From Patagonia to Tasmania: Paleo- and Environmental Magnetism of Long Continental Records in the Southern Hemisphere

English Abstract:

The sedimentary archive from Laguna Potrok Aike (52°S), Argentina, is the only continuous paleoenvironmental record from continental Patagonia that reaches back to the Last Glacial Period (106 m; 51,200 cal BP). On the other side of the hemisphere, Darwin Crater (42°S) in Tasmania, Australia, contains another long lacustrine sediment sequence (60 m) that spans several glacial cycles (< 780,000 cal BP). These two sites are critically located at the northern and southern limit of the Southern Hemisphere westerly wind belt, thus providing a unique opportunity to reconstruct past changes in aeolian activity and paleoclimate at both regional and hemispheric scales. Here we present rock-magnetic proxies of dust and wind intensity from the recent Potrok Aike Maar Lake Sediment Archive Drilling Project (PASADO) within the framework of the International Continental Drilling Program (ICDP). We also discuss preliminary results for a future continental drilling project at Darwin Crater in Tasmania. We will overview how the magnetic properties and physical grain size data from the PASADO record were used to develop magnetic proxies of dust and wind intensity in Patagonia. We will then evaluate the potential of using similar magnetic proxies in Tasmania by presenting preliminary data from Lake Selina, a low-resolution lacustrine record that is proximal (50 km north) to Darwin Crater and which spans several glacial cycles. Preliminary results from the Lake Selina sedimentary archive reveal two magnetic mineral components: one of low coercivity (likely iron oxides such as magnetite) and one of high coercivity (likely iron sulfides). The high coercivity component is likely to reflect environmental changes, suggesting an excellent potential for paleoenviromental reconstruction based on the magnetic properties. Importantly, the low coercivity component displays a strong and stable magnetization with a geomagnetic inclination varying around the geocentric axial dipole value, indicating a likely genuine geomagnetic record that will significantly bolster the development of a robust and independent chronology at the site using an integrated dating strategy.