Earth Seminar 30 October - Dr Agathe Lise-Pronovost

Dating long paleoclimate sediment records from Tasmania: a multi-proxy approach 

Abstract

Lake sediment archives covering several glacial cycles are scarce in the Southern Hemisphere and they are challenging to date. In this seminar, I will present recent work retrieving and dating long paleoclimate sediment records from western Tasmania, Australia: Lake Selina (5.5 m and 270 ka) and Darwin Crater (61 m and 800 ka). These records provide an opportunity to explore how terrestrial environments respond to large-scale and rapid climatic change and contribute to debated issues such as megafauna extinction and the impact and timing of human arrival on the Australian continent. However, their tractability depends on the ability to obtain a reliable chronology. 

The chronostratigraphy of Lake Selina was developed using a multi-proxy approach including radiometric dating (radiocarbon and OSL) and relative dating (paleomagnetism, authigenic ¹⁰Be/⁹Be ratio and climate comparisons). The Laschamp geomagnetic excursion (41 ka) is identified for the first time in Australia and provides a practical example for combining authigenic ¹⁰Be/⁹Be ratio and paleomagnetism to constrain the chronology of lake sediments. High-resolution XRF core scanning, beryllium isotopes and magnetic properties enable a matching of the sediment archive from Tasmania to ice core records of climate proxies in Antarctica. This agreement was used as a basis to date material beyond the range of radiometric methods (>80 ka) via a dynamic programming algorithm. A similar approach could be useful for dating Darwin Crater. The first results from core logging and multi-proxy analyses provide clear signatures of alternating, distinct glacial and interglacial lithologies, thus indicating good potential for tuning to changes in orbital geometry and associated insolation changes and global-scale climate records. 

Lise-Pronovost et al, 2019 Scientific Drilling https://sd.copernicus.org/articles/25/1/2019/ 

Biography

Agathe Lise-Pronovost is a paleomagnetist working in the fields of Geochronology, Quaternary climates, and Archaeological Sciences. She is currently a McKenzie Fellow in the School of Earth Sciences at the University of Melbourne. Prior to this she was a research fellow in Archaeomagnetism at La Trobe University, and she holds a PhD in Oceanography from the University of Quebec (Canada). 

Agathe is interested in the behavior of the Earth magnetic field through time to develop paleomagnetic dating. Her recent work focuses on the Southern Hemisphere and the Australasia region using a range of archives (marine and lake sediments, archaeological and historical artefacts, speleothems, and volcanic rocks). She is also passionate about promoting magnetism for paleoclimate and archaeology. She uses the magnetic properties of geological archives and artefacts as a versatile tool for multi-disciplinary investigations of past climates, ancient technologies, site occupation, and sourcing.