Offa's Dyke Path 6 Panorama EarthCache
Offa's Dyke Path 6 Panorama
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The unusual tilted layers of this cache are part of an underwater system of dunes that formed as part of a huge delta about 325 Ma (million years ago). These rocks are part of a geological Site of Special Scientific Interest (SSSI).
This EarthCache is one of a series of caches along the Denbighshire section of the Offa’s Dyke Path. Together they explore the rocks and landscape underpinning the heritage, culture and biodiversity of the area.
These rocks on The Panorama above Llangollen are a geological puzzle. Each layer of rock is only a few centimetres thick. The colours of the layers alternate between pale buff and yellow. The layers or ‘beds’ were probably formed by tides in a warm tropical sea. Together they form an underwater sand dune. The puzzle is how they were formed.
The lane here is called the Panorama as it has panoramic views high above the Vale of Llangollen and the Dee Valley
During the Carboniferous Period, between 350-290 Mathis part of Wales lay south of the equator. It had a tropical climate with huge rivers with coastal deltas hundreds of miles across. In slightly deeper water, limestone was forming from coral reefs and many other marine creatures (see ODP 5 Trevor Quarry EarthCache). Huge tropical forests dominated the land.
Sand and other sediment was carried by huge braided rivers from the land to the sea. When the rivers flowed out to sea through the deltas, the sediment dropped to the sea bed. This happened particularly at ‘slack tide’. A slack tide is at either high-water or low-water when the tide direction changes from flow to ebb or vice versa. Each thin layer in the rock is thought to be one slack tide. This is why there are two alternating types of bed, one for high-water and one for low-water. The waves and sea currents shaped these sands into dunes. The results are similar to those we see today on land.
The huge braided rivers and deltas formed about 330 million years ago, when Wales lay south of the equator, about the same position as the tropical rainforests of Africa & South America today. Since these sand dunes were formed, the plates of the Earth’s crust have moved north and have passed through several climatic zones and been uplifted by mountain-building events, from beneath the sea to where they are now around 450 metres above sea level.
To log this Earthcache:
1. How thick are the individual layers of sand?
2.. Do the layers you have just measured extend into the rock unit above?
Additional Hints
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