Byung-Su Lee

Conodonts from the Sesong Slate and Hwajeol Formation (Guzhangian to Furongian) in the Taebaeksan Basin, Korea

Abundant conodont elements have been recovered from the Hwajeol Formation, to allow five zones to be erected: Proconodontus, Eoconodontus notchpeakensis, Cambrooistodus minutus, Cordylodus proavus, and Fryxellodontus inornatus-Monocostodus sevierensis-Semiacontiodus lavadamensis zones, in ascending order. More confident biozones are recognized in the Sesong Slate and lower Hwajeol Formation in the Makgol section, a part of the southern limb of the Baekunsan syncline, Taebaeksan Basin, Korea, especially focusing on the conodont biostratigraphic boundary of two units, and the subdivision potential of the previous “Proconodontus Zone”, lowermost biozone of the Hwajeol Formation. Similarly, only a few conodont elements recovered from upper 14.5 m interval, namely the Furongian portion of the Sesong Slate, in the Makgol section did not allow erection of a biozone. Nevertheless, this part of the unit plus the basal 2.5 m interval of the Hwajeol Formation is characterized by the occurrence of Prooneotodus rotundatus (Druce and Jones), Teridontus nakamurai (Nogami), Phakelodus elongatus (An) and Phakelodus tenuis Muller, This interval marks the early Furongian “Prooneotodus rotundatus Zone”. The rest of the measured section yielded relatively abundant conodonts, so three conodont biozones are proposed, based on the successive appearance of key species: Proconodontus tenuiserratus, Proconodontus posterocostatus, and Proconodontus muelleri zones, in ascending order, and thus allowing subdivision of the previous “Proconodontus Zone”. The four conodont biozones are correlated with the relevant biozones of North and South China, and North America.

Late Cambrian conodonts from Cheungsan, Kangwon Province, Korea

Conodonts from 20 samples, collected from two measured sections in the Late Cambrian Hwajeol Formation in the Cheungsan area, Jeongseon-gun, Kangwon Province, Korea, are classified into 27 species and 18 genera by both multielement and form taxonomies. Five conodont biozones are recognized in the formation: Proconodontus, Eoconodontus notchpeakensis, Cambrooistodus minutus, Cordylodus proavus and Fryxellodontus inornatus-Monocostodus sevierensis-Semiacontiodus lavadamensis Zones in ascending stratigraphic order. These zones are correlatable with equivalents in other areas including the Paekunsan syncline of Korea, North China, Iran, Australia and North America.

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.

Recognition and significance of the Aurilobodus serratus Conodont Zone (Darriwilian) in lower Paleozoic sequence of the Jeongseon–Pyeongchang area, Korea

A total of 286 disjunct conodont elememets were recovered from 30 productive samples in 5 separate sections of the Haegmae and Hoedongri Formations, 18 m below to 36 m above the boundary between the two formations, in the Jeongseon–Pyeongchang area. Fifteen multielement and form species representing 12 genera are distinguished in the fauna of the two formations. Age-diagnostic species include Acontiodus viriosus Cui, Aurilobodus serratus Xiang and Zhang, A. simplex Xiang and Zhang, Drepanodus arcuatus Pander, Drepanodus reclinatus (Sergeeva), Drepanoistodus suberectus (Branson and Mehl), Eoplacognathus jigunsanenesis Lee and Lee, E. lindstroemi Hamar, Erraticodon tangshanensis Yang and Xu, Panderodus nogamii Lee, Parapanderodus paracornutiformis (Ethington and Clark), Plectodina onychodonta An and Xu, Scandodus choii n. sp., and Triangulodus changshanensis (Zhang). This assemblage was assigned to the Aurilobodus serratus Zone. That zone was first erected from the Middle Ordovician Machiakou Formation in the North China platform and is known also from the Duwibong Formation in Korea. These strata represent tropical, shallow marine paleobiogeographic facies. The presence of the zone on both sides of the boundary between the two formations means that the relationship between the Haengmae and Hoedongri formations is a conformity, not an unconformity, as previously thought. It is more likely that the overlying unsampled strata of the Hoedongri Formation are also Ordovician, rather than Silurian. One new species, Scandodus choii, is described here.

Revision of the conodont zonation of the uppermost Hwajeol Formation (Furongian), Taebaeksan Basin, Korea

The uppermost interval of the Hwajeol Formation, Taebaeksan Basin, has been assigned to the Fryxellodontus inornatus-Monocostodus sevierensis-Semiacontiodus lavadamensis Zone. The main species in the zone are Fryxellodontus inornatus Miller, Hirsutodontus hirsutus Miller, Monocostodus sevierensis (Miller), Semiacontiodus lavadamensis (Miller), S. nogamii Miller, Utahconus utahensis (Miller), and Cordylodus proavus Müller. These species were re-examined to evaluate the biostratigraphy of the Bangteogol and Maesangol sections. Data were added from eleven sections around the Taebaeksan Basin, which were studied previously by the first author. Conodont occurrences above the Cambrooistodus minutus Zone are characterized by a lack of vertical and lateral continuity in sections. Conodont recovery is relatively poor but is sufficient for biostratigraphic assignment. This trend of conodont occurrence seems to be related to sedimentary process, including debris slides and eustatic sea-level fluctuation. Nevertheless, detailed study of the characteristic species of the zone leads to the conclusion that retention of the zone is reasonable. However, it is renamed the M. sevierensis-S. lavadamensis Zone because Fryellodontus inornatus occurs stratigraphically lower than the other two nominate species. The M. sevierensis-S. lavadamensis Zone is correlated with equivalent zones of western USA, Canada, North China, and Australia.

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.

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)