The magnificent cliffs of the Murray river were deposited between 26 and 20 milion years ago in the early Miocene era. The Murray river cuts through a geological area called the Murray Basin. The Mannum formation, marine sediments stained an orange/yellow color, are composed of limey sandstone and sandy limestones. This formation is very fossiliferous. The colour of the cliffs changes to gold in the light of the setting sun.
Vertical limestone cliffs rise up to 90 meters above one side of the river. The sheer rock face is home for birds and lizards. At the river level some of the rock face has been undercut. The overhanging limestone has been perforated by solution tubes known as Avens. Solutions tubes grow when weathering forms a hole in the rock. The vertical hole then provides a localised environment for preferential weathering.
To get to GZ you will need to be on the river. As you float under the overhang you will see a number of round tubes. The tubes extend vertically into the limestone. You may also see some fossils and shells embedded in the rock matrix.
You are welcome to log a "Found it" log when you message or email the answers for the following questions. any "Found it" logs without the answers being sent will be deleted.
There are 2 overhangs with Avens and i will accept the answers for either overhang.
Take your time to examine the overhanging surface. Please supply answers to the following questions.
1. How many tubes do you see under the overhang? How big is the largest? Do you think the tubes are growing or shrinking?
2. What living animals are present in the tubes?