Palaeoenvironments and taphonomic preservation of dinosaur bone-bearing deposits in the Lower Cretaceous Hasandong Formation, Korea

Dinosaur (mostly sauropod) bone-bearing deposits of the Lower Cretaceous Hasandong Formation of the Gyeongsang Supergroup, Korea, were examined for context, bone mineralogy, geochemistry, and clay mineralogy of palaeosols, and for palaeoenvironmental and preservational interpretation. Most of the Hasandong dinosaur remains are in proximal to distal floodplain deposits. Dinosaur bones commonly occur as fragments, except at the Galsari locality where partially articulated cervical vertebrae, a dorsal vertebra, a dorsal rib, and a caudal rib are associated. It is characteristic that the Hasandong bone-bearing deposits are preserved as calcic and vertic palaeosols, and that the bone fragments are thus commonly encrusted by micrite to form nodules. The bones are composed of well-crystallized francolite. Illite is the most abundant clay mineral. Relatively low87Sr/86Sr ratios of the dinosaur bones and acid-leachable fractions of the host rocks suggest that both the bones and leachable fractions were derived from a low87Sr/86Sr source such as contemporaneous volcanics. Early Cretaceous sauropods of the Korean peninsula inhabited dry woodlands with oxidized soils. The carcasses lay on floodplains and were scavenged by carnivores and carrion beetles, and severely weathered before burial. Volcanic activity near the basin sometimes resulted in rapid burial of unweathered bones on distal floodplains as in the Galsari bone deposits. After burial, the bone deposits experienced calcareous pedogenesis, which assisted preservation. The predominance of bone deposits in the Hasandong Formation may be attributable to the abundance of calcic palaeosols.