Figure F50. Oxygen and hydrogen indices for samples from lower Aptian organic-rich horizons (OAE1a; Table T3) plotted on a modified van Krevelen diagram. The characteristics of organic-rich samples from Holes 1207B and 1213B, and from the Aptian at Holes 463 and 866A in the mid-Pacific are also shown. Data for Sites 463 and 866A are compiled from Dean et al. (1981), Mélières et al. (1981), and Baudin et al. (1995). The size of the data points is proportional to organic carbon contents. The lines designated I, II and III represent the evolutionary trends with thermal maturation of the three major kerogen types (Tissot et al., 1974). OI = oxygen index.
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