Duho Formation

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Coordinates: 36°00′N 129°12′E / 36.0°N 129.2°E / 36.0; 129.2
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Duho Formation
Stratigraphic range: Mid-Miocene
~15–12 Ma
TypeGeological formation
Unit ofYeonil Group
UnderliesAlluvium
OverliesHagjeon Formation
Thickness150–250 m (490–820 ft)[1]
Lithology
PrimaryMudstone
OtherSandstone, Shale
Location
Coordinates36°00′N 129°12′E / 36.0°N 129.2°E / 36.0; 129.2
RegionNorth Gyeongsang Province
CountrySouth Korea
ExtentPohang Basin (ko:포항 분지)
Type section
Named forDuho-dong, Pohang
Named byUm et al., 1964[2]

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.[3]

Geology

[edit]
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.[4] 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.[5] The basin was likely a pelagic zone around 17.6 to 11.5 million years ago based on biostratigraphy analysis.[6]

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,[7] 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.[8] 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.[9] 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.[10] It is probably not younger than 11.95 million years ago based on the radiolarians recovered from the formation.[11]

Paleoecology

[edit]

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.[1]

Fossil content

[edit]

Crustaceans

[edit]
Crustaceans of the Duho Formation[12]
GenusSpeciesRegionMemberMaterialNotesImage
Leesquilla
  • L. bajee
  • L. sunii
Mantis shrimp belonging to the family Squillidae
Pohsquilla
  • P. neonica
  • P. scissodentica
Mantis shrimp belonging to the family Squillidae
SquillaS. sp.Mantis shrimp belonging to the family Squillidae

Insects

[edit]

The probable ant fossil named as Aphaenogaster "koreana" in a 2018 conference abstracts is a nomen nudum.[13]

Insects of the Duho Formation
GenusSpeciesRegionMemberMaterialNotesImage
ScaritesS. sp.[14]A single individual known with part and counterpartFirst officially described terrestrial animal (ground beetle) from the deep marine Duho Formation

Echinoderms

[edit]
Echinoderms of the Duho Formation
GenusSpeciesRegionMemberMaterialNotesImage
OphiuraO. pohangensis[15]Brittle star fossils previously described from the same formation are probably conspecific with O. pohangensis
BrissopsisB. pohangensis[16]Sea urchin

Molluscs

[edit]
Molluscs of the Duho Formation[17]
GenusSpeciesRegionMemberMaterialNotesImage
AcharaxA. tokunagai
ConchoceleC. bisecta
DelectopectenD. peckhami
Lucinoma
  • L. acutilineatum
  • L. sp.
MacomaM. incongrua
MizuhopectenM. kimurai ugoensisReported as Patinopecten kimurai ugoensis,[18] but this species was already moved to a different genus Mizuhopecten by Mausda (1963)[19]
NuculanaN. pennula
PanomyaP. simotomensis
PatinopectenP. sp.
PhosP. cf. minoensis
PortlandiaP. cf. gratiosa
PropeamussiumP. tateiwai
Squiresica[20]S. yooniVesicomyid bivalve mollusc fossil originally assigned to as Calyptogena cf. elongata
YoldiaY. sagittaria

Mammals

[edit]
Mammals of the Duho Formation
GenusSpeciesRegionMemberMaterialNotesImage
Kentriodontidae[21]IndeterminatePartial maxilla (DWFM 10001)Extinct family of toothed whales
Pomatodelphininae[22]IndeterminatePartial rostrum and mandible (KIGAM VP 201101)River dolphin found in marine deposits and related to Pomatodelphis
Tursiops[23]T. sp.Partial skeleton measuring 70 cm (2.3 ft) long, with a nearly complete skullOnly 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[23]K. sp.Partial skull measuring 40 cm (1.3 ft) long, associated with the tooth of an adult tiger sharkOnly described in thesis, not officially published. Resembles the modern pygmy sperm whale and dwarf sperm whale

Bony fish

[edit]
Bony fish of the Duho Formation
GenusSpeciesRegionMemberMaterialNotesImage
Auxis
  • 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[26]C. duhoensisSingle complete specimenThe oldest nominal species of Cyclothone
Pleuronectiformes[27]Indeterminate4 individualsFirst record of flatfish from this formation, at least 2 individuals might be distinct from Pleuronichthys[28]
Pleuronichthys[28]P. sp.2 individuals, both juvenileSpecies unknown, due to both specimens being juvenile
Stenobrachius[29]S. sangsuniiSingle specimen, complete articulated skeleton with counterpartLanternfish
Vinciguerria[30]V. orientalis61 specimens, from articulated to disarticulated skeletonsDistinct from modern species of Vinciguerria in terms of caudal skeleton structure
Zaprora[31]Z. koreanaSingle specimen in part and counterpart, representing the caudal body regionSecond fossil record of the family Zaproridae

Cartilaginous fish

[edit]

The record of Otodus obliquus from this formation is most likely a misidentification of other otodontid or lamniform shark.[32]

Cartilaginous fish of the Duho Formation[1]
GenusSpeciesRegionMemberMaterialNotesImage
Carcharhinus
  • C. aff. C. plumbeus
  • C. aff. C. amblyrhynchos
  • C. aff. C. altimus
Teeth
CetorhinusC. huddlestoni[33]Gill rakers and oral tooth mold
Cosmopolitodus
  • C. hastalis[17]
  • C. planus
TeethUncertain whether it is a distinct genus or a junior synonym of Carcharodon
DalatiasD. orientalisTeethTwo teeth originally assigned to as D. licha (CNUNHM-F279) and D. cf. licha (CNUNHM-F392) respectively are now the paratypes of D. orientalis
GaleocerdoG. aduncusTeeth
HexanchusH. griseusToothMiocene record of the modern bluntnose sixgill sharkModern bluntnose sixgill shark in Santa Rosa Reef
Isurus
  • I. sp. 1
  • I. sp. 2
Teeth
MitsukurinaM. owstoniTeethAmong the oldest known record of the modern goblin shark; one tooth (CNUNHM-F268) was originally assigned to as M. cf. lineataJuvenile of a modern goblin shark
OtodusO. megalodonTeethLargest known macropredatory shark that ever livedRestoration of megaldodon
ParotodusP. benedeniiTooth

Plants

[edit]
Plants of the Duho Formation
GenusSpeciesRegionMemberMaterialNotesImage
Acer[34][35]
  • A. ezoanum
  • A. huziokae
  • A. nordenskioeldi
  • A. palaeoplatanoides
  • A. pohangense
  • A. protomiyabei
  • A. prototrifidium
  • A. pseudoginnala
  • A. rotundatum (=A. subpictum & A. pictum)
Alangium[36]A. aequalifolium
Albizia[37]A. miokalkora
Castanea[36]C. tanaii
Castanopsis[36]C. pohangensis
Carpinus[38][36]
  • C. hokoensis
  • C. kodairae-bracteata
  • C. miofargesiana
  • C. oblongibracteata
  • C. stenophylla
  • C. subcordata
Cinnamomum[36]C. lanceolatum
Cryptocarya[36]C. ennichiensis
Cunninghamia[39]C. protokonishii
Cyclobalanopsis[36]
  • C. huziokai
  • C. mandraliscae
  • C. yabei
Dipteronia[40]D. brownii
Entada[36]E. mioformosana
Fagus[36]F. cf. hayate
Firmiana[41]F. sinomiocenica
Fraxinus[42][36]
  • F. oishii
  • F. insularis
  • F. sp.
Ilex[43]I. protocornuta
Keteleeria[44]K. ezoana
Hemitrapa[36]H. yokoyamaeExtinct genus of aquatic plants related to water caltrop
Lindera[36]L. gaudini
Liriodendron[42]L. meisenense
Liquidambar[36]L. miosinica
Paliurus[36]P. koreanus
Pasania[36]
  • P. miohypophaea
  • P. protokonishii
Parrotia[36]P. fagifolia
Phoebe[36]P. mioformosana
Picea[44]P. kaneharai
Pinus[44]
  • P. miocenica
  • P. cf. prekesiya
Platanus[36]P. guillelmae
Pseudolarix[45]
  • P. japonica
  • P. sp. A
  • P. sp. B
Pterocarya[36]P. asymmetrosa
Rhododendron[36]R. tatewakii
Tilia[41]T. asiatica
Zelcova[36]Z. ungeri

Ichnofossils

[edit]
Ichnofossils of the Duho Formation[46]
GenusSpeciesRegionMemberMaterialNotesImage
Chondrites
  • C. isp. 1
  • C. isp. 2
Three deep-water ichnofossilsC. isp. 1 and C. isp. 2 are deposited under oxygen-depleted and oxygenated conditions respectively
PalaeophycusP. isp.
PlanolitesP. isp.
TaenidiumT. isp.

References

[edit]
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  46. ^ Kim, J.; Paik, I.S (2013). "Chondrites from the Duho Formation (Miocene) in the Yeonil Group, Pohang Basin, Korea: Occurrences and paleoenvironmental implications". Journal of the Geological Society of Korea. 49 (3): 407–416.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Duho_Formation&oldid=1330248198"
    Duho Formation
    Stratigraphic range: Mid-Miocene
    ~15–12 Ma
    TypeGeological formation
    Unit ofYeonil Group
    UnderliesAlluvium
    OverliesHagjeon Formation
    Thickness150–250 m (490–820 ft)[1]
    Lithology
    PrimaryMudstone
    OtherSandstone, Shale
    Location
    Coordinates36°00′N 129°12′E / 36.0°N 129.2°E / 36.0; 129.2
    RegionNorth Gyeongsang Province
    CountrySouth Korea
    ExtentPohang Basin (ko:포항 분지)
    Type section
    Named forDuho-dong, Pohang
    Named byUm et al., 1964[2]

    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.[3]

    Geology

    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.[4] 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.[5] The basin was likely a pelagic zone around 17.6 to 11.5 million years ago based on biostratigraphy analysis.[6]

    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,[7] 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.[8] 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.[9] 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.[10] It is probably not younger than 11.95 million years ago based on the radiolarians recovered from the formation.[11]

    Paleoecology

    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.[1]

    Fossil content

    Crustaceans

    Crustaceans of the Duho Formation[12]
    GenusSpeciesRegionMemberMaterialNotesImage
    Leesquilla
    • L. bajee
    • L. sunii
    		Mantis shrimp belonging to the family Squillidae
    Pohsquilla
    • P. neonica
    • P. scissodentica
    		Mantis shrimp belonging to the family Squillidae
    SquillaS. sp.Mantis shrimp belonging to the family Squillidae

    Insects

    The probable ant fossil named as Aphaenogaster "koreana" in a 2018 conference abstracts is a nomen nudum.[13]

    Insects of the Duho Formation
    GenusSpeciesRegionMemberMaterialNotesImage
    ScaritesS. sp.[14]A single individual known with part and counterpartFirst officially described terrestrial animal (ground beetle) from the deep marine Duho Formation

    Echinoderms

    Echinoderms of the Duho Formation
    GenusSpeciesRegionMemberMaterialNotesImage
    OphiuraO. pohangensis[15]Brittle star fossils previously described from the same formation are probably conspecific with O. pohangensis
    BrissopsisB. pohangensis[16]Sea urchin

    Molluscs

    Molluscs of the Duho Formation[17]
    GenusSpeciesRegionMemberMaterialNotesImage
    AcharaxA. tokunagai
    ConchoceleC. bisecta
    DelectopectenD. peckhami
    Lucinoma
    • L. acutilineatum
    • L. sp.
    MacomaM. incongrua
    MizuhopectenM. kimurai ugoensisReported as Patinopecten kimurai ugoensis,[18] but this species was already moved to a different genus Mizuhopecten by Mausda (1963)[19]
    NuculanaN. pennula
    PanomyaP. simotomensis
    PatinopectenP. sp.
    PhosP. cf. minoensis
    PortlandiaP. cf. gratiosa
    PropeamussiumP. tateiwai
    Squiresica[20]S. yooniVesicomyid bivalve mollusc fossil originally assigned to as Calyptogena cf. elongata
    YoldiaY. sagittaria

    Mammals

    Mammals of the Duho Formation
    GenusSpeciesRegionMemberMaterialNotesImage
    Kentriodontidae[21]IndeterminatePartial maxilla (DWFM 10001)Extinct family of toothed whales
    Pomatodelphininae[22]IndeterminatePartial rostrum and mandible (KIGAM VP 201101)River dolphin found in marine deposits and related to Pomatodelphis
    Tursiops[23]T. sp.Partial skeleton measuring 70 cm (2.3 ft) long, with a nearly complete skullOnly 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[23]K. sp.Partial skull measuring 40 cm (1.3 ft) long, associated with the tooth of an adult tiger sharkOnly described in thesis, not officially published. Resembles the modern pygmy sperm whale and dwarf sperm whale

    Bony fish

    Bony fish of the Duho Formation
    GenusSpeciesRegionMemberMaterialNotesImage
    Auxis
    • A. koreanus[24]
    • A. sp.[25]
    • 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[26]C. duhoensisSingle complete specimenThe oldest nominal species of Cyclothone
    Pleuronectiformes[27]Indeterminate4 individualsFirst record of flatfish from this formation, at least 2 individuals might be distinct from Pleuronichthys[28]
    Pleuronichthys[28]P. sp.2 individuals, both juvenileSpecies unknown, due to both specimens being juvenile
    Stenobrachius[29]S. sangsuniiSingle specimen, complete articulated skeleton with counterpartLanternfish
    Vinciguerria[30]V. orientalis61 specimens, from articulated to disarticulated skeletonsDistinct from modern species of Vinciguerria in terms of caudal skeleton structure
    Zaprora[31]Z. koreanaSingle specimen in part and counterpart, representing the caudal body regionSecond fossil record of the family Zaproridae

    Cartilaginous fish

    The record of Otodus obliquus from this formation is most likely a misidentification of other otodontid or lamniform shark.[32]

    Cartilaginous fish of the Duho Formation[1]
    GenusSpeciesRegionMemberMaterialNotesImage
    Carcharhinus
    • C. aff. C. plumbeus
    • C. aff. C. amblyrhynchos
    • C. aff. C. altimus
    		Teeth
    CetorhinusC. huddlestoni[33]Gill rakers and oral tooth mold
    Cosmopolitodus
    • C. hastalis[17]
    • C. planus
    		TeethUncertain whether it is a distinct genus or a junior synonym of Carcharodon
    DalatiasD. orientalisTeethTwo teeth originally assigned to as D. licha (CNUNHM-F279) and D. cf. licha (CNUNHM-F392) respectively are now the paratypes of D. orientalis
    GaleocerdoG. aduncusTeeth
    HexanchusH. griseusToothMiocene record of the modern bluntnose sixgill sharkModern bluntnose sixgill shark in Santa Rosa Reef
    Isurus
    • I. sp. 1
    • I. sp. 2
    		Teeth
    MitsukurinaM. owstoniTeethAmong the oldest known record of the modern goblin shark; one tooth (CNUNHM-F268) was originally assigned to as M. cf. lineataJuvenile of a modern goblin shark
    OtodusO. megalodonTeethLargest known macropredatory shark that ever livedRestoration of megaldodon
    ParotodusP. benedeniiTooth

    Plants

    Plants of the Duho Formation
    GenusSpeciesRegionMemberMaterialNotesImage
    Acer[34][35]
    • A. ezoanum
    • A. huziokae
    • A. nordenskioeldi
    • A. palaeoplatanoides
    • A. pohangense
    • A. protomiyabei
    • A. prototrifidium
    • A. pseudoginnala
    • A. rotundatum (=A. subpictum & A. pictum)
    Alangium[36]A. aequalifolium
    Albizia[37]A. miokalkora
    Castanea[36]C. tanaii
    Castanopsis[36]C. pohangensis
    Carpinus[38][36]
    • C. hokoensis
    • C. kodairae-bracteata
    • C. miofargesiana
    • C. oblongibracteata
    • C. stenophylla
    • C. subcordata
    Cinnamomum[36]C. lanceolatum
    Cryptocarya[36]C. ennichiensis
    Cunninghamia[39]C. protokonishii
    Cyclobalanopsis[36]
    • C. huziokai
    • C. mandraliscae
    • C. yabei
    Dipteronia[40]D. brownii
    Entada[36]E. mioformosana
    Fagus[36]F. cf. hayate
    Firmiana[41]F. sinomiocenica
    Fraxinus[42][36]
    • F. oishii
    • F. insularis
    • F. sp.
    Ilex[43]I. protocornuta
    Keteleeria[44]K. ezoana
    Hemitrapa[36]H. yokoyamaeExtinct genus of aquatic plants related to water caltrop
    Lindera[36]L. gaudini
    Liriodendron[42]L. meisenense
    Liquidambar[36]L. miosinica
    Paliurus[36]P. koreanus
    Pasania[36]
    • P. miohypophaea
    • P. protokonishii
    Parrotia[36]P. fagifolia
    Phoebe[36]P. mioformosana
    Picea[44]P. kaneharai
    Pinus[44]
    • P. miocenica
    • P. cf. prekesiya
    Platanus[36]P. guillelmae
    Pseudolarix[45]
    • P. japonica
    • P. sp. A
    • P. sp. B
    Pterocarya[36]P. asymmetrosa
    Rhododendron[36]R. tatewakii
    Tilia[41]T. asiatica
    Zelcova[36]Z. ungeri

    Ichnofossils

    Ichnofossils of the Duho Formation[46]
    GenusSpeciesRegionMemberMaterialNotesImage
    Chondrites
    • C. isp. 1
    • C. isp. 2
    		Three deep-water ichnofossilsC. isp. 1 and C. isp. 2 are deposited under oxygen-depleted and oxygenated conditions respectively
    PalaeophycusP. isp.
    PlanolitesP. isp.
    TaenidiumT. isp.

    References

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