Bill,
This is frustrating. On one of these lists you asked this question and I
provided the following. You didn't comment but now are asking the same
question again. I would appreciate it if you could to tell me why this
mechanism won't work, since the first quote specifically mentions keeping
fish from floating and would seem to answer your question.
"Microbial mats are one of the factors most widely invoked
to explain exceptional fossil preservation. They are believed to
prevent carcasses from floating and to protect them from
scavengers and currents. Microbial mats may also be sites of
rapid mineralization, perhaps because they create localized
oxygen-minimum environments."~Philip R. Wilby et al, "role of
Microbial Mats in the Fossilization of Soft Tissues," Geology,
Sept. 1996 24:787-790, p. 787
"Terrestrial leaf fossils often form through authigenic
preservation in which the leaf surface is coated by a variety of
minerals, especially iron oxides. The mechanism of this
fossilization is unclear, because the largely hydrophobic leaf
surfaces do not readily bind metal ions. Previously proposed
mechanisms for mineral encrustation include precipitation of
minerals in sediment pore space and precipitation of iron oxides
at the surface by decay-produced CO2. Here we demonstrate that
diverse bacterial species rapidly colonize leaf surfaces and form
a biofilm within days of the leaf's entry into a stream
environment. Experimental mineralization of fresh and
biofilm-coated leaves indicates that leaves without biofilm do
not mineralize, but leaves with biofilms rapidly adsorb metal
ions such as Fe3+ onto the anionic biofilm surface where the ions
form ferrihydrite. Once these mineralized leaves are buried by
the sediment, they are more likely to be converted to fossils
than non-mineralized leaves. Examination of a fossil leaf surface
by scanning electron microscopy shows bacteria-sized structures
resembling those found in biofilms. These experimental data imply
that bacterial colonization of leaves may be an essential
prerequisite for authigenic preservation."~K. A. Dunn, et
al, "Enhancement of Leaf Fossilization Potential by Bacterial
Biofilms," Geology 25(1997):12:119-1222, p. 1119
**
fossilization
"Under normal circumstances, leaves and other plant detritus
are colonized and decomposed by a variety of microorganisms and
macroinvertebrates. However, decay of whole plant organs such as
leaves can take as long as months to years, which provides a
window of time during which fossilization can occur. The caliber
of leaf fossils is greatly enhanced if mineralization can
commence before much decomposition can occur."~K. A. Dunn, et
al, "Enhancement of Leaf Fossilization Potential by Bacterial
Biofilms," Geology 25(1997):12:119-1222, p. 1119
**
fossilization
"Platanus leaves placed in the San Marcos River for five
days were colonized by a biofilm of naturally occurring bacteria
containing 10^7 colony-forming units (CFU) per square centimeter
of leaf surface. These organisms were not fully identified but
consisted primarily of Pseudomonas sp. and other gram-negative
rods. In contrast, fewer bacteria (<10^2 CFU per square
centimeter) were present on freshly picked platanus leaves."~K.
A. Dunn, et al, "Enhancement of Leaf Fossilization Potential by
Bacterial Biofilms," Geology 25(1997):12:119-1222, p. 1120
**
fossilization
"When the biofilm-containing Platanus and Taxodium leaves
were placed into either 10mM FeCl3 or 300 ppm silica, a color
change indicating mineral formation was readily observed within
5-10 min. Examination of the leaf surfaces by SEM confirmed the
presence of mineral formation in the presence of biofilms. No
mineral formation was observed in the leaves without a biofilm,
even after six weeks of incubation."~K. A. Dunn, et al,
"Enhancement of Leaf Fossilization Potential by Bacterial
Biofilms," Geology 25(1997):12:119-1222, p. 1120
**
fossilization
"Examination of some iron-encrusted fossil leaves shows
evidence for both rapid precipitation of iron at the leaf surface
and structures of probable bacterial origin. both are
well-illustrated by leaves of Nelumbrites minimus, an aquatic
angiosperm from the Lower Cretaceous Potomac Group of Virginia
and Maryland. Iron-encrusted leaves of N. minimus can show fine
scale surface detail including vein course, epidermal cell
outlines, shallow doming of epidermal cells, and stomata. In
addition, smaller-scale features of probable bacterial origin are
present on the surface. These include 1-2 [micro]m structures
resembling bacterial cells and material resembling a dehydrated
biofilm matrix."~K. A. Dunn, et al, "Enhancement of Leaf
Fossilization Potential by Bacterial Biofilms," Geology
25(1997):12:119-1222, p. 1120
**
fossilization
"Spicer noted that leaves in modern depositional settings can
develop an iron encrustation within a few weeks of their entry
into a stream depositional system. Iron-bacteria in particular
Spherotilus sp., were present on leaves examined from England,
and were proposed as the primary means of iron encrustation."~K.
A. Dunn, et al, "Enhancement of Leaf Fossilization Potential by
Bacterial Biofilms," Geology 25(1997):12:119-1222, p. 1121
glenn
Adam, Apes, and Anthropology: Finding the Soul of Fossil Man
and
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm