It is a dreadful hour of the the morning but I will try and get my
hypocaffeinemic brain round your email!
Bill Payne wrote:
>
>
> I would consider what you describe if I had ever seen such. Have you
> seen or read of these "laterally extensive rootlet horizons beneath
> paleosols" in the southeastern US? Every coal I can remember has either
> had no roots or a shallow (~ 3 inch) root zone.
I said laterally extensive, not vertically extensive. The depth of root
penetration is dependant on vegetation type and soil hydrology. I don't have
the references here at home, but even in well drained soils the main root
zone is generally within a 1 m or so of the surface. Individual roots do go
deeper of course. A rootlet zone of 7.5 cm seems shallow to me as well, but
if that is what the evidence says, that is how far they got. Clearly the
dominant vegetation in the original swamp (in the standard model) did not put
in deep roots. This is true of the ones I have seen also, though to to such
an extreme degree.
>
>
> Today, I revisited the Village Creek excavation in Birmingham. The
> excavation is now about 15 feet deeper than when I was last out there,
> and another coal seam (the American seam) is exposed. The American seam
> is sitting directly on light gray sandstone, and there is no evidence of
> any carbonaceous material below the coal. You could lay a knife blade on
> the contact and have coal above and sandstone below.
>
> I also noticed several sections of a fossil tree trunk in a pile of
> rubble. The base of the tree is as large as any I have seen, about 2
> feet in diameter. You would think if such trees grew in coal swamps,
> there would be some evidence of their stumps in the coal. Instead we see
> unbroken beds of impurities stretching hundreds of feet horizontally in
> coal seams. Where are the tree stumps if these trees once grew in coal
> swamps?
I will bow to your first hand experience! Without knowing the location
myself, or read other people's descriptions I can't comment on your
observations. I am not saying that all coal is formed in situ. Merely that
some is. Deciding which are in situ and which transported requires case by
case examination. The literature leads me to believe that in a world wide
sense most coals are predominantly in situ, but prove me (and the coal bods)
wrong.
> In his paper, Bob Gastaldo showed a diagram of a Lepidodendron tree with
> its Stigmaria axis system of roots. Gastaldo wrote: "Calculated depth
> of stigmarian penetration is provided for two commonly encountered angles
> of divergence [7 and 10 degrees from the horizontal] assuming no change
> in axial direction." At a distance of ~ 12 meters from the base of the
> tree, the deeper roots are ~ 4 meters below the surface. Why don't we
> see these roots penetrating the "paleosols" below coal seams? Do you see
> these roots below Australian coal? (Don't forget, you're looking at it
> upside down!) :-)
Don't be hemispherocentric - YOU are the ones looking at things the wrong way
round! Sure your are looking at the right side of the coal seam??? Only
kidding!
Sigh... I will just have to get Gastaldo's paper... The little I have read
about swamp vegetation, both freshwater and marginal marine, plus what I have
seen in excavations of such environments, is that the root systems are
generally quite shallow, although laterally extensive. So beneath a peat
layer it would be quite unusual have deep roots. Your citation of Gastaldo
seems about right from what I know.
With respect to Australian coals, I have looked at three such units, although
not in huge detail. Cores of Permian coals in the Cooper Basin of central
Australia contained both what I would call both transported coals (no
evidence of roots) and in situ coals (with rootlets and in some cases
bleaching of underlying sediment). It was a long time ago (17 years!), so
don't hold me to this, but I recall the rootlets occurring to 10-30 cm
beneath the base of the coal. I have only looked at the marginal facies of
Eocene coals of the Bremer Basin, Western Australia. Here lignitic seams
about 0.5 m thick contain stumps of trees 10-20 c m in diameter and up to 2 m
high . I have also seen logs up to 3 m long in these units and about 30 cm
across. Rootlets again went about 20-30 cm down into the underlying
material. I did not look too closely - we were pushed for time and always
had an eye over our shoulder for runaway ore trucks! Finally the Miocene of
the Latrobe Valley, Victoria. The lignites here are well gelified, but there
are stumps, and logs, and occasional rootlets. I have a nice Miocene stick
on my mantelpiece as a souvenir. As I recall, palynology suggests that the
main peat vegetation was sphagnum (spelling?) moss, so rootlets would be very
minor anyway.
As I think mentioned before, the best rootlet zones I have seen are not in
coals, but in dune sands.
>
>
> Bill
>
> After two cups of tea I feel much more with it and ready for a day at the
> office. I have two research proposals to write and a paper to edit. Oh
> what fun!
In Christ
Jonathan