澳门金沙网站开户网址

Australian beaches were made in Antarctica

作者:钭隗    发布时间:2019-03-08 01:07:10    

By Ian Anderson in Melbourne MUCH of the sand on Queensland’s famous Gold Coast beaches may have come from what is now Antarctica. Geologists have long been puzzled by the presence in the sands along Australia’s east coast of minerals including zirconium silicate, or zircon, which can’t be found in local rocks. But Keith Sircombe of the Australian National University in Canberra believes he has solved the mystery after analysing zircon samples from 10 beaches between Bundaberg in southern Queensland and Mallacoota in eastern Victoria. Sircombe measured the proportion of uranium to lead in each sample. Because uranium decays into lead at a known rate, Sircombe was able to show that the zircon deposits are almost all about 600 million years old, far older than any of the rocks in eastern Australia—but similar in age to Precambrian rocks in Antarctica. At the ScienceNOW! meeting in Melbourne last week, which highlighted the work of leading young Australian researchers, Sircombe revealed that the key to the mystery is a large deposit called the Hawkesbury sandstone in the Sydney basin, which was laid down about 240 million years ago. The deposits of zircon found up and down the coast were washed from this deposit by waves, he argues. But how did the Hawkesbury sandstone form? Australia and Antarctica were then joined as part of the supercontinent of Gondwanaland. Starting about 280 million years ago, eastern Antarctica was lifted up in a similar process to the uplift now taking place in the Himalayas. Sircombe says that a huge river flowed from there to the Sydney basin,

 

Copyright © 网站地图