Million-year lag times in a post-orogenic sediment conveyor

Area of Science:

• Geomorphology
• Quaternary Science
• Isotope Geochemistry

Background:

• Interpreting Earth's geologic record requires understanding how external forces like tectonics and climate are recorded in sediments.
• Sediment transport and storage dynamics can significantly alter, delay, or erase these signals, complicating geological interpretations.

Purpose of the Study:

• To estimate sediment transit times within Australia's Murray-Darling basin.
• To investigate the impact of sediment recycling on the fidelity of tectonic and climatic signals in river systems.

Main Methods:

• Utilized cosmogenic nuclide dating, specifically measuring downstream changes in aluminum-26/beryllium-10/carbon-14 (²⁶Al/¹⁰Be/¹⁴C) ratios.
• Analyzed modern river sediment samples from the Murray and Darling rivers.

Main Results:

• Sediments in the Murray-Darling basin exhibit multiple episodes of burial and reexposure.
• Cumulative sediment lag times exceed 1 million years in the downstream reaches of the Murray and Darling rivers.
• Low sediment supply rates and extensive old sediment cover characterize the landscape.

Conclusions:

• Sediment recycling is a significant and ongoing process in the Murray-Darling basin.
• This recycling substantially delays and modifies environmental forcing signals originating from the river system's hinterland.
• Accurate interpretation of the geologic record is challenged by these complex sediment dynamics.