Damn the generalities! Full speed ahead!
James Mahaffy wrote:
> Jonathan Clarke wrote:
> > I have seen stumps in coal in the Eocene and Miocene lignites of Western
> > Australia and Victoria, respectively. So they do exist, although are not
> > very common. Interestingly, studies of modern peat mounds and the ecological
> > succusion of ancient ones shows that the climax community of such ombrogenous
> > bogs (wonderful word!) is often dominated by mosses, with few trees. "Swamp
> > forest" occurs only in the the early stages of development.
> If I am not mistaken and, I looked at it fairly recently, the tropical
> ombrogenous peats of Sarawak and Brunei, which are perhaps the best analoges for
> the Carboniferous coals are still dominated by trees but more stunted trees and
> more open vegetation. In any case in these swamps there is still woody vegetation
> in the oldest raised peat mounds.
> I might also caution against seeing most coals as a simple successional
> sequence. The story does not appear to be that simple. It is true that one of
> the better earlier ecological studies by Smith (1962) of some Carboniferous coals
> (from Namurian to Westphalian B) showed bottom of the coal seam as a bright coal
> dominated by spores of a larger lycopod tree (Lycospora) and the top a dull coal
> (duritic) dominated by densospores toward the top of the seam. That almost fits
> with Jonathan Clarke's generalization, but a bit higher in the section
> (Westphalian D), where I did my palynological work, Densospores are not found and
> the whole seams up to the very top are generally bright (vitrain) coals. There
> are some differences in vegetation at the top of the coal seam but it is changes
> to other tree forms of lycopods and not small herbaceous forms.
> James and Florence Mahaffy 712 722-0381 (Home)
> 227 S. Main St. 712 722-6279 (Office)
> Sioux Center, IA 51250
You are of course right. I was generalising and obviously over generalised for those
more knowledgeable than I.
I completely agree with your comment about the ombrogenous bogs of Borneo. They do
have woody vegetation, although I understand that this is rather sparse and stunted
compared with normal SE Asian rain forest. The point that I was trying to make in
my usual muddleheaded way was that peat bogs do not always conform to the popular
mental image (even amongst geologists) of thickly forested swamps. In some trees may
be sparse or even absent. So people should not be to distressed if they don't always
find large sumps within a coal or peat succession. The large trees may never have
been there in the first place. It depends on each specific deposit.
Your work on Carboniferous coals is most interesting and shows the risks of
over-simplified models. Certainly the Miocene coals in the Latrobe valley appear to
pass from well forested to sparsely forested bog. However other ecological
successions are both possible and known in both modern and ancient bogs, as you show.
Hope this has clarified things.