Machari Formation Research Articles

Recent advances of trilobite research in Korea: Taxonomy, biostratigraphy, paleogeography, and ontogeny and phylogeny

Trilobites are among the most diverse and abundant fossil groups in Korea and occur in the Cambrian–Ordovician Joseon Supergroup of the Taebaeksan Basin. The Cambrian–Ordovician trilobites of the Joseon Supergroup have been intensively studied during the last quarter century, with emphasis on taxonomic revision, refining biostratigraphic zonation, paleogeographic implications, and ontogeny and phylogeny. A total of 243 species have hitherto been known to occur in the Joseon Supergroup of the Taebaeksan Basin: 118 and 110 species were reported in the Taebaek and Yeongwol groups, respectively, whilst 15 species were described from the Mungyeong Group. Contrasting trilobite faunal contents of the Taebaek and Yeongwol/Mungyeong groups resulted in two separate biostratigraphic schemes for the Cambrian–Ordovician of the Taebaeksan Basin: 22 biozones or fossiliferous horizons were recognized in the Taebaek Group; 19 zones were established in the Yeongwol Group; and four biozones were known from the Mungyeong Group. These trilobite biozones of the Taebaeksan Basin can be correlated well with those of North China, South China, and Australia. The distribution of some of the Cambrian and Ordovician endemic trilobites and the detrital zircon spectra of the pertinent areas suggest that the Sino-Korean Craton was located at the margin of east Gondwana and was separated from the South China Craton by an oceanic basin, and that the Taebaeksan Basin was a part of an epeiric sea in east Gondwana. Focus of the ontogenetic research of Korean trilobites was initially on the Cambrian trilobites from the Machari Formation of the Yeongwol Group, and then, was shifted to the silicified sclerites dissolved out of the carbonates of the Guzhangian to Tremadocian strata of the Taebaek Group, which have played a crucial role in resolving the trilobite phylogeny. Still, much of the carbonate strata of the Taebaek Group containing silicified trilobites has remained unstudied. The future ontogenetic research on the trilobites from the middle Cambrian (Cambrian Series 3) and the Furongian strata of the Taebaek Group would significantly contribute to elucidating the muddled trilobite phylogeny.

Cambrian series 3 agnostoid trilobitesPtychagnostus sinicusandPtychagnostus atavusfrom the Machari Formation, Yeongwol Group, Taebaeksan Basin, Korea

AbstractThis paper reports the successive occurrence ofPtychagnostus sinicusLu, 1957 andPtychagnostus atavus(Tullberg, 1880) from the lower part of the Machari Formation, Yeongwol Group, Korea. Morphometric approaches of using the landmark and principal component analyses make it possible to differentiateP.sinicusfromP.atavuswith clarity: pygidia ofP.sinicushave a relatively narrow M1, a transverse F2, and a weakly developed M2 tubercle, whereas those ofP.atavusare characterized by a broadly arching M1, a chevron-shaped F2, and a prominent M2 tubercle. Recognition ofP.atavus, for the first time in Korea, allows the determination of the base of the Drumian Stage in Korea and aids correlation with other parts of the world.

Middle Cambrian (Upper Series 3) protoconodonts and paraconodonts from the Machari Formation at Eodungol Section, Yeongwol, Korea

The Machari Formation ranges from the “upper Series 3” (Middle Cambrian) to Furongian (Upper Cambrian) in the Yeongwol area, Korea. It has been known to yield relatively diverse invertebrate fossils. Particularly, the trilobite biozones of the formation have been well defined. On the other hand, little has hitherto been studied on conodont microfossils for the formation. This paper reports a diverse and well-preserved protoconodonts and paraconodonts of Series 3 from the formation in the Eodungol Section, exposed along a southern mountain trail of Mt. Sambangsan, Yeongwol, Korea. Five of the 13 samples collected for conodont contain a rich protoconodont and paraconodont assemblage and numerous shelly fossils including trilobites, brachiopods, sponge spicules, hyolithids, and incertae sedis. Sample Eo 5 is extremely fossiliferous (465 elements, 96.5% of total collection), and the most abundant species was Phakelodus elongatus (236 elements, 62% of the Eo 5 collection). The preservation is relatively good, but some specimens are corroded and fragmentary. Some of the protoconodonts are exfoliated. Relatively larger ones were commonly preserved as phosphatized internal molds, particularly in specimens of Furnishina bigeminata, Furnishina leei n. sp., Muellerodus pomeranensis, Nogamiconus sinensis, and westergaardodids. Phakelodids were commonly preserved as clusters. Among 20 species referable to nine genera, Furnishina bigeminata, Furnishina leei n. sp., Nogamiconus sinensis, Huayuanodontus tricornis, Proscandodus obliquus, and Westergaardodina grandidens were previously undescribed species in Korea. This assemblage is named herein as the Westergaardodina matsushitai Zone, which is a new biozonal name replacing the old one, i.e., Gapparodus bisulcatus-Westergaardodina matsushitai-Westergaardodina moessebergensis Assemblage. The W. matsushitai Zone corresponds to the Lejopyge armata trilobite Zone and is well correlated with the upper Series 3 conodont biozones of the Westergaardodina matsushitai-Westergaardodina grandidens Zone of South China and the Westergaardodina matsushitai Zone of North China, respectively. The present data allow a useful correlation to China and Baltica in relation to new subdivision of the Cambrian. Furnishina leei n. sp. is newly described.

전기고생대 태백산분지 영월층군의 순차층서 연구를 통한 고지리적 추론

전기 고생대 태백산분지 영월층군은 탄산염-규산쇄설성 퇴적암 복합체로서 하부로부터 삼방산층, 마차리층, 와곡층, 문곡층, 영흥층으로 이루어져있다. 영월층군에 대한 순차층서학적 분석에 따르면 중기 캠브리아기에 일어난 범람에 의해 최하부의 규산쇄설성 사질 퇴적암이 우세한 삼방산층이 퇴적되었다. 이어지는 후중기 캠브리아기 ~ 전후기 캠브리아기에 지속적으로 발생한 빠른 해수면 상승으로 마차리층 하부에는 셰일, 입자암, 각력암층을 협재한 사면 혹은 심부 램프 시퀀스가 형성되었다. 후기 캠브리아기 동안 지속된 해수면 상승은 실질적인 퇴적가능공간을 창출하였고, 조하대 환경에 탄산염 퇴적물 공장이 만들어졌으며, 탄산염 대지에는 마차리층을 구성하는 탄산염암이 우세한 조하대 시퀀스가 형성되었다. 마차리층 상부의 와곡층은 후후기 캠브리아기의 완만한 해수면 상승국면에서 만들어진 탄산염 램프 시퀀스로 해석되며, 퇴적 당시에는 리본 탄산염암과 탄산염 역암을 포함하는 이회암으로 구성되었던 것으로 보인다. 와곡층은 퇴적직후에 일차적으로 캠브리아기와 오르도비스기 사이의 해수면 하강국면에서 불안전 백운암화 과정을 거치고, 후에 심부 매몰 속성환경에서 광범위한 백운암화 작용을 받은 것으로 해석된다. 전기 오르도비스기에도 세계적인 해수면 상승과 해침은 지속되었으며, 영월층군의 조하대 램프 퇴적환경은 그대로 유지되어 탄산염 역암층을 협재하는 석회이암과 이회암이 교호하는 전형적인 램프 시퀀스인 문곡층이 형성되었다. 문곡층은 중기 오르도비스기에 퇴적된 것으로 알려진 영흥층에 덮여 있다. 영흥층은 주로 윤회층리를 보이는 조석대지 탄산염암으로 이루어져 있으며, 문곡층의 최상부에서 조하대 퇴적환경이 영흥층의 조석대지 퇴적환경으로 변화한다. 세계적 1차 규모 순차 경계면인 소크(Sauk)와 티피카누(Tippecanoe) 시퀀스의 경계는 영흥층 중부에서 관찰되는 최소퇴적가능공간 부근에서 인지된다. 중기 오르도비스기 초기의 세계적 해수면 하강과 이어지는 해수면의 급격한 상승은 영흥층의 전반적인 상향 천해화 윤회층의 전진퇴적체를 형성하였다. 영월층군이 퇴적된 영월 탄산염 대지의 상대적 해수면 변동곡선을 복원해 보면 같은 태백산 분지의 태백층군이 퇴적된 태백 탄산염 대지의 해수면 변동 곡선과 유사함을 확인할 수 있다. 이것은 두 개의 탄산염 대지가 유사한 조 구조적 운동 역사를 갖는다는 것을 의미하며, 이러한 유사성은 영월층군이 형성된 영월 탄산염 대지가 비록 태백층군이 퇴적된 태백 탄산염 대지와 상이한 퇴적시스템을 갖기는 하지만 상대적으로 가까운 지역에 속해 있었음을 암시한다. 퇴적층서 분석결과에 따르면 영월 탄산염 대지는 태백 탄산염 대지에 비해 상대적으로 열린 천해 환경이었을 것으로 추측된다. 고생대 후기와 중생대 전기에 걸쳐 발생한 북중국지괴와 남중국지괴의 충돌 시기에 영월 탄산염 대지와 태백 탄산염 대지가 복잡한 이동과정을 거쳐 현재의 태백산 분지에 모이게 된 것으로 해석된다. The Yeongweol Group is a Lower Paleozoic mixed carbonate-siliciclastic sequence in the Taebaeksan Basin of Korea, and consists of five lithologic formations: Sambangsan, Machari, Wagok, Mungok, and Yeongheung in ascending order. Sequence stratigraphic interpretation of the group indicates that initial flooding in the Yeongweol area of the Taebaeksan Basin resulted in basal siliciclastic-dominated sequences of the Sambangsan Formation during the Middle Cambrian. The accelerated sea-level rise in the late Middle to early Late Cambrian generated a mixed carbonate-siliciclastic slope or deep ramp sequence of shale, grainstone and breccia intercalations, representing the lower part of the Machari Formation. The continued rise of sea level in the Late Cambrian made substantial accommodation space and activated subtidal carbonate factory, forming carbonate-dominated subtidal platform sequence in the middle and upper parts of the Machari Formation. The overlying Wagok Formation might originally be a ramp carbonate sequence of subtidal ribbon carbonates and marls with conglomerates, deposited during the normal rise of relative sea level in the late Late Cambrian. The formation was affected by unstable dolomitization shortly after the deposition during the relative sea-level fall in the latest Cambrian or earliest Ordovician. Subsequently, it was extensively dolomitized under the deep burial diagenetic condition. During the Early Ordovician (Tremadocian), global transgression (viz. Sauk) was continued, and subtidal ramp deposition was sustained in the Yeongweol platform, forming the Mungok Formation. The formation is overlain by the peritidal carbonates of the Yeongheung Formation, and is stacked by cyclic sedimentation during the Early to Middle Ordovician (Arenigian to Caradocian). The lithologic change from subtidal ramp to peritidal facies is preserved at the uppermost part of the Mungok Formation. The transition between Sauk and Tippecanoe sequences is recognized within the middle part of the Yeongheung Formation as a minimum accommodation zone. The global eustatic fall in the earliest Middle Ordovician and the ensuing rise of relative sea level during the Darrwillian to Caradocian produced broadly-prograding peritidal carbonates of shallowing-upward cyclic successions within the Yeongheung Formation. The reconstructed relative sea-level curve of the Yeongweol platform is very similar to that of the Taebaek platform. This reveals that the Yeongweol platform experienced same tectonic movements with the Taebaek platform, and consequently that both platform sequences might be located in a body or somewhere separately in the margin of the North China platform. The significant differences in lithologic and stratigraphic successions imply that the Yeongweol platform was much far from the Taebaek platform and not associated with the Taebaek platform as a single depositional system. The Yeongweol platform was probably located in relatively open shallow marine environments, whereas the Taebaek platform was a part of the restricted embayments. During the late Paleozoic to early Mesozoic amalgamations of the Korean massifs, the Yeongweol platform was probably pushed against the Taebaek platform by the complex movement, forming fragmented platform sequences of the Taebaeksan Basin.

Erratum to: Furongian conodonts from the Machari Formation in the Gokgeum section, Yeongwol, Korea

1. In the references list, the reference below is substituted with new one as follows. Roh, D.Y., 2011, Depositional environment of the Machari Formation in the Yeongweol area, Kangweon-do, Korea. Ms Thesis (unpublished). → Noh, D.Y., 2009, Stratigraphic Interpretation of the Middle to Upper Cambrian Machari Formation in Seo-Myeon, Yeongwol, Kangwon, Korea. B.Sc. thesis, Chungbuk National University, Cheongju, 43 p. (in Korean)

Furongian conodonts from the Machari Formation in the Gokgeum section, Yeongwol, Korea

This is a conodont biostratigraphic study on the Machari Formation in the Gokgeum section, exposed nearby Mt. Orosan, Hutan-ri, west Yeongwol-gun, Korea. Three biostratigraphic intervals are recognized by euconodont taxa in the Furongian part of the Gokgeum section: i.e., Unnamed, Proconodontus muelleri, and Eoconodontus notchpeakensis zones in ascending order. The Unnamed zone herein is equivalent to the previous “Barren Interzone”, the Proconodontus muelleri Zone is also equivalent to the previous Proconodontus muelleri-Cambrooistodus cambricus Zone, and the Eoconodontus notchpeakensis Zone is a new, uppermost one. Therefore, there are four conodont zones of the Machari Formation known hitherto; i.e., late Middle Cambrian Westergaardodina matsushitai Zone and three Furongian zones including Unnamed zone, Proconodontus muelleri Zone and Eoconodontus notchpeakensis Zone in ascending order. These Machari conodont biozones are correlated with conodont biozonal frameworks in western USA, Canada, Argentina, North and South China, Australia and Hwajeol Formation in the Duwibong area, Korea.

Stable Carbon Isotope Stratigraphy of the Cambrian Machari Formation in the Yeongweol Area, Gangweon Province, Korea

The Steptoean Positive Carbon Isotope Excursion (SPICE) is found in the Machari Formation which was interpreted to have been deposited on the middle to outer carbonate ramp environment. The Machari Formation is the Middle to Late Cambrian in age and distributed in the Yeongweol area, Gangweon Province, Korea. The SPICE event in the Machari Formation begins with the first appearance datum of trilobite Glyptagnostus reticulatus and ends with the first appearance of datum of trilobite Irvingella. The SPICE is found in approximately 120 m thick sequence and <TEX>${\delta}^{13}C$</TEX> values in the SPICE interval range from 0.6 to 4.4‰. The SPICE in the Machari Formation is interpreted to be caused by burial of organic matter in the sea floor and subsequent increase of <TEX>$^{13}C$</TEX> isotope of the Late Cambrian ocean. The SPICE interval in the Machari Formation corresponds to the highstand to transgressive systems tracts.

Upper Cambrian polymerid trilobites from the Machari Formation, Yongwol, Korea

This article deals with the systematic description of polymerid trilobites from the Upper Cambrian Eochuangia hana, Agnostotes orientalis, and Pseudoyuepingia asaphoides Zones of the Machari Formation, Konggiri section, Yongwol, Korea. Agnostoid trilobites from the same locality were reported in 2004. Described are 20 polymerid trilobite taxa, including two new genera ( Joshuaspis and Macharia) and four new species ( Metachangshania brachypyga, Proceratopyge promisca, Joshuaspis parvus, and Macharia pengi). While agnostoid trilobite assemblages were used for correlation with distant regions such as South China, Australia, Kazakhstan, Siberia, and Laurentia, these polymerid trilobite assemblages provide valuable information for correlation of the Machari Formation with the Furongian (Upper Cambrian) strata of North China.

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.

Heterochrony of the Late Cambrian olenid trilobites from the Machari Formation, Yeongwol, Korea: implications for biostratigraphy and intercontinental correlation

This study deals with the heterochrony of two Late Cambrian olenid trilobites,Olenus asiaticus Kobayashi, 1944 from theGlyptagnostus reticulatus Zone andHancrania brevilimbata Kobayashi, 1962 from theHancrania brevilimbata Zone, recovered from the Machari Formation in Yeongwol, Korea. Comparison of ontogenetic developments ofOlenus asiaticus andHancrania brevilimbata led to consider that the two species are phylogenetically related: viz.,Hanerania brevilimbata is a probable descendant ofOlenus asiaticus. The ontogenetic trajectories of the two species are closely comparable in the protaspid and early meraspid stages, but deviate in the late meraspid and holaspid stages. The morphological changes with growth in theOlenus asiaticus-Hancrania brevilimbata lineage may have resulted from combined heterochronic processes: i.e., the reduction of preglabellar field in the descendant is attained by paedomorphic progenesis, whereas the expansion of glabella is a consequence of peramorphic acceleration. Of these, the progressive reduction of preglabellar field has been known to occur in other parts of the world and thus is assumed to be useful in improving the biostratigraphic correlation among widely separated paleogeographic provinces, such as Baltica and Avalonia. TheGlyptagnostus reticulatus Zone of the Paleozoic Gondwana can be correlated with theOlenus gibbosus Subzone of Avalonia and Baltica, while theHancrania brevilimbata Zone of Korea with theO. attenuatus andO. dentatus subzones of Baltica and the lower part of theO. cataractes Subzone of Avalonia.

Upper Cambrian agnostoid trilobites from the Machari Formation, Yongwol, Korea

The Middle to Upper Cambrian Machari Formation in Korea is well known for abundant and diverse trilobites along with other invertebrate fossils. Based on recent reappraisal on the trilobites of the Machari Formation, eight trilobite zones have been proposed for the Upper Cambrian sequence: i.e., in ascending order the Glyptagnostus stolidotus, Glyptagnostus reticulatus, Proceratopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones. Trilobites from the lower five zones and part of the Pseudoyuepingia asaphoides Zone have been already published elsewhere. In this paper, we describe the agnostoid trilobites of the upper three zones, Eochuangia hana, Agnostotes orientalis and Pseudoyuepingia asaphoides zones, of the Machari Formation. These comprise 24 species belonging to 13 genera, including one new genus ( Yongwolagnostus) and ten new species ( Homagnostus? sulcatus, Ivshinagnostus alatus, Ivshinagnostus quadratus, Yongwolagnostus stenorhachis, Yongwolagnostus dubius, Nahannagnostus pratti, Pseudagnostus? dividuus, Pseudagnostus medius, Pseudorhaptagnostus? urceus and Ammagnostus serus). These biozones correlate well with middle Upper Cambrian zones established in South China, Australia, Kazakhstan, Siberia, and Canadian Rocky Mountains.

Trilobites from theLejopyge armataZone (upper Middle Cambrian) of the Machari Formation, Yongwol Group, Korea

Acid-resistant specimens of trilobites were recovered from the dissolved residues of lime mudstone collected from the lower part of the Machari Formation, Yongwol Group, Taebaeksan Basin, Korea. One of the samples yields a trilobite assemblage comprisingLejopyge armata(Linnarsson, 1869),Lisogoragnostus coreanicusn. sp., agnostid genus and species indeterminate, ammagnostid genus and species indeterminate, clavagnostid genus and species indeterminate,Cyclolorenzellasp., andEoshengia? sp. The stratigraphic interval yielding the trilobite assemblage is herein designated as theLejopyge armataZone, which is correlated well with the upper Middle Cambrian biozones established elsewhere. This provides the first biostratigraphic reference point for the upper Middle Cambrian sequence of the Yongwol Group and fills partially the biostratigraphic gap between theTonkinella(middle Middle Cambrian) and theGlyptagnostus stolidotus(uppermost Middle Cambrian) zones in the Machari Formation.

TRILOBITES FROM THE LEJOPYGE ARMATA ZONE (UPPER MIDDLE CAMBRIAN) OF THE MACHARI FORMATION, YONGWOL GROUP, KOREA

Acid-resistant specimens of trilobites were recovered from the dissolved residues of lime mudstone collected from the lower part of the Machari Formation, Yongwol Group, Taebaeksan Basin, Korea. One of the samples yields a trilobite assemblage comprising Lejopyge armata (Linnarsson, 1869), Lisogoragnostus coreanicus n. sp., agnostid genus and species indeterminate, am- magnostid genus and species indeterminate, clavagnostid genus and species indeterminate, Cyclolorenzella sp., and Eoshengia? sp. The stratigraphic interval yielding the trilobite assemblage is herein designated as the Lejopyge armata Zone, which is correlated well with the upper Middle Cambrian biozones established elsewhere. This provides the first biostratigraphic reference point for the upper Middle Cambrian sequence of the Yongwol Group and fills partially the biostratigraphic gap between theTonkinella (middle Middle Cambrian) and the Glyptagnostus stolidotus (uppermost Middle Cambrian) zones in the Machari Formation. HE MACHARI Formation in Korea has been well known to yield diverse and abundant Middle to Upper Cambrian tri- lobites with some brachiopods and gastropods, the so-called Ma- chari fauna (Kobayashi, 1962). Based on the faunal assemblages, Kobayashi (1962) established biostratigraphic zones within the formation: i.e., in ascending order Olenoides (including Tonki- nella and Eochuangia faunas), Komaspis-Iwayaspis, and Olenus- Glyptagnostus zones; and the Hancrania fauna was considered more or less contemporaneous with the Olenus-Glyptagnostus Zone. However, the trilobite faunal successions of the Machari Formation have not been well understood due to the complicated geologic structure of the Yongwol area. Nonetheless, these bio- stratigraphic units have been widely employed in Korea, until recently Lee and Choi (1994, 1995, 1996) and Choi and Lee (1995) documented systematically the Upper Cambrian trilobites of the Machari Formation and, based on the new collections, pro- posed a profoundly modified biostratigraphic zonation for the Up- per Cambrian portion. This scheme includes in ascending order the Glyptagnostus stolidotus, Glyptagnostus reticulatus, Procer- atopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis, and Pseudoyuepingia asaphoides zones (Lee et al., 1997). These Upper Cambrian bio- zones provided greatly improved biostratigraphic correlation of Korea with other parts of the world. To date, the Tonkinella Zone established by Kobayashi (1962) is the oldest zone within the Machari Formation representing a middle Middle Cambrian in age and is characterized by domi- nance of Tonkinella, Olenoides, Kootenia, and Peronopsis among others. The next higher biozone recognized is the Glyptagnostus stolidotus Zone of uppermost Middle Cambrian age. Therefore no upper Middle Cambrian trilobite faunas have hitherto been known in the Machari Formation. We recovered acid-resistant fossils from the putatively unfossiliferous lime mudstone beds that lie between the Tonkinella and Glyptagnostus stolidotuszones. They yield a trilobite assemblage comprising Lejopyge armata along with species previously undescribed in Korea. The occurrence of Lejopyge armata is particularly significant, as it is globally re- stricted within the upper Middle Cambrian (Robison, 1984). We propose the Lejopyge armata Zone for the interval yielding the nominal taxon and associated trilobites. The specific objectives of this article are to describe trilobites of the Lejopyge armataZone from the lower part of the Machari Formation and to address their significance in biostratigraphic correlation with other parts of the world. GEOLOGIC SETTING AND STRATIGRAPHY

A TERATOLOGICAL PYGIDIUM OF THE UPPER CAMBRIAN TRILOBITEEUGONOCARE(PSEUDEUGONOCARE)BISPINATUMFROM THE MACHARI FORMATION, KOREA

Abstract A teratological holaspid pygidium of Eugonocare (Pseudeugonocare) bispinatum (Kobayashi, 1962) is described from the Cambrian Machari Formation of Korea. The abnormality is represented by the development of two additional posterolateral spines on the left side. This feature probably resulted from a genetic defect. The nonlethal mutation caused formation on one side only of a spine array that mimics the spine arrangement of several Eugonocare species combined.

Ontogeny of the Late Cambrian trilobiteOlenus asiaticus Kobayashi, 1944 from the Machari Formation of Korea

Ontogeny of the Late Cambrian trilobiteOlenus asiaticus Kobayashi, 1944 was examined based on the material from theGlyptagnostus reticulatus Zone of the Machari Formation in Yongwol area, Korea. Protaspides are differentiated into anaprotaspid and metaprotaspid stages. Anaprotaspides are represented by circular dorsal shields with faintly segmented axis, while meta-protaspides have five axial rings, eye ridges, and a differentiated protopygidium. Most of meraspides, represented by disarticulated cranidia, are further divided into six morphological groups. The Group 1 is assumed to represent the meraspid degree 0, whereas the remaining groups are subdivided in convenience to describe the morphological development of cranidia. Morphological changes within the meraspid stages are gradual in general. The glabella is parallel-sided or tapers rearwards in the early meraspides, whereas it tapers forwards in the later forms. The preglabellar field appears in the Group 3 and becomes progressively longer in the later meraspid stages. The holaspid cranidia are distinct in having a subquadrate glabella with three pairs of lateral glabellar furrows.

Dolomitization of the periplatform carbonate slope deposit, the Machari Formation (Middle to Late Cambrian), Korea

An ancient periplatform carbonate slope deposit, the Machari Formation (late Middle to early Late Cambrian), Korea shows five dolomite types of which dolomitization conditions, dolomitizing fluids and recrystallization are closely associated with depositional setting and burial history.

Occurrence ofGlyptagnostus stolidotusӦpik, 1961 (Trilobita, Late Cambrian) in the Machari Formation of Korea

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