From the starting of the Cainozoic geological era, Australia is moving northwards at the rate of 7cm per year. During this era, at the same time, Eastern Australia encountered a powerful earthquake in the form of a tectonic uplift which leading to Queensland moving inland due to drainage divide. Due to the tectonic uplift, the continent also experienced a series of volcanic eruptions, leading to an erection of central and shield volcanoes and basalt streams. These volcanoes and basalt flows over time, cooled down, and settled down into huge high islands.
After forming the Coral Sea Basin, coral reefs began to nurture, but Queensland’s climate was still cold enough to support coral growth. About 25 million years back, Queensland floated into the tropical waters, the complex geological changes in coral reefs began to occur. Depending on how sea levels change, the growth and recession of coral reefs also change as they don’t grow deep in the ocean in need of sunlight, and neither can they grow above sea level. Their growth change can range from a diameter of 1cm to 3cm every year and vertically, 1cm to 25cm.
The land that forms the base for the coral reef to grow and other marine species to sustain are the remains of the sediments of the Great Dividing Range, Australia’s most extensive mountain range. When Queensland floated into the tropical waters 25 million years ago, coral reefs started to develop. Still, the creation of river deltas and oozes due to sedimentation from the Great Dividing Range harmed coral growth. The substrate of the Great Barrier Reef may have had to considerably build up so that it was far away enough from further sedimentation of the mountains.
Today’s structural base on which the new corals are growing is supposed to have formed 20,000 years ago. From 20,000 years ago till 6,000 years ago, sea levels grew progressively, and as they increased, coral reefs started forming on hills rather than on coastal plains. The hills became continental islands with growing sea levels, and corals grew around them as time went by. When the islands submerged, the reefs grew on them, known as the cays/reefs. In present times, the sea level has not prominently increased over the last 6,000 years. The present reef structure is estimated to be 6,000 to 8,000 years old.
The ancient remains of the Great Barrier Reef can be found at Kimberly, in North-Western Australia.
The Great Barrier Reef Heritage Area has been divided into 70 bioregions, 30 are reef bioregions, and 40 are non-reef bioregions. Coral reefs are categorised according to their types: Fringing reefs, Lagoonal reefs, Crescentic reefs, and Planar reefs and they together form the Great Barrier Reef or, as they call it - GBR.