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39

 

THE EVOLUTION OF THE EARTH’S CRUST

The Movement of Sedimentary Rocks

 

Chalk and limestone are very brittle substances and easily fracture under distortion. Many sedimentary structures were formed when the the Earth was much smaller in diameter and so their cords were more curved. As the Earth increased its size these cords had to ‘flatten out’. This flattening out caused the slabs to fracture into grids.

 

In areas where the more ductile rocks underlying these chalk sediments have undergone ‘necking’ or multi-axial creep, these fractured chalk slabs have separated from each other. This separation phenomenon can be illustrated by pasting some squares of card onto a balloon. When the balloon is additionally inflated, the pieces of card separate.

 

 

 

 

 

 

 

 

 

 

 

 

 

This phenomenon can be seen in the south-east of England. The white cliffs of Dover, for example, were once continuous with the white cliffs of Cap Blanc Nez, near Calais, France, but are now 35 km apart. The Beachy Head cliffs at the edge of the South Downs, accordingly, were at one time, contiguous with those around Etaple in France.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

By dating the uppermost layers of chalk, we can determine when the separation of the slabs began to take place, and this was likely to have been at the time when the Atlantic Ocean bed was starting to form, about 48 million years ago.

 

Limestones are similar sedimentary substances to chalk but the organisms that went into building them were very different. These were the graptolites, brachiopods, corals, foraminiferas, radiolarias, bivalves, depending upon the specific age of the limestone. By analysing the types of species in these limestones, we can date them and also confirm that slabs, now separated, were originally continuous with each other.

 

Limestones are often described as Karst Landscapes when they too have fractured into grid-like structures. The degree of separation between segments of the grid betrays the degree of stretching of the underlying basement.

 

For example, karst landscapes in South China must have a thick crust underlying them - because their segments have not separated much from each other - their ‘egg box’ appearance is largely due to erosion between their segments. However, the Indonesian and Philippine archipelagos are examples where their limestone fragments have been separated great distances from their former neighbours, and so the underlying crust will be thinner and more stretched.

 

With this in mind, we can extrapolate to their original positions and this enables the Indonesian and Philippine archipelagos to be re-positioned around the Thailand/Malaysian peninsula and the coast of Viet-Nam and China, in accordance with my Pangaean Model.

 

 

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