Geological Foundations of Shark Bay

Shark Bay’s spectacular coastal scenery contributed to its World Heritage status. The region’s contrasting red sandstone and white limestone are part of a geology that is simultaneously prehistoric and modern.

Ancient origins

The Shark Bay area is part of the Carnarvon Basin, a geological depression stretching along the western coastline of Western Australia. It comprises two main layers of marine sediments: a 4 km-thick Silurian sequence, dating from about 434–410 million years ago, and a 2 km-thick Devonian-Lower Carboniferous sequence, dating from about 410–320 million years ago. On top of this is another layer of chalky limestone called Toolonga Calcilutite, formed during the Cretaceous period some 144–65 million years ago.

Shark Bay geology fact sheet link

Visit our geology of Shark Bay fact sheet for all the information on how the bay was formed.

Generalised geological map of Shark Bay

Surface geology

By contrast, Shark Bay’s surface geology is relatively young. It is mostly sandstone and limestone, composed of sediments deposited by the wind and sea during the last two million years (Quaternary period). This map shows how Peron Sandstone and Tamala Limestone dominate the Shark Bay region.

Peron Sandstone

Peron Sandstone underlies most of the region, but is exposed only on Peron Peninsula and Fauré Island, off Monkey Mia. Its rich red colour comes from the thin layer of iron oxide coating each grain of quartz.

Peron Sandstone had its origins in an ancient seabed hundreds of kilometres east of Shark Bay, in the Gascoyne interior.

About 250,000 years ago sediments from this ancient seabed were blasted to the coast by easterly winds, or shorn off by torrential rains and carried down rivers to the sea.

Over thousands of years, these sediments accumulated against a long, exposed ridge in the terrain called the Peron anticline. Stabilised by vegetation, the sediments slowly consolidated into rock. The wind has been eating away this rock ever since, forming spectacular dunes.

Tamala Limestone

The white Tamala Limestone is a stunning contrast to the red Peron Sandstone. This limestone, which overlays most of Shark Bay, was formed from shells and other marine skeletons.

During the last glacial period (or ‘ice age’) some 125,000 years ago, falling sea levels exposed the shells to the winds, which eroded them into sand particles and blew them into enormous dunes.

These dunes accumulated against an anticline that underlies present-day Edel Land, Dirk Hartog Island, and Bernier and Dorre Islands.

Over time, calcium carbonate (lime) from percolating rainwater cemented the sand into stone. The Zuytdorp Cliffs are made of Tamala Limestone.

Geological cross section through Shark Bay

Geological cross section of Shark Bay

Formation of Tamala limestone

Tamala Limestone was formed from marine deposits – shells, skeletons and corals – eroded by the severe Shark Bay winds.

Later, a rise in sea levels during the Holocene epoch (the most recent 10,000 years) flooded the region and created Shark Bay’s unique double-basin form. It also left more marine deposits, which were exposed during a later drop in sea-level and slowly eroded into sand to form giant white dunes overlaying the Tamala Limestone. The wind’s cycle of formation and destruction can still be seen today; an interplay of elements as old and dynamic as this ancient, fragile land.