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Shark Bay

Geological Places

Shark Bay is a World Heritage Site located north of Perth on the western coast of Australia, renowned for its diverse marine and terrestrial ecosystems.

Stromatolites, Shark Bay, Australia
Stromatolites, Shark Bay, Australia

Geological Setting

Shark Bay is situated within the Carnarvon Basin, a geological region known for its sedimentary rock formations. The basin formed during the Late Permian to Early Jurassic periods as a result of tectonic processes, including the breakup of the supercontinent Pangaea.

Depositional History

Shark Bay has been shaped by sedimentation and the accumulation of materials over time. Sediments from nearby land areas, rivers, and marine sources contributed to the formation of distinct sedimentary layers.

Coastal Features

The bay itself is characterized by a series of peninsulas, bays, and inlets that have developed through the interaction of ocean currents, tides, and sediment deposition. These features contribute to the bay’s coastal geography.

Fossil Record

The region’s geological history is also reflected in its fossil record. Fossils found in the area provide insights into the ancient flora and fauna that inhabited the region during different geological periods.

Mineral Resources

Shark Bay has limited mineral resources compared to some other areas of Australia. Some salt mining occurs in the region, but the bay’s geological significance is more closely tied to its unique natural features and ecosystems.

Stromatolites

Shark Bay’s most famous geological feature are the stromatolites in Hamelin Pool. Stromatolites are microbial mats that form layered structures over time. They offer valuable insights into early life on Earth and because they form only very slowly, are evidence of the bay’s long relatively stable history.

Formation

Stromatolites are formed by the interaction between microbial communities, sediments, and water chemistry. In Shark Bay’s Hamelin Pool, the stromatolites are primarily composed of layers of cyanobacteria, also known as blue-green algae.

Microbial Mats

The stromatolites start as thin layers of microbial mats on the shallow seafloor. These mats are composed of different types of microorganisms, with cyanobacteria being the most prominent. Cyanobacteria are photosynthetic organisms that can tolerate high salt concentrations.

Layered Growth

Over time, the cyanobacteria trap and bind sediments with their sticky secretions. As these microbial mats grow and trap sediments, they create successive layers. The process of sediment trapping and binding contributes to the unique laminated structure of the stromatolites.

Mineral Precipitation

The microbial mats also influence the chemistry of the surrounding water. They release calcium carbonate, a mineral that can precipitate out of the water and accumulate around the cyanobacteria. This contributes to cementing of the layering and growth of the stromatolites.

Slow Growth

Stromatolite growth is exceptionally slow, often only a few millimeters per year, or even less. The growth depends on the sedimentation rate. Too little, and the structure doesn’t grow, too much, and the microbial mat is buried too deep and is starved of the sunlight the photosynthetic organisms need to survive.

Ancient Analogues

While modern stromatolites like those in Shark Bay are relatively recent formations (a few thousand years old), they provide insight into Earth’s ancient past. Fossilized stromatolites dating back over 3 billion years are found in the geological record and are considered some of the earliest evidence of life on Earth.

Freshwater stromatolites exist too, and fossils of them are found in Arizona. Some are on display at the Museum.

Scientific Significance

Shark Bay’s stromatolites are of great interest to scientists studying the evolution of life, microbial ecosystems, and the conditions of early Earth. They help researchers understand how microbial communities can shape their environments and contribute to the cycling of nutrients.

Hamelin Pool has a walkway built over the area with stromatolites, and it is open to visitors. But if you go, please leave them alone! Even a touch can profoundly disturb their growth for decades, or even longer.