily eroded course along the fractured fault line. And yet the hills each side, to north and south, are both on synclines. So we can wonder how much rock has been removed by erosion and weathering to enable downfolds to appear as hills.
The youngest rocks of the area lie in Bantry Bay - those on Whiddy Island (location 4) date from the Mid Carboniferous Tournaisian period and are the remnants of what were much more extensive deposits. Bantry Bay (location 5) itself more than likely represents the base of a synclinal fold structure and as such is probably floored by rocks of Dinantian to Tournaisian age, now buried beneath sediments and kelp forests.
The oldest rocks on the map are some of the first sediments laid down in the arid Munster Basin - the Valentia Slate which can be seen around Valentia Island (location 6) and SW Iveragh (7); and the Sherkin Formation which form Clear and Sherkin Islands (8) and runs parallel to the south coast through Lough Hyne (9) and onto the Castlehaven Inlet (10).
The map covers an area about 95 km north to south by 150 km east to west – a total of over 14,000 km2 – of West Cork and Kerry. This area covered is basically that of the most actively subsiding part of the Munster Basin at the time these sediments were deposited, from the Mid Devonian to the Late Carboniferous - 390 million to 320 million years ago (Ma). Orientation is with North at the top - the slight skew is a result of the Coordinate System of the rectangle that was selected for mapping.
Initially, note the correlation between the rock types both onshore and offshore (browns are Devonian, blues are Carboniferous, by convention) with the peninsulas. The Devonian rocks are generally harder and more silica based, making them more resistant to erosion and weathering; the Carboniferous rocks are marine sediments with lower silica and higher lime (calcium) and thus more susceptible to weathering (especially chemical) and erosion. The most striking thing is the general SW to NE alignment within the map, both the penisulas and the geological units. This is a direct result of tremedous forces squeezing this part of the earths crust from the south east. An oblique continental collision similar to what is happening in some parts of the world today, crushed this part of the crust between the incoming plate in the south and south east, against the more massive continent to the north. This collision affected most of northern Europe and across into North America (which was right next door at that time, before the Atlantic ocean had formed). This mountain building was known as the Variscan Orogeny and took place from Mid Devonian through until the end of the Carboniferous period, between about 350 and 280 Ma. The crust was heavily folded and under such strain faulting also occurred- use the legend to switch on Geological Linework, the lines that demarcate folds and faults.
Black lines are faults - those in a N-S or NW-SE orientation are largely slip faults where the pressures causing the crustal folds (see later) became too much to sustain. These have caused the jagged confusion that we can now see. The faults in a SW to NE orientation are in many cases old faults that originally gave rise to down slipping of the crust as the basin was subsiding, caused by a pull apart extension strain; but under pressure from the south east these were reactivated and moved in an opposite sense, resulting in the crust becoming compressed. Some of these even developed further into thrust faults - green lines - giving rise to serious crustal shortening. This part of the crust eventually suffered a 50% reduction in a N-S sense as a result of this compression.
The anticlines (upfolds - an anticline axis is marked by red lines) and synclines (downfolds - the axis marked by yellow lines) are best thought of in the sense of a piles of magazines, squeezed from two sides. Having developed the upfolds and downfolds, next imagine cutting the top off all of them. For the upfolds, the layers exposed in the middle will be progressively older (from lower in the pile), while for the downfolds the middle of the folds will be the younger layers, from higher in the pile. This is exactly what we can see in the repeating patterns of rock formations across the map area. In addition to this are two more things. The very inside of the axis of both the synclines and anticlines can be subject to enormous pressure and can rupture, crack and fault. It has not happened so much in West Cork, but where the pressures were much higher, further south - as can be seen on the coast of South Devon where there are some incredible sharp angled and heavily disrupted folds and faults - the effect could be severe. And also these synclines and anticlines, like vast corrugations of the earths surface, tend to plunge down into the earth, one way or the other or even at both ends. Look at the Mizen peninsula and see how the formations decrease as the axis of the anticline progresses east (11). The same happens offshore going west (12). The forces involved are unimaginably vast.
A final demonstration of the distortion caused by such pressures is the fact that so many of the rocks we see today in West Cork are lying in a vertical sense. The sediments were deposited in a set of horizontal layers by flood waters, rivers and the sea. As a mental exercise just give a thought as to how a thickness of several kilometres of rock can be upended from horizontal to vertical...
Of particular note in this area are;
The map has been generated, using a program called QGIS2Web, from an Open Source GIS called QGIS. This software is constantly being improved and, like all open source products, is highly efficient and free. The layers have all originated from data made freely available to the public domain. There are some inconsistencies in the map, arising partly through the different sources the data came from not being in alignment either with accuracy, completeness or definition.
Read more about how these maps are made and where the data comes from.Copyright © 2020 - All Rights Reserved - www.westcorkpalaeo.com
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