Kathryn E. Fitzsimmons

Excavations at Parnkupirti, Lake Gregory, Great Sandy Desert: OSL Ages for Occupation Before the Last Glacial Maximum

Abstract We report on early occupation from the Parnkupirti site on Salt Pan Creek at Lake Gregory, on the edge of the Great Sandy Desert of northwest Australia. OSL ages from excavations, and stratigraphic correlations between dated exposures along Salt Pan Creek, show some stone artefacts in situ in sediments dating from greater than 37ka and most probably on stratigraphic grounds in the range of ~50–45ka. The deep stratigraphic section at Parnkupirti also provides a long record of the Quaternary history of Lake Gregory, which remained a freshwater system during the Late Quaternary.

The Campanian Ignimbrite eruption: new data on volcanic ash dispersal and its potential impact on human evolution.

The Campanian Ignimbrite (CI) volcanic eruption was the most explosive in Europe in the last 200,000 years. The event coincided with the onset of an extremely cold climatic phase known as Heinrich Event 4 (HE4) approximately 40,000 years ago. Their combined effect may have exacerbated the severity of the climate through positive feedbacks across Europe and possibly globally. The CI event is of particular interest not only to investigate the role of volcanism on climate forcing and palaeoenvironments, but also because its timing coincides with the arrival into Europe of anatomically modern humans, the demise of Neanderthals, and an associated major shift in lithic technology. At this stage, however, the degree of interaction between these factors is poorly known, based on fragmentary and widely dispersed data points. In this study we provide important new data from Eastern Europe which indicate that the magnitude of the CI eruption and impact of associated distal ash (tephra) deposits may have been substantially greater than existing models suggest. The scale of the eruption is modelled by tephra distribution and thickness, supported by local data points. CI ashfall extends as far as the Russian Plain, Eastern Mediterranean and northern Africa. However, modelling input is limited by very few data points in Eastern Europe. Here we investigate an unexpectedly thick CI tephra deposit in the southeast Romanian loess steppe, positively identified using geochemical and geochronological analyses. We establish the tephra as a widespread primary deposit, which blanketed the topography both thickly and rapidly, with potentially catastrophic impacts on local ecosystems. Our discovery not only highlights the need to reassess models for the magnitude of the eruption and its role in climatic transition, but also suggests that it may have substantially influenced hominin population and subsistence dynamics in a region strategic for human migration into Europe.

Holocene hydrologic variability in temperate southeastern Australia: An example from Lake George, New South Wales

Lake George is one of the largest freshwater lakes in Australia when full, and provides one of the most complete records of Quaternary sedimentation in the southeastern part of the continent. The lake is currently ephemeral, but sediments within the basin preserve evidence of multiple permanent and dry lake conditions in the past. We present an optically stimulated luminescence (OSL) chronology of recent lake shoreline sediments in order to reconstruct Holocene hydrologic variability at Lake George, providing past climatic context for the presently ephemeral lake conditions. The OSL chronology indicates three distinct periods of permanent lake conditions up to 15—18 m depth over the Holocene period, at approximately 10—8, 6—2.4 and 0.7—0.3 ka, with lower lake levels occurring in between those events. There appears to be a trend towards lake regression over this period despite relatively recent high lake levels. The chronology is broadly synchronous with comparable records of Holocene climatic variability across southeastern Australia. We also investigate the intrinsic luminescence characteristics of different sediment types as diagnostic tools, but these appear not to be appropriate in this context or form.

Aridity in the monsoon zone as indicated by desert dune formation in the Gregory Lakes basin, northwestern Australia

Desert dunes within the monsoon-fed Gregory Lakes basin form valuable archives for Quaternary paleoenvironments, in a region where such records are scarce. Optically stimulated luminescence (OSL) chronologies from two dunes identify the timing of eolian processes, interpreted as a complex response to aridification and increased sediment availability during lake transgressions and associated fluvial activity. The earliest eolian deposition in our record occurred ca 91.5 ka, which postdates the last ‘mega-lake’ phase but predates a smaller lake transgression during early MIS 3. Sand plain accretion took place around ca 47 ka during contemporaneous periodic high lake levels. This was followed by intermittent linear dune building, between ca 35 and 11.5 ka, which most likely took place during an interval of relative aridity. Close spacing of mid-Holocene ages within one dune indicates rapid sediment accumulation in a single arid event ca 5 ka. At no time in the last 50 ka have lake levels reached those of the last ‘mega-lake’ phase prior to ca 91.5 ka, suggesting a substantially weakened present-day monsoon.

An assessment of the luminescence sensitivity of Australian quartz with respect to sediment history

This study provides a preliminary systematic characterisation of OSL sensitivity, with respect to sediment history, of single grains of Australian quartz from a variety of source rocks and depositional contexts. Samples from two distinct lithologies and with relatively short modern sedimentary histories were compared in an examination of the influence of rock type on OSL sensitivity. Sediments derived from weathered sandstone were found to be brighter than those from metamorphosed schists, suggesting that sensitivity may be inherited from the source rock and its earlier sedimentary history. Secondly, quartz from the same source, but different modes of deposition, was compared to assess the effect on sensitivity of nature of exposure to light during the most recent bleaching event. Quartz grain sensitivity appears not to vary depending on the mode of sediment deposition, suggesting that the nature of exposure to light during deposition is less important in the sensitisation process. This study highlights the complexity and variety of natural sedimentary quartz, demonstrating the limitations of an investigation based solely on OSL sensitivity. Further systematic investigation into the physical, geological and geomorphological characteristics of sediments is proposed to better understand the mechanisms of luminescence sensitisation in quartz.

Dealul Guran: evidence for Lower Palaeolithic (MIS 11) occupation of the Lower Danube loess steppe

Owing to a thick blanket of loess and other later geological disruptions, the earliest hominins to reach Europe are hard to find. To a handful of possible sites, our authors add a new assemblage of lithics with a clear local context and corroborated OSL ages. Ancient humans were present in what is now Romania between 300 000 and 400 000 years ago.

The Mungo mega-lake event, semi-arid Australia: non-linear descent into the last ice age, implications for human behaviour

The Willandra Lakes complex is one of the few locations in semi-arid Australia to preserve both paleoenvironmental and Paleolithic archeological archives at high resolution. The stratigraphy of transverse lunette dunes on the lakes’ downwind margins record a late Quaternary sequence of wetting and drying. Within the Willandra system, the Lake Mungo lunette is best known for its preservation of the world’s oldest known ritual burials, and high densities of archeological traces documenting human adaptation to changing environmental conditions over the last 45 ka. Here we identify evidence at Lake Mungo for a previously unrecognised short-lived, very high lake filling phase at 24 ka, just prior to the Last Glacial Maximum. Mega-lake Mungo was up to 5 m deeper than preceding or subsequent lake full events and represented a lake volume increase of almost 250%. Lake Mungo was linked with neighboring Lake Leaghur at two overflow points, creating an island from the northern part of the Mungo lunette. This event was most likely caused by a pulse of high catchment rainfall and runoff, combined with neotectonic activity which may have warped the lake basin. It indicates a non-linear transition to more arid ice age conditions. The mega-lake restricted mobility for people living in the area, yet archeological traces indicate that humans rapidly adapted to the new conditions. People repeatedly visited the island, transporting stone tools across water and exploiting food resources stranded there. They either swam or used watercraft to facilitate access to the island and across the lake. Since there is no evidence for watercraft use in Australia between initial colonization of the continent prior to 45 ka and the mid-Holocene, repeated visits to the island may represent a resurrection of waterfaring technologies following a hiatus of at least 20 ky.

SEDIMENTARY HISTORY AND THE INTERPRETATION OF LATE QUATERNARY DUNE RECORDS: EXAMPLES FROM THE TIRARI DESERT, AUSTRALIA AND THE KALAHARI, SOUTH ÁFRICA

Stabilized sand deposits from arid regions are often used as palaeoenvironmental proxies for past periods of enhanced aeolian activity. Although widespread use of optically stimulated luminescence (OSL) dating techniques has opened up the possibility of systematic analyses of dune building chronologies, palaeoenvironmental histories cannot be reconstructed from chronological data alone. The reconstruction of regional palaeoenvironmental histories should consider all available evidence - stratigraphic, sedimentological and micromorphological, and chronological. This paper highlights potential issues with the interpretation of dune records in the context of stratigraphic preservation, using examples from the Tirari Desert in Australia and the Kalahari Desert in southern Africa. Sedimentological characterisation of linear dunes in the Tirari Desert demonstrates that reworking of underlying dune sediments and buried soils is common, thereby calling into question simplistic interpretations of dune formation involving sequential deposition and pedogenesis. This case study highlights the limitation of the augering technique, although useful information can be gained nonetheless. Three OSL age estimates confirm the presence of at least two Holocene dune building episodes, but cannot constrain the timing of the onset of dune building. Higher frequency sampling and micromorphological analyses may further elucidate the palaeoenvironmental history of individual dunes. In the Southwestern Kalahari, interdune sediments have been described as the least sensitive part of the aeolian landscape, thus offering the potential for longer records of aeolian deposition. This is found not to be the case at Witpan, where interdune sands are extensively mixed and probably younger than the linear dune cores. The lunette at Witpan records numerous short-lived and rapid deflationary events from the nearby pan (playa). These are considered to reflect changes in sediment source rather than pedogenesis. These examples highlight the value of combining micromorphological, sedimentological and chronological studies for palaeoenvironmental reconstruction.

Multi-method luminescence investigations on quartz grains of different sizes extracted from a loess section in Southeast Romania interbedding the Campanian Ignimbrite ash layer

In this study we present luminescence investigations of four samples of loess bracketing the Campanian Ignimbrite/Y5 tephra at the Rasova-Valea cu Pietre site, on the eastern bank of the Danube River, southeastern Romania. Investigations involved SAR-OSL dating on aliquots of fine (4–11 μm) and medium-grained (63–90 μm) quartz, as well as single grain analyses on 125–180 μm quartz. Luminescence dating results coupled with glass-shard chemical fingerprinting assign the depositional age and origin of the ash layer to that of the Campanian Ignimbrite/Y5 tephra, dated elsewhere using 40Ar/39Ar to 39.28 ± 0.11 ka. Fine-grained (4–11 μm) quartz SAR-OSL analyses yielded ages of 44.4 ± 4.5 ka below the ash, and 41.4 ± 4.2 ka above the ash layer. Single grain analysis on coarse-grained quartz, however, demonstrates that coarse material from these samples exhibits low sensitivity and responds poorly to internal checks of the SAR protocol in comparison with the finer sediment. This observation highlights the need for more extensive investigations into the luminescence properties of quartz as well as into the origin of quartz contributions from different primary sources in the Lower Danube loess steppe.

A New Chronology for Rhafas, Northeast Morocco, Spanning the North African Middle Stone Age through to the Neolithic

Archaeological sites in northern Africa provide a rich record of increasing importance for the origins of modern human behaviour and for understanding human dispersal out of Africa. However, the timing and nature of Palaeolithic human behaviour and dispersal across north-western Africa (the Maghreb), and their relationship to local environmental conditions, remain poorly understood. The cave of Rhafas (northeast Morocco) provides valuable chronological information about cultural changes in the Maghreb during the Palaeolithic due to its long stratified archaeological sequence comprising Middle Stone Age (MSA), Later Stone Age (LSA) and Neolithic occupation layers. In this study, we apply optically stimulated luminescence (OSL) dating on sand-sized quartz grains to the cave deposits of Rhafas, as well as to a recently excavated section on the terrace in front of the cave entrance. We hereby provide a revised chronostratigraphy for the archaeological sequence at the site. We combine these results with geological and sedimentological multi-proxy investigations to gain insights into site formation processes and the palaeoenvironmental record of the region. The older sedimentological units at Rhafas were deposited between 135 ka and 57 ka (MIS 6 –MIS 3) and are associated with the MSA technocomplex. Tanged pieces start to occur in the archaeological layers around 109 ka, which is consistent with previously published chronological data from the Maghreb. A well indurated duricrust indicates favourable climatic conditions for the pedogenic cementation by carbonates of sediment layers at the site after 57 ka. Overlying deposits attributed to the LSA technocomplex yield ages of ~21 ka and ~15 ka, corresponding to the last glacial period, and fall well within the previously established occupation phase in the Maghreb. The last occupation phase at Rhafas took place during the Neolithic and is dated to ~7.8 ka.