Duho Formation

.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent;color:inherit}.mw-parser-output .infobox-3cols-child{margin:-3px}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}

Duho Formation
Stratigraphic range: Mid-Miocene ~
Geological formation
Yeonil Group
Alluvium
Hagjeon Formation
150–250 m (490–820 ft)
Mudstone
Sandstone, Shale
.mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct,.mw-parser-output .geo-inline-hidden{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}36°00′N 129°12′E / 36.0°N 129.2°E / 36.0; 129.2
North Gyeongsang Province
South Korea
Pohang Basin (ko:포항 분지)
Duho-dong, Pohang
Um et al., 1964
Geological map and stratigraphy of the Pohang Basin

The Duho Formation (Korean: 두호층; Hanja: 斗湖層; RR: Duho-cheung) is a Middle Miocene geological formation in Pohang, South Korea. This formation is deposited in a deep marine environment and is roughly dated to around 15 to 12 million years ago based on various analyses. It is the uppermost unit of the Yeonil Group of Pohang Basin and mainly composed of yellow-brown to dark gray mudstones.

Fossil locality in the Pohang Basin

The deposition of the Pohang Basin began some time after 21.89 to 21.68 million years ago, corresponding to the Early Miocene, based on zircon U-Pb dating. This deep-marine basin was probably produced by rapid subsidence around 17 million years ago, following the abrupt ending of the strike-slip deformation and volcanic activity, and experienced tectonic inactivity for 5 to 7 million years until the crustal uplift in southeastern Korea around 10 million years ago which caused the sedimentation to cease. The basin was likely a pelagic zone around 17.6 to 11.5 million years ago based on biostratigraphy analysis.

The intrusive basalt of the Yeonil Group from the southern part of the basin is dated to the lower Middle Miocene around 15.16 to 14.82 million years ago based on K-Ar dating, which implies the evolution of back-arc basin in the seas of southeastern Korea, followed by the tectonic inversion which changed the geodynamic setting and basaltic magma composition. Paleomagnetic dating (analysis of the sediments' ancient magnetic fields) of the Duho Formation yielded the age estimate ranging from 14.7 to 11.6 million years ago. The age estimate of the Yeonil Group based on the same technique is around 17.3 to 11.3 million years ago for the lower and upper part respectively with a reliable pole position of 15 million years ago, while biostratigraphy analysis indicated that the age of the Duho Formation likely ranged from 14 to 12 million years ago. It is probably not younger than 11.95 million years ago based on the radiolarians recovered from the formation.

Notable fossils from the Duho Formation include a variety of aquatic invertebrates such as ophiuroids, bivalves and mantis shrimps, numerous extant genera of plants, indeterminate remains of toothed whales with some diagnostic to the genus level, and diverse ichthyofauna ranging from small bony fish to large cartilaginous fish like the giant lamniform shark Otodus megalodon which would have been the apex predator of the Miocene seas of Korea. While the fauna consists of species ranging from the shallow coastal waters (neritic and epipelagic zone) to the depths of over 1,000 metres (3,300 ft) (bathypelagic zone), the sediments were probably deposited in a pelagic deep-water setting as evidenced by the paleoecological and bathymetric features of the fossil assemblage.

.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}

Column 1	Column 2
	This list is incomplete; you can help by adding missing items. (February 2025)

Crustaceans of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Leesquilla	L. bajee
L. sunii				Mantis shrimp belonging to the family Squillidae
Pohsquilla	P. neonica
P. scissodentica				Mantis shrimp belonging to the family Squillidae
Squilla	S. sp.				Mantis shrimp belonging to the family Squillidae

The probable ant fossil named as Aphaenogaster "koreana" in a 2018 conference abstracts is a nomen nudum.

Insects of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Scarites	S. sp.			A single individual known with part and counterpart	First officially described terrestrial animal (ground beetle) from the deep marine Duho Formation

Echinoderms of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Ophiura	O. pohangensis				Brittle star fossils previously described from the same formation are probably conspecific with O. pohangensis
Brissopsis	B. pohangensis				Sea urchin

Molluscs of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Acharax	A. tokunagai
Conchocele	C. bisecta
Delectopecten	D. peckhami
Lucinoma	L. acutilineatum
L. sp.
Macoma	M. incongrua
Mizuhopecten	M. kimurai ugoensis				Reported as Patinopecten kimurai ugoensis, but this species was already moved to a different genus Mizuhopecten by Mausda (1963)
Nuculana	N. pennula
Panomya	P. simotomensis
Patinopecten	P. sp.
Phos	P. cf. minoensis
Portlandia	P. cf. gratiosa
Propeamussium	P. tateiwai
Squiresica	S. yooni				Vesicomyid bivalve mollusc fossil originally assigned to as Calyptogena cf. elongata
Yoldia	Y. sagittaria

Mammals of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Kentriodontidae	Indeterminate			Partial maxilla (DWFM 10001)	Extinct family of toothed whales
Pomatodelphininae	Indeterminate			Partial rostrum and mandible (KIGAM VP 201101)	River dolphin found in marine deposits and related to Pomatodelphis
Tursiops	T. sp.			Partial skeleton measuring 70 cm (2.3 ft) long, with a nearly complete skull	Only described in thesis, not officially published. Resembles the modern bottlenose dolphin with the estimated complete length of the specimen around 1.5–2 m (4.9–6.6 ft)
Kogia	K. sp.			Partial skull measuring 40 cm (1.3 ft) long, associated with the tooth of an adult tiger shark	Only described in thesis, not officially published. Resembles the modern pygmy sperm whale and dwarf sperm whale

Bony fish of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Auxis	A. koreanus
A. sp.			Two fragmentary, disarticulated specimens distinguished from the extant species by the osteological differences in the skull
Partial caudal vertebrae (GNUE322001) associated with a leaf imprint	First and second fossil record of the genus Auxis in Korea	Auxis sp. (GNUE322001)
Cyclothone	C. duhoensis			Single complete specimen	The oldest nominal species of Cyclothone
Pleuronectiformes	Indeterminate			4 individuals	First record of flatfish from this formation, at least 2 individuals might be distinct from Pleuronichthys
Pleuronichthys	P. sp.			2 individuals, both juvenile	Species unknown, due to both specimens being juvenile
Stenobrachius	S. sangsunii			Single specimen, complete articulated skeleton with counterpart	Lanternfish
Vinciguerria	V. orientalis			61 specimens, from articulated to disarticulated skeletons	Distinct from modern species of Vinciguerria in terms of caudal skeleton structure
Zaprora	Z. koreana			Single specimen in part and counterpart, representing the caudal body region	Second fossil record of the family Zaproridae

The record of Otodus obliquus from this formation is most likely a misidentification of other otodontid or lamniform shark.

Cartilaginous fish of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Carcharhinus	C. aff. C. plumbeus
C. aff. C. amblyrhynchos
C. aff. C. altimus			Teeth
Cetorhinus	C. huddlestoni			Gill rakers and oral tooth mold
Cosmopolitodus	C. hastalis
C. planus			Teeth	Uncertain whether it is a distinct genus or a junior synonym of Carcharodon
Dalatias	D. orientalis			Teeth	Two teeth originally assigned to as D. licha (CNUNHM-F279) and D. cf. licha (CNUNHM-F392) respectively are now the paratypes of D. orientalis
Galeocerdo	G. aduncus			Teeth
Hexanchus	H. griseus			Tooth	Miocene record of the modern bluntnose sixgill shark
Isurus	I. sp. 1
I. sp. 2			Teeth
Mitsukurina	M. owstoni			Teeth	Among the oldest known record of the modern goblin shark; one tooth (CNUNHM-F268) was originally assigned to as M. cf. lineata
Otodus	O. megalodon			Teeth	Largest known macropredatory shark that ever lived
Parotodus	P. benedenii			Tooth

Plants of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Acer	A. ezoanum
A. huziokae
A. nordenskioeldi
A. palaeoplatanoides
A. pohangense
A. protomiyabei
A. prototrifidium
A. pseudoginnala
A. rotundatum (=A. subpictum & A. pictum)
Alangium	A. aequalifolium
Albizia	A. miokalkora
Castanea	C. tanaii
Castanopsis	C. pohangensis
Carpinus	C. hokoensis
C. kodairae-bracteata
C. miofargesiana
C. oblongibracteata
C. stenophylla
C. subcordata
Cinnamomum	C. lanceolatum
Cryptocarya	C. ennichiensis
Cunninghamia	C. protokonishii
Cyclobalanopsis	C. huziokai
C. mandraliscae
C. yabei
Dipteronia	D. brownii
Entada	E. mioformosana
Fagus	F. cf. hayate
Firmiana	F. sinomiocenica
Fraxinus	F. oishii
F. insularis
F. sp.
Ilex	I. protocornuta
Keteleeria	K. ezoana
Hemitrapa	H. yokoyamae				Extinct genus of aquatic plants related to water caltrop
Lindera	L. gaudini
Liriodendron	L. meisenense
Liquidambar	L. miosinica
Paliurus	P. koreanus
Pasania	P. miohypophaea
P. protokonishii
Parrotia	P. fagifolia
Phoebe	P. mioformosana
Picea	P. kaneharai
Pinus	P. miocenica
P. cf. prekesiya
Platanus	P. guillelmae
Pseudolarix	P. japonica
P. sp. A
P. sp. B
Pterocarya	P. asymmetrosa
Rhododendron	R. tatewakii
Tilia	T. asiatica
T. pentagona
T. perpendicularis
Zelcova	Z. ungeri

Ichnofossils of the Duho Formation
Genus	Species	Region	Member	Material	Notes	Image
Chondrites	C. isp. 1
C. isp. 2			Three deep-water ichnofossils	C. isp. 1 and C. isp. 2 are deposited under oxygen-depleted and oxygenated conditions respectively
Palaeophycus	P. isp.
Planolites	P. isp.
Taenidium	T. isp.

.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}body.skin-vector-2022 .mw-parser-output .reflist-columns-2{column-width:27em}body.skin-vector-2022 .mw-parser-output .reflist-columns-3{column-width:22.5em}.mw-parser-output .references[data-mw-group=upper-alpha]{list-style-type:upper-alpha}.mw-parser-output .references[data-mw-group=upper-roman]{list-style-type:upper-roman}.mw-parser-output .references[data-mw-group=lower-alpha]{list-style-type:lower-alpha}.mw-parser-output .references[data-mw-group=lower-greek]{list-style-type:lower-greek}.mw-parser-output .references[data-mw-group=lower-roman]{list-style-type:lower-roman}.mw-parser-output div.reflist-liststyle-upper-alpha .references{list-style-type:upper-alpha}.mw-parser-output div.reflist-liststyle-upper-roman .references{list-style-type:upper-roman}.mw-parser-output div.reflist-liststyle-lower-alpha .references{list-style-type:lower-alpha}.mw-parser-output div.reflist-liststyle-lower-greek .references{list-style-type:lower-greek}.mw-parser-output div.reflist-liststyle-lower-roman .references{list-style-type:lower-roman}