New Riversleigh Survey, The Cavers And Dating
Many years ago a former University of New South Wales (“UNSW”) student, Ned Stephenson, developed a map of the RWHA and surrounding areas using multi-spectral satellite imagery. His map revealed a vast area to the west of the RWHA that emitted the same electromagnetic signals as the fossiliferous sites in the RWHA. We have now been surveying the New Riversleigh area for several years and continued the exercise this year. While “Old Riversleigh” is accessible by the 4×4 vehicles, there are no suitable tracks into the New Riversleigh area.
Davin, our helicopter pilot (Figure 8) from Cloncurry Mustering arrived on the night of 1st of July. He spent his time shuttling the New Riversleigh survey teams, the caving team and others groups around the inaccessible regions of both Old and New Riversleigh.
We transported a drum of aviation gas to Old Riversleigh by road each day to minimise the helicopter flights back to Adels Grove for refuelling. The helicopter would have to transfer the full drum off the tray back (Figure 9) at our staging area each morning.
The New Riversleigh survey consisted of two teams of 3 persons. The two teams were transported to their drop off locations and made their way along planned routes using GPS units. We were then picked up at set pick up points. As the distances were far off, our UHF walkie-talkies would sometimes be out of radio communications reach. At preset times, the helicopter would be taken off the ground so the survey teams would be in communication as the radio signals worked best with line-of-sight endpoints.
The limestone at both Old and New Riversleigh were formed and re-formed during many different geological periods, the earliest being Pre-Cambrian and the latest in the Pleistocene. While we did not find any teeth or bones in New Riversleigh this year, we found many indicators of potentially fossiliferous deposits in this area.
Speleothem (Figure 10), cave deposits consisting of stalactites, stalagmites, flowstone and cave crystals are formed from the precipitation of calcium carbonate in solutions. Some of these caves acted as pit traps where animals would fall in and their remains would get fossilised in the lime rich environment. We found many areas in New Riversleigh with chunks of speleothem lying on the surface.
The other indicator we searched for were the presence of snail shells on the surface of limestone rock (Figure 11) as these deposits formed in the mid Oligocene and are potentially suitable for the fossilisation of animals of interest. There were long stretches of our survey routes where we found these fossilised snails.
All our survey tracks and GPS coordinates for the speleothem and snail areas were logged into our GPS database and will be used for further investigation in future years.
The caving team consisted of Blake Dickson, Jon Woodhead and John Prince. They were transported by helicopter to caves around the Old and New Riversleigh. Some of these caves were located in previous years, and new caves were discovered from the helicopter by locating vegetation accumulating near sinkholes where the water drains downwards.
The caving team collected speleothem and fossils from the caves. The stalactite (Figure 12) would be embedded in resin and sliced lengthwise to determine the geological period it was formed.
Jon with other members of the excavation group spent a bit of time locating good clean samples of speleothems (Figure 13) from other sites for dating in his University of Melbourne laboratory by measuring the proportion of uranium in the sample compared to it’s products of decay.