and stumps of clubmoss trees II I
Fig. 11. Reconstruction of the Stigmaria system. A. The network of
Fig. 11. Reconstruction of the Stigmaria system. A. The network of
Fig. 12. Photo from 1887 of The Fossil Grove, the petrified 'forest' of stumps of clubmoss trees in Victoria Park in Glasgow. Nowadays part of it is covered and can be visited.
Complete root systems
More or less complete Stigmaria systems have relatively rarely survived. A well-known example is the one in museum Am Schölerberg in Osnabrück (Fig.13). It was discovered in 1886 in the Piesberg and put together in parts. The diameter of the system is about 8 m and it weighs three tons.
A very beautiful root system was (also) found in 1886 in a quarry in Clayton (Yorkshire) by Prof. Williamson. He had it excavated and set up at his own expense in the Manchester Museum (fig. 14). The original diameter was 9 m but due to lack of space it is limited to 6 m in the museum.
Fig. 13. The Piesberg root system in the museum Am Schölerberg in
Fig. 14. Stigmaria in the Manchester Museum, from a quarry in
& Seyfullah (2015) describe a fossil 'forest' found in a quarry in
Brymbo, North Wales. It consists of 20 upright trunks up to 1.5 m in
diameter and up to 2.5 m high. However, these don't have preserved Stigmaria.
In a somewhat higher layer a fairly complete root system has been found
which has been completely uncovered and from which they were able to
draw conclusions about the way in which this system has been preserved.
The twenty tree trunks preserved without Stigmaria were found in a 2 m thick layer of shale/claystone that turned towards the top into the slightly less fine-grained siltstone. The trunk with the Stigmaria was found in a layer of sandstone. It has a diameter of about 5 m and the trunk is 50 cm thick and 1.7 m high. The root system has been completely excavated to preserve it (Fig. 15). A loose Stigmaria axis of 8 m long was found in the same layer.
does such a petrified 'forest' arise? It is generally assumed that the
decaying parts of the trunk and root system are filled with sediment
that subsequently hardens. However, the question is how the shape of
the trunk and the underground parts are preserved in this process. In
the Brymbo fossil a thin hard brown layer of iron oxide (FeO(OH)) was
found on the outside. This mineral is also often found at the bottom of
lakes and creeks and is formed when ferrous water comes into contact
with oxygen from plant cells. This layer can ensure that the shape of
trunk and Stigmaria remains
intact when the interior decays and is replaced by sediment. The ends
of the root systems are almost always missing, which is almost
certainly due to the fact that they consisted of softer material and
therefore decayed faster.
This process may also have occurred in some other systems.
Fig. 15. Stigmaria system of Brymbo.
From Thomas & Seyfullah (2015). Photo: B. Thomas.
Fig. 16. The layers from the Carboniferous near Joggins (Nova Scotia, Canada). A group of excursionists look at a tree stump in the deposit.
Photo: L. Nichol.
At Joggins in Nova Scotia in the far north-east of Canada, the process has certainly been different. For almost two centuries, the coast near the town of Joggins has been a famous site for carboniferous clubmoss tree trunks and stumps (Fig. 16). Due to tidal differences of up to 12 meters and violent storms and rains, the cliffs there crumble regularly. New trunks constantly emerge, which disappear in an average of three years due to erosion. What has made the place especially famous is the fact that remains of carboniferous quadrupeds have been found in some of these trunks. The most famous is the Hylonomus lyelli, the oldest reptile found so far. The 20 cm long animal was discovered by Dawson in 1852, and described by him in 1860. Not until 100 years after the discovery it was discovered to be a reptile.
The famous geologist Lyell was collecting there together with Dawson.
Due to rising and falling sea levels in the Late Carboniferous, the marshes drowned from time to time and were re-formed. The flood plains were covered by enormous mudflows, with the present forests being embedded in sediment. That the sedimentation at Joggins was very fast is shown by the fact that the deposits of 900 meters were formed in one million years. After a short period of time, the mud hardened and encircled the lower few metres of the clubmoss trees. The soft material, which the trunks largely consisted of, rotted away and holes came into existence in the ground. It has always been assumed that animals fell in, died and were embedded in the next muddy stream. But a new theory states that the animals may have used the hollow trunk holes as hiding or living places.
The Joggins coast was placed on the World Heritage list in 2008.
Probably the formation of fossil 'forests' went in most cases comparably to Joggins, albeit in a more moderate form because there are no other known places where fossil animals have been found in the trunks.
Coal balls, Stigmaria systems and fossil 'forests' of tree stumps tell a lot about the structure and growth of the clubmoss trees in the Carboniferous. The trees stood quite close together, with extensive root plates anchored in the swampy ground. And although there was a lot of light on the ground, undergrowth was only in open, often higher areas. Mudslides, caused by faster soil subsidence or rising sea levels, destroyed the forest but bedded the lower parts of the trunks and the root systems. In the hardening sediments the trunks and Stigmaria's rotted away, creating cavities that were later filled with new sediment. Because there was a discontinuity between the casts of the tree parts and the surrounding sediment, the forms could continue to exist for hundreds of millions of years.
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