> I've heard that the southern hemisphere coals are different from the
> northern half, but I don't know how. What age are they? I think I have
> heard of Australian coals with pine trees jumbled up in the coal? Is
> that true?
As far as I know all Gondwanan coals overlie the Permo-Carboniferous glacials. The
coals themselves vary from Early to Late Permian, depending on the basin. My
experience with Australian Permian coals is limited, except for a little bit of work
in the Arckaringa Basin and working through some wells in the Cooper Basin. The
latter is too deep for mining, but an excellent gas producer. However, from this
limited experience and from the literature, most of these coals appear in situ.
They are underlain (for the most part) with rootlet horizons and are associated with
different clastic sedimentary packages indicating deposition in a wide range of
settings, including alluvial fan, coastal plains, topographic basins, and river
flood plains. Fossil plant communities and coal types vary according to the
depositional environment, and include a spectrum of ecosystems such as dry forest,
wet forest, reed moor, and moor lake.
There were few or no pine trees in the Permian, although lots of conifers. Fossil
logs and stumps are present in the coal of course. and I believe there are some
fossil log jams in river sediments. Younger Australian coals (Cretaceous, Eocene and
Miocene) certainly do contain fossil pines. There are several different genera of
Australian pines that are only distantly related to northern hemisphere pines.
The only jumbled up logs I have seen have been in Triassic fluvial sediments where
they occur in the bottom of channels and probably formed as log jams.
Two useful references on Australian coals are C.F.K Diessel (1992), "Coal-bearing
depositional environments", published by Springer Verlag, and CR Ward, HJ
Harrington, CW Mallett & JW Beeston (1995) "Geology of Australian coal basins",
special publication of the coal geology group No. 1, Geological Society of