• Journal of the Korean earth science society
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• v.22 no.6
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• pp.558-570
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• 2001

The Middle Carboniferous Manhang and Geumcheon Formations exposed in the Taebaek area, Kangwondo, Korea consist of sandstones and shales with some intercalation of limestone beds. The limestones of the formations contain abundant conodonts and other fossils. The purpose of this study is (1) to investigate the conodont fauna, (2) to assign conodont biozones of the Manhang and Geumcheon Formations, and (3) to refine their geologic age more exactly. The conodonts of the Manhang and Geumcheon Formations are 6 genera distributed into 11 species. Conodonts found from limestones of the Manhang Formation are Idiognathodus delicatus, Hindeodus minutus, Streptognathodus sp., Diplognathodus coloradoensis, N. bothorops, and N. medexultimus. This conodont fauna can be assigned to the Neognathodus bothrops Zone. This conodont biozone indicates that the geologic age of the Manghang Formation is the Atokan stage of the Middle Carboniferous Period. Conodonts came from limestones of the Geumcheon Formation are Idiognathodus delicatus, N. medexultimus, N. roundyi, N. dilatus, Diplognathodus edentulus, Hindeodus minutus, Streptognathodus elegantulus, and Gondolella bella. These conodonts permit them to be assigned to the Neognathodus roundyi Zone. This Conodont biozone indicates that the geologic age of the Geumcheon Formation is the Desmoinesian stage of the Middle Carboniferous Period.

• Journal of the Korean earth science society
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• v.21 no.3
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• pp.337-348
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• 2000

The Middle Carboniferous Manhang and Geumcheon formations in Taebaek area consist of sandstones, shales, and limestones. The limestones of the formations contain abundant conodonts, fusulinids, crinoids, brachiopods, bryozoans, corals, etc. This study was carried out to investigate the microfacies of limestones and conodont faunas of the formations and to determine their paleoecology in detail. The limestones of the Manhang and Geumcheon formations of the study area consist of wackestone and packstone which are composed of crinoid fragments and other various fossil fragments. Some limestone beds of the Geumcheon Formation consist of only Chaetetes corals which indicate that the limestones deposited in a warm shallow sea. Conodonts found from limestones of the Manhang Formation are Neognathodus bothrops, N. medexultimus, Hindeodus minutus, Diplognathodus coloradoensis, D. edentulus, Idiognathodus delicatus, Streptognathodus elegantulus, and S. sp. And conodonts found from the limestones of the Geumcheon Formation are Neognathodus medexultimus, N. roundyi, N. dilatus, Gondolella bella, Diplognathodus coloradoensis, D. edentulus, Hindeodus minutus, Idiognathodus delicatus, and Streptognathodus elegantulus. Among these conodonts, Diplognathodus coloradoensis, D. edentulus, and Hindeodus minutu, are found generally from limestones which deposited in the shallow seas. According to the limestone facies and conodont faunas of the Manhang and Geumcheon formations of the study area, it can be concluded that the limestones of the formations deposited in the shallow sea.

• Economic and Environmental Geology
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• v.6 no.2
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• pp.81-114
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• 1973

The purpose of the present study is to clarify the stratigraphy and geologic structure of the Great Limestone Series by means of study on fossil conodonts and detail investigation of geologic structure. In recent years very few geologists in Korea argue without confident evidences against the age and stratigraphy of the Great Limestone Series which have been rather well established previously in most parts of the regions although it is ambiguous and has not been studied in other areas. Five type localities in the Kangweon basin where the Great Limestone Series is well cropped out were chosen for the study. Total 26 genus and 66 species of conodont were identified from 290 samples collected and treated. From the study on conodonts the age of each formations of the Great Limestone Series has been determined as follows: The Great Limestone Series of Duwibong type Duwibong limestone: Caradocian (mid-Ord.) Jikunsan shale: Landeilian (mid-Ord.) Maggol limestone: Llanvirn-Llandeilian (mid-Ord.) Dumugol: Arenigian (Ord.) Hwajeol: Upper Cambrian The Great Limestone Series of Yeongweol type Mungok (Samtaesan) : Ordovician Machari: upper Cambrian The Great Limestone Series of Jeongseon type Erstwhile Jeongseon limestone: mid-Ord. The erstwhile Jongseon Limestone formation in Jeongseon district is separated into Hwajeol, Dongjeom, Dumudong, and Maggol formations which were cropped out repeatedly by folding and faulting, but Maggol is predominant in areal distribution. Yemi Limestone Breccia bed is not a single bed but distributed in several horizons so that it bears no stratigraphic significance. The limestone bed above Yemi Limestone Breccia, which was believed by some geologists to be much younger than Ordovician, is identified to be Maggol and its age is determined to be mid-Ordovician. Sambangsan formation in Yeongweol district was believed to be Cambrian age and lower horizon than Machari formation by Kobayashi, but C. M. Son believed that it might belong to later than Ordovician and lies above the Great Limestone Series of Yeongweol type. It was identified to be upper Cambrian and lies beneath the Machari formation and above the Daeki formation, the lower most horizon of the Great Limestone Series. The age of Yeongweol type Choseon system is contemporaneous with that of Duwibong type Choseon system. The difference in lithofacies is not due to lateral facies change, but due to the difference in its depositional environment. The Yeongweol type Choseon system is believed to be deposited in the small Yeongweol basin which was separated from the main Kangweon sedimentary basin. Judging from these facts it is definitely concluded that there exists no Gotlandian formation in the regions studied. Structurally the Kangweon basin comprises five basins and two uplifted areas. These structures were originated by at least two crustal movements, that is, Songrim disturbance of Triassic and Daebo orogeny of Jurasic age.

• Journal of the Korean earth science society
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• v.28 no.4
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• pp.497-540
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• 2007

Late Tremadocian radiolarian faunas were first recovered from the Cow Head Group, Newfoundland, Canada. Three faunal assemblages were recognized, one from Martin Point and two from Western Brook Pond in Gros Morne National Park. These radiolarian faunas include six families, 11 genera, and 26 species. In these faunas, six genera (Archeoproventocitum, Cowheadia, Neopalaeospiculum, Protospongentactinia, Protoproventocitum and Westernbrookia) and 17 species (Archeoproventocitum nudiformum, A. retiformum, Aspiculum densum, A. jamesi, A. multistratum, A. gigantium, Cowheadia duplextesta, Neopalaeospiculum densum, N. laxum, N. transformum, Pararcheoentactinia stilla, Protospongentactinia spongiosa, Protoproventocium nazarovii, P. aitchisoni, Westernbrookia cancella, W. diversa, and W. ovata) are new. Late Tremadocian faunas are characterized by the appearance of proventocitiids and diversification of aspiculumids and reduction of protoentactiniids and echidniniids that had flourished in the early Tremadocian faunas. An examination of the biostratigraphic range of co-occurring conodonts indicates that the radiolarian faunas described here belong to the late Tremadocian, from the Lower Diversity Interval through the M. dianae Zone to the lower P. proteus Zone. With the recovery of conodonts of the R. manitouensis Zone from other localities in the study area, the correlation among Martin Point, Western Brook Pond, Broom Point, and St. Paul's Inlet strata has became more precise. Also, the middle and late Tremadocian Cow Head Group can be subdivided into the R. manitouensis Zone, the Low Diversity Interval, and the M. dianae Zone of North America. The lower P. proteus Zone of the latest Tremadocian for northern Europe is recognized in the Western Brook Pond South section.

• Economic and Environmental Geology
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• v.53 no.4
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• pp.383-395
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• 2020

The stratigraphical position of the Haengmae Formation can provide clues towards solving the hot issue on the Silurian formation, also known as Hoedongri Formation. Since the 2010s, there have been several reports denying the Haengmae Formation as a lithostratigraphic unit. This study aimed to clarify the lithostratigraphic and chronostratigraphic significance of the Haengmae Formation. The distribution and structural geometry of the Haengmae Formation were studied through geologic mapping, and the correlation of relative geologic age and the absolute age was performed through conodont biostratigraphy and zircon U-Pb dating respectively. The representative rock of the Haengmae Formation is massive and yellow-yellowish brown pebble-bearing carbonate rocks with a granular texture similar to sandstone. Its surface is rough with a considerable amount of pores. By studying the mineral composition, contents, and microstructure of the rocks, they have been classified as pebble-bearing clastic rocks composed of dolomite pebbles and matrix. They chiefly comprise of euhedral or subhedral dolomite, and rounded, well-sorted fine-grained quartz, which are continuously distributed in the study area from Biryong-dong to Pyeongan-ri. Bedding attitude and the thickness of the Haengmae Formation are similar to that of the Hoedongri Formation in the north-eastern area (Biryong-dong to Haengmae-dong). The dip-direction attitudes were maintained 340°/15° from Biryong-dong to Haengmae-dong with a thickness of ca. 200 m. However, around the southwest of the studied area, the attitude is suddenly changed and the stratigraphic sequence is in disorder because of fold and thrust. Consequently, the formation is exposed to a wide low-relief area of 1.5 km × 2.5 km. Zircon U-Pb age dating results ranged from 470 to 449 Ma, which indicates that the Haengmae Formation formed during the Upper Ordovician or later. The pebble-bearing carbonate rock consisted of clastic sediments, suggesting that the Middle Ordovician conodonts from the Haengmae Formation must be reworked. Therefore, the above-stated evidence supports that the geologic age of the Haengmae Formation should be Upper Ordovician or later. This study revealed that the Haengmae Formation is neither shear zone, nor an upper part of the Jeongseon Limestone, and is also not the same age as the Jeongseon Limestone. Furthermore, it was confirmed that the Haengmae Formation should be considered a unit of lithostratigraphy in accordance with the stratigraphic guide of the International Commission on Stratigraphy (ICS).