66
S. Pantoja· S. Wakeham
sed during the CuO reaction. Like monomeric phenols, the dimers may be used to
develop dimer parameters that appear to be more source specific and less diagenetically sensitive than the conventional monomer-based ratios.
2.2.4.3
Lignin Phenols as Diagenetic Indicators
Lignin phenol distributions aid in assessing diagenetic status of organic material.
Degradation by white-rot fungi, the major lignin decomposers, results in pronounced
mass loss, decrease in carbon-normalized lignin concentration, and increase in
acid/aldehyde ratios, for example vanillic acid to vanillin [(Ad/ Al)v] (Hedges et al.
1988bj Gofii et al. 1993). Brown-rot fungus, while less efficient at degrading lignin, produced some new monomers and dimers. An indication of the extent of fungal degradation in sediments can thus be obtained. For example, in the size-fractionated sediments described above (Fig. 2.17), increasing [(Ad/Al)v] from 0.2 in sands to 0.8 in
clays suggests that lignin in the sand-sized fraction is only slightly modified vascular
plant material but lignin in clays is highly degraded (Hedges and Oades 1997j Keil et al.
1998). The combination of phenol monomers and dimers enhances the information
yield for CuO oxidation (Gofii and Hedges 1992). Ratios of dimer to monomer reflect
the fraction of lignin phenolic units linked by carbon-carbon bonds rather than ether
bonds that are easily hydrolysed during CuO oxidation. Distributions of dimers give
information on the type of C-C bonding present in the lignin macromolecule. Angiosperm woods, for example, contain lignin with C bonding through side chain linkages at the C I ring carbon, as indicated by elevated ratio of side-chain dimers to ringring dimersj gymnosperm tissues appear rich in s-s'-ring-ring bonds. Variations in
ratios of selected dimers may also indicate effects of selective alteration of linkages.
Finally, dime ric acids/aldehyde ratios support inferences regarding lignin alteration
made from monomeric acid/aldehyde ratios.
2.2.4.4
Cutin Acids
CuO oxidation of plant tissues and sediments also yields a series of non-lignin products, notably long-chain CWC IS hydroxy acids whose structural characteristics suggest cutin as their vascular plant source (Gofii and Hedges 1990a,b,c). Cutin is a polyester-like biopolymer that comprises part of the cuticle of vascular plants and provides a protective covering for aerial parts. Unlike waxy epicuticular coatings that are
soluble in non-polar organic solvents, and hence are "lipids", cutin is insoluble and
requires alkaline hydrolysis to release the cutin acids. Like lignin phenols, cutin acids
are diagnostic for different cutin-bearing plant. Gymnosperms, for instance, yield
hydroxy acids dominated by CI6 acids, predominately 9,16- and 10,16-dihydroxy-hexadecanoic acids. Angiosperms were rich in CIS acids, notably 9,10,18-trihydroxy-octadecanoic acid in dicotyledons. Also like lignin phenols, a series of cutin acid parameters have been developed. Ratios of 9,1O-W-Cls/total cutin acids in excess of 0.2 are
typical of gymnosperms whereas ratios for monocotyledons average 0.02, and a plot
of x,w-C I6 /total cutin acids vs 9,10,W-Cls/total cutin acids provides a good means of
distinguishing non-woody tissues from gymnosperms vs. those of angiosperms.
S. Pantoja· S. Wakeham
sed during the CuO reaction. Like monomeric phenols, the dimers may be used to
develop dimer parameters that appear to be more source specific and less diagenetically sensitive than the conventional monomer-based ratios.
2.2.4.3
Lignin Phenols as Diagenetic Indicators
Lignin phenol distributions aid in assessing diagenetic status of organic material.
Degradation by white-rot fungi, the major lignin decomposers, results in pronounced
mass loss, decrease in carbon-normalized lignin concentration, and increase in
acid/aldehyde ratios, for example vanillic acid to vanillin [(Ad/ Al)v] (Hedges et al.
1988bj Gofii et al. 1993). Brown-rot fungus, while less efficient at degrading lignin, produced some new monomers and dimers. An indication of the extent of fungal degradation in sediments can thus be obtained. For example, in the size-fractionated sediments described above (Fig. 2.17), increasing [(Ad/Al)v] from 0.2 in sands to 0.8 in
clays suggests that lignin in the sand-sized fraction is only slightly modified vascular
plant material but lignin in clays is highly degraded (Hedges and Oades 1997j Keil et al.
1998). The combination of phenol monomers and dimers enhances the information
yield for CuO oxidation (Gofii and Hedges 1992). Ratios of dimer to monomer reflect
the fraction of lignin phenolic units linked by carbon-carbon bonds rather than ether
bonds that are easily hydrolysed during CuO oxidation. Distributions of dimers give
information on the type of C-C bonding present in the lignin macromolecule. Angiosperm woods, for example, contain lignin with C bonding through side chain linkages at the C I ring carbon, as indicated by elevated ratio of side-chain dimers to ringring dimersj gymnosperm tissues appear rich in s-s'-ring-ring bonds. Variations in
ratios of selected dimers may also indicate effects of selective alteration of linkages.
Finally, dime ric acids/aldehyde ratios support inferences regarding lignin alteration
made from monomeric acid/aldehyde ratios.
2.2.4.4
Cutin Acids
CuO oxidation of plant tissues and sediments also yields a series of non-lignin products, notably long-chain CWC IS hydroxy acids whose structural characteristics suggest cutin as their vascular plant source (Gofii and Hedges 1990a,b,c). Cutin is a polyester-like biopolymer that comprises part of the cuticle of vascular plants and provides a protective covering for aerial parts. Unlike waxy epicuticular coatings that are
soluble in non-polar organic solvents, and hence are "lipids", cutin is insoluble and
requires alkaline hydrolysis to release the cutin acids. Like lignin phenols, cutin acids
are diagnostic for different cutin-bearing plant. Gymnosperms, for instance, yield
hydroxy acids dominated by CI6 acids, predominately 9,16- and 10,16-dihydroxy-hexadecanoic acids. Angiosperms were rich in CIS acids, notably 9,10,18-trihydroxy-octadecanoic acid in dicotyledons. Also like lignin phenols, a series of cutin acid parameters have been developed. Ratios of 9,1O-W-Cls/total cutin acids in excess of 0.2 are
typical of gymnosperms whereas ratios for monocotyledons average 0.02, and a plot
of x,w-C I6 /total cutin acids vs 9,10,W-Cls/total cutin acids provides a good means of
distinguishing non-woody tissues from gymnosperms vs. those of angiosperms.