The Iapetus Ocean existed for some180–200 million years but then disappeared again as the crustal plates collided back together in a new configuration of continents. That collision ultimately created the Caledonian mountain belt, in an event which geologists call the Caledonian Orogeny. Scotland now preserves only the roots of that ancient mountain belt, which originally is likely to have been comparable in scale to the Himalayas. The rocks of the Caledonian mountain belt in Scotland are similar in many respects to rocks of the same age now preserved from eastern Greenland to the Appalachians, all of which experienced the Caledonian Orogeny. The metamorphic and igneous rocks hat dominate the bedrock geology of Northeast Scotland preserve a record of that Caledonian episode of Earth history. Younger sedimentary rocks deposited on these metamorphic and igneous rocks record the later history of the Caledonian mountain belt, including the start of a long period of erosion which has continued through the recent glacial history of the region until the present day.
Geologists refer to the oldest rocks which we now see in the northeast of Scotland as the Dalradian. These rocks,which date back to the Precambrian Era, tell us the history of the ancient 'Scottish' margin of the Iapetus Ocean. Layers of sand, mud and limestone accumulated first in relatively shallow, near-shore marine conditions but in time, as the Iapetus Ocean began to develop and the ancient continents moved farther apart, sediments and volcanic deposits accumulated in deeper and deeper water farther from the coastline. Similar sequences of sedimentary and volcanic rocks, developed at the European continental margin of the North Atlantic over thelast 60 million years, provide a good indication of the Precambrian rocks that would have formed along the 'Scottish' margin of Laurentia. Most of these Dalradian sediments accumulated at a time before the Cambrian explosion of life on Earth, and so the Dalradian rocks of Northeast Scotland contain no shelly fossils.
The Dalradian sediments were all deeply buried, heated and compressed as a consequence of the Caledonian mountain-building event. Soft sediments were converted to sedimentary rock, then further deformed and metamorphosed so that we now find schists and marbles instead of the original sandstones, mudstones and limestones. As the rocks were squeezed between the converging crustal plates, the rock layers were folded and contorted, and often turned upside down. The resulting fold structures can be seen in many places along the Moray Firth coast. As these rocks were compressed and heated during deformation,crystals of new metamorphic minerals grew in the rocks. These crystals were typically aligned parallel to each other, so that the metamorphic rocks we now see at the surface have a marked tendency to split more easily in a single preferred direction. The metamorphic minerals recognised in the rocks of Northeast Scotland are different in detail to those found in the metamorphic rocks of the southern Highlands. Over fifty years ago, the metamorphic rocks of Moray/Buchan were used by the geologist H.H. Read to define the Buchan zones of regional metamorphism. These differed from another set of zones, the Barrovian zones, which had been defined by George Barrow in the Southern Highlands. Both schemes are now recognised as regional variations in the metamorphism which was generated by building the Caledonian mountain belt, and have been applied worldwide in understanding this type of metamorphism.
The Needle's Eye at Tarlair,is an arch eroded in metamorphosed Dalradian sandstone, these rocks were originally sediments deposited in an ocean in the region of 600 million years ago.An intersting feature of them is that you can still see relicts of some of the original sedimentary structures in them.
To claim this earth cache, email me via my profile ( please do not post in your online log) the answers to the following tasks :
1 ~ How many feet long is the rock running from the top of the Needles Eye to the beach on the Left Hand Side as you look at it and at what angle does it lay ?
2~ How high is the eye (opening) at it's tallest part ?
3~ In the UK, Pre-Cambrian rock formations occur mainly in North Scotland, and can be divided into four groups. Dalradian rocks - which form The Needles Eye - are the youngest of these. What are the other three formations called?
4~ Describe the coloured layers that you see , are they rough/smooth to touch,can you name any of the minerals in the rock ?
Optional task to post a photo of yourself and/or GPS somewhere on the beach here .
You must carry out these educational tasks as required by the Earthcaching organisation as a condition of logging the cache. Logs that do not adhere to these guidelines will be deleted without notification. See www.earthcache.org
Please stay safe at the waters edge, you may get wet at high tide ! Tide times can be found here http://www.bbc.co.uk/weather/coast_and_sea/tide_tables/7/247#tide-details