|Aghnadarragh: east shore, 23 October 1987. Ulster Museum Geology slide 31/888.|
|Site Type: ||Pit|
|Site Status: ||PASSI|
|District: ||Antrim Borough Council|
|Grid Reference: ||J130733|
|Rock Age: ||Quaternary (Early Midlandian, Late Midlandian, Middle Midlandian)|
|Fossil Groups: ||Plant, Vertebrates|
|Other interest: ||No data, Glaciotectonic, Interstadial, till|
Summary of site:
Aghnadarragh is an artificial outcrop in the wall of a large open pit which was cut to expose Oligocene brown coal and to test the mechanical properties of the overlying Pleistocene sediments. These Pleistocene deposits record a series of events at the close of the last interglacial period and the onset of Irelandís last major glaciation, the Midlandian. It is the most complete Midlandian sequence in the British Isles and is of international importance.
10 discrete beds are present in the sequence. Starting at the base these are:
- Oligocene lignite heavily disrupted by glacial action.
- A glacial till 5m thick containing glacial erratics recognisable as igneous rocks from Co. Tyrone.
- The till grades into a thick bed of mud.
- The mud grades over 30cm into 3m of thin beds (laminations) of sands, some with ripple marks.
- A unit of diamict (sediment of mixed grain sizes, up to pebbles), around 5m thick, incorporating lenses of sand and sandy mud. Skeletal remains of woolly mammoth are frequent in this bed and the only known remains of musk ox in Ireland (a skull and teeth) were found at this level. Modern dating techniques suggest ages of between 75,000 and 95,000 years for the mammoth remains, making them the oldest in Ireland. Pollen grains from the bed reveal an Arctic flora.
- A layer of peat with recognisable woody remains of pine, spruce and birch, plus pollen grains of hazel. Beetle fragments are of species now only found in Scandinavia.
- A unit of pebbly sands, gravels and diamicts.
- A thin layer of organic mud and thin sands yielding pollen of sedges and grasses and remains of insects now only found in Arctic Scandinavia.
- A thick sequence of faintly bedded sands with some beds showing deltaic structures.
- A glacial till up to 7m thick dominated by basaltic material with some chalk.
The section tells a clear story of fluctuating climatic conditions. Bed 1 is bedrock and the till of bed 2 was deposited on it by an ice sheet flowing from the west. Beds 3 and 4 are clear evidence of a meltwater lake in the front of a glacier, at a time of intense cold. The conditions revealed in bed 5 are again intensely cold but with an Arctic flora sufficient to support herds of woolly mammoth and musk oxen in summer. The ground was frozen to a considerable depth but in summer the surface thawed into a mantle of slushy, gravely mud that rafted dead animals and their bones down slope. Bed 6 shows a significant climatic improvement to conditions, slightly colder than today, which persisted long enough to allow pine, spruce and birch to migrate north and form local forests. Bed 7 suggests a climatic cooling while the grasses and sedges of bed 8 indicate a return to a cold, harsh and treeless landscape. The thick sands of bed 9 represent the margins of a wide sand plain, expanding in front of advancing glacial ice, which eventually mantled the area and deposited the glacial till of bed 10.
The exceptional range of interest and the unique clarity of Aghnadarragh make it a classic site, not simply in Northern Ireland, but world-wide. It is one of only a handful of elite sites of this age and, as such, it is of supreme national and international importance. There are conservation problems, however, caused by the unconsolidated nature of the sediments and the flooding of the pit.
Vertebrate remains are preserved in the collections of the Ulster Museum.