Geological History
The geological history of the Falkland Islands began more than 1000 million years ago, before they existed as separate islands. The breakup of Gondwana led to the formation of a large number of minor crustal fragments, including the Falkland Islands. At first, the fragment containing the islands separated from the southeastern part of Africa on a section that would become Antarctica and later rotate by almost 180°. The interior of Gondwana was based on with crystalline rocks more than a billion years old; in the Falklands today these are found in the Cape Meredith complex. Sediments of sand and mud filled and eventually covered the developing continental rifts. Later the sediments covering the rifts hardened into rock, forming layers of rock known as rock sequences. These rock sequences from Gondwana's break-up can be identified in places as far apart as South Africa, western Antarctica, and Brazil. In the Falkland Islands these sequences are known as the West Falkland Group.
Two hundred million years ago, tectonic forces tore Gondwana apart. Sheets of liquid basalt intruded into the cracks that formed between the sedimentary layers. The resulting solidified sheets can now be seen in the form of dikes that cut the oldest sedimentary layers, those that lie principally in the southern part of East Falkland and in South Africa.
Tectonic forces continued to form the region: a mountainous chain formed, part of which now creates Wickham Heights on East Falkland Island and extends westwards through West Falkland into the Jason Islands. A basin developed and was filled with land-based, or terrigenous, sediments. These layers of sand and mud filled the basin as it sank and as they hardened they produced the rocks of the sedimentary Lafonia Group of the Falklands. These rocks are similar to those in southern Africa's Karoo basin.
About 290 million years ago, in the Carboniferous period, an ice age engulfed the area as glaciers advanced from the polar region eroding and transporting rocks. These rocks were deposited as extensive moraines and glacial till, or they sank in the sea while the glacier floated in a layer of ice. When the glacial sediments were turned into stone they formed the rocks that now make up the Fitzroy Tillite Formation in the Falklands. Identical rocks are found in southern Africa.
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