Jusun Woo

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.

CHAMBERS OF EPIPHYTON THALLI IN MICROBIAL BUILDUPS, ZHANGXIA FORMATION (MIDDLE CAMBRIAN), SHANDONG PROVINCE, CHINA

Abstract Microscopic morphologic variations of Epiphyton thalli in microbial buildups were examined in order to detail controlling factors on morphology and calcification processes, and their implications for identification of calcified microbes. Microbial carbonate of the Zhangxia Formation (Middle Cambrian), Shandong Province, China comprises thrombolites, stromatolites, and Epiphyton buildups, as well as consortia of microbial and metazoan communities. Epiphyton, a rigid framework of the buildups, is subdivided into four types based on characteristics of the branches. Type 1 consists of ∼75-μm-diameter dendritic rods of dense micrite that form bush-shaped and chambered thalli. Type 2 has ∼80-μm-thick branches characterized by transverse segments. Type 3 consists of thin, ∼50-μm diameter micritic branches that form round thalli. Type 4 is characterized by laterally arrayed, branching tubes that form fan-shaped thalli. All morphologic types have bipartite branched filaments as a basic growth pattern. Bush-shaped thalli are dominant in the inner part of the Epiphyton bioherms, while chambered thalli, which are solitary, connected, and tiered, are common in the outer part. Such physical energy conditions as currents or waves control the density, length, and sheath thickness of the branches and propagation pattern of the thalli. Chamber outlines of Epiphyton thalli resemble those of Renalcis, although internal structures of the branching rods and tubes in the chamber walls are distinct. Thalli become similar to that of Renalcis when calcification and diagenesis remove or obliterate the internal fabric of the chamber wall. Morphologic variations of Epiphyton thalli and subsequent textural changes can result in identification as different groups of calcified microbial taxa.

A stem-group cnidarian described from the mid-Cambrian of China and its significance for cnidarian evolution

Palaeontological data of extinct groups often sheds light on the evolutionary sequences leading to extant groups, but has failed to resolve the basal metazoan phylogeny including the origin of the Cnidaria. Here we report the occurrence of a stem-group cnidarian, Cambroctoconus orientalis gen. et sp. nov., from the mid-Cambrian of China, which is a colonial organism with calcareous octagonal conical cup-shaped skeletons. It bears cnidarian features including longitudinal septa arranged in octoradial symmetry and colonial occurrence, but lacks a jelly-like mesenchyme. Such morphological characteristics suggest that the colonial occurrence with polyps of octoradial symmetry is the plesiomorphic condition of the Cnidaria and appeared earlier than the jelly-like mesenchyme during the course of evolution.

Revised stratigraphy of the Xiazhen Formation (Upper Ordovician) at Zhuzhai, South China, based on palaeontological and lithological data

Lee, D.-C., Park, J., Woo, J., Kwon, Y.K., Lee, J.-G., Guan, L., Sun, N., Lee, S.-B., Liang, K., Liu, L., Rhee, C.-W., Choh, S.-J., Kim, B.-S. & Lee, D.-J., September 2012. Revised stratigraphy of the Xiazhen Formation (Upper Ordovician) at Zhuzhai, South China, based on palaeontological and lithological data. Alcheringa 36, 393–412. ISSN 0311-5518. Three exposures of the Upper Ordovician Xiazhen Formation at Zhuzhai, Yushan, Jiangxi Province, China are re-measured and described in detail. Comparison of palaeontological and lithological data from the exposures (designated sub-sections ZU1, ZU2 and ZU3) reveals that the sub-sections overlap stratigraphically. Nearly identical assemblages of trilobites and brachiopods occur in mudstones of ZU1 and ZU3, whereas a different assemblage occurs in those of ZU2. Identical coral species occur in the overlapped intervals of ZU1 and ZU2, and ZU1 and ZU3, respectively. In addition, a distinctive identical lithological succession consisting of brachiopod-bearing nodular limestone at the base to coral floatstone at the top is evident in the overlapped interval of ZU1 and ZU2; prism-cracked algal laminites are found in the same interval; and bioclastic limestone beds, which represent bioherms consisting mainly of corals and stromatoporoids, occur in both ZU1 and ZU3. A thrust fault system appears to be responsible for the repetition in the subsections, and the faulting was probably due to the major post-Ordovician structural movements exerted on the Zhe-Gan Platform of the Jiangnan Region of the South China Block. Dong-Chan Lee [dclee@hit.ac.kr], Department of Heritage Studies, Daejeon Health Sciences College, 300-711, Daejeon, Republic of Korea; Jino Park [jinopark@korea.ac.kr], Suk-Joo Choh [sjchoh@korea.ac.kr], Department of Earth and Environmental Sciences, Korea University, 136-701, Seoul, Republic of Korea; Jusun Woo [jusunwoo@kopri.re.kr], Division of Polar Earth-System Sciences, Korea Polar Research Institute, 406-840, Incheon, Republic of Korea; Yi Kyun Kwon [kyk70@kigam.re.kr], Marine and Petroleum Division, Korea Institutue of Geoscience and Mineral Resources, 305-350, Daejeon, Republic of Korea; Jeong-Gu Lee [leejg@mest.go.kr], Seung-Bae Lee [sblee@mest.go.kr], Exhibition Planning and Coordination Division, Gwacheon National Science Museum, 427-060, Gwacheon, Republic of Korea; Liming Guan [glm.1103218@yahoo.com], Ning Sun [sun@andong.ac.kr], Kun Liang [ibcaskun@126.com], Lu Liu [liulu323@hotmail.com], Department of Earth and Environmental Sciences, Andong National University, 760-749, Andong, Republic of Korea; Dong-Jin Lee [djlee@andong.ac.kr], Department of Earth and Environmental Sciences, Andong National University, 760-749, Andong, Republic of Korea and College of Earth Science, Jilin University, Changchun 130061, PR China; Chul-Woo Rhee [gloryees@chungbuk.ac.kr], Department of Earth and Environmental Sciences, Chungbuk National University, 361-763, Cheongju, Republic of Korea; Byong-Song Kim [kbs1972@163.com], Department of Resources Exploration Engineering, Kim Chaek University of Technology, Pyongyang, Democratic Peoples Republic of Korea and College of Earth Science, Jilin University, Changchun 130061, PR China. Received 16.10.2011, revised 4.1.2012, accepted 16.1.2012.

Early Ordovician reefs from the Taebaek Group, Korea: constituents, types, and geological implications

The Early Ordovician (early to middle Floian) bioherms of the Dumugol Formation, Korea, are compiled and their paleoenvironmental and paleogeographic implications are discussed. These reefs are mostly made up of microbialite (stromatolite and thrombolite) and lithistid sponge Archaeoscyphia, with subordinate “receptaculitid” calathids. Three types of reefs are identified based on biotic association and texture: 1) lithistid sponge-microbialite, 2) microbialite (thrombolite) with minor lithistid sponge, and 3) lithistid sponge-microbialite-calathid. The first and third type reefs are surrounded by intraclastic-skeletal packstone to grainstone and overlain by lime mudstone, whereas the second type reefs are surrounded and overlain by bioturbated wackestone and nodulebearing shale. These relationships appear to reflect varying depositional conditions during development of the reefs. The constituents of the Dumugol reefs are roughly comparable to coeval structures of Laurentia and South China with the exception of the absence of incorporated sessile organisms (i.e., Lichenaria, Pulchrilamina, and bryozoan) and delayed arrival (more than 10 myr) of calathids in the Sino-Korean Craton. This temporal disparity of biotic appearance is probably related to differential dispersal rates and patterns of sessile organisms which are largely controlled by the relative position of landmasses, epicontinental seas and major oceans. Further discovery and study of the Early Ordovician reefs from the Sino-Korean Craton will provide crucial information for understanding migration pathways of sessile organisms and paleogeographic reconstruction of the western margin of Gondwana in the Early Paleozoic.

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 Okcheon Supergroup in the Lake Chungju area, Korea: Neoproterozoic volcanic and glaciogenic sedimentary successions in a rift basin

The Okcheon Belt in southern Korea is an NE-SW trending fold-and-thrust belt consisting of two sedimentary basins of different origins: namely, the Chungcheong Basin and the Taebaeksan Basin. The Chungcheong Basin was a Neoproterozoic rift basin belonging to the South China Craton, while the Taebaeksan Basin was a Paleozoic shallow marine to non-marine sedimentary basin fringing the Sino-Korean Craton. These two basins merged to form the Okcheon Belt in the early Triassic by the collision of Sino-Korean and South China cratons and their boundary is currently demarcated by the South Korean Tectonic Line. The Okcheon Supergroup is herein refined to include the Neoproterozoic volcanic and glaciogenic sedimentary successions deposited in the Chungcheong Basin and is divided into the two groups: the Chungju Group consists of the Gyemyeongsan Formation, Hyangsanni Dolomite, and Daehyangsan Quartzite and the Suanbo Group is proposed to include the Munjuri, Hwanggangni, Myeongori, and Gounni formations in ascending order. The Myeongori Formation is emended to comprise the Geumgang Limestone and the Seochangni members. This lithostratigraphic scheme is correlatable with that of the Nanhua Basin in South China, suggesting that the Chungcheong Basin was an eastward extension of the Nanhua Basin during the Neoproterozoic. The geological structure of the Okcheon Supergroup in the Lake Chungju area is characterized by a number of isoclinal to tight, frequently overturned, anticlines and synclines. No major thrust faults were recognized within the study area, except the constraining bend of the South Korean Tectonic Line. Three deformational phases are empirically differentiated: D1 deformation most strongly affected the rocks of the Okcheon Supergroup; D2 deformation was produced by the collision between the Sino-Korean and South China cratons; and D3 deformation is represented by normal to strike-slip faults. D1, D2 and D3 deformational phases are referred to the Okcheon (mid-Paleozoic), Songnim (Triassic) and/or Daebo (Jurassic) orogenies, and post-Jurassic events, respectively. The Chungcheong Basin was initiated as a part of an intracratonic rift basin (Nanhua Basin) within the South China Craton in association with early Neoproterozoic break-up event of the supercontinent Rodinia. The bimodal volcanic succession of the Gyemyeongsan Formation corresponds to the initial rift episode of the Chungcheong Basin, and was succeeded by shallow marine Hyangsanni Dolomite and Daehyangsan Quartzite. The second phase of rifting at ∼750 Ma accumulated a thick bimodal volcanic succession of the Munjuri Formation which is overlain by the diamictites of the Hwanggangni Formation representing the Cryogenian global glacial event, snowball Earth. The immediately-succeeding cap carbonate, Geumgang Limestone Member of the Myeongori Formation, recorded the deglaciation event. The Seochangni Member of the Myeongori Formation is characterized by dark gray slate/phyllite facies indicating a poorly-oxygenated basin during the Ediacaran. No stratigraphic unit overlying the Gounni Formation, the youngest Neoproterozoic formation of the Okcheon Supergroup, occurs in the Lake Chungju area, and thus little is known on the Paleozoic tectonic evolution of the Chungcheong Basin. It is inferred that the medium-pressure type regional metamorphism and the predominance of ductile deformation of the Okcheon Supergroup can be attributed to the mid-Paleozoic Okcheon Orogeny which would have been in line with the Wuyun Orogeny of South China. The South China and Sino-Korean cratons should have been drifted away from the Gondwana sometime during the mid-Paleozoic and collided to form the East Asian continent at ∼250 Ma.

The earliest reef-building anthaspidellid sponge Rankenella zhangxianensis n. sp. from the Zhangxia Formation (Cambrian Series 3), Shandong Province, China

Abstract This study reports the earliest known reef-building anthaspidellid sponge, Rankenella zhangxianensis n. sp., from the Cambrian Series 3 (late Stage 5—early Guzhangian) deposit of the Zhangxia Formation, Shandong Province, China. Rankenella zhangxianensis mostly occurs within Epiphyton-Rankenella-Cambroctoconus reefs, with minor occurrence from inter-reef grainstone. The species has anthaspidellid-type regular ladderlike spicule networks consisting of dendroclones and trabs, and is characterized by trabs parallel/subparallel to the gastral surface that diverge and meet the dermal surface, which is typical of the genus. Compared to R. mors and R. hamdii, reported from the late Cambrian Series 2—late Cambrian Series 3 of Australia and the late Cambrian Series 3—early Furongian of Iran, respectively, R. zhangxianensis is characterized by a relatively thicker wall, high angle (∼90°) between dermal surfaces and intersecting trabs, and minor occurrence of differentiated canals. On the other hand, R. zhangxianensis mainly shows obconical shape, which is far less diverse than the other two species showing conicocylindrical, digitate, explanate, or bowl shapes. These Cambrian Series 3 reefs from China are the ancestors of the Furongian anthaspidellid-microbial reefs and the Early Ordovician anthaspidellid-microbial reefs that flourished worldwide. They represent the resurgence of reef-building metazoans after the extinction of archaeocyaths at the end of Cambrian Series 2.

Depositional processes and sequence stratigraphy of the Jigunsan Formation (Middle Ordovician), Taebaeksan Basin, mideast Korea: implications for basin geometry and sequence development

This study focuses on the depositional processes of the Middle Ordovician Jigunsan Formation of the Taebaeksan Basin, mideast Korea, an extensive fine-grained deposit (greenish to dark gray mudstone and interbedded limestone), in view of the recent plate reconstruction of the Sino-Korean Block. The Jigunsan Formation and the bounding formations are represented by eleven sedimentary facies that are organized into sis successive facies associations (FAs). The facies successions reflect an overall development of a carbonate platform that was inundated during an initial phase of transgression (lower part of FA1) forming deep subtidal to basinal environments which were influenced by dilute turbidity currents and occasional storm-induced density currents (FAs 2,3, and 4). During a stillstand in sea level, shallow platform sediments (FAs 5 and 6) prograded over the deep subtidal to basinal area. The initial flooding surface of the platform is the top of a supratidal deposit that is underlain by a peloidal grainstone (Gp) bed. The surface is interpreted as a sequence boundary/transgressive surface. The maximum flooding zone (MFZ) occurs in the upper part of facies association 2, which is characterized by a mudstone interval. The conodont and trilobite biostratigraphy suggests that the Jigunsan Formation represents a third-order (0.5−3 My) rise in sea level. The deposit formed in the early Darriwilian in the eastern end of a large-scale (ca. 1000 km long and 50 km wide) eastward-deepening embayment, an eastward extending arm of the North China Platform across the Pyeongnam Basin, North Korea. The early Middle Ordovician sequence boundary in the Taebaeksan Basin was formed by eustatic sea-level fall During the subsequent transgression, the eastern arm was largely inundated and under a tidal regime. In the deepening eastern end of the arm (Taebaeksan Basin), however, deposition was largely influenced by the input of siliciclastic sediment and the expansion of oxygenrestricted deep water due to the proximity to the hinterland and the semi-enclosed basin configuration, respectively.

Cambrian Stem-group Cnidarians with a New Species from the Cambrian Series 3 of the Taebaeksan Basin, Korea

Five species, Lipopora lissa Jell and Jell, 1976, Lipopora daseia Jell and Jell, 1976, Tretocylichne perplexa Engelbretsen, 1993 from Australia, Cambroctoconus orientalis Park, Woo, Lee, Lee, Lee, Han and Chough, 2011 from China, and Cambroctoconus kyrgyzstanicus Peel, 2014 from Kyrgyzstan, belonging to the Cambrian stem-group cnidarians have been documented in the fossil record. Cambroctoconus coreaensis sp. nov., interpreted here as a stem-group cnidarian, from the Seokgaejae section in the Daegi Formation, Taebaek Group (Cambrian Series 3), Taebaeksan Basin, central-eastern Korean Peninsula, has a slender cup-shaped skeleton. A cladistic analysis produced 21 most parsimonious trees, which invariably placed the six stem-group cnidarians below the crown-group, but their relationships within the stem-group are unresolved. Nine out of the 21 trees suggest a monophyletic relationship for the Cambrian stem-group cnidarians, whereas in six other trees a monophyly of Cambroctoconus and Tretocylichne appeared as the sister-group to the crown-group cnidarians with Lipopora at the most basal branch. This result may reflect the fact that crown-group cnidarians evolved in the Precambrian, and suggests that the diversity of stem-group cnidarians was a result of an independent radiation in the Cambrian.