Daniele Questiaux

Continuous 150 k.y. monsoon record from Lake Eyre, Australia: Insolation-forcing implications and unexpected Holocene failure

Our reconstructed history of Lake Eyre provides the first continuous continental proxy record of Australian monsoon intensity over the past 150 k.y. This continental records broad correspondence to the marine isotope record demonstrates that this very large catchment, with its hydrology dependent on a planetary-scale climate element, responds to Milankovitch-scale climate forcing. Abrupt transitions from dry phases to wet phases (ca. 125 and 12 ka) coincide with Northern Hemisphere winter insolation minima rather than Southern Hemisphere summer insolation maxima, indicating that Northern Hemi- sphere insolation exerts a dominant control over the intensity of the Australian monsoon. Stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but, within the uncertainties, are consistent with Northern Hemisphere forcing. Regardless of the hemispheric forcing, the low intensity of the early Holocene Australian monsoon—by comparison with the last interglacial and particularly the last high-level lacustrine event at 65-60 ka when all forcing elements were modest— is an enigma that can be explained by a change in boundary conditions within Australia.

Kinetics of red, blue and UV thermoluminescence and optically-stimulated luminescence from quartz

The duration over which charge is retained at trapping sites is of fundamental importance for trapped electron dating. Here, we report measurements of the kinetic parameters of the prominent thermoluminescence (TL) glow peaks of quartz, and of the optically-stimulated luminescence (OSL) signal from quartz utilised for optical dating. The similarity in trapping lifetimes of the 325°C TL peak and the dominant component of the OSL signal are taken as further support for the hypothesis of their common origin in the same trapped electron population.

Palaeodose underestimates caused by extended-duration preheats in the optical dating of quartz

Abstract An optical dating study of some quartzose sediments from northern and southern Australia, north Africa and north-western Europe has revealed that palaeodose ( P ) underestimates of 10–40% are obtained when an extended-duration preheat of 160°C for 16 h is used. For these samples in the 0–60 ka age range, a preheat of 220°C for 5 min produces the correct P , as inferred from the concordance with thermoluminescence (TL) palaeodose determinations on the same sedimentary sample or on burnt flint. Independent support for use of the 220°C preheat is given by the agreement between optical ages younger than 30 ka and 14 C age determinations on associated charcoal. The deleterious effect of the 160°C preheat is illustrated by growth curves of optically stimulated luminescence (OSL) vs added dose. These curves show that the 160°C preheat induces a dose-dependent increase in sample sensitivity, which may be related to activation of the pre-dose mechanism. The 160°C preheat also causes low-dose supralinearity, although the supralinearity correction is insufficient to reduce significantly the degree of P underestimation. A normalization method based on preheat-induced sensitivity changes of the 110°C TL peak, albeit limited by saturation effects, warrants further investigation.

Cultural innovation and megafauna interaction in the early settlement of arid Australia

Elucidating the material culture of early people in arid Australia and the nature of their environmental interactions is essential for understanding the adaptability of populations and the potential causes of megafaunal extinctions 50–40 thousand years ago (ka). Humans colonized the continent by 50 ka, but an apparent lack of cultural innovations compared to people in Europe and Africa has been deemed a barrier to early settlement in the extensive arid zone. Here we present evidence from Warratyi rock shelter in the southern interior that shows that humans occupied arid Australia by around 49 ka, 10 thousand years (kyr) earlier than previously reported. The site preserves the only reliably dated, stratified evidence of extinct Australian megafauna, including the giant marsupial Diprotodon optatum, alongside artefacts more than 46 kyr old. We also report on the earliest-known use of ochre in Australia and Southeast Asia (at or before 49–46 ka), gypsum pigment (40–33 ka), bone tools (40–38 ka), hafted tools (38–35 ka), and backed artefacts (30–24 ka), each up to 10 kyr older than any other known occurrence. Thus, our evidence shows that people not only settled in the arid interior within a few millennia of entering the continent, but also developed key technologies much earlier than previously recorded for Australia and Southeast Asia.

Addition of aeolian dusts to soils in southeastern Australia: red silty clay trapped in dunes bordering Murrumbidgee River in the Wagga Wagga region

In southeastern Australia, aeolian dust deposits are very common and have a significant influence on soil properties and soil landscapes. However, the characteristics of the pure dust materials and the rates of dust-fall in the past are unclear because of the low overall rate of dust deposition and mixing with locally derived sediments. In the Wagga Wagga region, some dunes have functioned as dust traps. Thin (<1 cm thick) red clayey bands and thick (up to 2.5 m) red clayey layers within the dune sequences are likely to represent illuviated aeolian dust. These dust materials are characterised by a bi-modal particle size distribution, one mode in the clay and another in the coarse-medium silt. The clay minerals are dominated by kaolinite, illite and smectite. Both 14C and optical dating indicate the most recent period of dune formation was around 3–4 ka. In an example of these young dunes, there is a total of 2 cm equivalent thickness of dust materials, giving a deposition rate of 0.5–0.7 cm ka−1. All three samples from an elevated dune are saturated with respect to environmental radiation dosage, and give minimum optical ages in excess of 80 ka. In this higher dune, the total thickness of dust is 50–80 cm, similar to that (50–100 cm) of the Yarabee Parna, the youngest aeolian dust deposit in the Wagga Wagga region. This may have been deposited unevenly, being more concentrated during the period 25–16 ka, which has been identified as a major dust deposition period in the Tasman Sea. If this variation occurred, the dust deposition rate indicated by the 50–80 cm dust material in the dune could have been as high as 5 cm ka−1 for the period 25–16 ka.

The central lowlands of the Hunter Valley, NSW: Why so few early sites have been found in this archaeologically-rich landscape

Abstract The central lowlands of the Hunter Valley are rich in Holocene-aged open stone artefact concentrations but, to date, very few verified traces of Pleistocene occupation have been found there. The central lowlands would have been a reasonably attractive place to live, so logic suggests that there should be Pleistocene sites. Given the geomorphic and soil formation processes that have operated over the potentially long period of Aboriginal occupation of the central lowlands, however, it is likely that most archaeological materials older than ca 10,000 years have been either completely removed or widely dispersed across the landscape and are no longer recognisable as discrete Pleistocene-aged assemblages. Sand bodies have the greatest potential to contain older sites, but in most, if not all, cases their stratigraphic integrity has been compromised, principally by bioturbation. Understanding the landscape history over the last 90,000 years is the key to understanding why finding Pleistocene sites in the Hunter Valley has proven to be so difficult. Geoarchaeological evidence which illustrates this difficulty is presented from sites in three deposits of probable Pleistocene to early Holocene age—two in sand bodies and one in colluvium. On one sand body (the Warkworth sand sheet) there is contestable evidence for traces of pre-LGM occupation beginning more than ~23,000, possibly 50,000, years ago, but on the other (the Cheshunt dune) there is no evidence of occupation beyond the mid-Holocene.