Geology of the Big Scrub Rainforest (Part 3)

Gondwana

The late Jurassic and Cretaceous marks a very important geological time. It is the time that the huge supercontinent of Pangea broke up. This when Gondwana became its own continent with present day Australia and Antarctica being a large part of a new smaller, but still impressive super-continent. Our region was actually quite close to the pole but, yet temperatures in our area were quite warm because the climate of whole of the earth was warmer and wetter than it is today. Life was abundant because summer days were nearly 24 hours long and the concentration of carbon dioxide in the atmosphere along with the warmth and moisture super-charged plant growth (in fact permanent ice did not exist anywhere on earth at this time). It was at this time that many of the plants synonymous with Australia and more specifically the ‘Bigscrub’ began their evolution (including the plant order Myrtales which includes eucalypts, bottlebrushes and lillypillys).

As the Jurassic gave way to the Cretaceous period big changes continued. India followed by Antarctica began to separate from Gondwana and finally at around 80Ma the Tasman Sea started to form. Prior to the Tasman Sea formation the landmass extended hundreds or even thousands of kilometers to the east before reaching the sea. The Tasman Sea caused major changes to the landscape. This area is known as Zealandia and as separation occurred it sank below the sea and is now known as the Lord Howe submarine rise. A bit like the mythical land of Atlantis, a huge land submerged under the ocean. The Australian continent now finishing only several of kilometres off the coast from the future Cape Byron. The detachment of Zealandia reduced the weight on the eastern side of Australia which then began to rise and form many of the inland ranges that now make up the Great Dividing Range. This continental crust “rebound” would progress over a long time and by the end of the Cretaceous the physical form of Eastern Australia was set for its last major changes through the actions of volcanoes.