The Devonian Period

The Taklamakan Desert in China - a comparable present day environmentZoom Map to show locations of Shetland's Devonian rocksZoomThe Devonian Period followed the closure of the Iapetus Ocean when early versions of North America and Europe collided, forming the continent of Euramerica and the huge Caledonian mountain chain - the remains of which can be seen as far afield as North America, Ireland, Scotland and Scandinavia today. It is named after Devon, in south-western England, where marine sedimentary rocks of this period were first studied. Elsewhere in Britain the Devonian is represented by terrestrial sediments comprising mainly distinctive red and brown sandstones which are collectively known as 'Old Red Sandstone'.? The Devonian extends from 416 million years ago to 359 million years ago, although Shetland's Devonian rocks were formed from 394-384 million years ago. At this time the rocks of northern Britain lay just south of the Equator and far inland, with mountains to the northwest and the open sea to the south-east. Between the mountains and the sea was a vast desert plain. ?The climate varied from warm and humid to dry and arid in cycles of several thousand years driven by the Milankovitch cycles of Earth's orbit round the Sun. It was a volcanically active time throughout Scotland and volcanic rocks from this period can be found near Oban, in Fife, and east of Jedburgh in the Scottish Borders as well as on Shetland. Theexposed remains of magma chambers that once fed the volcanoes can also be seen in Shetland and many parts of Scotland.