We show with multiple luminescence dating techniques that the sedimentary record for Lake Eyre, Australia's largest lake, extends beyond 200 thousand years (ka) to Marine Isotope Stage (MIS) 7. Transgressive clayey sand and finely laminated clays overlying the Miocene Etadunna Formation in Lake Eyre North document the deep-lake phases of central South Australia in the past. Until now, unresolved chronology has hampered our ability to interpret these sedimentary records, which are important for understanding the timing of the wettest phase of central Australia's late Quaternary climate. In this study, we apply quartz optically stimulated luminescence (OSL) dating, thermally-transferred OSL (TT-OSL) dating and K-feldspar post infrared infrared stimulated luminescence (pIRIR) dating to lake-floor sediments near Williams Point in Madigan Gulf to provide new age constraint for the lacustrine sediments of Lake Eyre. Methodological studies on quartz and K-feldspar demonstrate that these luminescence dating procedures are suitable for the Lake Eyre lacustrine samples and produce consistent replicate ages. A Bayesian model applied to the new dating results provides a chronological model of lacustrine deposition and shows that the transgressive clayey sand were deposited 221 ± 19 ka to 201 ± 10 ka and that the deep-water sediments were laid down in early MIS 6 (191 ± 9 ka to 181 ± 9 ka). We also find evidence for a potential depositional hiatus in mid MIS 6 and the likely formation of a palaeo-playa later in MIS 6 from 158 ± 11 ka to 143 ± 15 ka. In contrast, the MIS 5 sediments are characterised by oscillating deep- and shallow-water lacustrine units deposited 130 ± 16 ka to 113 ± 20 ka. This study is the first of its kind to provide evidence for a wet desert interior in Australia beyond the last glacial cycle using comprehensive numerical dating. Our results show that past deep-lake episodes of central South Australia, which were previously thought to represent peak interglacial conditions, are actually associated with both warm interglacial and cold glacial periods, with all the wettest episodes generally coinciding with the intervening periods between the glacial and interglacial maximums. We assume from these results that orbital forcing is not a first order control for the long-term dynamics of the Lake Eyre basin and the Indo-Australian monsoon. The high lake-level events of Lake Eyre are well correlated with millennial-scale cooling events and stadials of the North Atlantic, and coincide with weakened episodes/events for the East Asia summer monsoon. This may imply an important role for the northern high latitudes in influencing the Indo-Australian monsoon, which may be associated with a southward migration of the Intertropical Convergence Zone (ITCZ) during cooling periods in the North Atlantic.
Available for download on Monday, March 19, 2018