Early diagenesis of organic carbon

Tromp T. K., Cappellen P. V., and Key R. M. (1995) A global model for the early diagenesis of organic carbon and organic phosphorus in marine sediments. Geochim. Cosmochim. Acta 59, 1259-1284. 

Filipek L. H. and Owen R. M. (1980) Early diagenesis of organic carbon and sulfur in outer shelf sediments from the Gulf of Mexico. Am. J. Sci. 280(10), 1097-1112. 

Herezeg, A., 1988. Early diagenesis of organic matter in lake sediments A stable carbon isotope... 

Fig. 4.14 Plot of weight percent organic carbon vs. weight percent pyrite sulfur for normal-marine modern sediments. Each plotted point represents the average value of samples in a given core, taken at a sediment depth where contents of organic carbon and pyrite have attained quasi-steady-state values, i.e. where early diagenesis of carbon and sulfur is (essentially) complete. The dashed lines enclose data from a variety of other studies (after Berner and Raiswell 1983). Sediments deposited under anoxic (euxinic) conditions would plot above the trend line, freshwater sediments significantly below.

Sarazin, G., G. Michard, I. A1 Gharib M. Bernat, 1992. Sedimentation rate and early diagenesis of particulate organic nitrogen and carbon in Aydat Lake (Puy de Dome, France). Chem. Geol. 98 307-316. 

The resin fractions of organic sulfur-rich bitumens are for a substantial part composed of monomers with linear, isoprenoid, steroid, hopanoid and carotenoid carbon skeletons connected to each other by (poly)sulfide linkages. These structural units may contain additional intramolecular sulfur linkages. This sulfur-rich geopolymer is also formed by sulfur incorporation into functionalised lipids in an intermolecular fashion during early diagenesis. 

Many studies of the impact of chemical diagenesis on the carbonate chemistry of anoxic sediments have focused primarily on the fact that sulfate reduction results in the production of alkalinity, which can cause precipitation of carbonate minerals (see previous discussion). However, during the early stages of sulfate reduction (—2-35%), this reaction may not cause precipitation, but dissolution of carbonate minerals, because the impact of a lower pH is greater than that of increased alkalinity (Figure 4). Carbonate ion activity decreases rapidly as it is titrated by CO2 from organic matter decomposition leading to a decrease in pore-water saturation state. This process is evident in data for the Fe-poor, shallow-water carbonate sediments of Morse et al. (1985) from the Bahamas and has been confirmed in studies by Walter and Burton (1990), Walter et al. (1993), and Ku et al. (1999) for Florida Bay, Tribble (1990) in Checker Reef, Oahu, and Wollast and Mackenzie (unpublished data) for Bermuda sediments. 

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