Paleomagnetism in South East Australia from Archaeological Artefacts, Lava Flows and Lake Sediments

English Abstract:

Late Quaternary paleomagnetic data from the Southern Hemisphere is limited. One reason for this is because archaeological artefacts, lava flows and most high-resolution sedimentary sequences are found on and near the continents and islands, which represent only about one fourth of the Southern Hemisphere surface. The Australian continent is one of these regions and despite its long human occupation since ca. 50,000 cal BP and abundant materials likely suitable for archaeo- and paleomagnetic studies including fireplaces, heat retainers, heat treated stone tools, bricks, kilns, pottery, ovens, lake sediment and volcanic rocks, it remains poorly documented. Here we present archaeo- and paleomagnetic results derived from a variety of burnt archaeological artefacts (from ca. 25,000 to 15,000 cal BP and since 4000 cal BP), young lava flows (ca. 35, 000 and 30,000 cal BP) and lake sediments (since ca. 250,000 cal BP) from south-east Australia. Standard procedures of alternating field and thermal demagnetization as well as Thellier-Coe archaeointensity determinations with partial thermoremanent magnetisation checks on selected lava flows and archaeological samples were performed at The Australian Archaeomagnetism Laboratory (TAAL). The results reveal generally strong and stable remanent magnetisation, often displaying single components that are ideal for palaeointensity determinations. Some of the archaeological materials also display complex heating histories informing on the formation, firing conditions and usage of the campfires. This was further investigated with experimental cobbles and clay balls heat retainers in order to document the magnetic remanence acquisition under different firing conditions. The new paleomagnetic direction and intensity data from southeast Australia are compared with global reference curves, geomagnetic field models and the nearest available records. Altogether the results highlight the great potential of archaeo- and paleomagnetic research in Australia for better understanding past behaviour of the Earth’s magnetic field in the Southern Hemisphere and for building the first Australian Archaeomagnetic Dating Reference Curve.