Aboriginal Archaeology

The Aboriginal Archaeology Salvage Program commenced in 2016 with the careful manual excavation of two large open areas (totalling 150 square metres) within the lower Thompson Square parkland. However, following initial removal of modern overburden and later 19th Century historical deposits, it became clear that large parts of the area had been subjected to extensive modification, which had resulted in the removal, reworking and/or loss of Aboriginal cultural material.

These unexpected disturbances were, in part, due to the installation of an early colonial drainage system that was too deep (ie more than 4 metres below the surface) to have been found during test excavations. The colonial drainage system cut a trench of 5-11 metres through the proposed excavation area and, when the work was back-filled, sediment from the natural soil profile was re-used, thereby making it hard to determine pre-colonial soil layers from reworked deposits until large areas had been cleared.

Consequently, the archaeological excavation proceeded only in those areas where undisturbed pre-colonial soil profiles were identified. These consisted of three separate areas of the site totalling approximately 59 square metres: the Eastern and Western Salvage Areas situated on either side of the colonial drainage system and the Southern Salvage Area, located on the highest point of the site at the junction of Bridge Street and Old Bridge Street. Later, a fourth area identified as the Western Expansion Salvage Area, effectively a continuation of the Western Salvage Area and including areas adjacent to Bridge Street, was excavated, ultimately expanding the total excavation area to 95 square metres.

Within these four areas, a pre-colonial soil profile in various condition was observed, with the Western and Western Expansion Salvage Areas having a relatively undisturbed 1 metre deep soil profile, while the Eastern and Southern Salvage Areas exhibited significant truncation (some 50 cm and 40cm deep, respectively). In addition, the excavations extended into, and investigated, the culturally sterile sand units underlying the study area. The excavations recovered some 3,267 stone artefacts from a mixture of fluvial, alluvial and aeolian deposits, dating from approximately 30,000 years ago to the early colonial (approximately 250 years ago) period.

This assemblage could be divided into three main phases of visitation and occupation: at approximately 27-19 thousand years ago, 13-8.5 thousand years ago and 5-0 thousand years ago, which align with major climatic changes in the past – including the Last Glacial Maximum (LGM), the Meltwater Pulse 1a (and associated coastal inundation) and the El Niño Southern Oscillation, respectively. A range of Optically-Stimulated Luminescence (OSL) ages and other paleo-environmental data was also collected to provide information on both the climatic changes and Aboriginal activities within the study area during these times. Along with other nearby sites of great antiquity, they indicate that the river corridor likely formed an ecological refuge within which Aboriginal people visited, lived and/or exploited during these periods of climatic disruption.

The artefactual assemblage was dominated by ‘Indurated mudstone/tuff/chert’ (IMTC) raw materials, suggesting an exploitation of nearby river gravels, and was characterised by rudimentary flaking technology. Comparison with assemblages at Pitt Town show numerous similarities, including close correlation of mobility, and suggesting the sites are connected either through the same land use strategy and/or discrete populations in communication with each other. Of note, and for future investigation, was the general consistency in technological attributes of the assemblage, indicative of similar hunter-gatherer behaviour and use, throughout the LGM, the ‘Last Glacial to Interglacial Transition’ period (LGIT) and the early Holocene, despite very differing climatic conditions over this time. Along with other sites along the river corridor, the region appeared to have formed less of a focus for Aboriginal populations compared with earlier phases, possibly reflecting a diffusion of people across the more marginal landscape, such as the Cumberland Plain, in line with increasing populations at this time. However, this must be caveated by the un-stratified recovery of a significant assemblage from the earlier-colonial period deposits.

In addition to the four excavations, some 300 cubic metres of the colonial drainage system trench fill material was also recovered and sieved for cultural material (since the trench fill consisted of re-worked, pre-colonial soil profiles likely sourced from within the study area). Some 14,777 stone artefacts were recovered from these deposits, which were dominated by silcrete raw materials and likely reflect activity primarily in the last 5,000 years. On face value, these numbers suggest a sevenfold increase in artefacts compared with the earlier phases of site use, however, the larger volume of sediment recovered from the drainage system must be taken into account (i.e. approximately 5 times the volume of sediment than that of the salvage excavations). When comparing the two phases as artefacts-per-square-metre, it suggests a more- likely two-fold increase in artefacts (ie 35 artefacts per m2 versus approx. 73 artefacts per m2) – a finding which agrees with the broader models of increasing populations at this time.

A significance assessment of the cultural deposits recovered (and those still present in other parts of the study area) shows that they are of high (State) scientific significance, representing one of only a handful of examples of a Pleistocene ecological refuge used by Aboriginal people in the past, and the study area has ongoing research potential. This classification is, in part, the result of the post-excavation work that has undertaken detailed investigation and characterisation of the deposit – including developing one of the strongest chronological frameworks for an archaeological site in the Sydney Basin. Input from the Aboriginal community has yet to be formally obtained but, consistently, archaeological sites along the Hawkesbury-Nepean River corridor are assigned high cultural values.

The above information was extracted (and edited) from the Executive Summary – Windsor Bridge Replacement Project Salvage Excavation Report – Aboriginal Heritage, AAJV, August 2019.