#caledonian mountains

[mineralsrocksandfossiltalks]

Monday Musings: The Beginnings of Mountains

The Silurian Period started at the end of the Ordovician Period 443.8 Ma and ended at the beginning of the Devonian Period 419.2 Ma. This was a time of rising seas as the Ordovician glaciers melted. If you recall, these glaciers caused a mass extinction. Because sea level rose so much, new marine environments were created including many warm shallow seas as deep ocean basins closed because continents were moving closer together. These warm shallow seas allowed the first coral reefs to form.

At the beginning of the Silurian Period, a large ocean sat over the north pole while Gondwana was still over the south pole. Fragmented landmasses such as Laurentia, Avalonia, and Baltica hovered around the equator.

There wasn’t a huge variety in topography but there was a significant mountain-building event throughout the entire period. The Caledonian Orogeny, named for the Latin name of Scotland, was the convergence of Avalonia, Baltica, and Laurentia. This happened in a series of phases: the Grampian Orogeny, the docking of Eastern Avalonia with Baltica, the Scandian phase and the Acadian Phase.

The Grampian Orogeny was the result of Laurentia (North America) colliding with an ocean island arc (Scotland and northern/western Ireland). This collision actually occurred in the middle Ordovician at about the same time as the Taconic Orogeny, an early mountain-building event in New England that began the Appalachians.

At the end of the Ordovician, eastern Avalonia and Baltica collided in a more gentle convergence called a docking. This created what is called the Trans-European Suture Zone from the North Sea close to Denmark, through part of the Baltic Sea and Poland, then follows the Eastern Carpathian Mountains of Ukraine to the Black Sea.

During the early Silurian until the mid-Devonian, the Scandian phase occurred. This was the result of the Fennoscandian peninsula colliding with Greenland. It also created thrusting in the Northern Highlands of Scotland and the Outer Hebrides.

The last phase occurred during the Devonian Period. The Acadian Orogeny was the final mountain-building event for the Appalachian Mountains. It also involved connecting England and Wales to the rest of Great Britain (they were part of Avalonia rather than the island arcs).

Altogether, this orogeny was the start of building the great Central Pangean Mountains that would exist from the Carboniferous through the Triassic.

 Thanks for coming to today’s lesson and tune in tomorrow to participate in some trivia! Fossilize you later!

[mineralsrocksandfossiltalks]

Monday Musings: The Central Pangean Mountains

The mountains we know today have not always existed. In fact, several mountains have come and gone over the millenia. Some of our mountains are remnants of these ancient ranges. One such ancient mountain range was the Central Pangean Mountains.

These mountains formed when Gondwana collided with Euramerica during the Carboniferous Period 340 million years ago. They were a northeast-southwest trending mountain range. There were several different orogenic events (mountain-building) that built this range until it reached its maximum height in the early Permian Period.

The mountains sat near the equator meaning the climate was tropical. Climate models suggest that the mountains were responsible for the large peat bogs that now form the vast coal deposits from Carboniferous rocks. The mountains formed an area of intense precipitation with no dry season allowing for intense growth.

By the early Jurassic most of the mountains had been reduced to little more than hills. Remnants of this massive mountain range still exist though. The Atlas Mountains in northern Africa,

The Caledonian Mountains in Scotland and Scandinavia,

and the Appalachian Mountains of North America are some of those remnants.

Tune in tomorrow for some mountainous trivia. Fossilize you later!

[mapsontheweb]

The Caledonian Mountains used to stretch from Norway and Greenland down to Florida and Morocco. They were created when two continents collided) and were doomed when when North America split off from Europe and Africa.

[uk-fossils]

The Armboth Dyke, Lake District

The Armboth Dyke makes a good half day geology excursion in a scenic but quiet part of the UK Lake District. Parking is on the west shore of Thirlmere, in a pay-and-display car park accessed by the narrow road that winds around that side of the lake (Grid reference NY 305 172). The car park is in an excellent setting, with direct access to the wooded lake shore, and would be a great place for the…

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[earthstory]

The Devonian The Devonian Period starts 416ma and extends to 359ma ( see www.stratigraphy.org for the latest information on boundaries), and is named after the county of Devon, in England, where rocks from this period were first described. In classical geology text books the time period is known as “The Old Red Age” referring to the abundance of “Old Red Sandstone” a common rock type found from this period. (We wrote a post on the Old Red Sandstone a couple of months back; http://www.facebook.com/photo.php?fbid=358835994177451&set=a.352867368107647.80532.352857924775258&type=3). It has also been described as the “Age of Fishes” in reference to the evolution of several major groups of fish, which occurred during this time period.

The Devonian has often been described as both a Greenhouse world, and a hot-house world, but this could be a bias from the available evidence. Many of the samples taken for palaeoclimate work come from Western Europe, where Devonian age rocks and preserved beautifully and in great abundance; however, palaeogeography has shown that during the Devonian this area sat upon the equator. (http://www.sciencedirect.com/science/article/pii/003101829390034G) Tectonics and Palaeogeography; During the Devonian all of the world’s land masses were concentrated into two supercontinents Gondwana and Euamerica, and these two supercontinents were surrounded on all sides by subduction zones. This set into motion the formation of the supercontinent Pangea, which finally came to be during the Permian period. Sea level was relatively high in all locations and much of the land mass was under shallow seas. There were several mountain building events associated with the collision of Gondwana and Euramerica; The building of the Caledonian mountains in Europe and the Appalachian in North America, as well as the intrusion of large volumes of Granite in North America. The Antler orogeny in now modern day Mississippi also occurred, and this was the uplift of deepwater deposits found on the continental shelf. Palaeoclimate The Devonian has been described as a greenhouse world and it is likely that there were no Ice caps or glaciers on the Earth at this time. Evidence from fossils suggests that during the early Devonian average Sea Surface Temperatures were 30 degrees Celsius, however with the growth of forests on the continents carbon levels in the atmosphere dropped and there is evidence of the 5 degrees Celsius drop in temperature during the middle Devonian. Towards the end of the Devonian temperature started to elevate towards levels seen during the Early Devonian, and whilst there is no evidence that Carbon levels also increased, greater continental weathering and plant fossils support the increasing temperature claim. Life and Extinction Devonian seas were dominated by brachiopods and tabulate and rugose corals. These corals along with encrusting red algae built extensive reef systems. Bivalves, crinoid and blastoid echinoderms, graptolites, and trilobites can also be found in Devonian strata, however the trilobites had all but disappeared towards the end of the Devonian. The Ammonoids had also started to appear, and limestone from the Devonian period is often found with their shells preserved in. On the land terrestrial vegetation had started to spread and radiate, and with this came the first soils. These early land plants would have been no more than a few centimetres tall, and among them would have lived primitive wingless insects, and although a few isolated fossils have been found not much is known about these early insect forms. By the late Devonian we see fossils of lycophytes, sphenophytes, ferns, and progymnosperm preserved. It was during the Devonian that the first seeds also appeared. A major extinction occurred during the early part of the last stage of the Devonian period, one fo the “Big 5” Mass Extinctions, it is known as the “Late Devonian”. It mainly effected the warm, shallow water marine communities, including fish, corals, algae, brachiopods, trilobites, ammonites, conodonts. Land plants and freshwater species such as the early tetrapods appear to have been unaffected by the extinction event. There is no clear cause for the Late Devonian mass extinction, although bolide impact has been suggest. Whilst there are craters of Devonian age, none found have been large enough to have caused the event, however any impact into the ocean would have been long ago subducted, so the evidence will no longer exist. -LL Links for more information; http://www.devoniantimes.org/index.html http://www.ucmp.berkeley.edu/devonian/devonian.php http://science.nationalgeographic.com/science/prehistoric-world/devonian/ http://www.scotese.com/newpage3.htm http://park.org/Canada/Museum/extinction/devmass.html http://www.mvr.usace.army.mil/coralville/devonian_fossil_gorge.htm http://www.fossils-facts-and-finds.com/devonian_period.html