How Sand From Antarctica Made It To Sydney

Antarctic Sand in Sydney’s Stone: 

How did sand from Antarctica make it all the way to Sydney?

In this article, we’re exploring the extraordinary geological connection between Antarctica and New South Wales. During the Triassic, when Australia and Antarctica were still joined as part of Gondwana, powerful braided rivers transported sand from highlands deep in East Antarctica across a vast landscape — ultimately reaching the Sydney region

Around 250 million years ago in the Triassic Period, the world’s landmasses were fused in the supercontinent Gondwana, which joined what is now Australia, Antarctica, Africa, South America, and India. Eastern Australia and East Antarctica lay side-by-side, part of a continuous land expanse far in the Southern Hemisphere. Earth’s atmosphere held several times today’s CO₂ levels, creating a greenhouse climate even at high latitudes. This was a world of lush forests and dynamic rivers rather than polar ice. In this paleogeographic context, eastern Gondwana had no ocean between Australia and Antarctica; instead, rivers could flow freely across a vast landscape from what is now the frozen interior of Antarctica to the sites of future Australian cities.

During the Triassic, eastern Australia (including present-day New South Wales, Victoria, and Tasmania) formed the margin of Gondwana facing the Paleo Pacific Ocean to the east. To the south, East Antarctica adjoined Australia, with regions like Wilkes Land and Queen Mary Land pressed against what is now the Tasman Sea coast of Australia. Crucially, geologists believe that mountain ranges existed along this Gondwanan margin. A Late Palaeozoic mountain-building event, the Gondwanide Orogeny, had raised highlands along the supercontinent’s southern edge (including East Antarctica and parts of eastern Australia) by the early Triassic. In Australia, we called this orogeny the Hunter–Bowen Orogeny. These highlands would have been sources of abundant sediment, supplying sand and gravel to rivers. In East Antarctica, evidence points to uplifts such as the “Ross High” in the Transantarctic region, which was elevated in the Early Triassic (around 250–242 Ma). Simply put, at the time the Hawkesbury Sandstone — a massive Triassic river-laid sandstone that underlies much of the Sydney Basin — was forming, Antarctica boasted mountains and high ground, not ice sheets – a potential motherlode of sand waiting to be eroded.

East Antarctica: A Mountainous Source of Sand

If we travel back in time, we would see a towering mountain range in what is now East Antarctica’s interior, shedding rock debris under a warmer Triassic climate. Those Antarctic highlands, likely composed of ancient granites and metamorphic rocks, weathered and broke down to yield billions of sand grains (mostly durable quartz). Geochemical clues from tiny minerals called zircons – often found in sandstones – give us a “fingerprint” of those source rocks. In the Hawkesbury Sandstone of New South Wales, many detrital zircons (zircon grains deposited with the sand) have age signatures around 700–500 million years old. That age range doesn’t match the nearer Australian geologic sources. For example, the Lachlan Fold Belt in NSW is dominated by 450–300 Ma zircons, which are present in the Hawkesbury Sandstone but are often outnumbered by older grains in many samples — suggesting a mix of local and distant sediment sources. Instead, the 700–500 Ma ages correspond to the Pan-African orogeny belts – rocks common in parts of East Antarctica. In fact, researchers point specifically to Wilkes Land, East Antarctica as a likely provenance area, because beneath the East Antarctic Ice Sheet are crustal blocks with those Neoproterozoic–Cambrian ages. One geologist noted that the “basement of the Wilkes Subglacial Basin” in Antarctica could have been the ultimate source of the sand – an area now buried under Antarctic ice, some 5,000–7,000 km south of Sydney.

By Triassic times, those mountains were no doubt eroding rapidly. Rivers and rain would wash rock particles northward. Importantly, the sand grains that would form some of the Hawkesbury Sandstone are overwhelmingly quartzose (silica-rich) and well-rounded, indicating they had travelled far from their source. The chemical and age “fingerprint” of these sands fits East Antarctica’s geology much better than any local Australian source. This is a strong hint that Antarctica was feeding the sediment.

A Pathway Through Tasmania and Victoria

But how did sand from Antarctica actually get to New South Wales? To envision the route, we must remember the map of Gondwana. In the Triassic, Tasmania was not an island – it was the connection between Australia and Antarctica. The area that is now Bass Strait (separating Tasmania from mainland Australia) did not exist yet; instead, a continuous land corridor joined East Antarctica to Tasmania and on to mainland Australia. Through this corridor, a vast river system could carry sediment northward. Geologists have pieced together evidence that Triassic sandstone units in Tasmania and Victoria are the same age and type as the Hawkesbury Sandstone, suggesting they were laid down by the same enormous river system. For example, the Ross Sandstone in Tasmania is a Middle Triassic quartz sandstone coeval with the Hawkesbury Sandstone, and both were deposited by a big river system that came all the way from Antarctica. This implies that as the river flowed out of East Antarctica, it likely coursed across what is now Tasmania, depositing sand along the way, and continued into the region of today’s Sydney Basin.

Imagine standing in Triassic Tasmania: you’d see a broad swath of braided river channels carrying silica-rich sand, all moving north or northeast. As the river entered what is now Victoria and New South Wales, it spread into a wide alluvial plain. The transport pathway would have been guided by the topography – sloping downhill from Antarctic highlands toward lower lands in the north. In fact, reconstructions indicate the surface over which the Hawkesbury Sandstone was deposited sloped gently north-northeast from high ground in Antarctica. Essentially, gravity did the work: Antarctic mountains were the elevated source, and the Sydney region was downstream. The river likely passed through broad valleys or lowlands in the supercontinent, possibly following rift valleys or foreland basins on Gondwana’s interior. Paleogeographic maps of Gondwana show a contiguous system of Permian-Triassic sedimentary basins stretching from Antarctica into Australia. 

By the time the river reached the Sydney area, it had already travelled on the order of 1,500–2,000 kilometres or more. It likely picked up additional sediment tributaries along the way (including input from parts of what are now Victoria’s highlands or New England’s ranges to the west). But the bulk of the sand remained that distinctive Antarctic-derived quartz. Supporting this pathway idea, paleocurrent measurements (determined from sandstone cross-beds) in the Hawkesbury Sandstone consistently show flow from the southwest to northeast. In other words, the ancient current directions recorded in the rock point back toward the former position of Antarctica. Thousands of cross-bed orientations have been measured, and they show a strong bias indicating the water was moving northward (to the northeast) across the Sydney region. This is exactly what we’d expect if the sand-laden rivers were coming from the Antarctic-Tasmanian direction in the south or southwest.

The Mighty Triassic Braided River

Geologists envision the Hawkesbury Sandstone as the product of a massive, braided river system – truly one of the giants of its time. Braided rivers are characterized by multiple interweaving channels that constantly split and rejoin, with ephemeral islands of sediment (sand or gravel bars) between them. Today, braided rivers occur in places with high sediment supply and variable flow, often near mountains. A classic modern example is the Brahmaputra River in Asia, which drains the Himalayas. The Triassic River that deposited the Hawkesbury Sandstone may have been similar to the Brahmaputra in scale and style. In fact, one interpretation explicitly likens the Triassic River to the Brahmaputra, which carries huge volumes of sand and silt from the Himalayan highlands through braided channels across Bangladesh. Like the Brahmaputra, the Triassic River would have been several kilometres wide in places, with shifting channels across a broad alluvial plain.

But How big is big? We can gather an idea from the rock itself. The Hawkesbury Sandstone formation is massive – up to 240 meters thick in some areas, and it extends over 12,500 square kilometers under the Sydney Basin. It consists mostly of sandstone with minor shale lenses, indicating deposition by energetic water flows. The sandstone often shows very large-scale cross-bedding – which are the diagonal layers formed as sand dunes migrate in the river’s channels. Some cross-beds in the Hawkesbury Sandstone are on the order of meters in scale, suggesting dunes that were tens of meters wide migrating along the riverbed. Such large dunes and thick sand bodies imply the river’s channels were deep and broad, carrying tremendous discharge. The sand grains are well sorted and predominantly quartz, pointing to prolonged transport (allowing weaker minerals to break down and only hardy quartz to remain). Occasional thin layers of quartz-pebble conglomerate within the Hawkesbury Sandstone hint at flood events strong enough to move coarse gravel. All these features paint a picture of a powerful, high-energy river system capable of hauling sediment across a continent.

*This picture shows the Hawkesberry Sandstone Layer in Sydney.

From River Sediment to Solid Sandstone

As the Triassic mega-river waned (or the basin subsided), the layers of sand it left behind became buried under additional sediments. Over millions of years, this pile of sand compressed and lithified – turning into solid rock. The result is the Hawkesbury Sandstone formation, dated to the Middle Triassic (~247–242 million years ago). We can think of the Hawkesbury Sandstone as essentially an ancient river deposit that has been frozen in time. Its massive sheets of sandstone were once the river’s channel sands, and the occasional thin shale lenses were overbank mud or floodplain deposits that settled in quieter waters between the shifting channels.

Over time, tectonic changes gently uplifted the Sydney Basin, and erosion has since exposed the sandstone we see today. The Hawkesbury Sandstone now forms the familiar golden cliffs and gorges around Sydney – from the sea cliffs and headlands to the Blue Mountains inland. It’s sobering to realize that each sparkling quartz grain in those rocks may have originated in a far-off Antarctic Mountain and travelled across Gondwana in a river long lost to time.

Debates and Uncertainties: Was It Really an Antarctic River?

The idea of an Antarctic-sourced “mega-river” feeding the Hawkesbury Sandstone is compelling and supported by multiple lines of evidence like zircon ages, paleocurrent data, matching coeval sands in Tasmania, etc., but it is not without debate. Geology often has differing interpretations, and the Triassic Hawkesbury Sandstone is no exception. Some scientists have proposed alternative scenarios for the sandstone’s origin, questioning whether a single enormous river from Antarctica was necessary.

A Grand Geologic Story

Despite debates, the idea that sand from Antarctica ended up building Sydney’s sandstone cliffs captures the imagination and offers a grand sense of scale. It’s a plausible scenario given the geologic evidence and the configuration of Triassic Gondwana. Picture it: a colossal river system carrying sediment from an Antarctic mountain range, flowing for thousands of kilometres across a warm, river-laced supercontinent, and depositing a sand formation so extensive that it still dominates Sydney’s landscape today. The Hawkesbury Sandstone serves as a rock record of that Triassic journey. Tiny zircon crystals in the rock act like time capsules, whispering of an origin in Antarctic bedrock. Cross-beds frozen in stone still point northeasterly, recording the direction of an ancient current. Through these clues, we connect the sandstone under Sydney’s feet to a story that begins near the South Pole.

Here is the video we made on this on the OzGeology YouTube channel: