Yeongheung Formation Research Articles

Kayseraspis (Trilobita) from the Mungok Formation in Yeongwol area and its significance for the Lower Ordovician biostratigraphy and chronostratigraphy of the Taebaeksan Basin, Korea

This study reports the occurrence of a trilobite Kayseraspis from the uppermost part of the Mungok Formation, Yeongwol Group, Korea. This genus has been known to occur in the upper part of the Dumugol Formation of the Taebaek Group and in the lower part of the Yeongheung Formation of the Yeongwol Group, and to indicate the lowermost Floian in the Taebaeksan Basin. However, the occurrence of Kayseraspis from the Mungok Formation and the comparison between the biostratigraphy of trilobites and graptolites suggest that the Kayseraspis-bearing faunas in Korea can be assigned to the upper Tremadocian. Accordingly, it is plausible that the base of the Floian may be positioned in the overlying strata, the Yeongheung Formation of the Yeongwol Group and the Makgol Formation of the Taebaek Group. In order to consolidate the Lower Ordovician chronostratigraphy of the Taebaeksan Basin, additional integrative studies on trilobites, graptolites, and conodonts are required.

Sequence stratigraphy in the Middle Ordovician carbonate successions (Yeongheung Formation), mid-east Korea: Paleogeographic implications for a land-detached ramp-type platform

This study reveals the origin of the stratigraphic discrepancy between the Yeongweol and Taebaek groups and reconstructs paleogeographic model for the Taebaeksan Basin on the Sino-Korean Craton (SKC). The global sea-level fall in the earliest Middle Ordovician would have subaerially extensively exposed the Lower Ordovician peritidal successions, forming the solution-collapsed breccia zones on the Sauk-Tippecanoe bounding surface. The successive rise in sea level generated the fine-grained siliciclastic successions in the Taebaek Group during early transgression since the carbonate production of the group was hampered by the strong input of siliciclastic sediments from terrestrial sources. However, such successions are absent in the Yeongweol Group because the Yeongweol platform was distant from the siliciclastic sources and sustained carbonate production due to isolation from terrestrial influences. The Yeongweol Group is interpreted as a “land-detached (isolated) ramp-type platform” as it responded to sea-level fluctuations with restricted terrestrial influence, whereas the Taebaek Group can be described as a “land-attached ramp-type platform” affected by a large input of siliciclastic sediments during lowstand and early transgression. Based on the comparison of stratigraphic patterns and configurations of land-attached and -detached ramp-type successions, this study concludes that the Yeongweol sequence would have been formed on a land-detached (isolated) carbonate ramp-type platform located at the SKC along the northeastern Gondwana margin.

Upper Ordovician (Sandbian) conodonts from the Hoedongri Formation of western Jeongseon, Korea

Five sections in western Jeongseon-eastern Pyeongchang provide a relatively complete composite section of carbonate platform facies through the upper part of the Hoedongri Formation. A total of 29 samples (125 kg) yielded 669 relatively well-preserved conodont specimens, which are classified into 16 species representing 10 genera. The fauna is dominated by Panderodus gracilis (Branson and Mehl) (55%), which generally is believed to have been pelagic and eurytopic, and comprises characteristic elements of North China faunal affinities. Other taxa include Aphelognathus solidum Pei, Belodina sp., Eoligonodina prima (Branson and Mehl), Erismodus asymmetricus (Branson and Mehl), E. quadridactylus (Stauffer), Plectodina aculeata (Stauffer), P. alatheta An, Tasmanognathus careyi Burrett, and T. sishuiensis Zhang. This assemblage was assigned to the Tasmanognathus sishuiensis-Erismodus asymmetricus Zone herein. The interval of the zone is between the first and last occurrences of the eponymous species. The lower limit of the zone is unclear due to the absence of conodont data from underlying dolomitic limestone beds. The T. sishuiensis-E. asymmetricus Zone is the youngest conodont zone in the Taebaeksan Basin, Korea and was correlated to the ‘upper fauna’ of the Yeongheung Formation in Yeongwol, Korea, to the Belodina compressa-Microcoelodus symmetricus Zone in Shandong, to the T. sishuiensis-Erismodus typus Zone in Gansu, and to the T. sishuiensis Zone in the Ordos Basin, North China, representing the interior platform and slope facies of Sandbian age. Based on the recent recognition of the Aurilobodus serratus Zone and T. sishuiensis-E. asymmetricus Zone, the Hoedongri Formation was assigned to the Middle Ordovician to early Late Ordovician (Darriwilian, D3 to Sandbian, Sa2).

Early labechiid stromatoporoids of the Yeongheung Formation (Middle Ordovician), Yeongwol Group, mideastern Korean Peninsula: Part II. Systematic paleontology and paleogeographic implications

Three species belonging to two genera of labechiid stromatoporoids are described from the Yeongheung Formation (Darriwilian, Middle Ordovician), Yeongwol Group of the Taebaeksan Basin, mid-eastern Korean Peninsula. Sixteen stromatoporoid-bearing stratigraphic intervals have been recognized in the Namgyo section. All stromatoporoids occur in the peloidal and bioclastic packstone to grainstone facies. Labechia yeongwolense sp. nov. is the dominant species, occurring throughout the lower and middle parts of the section. In contrast, Labechiella mingshankouensis is restricted to the lower-middle part and Labechiella regularis occurs mostly in the upper part of the section. The occurrence of the early labechiids in the Yeongwol Group is suggestive of a close biogeographic affinity with the Liaoning and Shandong provinces of northeastern China.

Early labechiid stromatoporoids of the Yeongheung Formation (Middle Ordovician), Yeongwol Group, mideastern Korean Peninsula: Part I. Environmental distribution

This study examines depositional facies and environmental significance of early labechiid stromatoporoids in the Yeongheung Formation (late Middle Ordovician), Yeongwol Group in the mideastern part of the Korean Peninsula. The formation is composed of five depositional facies: lime mudstone to wackestone (LM/W), peloidal, intraclastic and bioclastic packstone to grainstone (P/G), laminated dolomitic lime mudstone (LMdl), algal laminite (La), and oolitic packstone to grainstone (P/Go). Three types of shallowing upward cycles in the succession are identified, including subtidal (LM/W–P/G), subtidal to peritidal (LM/W–P/G–LMdl–La), and peritidal cycles (LMdl–La). The stromatoporoids occur exclusively in the packstone to grainstone (P/G) facies of the subtidal cycle. These early labechiids inhabited on a grainy substrate under moderate- to high-energy conditions, conforming to the previous notion that stromatoporoids primarily occupied level-bottom or reefs, surrounded by grainy calcareous sediments during the Middle Ordovician.

Construction of the earliest stromatoporoid framework: Labechiid reefs from the Middle Ordovician of Korea

The Great Ordovician Biodiversification Event (GOBE) involved a remarkable rise of skeletal reefs during the late Middle Ordovician. A new type of skeletal patch reef built by labechiid stromatoporoids is reported from the Yeongheung Formation (Darriwilian) of the Korean Peninsula, part of the eastern North China Block, a hot-spot for late Middle Ordovician diversification of early labechiids. The attachment of laminar labechiids, subordinate peloidal micritic crusts and spiculate sponges, and minor bryozoans on peloidal–intraclastic packstone to grainstone substrates, and upward growth of these organisms by repeated encrustation, resulted in the construction of centimeter-scale domal tight frame structures. These skeletal frames were in turn veneered by larger labechiids, forming sub-meter-scale laminar skeletal reefs with primary cavities. Such skeletal reefs that formed by the encrustation and binding of labechiid stromatoporoids are analogous to the bindstone frameworks of coeval Laurentian reef mounds and skeletal reefs, though they differ markedly in composition, as is apparent in the absence of tabulate corals and markedly lower contribution of bryozoans, both of which were key elements of the Chazy reefs of Laurentia. The Yeongheung reefs described herein represent some of the oldest labechiid skeletal reefs known to date, and formed mainly by the aggregation of early stromatoporoids prior to the arrival of corals and other robust constructors in the region. This discovery provides new information on the evolutionary trends of early skeletal reefs in response to the appearance of new reef-building organisms and their regional distributions during the Ordovician radiation.

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.

Origin and modification of early dolomites in cyclic shallow platform carbonates, Yeongheung Formation (middle Ordovician), Korea

The middle Ordovician Yeongheung Formation, Korea, consists of numerous metre-scale, shallowing-upward cycles, which were deposited on a shallow-marine carbonate platform. Depositional sequences developed on the inner platform were completely dolomitized regardless of constituting lithology, whereas those developed on the outer platform were partially dolomitized. The amount of replacement dolomite within a metre-scale, shallowing-upward peritidal cycle decreases downward from the peritidal cycle cap in the partially dolomitized depositional sequences. The cross-platform distribution of dolomites and their stratigraphic position in the sequences suggest that the Yeongheung dolomite formed syndepositionally. The common existence of pseudomorphs of evaporite minerals and nodules in the Yeongheung Formation indicates that dolomitization of the Yeongheung Formation occurred in a sabkha-type tidal-flat environment. It also occurred during each cycle of deposition influenced by high-frequency sea-level oscillations. The present-day Yeongheung replacement dolomites are characterized by near-stoichiometric to stoichiometric composition (49.9 to 52.1 CaCO 3 mole%), and low strontium concentration (52 to 133 ppm). The δ 18O value of the replacement dolomites ranges from −7.7 to −5.2‰ (PDB); this is much depleted relative to that of contemporary sabkha-type dolomites. These geochemical characteristics of Yeongheung dolomite indicate significant post-depositional modification. The common existence of oomolds, leached skeletal grains and dissolved evaporites in the Yeongheung Formation illustrates invasion of meteoric water into the sediments. Recrystallization of Yeongheung dolomites in the infiltrated meteoric water at slightly elevated temperatures during shallow burial resulted in lighter δ 18O values and lower strontium concentration.

Depositional cyclicity of the Middle Ordovician Yeongheung Formation, Korea

The Middle Ordovician Yeongheung Formation consists of numerous meter-scale, shallowing-upward cycles, which were deposited on a shallow-marine carbonate platform. Two types of shallowing-upward cycles, peritidal and shallow subtidal cycles, are recognized in the Yeongheung Formation. The peritidal cycles are composed of shallow subtidal lithofacies capped by tidal-flat lithofacies, whereas the shallow subtidal cycles are entirely subtidal lithofacies with no tidal-flat caps or subaerial exposure features. Stacking of shallow subtidal cycles, the similtaneous development of peritidal and subtidal cycles on different parts of the carbonate platform, and persistent vertical stacking of meter-scale, shallowing-upward cycles suggest that most of the cycles were formed in response to high-frequency eustatic sea level oscillations.

Behavioral patterns expressed in scribbling trace fossils from Ordovician strata of yeongweol, Korea

Ancient behavioral patterns expressed in scribbling trace fossils from the Ordovician Mungok and Yeongheung formations of the Yeongweol area of Korea are compared and interpreted. Scribbling trace fossils from the Tremadocian to early Arenigian Mungok Formation consist of a continuous series of uniform circles with slightly changing centers. Diameters of circles and trails are about 50 mm and 1–2 mm, respectively. Scribbling trace fossils from the late Arenigian to early Caradocian Yeongheung Formation are not well preserved. The size of the circles is about 100–150 mm and trail diameters are up to 5 mm. Scribbling trace fossils from the Mungok Formation are interpreted to be a result of repetitious grazing whereby the animal pursued a circular course and followed some part of that previous trail before leaving it to make another new circle. This behavior may be a primitive grazing method for scribbling traces. Scribbling traces from the younger Yeongheung Formation are also interpreted to be a result of ...

A unique occurrence ofLockeiafrom the Yeongheung Formation (Middle Ordovician), Yeongweol, Korea

Numerous and diverse forms of Lockeia are excellently preserved in the dolomitic mudstone of the Middle Ordovician Yeongheung Formation, Yeongweol, Korea. They allow a description of L. siliquaria, L. amygdaloides, L. ichnosp. and L. triangulichnus nov. ichnosp. L. siliquaria is a thin, seed‐like form, tapered at both ends. L. amygdaloides is a relatively plump, almond‐shaped form, tapered at one end while the other end is obtusely pointed or somewhat rounded. L. triangulichnus is a small triangular trace with three ridges from apex, resembling a pyramid, preserved in convex hypo‐relief and concave epirelief. L. ichnosp. is a pear‐shaped or irregular form. Usually, populations of Lockeia are monospecific and this occurrence is unique. Since all four ichnospecies of Lockeia are found on a single bedding plane of the Yeongheung Formation, the criteria used for ichnospecific differentiation appear valid.

Original mineralogy of ordovician stromatoporoids

Stromatoporoids in the Middle Ordovician Yeongheung Formation show delicate reticulate structures of persistent laminae and discontinuous pillars. Abundant microdolomite inclusions are found in the stromatoporoid skeletons. Coexisting aragonite precursor grains such as gastropod and cephalopod preserve no internal microstructures due to extensive dissolution and subsequent filling by low-magnesian calcite. Brachiopods (low-magnesian calcite precursor) show well preserved skeletal microstructures, but do not contain any microdolomite inclusions. Stromatoporoids were not dissolved as completely as original aragonitic shells, but recrystallized more than shells with a low-magnesian calcite precursor. The similarity of the stromatoporoid preservation pattern to that of echinoderm grains (high-magnesian calcite precursor) and the widespread occurrences of microdolomite rhombs in the stromatoporoid skeletons indicate that the Middle Ordovician stromatoporoids were originally composed of high-magnesian calcite.