Australia: The Land Where Time Began

A biography of the Australian continent 

Argo Abyssal Plain                                                                                                                   

This abyssal plain lies in the Indian Ocean off northwest Australia. Seafloor spreading in this plain began about 154.3 Ma, during the Jurassic (Oxfordian). It was the spreading of the seafloor as Argoland moved away from the Australian coast that allowed the sea to flood the Canning Basin. It is believed that the separation of Argoland may have led to an island chain that maintained a connection with Asia for a period before eventually becoming attached to the Asian landmass, forming Sundaland, as the spreading progressed.

The seafloor spreading that led to the separation of Greater India from Australia began about 136-131.9 Ma. To the east of Australia, at about this time, long-term subduction ceased. Subduction of the Phoenix-Pacific spreading ridge is believed to have been responsible for cessation of subduction, changing this plate boundary to a transform margin.

At about 99 Ma, there was a large change in the direction of spreading between India and Australia, from NW-SE to N-S.

At about 95 Ma, rifting began between Australia and the Lord Howe Rise, the result of which was the opening of the Tasman Sea about 84 Ma.

About 61 Ma (chron 27), the spreading direction between Australia and Antarctica changed from NW-SE to N-S, and rifting between Broken Ridge and the Kerguelen Ridge began. At this time the Coral Sea began to open off the NE coast of Australia, and there was a change in direction of spreading between the Australian Plate and Antarctic Plates It has been suggested that the stepwise subduction of the Neo-Tethyan Ridge may have cause the events at 99 Ma and 61 Ma. It has also been suggested that the 99 Ma change may even have been caused by a change in the motion of the Pacific Plate.

At 43 Ma it is believed that a tectonic event may mark the resumption of subduction east of Australia. A triple junction from north of the Ross Sea before 43 Ma that accommodated incipient motion between East Antarctica and West Antarctica. At the same time spreading ceased in the Wharton Basin between India and Australia. Subduction of the Solomon Plate north of New Guinea commenced, probably in the Late Eocene. Since 20 Ma, the Indo-Australian Plate broke up and there were various collisions and reorganisation of plate boundary north and east of Australia.

Sources & Further reading

  1. After the Greening, The Browning of Australia, Mary E. White, Kangaroo Press, 1994
  2. J. J Veevers (ed.) Billion-year earth history of Australia and neighbours in Gondwanaland, GEMOC Press Sydney, 2000


Sedimentation of the Argo and Gascoyne Abyssal Plains NW Auastralia: report on Ocean Drilling Program Leg 123 (Sep 1- Nov 1, 1988)

The seafloor-spreading history of the eastern Indian Ocean


Author: M. H. Monroe
Last Updated 18/08/2012

Australian Palaeoclimate and Palaeogeography - Jurassic


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