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(a,b) δ13C vs. δ18O diagram of 11 Gigantoproductus shells. Well-preserved areas (filled-in black), dorsal valve (blue circles) and poorly preserved areas (red diamonds). (b) Values of well-preserved areas of the tertiary layer in each region. Plan of the shell with underscored shell regions. U: umbonal region; Tk: thick region; T: thin region; DV: Dorsal Valve.
