Discover Western Australia and Explore the Geodiversity and Fossils of Hamelin Pool in Shark Bay
- Wayne Munday
- 5 minutes ago
- 5 min read
Sip back and discover Western Australia and explore the geodiversity and living Stromatolite fossils of Hamelin Pool in the Shark Bay World Heritage Area approximately 800 Km north of Perth via National Route 1 or a 2 hour flight to Carnarvon (YCAR). Shark Bay is situated at the most westerly point of Australia and exposed to the Indian Ocean. Spanning over 22,000 Km2 over 70% of the region is made up of marine waters. Shark Bay was named in 1699 by William Dampier (1651 – 1715) who was a buccaneer who later explored Australia's coast and the Islands Region of Papua New Guinea for the British Admiralty. During his voyage to Shark Bay he encountered numerous species sharks. The calm, shallow and sheltered coastal waters of Shark Bay is also home to the Wooramel Seagrass Bank the world’s largest seagrass bank where 12 of 60 seagrass species including Posidonia australis grow. The biodiversity of Shark Bay includes a large population of Dugongs and the nesting grounds for the endangered Green and Loggerhead Turtles. Sharks are present all year-round along with dolphins numerous species of fish and is an important stopover for Humpback whales migrating south in Spring heading towards colder Antarctic waters to feed.
Hamelin Pool’s is a hyperarid barred basin a specific type of sedimentary basin found in extremely dry environments where water flow is limited by a natural barrier or sill creating hypersaline seawater. In this environment there are few algae consuming organisms that can survive so allowing Entophysalis a genus of single celled cyanobacteria to slowly grow and extensively colonise sublittoral and intertidal zones with Stromatolites.
Entophysalis is a photosynthetic microorganism that converts sunlight, water, and carbon dioxide into food and releases oxygen as a byproduct. These microorganisms represent some of the earliest life on Earth and played a pivotal role in the Great Oxygenation Event (GOE) between 2.4 - 2.1 billion years ago during the Rhyacian Period of the Paleoproterozoic Era.
The Great Oxygenation Event marked the first permanent rise of oxygen in both Earth’s atmosphere and oceans. Earth's transformation from an oxygen poor to an oxygen rich environment was driven by cyanobacteria who began to produce oxygen by photosynthesis.
This environmental change was in fact an Oxygen Catastrophe for some species leading to the widespread extinction of many anaerobic microorganism species of Archaea. The Great Oxygenation Event would be a fundamental driver in life’s evolution as we know it today. The evolution and adaption to aerobic respiration or simply the ability for species to breathe air set the stage for more complex organisms like single celled eukaryotes and multi-celled animals to prevail.
Stromatolites whose name means "layered rock" in Greek are microbial reefs formed by cyanobacteria that traps and binds sediment and precipitate minerals to build up layers. Stromatolites grow extremely slowly at less than 1 mm per year. The surface of a Stromatolite hosts living microorganisms while the underlying layers preserve lithified trace fossils of previous microbial communities.
Shark Bay is regarded a productive aquatic ecosystem dominated by carbonates that are not associated with coral reef structures so making it geologically distinct. The hypersaline waters contribute to the precipitation of calcium carbonate leading to extensive limestone deposits.
Shark Bay is shaped by the natural formation of the Faure Sill a submarine bank that restricts water exchange to the southern bay areas of Hamelin Pool and L'Haridon Bight. Combined with the arid climate and hypersaline conditions its ideal for supporting Stromatolites, coquinas or sediments of shell fragments and oolitic shoals of spherical sand-like grains called ooids of calcium carbonate. These white sands make up the Edel Land Peninsula and nearby islands and composed of the Tamala Limestone formed by the marine debris.
Shark Bay is a dynamic channel bank system that began to form around 8,500 years ago during the current Holocene Epoch as sea levels changed, sediment accumulated and seagrass colonised the area.
Shark Bay’s landscape is striking. To the east are the red sands of Peron Peninsula that contrast with white beaches and dramatic coastal cliffs to the west. Approximately two million years ago the red sediments eroded from the sandstone plateau of the Kennedy Ranges and were transported to Shark Bay. These sediments were reduced to fine quartz sand grains that now form the dunes along the Peron anticline and Peron Sandstone that now underlies much of Shark Bay.
One of Shark Bay’s most prominent geological features is the Zuytdorp Cliffs that rise to a maximum height of 250 meters at their highest point near Womerangee Hill. Located to the west of Shark Bay they are composed of Tamala Limestone and follow the coastline for over 200 Km from Steep Point to Kalbarri.
The Zuytdorp Cliffs is Australia’s longest fault scarp formed between 5,000 - 10,000 years ago by an earthquake that caused vertical movement of the rock along the Zuytdorp Fault line. These cliffs are repeatedly undercut by the waves causing them to collapse and erode into wave cut platforms and blowholes.
Another defining feature of Shark Bay and especially prominent in Francois Peron National Park is the Birridas. This is a series of saline hollows that initially originated as lakes during high sea levels. As the sea regressed the lakes dried leaving behind gypsum deposits and forming depressions ranging from small circular basins to large elongated hollows forming shallow bays crucial as marine nurseries.
Shark bay is home to one of the world’s largest populations Dugongs as well as the nesting grounds for the endangered Green and Loggerhead Turtles. Migratory Humpback and Southern Right Whales pass through its waters as well as sharks and a pod of Bottlenose Dolphins that live in coves and seagrass habitats.
The Stromatolites at Hamelin Pool vary by depth and elevation with living forms found from 3.5 meters below the sea surface up to the high-water-spring tide mark. Stromatolites also vary in shape depending upon their location. For example, flat Stromatolites are found in the high intertidal zone; the large bulbous shaped Stromatolites are located in the in the lower intertidal and the columnar Stromatolites are found in the shallow subtidal zone.
There are a number of distinct living "Stromatolite Provinces" found around the world including the Bahamas at Exuma Cays contain living stromatolites; Lake Tanganyika of the East African Rift; the interior western regions of Argentina; the Gulf of California lagoons and Yucatán’s Laguna de Bacalar in Mexico; Chetumal Bay in Belize and freshwater Stromatolites of Lake Van and Lake Salda in Turkey and Pavilion Lake and Kelly Lake in British Columbia, Canada.
Stromatolites serve as indicators of environmental health in aquatic ecosystems. Their presence suggests clean, stable and well lit waters with adequate oxygen and minimal ecological disturbance. Additionally, fossilised stromatolites provide valuable records of ancient atmospheric and oceanic conditions. While Stromatolites indicate certain signs of ecosystem stability their presence may also reflect an unique or marginal habitat rather than broadly healthy environment.