Here are some important data/interpretations that must be addressed:
1) The coal-forming vegetation of the Carboniferous is part of long
evolutionary history of terrrestrial vegetation extending from at least the
Silurian through the Present.
2) The evolution of terrestrial plants is integrated with the evolution of
terrestrial animal communities in such a way that coherent ecological
interpretations have been made.
3) The coals occur within the context of cyclic sedimentary packages called
cyclothems. The periodicity and stacking patterns of these cycles are
consistent with forcing by Milankovitch orbital cycles. The sealevel
fluctuations occur coincidently with known glacial epochs in Gondwana.
4) The facies within these cyclothems include a wide array of both
terrestrial and marine depositional units. These units have been widely
correlated (regional and conteinental scales) allowing for detailed
paleogeographic and environmental reconstructions.
5) Coals commonly occur within stratigraphic units containing fluvial
channels. These river channel patterns have been mapped for given
stratigraphic intervals. Tidally influenced deposits also commonly overly
coals. Daily, monthly and years tidal patterns can be recongized within
these deposits. Furthermore the type of tidal regime (diurnal.
semi-diurnal. mixed) can often be determined by computer analysis of lamine
thickness. These patterns are virtually identical to those found in modern
tidal deposits.
6) The species composition of the coals, deduced from both plant fossils
and spores, varies both laterally and vertically within coal beds. Species
also vary with characterisitics of coals (eg. clay content). These
patterns of vegetational change can be used to reconstruct the ecology of
the fossil species.
7) Different types of swamps (eg. planar or domed) can be recognized from
the type of coal and the compositon and preservation of paleofloras.
8) Changes in the plant community composition of coals over time (from coal
to coal) are consistent with independent geologic evidence of climate
change. These climate changes can in turn be modelled using plate tectonic
reconstructions based on yet other independent data (paleomagnetism).
9) Paleosols (ancient soil profiles) are ubiquitous within Carboniferous
and Permian cycles. Some of these are directly associated with coals,
other are not. Soil features preserved at both the outcrop and
microscopic-scale enable paleosols to be classified using modern soil
classification systems. (Note: I have previously posted a list of basic
references on the identification of soil fabrics.) Interestingly these
paleosols show stratigraphic patterns in their development that are
consistent with both sedimentologic data on cycle durations and with data
on ancient climate change.
10) The "underclays" of coal beds may or may not be related to the
formation of the overlying peat. In some cases the underclays are
paleosols formed during times of extensive exposure that significantly
preceeded the development of peats. These may have developed under
significantly different environmental and climatic conditions from those
that produced the coals. Some extensive coals are associated with
transgressions of the sea over the previously exposed continental margins.
The paleosols produced during sealevel lowstands may be much more
geographically extensive than the coal beds overlying them. There is
present ongoing work which has traced such exposure surfaces nearly across
the North American continent.
11) The water-saturated conditions of a swamp generate soils with poorly
developed structure. This is because soil structure primarily results from
the vertical movement of material and fluids through the profile.
12) Many modern peats are formed by vegetation (including trees) that is
detached from the underlying substrate. The decomposing bottom of the mat
contributes the organic matter that accumulates to form the peat. This is
the case for much of the Mississippi delta.
I do not intend to devote any significant time to this issue on this forum
in the future. I am already far behind in my own research
responsibilities. My hope is that the active parties to this discussion
will avail themselves of these sources. The amount of available data is so
extensive that discussing the origin of coal without familiarity with this
literature will not be fruitful.
A very brief bibliography:
Note: many of the above were chosen as much for their bibliographies as for
their content. By searching the articles referenced in the publications
above, a person will quickly have literally hundreds of sources at their
disposal. The literature on these topics is vast.
Archer, A.W., 1991, Modeling of tidal rhythmites using modern tidal
periodicities and implications for short-term sedimentation rates: Kansas
Geological Survey Bulletin 233: 185-194.
Archer, A.W., Lanier, W.P., and Feldman, H.R., 1994, Stratigraphy and
depositional history within incised-paleovalley fills and related facies,
Douglas Group (Missourian/Virgilian; Upper Carboniferous) of Kansas, USA:
SEPM Special Publication 51: 175-190.
Behrensmeyer, A.K., Damuth, J.D., Di Michele, W.A., Potts, R., Sues, H-D.,
and Wing, S.L., (eds.), 1992, Terrestrial Ecosystems through Time:
Evolutionary Paleoecology of Terrestrial Plants and Animals: Chicago,
University of Chicago Press, 568 p.
Cecil, C.B. and Eble, C.F., 1992, Paleoclimate controls on Carboniferous
sedimentation and cyclic stratigraphy in the Appalachian Basin: USGS Open
File Report 92-546.
Cross, A.T. and Phillips, T.L., 1990, Coal-forming plants through time in
North America: International Journal of Coal Geology 16: 1-46.
Crowley, T.J. and Baum, S.K., 1991, Estimating Carboniferous sea-level
fluctuations from Gondwanan ice extent: Geology 19: 975-977.
DiMichele, W.A. and Aronson, R.B., 1992, The Pennsylvanian-Permian
vegetational transition : A terrestrial analogue to the onshore-offshore
hypothesis: Evolution 46:807-824.
DiMichele, W.A., Pfefferkorn, H.W., Phillips, T.L., 1996, Persistence of
Late Carboniferous tropical vegetation during glacially driven climatic and
sea-level fluctuations: Palaeogeography Palaeoclimatology Palaeoecology
125: 105-128.
Eble, C.F. and Grady, W.C., 1990, Paleoecological interpretation of a
Middle Pennsylvanian coal bed in the central Appalachian basin, USA:
International Journal of Coal Geology 16: 255-286.
Heckel, P.H., 1986, Sea-level curve for Pennsylvanian eustatic marine
transgressive-regressive depositional cycles along midcontinent outcrop
belt, North America: Geology 14: 330-334.
Joeckel, R.M., 1995, Upper Pennsylvanian paleosols in the Platte and
Missouri valleys, southeastern Nebraska. IN, Geologic Field Trips in
Nebraska and Adjacent Parts of Kansas and South Dakota: Conservation and
Survey Division, University of Nebraska-lincoln, p. 121-135.
Miller, K.B., McCahon, T.J., and West, R.R., 1996, Lower Permian
(Wolfcampian) paleosol-bearing cycles of the U.S. midcontinent: evidence of
climatic cyclicity: Journal of Sedimentary Research 66: 71-84.
Parrish, J.T., 1993, Climate of the supercontinent Pangea: Journal of
Geology 101: 215-233.
Phillips, T.L., and DiMichele, W.A., 1998, A transect through a
clastic-swamp to peat-swamp ecotone in the Springfield Coal, Middle
Pennsylvanian age of Indiana, USA: Palaios 13: 113-128.
Phillips, T.L. and Peppers, R.A., 1984, Changing patterns of Pennsylvanian
coal-swamp vegetation and implications of climatic control on coal
occurrence: International Journal of Coal Geology 3: 205-255.
Phillips, T.L., Peppers, R.A., and DiMichele, W.A., 1985, Stratigraphic and
interregional changes in Pennsylvanian coal-swamp vegetation: environmental
inferences: International Journal of Coal Geology 5: 43-109.
Stewart, W.N., 1983, Paleobotany and the Evolution of Plants: Cambridge,
Cambridge University Press, 405 p.
West, R.R., Archer, A.W., and Miller, K.B., 1997, The role of climate in
stratigraphic patterns exhibited by late Palaeozoic rocks exposed in
Kansas: Palaeogeography Palaeoclimatology Palaeoecology 128: 1-16.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.ksu.edu
http://www-personal.ksu.edu/~kbmill/