As you look over the cascades at the GZ you are in fact watching rocks grow and new fossils formed. Tufa is a variety of limestone, formed by the precipitation of carbonate minerals from ambient temperature water bodies.
The process starts deep within the earth. Limestone dominates the geology of this area and the flora river is fed by many springs that flow up through this limestone layer. This causes the water that emerges to the surface to be mineral rich, the dominate mineral being calcium carbonate.
As the water tumbles over rocks, plant and animal debris in the rive,r oxygenation of the water causes the dissolved calcium carbonate to precipitate (solidify), covering and fossilising debris such as shells, snails, rocks and animal remains. This is a bit like a layer of salt being left behind when water evaporates from salt water except calcium carbonate precipitates while the water is still there.
The result of this process is tufa, and the amazing fact that as you stand at the GZ you are in fact watching rocks grow and fossils formed. There are many “new” fossils in the tufa here.
Modern and fossil tufa deposits abound with wetland plants and as such many tufa deposits are characterised by their large macrobiological component and are highly porous. Tufa forms either in fluvial channels or in lacustrine settings
Fluvial deposits
Fluvian deposits can be classified by their depositional environment, that is by the vegetation or petrography (the mineral content and the textural relationships within the rock). Fluvial deposits can be classified as:
- Spring – Deposits form on emergence from a spring/seep.
- Braided channel – Deposits form within a fluvial channel, dominated by oncoids (sedimentary structures formed by Cyanobacteria e.g. blue-green alage.)
- Cascade – Deposits form at waterfalls, deposition is focussed here due to accelerated flow of water.
- Barrage – Deposits form as a series of phytoherm barrages (fresh water reef) across a channel, which may grow up to several metres in height.
Lacustrine deposits
Lacustrine tufas are generally formed at the periphery of lakes and build up phytoherms (freshwater reefs) and stromatolites (layered bio-chemical structures formed in shallow water by the trapping, binding and cementation of sedimentary grains.) Oncoids are also common in these environments.
There are some informative diagrams at the GZ which illustrate the processes involved in forming Tufa here at the Flora River.
To log this cache you need to answer the following questions and email your answers to the CO.
- What kind of deposit (Fluvian or Lacustrine) forms the tufa here at Flora River?
- What colour is the water and what gives the water its beautiful colour?
- What other forces applied to calcium rich water can cause tufa to form?
Flora River Nature Park is 45 kms off the highway on good formed dirt road although the last 10kms, once you enter the park, is extremely corrugated so go slow. The park is closed during the wet season so this cache is only available from March/April (depending on how wet the wet has been) until November/December (depending on how early the rain comes). Check at www.parksandwildlife.nt.gov/au to see if the park is open.
Parking is available at the waypoint/trail head. There is a second, shorter trail to another tufa dam leading from the waypoint that we highly recommend you take a look at. Camping is also available at the waypoint with hot showers and flushing loos!
We hope you enjoy this beautiful spot.