Organic carbon cements

Limestone. This is a sedimentary rock that is formed by the accumulation of organic marine life remains (shells or coral). Its main component is calcium carbonate. Cement rock. This is a sedimentary rock that has a similar composition as the industrially produced cement. 

Their studies are remarkable in indicating that organic matter may be important for the formation of magnesian calcite radial ooids, but not aragonitic tangential ooids. This observation is contrary to general concensus on the formation of these two types of ooids. It may also offer a major clue to the formation of aragonitic and calcitic carbonate cements. 

Mitterer R.M. (1971) Influences of natural organic matter on CaCC>3 precipitation. In Carbonate Cements (ed. O.P. Bricker), pp. 254-258. The Johns Hopkins Press, Baltimore. 

Mitterer R.M. and Cunningham R Jr. (1985) The interaction of natural organic matter with grains surfaces Implications for calcium carbonate precipitation. In Carbonate Cements (eds. N. Schneidermann and P.M. Harris), pp. 17-31. Soc. Econom. Paleontoligists and Mineralogists, Tulsa, OK. 

Hypothesis 2. Diffusion of DOC and sulfate from confining bed pore waters provides sources of electron donor (organic carbon) and electron acceptor (sulfate). Carbon dioxide produced by this reaction drives shell material dissolution/ calcite cement precipitation which can explain the major ion and carbon isotope composition of Black Creek aquifer water. 

The overall carbon balance in the Black Creek aquifer implied by hypothesis 3 is shown in Table 11. According to this balance, shell material has contributed 83-87% of the carbon to DIC in the aquifer, compared to 13-17% from organic carbon. Of the total carbon added from shell material and organic carbon, —74% was subsequently removed as calcite cement in the... 

The absence of dolomite cement at sandbody bases and its abundance at sandbody tops, the reported organic carbon isotope signal in the rhombic ferroan dolomite and the mixture of pedogenic dolomite textures and burial diagenetic textures in the sandbodies suggests that options 1 and 4 together are probably responsible for, the distribution of dolomite in the Chaunoy sandbodies. 

Reaction paths by which organic carbon could be sequestered in cements include bacterial sulphate reduction or direct microbial oxidation of organic matter, oxidation of methane, and/or the thermal degradation of organic matter (see Curtis, 1977 Irwin et al., 1977). In our samples the depth of cementation was at least several hundred metres, which is deeper than the depth to which marine sulphate survives (Hesse, 1990). Therefore, the organic carbon must have been derived from the oxidation of methane or, more likely, from the thermal degradation of organic matter. 

This study aims to decipher and compare the dia-genetic evolution of hybrid arenites and arenites rich in carbonate rock fragments belonging to the Bismantova-Termina succession, a synorogenic sequence of the northern Apennines (Fig. 1). Special emphasis is given to the roles of the complex detrital composition, provenance and facies organization of the arenites in their carbonate cementation. 

Carbonate cements occur in small amounts in many sandstone hydrocarbon reservoirs of the San Joaquin basin. The cements formed throughout much of the burial history of the basin, and thus provide an extensive record of organic-inorganic diagenesis. Moreover, the cements record the nature and mag-... 

Finally, carbonate cements reveal the sources of dissolved carbon in the evolving pore waters of the San Joaquin basin. The clastic-rich basin is free of carbonate rocks but contains a considerable amount of organic matter, both in fine-grained sediment and as relatively recent hydrocarbon accumulations. Potential carbon sources for the carbonate cements are marine shell tests, thermogenesis and, possibly, organic reactions related to the presence of the oil. 

Table 5. Comparison of the characteristics of the major carbonate-cemented zones and their Jurassic host sandstones in the Angel and Gidgealpa Fields, including present-day temperatures and organic maturity for adjacent source rocks.

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