25th International Meeting on Organic Geochemistry IMOG 2011

P-036
Geochemical characteristics of organic matter preserved in
silicified wood of variable age
Monika Fabiańska
University of Silesia, Sosnowiec, Poland (corresponding author:monika.fabianska@us.edu.pl)
Ancient wood can be preserved when silica
dissolved in ground waters infiltrate its cellular voids
and crystallise in them. Since this occurs when wood
structure is relatively intact, wood fossils preserve the
original pattern of tissues, both in its macro-forms and
its microscopic structure [1]. Organic substances are
entrapped by layers of precipitating silica and
preserved, despite unfavourable conditions or their
relative low resistance. Due to its high hardness,
silicified wood is very durable, and can survive
weathering and reworking, unlike the most of fossils.
Chemical investigations of such well-preserved fossil
remains has enabled recognition of their main
constituents - macromolecular and bituminous organic
matter (e.g. [2]).
The aim was (i) to characterise organic matter
found in silicified wood; and (ii) to identify its biological
source. Analyses included solvent extraction and gas
chromatography-mass spectrometry. Cellular
structure preservation was examined by reflected light
microscopy under white and UV light.
Samples show well preserved xylem cellular
structure, with rare deformation of cell walls. Better
preserved are interiors of larger fragments. The cell
lumina are filled with monocrystaline quartz, much
lighter in colour than the cell-wall filling. The darker
outline of the cell walls most probably indicates
organic material preserved between layers of
crystallised silica. Strong fluorescence of cell walls
and weak fluorescence of cell lumina suggests that
cell walls are the main site of organic matter
occurrence in silicified wood. This agrees with the
supposed order of wood tissue decay with the living
cell content destroyed as the first.
Silicified wood shows low extract yields in the
range of 0.001-0.065% (wt.), particularly in fragments
transported by water or glacier and re-deposited in
the Quaternary beds. Age influence seems to be of
the lower importance here.
Several groups of compounds were found in the
wood extracts. The range of n-alkanes correspond to
the range of terrestrial plants fatty acids and alkanols
and their distributions show slight odd-over-even
carbon number predominance (CPI = 1.1-1.6).
Diterpanes related to wood resin included 16�(H)phyllocladane
(Podocarpaceae family), ent-beyerane
and abietane. Hopanes show low concentration, what
may indicate low bacterial degradation of preserved
wood tissue, i.e. cell walls. It seems that bacterial
influence was limited to the organic cell content. Next
this part of xylem was replaced by silica with only low
amount of organic matter (low or no fluorescence in
UV light) leaving intact or almost intact cell walls.
Steranes distributions are of terrestrial type, i.e.
dominated by stigmastanes (C29 sterane) while the
distribution of triaromatic steroids contains higher
amounts of C28 steroids deriving from their C29
sterane precursors. Polycadinene derivatives found in
only one sample, probably of angiosperm wood (oak),
comprised two calamenene isomers, curcumene, and
cadalene.
Fatty acids esters with even-carbon-number
aliphatic alcohols such as esters of lauric) (C12),
myristic (C14), palmitic (C16), stearic ( (C18) and
behenic (C22) acids were found. Esters with oddcarbon
number aliphatic alcohols occurred in lower
concentration. Water washing did not affected these
compounds since their biological function is to protect
tissues against water. As a result even the samples
which organic matter was highly altered in transport
show wide distributions of these compounds.
Identified compound groups predominantly come
from wood tissue, mostly cell walls which seem to be
main source of organic material in silicified wood.
Some features of organic remains are different that
these found in organic material dispersed in
sediments and coals of various maturity, e.g. low
content or absence of pentacyclic triterpanes and
preservation of intact ester waxes. It may be assumed
that rapid enclosing of cell walls material by siliica
organic matter together with less stable compounds
and prevent its water washing or bacterial
degradation.
[1] Manchester R. (1996) Petrified woods in Florida,
Papers in Florida Paleontology No. 8,
[2] Ewbank G., Edwards D. and Abbott G.D. (1996)
Chemical characterisation of Lower Devonian
vascular plants. Org. Geochem. 25, 461-473.
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