Earthcache I - a simple geology tour of Wasp Head EarthCache

Introduction to the Tour Around 280 million years ago this area lay in a shallow sea to the east of the primitive Australian landmass. The Earth at that time, know by geologists as the Permian, was gripped in an ice age and glaciers moved across the landmass, picking up rocks as they traveled, then sheared off at the coast and formed numerous icebergs. As these icebergs drifted over the sea they melted dropping their encased rocks into the mud on the sea floor. Life on the ocean floor at this time was a difficult existence. Living in cold waters and the constant rain of stones from above made for hard times. Still life was varied and abundant.

Start Location : Worm Burrows (35o 40.042S 150o 18.302E) Not all fossils are the remains of animal shells or bones. Trace fossils are the preserved marks, tracks and burrows of animals in sediments that later turn into rock. At this location, trace fossils of worm and other animal burrows are very abundant. They appear as dark marks on the light gray rock.

Location 2 : Split joint (35o 40.029S 150o 18.336E) As sediments turn into rock they form a criss-cross pattern of cracks called joints. These joints are zones of weakness along which the rocks will later split when they are exposed at the surface. North of this area a huge cliff has formed where the rocks have split and collapsed along these joints when the ocean has under cut the cliffs. At this location, a large slab of rock has split off along a joint. If you walk inside the split you can see where some of the pebbles in one side have a matching pebble on the other side.

Location 3: Dike (35o 40.083S 150o 18.401E) Long after these sediments became rock, some very hot molten rock was squeezed up into a crack and cooled to form what geologists call a dike. At this location the once molten rock was softer than the surrounding sedimentary rocks and has been eroded away by the ocean leaving a straight 'channel' in the rocks. You can see in some places the heat from the original molten rock as cooked the sedimentary rocks making them slightly harder so that they form a higher lip to the channel.

Location 4 : Drop Stones (35o 40.043S 150o 18.374E) As the icebergs floating on this ancient sea melted they dropped all their contained rocks down into the mud on the sea floor. Geologists call these drop stones. Some of these rocks have been transported by glaciers many hundreds of kilometers inland from the coast. At this location you can see one of the larger of these stones. You can see a few other large drop stones from this location - and all of these are different types of rocks from different distant locations.

Location 5: Fossils (35o 40.129S 150o 18.411E) To live on the sea floor during this time was quite dangerous. Some animals developed thick shells to protect them from the stones dropping out of the icebergs above. The fossils of these can be found at this location. They are a dark gray in color and belong to a few different animals. The smooth shells are a type of bivalve (eurydesa) and the ribbed shells belong to brachiopods (spirifid). You can find many of these fossils in this layer of rock. It’s worth having a hunt around for good examples. Some of these fossils have shells a couple of centimeters thick, and some of the shells are 15cm across. An occasional pectin shell (just like the Shell Petrol Station sign) can be found.

Location 6: Bryozoan colony (35o 40.120S 150o 18.405E) An unusual fossil found at this location is a colony of tiny animals called bryozoans. Bryozoans are not unlike corals, except they have a more developed internal structure (mainly they have a mouth and an anus - corals only have one opening). The colony found here would have been a fan like structure, but all we now see is a cut away through some of its 'fronds'. It would have been up to 1 meter across. Unfortunately someone tried to collect this colony and have destroyed some of the fossil - making it not as nice for you to see (thoughtless collectors often damage far more fossils than they ever collect. Also to collect fossils from here would result in a fine or even a gaol term - its a National Park remember!!).