Definition
The Hasandong Formation is a geologic formation in South Korea that dates to the Early Cretaceous period. It is recognized for preserving a diverse assemblage of fossil flora and fauna, including vertebrate remains such as dinosaurs, fish, and amphibians.
Overview
The formation is located primarily in the western part of the Gyeongsang Basin, within the provinces of South Gyeongsang and North Jeolla. Stratigraphically, it overlies the Jindong Formation and underlies the Jinju Formation, forming part of the broader Gyeongsang Supergroup. Sediments of the Hasandong Formation were deposited in fluvial and lacustrine environments, reflecting a setting of rivers, floodplains, and associated lakes during the Early Cretaceous (approximately 125–100 million years ago).
Significant paleontological discoveries from the Hasandong Formation include:
- Dinosaur remains – Notably the basal neornithischian Koreanosaurus happonensis and fragmentary theropod material.
- Fish fossils – A variety of actinopterygian (ray‑finned fish) specimens have been recovered, indicating well‑preserved freshwater ecosystems.
- Amphibians and reptiles – Isolated vertebrate fossils such as salamanders and crocodylomorphs are present.
- Plant fossils – Palynological and macrofloral evidence points to a mixed conifer‑gymnosperm and fern vegetation.
These finds have contributed to the understanding of Early Cretaceous terrestrial ecosystems on the Korean peninsula and have implications for biogeographic linkages with contemporaneous Asian faunas.
Etymology/Origin
The name “Hasandong” derives from the locality of Hasandong (also transliterated as “Hasang‑dong”), a village or district within the region where the formation’s type section was first described. The suffix “‑dong” in Korean denotes a neighborhood or district.
Characteristics
| Aspect | Description |
|---|---|
| Age | Early Cretaceous (Aptian–Albian stages, ~125–100 Ma) |
| Lithology | Dominantly mudstone, shale, and fine‑grained sandstone; occasional siltstone and conglomerate beds |
| Depositional environment | Fluvial (river channels and overbank deposits) and lacustrine (lake) settings |
| Thickness | Variable; commonly reported thickness ranges from 100 m to over 300 m in different sections |
| Fossil content | Vertebrate fossils (dinosaurs, fish, amphibians, crocodylomorphs), plant remains, and trace fossils (including dinosaur footprints) |
| Stratigraphic relationships | Overlies the Jindong Formation; underlies the Jinju Formation within the Gyeongsang Supergroup |
Related Topics
- Gyeongsang Supergroup – The larger stratigraphic unit encompassing the Hasandong Formation and other Cretaceous formations in Korea.
- Early Cretaceous paleogeography of East Asia – Contextual framework for interpreting the fauna and flora preserved in the formation.
- Koreanosaurus happonensis – A basal neornithischian dinosaur described from material recovered in the Hasandong Formation.
- Dinosaur trace fossils in Korea – The formation includes several ichnofossil sites with tracks attributed to theropods and ornithopods.
- Fluvial–lacustrine sedimentary systems – The depositional processes that characterize the Hasandong formation’s lithology and fossil preservation.