Stable isotopic composition of dinosaur eggshells and pedogenic carbonates in the upper cretaceous seonso formation, South Korea: Paleoenvironmental and diagenetic implications

Stable isotopic compositions of the pedogenic calcites and calcitic dinosaur eggshells analyzed from the Seonso Formation in southern Korea provide information on the paleoenvironmental conditions that dominated the region during the Upper Cretaceous as well as on the nature of the diagenetic fluids. The δ18O values of the calcites recovered from the paleosols (−15.46 to −26.22 ‰ VPDB) indicate that they were precipitated and/or altered under a high temperature regime, whereas the δ13C values (−3.88 to −7.72 ‰ VPDB) suggest that these carbonates received contributions from hydrothermal fluids during shallow burial and possibly from C3-type vegetation. 8O and δ13C of partially to well-preserved calcite eggshells are significantly different from those of the paleosols, indicating a departure from the earlier environmental conditions. The observed shift in δ18O values between the dinosaur eggshells (−3.43 to −14.09 ‰) and pedogenic calcites indicates different environmental and thermal conditions and suggesting two possible scenarios; either that the timing of egg laying by the dinosaur and the soil formation were not synchronous, or that the dinosaur consumed water from the rivers and evaporated ponds. In contrast, isotopic compositions of vein calcites cross-cutting paleosols (−19.06 to −21.72 for δ18O, and −3.78 to −4.79 for δ13C) reflect their precipitation under hydrothermal conditions. rrow range in the δ13C values of the eggshells (−7.04 to −8.69 ‰) reflect a uniform source for carbon; mostly representing fresh water charged with CO2 from hydrothermal sources as dissolved carbon.