Posted by: Rob Viens | March 23, 2013

The Slow Boat from Africa (Falkland Geology Part II)

Today you can cross the Atlantic in less than a day.  It took Darwin the better part of a month back in February of 1832.  For the Falkland Islands, the trip took well over a hundred and twenty-five million years. Though to be fair, the Atlantic did not exist when the islands started their journey, so in some sense they didn’t move at all – the space around them just “expanded” from the ever-continuous motion of the Earth’s surface.

That’s right – if you go back far enough – say about 300 to 400 million years – you would find the Falkland Islands located southeast of the southern tip of Africa in the middle of a large continent known as Gondwanaland.  Around 250 million years ago Gondwanaland collided with other continents to form the well-know “supercontient” of Pangaea.  Though, like all things on the Earth, Pangaea was a temporary feature, and it too split apart forming the northern continent of Laurasia and the southern continent of Gondwana. (Yes, I’m a geologist and the similar naming of these landmasses still messes me up sometimes!)  After about 200 million years ago Gondwana – made up of the present day continents of South America, Africa, Indi, Australia and Antarctica – began to break up piece by piece, separating into the modern continents of the southern hemisphere.

Throughout this time, the Falkland Islands remained isolated near the center of a continent (whether it be Gondwanaland, Pangaea or Gonwana). The rocks found in the islands tell the story of the rise and fall of sea level and the coming and going of glaciers (as discussed in the previous post). And like a GPS tracking device, they help to reveal the former location of the islands.  One way they do this is through affinity – all of the major rock units in the Falklands match up with rock units in South Africa.

For example, the FitzRoy Tillite matches up Dwyka TIllite in South Africa – representing a time when the continent of Gondwanaland was located near the south pole and covered in ice (much like Antarctica is today). Darwin’s fossils from the West Falkland Group match fossils in the Cape Supergroup, and the Lafonia Group correlates with the rocks of the Karoo Basin. The evidence is in the rocks. Like pieces of a puzzle, the Falkland Islands and South Africa, when placed together, create a “picture” that makes sense.

FitzRoy Tillite and the Dwyka Tillite – now separated by the Atlantic Ocean (Dwyka Tillite image from the blog Clastic Detrius; FitzRoy from the British Geological Survey)

Tillite

Here is an example of a geologic map showing the Falklands in their ancient homeland along the coast of Africa and the similarity of the rock units (note that some of the units have slightly different names in this map from those discussed earlier / from the British Geological Survey):

Paleozoic map of Falkland Islands

Around 125 million years ago, South America and Africa began to diverge from one another and the young Atlantic Ocean was born.  This continuous “spreading” led to the opening up of the Atlantic Ocean and the slow by steady movement of South America and the Falkland Islands away from Africa.

Notice that in the geologic map above, the Falkland Islands are “upside down” relative to their modern orientation.  This is because, during their 125 million year journey, the fragment of crust on which the islands sit rotated about 180°.  How cool is that!

The journey of the Falkland Islands from about 350 to about 100 million years ago:

Falkland Island Plate Motion

By the way – no new entries from our man in the field.  Darwin’s diary was still experiencing a rather quiet spell in the Falklands. (RJV)

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Responses

  1. […] land masses for over 100 million years (for more on the movement of South America, see The Slow Boat from Africa (Falkland Geology Part II)). This isolation caused some species to divergent (such as the New World monkeys that evolved along […]

  2. […] PS – For more on the geology of the Falklands see Falkland Geology Part I: Ancient Shells and Glacial Remains and The Slow Boat from Africa (Falkland Geology Part II). […]


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