Article 20512 of talk.origins:
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From: isaak@aurora.com (Mark Isaak)
Subject: Response to the Response to the Flood FAQ, part 2
Message-ID: <1992Dec31.184608.6523@aurora.com>
Reply-To: macrae@pandora.geo.ucalgary.ca (Andrew MacRae)
Organization: The Aurora Group
Date: Thu, 31 Dec 92 18:46:08 GMT
Lines: 279


[More contributions from Andrew MacRae, who himself can't post.]

3. FOSSIL SORTING and "STRATIGRAPHIC LEAK"
> folta@cs.umd.edu (Wayne Folta)

>>[fossil sorting]

>This section of questions does raise difficulties.
	Oh ?
>But no more difficulties than that spores and wood are found in Cambrian
>rocks (from Morris & Parker, quoting Weier, Stocking, and Barbour's
>textbook).

	Oh, ok, you want to avoid the question, and talk about supposed
"difficulties" in the conventional interpretation.  Fine.
	Ha!  If the original source of this information is what I think it
is, [Stainforth, 1966, Nature, v.210, p.292-294.] it is a clear case of
contamination.  I will elaborate further if this is the case.  Please let me
know what the original source of the information is.

I am a paleopalynologist - I study fossil pollen, spores, and microscopic
algae.  There are plenty of processes that can mechanically introduce
palynomorphs (i.e. the spores you mention) into otherwise barren rock.  You
can find a good summary of this in Traverse, 1988 (for instance): [Traverse,
A, 1988, Paleopalynology.  Unwin Hyman:Boston, 600pp.  The particular part
that discusses contamination problems is p.428].
        The basic problem is that spores and pollen are very durable and
very small, so they can be transported into cracks within the rock, with
little evidence of their transport.  Sometimes I find _modern_ pollen in my
sample preparations (easy to recognize because protoplasm is still present
inside!) despite careful cleaning of samples.
	However, the "wood" is intriguing, and I would like to know more
about what the authors claim.  There are some Precambrian plant tissues
reported from China, but they are not wood in the sense that they are from
land plants - they are from marine plants - "algae".  There are also
"spores" (in a very broad sense) of marine algae in Cambrian and Precambrian
rocks, but they are _very_ different from the spores of land plants.

>Also, Morris claims that fossils are found out of order, with the
>terminology "stratigraphic leak" applied to them.

	Yes, you and Morris are right, "stratigraphic leak" is a term for a
host of contamination problems that are observed.  However, you are implying
that there is no explanation, and that the occurrence of "stratigraphic
leak" somehow invalidates the majority of fossil occurrences that have no
such problems.  The explanation is simple, and even expected.  There are two
possible "out of order" conditions:
    1) anomalously "old" fossils in young rocks,
    2) anomalously "young" fossis in older rocks.
	The first is by far the most common.  For example, if you find a
dinosaur bone in a modern stream bed, it is condition 1.  It is a fairly
common occurrence, and happens because many fossils are durable (shells,
bones, plant spores, etc.), and have the potential to be eroded out of an
older rock sequence, and deposited in another, younger sequence.  This
process is called "reworking".  You see this happening _now_ if you go to a
bedrock outcrop where fossils are being eroded out of a cliff, and deposited
in beach sediments.  If the beach sediments are preserved, you will find
reworked, older fossils mixed in the modern sediments - potentially very
confusing if you are as simple-minded as Morris seems to think geologists
are.
	However, notice four features of the reworked fossils:
	1) They were embedded in older rocks, so they are probably
preserved in a different fashion from modern shells.
	2) They were eroded, so they should show signs of wear.
	3) They will be _mixed_ with younger fossils of a definite age (i.e.
the modern shells on the beach), so you will have fossils of two distinct
ages in one rock sequence.
	4) Since they have been eroded, many are destroyed before being
redeposited.  Usually the "in place" fossils are much more common than the
reworked ones.
	The fact is, in cases of "stratigraphic leak" with "older" fossils
in younger rock, some or all of these features are observed, and make it
clear that the "anomalously old" fossils are reworked.  Since you would
expect fossils to be reworked (since it happens in modern environments), it
is no surprise to geologists that it occurs in the past too.
	Reworking actually provides additional information to geologists,
since it indicates erosion of older rocks nearby.  This can be a useful tool
for working out the history of uplift in a mountain range beside a
depositional basin.  As predicted, reworked fossils in such a situation have
a reverse ordering because the youngest rocks at the top of the mountains
are eroded first, then deeper and deeper rocks.
	Reworked palynomorphs (fossil pollen and spores) are commonly darker
than the "in place" fossils, because they have been "cooked" in the
sediments for a longer period of time.  In my B.Sc. study [MacRae, R.  A.,
1989.  Palynology and stratigraphy of an upper Cretaceous
sedimentary-volcanic sequence, Emma Fiord, northwest Ellesmere Island,
N.W.T., Canada.  Unpublished B.Sc. thesis, Dalhousie University, Halifax,
Nova Scotia, 159 pages, 24 plates.] , I examined palynomorphs that were
deposited in Cretaceous sediments unconformably overlying a deeply weathered
limestone of Permian age.  I was not surprised to find a few very dark brown
Permian palynomorphs mixed with the light coloured Cretaceous ones.  In
partial confirmation of this, conglomerates in the Cretaceous sediments
contained chert pebbles that contained Permian age corals and foraminfera
with identical preservation to the underlying, in-place Permian cherty
limestones.
	The second condition, anomalously "young" fossils in older rocks, is
_very_ uncommon.  You don't, for instance, usually find Mesozoic dinosaur
fossils mixed with Cambrian trilobites.  In all the examples I have seen,
contamination of lower rocks by material from higher up is the explanation.
For example, some Ordovician or Silurian marine limestones in the central
U.S. contain what appear to be Carboniferous-age land vertebrates
(amphibians or reptiles, I can't remember).  No doubt Morris or other flood
creationists would jump on this as a clear anomaly.  However, the
explanation is again simple, since the land vertebrates occur in narrow
vertical crevasses in the limestone, filled with reddish terrestrial
sediments.  The interpretation is that they fell into the crevasses from
above, while the limestones were exposed to erosion during the
Carboniferous.  When spores are analyzed from the crevasse sediments, they
too are Carboniferous.
	Another common example of this condition is in oil wells.  As the
well is drilled deeper, chips of rock fall from the walls higher in the
borehole, and are eventually carried up the surface, and mixed with the
chips from the level the drill bit is currently penetrating.  This process
is called "caving".  When the microfossils in a sample of the chips are
examined, younger ones could be mixed in.  It is for this reason that
paleontologists working in wells use the _youngest/highest_ occurrence of a
fossil to work out the stratigraphy, rather than the oldest/lowest
occurrence.
	So, yes, "stratigraphic leak" is a problem, but it is not very
common, and it is easily recognizable because of other evidence left by the
processes responsible.

[huge deletions]

	-Andrew
	macrae@geo.ucalgary.ca