Rachel Wood's research while affiliated with Oxford Archaeology and other places

Radiocarbon dates on multiple individual charcoal fragments floating together down the Macdonald River, New South Wales, Australia, have calibrated ages spanning >1700 years. Partial explanations of this range of inherited ages can be attributed to the inbuilt age of living biomass, charcoalisation conditions, hillslope transport and storage and/or valley floor (fluvial) transport and storage, but the contribution of each of these components can be constrained only rarely. These results caution against using radiocarbon dating of charcoal as the sole dating technique to interpret Late-Holocene sedimentary histories. These findings also show that it is unlikely that deposit age has a dependable relationship to charcoal age.

The peopling of Sahul (the combined landmass of New Guinea and Australia) is a topic of much debate. The Kimberley region of Western Australia holds many of Australia's oldest known archaeological sites. Here, we review the chronological and archaeological data available for the Kimberley from early Marine Isotope Stage 3 to the present, linking episodes of site establishment and the appearance of new technologies with periods of climatic and sea-level change. We report optical ages showing human occupation of Widgingarri 1, a rockshelter located on the Kimberley coast of northwest Australia, as early as 50,000 years ago, when the site was located more than 100 km from the Late Pleistocene coastline. We also present the first detailed analysis of the stone artefacts, including flakes from ground stone axes, grinding stones and ground haematite recovered from the deepest excavated layer. The high proportion of flakes from ground axe production and resharpening in the earliest occupation phase emphasises the importance of this complex technology in the first peopling of northern Sahul. Artefact analyses indicate changes in settlement patterns through time, with an increase in mobility in the terminal Pleistocene and a shift to lower mobility during the late Holocene. The optical ages for Widgingarri 1 mean that the Kimberley now contains the greatest number of sites in Sahul with earliest occupation dated to more than 46,000 years ago, overlapping with the time of initial occupation of sites in other regions across the continent.

In hot environments, collagen, which is normally targeted when radiocarbon ( ¹⁴ C) dating bone, rapidly degrades. With little other skeletal material suitable for ¹⁴ C dating, it can be impossible to obtain dates directly on skeletal materials. A small amount of carbonate occurs in hydroxyapatite, the mineral phase of bone and tooth enamel, and has been used as an alternative to collagen. Unfortunately, the mineral phase is often heavily contaminated with exogenous carbonate causing ¹⁴ C dates to underestimate the true age of a sample. Although tooth enamel, with its larger, more stable crystals and lower porosity, is likely to be more robust to diagenesis than bone, little work has been undertaken to investigate how exogenous carbonate can be effectively removed prior to ¹⁴ C dating. Typically, acid is used to dissolve calcite and etch the surface of the enamel, but it is unclear which acid is most effective. This study repeats and extends earlier work using a wider range of samples and acids and chelating agents (hydrochloric, lactic, acetic and propionic acids, and EDTA). We find that weaker acids remove carbonate contaminants more effectively than stronger acids, and acetic acid is the most effective. However, accurate dates cannot always be obtained.

Insects form an important source of food for many people around the world, but little is known of the deep-time history of insect harvesting from the archaeological record. In Australia, early settler writings from the 1830s to mid-1800s reported congregations of Aboriginal groups from multiple clans and language groups taking advantage of the annual migration of Bogong moths (Agrotis infusa) in and near the Australian Alps, the continent’s highest mountain range. The moths were targeted as a food item for their large numbers and high fat contents. Within 30 years of initial colonial contact, however, the Bogong moth festivals had ceased until their recent revival. No reliable archaeological evidence of Bogong moth exploitation or processing has ever been discovered, signalling a major gap in the archaeological history of Aboriginal groups. Here we report on microscopic remains of ground and cooked Bogong moths on a recently excavated grindstone from Cloggs Cave, in the southern foothills of the Australian Alps. These findings represent the first conclusive archaeological evidence of insect foods in Australia, and, as far as we know, of their remains on stone artefacts in the world. They provide insights into the antiquity of important Aboriginal dietary practices that have until now remained archaeologically invisible.

New research undertaken at Cloggs Cave, in the foothills of the Australian Alps, employed an integrated geological -geomorphological-archaeological approach with manifold dating methods and fine resolution LiDAR 3D mapping. Long-standing questions about the site's chronostratigraphy (e.g. the exact relationship between basal megafaunal deposits and archaeological layers), sedimentation processes and geomorphic changes were resolved. The cave's formation history was reconstructed to understand its changing morphology and morphogenic processes, and to clarify how these processes shaped the cave's deposits. Key findings include the identification of: 1) the geomorphological processes that caused the lateral juxtaposition of 52,000 year-old megafaunal and later occupational layers; 2) the existence of one and possibly two (now-buried) palaeo-entrance(s) that enabled now-extinct megafauna and extant large fauna to enter the cave, most likely via a free-roaming passage rather than a pit drop; 3) morphological changes to the cave during the time of the Old People, including the timing of changes to the inclination of palaeo-surfaces; and 4) modifications to stalactites, crushing of calcite formations for the manufacture of powder, construction of a stone arrangement, and movement of large limestone blocks by the Old People. Ultimately, these findings demonstrate that to properly understand what Cloggs Cave was like when the Old People visited the site requires the construction of a narrative that spans some 400 million years and the development of an approach capable of integrating the many scales and processes (e.g. geological, geomorphological, archaeological) that configured to shape the site.

The 2016 version of the FosSahul database compiled non-human vertebrate megafauna fossil ages from Sahul published up to 2013 in a standardised format. Its purpose was to create a publicly available, centralized, and comprehensive database for palaeoecological investigations of the continent. Such databases require regular updates and improvements to reflect recent scientific findings. Here we present an updated FosSahul (2.0) containing 11,871 dated non-human vertebrate fossil records from the Late Quaternary published up to 2018. Furthermore, we have extended the information captured in the database to include methodological details and have developed an algorithm to automate the quality-rating process. The algorithm makes the quality-rating more transparent and easier to reproduce, facilitating future database extensions and dissemination. FosSahul has already enabled several palaeoecological analyses, and its updated version will continue to provide a centralized organisation of Sahul’s fossil records. As an example of an application of the database, we present the temporal pattern in megafauna genus richness inferred from available data in relation to palaeoclimate indices over the past 180,000 years.

Drivers of Late Quaternary megafaunal extinctions are relevant to modern conservation policy in a world of growing human population density, climate change, and faunal decline. Traditional debates tend toward global solutions, blaming either dramatic climate change or dispersals of Homo sapiens to new regions. Inherent limitations to archaeological and paleontological data sets often require reliance on scant, poorly resolved lines of evidence. However, recent developments in scientific technologies allow for more local, context-specific approaches. In the present article, we highlight how developments in five such methodologies (radiocarbon approaches, stable isotope analysis, ancient DNA, ancient proteomics, microscopy) have helped drive detailed analysis of specific megafaunal species, their particular ecological settings, and responses to new competitors or predators, climate change, and other external phenomena. The detailed case studies of faunal community composition, extinction chronologies, and demographic trends enabled by these methods examine megafaunal extinctions at scales appropriate for practical understanding of threats against particular species in their habitats today.

New Zealand was first settled by Māori soon after 1200 CE, however the age, and so the social and environmental contexts of the rock art they made remains uncertain. We report the first attempts at the direct dating of New Zealand rock art through radiocarbon analysis focusing on the return of an unexpectedly early date. Historical information and pigment testing indicates that the particular figures that returned the early date were retouched with modern crayons. We report the use of portable X-ray fluorescence to identify rock art figures that have been retouched in this way. Results emphasise the need to consider historical information in future assessments of material for dating Māori rock art.