Displacement of the Great Divide in north Queensland associated with Neogene lava flows

Abstract

In north Queensland, Australia, the ‘Great Divide’ forms the border between catchments draining into the Gulf of Carpentaria, including the Mitchell River, and those draining into the Coral Sea, including the Barron River. Until recently, it was commonly proposed that what is now the upper Barron River previously drained into the Mitchell River. However, little evidence was presented, and the assertion has been disputed. Our examination of borehole data, combined with accurate surveying of bedrock in the present Barron River channel, provides definitive evidence that paleochannels of the Mitchell River previously drained what is now the upper Barron River subcatchment. Lava that flowed down these channels at ca 1.79 Ma is evident in some of the boreholes and is exposed in the Barron River channel. The lava flows blocked the river channel, diverting the headwaters of the paleo-Mitchell River east into the Barron River, resulting in the western migration of the Great Divide. The consequent reduction in stream energy available to the truncated headwaters of Mitchell River has led to channel infill and aggradation of more than 40 m since the diversion of the Barron River. Subsurface paleochannels may be directing groundwater across the present drainage divide from the upper Barron River catchment into the Mitchell River catchment.

在澳大利亚昆士兰州北部，“大分水岭”形成往Carpentaria湾排水的蓄水区之间的界线，其中包括Mitchell河，往珊瑚海排水的蓄水区，包括Barron河。直至最近，人们普遍认为，现在的上巴伦河曾排入Mitchell河。然而，对此几乎没有提出什么证据，而是一直有争议的。我们对钻孔资料进行的检测，结合对Barron河通道基岩的精确测量，提供了明确的证据表明，以前排水的Mitchell河古河道是现在的上Barron河亚蓄水区。钻孔资料表明，显然，在约1.79Ma熔岩流入这些河道，并出露于Barron河道。 熔岩流阻塞河道，将古Mitchell河的头水向东引入 Barron河，造成大分水岭向西迁移。随之降低的Mitchell河头水能量导致河道充填和自Barron河改向以来的40多米的淤积。地下古河道可能引导地下水跨越从上Barron河蓄水区进入Mitchell河蓄水区的排水划分。

KEY WORDS:

• Australia
• Great Divide
• Barron River
• basalt
• drainage basin
• drainage evolution
• Mitchell River

ACKNOWLEDGEMENTS

We are grateful to Evan McGrath and Giuseppe and Giovanni Galati for their help and for giving us access to their properties. Curtis Link and Dale Heiner carried out seismic surveys to try and locate depth to bedrock in locations without boreholes. Unfortunately, the bedrock was too deep to be detected using the muscle-operated seismic source. We are also grateful to reviewers Gary Jensen and Ian Withnall for their helpful comments.