Unlocking the Kimberley’s past: the applicability of organic spring deposits for reconstructing late Quaternary climatic and environmental change

Abstract

There are limited high-resolution records of climatic and environmental change from the Kimberley region of northwest Australia. This has hindered the development of knowledge of climate and environmental change in Australia's monsoonal tropics, and the ability to provide context for the area's rich archaeological record and globally renowned rock art. The lack of high-resolution records from this region is primarily a result of the monsoonal climate which limits the presence of "classic" palaeoenvironmental archives such as perennial lakes and wetlands. Organic spring deposits are unconventional archives of past environmental change yet offer potential to provide outstanding records in arid and semi-arid regions such as the Kimberley. Despite this, the majority of existing research demonstrates complications with their use, in particular the application of standard radiocarbon (14 C) techniques to build robust chronologies of their development. Because of the importance of springs as critical palaeoenvironmental archives, and the pressing need for high-resolution records from northwest Australia, this thesis utilised three organic spring deposits to develop new, high-resolution records of climate and environmental change for the Kimberley. These records span the last ~14,500 years, and were underpinned by a new protocol for establishing robust chronologies from these settings which was developed via a rigorous geochronological investigation. Initial 14 C results from a core collected from Black Springs in 2005 were confusing, with convoluted ages below 94.5 cm limiting the reliability of an initial palaeoenvironmental reconstruction >9070 cal. yr BP. A new protocol for obtaining robust chronologies from organic spring deposits was therefore developed for cores collected from the three sites in 2015, utilising multiple geochronological methodologies including 14 C dating of different carbon fractions (stable polycyclic aromatic carbon (SPAC), macro-charcoal, pollen concentrate, bulk sediment and roots), 210 Pb dating, the application of 239+240 Pu, and high-spatial resolution, luminescence techniques (natural sensitivity-corrected luminescence (L n /T n)). Whilst L n /T n demonstrated that the organic spring deposits contained a relatively uncompromised stratigraphic record, 14 C dates were contaminated by roots, groundwater fluctuations, and incorporation of allochthonous "old" carbon. SPAC isolated by the hydrogen pyrolysis (HyPy) pre-treatment appeared to remove postdepositional sources of alteration, and therefore provided a viable approach for constructing chronologies in these settings. Developing more recent chronologies (i.e. the past 100 years) using 210 Pb was found to be problematic due to the behaviour of the springs as an open system with regards to uranium, suggesting this may not be possible in many spring environments. Whilst this investigation was made with respect to springs, the contamination pathways are not unique to these Publications during candidature Peer reviewed papers:

Investigating the Anthropic Construction of Rock Art Sites Through Archaeomorphology: the Case of Borologa, Kimberley, Australia

“…Radiocarbon dating of charcoal on the rock surface at the very base of the sand layer effectively dates both the antiquity of this occupation phase and the commencement of aeolian sand deposition to c. 2500-2700 cal BP, with the collapse of the underlying ceiling slabs taking place sometime earlier (David et al 2019). This onset of aeolian sedimentation c. 2500-2700 cal BP at Borologa 1 corresponds well with a period of peak aridity beginning c. 2600-2750 cal BP across the Kimberley (Field 2010;McGowan et al 2012;see above). This means that the physical setting fronting Art Panel B1 was slightly different to now, as the floor consisted of large collapsed rock slabs with expansive flat surfaces.…”