Local Geology & Fossils

The rocks and landscapes of the Nyanda–Carnarvon Gorge area are highly significant for both their natural beauty and scientific value. Uniquely, the concentration of diverse geological processes, events and time ranges here surpasses all other places in Queensland. Going from one horizon to the other, we see a rich record of multiple changes to the environment documented in the rocks: from river plains and peat swamps to deltas, glaciers and the open ocean. We also see a rich record of major geological events to happen to eastern Australia over the past 290 million years, including crustal extension (e.g., rifting) and compression (e.g., mountain building), land subsidence and uplift, sea level rise and fall, volcanism and erosion. Nowhere else in Queensland – or Australia, for that matter – is such a rich history of environmental and geological change at your fingertips.

 

Owing to this rich history, the region has been critical to the development of scientific understanding of the Bowen Basin over the past 100 years. Within the boundary of Nyanda station are the type sections of the Cattle Creek, Bandana and Arcadia Formations, and the type sections of many other geological units – Aldebaran and Catherine Sandstones, Freitag, Ingelara and Peawaddy Formations, and the Black Alley Shale – are located in the immediate surrounding area. Improvements in scientific understanding and development of geological frameworks have contributed immensely to coal mining and gas exploration throughout central Queensland.

 

Of further economic and societal relevance, immediately to the west and south of Nyanda station is The Great Unconformity. This is an erosional surface separating the westward-dipping, Triassic strata of the Bowen Basin (Arcadia to Moolayember Formations) and the largely flat-lying, Jurassic strata of the Surat Basin (Precipice Sandstone). This unconformity represents a major gap in geological time – in excess of 35 million years – due to uplift and erosion of the landscape. More importantly, it is crucial to the existence of the Great Artesian Basin, which supplies water to agriculture and communities in much of western Queensland. Rainwater is absorbed by and percolates through the porous rocks of the Surat Basin, with the Precipice Sandstone acting as a major aquifer. However, the rocks underlying the unconformity, especially the Moolayember Formation, are mostly impermeable, forming a seal (aquitard) that prevents groundwater from percolating further down, forcing it to move laterally (westward) instead. This process can be observed in Carnarvon Gorge and the headwaters of Consuelo Creek, where water seeping downward through the Precipice Sandstone encounters the seal of the unconformity and is forced to move laterally, seeping out of the walls of the cliffs and canyons as springs.

 

Mirroring its geological history, the Nyanda–Carnarvon Gorge area also is host to a diverse array of fossil fauna and flora. Again, the sheer concentration of these in a localized area is unique to Queensland. These palaeontological discoveries have been crucial to understanding the sequence of different marine and terrestrial ecosystems in central Queensland and beyond. They have also played key roles in developments of our geological understanding of the planet. Many of the fossils of the region contributed to the emergence of the theories of continental drift (circa 1915) and plate tectonics (1960s). For example, land-dwelling plants, like the Permian Glossopteris, and animals like the Triassic Lystrosaurus[1], are found in Queensland (and other parts of eastern Australia), Antarctica, India, southern Africa and southern South America. The only way these species could be found in such far-flung places is if the continents were once joined together. Additional evidence for this ancient supercontinent (Gondwana) has subsequently been identified from more recent sedimentology, palaeomagnetism, and petrological studies.

 

The rocks of Nyanda station also capture one of the most important biotic events in the past 500 million years – the Permo-Triassic extinction around 252 million years ago. Marking the end of the Palaeozoic and start of the Mesozoic, this event saw massive ecosystem collapse followed by a slow recovery, which saw the end of many groups of plants and animals as well as the origins of new ones. The extinction boundary is crisscrossed by numerous creeks on the station: you can literally stand with one foot in the Permian and the other in the Triassic. There are only a handful of places in the world where the boundary can be directly observed in this way (e.g., South Africa, China, and near Newcastle and Hobart).

Despite the rich trove of geological and palaeontological insights the Nyanda–Carnarvon Gorge area have afforded us over the past 100 years, there is still much to learn and discover!

 

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