Taebaek Group Research Articles

Ontogeny of the Ptychaspidid TrilobiteQuadraticephalus elongatusKobayashi, 1935 from the Furongian (Late Cambrian) Hwajeol Formation, Korea

The development of the trilobite pygidium involves both an articulation process at the frontal part and the formation of new segments at the rear end, and hence the development of the meraspid pygidium entails complicated morphological changes. This study deals with the ontogeny of the Furongian (late Cambrian) ptychaspidid trilobite,Quadraticephalus elongatus(Kobayashi, 1935), from the Hwajeol Formation of the Taebaek Group, Taebaeksan Basin, Korea, with a special focus on the segmentation process during the meraspid pygidial development. Compared to the ontogeny of a ptychaspidid trilobite,Asioptychaspis subglobosa(Sun, 1924), which is assumed to be an ancestral species ofQ. elongatus, the convexity of the cranidium ofQ. elongatusincreased in a slower rate; the yoked free cheek ofQ. elongatussplits to form a ventral median suture in a later developmental stage; and, a rim-like ridge, which disappeared in the early holaspid pygidium ofA. subglobosa, was maintained in the late holaspid period ofQ. elongatus. These morphological changes with growth imply that paedomorphosis was involved in the evolution ofQ. elongatus. Eleven stages are recognized for the meraspid pygidial development, which began with an accumulation phase during which the number of segments increased from three to seven, followed by an equilibrium phase with seven segments, and ended up with a depletion phase during which the number of segments within the pygidium decreased to four. During the depletion phase, the pygidial length did not increase or even slightly decreased. The onset of the epimorphic phase, in which the total number of trunk segments does not increase anymore, precedes the onset of the holaspid period, demonstrating that the developmental mode ofQ. elongatusis protomeric.

Middle Furongian (late Cambrian) polymerid trilobites from the upper part of the Sesong Formation, Taebaeksan Basin, Korea

The upper part of the Sesong Formation of the Taebaek Group, Taebaeksan Basin, Korea, is known to contain the Kaolishania Zone which can be equated to the Kaolishania Zone of North China. Silicified trilobite sclerites were recovered from six horizons of the upper part of the Sesong Formation at the Sagundari section, which include a total of thirteen polymerid species: i.e., Shirakiella elongata Kobayashi, 1935, Shirakiella sp. 1, Taishania? sp. 1, Acanthometopus sp. 1, Pagodia sp. cf. P. spina Qian, 1994, Kaolishania granulosa Kobayashi, 1933, Gumunsoia triangularis gen. et sp. nov., Gumunsoia sp. 1, kaolishaniid genus and species indeterminate 1, Elaphraella? taebaeksanensis Park and Choi, 2012, Elaphraella microforma Lu and Qian, 1983, Elaphraella nodus (Qian, 1994), and Lingyuanaspis sp. The occurrence of Kaolishania suggests that the studied interval may be part of the Kaolishania Zone. However, Kaolishania occurs only from the lowermost horizon, and the full stratigraphic range of Kaolishania is unknown at present. Accordingly, the studied interval is provisionally called the Kaolishania fauna. The uppermost interval of this Kaolishania fauna produces Acanthometopus sp. 1, and thus can be correlated with the Acanthometopus Zone in Northeast China, which is underlain by the Kaolishania Zone.

Middle Furongian (late Cambrian) shumardiids from the Sesong Formation, Taebaek Group, Korea

The trilobite family Shumardiidae is characterized by small size, lack of eyes, yoked librigenae, and a small number of thoracic segments. Here we report the successive occurrence of three middle Furongian shumardiid species from the Sesong Formation of Korea: Elaphraella? taebaeksanensis n. sp., Elaphraella microforma, and Elaphraella nodus. They appear to represent the oldest shumardiid morphology known so far. This genus lacks the anterolateral swellings on the glabella and has a conical glabella. Its yoked librigenae also encompass a comparatively wide genal field. Elaphraella? taebaeksanensis has a highly inflexed facial suture which may reflect the presence of small palpebral lobes. Taken together, the plesiomorphic morphology of the Shumardiidae can be summarized as having a conical glabella, small palpebral lobes, highly arched anterior cephalic margin, a wide librigenal field, and no anterolateral swellings on the glabella.

Cretaceous reactivation of the Deokpori Thrust, Taebaeksan Basin, South Korea, constrained by K‐Ar dating of clayey fault gouge

The Deokpori Thrust, juxtaposing the early Paleozoic Yeongwol‐type Joseon Supergroup (Yeongwol Group) against the Duwibong‐type Joseon Supergroup (Taebaek Group) in the Okcheon belt, is an important regional structure in the Phanerozoic tectonic evolution of Korea. Although the initiation of the thrust has recently been conjectured to occur during the Middle Jurassic Daebo tectonic event in a continental magmatic arc setting, its movement history has never been studied. We report timing of brittle reactivation of the thrust obtained from K‐Ar dating of fault gouges in the core of the Deokpori Thrust zone. K‐Ar illite age data of fault gouges suggest reactivation of the thrust at ca. 72 Ma after a contact metamorphism around 94 Ma. Our result is the first documentation of the reactivation of a major Jurassic ‘Daebo’ structure and the reactivation may represent a significant contractional tectonic event during the Late Cretaceous in the Korean Peninsula.

Trilobite faunal successions across the base of the Furongian Series in the Taebaek Group, Taebaeksan Basin, Korea

The base of the Furongian Series in the Sino-Korean Block has not been clearly defined due to the lack of the index taxon, Glyptagnostus reticulatus. The Sesong Formation of the Taebaek Group, Taebaeksan Basin, Korea, has been known to range from the Guzhangian Stage of the Cambrian Series 3 to the middle Furongian Series, hence embracing the base of the Furongian Series. Silicified polymerid trilobites were recovered from the middle part of the Sesong Formation. Described are a total of 18 polymerid species of 13 genera: Neodrepanura sp. 1, Teinistion sp. 1, Huzhuia sp. 1, Huzhuia sp. 2, Liostracina simesi, Liostracina sp. 1, Parachangshania monkei, Parachangshania rectangularis nov. sp., Placosema bigranulosum, Fenghuangella laevis nov. sp., Baikadamaspis jikdongensis nov. sp., Baikadamaspis sp. 1, Prochuangia mansuyi, Maladioides coreanicus, Alataspis sesongensis nov. gen., nov. sp., Chuangia sp. 1, and ceratopygids genus and species indeterminate 1 and 2. The stratigraphic occurrence of these trilobites provides a basis for recognition of five zones across the base of the Furongian Series (in ascending order): the Neodrepanura, Liostracina simesi, Fenghuangella laevis, Prochuangia mansuyi, and Chuangia zones. The Neodrepanura and Chuangia zones are provisionally adopted from the previous biostratigraphic scheme, while the three other ones are newly proposed. The recommended base of the Furongian Series in the Taebaek Group of Korea coincides with the base of the Fenghuangella laevis Zone, which appears to represent an episode of profound trilobite faunal turnover.

Dikelocephalid trilobites from theEosaukiafauna (Upper Furongian) of the Taebaek Group, Korea

TheEosaukiafauna is proposed for the upper Furongian trilobite assemblage from the interval spanning from the upper part of the Hwajeol Formation to the lowermost part of the Dongjeom Formation in the Taebaek Group, Taebaeksan Basin, Korea. It is characterized by the dominance of dikelocephalid trilobites comprisingEosaukia micropora, E. bella, E. acuta, Mictosaukiacf.M. globosa, andTaebaeksaukia spinatan. gen. n. sp. Taxonomic reappraisal of the genusMictosaukiathat has been employed as an upper Cambrian index taxon in eastern Gondwana reveals that more than half of the species ofMictosaukiabelong inEosaukia.This study clarifies the generic concept ofEosaukia, which provides a more reliable biostratigraphic correlation for the upper Furongian strata in eastern Gondwanan regions. TheEosaukiafauna is correlated with the“Mictosaukia”faunas from the upper Fengshanian of North China, upper Taoyuanian of South China, and upper Payntonian of Australia.

Middle cambrian trilobites and biostratigraphy of the daegi formation (Taebaek Group) in the Seokgaejae section, Taebaeksan Basin, Korea

The Daegi Formation in the Taebaeksan Basin of Korea is composed of shallow marine carbonate facies and has been known to yield relatively diverse invertebrate fossils of middle Cambrian age. This paper describes seventeen trilobite species belonging to fifteen genera from the Daegi Formation exposed in the Seokgaejae section, located at southeastern corner of the Taebaeksan Basin. They comprise two agnostoid species(Ammagnostus laiwuensis andAmmagnostus sp.) and fifteen polymerid taxa (Dorypyge richthofeni, Amphoton deois, Blackwelderia sp.,Teinistion? sp.,Palaeadotes? sp.,Anomocarella temenus, ptychopariid gen. and sp. indeterminate.,Changqingia deprati, Crepicephalina damia, Cyclolorenzella rotundata, Cyclolorenzella sp.,Proasaphiscus sp.,Manchuriella macar, Ignotogregatus manholi, and Metanomocarella tumida). The stratigraphic distribution of these trilobites provides a basis for establishment of new trilobite zones within the formation: Le., theCrepicephalina, Amphoton, andCyclolorenzella zones in ascending order. TheCrepicephalina Zone is dominated byCrepicephalina damia, Manchuriella macar, Ignotogregatus sp. cf.I. manholi, andAmmagnostus laiwuensis. TheAmphoton Zone is recognized by the restricted occurrence ofAmphoton deois and dominance ofDorypyge richthofeni. TheCyclolorenzella Zone is characterized by the occurrence ofCyclolorenzella rotundata and some damesellid trilobites. These three biozones belong to middle to upper middle Cambrian in age and are closely correlated with theCrepicephalina, Amphoton, andDamesella-Yabeia zones of North China, respectively.

Trilobites of thePseudokoldinioidiaFauna (Uppermost Cambrian) from the Taebaek Group, Taebaeksan Basin, Korea

ThePseudokoldinioidiaFauna is a newly documented uppermost Cambrian trilobite assemblage from the Dongjeom Formation of the Taebaek Group, Taebaeksan Basin, Korea. It is characterized by low species diversity comprising six trilobite taxa:Micragnostus chiushuensis, Koldinioidia typicalis, leiostegiid genus and species indeterminate,Pseudokoldinioidia perpetis, Onychopyge borealis, and pilekiid genus and species indeterminate. Of these, special attention has been paid toPseudokoldinioidia perpetis, which was originally assigned toMissisquoia, an index fossil for the uppermost Cambrian in Laurentia.Pseudokoldinioidiais restricted to eastern Asia, whereasMissisquoiais confined to Laurentia. The appearance of thePseudokoldinioidiaFauna is interpreted as contemporaneous with the base of the‘Missisquoia’ perpetisZone of North China, which in turn is correlated with the base of theMissisquoia typicalisSubzone of Laurentia. The associatedKoldinioidiaandOnychopygemake it possible to compare thePseudokoldinioidiaFauna of Korea and North China with the latest Cambrian trilobite assemblages of South China, Australia, South America, and Mexico, and also suggests an interesting biogeographic connection among these areas in the latest Cambrian.

Occurrence of Changshania (Trilobita, Cambrian) in the Taebaeksan Basin, Korea and its stratigraphic and paleogeographic significance

In the Cambrian the Taebaeksan Basin was a shallow marine siliciclastic–carbonate system, in which two contrasting types of lithofacies and biofacies occur in juxtaposition. The shallow marine facies (Taebaek Group) comprises diverse trilobite taxa endemic to the Sino–Korean block, whereas the deep-water oceanic facies (Yeongwol Group) is characterized by predominance of cosmopolitan and pelagic trilobites. Changshania is a representative Furongian trilobite genus endemic to the Sino–Korean block and has been employed as a zonal taxon for middle Furongian in North China. This article reports the occurrence of Changshania from the deep-water facies (Machari Formation, Yeongwol Group) of the Taebaeksan Basin, for the first time in Korea. This observation enables to correlate the Eochuangia hana Zone of Korea with the Changshania– Irvingella Zone of North China with confidence. The dominance of laminated dark gray to black shale and pandemic trilobites in the Machari Formation has been interpreted to indicate deposition in a dysaerobic deep-water environment. The occurrence of Changshania along with some endemic polymerid trilobites, though uncommon, in the deeper-water oceanic facies suggests that the Machari Formation was formed in the offshore region fringing the Sino–Korean block during the Cambrian.

Sequence stratigraphy of the Taebaek Group (Cambrian–Ordovician), mideast Korea

This study focuses on the sequence stratigraphic implications of the Taebaek Group (Cambrian–Ordovician), a mixed carbonate–siliciclastic sequence (ca. 1200 m thick), in the mideastern part of the Korean peninsula. The group contains 11 lithologic units (formations) that can be partitioned into four packages (supersequences I–IV). Each package comprises alternation of siliciclastic and carbonate successions, corresponding to the second-order sequence (supersequence) formed in a period of 10–100 m.y. Supersequence I (Jangsan/Myeonsan, Myobong, and Daegi fms) represents the initial inundation and subsequent drowning during the late Early to middle Middle Cambrian. It experienced the drowning between the middle and late Middle Cambrian, forming type-3 sequence boundary. Supersequence II (Sesong and Hwajeol fms) was formed by prolonged marine flooding during the late Middle and Late Cambrian. It was terminated by a large supply of siliciclastics due to the rejuvenation of the drainage basin, and the subsequent shallowing at the Cambrian–Ordovician boundary (type-2 sequence boundary). Supersequence III (Dongjeom, Dumugol, and Makgol fms) comprises the lowstand coarse-grained siliciclastics, transgressive shale by marine flooding, and shallow platform carbonates by highstand progradation in the Early Ordovician. Following the large-scale eustatic fall of sea level in the earliest Middle Ordovician, supersequence IV (Jigunsan and Duwibong fms) formed on the subaerial exposure surface (type-1 sequence boundary) by resumed marine flooding in the Middle Ordovician. This study provides basis for basin-scale correlation with the coeval sequences in northeastern China.

The Jangsan and Myeonsan formations (Early Cambrian) of the Taebaek Group, mideast Korea: depositional processes and environments

The present study focuses on the depositional processes and environments of the lower part of the Taebaek Group (Cambrian-Ordovician) during the initial basin-forming inundation of the Taebaeksan Basin, an eastern margin of the North China platform. The lowermost part of the Taebaek Group is represented by two contrasting lithologic units, the Jangsan and Myeonsan formations. The Jangsan Formation consists of cross-bedded, massive, and foreset-bedded quartzose sandstone (quartzite) interpreted as shallow marine deposits ranging from inner shelf to nearshore environments. Deposition occurred in a stable cratonic basin where continuous subsidence and the accompanied sea-level rise accommodated large supply of sediments. The Myeonsan Formation comprises basal disorganized conglomerate, cross-bedded and laminated sandstone, and homogeneous or laminated mudstone, which largely formed in a tidally influenced restricted embayment. The formation is localized in the margin of the basin, as represented by the basal mass-flow conglomerate and the rapid transition to the tide-influenced marine succession. In the Early Cambrian, initial sedimentation in the Taebaeksan Basin was largely controlled by abundant sediment supply, accompanied with sea-level rise.

The Cambrian-Ordovician stratigraphy of the Taebaeksan Basin, Korea: a review

The lower Paleozoic sedimentary rocks in Korea, Joseon Supergroup, are mainly exposed in the Taebaeksan Basin. The Joseon Supergroup is a siliciclastic-carbonate succession that ranges from late Early Cambrian to Middle Ordovician in age. It can be subdivided into the Taebaek, Yeongwol, Yongtan, Pyeongchang, and Mungyeong groups, based on lithologic characteristics and geographic distribution. The stratigraphy of the Taebaek and Yeongwol groups is relatively well established due to prolific occurrence of trilobites and conodonts, whereas the latter three groups are poorly understood. The Taebaek Group comprises in ascending order the Jangsan/Myeonsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol, Makgol, Jigunsan, and Duwibong formations. The Cambrian-Ordovician boundary in the Taebaek Group can be drawn within the lowermost part of the Dongjeom Formation. The Yeongwol Group consists of the Sambangsan, Machari, Wagok, Mungok, and Yeongheung formations in ascending order. The Cambrian-Ordovician boundary in the Yeongwol Group has been placed at the base of the Mungok Formation. The trilobite faunal assemblages of the Taebaek and Yeongwol groups display a profound contrast in faunal contents, which resulted in two separate biostratigraphic schemes. A total of 19 biozones are recognized in the Taebaek Group comprises in ascending order theRedlichia, Elrathia, Mapania, Bailiella, Megagraulos, Solenoparia, Olenoides, Stephanocare, Drepanura, Prochuangia, Chuangia, Kaolishania, Dietyites, Eoorthis, Pseudokainella, Asaphellus, Protopliomerops, Kayseraspis, andDolerobasilicus zones. However, most of these biozones have not been well defined. On the other hand, the biostratigraphy of the Yeongwol Group is well established: from oldest to youngest, theMetagraulos sampoensis, Megagraulos semicircularis, Tonkinella, Lejopyge armata, Glyptagnostus stolidotus, G reticulatus, Proceratopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis, Pseudoyuepingia asaphoides, Fatocephalus hunjiangensis, Yosimuraspis vulgaris, Kainella euryrachis, Shumaridia pellizzarii, andKayseraspis zones. Little attention has hitherto been paid to the Cambrian-Ordovician chronostratigraphy of the Taebaeksan Basin. The Taebaek area includes the Iyeonnaeian and Homyeongian series for the Cambrian and the Mungogian and Yemisanian series for the Ordovician. Stages for the Cambrian-Ordovician of the Yeongwol area are the Eodungolian, Deokuan, Bundeokchian, Gonggirian, Garamian, and maepoan stages in ascending order. The refined biostratigraphy and chronostratigraphy provide an enhanced and more reliable correlation with coeval units elsewhere.

Taebaek Group (Cambrian-Ordovician) in the Seokgaejae section, Taebaeksan Basin: a refined lower Paleozoic stratigraphy in Korea

The Taebaek Group (Cambrian-Ordovician) in the Taebaeksan Basin comprises mixed carbonate-siliciclastic sequence and is exposed well in the Seokgaejae section located in the central-eastern part of the Korean Peninsula. The group in the Seokgaejae section consists of in ascending order the Myeonsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol, Makgol, Jigunsan and Duwibong formations. This study describes in detail the well-exposed outcrop sections of the Taebaek Group in the Seokgaejae Pass in order to refine the lithostratigraphy of the lower Paleozoic strata in the Taebaeksan Basin, Korea. The refined lithostratigraphy delineates clearly the lithologic boundary between the Myobong and Daegi formations, the Hwajeol and Dongjeom formations, the Dumugol and Makgol formations, and the Makgol and Jigunsan formations. The preliminary information on trilobite faunal assemblages suggests that the Cambrian-Ordovician boundary can be placed within the lowermost part of the Dongjeom Formation.

Lower Ordovician sponge bioherms in the Makkol Formation, Taebaeksan Basin, mideast Korea

Isolated sponge bioherms are documented from the Lower Ordovician Makkol Formation of the Taebaek Group in the Taebaeksan Basin, mideast Korea. They are formed by an association of a lithistid spongeArchaeoscyphia, a receptaculidCalathium and stromatolitic algae, and share many features with the Lower Ordovician buildups known elsewhere. These bioherms were established in an incised bottom and reached up to about 1 m in height. As the bioherms grew upward, they were more severely affected by intense wave action and frequent storms, which eventually perished the bioherms. The occurrence ofArchaeoscyphia-Calathium association suggests a close biogeographic link between Korea and North China, supporting the paleogeographic model that the Taebaeksan Basin was connected through contiguous shallow waters to North China in the early Paleozoic.

Trilobite faunal successions across the Cambrian–Ordovician boundary intervals in Korea and their correlation with China and Australia

The Cambrian–Ordovician boundary in Korea lies within the Choson Supergroup exposed in the Taebaeksan Basin and has been recognized in the Taebaek and Yongwol groups. The Taebaek and Yongwol groups show slightly different trilobite faunal successions across the putative Cambrian–Ordovician boundary intervals. In the Taebaek Group, saukiid-dominated, Missisquoia/ Onychopyge, and kainellid-dominated faunas occur successively in the basal part of the Tongjom Formation. While the remaining part of the Tongjom Formation is poorly fossiliferous, the succeeding Tumugol Formation yields fairly diverse trilobite faunal assemblages of late Tremadocian age. This implies that the Cambrian–Ordovician boundary in the Taebaek Group should be placed somewhere within the interval yielding the kainellid-dominated fauna. In the Yongwol Group, an uppermost Cambrian Fatocephalus fauna is more or less contemporaneous with the saukiid-dominated fauna of the Taebaek Group, while three Tremadocian trilobite faunas, i.e. Yosimuraspis, Kainella, and Shumardia zones in ascending order, are well represented in the Mungok Formation. The occurrence of Jujuyaspis in the Yosimuraspis Zone provides a firm basis for locating the Cambrian–Ordovician boundary at the base of the Mungok Formation. These Cambrian–Ordovician trilobite faunas of Korea are in general well correlated with those of China and Australia.

The Yongwol Group (Cambrian-Ordovician) redefined: a proposal for the stratigraphic nomenclature of the Choson Supergroup

The Yongwol Group is newly defined to comprise exclusively the Cambrian-Ordovician strata distributed in Yongwol area and replaces the Yongwol-type Choson Supergroup. It consists of the Sambangsan, Machari, Wagok, Mungok and Yonghung formations in ascending order. The Yongwol Group is bounded to the east by the Kaktong thrust, to the north by the Sangri thrust, and to the northwest by the Chonggok-Yonbongjong thrust. On the other hand, the southwestern extent of the group is obscure, as the Tanyang-Chechon area is represented by metasedimentary sequence of complex stratigraphy and contrasting lithologic successions. Based on the trilobite and conodont fossils, the Yongwol Group ranges in age from the middle Middle Cambrian to the early Late Ordovician. Other Cambrian-Ordovician sequences in the Taebaeksan region are accordingly renamed or redefined: i.e., Taebaek, Yongtan, Pyongchang, and Mungyong groups which replace the Tuwibong-type, Chongson-type Pyongchang-type, and Mungyong-type Choson supergroups, respectively. The Taebaek Group is further subdivided into the Chiktong and Sangdong subgroups.