Silurian carbon content

Fig. 5.3. Organic isotope and geochemical data, Triassic Province, a Carbon isotope composition of oil and bitumenoid fractions for Paleozoic sediments, Triassic Province b Carbon isotope composition of oil from Saharian fields c Geochemical log for Takhoukht geological section based on shale pyrolysis data d Classification diagram HI-OI for Silurian and Devonian shale sediments, Triassic Province e Distribution of residual oil potentials vs. organic carbon content in Silurian and Devonian oil source rocks, Triassic Province...

As stated above, carbonate rocks comprise —30% of the mass of Phanerozoic sediments. Given and Wilkinson (1987) reevaluated aU the existing data on Phanerozoic carbonate rocks, their masses, and their relative calcite and dolomite contents (Figure 38). It can be seen that, as with the total sedimentary mass (Garrels and Mackenzie, 1971a,b), the mass of carbonate rock preserved is pushed toward the front of geologic time. The Tertiary, Carboniferous, and Cambrian periods are times of significant carbonate preservation, whereas the preservation of Silurian and Triassic carbonates is minimal. 

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