In coastal sections at Hallett Cove and Sellicks Beach, south of Adelaide, and
at Redbanks section on Kangaroo Island, the Brunhes/Matuyama polarity
transition (780 ka) is identified in the strongly oxide-mottled Ochre Cove
Formation. At all 3 sections, the Ochre Cove Formation is overlain by a
calcareous grey-green aeolian clay, called Ngaltinga Clay, which in turn is
overlain by calcareous sediments of the Taringa and Christies Beach
Formations. The marked change from an oxide-dominated weathering regime to a
carbonate-dominated weathering regime, estimated to have occurred at about
500–600 ka, is interpreted as a major arid shift in regional climates.
Similar arid shifts are known from Lake Bungunnia in the Murray Basin and Lake
Lefroy in southern Western Australia, where changes from lacustrine clays to
evaporites and dune sediments are estimated to have occurred between 400 and
700 ka, and about 500 ka, respectively. An increase in aeolian dust accession
in south-eastern Australia, consistent with increased aridity in the interior
source area, occurred after 780 ka, and was probably coeval with increased
dust input to Tasman Sea sediments since 350 ka.
Between 600 and 900 ka, oxygen isotope fluctuations in deep-sea cores showed a
pronounced change in frequency, from a 40 ka (obliquity dominated) to a 100 ka
(eccentricity dominated) pattern. At the same time, glacial-interglacial
amplitudes increased, with a marked enrichment of glacial
d18O values consistent with larger continental based
ice-sheets. Colder global temperatures, and lower sea levels during glacials,
may have played a part in the mid Pleistocene arid shift recorded in southern
Australia. Associated variations in the strength of the warm Leeuwin Current
may also have affected regional rainfall patterns in southern Australia.
Fidelity and time resolution of the magnetostratigraphic record in Siwalik sediments: high-resolution study of a complete polarity transition and evidence for cryptochrons in a Miocene fluviatile section
