Diagenetic pathways

Figure 2. Sterane end products of the early diagenetic pathways of A5- and A7 sterols. Data from ref. 11.

Figure 13. Proposed early diagenetic pathways of bacteriohopanetetrol.

The Bermudian biosparites are composed of a mixture of calcite, magnesian calcite and aragonite. The diagenetic pathway of these sediments is controlled to a... 

Figure 7.39. Schematic diagram illustrating the effects of climate on meteoric diagenetic pathways for coeval carbonates originally composed of a polymineralic assemblage of calcite with various amounts of magnesium and strontium-rich aragonite. (After James and Choquette, 1984.)...

Plate tectonics is a major driving force affecting Earth s surface environment. The kind and intensity of the physico-chemical parameters that control diagenetic pathways are determined to some degree directly or indirectly by plate tectonic processes. The plate tectonic environment exerts a direct control on diagenesis, whereas changes in Earth s surface chemistry induced by changes in... 

Burial diagenesis and subsequent alteration of chalk The Overall Diagenetic Pathway... 

Friedrich, J., Dinkel, C., Friedl, G., Pimenov, N., Wijsman, J., Gomoiu, M.-T., Cociasu, A., Popa, L., and Wehrli, B. (2002) Benthic nutrient cycling and diagenetic pathways in the north-western Black Sea. Estuar. Coastal Shelf Sci. 54,369-383. 

Lipiatou and Saliot, 1991). The origin of perylene has been linked to terrestrial precursors (4,9-dihydroxyperylene-3,10-quinone, the possible candidate), marine precursors, and anthropogenic inputs (Blumer et ai, 1977 Laflamme and Hites, 1978 Prahl and Carpenter, 1979 Venkatesan, 1988 Lipiatou and Saliot, 1991). The diagenetic pathway for retene is well constrained (Figure 7), but it can also be produced from wood combustion (Wakeham et al., 1980b Lipiatou and Saliot, 1991 Neilson and Hynning, 1998). 

Figure 7 Diagenetic pathway for formation of retene from abietic acid (after Wakeham et al., 1980a).

Suites of sedimentary compounds are also considered as starting compounds in chemical diagenetic pathways. 

In the above discussed examples we have dealt with sedimentary organic compounds which probably occur as such in living organisms. Hereafter several examples will be discussed in which information is also obtained about diagenetic pathways. 

Loliolides and dihydroactinidiolide. Although loliolides as such occur in living systems the recently discovered sedimentary loliolides (XV, XVI, XVII) isolated from Namibian Shelf diatomaceous ooze are thought to be compounds which have been generated by very early stage diagenetical pathways from carotenoids in the oxic zone of the water column (32). 

Figure 10. Possible diagenetic pathway for A-nor steroidal hydrocarbons.

The above discussed loliolides, A-nor-steranes and De-A-steranes, are thought to carry information about particular diagenetic pathways since it is assumed that these compounds do not reflect compounds which, as such, occur in living biota. Once a certain pathway is proven, the precursor molecules are known and in this way additional information about the biological origins can be obtained. 

Humic isolates from different layers of an organic matter rich algal sapropel from Mangrove Lake, Bermuda, have been analyzed using solid-state N NMR in order to reveal chemical structural interrelationships that allow delineation of diagenetic pathways. ... 

Fig. 5.8 Possible early diagenetic pathways for fucoxanthin under anoxic sedimentary conditions. Only the left side of the molecule is shown for intermediates in loliolide formation by epoxide opening large arrow indicates biogenic input (after Repeta 1989).

Fig. 5.14 Diagenetic pathways of carotenes and P-cyclic xanthophylls in anoxic sediments (large arrows indicate biogenic inputs after Repeta 1989).

Fig. 5.16 Summary of postulated diagenetic pathways for 4-methylsterols (large arrows indicate biogenic input aromatic steroid formation as for regular steroids in Fig. 5.14 after de Leeuw et al. 1989 Peakman et al. 1992 Rechka et al. 1992).

Fig. 5.18 Possible diagenetic pathways for the formation ofretene from diterpenoidal resin components (large arrows indicate biogenic inputs after Simoneit 1977, 1986 Simoneit et al. 1986a Alexander et al. 1987). Note different number schemes for abietoids and phenanthrenes. (18-norabieta-8,ll,13-triene is also known as dehydroabietin.)...

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