Suk Joo Choh

Furongian (late Cambrian) sponge-microbial maze-like reefs in the North China Platform

ABSTRACT During the Furongian (late Cambrian) and Early Ordovician, maze-like (maceriate) microbialites flourished in both Laurentia and Gondwana. The maze-like microbialites are characterized by centimeter- to decimeter-scale branching, complex structures. However, organisms responsible for the formation of maze-like structures are poorly known. In order to understand formational processes of maze-like microbialites, this study focuses on the Furongian microbialites of the North China Platform in which microbial components and siliceous sponges co-occur. The maze-like structures consist of microbial components such as microstromatolites, Girvanella, and Renalcis-like forms, as well as sponge spicule networks, whereas lime mud and bioclasts occupy the space between the structures. The maze-like structures developed on a relatively flat seafloor, forming low synoptic relief (<1 cm) above the sediment surface. Continuous growth of maze-like structures with balanced deposition of sediments led to meter-scale bioherms and biostromes, under the control of both microbes and siliceous sponges. This study suggests that siliceous sponges may have played an important role in the construction of maze-like structures between the end-Cambrian Series 2 extinction and the Great Ordovician Biodiversification Event.

Tales from the crypt: early adaptation of cryptobiontic sessile metazoans

ABSTRACT Cryptic ecosystems of modern and ancient reefs contain substantial amounts of biodiversity. It remains uncertain, however, when and how metazoans adapted to such space. Early Cambrian reef systems witnessed the rise and fall of the earliest known cryptic sessile metazoans. Subsequent Middle Cambrian to Early Ordovician microbial-dominated reefs were generally devoid of true frame-building metazoans, as well as cryptic sessile fauna. The Early Ordovician microbial–siliceous sponge patch reefs of the Dumugol Formation, Korea represent one of the oldest in situ spiculate sponge-bearing cryptic communities exploiting intraskeletal cryptic environments. Less than half of these small millimeter- to centimeter-scale crypts contain low-diversity sessile cryptic assemblages of spiculate sponges and microbialites. The cryptic sponges that attach to the walls of the cavities or on top of internal sediments do not show any skeletal distortion at their contacts with host organisms. The spiculate sponges occur both in open spaces as well as in crypts, and are interpreted to be pioneers of intraskeletal crypts after the death of the cavity-providing organisms. The behavior of occupying transient cryptic habitats is interpreted as an incipient stage of sessile metazoan adaptation to a cryptic space by an opportunistic member of the epibenthic community. This resulted in the extension of the open surface community into crypts which occurred far in advance of the eventual establishment of obligate cryptic forms. The present study provides a critical link for establishing the origin and evolutionary history of early cryptic sessile metazoan adaptation.

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.

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.

First report of Cystostroma (Stromatoporoidea; Ordovician) from Sino-Korean Craton

A primitive stromatoporoid Cystostroma is reported from the Middle Ordovician Duwibong Formation of Taebaeksan Basin for the first time in Korea, which occupies the eastern margin of Sino-Korean Craton. It occurs as oncoid-like structures with hemispheroidal thin laminae and stromatolite-like columns composed mainly of stacked domal to bulbous encrusting laminae alternating with bryozoans. The former mainly occur within grainstone facies whereas the latter are surrounded by muddy facies. These contrasting growth forms may have resulted from the differences in energy-level and/or effect of intergrowth with other encrusting organisms. Though internal texture of Cystostroma is poorly preserved, application of the “white card technique” reveals imbricated small convex-upward cysts which are diagnostic of the genus. Previously reported occurrences of early Cystostroma are confined to the upper Middle Ordovician Chazy Group of North America which is more-or-less contemporaneous with the Duwibong Formation in age. The Sino-Korean Craton contains considerable records of early stromatoporoids and the present study adds another occurrence of a primitive stromatoporoid Cystostroma which may have possibly been related to the origination of stromatoporoids in the region. This finding is expected to provide a better understanding for the origin and dispersal of early stromatoporoids during the Early Paleozoic.

Virtual carbonate thin section using PDF: New method for interactive visualization and archiving

As personal computers increase in processing power and storage capacity, it has become feasible to digitize an entire carbonate thin section area, and to digitally manipulate and archive such digital image files for research collaborations and teaching purposes. This paper describes procedures for creating and authoring virtual carbonate thin sections in PDF format with a 35-mm film scanner, bitmap image editing software, and a Windows or Macintosh, personal computer running Adobe Acrobat. A petrographic thin section is scanned at a maximum optical resolution of the 35-mm film scanner and the scanned image is used as a base layer of the PDF file. A digital microscope camera is used to capture high magnification photomicrographs that can be linked to the base layer to highlight specific features of the thin section. Collapsible text boxes are used for text annotation and various graphical annotation marks are used to indicate ‘hot areas’ that are linked to other photomicrographs for interactive viewing of the image. This method is highly flexible and platform independent, and can be beneficially used in various ways such as a note taking tool for routine petrographic work, creation of virtual samples for classroom use where the students have limited access time to the reference sample, long-distance research collaborations between scientists, and ultimately, creation of teaching-and research-grade visual carbonate petrography databases.

Where art thou “the great hiatus?” — review of Late Ordovician to Devonian fossil-bearing strata in the Korean Peninsula and its tectonostratigraphic implications

We review paleontologic evidence from the Upper Ordovician to Devonian strata in the Korean Peninsula and discuss their tectonostratigraphic origin. The Upper Ordovician–Devonian fossil-bearing strata are largely distributed in North Korea, and tectonostratigraphically in the southern margin of the Pyeongnam Basin and in the northern part of the Imjingang Belt. The fossils have been regarded as evidence that the “great hiatus” of the middle Paleozoic is not a prevalent phenomenon across the Sino-Korean Block. Examination of selected fossils with stratigraphic and paleogeographic significance reveals that the fossils from the Sangsori, Koksan and Wolyangri series and the Rimjin System are of the Late Ordovician to Devonian and display affinity to those of the coeval strata of South China. In addition, the fossils included within clasts of the Songrim Conglomerate, the basal unit of the Jurassic Taedong System, are of the Silurian to Devonian, which also display affinity to South China. The faunal and floral affinity suggests that the Upper Ordovician to Devonian strata in North Korea most likely formed in a basin(s) of or peripheral to the South China Block, which indicates that the strata are allochthonous, contrary to the traditional interpretation of their autochthonous origin by North Korean geologists. The Permo-Triassic collision between the two Chinese cratons which resulted in the amalgamation of three massifs of the Korean Peninsula is considered to be responsible for the accretion and juxtaposition of the Upper Ordovician to Devonian strata onto the Sino-Korean Block. The autochthonous origin of the strata suggests the absence of the “great hiatus” at least in North Korea, whereas the allochthonous origin its presence across the Sino-Korean Block.

Cambrian Reefs in the Western North China Platform, Wuhai, Inner Mongolia

Mid to late Cambrian thrombolites and maze-like maceriate reefs from the western North China Platform, Wuhai, Inner Mongolia, northwestern China, occur in the middle of a succession dominated by thin-bedded lime mudstone-shale/marlstone alternations, and are laterally surrounded by limestone conglomerate and/or grainstone. Thrombolite, characterized by meter-scale lenticular mounds composed of millimeter- to centimeter-scale mesoclots and wackestone matrix, occurs in the lower middle part of the sequence. Thrombolite mesoclots are composed of microstromatolites with alternating dark gray and light gray micritic laminae. The maze-like maceriate reefs occur in the middle to the upper part of the sequence, commonly forming lenticular mounds up to 1 m thick. They are characterized by centimeter- to decimeter-scale branched maze-like structures, whose biogenic portions (maceria) are selectively dolomitized. The maceriae are composed of poorly preserved microstromatolites and siliceous sponges. Inter-macerial sediments consist of lime mud and scattered bioclasts. These Wuhai reefs are generally similar to but older than various other Cambrian reefs previously reported from the Shandong region, northeastern China.

Morphometrics and palaeoecology of the coral Agetolites from the Xiazhen Formation (Upper Ordovician), Zhuzhai, South China

Sun, N., Elias, R.J., Choh, S.-J., Lee, D.-C., Wang, X.-L. & Lee, D.-J., February 2016. Morphometrics and palaeoecology of the coral Agetolites from the Xiazhen Formation (Upper Ordovician), Zhuzhai, South China. Alcheringa 40, xxx–xxx. ISSN 0311-5518. Agetolites is a peculiar cerioid coral possessing traits of both tabulates and rugosans. The presence of numerous mural pores has been considered by some workers to indicate a relation to tabulates, although an affinity to rugosans has also been proposed based mainly on well-developed septa that alternate in length. Agetolites is by far the most common colonial coral in the Upper Ordovician Xiazhen Formation at Zhuzhai, in the JCY (Jiangshan–Changshan–Yushan) triangle region of South China. It occurs in various lithofacies representing a wide range of depositional environments. Five species are recognized and verified by cluster analysis, discriminant analysis, descriptive statistics and bivariate plots: A. yushanensis Lin, 1960, A. raritabulatus Lin, 1960, A. waicunensis (Lin & Chow, 1977), A. oculiporoides Lin, 1960 (including A. huangi Lin, 1960 as a junior synonym) and A. maxima (Lin & Chow, 1977). Agetolitids from the JCY triangle described previously under the generic name Agetolitella are herein transferred to Agetolites. In the Xiazhen Formation at Zhuzhai, A. waicunensis and A. maxima are restricted to the lower part of the formation, whereas A. yushanensis occurs in the upper part. Agetolites raritabulatus and A. oculiporoides have greater stratigraphic ranges in the lower and upper parts of the formation. The size and shape of Agetolites coralla at Zhuzhai are considered primarily to be intrinsic characteristics of the species but in some cases also seem to be related to lithofacies; large and domical coralla are dominant in calcareous mudstone facies, whereas small coralla with various forms are commonly found in reef or reef-related facies. In the latter facies, spatial competition is indicated by common occurrences of both Agetolites encrusting stromatoporoids and stromatoporoids encrusting Agetolites. Ning Sun [nsun@cugb.edu.cn], School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, PR China; Robert J. Elias [eliasrj@cc.umanitoba.ca], Department of Geological Sciences, The University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada; Suk-Joo Choh [sjchoh@korea.ac.kr], Department of Earth and Environmental Sciences, Korea University, Seoul 136-701, Korea; Dong-Chan Lee [dclee@chungbuk.ac.kr], Department of Earth and Environmental Sciences, Chungbuk National University, Cheongju, 361-763, Korea; Xun-Lian Wang [wxl@cugb.edu.cn], School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, PR China; Dong-Jin Lee* [djlee@andong.ac.kr], Department of Earth and Environmental Sciences, Andong National University, Andong 760-747, Korea. *Also affiliated with College of Earth Science, Jilin University, Changchun 130061, PR China.