silurian
The Silurian lasted from approximately 439 to 409 million years ago, and was a time of a fairly warm climate, with a significant amount of tectonic activity as the Iapetus Ocean began to close and England and Scotland (separate at this point) gradually became closer together. Sea levels throughout the period rose throughout the Early Silurian as the glacial ices from the Ordovician were continuing to melt, and then began to fall again as the period concluded. This flooded low-lying areas, so the main geology from the Silurian in Britain is marine sediments that are found in mainly Wales, Southern Scotland and Ireland and the Lake District.
England and Wales were about 30°S of the equator, creating a warm, tropical marine environment where life was able to flourish in shallow zones. This lead to the deposition of limestones and shales rich in fossils such as bivalves, brachiopods and trilobites and the famous landmark of Wenlcock Edge is a significant outcrop for some of the carbonate depositions consisting of corals, crinoids and stromatoporoids, showing a significant period where there was a lush, tropical climate.
In Central Wales and the Lake District, turbidite currents indicate the presence of an ocean basin, where inbetween these turbidites there are periods where only soft, fine muds were deposited which preserved graptoites and orthocones exceptionally well, but also indicates time where there was stagnation in the ocean basin with anoxia.
Significant volcanic activity South Wales occurred, as in Pembrokeshire mafic lava flows can be found to have extruded onto the land, and can also be found around Bridgend, Cardiff, near Bristol and around the Mendip Hills. As well as this layers of fine ash can be found in strata throughout the Silurian Geology, so England and Wales would have been part of a fairly volcanic area. .
Significant volcanic activity South Wales occurred, as in Pembrokeshire mafic lava flows can be found to have extruded onto the land, and can also be found around Bridgend, Cardiff, near Bristol and around the Mendip Hills. As well as this layers of fine ash can be found in strata throughout the Silurian Geology, so England and Wales would have been part of a fairly volcanic area. .
In Scotland, on the other side of the closing Iapetus Ocean, marine sediments were also the dominate environment of the period with two contrasting environments existing. Firstly to the north and north west of the Southern Upland fault shelly marine sediments from a shallow water environment can be found, consisting of mainly sandstones and shales, indicating a fairly calm environment of depositions. On the other side of the Southern Upland Fault, there can be found very dark black shales containing many fossils of graptolites , indicating an anoxic deep marine sea environment, and overlaying these were layers of coarse greywacke deposited by turbidity currents.
As the Silurian period drew to a close temperatures began to increase and the collision of Avalonia and Baltica lead to a continental uplift giving rise to the deposition of Old Red Sandstone facies which became the main strata for the following period, the Devonian.
As the Silurian period drew to a close temperatures began to increase and the collision of Avalonia and Baltica lead to a continental uplift giving rise to the deposition of Old Red Sandstone facies which became the main strata for the following period, the Devonian.