| Significance |
STATEMENT OF HERITAGE SIGNIFICANCE
The Green Waterhole - Tank Cave Fossil Complex contains the only known extensive underwater vertebrate fossil deposits in Australia. This unique freshwater depositional environment has ensured the preservation of extinct species not found anywhere else, with several additional species new to science recovered and awaiting description.
The underwater deposits have also resulted in a completeness and preservation of fossil assemblies almost unique for Australia. This provides an important opportunity to investigate the evolution of South Australian mammals and birds. The impacts of this type of site on the age and nature of the fossil remains have yet to be fully studied.
The complex represents unusual geological formations including the occurrence of a shallow fresh waterhole not usually found in sinkholes in the South East, and evidence of rare volcanogenic influences in the formation of the cave system.
The cave complex also demonstrates rare speleological features, including length of cave passageways, clarity of water, underwater speleothems, and being a type locality for stygofauna. The complex also holds importance for the development of cave diving in the country and is closely associated with the Cave Divers Association of Australia.
It is also acknowledged as a place of significance for the Boandik people.
STATEMENT OF PALAEONTOLOGICAL SIGNIFICANCE
Designation date: 23-JUN-2022
The Green Waterhole - Tank Cave Fossil Complex is highly significant for palaeontology in three important ways.
First, it is the best example of underwater Pleistocene vertebrate deposits anywhere in Australia. Although fossils of this age are found in underwater settings throughout the Mt Gambier region, fossils in the Green Waterhole - Tank Cave Fossil Complex are incredibly numerous, very well preserved, and found in situ.
Second, the site contains fossil species found nowhere else in Australia, or else are incredibly rare. These include both bird and kangaroo species.
Third, the site offers the rare opportunity to study the taphonomy of underwater deposits. Evidence for at least one wetting and drying phase in the cave has the potential to provide important information for understanding how fossil deposits are formed and preserved in cave settings.
The significant palaeontological features contained within the complex are:
* Oligo-Miocene marine species throughout the cave walls and ceilings
* Incredibly well-preserved and diverse underwater vertebrate fossil deposits
* Type site for extinct kangaroo Simosthenurus newtonae
* Type site for extinct birds Centropus colossus and Orthonyx hypsilophus
* Untouched* fossil and sedimentary deposits in Green Waterhole/Tank Cave
* Presence of rare megafauna taxa such as Propleopus
* Underwater taphonomic processes including microbial activity, mineral dissolution and deposition, weathering, fragmentation, and disarticulation
* Diverse and rich avifaunal deposits
*Several sites within the complex are almost untouched, in particular some sedimentary beds. Sedimentary deposits are a well-known source of palaeoenvironmental information that can inform on precipitation and vegetation histories. Science recognises the intrinsic value of preserving important elements of the caves in their original (pre-human) condition. This provides a significant undisturbed record of the State's palaeoenvironment. Science also recognises that such preservation may enable future examination and enhanced interpretation using techniques not yet devised or invented for understanding our State's past environment.
STATEMENT OF SPELEOLOGICAL SIGNIFICANCE
Designation date: 23-JUN-2022
The Green Waterhole - Tank Cave Fossil Complex is situated at the Western end of the longest underwater cave system in South Australia, widely acclaimed as one of the premier cave diving localities in Australia. The Green Waterhole - Tank Cave system has a long history in the development of the sport of cave diving in Australia.
In addition to the 10 kms of passageways that can be explored by divers, the complex preserves important speleological formations, features, and fauna that are rare or not found in other caves in the area.
The significant speleological features contained within the complex are:
* Extensive phreatic joint-controlled maze cave system with outstanding exploration potential
* Twilight and dark underwater zones accessible by divers
* Cave collapse features and boulders in Green Waterhole
* Underwater speleothem formations
* Calcite raft deposits
* Undisturbed mud cracks and significant sediment accumulations
* Marine and vertebrate fossils in the walls and on the floor, respectively
* Preservation of stromatolites around the cave entrance
* Type locality for Koonunga crenarum (a syncarid crustacean)
* Habitat for over 40 other species of stygofauna
* Scalloping and phreatic erosion above the current water table
STATEMENT OF GEOLOGICAL SIGNIFICANCE
Designation date: 23-JUN2022
The broad Gambier Limestone Plain extends from the coastline to the Bordertown/Kingston area and is a raised sea floor, elevated over 1-2 million years by tectonic forces associated with the volcanic activity across the region. Fresh groundwater from rainfall percolates through the limestone from inland to the coast, dissolving cave systems particularly along major fracture lines (geological faults). Volcanoes also have also erupted along two large regional faults in the Mount Gambier region. Many large deep sinkholes (`cenotes') have developed south of Mount Gambier reaching the water table and extending deep below them (50-120m).
The combined Green Waterhole-Tank Cave system is shallow by comparison (20m) with other sinkholes in the region, and is the longest underwater cave system by far in South Australia, developed by solution in a large complex grid system (see site map overlay). Initiation and enlargement of the cenotes and possibly the Green Waterhole-Tank Cave system itself has been assisted by volcanic CO2 gases rising up fault lines and acidifying the groundwater, stimulating large-scale solution of passages in the limestone (Webb et al 2010). This is a rare process in global cave development known as `volcanogenesis' and requires the coexistence of volcanoes, extensive limestone and abundant groundwater, which occurs at this location. Ongoing research will establish if this process has been applied throughout the development of the Green Waterhole-Tank Cave system.
Green Waterhole is a shallow cenote that is attractive to animals and humans, being more accessible for drinking during dry periods than most other sinkholes in the region. The waterhole made water available in a pool perched above the regional water table during low sea levels. The cave complex provides an excellent opportunity to study the relationship between changing sea-levels, ground water, and environment, and their effects on the evolution and extinction of fauna in the region over a long time period.
The significant geological features contained within the complex are:
* Soft limestone caves including connections between doline and dissolution passages
* Exposure of the regional water table and associated freshwater semi-troglobitic aquatic life
* Untouched sedimentary deposits preserving pollen and spores over thousands of years
* Solutional/Erosional features indicative of higher and lower water levels in the past and their various effects upon cave development in the limestone mass
* Capacity for examination in detail of possible impact of rare `volcanogenic' influences. |