The Central Queensland sandstone belt covers an area of approx 82,000 square km. At least 25 separate mountain ranges radiate from the Great Dividing Range in this region, forming a rugged and varied landscape.
Etched deep into porous Precipice Sandstone the 30km long Carnarvon Gorge formed where weathering and erosion attacked weaknesses in the rock. The gorge will not get much deeper because shales of the Moolayember Formation below are resistant to the erosive action of running water.
However, it wasn’t always like this.
1. Carnarvon Gorge was once part of a large, shallow inland sea that filled with sediment. Over time the sediment compressed into shale and sandstone beds. At times, due to earth movements and changes in sea level, the water retreated or land was forced upwards to leave the area high and dry.
2. The Precipice Sandstone formed around the time of dinosaurs (about 200 million years ago) when an extensive inland river system deposited vast quantities of coarse sediment over much of southern Queensland. Millions of years later the area was once again covered by the sea.
3. Massive earth movements about 40 million years ago pushed and folded the ‘soft’ rocks forming the Great Dividing Range and Carnarvon Ranges. Soon after, during periods of volcanic activity, lava covered the layers of sandstone with a thick basalt cap up to 300m deep.
4. The basalt cap weathered away in places to expose underlying Precipice Sandstone. Carnarvon Creek quickly gouged deeply into this ‘soft’ rock forming the spectacular gorge system. Weathering will eventually produce a flat surface.
The landscape of Carnarvon Gorge continues to be sculpted. The erosive force of water acts on lines of weakness (joints) in the sandstone. This causes large, straight-sided blocks to break away.
Alternate wetting and drying of the sandstone also causes the expansion and contraction of the fine clay particles which hold sand (quartz) grains together. Over time these grains are dislodged. The rounded caves and overhangs, particularly at cliff bases, are a combination of this weathering process and wind-blown sand eroding the rock face.
For more information and interactive displays drop into the Visitor Information Centre at the end of the entry road.
Now for the cache. To walk the main gorge you will cover 11km one way of extremely difficult terrain and it will take a day or two. Many of us cannot achieve that task so this Earthcache is designed to be a much more achievable and comfortable walk for all ages and levels of fitness.
Start from the Mickey Creek carpark. Wander along the Mickey Creek track until you reach the sign at a junction of two gorges. You can choose to investigate either Mickey Creek Gorge or Warrumbah Creek Gorge (or both). On the way to the junction the walking track is good for 1.5km but eventually becomes a fun rock-hopping adventure if you decide to continue on.
If you choose to explore the fabulous Mickey Creek Gorge please answer these questions.
M1. Go to S25 04.520 E148 13.972 Face “The formed track ends here” sign and look north (to your right). What colour sandstone forms the top of the gorge?
M2. Now look south. Describe the rocky feature you can see?
M3. What evidence can you see that indicates water helped to form this pathway?
If you choose to explore the wonderful Warrumbah Creek Gorge please answer these questions.
W1. Go to S25 04.408 E148 14.050 Describe the large rock formation nearby.
W2. Describe what is under your feet at this same point. Include colour and size.
W3. What evidence can you see that indicates the walls of the gorge have been eroded by water?
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.
You are welcome to post a photo of yourself enjoying this cache. No spoilers please.
Remember to take only photos and leave no trace of your visit. We hope you enjoy your visit to this spectacular Australian geological formation.