Footprints are just marks on the ground without scientific interpretation. The Dinosaur Stampede Trackways at Lark Quarry provide the interpretation of over 3,300 tracks immortalised in stone. These fossilised footprints mark the only known dinosaur stampede on our planet. It is a globally unique and historical geological site.
But how have these tracks survived over the millenia? It is all down to geology.
This is ‘Jump-Up’ country - a landscape of mesas, gullies and steep escarpments. These extensive plains and uplands of western Queensland span some two billion years of geological time. This geological makeup controls almost all aspects of the physical and economic conditions of the Outback – the locations of mineral, oil and gas deposits, the landforms, the soils and hence the location of grasslands, desert uplands and channel country.
Yet this dry and dramatic landscape has been created by water. Geologists call this landscape “dissected residuals” - the sediments laid down by ancient lakes and seas have been carved over the millenia by runoff from countless summer storms.
The flow of underground water is inextricably linked to the geology. 95 million years ago this area was part of a great river plain with sandy channels, swamps and lakes. Layer upon layer of fine-grained silt and sands were laid down over time by lakes while the thick rocky layers of mudstones were laid down by faster streams. In some places there are water patterns in the rock where currents met.
Over the millenia, waterborne chemicals hardened the sediment layer, which is now on top of the uplands, making it more resistant to erosion. The softer sides have continued to erode creating the mesas in the area. River sediment and ‘thrust up’ ranges were continually eroded. Constant wind and water erosion have carved out many caves and overhangs. The actions of wind and water are still eroding the area today.
This sedimentary layer here is known as the Winton Formation. The thickness and extent of the Winton Formation makes it one of the biggest geological formations on the continent. They are the rocks in which Lark Quarry’s trackways and Winton's many other dinosaurs have been found.
Much of the sediment which formed the Winton Formation was derived from volcanoes far to the east. It is these deposits of silt up to a kilometre thick that entomb the skeletons of Australia’s largest dinosaurs as well as many other fossils. Dinosaur fossils are not generally found in the deeply weathered rocks. It is only in the less weathered areas that their fossilised bones have been recovered.
At Lark Quarry a team of paleontologists, geologists and other scientists spent 18 months removing part of the hill to expose the trackways layer. They traced the sediment layer the tracks were found in back to a second hill farther to the east. They predicted there would be more tracks at the same level and they were right. They are of Cretaceous age and are between 98-95 million years old.
Remember to take only photos and leave no trace of your visit. We hope you enjoy your visit to this remarkable Australian geological formation.
You may log this Earthcache straight away but then please email your answers to the questions to the CO. We will contact you ONLY if your answers need extra work. Logs with no answers sent will be deleted. Use the many information boards and displays to find the answers.
1. How many tonnes of rock were excavated to uncover the footprints?
2. How many types of dinosaurs feature in the stampede?
3. What is the width of the large theropod footprint?
4. How many years ago did Gondwana, the great southern land, begin to break apart?
5. Name and describe one of the many fossils on display.
6. Look at the landscape. Describe what a nearby mesa looks like.
You are welcome to post a photo of yourself enjoying this cache. No spoilers please.