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THE QUESTIONS:
1.) What is the most prevalent colour in the fossil?
2.) Keeping in mind the above answer and the minerals named in the lesson….What do you think are the primary minerals that have replaced the organic material here?
3.) Explain how you can tell the feature is petrified wood and not a man made object?
4.) Post a photo of you at the location with your log, (please do not show the subject of the questions up close in your photo). Of course, if you do not want to appear in the photo, a personal item in the photo is enough proof of your presence. You may log the cache as soon as you submit your answers to us via messenger.
Logs without accompanying answers sent and / or without a photo uploaded may be deleted without notice. If you are part of a group feel free to submit your answers via one profile making sure you include the names of each team you are submitting for.
THE LESSON:
At GZ on the rock platform there is what looks like an iron bar embedded in the rock.
This is actually petrified wood. Although highly altered from how it would have looked, it is known to be from the genus Glossopteris.
Image - an artists impression of a Glossopteris
Glossopteris was a vascular plant, these plants had vascular tissue, including xylem and phloem for conducting water and integrating food through the plant. Xylem: primarily responsible for the distribution of water and minerals taken up by the roots; also the primary component of wood which gives the plant rigidity and allows it to grow tall. Phloem: primarily responsible for the distribution of sugars and nutrients manufactured in the shoot. The leaves were characterised by their distinctive tongue shape. Glossopteris plants grew as woody, seed-bearing trees and shrubs. Their trunks had a maximum diameter of 80cm, with some likely reaching a height of 30 metres.
The species of Glossopteris were the dominant trees of the middle to high-latitude lowland vegetation, often growing in swampy environments, across Gondwana during the Permian Period (approximately 299 to 251 million years ago).
*The above diagram gives you an idea of where the landmasses were positioned during the Permian period compared to Australia’s current position now.
These fossils were critical in recognizing former connections between the various fragments of Gondwana: South America, Africa, India, Australia, New Zealand, and Antarctica.
The Glossopteris forest ecosystems became extinct as part of the end Permian mass extinction event which was caused by an abrupt rise in temperatures.
An example of what the Wasp Head environment may have looked like when Glossopterisis was alive.
Glossopteris became fossilised through the process of petrifaction.
First there was an….
*Accumulation of Organic Matter: Extensive forests thrived in the Permian climate of Gondwana. Abundant plant matter accumulated in large quantities, especially in wet, swampy environments like those found in the ancient Sydney Basin.
This was followed by…
*Rapid Sedimentation: Over millions of years, thick layers of sand and mud sediments were deposited over this organic material. This burial minimised oxygen levels, protecting the plant remains from decay and the elements.
*Compression and Mineralization: As more sediments accumulated, the weight compressed the buried plant material. Coupled with low oxygen and abundant mineral-rich groundwater, the process of permineralization began. The groundwater carrying dissolved minerals precipitated through the sedimentary layers, infiltrating the plant tissues.
The minerals most commonly involved in this process are;
silica: silicon dioxide. Silica is the predominant mineral in petrified wood and is responsible for creating the stone-like appearance. It can be found in various forms such as quartz, chalcedony, and opal. Silica makes the wood very hard and can give it a glossy appearance. It can be colorless, pink, orange, white, green, yellow, blue, purple, dark brown, or black;
calcite: a carbonate, typically colorless or creamy white;
apatite: a phosphate mineral. Usually green, less often colorless, yellow, blue to violet or pink;
siderite: an iron carbonate. Its colour varies from pale yellow to tan, grey, brown, green, red, black but does rust to the typical red.
pyrite: iron sulfide. Its colours are generally pale brass-yellow but tarnishes darker or iridescent and does rust.
hematite: iron oxide. Colours include metallic grey, dull to bright "rust-red".
goethite: iron oxide-hydroxide. Colours vary from yellowish to reddish to dark brown or grey to black.
chalcopyrite: copper iron sulfide. Tends to be brass yellow, may have iridescent purplish tarnish and weathers to greens and blues.
*Replacement: the minerals eventually replaced the organic matter preserving the fine details of the Glossopteris wood and leaves. As the dissolved minerals precipitate out of the water they fill the open pore spaces and cavities of the plant. The minerals form internal casts, with the plants cell walls acting as a template and the minerals effectively dissolve and replace the organic material.
Replacement can take place extremely slowly, replicating the microscopic structure of the organism. The slower the rate of the process, the better defined the microscopic structure will be.
In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions, compressions or trace fossils, petrified wood is a three-dimensional representation of the original organic material in a hardened rock form.
Looking South
Resources:
https://weekendgeology.com/geology-of-victoria-2/
https://ozgeotours.yolasite.com/resources/Wasp%20Head%20Myrtle%20Beach%20excursion%20notes.pdf
https://prehistoricearth.fandom.com/wiki/Glossopteris
https://www.researchgate.net/figure/Reconstruction-of-the-leafy-shoot-Glossopteris-with-the-Partha-sp-female-reproductive_fig3_302240595