Hasandong Formation

The Hasandong Formation (Korean: 하산동층; Hanja: 霞山洞層; RR: Hasandong-cheung) is an Early Cretaceous geologic formation in South Korea. It has been dated to the Aptian to possibly the earliest Albian stage.

The Hasandong Formation could be distinguished from the underlying Nakdong Formation and the overlying Jinju Formation by frequent intercalations of reddish beds. The paleoenvironment of this formation represents a floodplain with a meandering channel including occasional pond deposits. Meanwhile, the paleoclimate has been interpreted as a seasonal alternation of wet and dry seasons.

Based on detrital zircons, Lee et al. 2010 and 2018 estimated the maximum depositional age of the formation at 118.0 ± 2.6 Ma, and suggested that the overlying Jinju Formation likely had a maximum depositional age of 112.4 ± 1.3 Ma. Chae et al. (2026) examined two fossiliferous localities of the upper Hasandong Formation on Yusu-ri, Jinju and on Jangguseom Island of Jungpyeong-ri, Hadong, and estimated the maximum depositional age on each site at 116.9 ± 1.5 Ma and 113.4 ± 1.4 Ma respectively. Fossils including plants, molluscs, diverse vertebrate remains including dinosaurs, turtles, and pterosaurs are known from this formation.

Fossil content

Invertebrate fossils

Few fragments of insects have been discovered from the formation.

Molluscs

Molluscs reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Plicatounio	P. naktongensis
P. okjuni
P. yooni
Nagdongia	N. soni
Trigonioides	T. jaehoi
T. kodairai
T. tamurai
Brotiopsis	B. kobayashii
B. naktongensis
B. ryohoriensis
B. wakinoensis
Viviparus	V. sp.				Architaenioglossan gastropod, probably V. keishoensis
Probaicalia	P. katoensis				Hydrobiidae gastropod; species previously assigned to the genus Micromelania

Ostracods

Ostracod carapaces have been discovered from the formation.

Ostracods reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Cypridea	C. cf. trita

Vertebrate fossils

Actinopterygii

Ray-finned fish reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Sinamia	S. sp.			Partial Skeleton
Lepidotes	L. sp.			Partial Skeleton

Testudines

Shell fragments of testudines have been discovered.

Turtles reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Byeoljubuchelys	B. yeosuensis			Nearly complete carapace and plastron and associated post-cranial bones	A carettochelyid turtle
Proadocus	P. hadongensis			Partial Skeleton	An adocid turtle

Crocodylomorpha

Several teeth remain have been reported but are not assigned to the specific clade.

Crocodylomorphs reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
"Hadongsuchus"	"H. acerdentis"			Skull	nomen nudum

Pterosaurs

Pterosaurs reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Pterodactyloidea	Indeterminate			Teeth and a partial second wing phalanx	Dental remains belong to either Boreopteridae or Anhanguerian
Dsungaripterus	D.? cf. D. weii			Incomplete wing phalanx belonging to Dsungaripteridae

Dinosaurs

Several indeterminate theropod teeth remains have been reported.

Dinosaurs reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Carcharodontosauridae	Indeterminate			Teeth	Some dental remains show similarities with Acrocanthosaurus
Hadrosauroidea	Indeterminate			Tooth
Titanosauriformes	Indeterminate			A partial skeleton and several teeth showing different morphotypes	Includes Chiayusaurus sp. and Pukyongosaurus milleniumi, both of which are nomen dubium
Tyrannosauroidea	Indeterminate			Tooth, estimated crown length ~18mm

Eggs

Unnamed dinosaur egg fossils have been reported.

Eggs reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Testudoolithus	T. aff. curiosa				Turtle eggs

Ichnofossils

Tracks of theropods, sauropods and ornithopods have been discovered from the formation. Possible amphibian tracks are also known.

Ichnofossils reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Pteraichnus	P. koreanensis				Pterosaur tracks
Sauripes	S. hadongensis				The oldest lizard tracks showing possible bipedalism, though potentially a nomen dubium due to insufficient description and problematic holotype designation
Diplocraterion	D. luniforme
Beaconites	B. coronus
Circulichnus	C. montanus
Cochlichnus	C. anguineus
Chondrites	C. isp.
Helminthopsis	H. abeli & H. hieroglyphica
Laevicyclus	L. isp.
Planolites	P. annularius, P. beverleyensis & P. montanus
Skolithos	S. magnus, S. verticalis & S. isp.
Spirodesmos	S. isp.
Taenidium	T. barretti
Thalassinoides	T. paradoxicus & T. suevicus

Paleoflora

Macroflora of the Hasandong Formation suggests a shift toward seasonally semiarid conditions, dominated by conifers, compared to the underlying Nakdong Formation.

Plants reported from the Hasandong Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Brachyphyllum	B. japonicum				Conifer with an unknown systematic position
Cladophlebis	C. denticulata
C. (Eboracia?) lobifolia
C. (Klukia?) koraiensis
C. shinshuensis
Elatocladus	E. tennerima				Conifer with an unknown systematic position
Onychiopsis	O. elongata				Leptosporangiate fern
Ptilophyllum	P. sp.				Bennettitales (extinct order of seed plants)
Ruffordia	R. sp.				Schizaeaceae ferns
Taeniopteris	T.? sp. cf. T. auriculata				The specific systematic position of this form genus is unknown.
Thallites	T. yabei				Liverwort

Photo

36°27′10.0″N 128°30′40.0″E/36.452778°N 128.511111°E/ 36.452778; 128.511111
Boundary of Hasandong Formation (under) and Jinju Formation (upper) 36°24′04.0″N 128°32′40.0″E/36.401111°N 128.544444°E/ 36.401111; 128.544444

35°00′15.8″N 127°55′16.7″E/35.004389°N 127.921306°E/ 35.004389; 127.921306
35°00′15.7″N 127°55′17.7″E/35.004361°N 127.921583°E/ 35.004361; 127.921583
34°59′59.6″N 127°55′08.2″E/34.999889°N 127.918944°E/ 34.999889; 127.918944
35°00′02.8″N 127°55′10.0″E/35.000778°N 127.919444°E/ 35.000778; 127.919444
Ripple marks 35°00′02.0″N 127°55′09.6″E/35.000556°N 127.919333°E/ 35.000556; 127.919333
Normal Faults 34°59′59.6″N 127°55′08.1″E/34.999889°N 127.918917°E/ 34.999889; 127.918917
34°59′59.7″N 127°55′08.1″E/34.999917°N 127.918917°E/ 34.999917; 127.918917
34°59′23.9″N 127°55′09.1″E/34.989972°N 127.919194°E/ 34.989972; 127.919194

34°57′31.2″N 127°53′52.6″E/34.958667°N 127.897944°E/ 34.958667; 127.897944
34°57′32.9″N 127°53′53.8″E/34.959139°N 127.898278°E/ 34.959139; 127.898278
34°57′33.8″N 127°53′53.9″E/34.959389°N 127.898306°E/ 34.959389; 127.898306
34°57′33.8″N 127°53′53.9″E/34.959389°N 127.898306°E/ 34.959389; 127.898306
34°57′34.1″N 127°53′53.8″E/34.959472°N 127.898278°E/ 34.959472; 127.898278
34°57′29.6″N 127°53′41.0″E/34.958222°N 127.894722°E/ 34.958222; 127.894722
34°57′29.3″N 127°53′39.9″E/34.958139°N 127.894417°E/ 34.958139; 127.894417
34°57′27.3″N 127°53′43.0″E/34.957583°N 127.895278°E/ 34.957583; 127.895278
34°57′27.4″N 127°53′43.0″E/34.957611°N 127.895278°E/ 34.957611; 127.895278
34°57′27.0″N 127°53′43.1″E/34.957500°N 127.895306°E/ 34.957500; 127.895306

34°56′50.8″N 127°51′08.1″E/34.947444°N 127.852250°E/ 34.947444; 127.852250
Cross-bedding 34°56′50.9″N 127°51′08.5″E/34.947472°N 127.852361°E/ 34.947472; 127.852361
34°56′50.6″N 127°51′08.7″E/34.947389°N 127.852417°E/ 34.947389; 127.852417
Cross-bedding 34°56′50.9″N 127°51′08.5″E/34.947472°N 127.852361°E/ 34.947472; 127.852361
Cross-bedding 34°56′51.0″N 127°51′08.7″E/34.947500°N 127.852417°E/ 34.947500; 127.852417
34°56′51.1″N 127°51′08.3″E/34.947528°N 127.852306°E/ 34.947528; 127.852306
34°56′51.6″N 127°51′08.5″E/34.947667°N 127.852361°E/ 34.947667; 127.852361
34°57′28.2″N 127°48′37.1″E/34.957833°N 127.810306°E/ 34.957833; 127.810306