이찬영 1 ·김보성 2 ·김명지 3 ·김정빈 4, * 1 전남과학고등학교, 520-824, 전라남도 나주시 금천면 오강길 33 2 목포자연사박물관, 530-830, 전라남도 목포시 남농로 135 3 대성여자고등학교, 503-330, 광주광역시 남구 서문대로 663번길 37 4 순천대학교 물리교육과, 540-950, 전라남도 순천시 중앙로 255Abstract: In September 2009, a perfectly preserved fossil of a dinosaur egg nest was discovered in the Cretaceous formations of the Aphaedo area in Shinan, Jeollanam-do, South Korea. In order to estimate the age of dinosaur eggshells and the depositional age of the Cretaceous sediments in Aphaedo area, a whole-rock K-Ar dating was carried out on volcanic pebbles showing a sedimentary structure contemporaneous with the Aphaedo strata, acidic tuffs overlaying the strata conformably, and acidic dike rocks intrude to both of them. Volcanic rocks observed in the strata are 3-20 cm in diameter as pebbles found in lenticular conglomerate and pebble bearing mudstone strata. K-Ar whole-rock dating was performed on six different volcanic pebbles which show a sedimentary structure contemporaneous with the dinosaur egg nest contained in the strata, and all samples show Late Cretaceous ages: Cenomanian (97.6±1.9 Ma), Coniacian (87.6±1.7 Ma), Santonian (84.5±1.7 Ma) or Campanian (82.5±1.6, 77.3±1.5, 75.7±1.5 Ma). The K-Ar whole-rock age of acidic tuffs overlaying the Cretaceous formation conformably was estimated to be Campanian (79.2±1.6 or 77.3±1.5 Ma), when the dating was carried out under the same conditions. The acidic dike intruding both Cretaceous formation and acidic tuff showed a K-Ar whole-rock age of 70.9±1.4 Ma (Campanian). Therefore, the depositional age of the Cretaceous formation in the Aphaedo area and the time when dinosaurs lived in the study area are considered to be 77-83 Ma. Such results indicate that the ages of dinosaur eggshells from Aphaedo area can be correlated with the ages of the Seonso Formation (81 Ma) with dinosaur egg nest fossils and the Uhangri Formation (79-81 Ma) with dinosaur, pterosaur and web-footed bird tracks.