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Anyone got a better explanation?
Quote from: Andrew K Fletcher on 07/10/2007 21:35:57Anyone got a better explanation?After a tree has fallen and is buried in sediments minerals replace the organic material. If this occurs slowly enough much of the original structure of tree will be preserved.Andrew, your explanation, while charming, bears no relationship to reality.
Take a 0.25 cm slice of rock, mount it on a slide, grind it until it is transparent and place a cover glass over it so you don't damage the microscope lens and - Presto!,
Could be anything Karen. Mexico has many diverse climate/vegetation regions (though it does remind me of my acacia piece)Can you read the name where your grandma found it? Maybe we can make an educated guess.4.05am  what are you doing?!?!?!
In the desert east of Cairo there are square kilometres cvovered with the fossilised remains of a forest of trees, all lying flat on the ground. (I am looking at the fragment of one on my window sill as I type.) This is how the majority of trees are fossilised.
Preservation of any organism as a fossil is a rare occurence: most of the time, most organisms leave no detectable trace after death. this is especially treu for organisms with no mineral skeletal structure. So plants and trees are extra hard to preserve. You are therefore correct that special conidtions are necessary for a tree to be fossilised. Note that we do not require the wood to avoid decay, only that the mineralisation of the wood should occur at a faster rate than the decay.You have mentioned a dry environment as one where decay can be avoided or at least delayed. Immersion in volcanic ash is another - this happened in the petrified forest of Lesvos. Or immersion in anoxic conditions - there are timbers on the floor of the Black Sea that are probably thousands of years old. Finding an occasional example where the stump of a tree (six feet tall in your example) is preserved upright does not invalidate the mechanism. In general we believe that the trees fall and are submerged in sediment, but teh key word here is submerged. It is entirely possible in flood conditions for a massive amount of sediment to be deposited around a tree whose upper portion has been broken off.In the desert east of Cairo there are square kilometres cvovered with the fossilised remains of a forest of trees, all lying flat on the ground. (I am looking at the fragment of one on my window sill as I type.) This is how the majority of trees are fossilised.
Damn, just realised something here that suggests that the trees must have been standing during petrification. First of all as suggested above the distance between each segment of the trunk indicates the tree shattered when it fell and tossed the segments apart from each other. Pretty obvious really. But more important observation is the clean snap between each segment, indicating a brittle trunk shattering rather than a tree trunk breaking which we all know would splinter.Petrified forest on top of a hill: Many examples of very tall petrified forests in situ. On a hill way above sedimentation levels also. http://www.nps.gov/archive/yell/slidefile/geology/paleontology/Page.htm