John Jackson (Rock Doctor) Guided
Bus Tour 2 To Brooms Head
On Friday 4th November PYHS members ounce again enjoyed stories about the geological formation of Redcliff and Brooms Head as explained by Dr John Jackson (Bus Trip 2)
THE EARLY CLARENCE
(a pre-historic story)
A recent excursion to Red Cliff, just north of Brooms Head, revealed rocks that told stories of the early Clarence Valley. A fabric painting on calico was used to highlight the geological history. All the coloured areas represent known action or the birth of rocks. The black areas represent unknown, missing or eroded history.
At the bottom are the bluish-green, folded and faulted marine rocks. They form the basement on which the Clarence Valley rests - purple coals, orange and yellow sandstones. They were folded into a mountain range about 290 million years ago (mya). The mountain range was then intruded by granites (red “blobs”). After being uplifted the mountain range was eroded down until sediments were being deposited in the valleys.
In this photograph the rocks tell the stories of flash floods some 200 mya. Occasionally between the floods, the surrounding forests deposited woody material into lakes where they were preserved as peat and then compressed and “cooked” into coal (purple colours). The early Clarence Valley appears to have flowed westwards into an inland-sea and this continued until about 140 mya.
The black area immediately above the yellow shows we are missing part of our story here. But soon after the land begins to rise (large blue triangle) as magma is injected (132- 95 mya, the formation of the Whitsunday mama province). This breaks apart the remnants of the mountain range and inserts an oceanic floor for the Tasman Sea (83-56 mya - blue triangle at top right).
The small pink triangle at the very top represents volcanic injections from a mantle plume just east of Baryugil. This happened around 19 mya as Australia drifted north over the plume. Australia is the fastest moving continental plate on the planet and the Red Cliff location has drifted from Bass Strait to its present location in just 19 million years.