Diagenesis chlorophyll

Daley, R.J. (1973) Experimental characterization of lacustrine chlorophyll diagenesis. II. Bacterial, viral, and herbivore grazing effects. Arch. Hydrobiol. 72, 409-439. 

These data expose some pertinent new facts concerning porphyrin diagenesis as well as shedding hght on the origin of petroporphyrins which have long been believed to be the products of chlorophyll diagenesis (24,25). Temperature is the promoter of both transalkylation and dealkylation reactions which can occur in deeply buried sediments. However, because of the extreme temperatures (300°-1000°C) to which the sediments in this case were exposed, dealkylation was favored over transalkylation. Under milder conditions (50°-150°C) the transalkylation... 

The rapid alteration of chlorophyll-a as phytoplankton leave the euphotic zone may well be expected to continue as passage through additional links in the food chain occurs. Thus, the detrital forms of chlorophyll-a, available to sedimentary diagenesis should contain a dominance of pheophorbide-a. 

The main point of this simple study is that, in cases such as peat/coal and aquatic sapropel/ paper shale accumulations, ultimate geoporphyrin (i.e. DPEP-series) precursors beside chlorophyll-a need to be considered. In order to mold bacteriochl orophyl 1-a into current modified Treib s scheme diagenesis (3-5) only the removal of the 3,4-dihydro and 2-acetyl features are required. That is, an aromatization and reduction/dehydration. 

Conclusion Modified "Treibs Scheme" Diagenesis of Chlorophyll. 

Figure 12. Proposed diagenesis of chlorophyll-a derivatives. Code MESO = 2-vinyl reduced to ethyl PYRO = lacks C 10 carbo-methoxy group OD = 9-oxydeoxo asterisk = possible 6,y-cyclo-etheno intermediate LMWCC = low molecular weight colorless compounds (cf. Figure 1).

Phytol is an important part of phytoplanktonic chlorophylls, from which it appears to be released early on during diagenesis in the water column (see Section 5.3.2b). Early studies of the diagenetic fate of phytol (Didyk et al. 1978) suggested that different products are formed under different redox conditions (Fig. 5.33). 

Ishiwatari M., Ishiwatari R. and Yamada K. (1997) Two possible pathways of formation of Pr and phytane from chlorophylls on diagenesis carbon isotopic results from laboratory heating of chlorophyll-a. Chem. Lett., 355-356. 

Ll M., Larter S. R., Taylor P., Jones D. M., Bowler B. and Bjoroy M. (1995) Biomarkers or not biomarker A new hypothesis for the origin of pristane involving derivation from methyltrimethyltridecylchromans (MTTCs) formed during diagenesis from chlorophyll and alkylphenols. Org. Geochem. 23(2), 159-167. 

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