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Today we have a bunch of specimens to discuss and they all represent a fascinating kind of fossils called petrified wood. What is cool about petrified wood? First of all, many specimens are huge chunks of colorful gem stones with unique patterns.
Secondly, the fossilized trees represent organisms that lived many million years ago and even though, it was Earth, the Earth itself was a quite different planet at that time and who knows what beasts were hiding under the shadows of these trees. Nonetheless, the most amazing feature of petrified wood, in my view, is exceptional preservation of minute details down to the cellular structure. Eons have passed since the trees were alive and it is mind blowing that you can still recognize individual cells looking under the microscope at a polished slab. However, many people, even those that collect petrified wood, rarely have a chance to actually observe the microscopic beauty of their specimens.
In this particular slab of Paleo osmunda from Australia, the plant tissues were replaced with semitransparent silica helping to make the three-dimensional structures inside the wood visible, especially when the slab is placed in front of a bright light source.
The central part of the stem cross-section consists of pith, xylem and phloem bundles.
Note the elongated loops of xylem strands. These large cells arranged in a honey-comb pattern are cells of xylem, supporting the flow of water and minerals up against gravity towards the leaves. The anatomical features are extremely well-preserved, and it’s hard to believe that they lasted from Jurassic period and the plant was growing sometime between 145 and 200 million years ago. The common name of Osmunda is “royal fern”. The specimens of Osmunda are often found as rounded rocks because original sediments of the Jurassic age eroded and pieces of petrified wood ended up among the gravel in the riverbeds of more recent rivers. So, the perfect cross-sections are hard to find.
Let’s check out this slab under UV light. The ability of petrified wood to emit fluorescence is well known. Many minerals can be fluorescent but, in most cases, a small amount of certain impurities is needed to make the fluorescence possible. The presence of calcite and chalcedony is probably the main reason why petrified wood is fluorescent. The rest is determined by the unique mineral composition of each specimen.
Let’s switch to another tree fern. We identified this one as Psaronius brasiliensis based on the long and curvy bands of xylem in the center of the trunk. Another similar type of fossilized fern, Tietea singularis, has short and round, often C-shaped, xylem bands. The specimen was collected in the previous century by local villagers in Brazilian state of Tocantins, supposedly somewhere between towns Araguaína and Carolina.
It likely came from the deposits of the Early Permian age, meaning it is approximately 280 million years-old. The fossil plants from this region usually have pleasant hues of pink and gray. The tree ferns did not have branches, just long stems with leaves sticking out at the top to catch the solar energy and roots protruding into soil to absorb water and to support the plant in vertical position. As a result, the cross sections from the bottom of the now-petrified stems have thicker layers of the root mantle. The petrified tree ferns from Brazil are historically assigned to either to Pedra de Fogo or Motuca formation of middle to late Permian period with high probability that petrified wood from Araguaína- Filadélfia area belongs to the lower part of Motuca formation. The fossil plants from this place are found in intermixed sand and mudstones indicating that they were dislodged during the floods and deposited in fluvial channels under mineral-rich mud near the shores of a large ancient lake or river. The analysis of the matrix surrounding the fossils, a presence of evaporates with gypsum, in particular, and the xenomorphic anatomy of the ancient plants suggests that they were grown in the environment with seasonal droughts...
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Негізгі бет Үй жануарлары мен аңдар Everything about petrified wood. Part 2. Agates in ancient trees. It's never enough.
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