Ancient landscape evolution tracked through cosmogenic krypton in detrital zircon

Area of Science:

• Geomorphology and Quaternary Science
• Isotope Geochemistry
• Sedimentary Geology

Background:

• Cosmogenic nuclides are crucial for quantifying landscape processes like erosion and exposure.
• Previous methods had limitations in extending the temporal reach for landscape evolution studies.
• Detrital zircon is a valuable mineral for geochronology and geochemical analysis.

Purpose of the Study:

• To extend the temporal limits of cosmogenic nuclide applications using stable cosmogenic krypton in detrital zircon.
• To reconstruct Eocene landscape evolution in southern Australia using drill core data.
• To investigate paleodenudation rates and sediment transport dynamics in ancient landscapes.

Main Methods:

• Integration of stable cosmogenic krypton (Kr) measurements in detrital zircon with U-Pb geochronology.
• Analysis of drill cores from Eocene placer deposits in southern Australia.
• Calculation of paleodenudation rates and apparent exposure times from cosmogenic Kr concentrations.

Main Results:

• Zircon U-Pb ages indicate paleodrainage from a ~800,000 km² hinterland via a ~1,000 km littoral drift system.
• Cosmogenic ⁷⁸Kr concentrations suggest low paleodenudation rates (0.3–0.7 m/My), potentially underestimated due to re-exposure.
• Apparent exposure times range from 0.9 to 2.1 million years (My), indicating a shift from prolonged sediment storage to a more dynamic transport regime.

Conclusions:

• Stable cosmogenic krypton in zircon provides a novel approach to reconstruct long-term landscape evolution.
• The study reveals a transition in sediment dynamics during the Eocene, influenced by eustatic and tectonic factors.
• This method enhances our understanding of the coevolution of ancient landscapes and sedimentary records.