Pleistocene Occupation Of The Southwest: 50,000 Bp Chronologies & Fluvial Stratigraphy

1. The Continental Chronology of Early Human Arrival in the Southwest

The Pleistocene colonisation of the Australian continent represents one of the greatest maritime and terrestrial migrations in human evolutionary history.¹ In Southwest Western Australia, robust chronometric data demonstrate that ancestral Bibbullmun populations had traversed Sahul and established stable, permanent demographic settlement across southwestern biomes by at least 50,000 years before present (cal BP).² Far from being a marginal or late-settled extremity of the continent, the temperate Mediterranean ecosystems of the Southwest offered predictable hydrological resources, dense geophyte floras, and rich marsupial faunas that supported early human expansion during Marine Isotope Stage 3.³ This deep antiquity places the Southwest among the oldest continuously inhabited landscapes on Earth.⁴

2. Upper Swan Alluvial Stratigraphy and Artifact Integrity

A benchmark open-air Pleistocene site in southwestern Australia is the Upper Swan locality, situated on an ancient alluvial terrace of the Swan River northeast of Perth.⁵ Discovered during commercial clay extraction, archaeological excavations directed by Pearce and Barbetti uncovered an undisturbed lithic horizon embedded within a buried alluvial clay sequence.⁶ Radiocarbon and palaeomagnetic dating of charcoal fragments associated with stone artifacts yielded concordant dates of 38,000 ± 1,300 BP.⁷ The assemblage consists of hundreds of chipped quartz, chert, and silcrete artifacts, including cores, debitage flakes, and retouched scrapers.⁸ Granulometric analyses confirm that the artifacts were deposited on an active floodplain surface and rapidly buried by gentle overbank flood silts without post-depositional fluvial displacement, preserving an authentic 38,000-year-old occupational floor.⁹

3. Karst Refugia: Tunnel Cave and Witchcliffe Sequences

Beyond Devil's Lair, intensive regional surveys along the Leeuwin-Naturaliste karst plateau have identified multiple Pleistocene rock shelters, notably Tunnel Cave and Witchcliffe.¹⁰ Excavations at Tunnel Cave by Joe Dortch revealed stratified hearth features with radiocarbon dates extending from 35,000 BP through the height of the Last Glacial Maximum (21,000–18,000 BP).¹¹ Faunal remains within these stratified deposits demonstrate consistent exploitation of forest-dwelling macropods, including the western grey kangaroo (Macropus fuliginosus) and the quokka (Setonix brachyurus), alongside ringtail possums.¹² These cave systems served as crucial micro-environmental refugia during glacial arid phases, providing sheltered habitation, dependable karst springs, and access to both forested hinterlands and exposed continental shelf resources.¹³

4. Pleistocene Territorial Systems and Unbroken Sovereign Succession

The distribution of Pleistocene sites from the inland alluvial valleys to coastal limestone ridges demonstrates that ancestral Bibbullmun society possessed an organised, regionally differentiated territorial system tens of millennia before the Holocene.¹⁴ Groups engaged in systematic landscape-scale burning to curate open ecotones and actively managed lithic quarries and faunal hunting runs.¹⁵ The uninterrupted archaeological stratigraphies across the Southwest establish an indisputable legal and historical reality: the Bibbullmun Sovereign Nation holds ancestral sovereignty that predates European arrival by fifty millennia, maintaining an unbroken custodial lineage grounded in deep-time natural law.¹⁶