Previously, I had sent two posts summarizing Bob Gastaldo's paper: A
CASE AGAINST PELAGOCHTHONY: THE UNTENABILITY OF CARBONIFEROUS
ARBORESCENT LYCOPOD-DOMINATED FLOATING PEAT MATS, by Robert A. Gastaldo,
Department of Geology, Auburn University, Alabama 36849. If anyone
needs to refer back to those posts, they are located at:
Now, at last, for my critique of Bob Gastaldo's paper, which Steve
Schimmlich had originally suggested.
So that everyone would have the bulk of Bob's paper, I took the time to
post all of the critical points he made. However, the general thrust of
his argument is summarized in the following paragraph:
"Morphological considerations suggest that these plants were adapted to
extreme swampy conditions, and the disposition of the stigmarian axes
within various lithologies can only be interpreted as recording growth
in situ. The variable angle of axial penetration and their cross-cutting
relationships, the helical and undisturbed arrangement of the
'rootlets', and the abiotically undisturbed sediment surrounding the
axial/appendage system, lend support to their autochthonous character."
IOW, since neither the stigmarian axes, the "rootlets", nor the sediment
layers are disturbed, then the roots must have grown in situ. It is
this foundational assumption which I believe is in error, and this will
be the basis of my rebuttal. If I can show that the stigmarian axes,
the "rootlets", and the sediment layers could have been emplaced
abiotically AND without being disturbed, then Bob's argument falls
I have observed a number of fossil vertical tree trunks preserved in
clays, sandstones and shales associated with coal seams. I think we
would all agree that these tree trunks did not grow "in situ" up through
the encasing strata (in the same way roots grow through soil), but the
fossil tree trunks were buried in growth position. The striking thing I
have noticed about these fossil tree trunks is that they crosscut the
strata which they penetrate; the thin-bedded strata either butt
perpendicularly into the tree trunks, or they occasionally incline
slightly upward against the trunk (on one side only, as I recall). So
here we have two of the features cited by Bob Gastaldo as indicative of
in situ (autochthonous) growth: the crosscutting relationship of the
stigmarian axial systems with the thin-bedded sediment, and abiotically
undisturbed sediment surrounding the axial/appendage systems, which,
according to Bob, "lend support to their autochthonous character."
However, in the case of vertical fossil tree trunks, we don't believe
that the trunks grew "in situ". Instead, they were *buried* in growth
Is it possible, then, that the stigmarian axial root systems were also
buried while floating in sediment-laden water, rather than having grown
in situ as assumed by Bob?
Last November I was logging core on a bridge-pier-drilling project. We
were drilling in the flood plain of a creek which is about 25 feet
across, averaging about two feet deep, and flowing probably ten feet per
second. The static water level in the flood plain is shallow - about
one or two feet below ground surface.
While the drilling was in progress, I was pulled off and sent to another
project. When I got back to the bridge-drilling site in February, I
noticed an uprooted tree lying across an open area of the flood plain,
which had not been there when I was back in November. I asked the
driller about the tree, and he said that it had been in the way of the
rig for one of the holes they had to drill. He had wrapped a cable
around the tree and pulled it up with the drill rig, along with the root
ball, and out of their way. This was in November, and, by the time I
saw it in February, the winter rains had washed most of the soil away
from the root ball, leaving the roots exposed.
The smallest roots I saw were extremely fine, about the diameter of
human hair. Given the violent uprooting the tree experienced, I would
have expected the fine roots would have been left in the ground.
However, since the ground was wet and since the entire root ball with
soil was extracted, the fine roots stayed intact and were exposed later.
If this tree were picked up today and put in a lake, it might float
vertically with the heavier root end down. If sediment was washing into
the lake and if the water-logged tree with root-end down was floating
near the bottom where sedimentation was occurring, the roots would be
buried in the sediment, *not because they were pushed into the sediment
(as assumed by Bob), but because they were buried by the sediment as it
piled up around the roots.* The result would be undistorted roots
encased in and crosscutting the undisturbed, thin-bedded sediment. This
is exactly the process we assume for vertical fossil tree trunks, and
this is exactly the process observed at Mt. St. Helens where numerous
trees have settled to the bottom and have been buried in growth
position. This transported tree would meet every criteria offered by Bob
as evidence of being autochthonous, yet it would be allocthtonous.
I think it is important to note that I do not disagree with Bob's
observations, although I personally have not seen in outcrop the
stigmarian axial root systems with "rootlets" described by Bob; I have
not seen these features either above, in, or below a coal seam.
This in itself raises a question about why the roots of the trees which
supposedly grew in vast swamps are virtually absent, at least in a
crosscutting relationship, especially in and immediately below the coal
To say that the roots in the underclay have rotted out and therefore are
not preserved seems to me to be an unsupported, ad hoc attempt to defend
the lack of data. In his 4 May 1998 20:04:01 -0600 post to the ASA (5
May 1998 10:20:27 -0600 post to the ACG), Keith Miller stated: "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." Bob Gastaldo
emphasized how tall ("in excess of 38 meters in height") and heavy
("these trees were not frail or lightly built") these arborescent
lycopods were. "The three-dimensional disposition of the axial system
precludes the general notion of a shallowly buried support system..."
(Gastaldo quotes are from his Conclusions). According to Bob, and I
would agree, the nature of these trees implies that they were rooted
into the substrate soil, not just into the vegetation mat where the
roots later decayed.
A second observation, which supports this notion of non-decaying
organics in the underclay, is a vertical fossil tree trunk, which I
found in the underclay immediately below a coal seam. All that is
preserved of the tree is the outer layer, which averages about 3/8 inch
thick and consists of coal. The fact that this tree trunk is preserved
argues against the possibility that roots once penetrated this underclay
and then rotted away. Furthermore, if the underclay had been intensely
rooted over thousands of years while swamp trees gradually accumulated
enough organics to form 14 inches of coal, then the delicate, thin
interbeds of very fine-grained sand in the underclay would have been
disturbed. But the underclay bedding is undisturbed. These two lines
of evidence alone suggest that both Keith Miller and Bob Gastaldo have
imposed the wrong modern analog to explain the origin of coal.
I can accept Bob's observations, but, with a different interpretation,
reach the opposite conclusion. The question then becomes, which
conclusion is more strongly supported by the data; is Carboniferous coal
generally allocthtonous or autochthonous? Due to the general lack of
crosscutting stigmarian axial systems in and immediately below
Carboniferous coal seams, the weight of evidence favors an allocthtonous
origin for these coals.