Timeless Timber 🌏 EarthCache

The Cache maybe dificult to locate during a high tide.

You can check Tide times here

Take the stairs down onto the beach and make your way around the rock platform to GZ and waypoint 2. They are close to each other.

At GZ there are 3 fossils to see, 1 is long and obviously different to the other 2

THE QUESTIONS:

1. GZ  (Wpt 1.) : embedded in the rock, look at the longer log

What is the most prevalent colour/s in the fossil? Keeping in mind your answer and the minerals named in the lesson….name 2 minerals you think have replaced the organic material here?

2. (Wpt 1): look at the shorter, partly buried logs:

What is the most prevalent colour/s in the fossil? Keeping in mind your answer and the minerals named in the lesson….name 2 minerals you think have replaced the organic material here?

3. (Wpt 2) :  

What type of fossil are you looking at? Is it petrified wood a mould or a cast? Give reason for your answer.

4. Explain how you can tell the features are wood fossils and not man made objects?

5. 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 or without a photo uploaded may be deleted without notice.

THE LESSON: 

The sediments of the Landsborough Sandstone formation were deposited mainly in the channels and associated floodplains of large, north-easterly flowing, braided river systems that existed here around 250–175 million years ago. The rocks are mostly thick-bedded sandstones but siltstones, gravel conglomerates and a few coal beds are also preserved within the formation. You can see sandstone, conglomerates and siltstones on this rock platform.

Geological periods of deposition are difficult to age because the most common rock type formed—sedimentary rocks—are made up of eroded, degraded and decayed older rock and it often lacks the suitable minerals for precise dating methods. Scientists rely on other methods, such as dating associated igneous rocks that are younger or older than the sedimentary layers in the rock record, or the use of fossils in the sedimentary rock for relative dating.

Here, on this rock platform is fossilised material. At waypoint 1 and 2 there are examples of petrified wood and waypoint 3 is a different type log fossil.

* image: an artists impression of ancient conifers

Petrified wood on this part of the Sunshine Coast is most likely to be ancient conifers, possibly either Palissya (an extinct form of conifer) or conifers in the Araucaria family (similar to modern Bunya, Kauri and Wollemi pines). These trees were probably transported down a river all those years ago – most likely in flood waters following storm events. On reaching the coast, the waterlogged trees sunk into the sediments, where they were then became buried. The trees were heavy enough to make an impression in the sediment. Eventually the surrounding sand was lithified, ie became rock.

There are many different ways that fossils may be preserved. 

We see 2 types here: 

Re-formed preservation; after death, an organism undergoes alteration in the form of permineralization (petrification), replacement or recrystallization.

Indirect Preservation; this includes (a) trace fossils -tracks, trails and burrows, (b) coprolites -solid excretory waste products of animals) or (c) imprints, moulds and casts -in which the original soft or hard parts of the organism have gone, but their character can still be determined from the surrounding sediment.

Both of these processes require an….

*Accumulation of Organic Matter: Extensive forests of conifer trees thrived in the Permian climate of Gondwana. Their abundant leaves and plant matter accumulated in large quantities, especially in wet, swampy environments.

Followed by…

*Rapid Sedimentation: Over millions of years, thick layers of sand and mud sediments were deposited over this organic material. Speedy burial was crucial in depriving the environment of oxygen, protecting the plant remains from decay and the elements. 

**For a re-formed fossil like petrified wood you then have….compression, mineralization and replacement…..

*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 carried dissolved minerals precipitated through the sedimentary layers, infiltrating the plant tissues. The minerals commonly involved 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 browns 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: These minerals eventually replace organic matter with mineral compounds 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 specimens. The minerals forming internal casts with the plants cell walls acting as a template as the minerals effectively replacing 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.

*image: an example of polished petrified wood; minerals in this slice is silica in the form of quartz (white), goethite (yellows), hematite (rust red), the brown lines are staining from the original organic material.

**For an Indirect fossil like imprints, moulds or casts the process involves….

The original organic material of the organism dissolves or decays away leaving behind a hollow space or impression in the rock that is an exact replica of the organism's shape.

This empty space is called an external mould. If sediment fills the inside of a hollow structure before the original material is gone, it creates an internal mould (also called an endocast) after the original object dissolves. 

If groundwater containing dissolved minerals then seeps into the mold, minerals can be deposited and any sediments and mineral then harden. This infilling of the mold by mineral-rich sediment creates a new rock in the exact shape of the original organism. This new fossil is called a cast.

Image: examples of how cast and mould fossils form.

Resources:

https://pacifichorticulture.org/articles/the-araucaria-family-past-present/

https://www.diva-portal.org/smash/get/diva2:862075/FULLTEXT01.pdf