Episodes does not have to share the same opinion as reviewers and we do not take responsibility f... more Episodes does not have to share the same opinion as reviewers and we do not take responsibility for reviews and comments.
The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergr... more The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergroup exposed in the Taebaeksan Basin of South Korea and the Pyeongnam Basin of North Korea. This review summarises the advances made on these successions during the past two decades, focusing on the Taebaeksan Basin. The Ordovician succession in the Taebaeksan Basin comprises the Taebaek, Yeongwol, Yongtan, Pyeongchang, and Mungyeong groups, of which the Taebaek and Yeongwol groups have been studied in detail. These strata are mixed carbonate-siliciclastic deposits formed in peritidal to deep-subtidal environments. Sedimentological and palaeontological studies show that the Korean Ordovician succession represents local variations of the Great Ordovician Biodiversification Event, exemplified by reef evolution, changes in sedimentary systems, and changes in invertebrate fossil assemblages. Recent studies on the Yongtan, Pyeongchang, and Mungyeong groups have demonstrated that these units ar...
The thickness and distribution of early syn‐rift deposits record the evolution of structures acco... more The thickness and distribution of early syn‐rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono‐sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn‐rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn‐rift and post‐rift deposits. To improve our understanding of the tectono‐sedimentary development of early syn‐rift strata during the initial stages of rifting, we examined quasi‐3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half‐graben formation adjacent to surface‐breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non‐marine, early syn‐rift deposits. Fluvial systems incised into underlying pre‐rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold‐bound syncline rather than a fault‐bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra‐basin extensional forced folds. Fault‐driven subsidence, perhaps augmented by a eustatic sea‐level rise, resulted in basin deepening and the deposition of a series of fluvial‐dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface‐breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandstone and fan‐delta conglomerates. Because growth folding and faulting were coeval along‐strike, syn‐rift stratal units deposited at this time show a highly variable along‐strike stratigraphic architecture, locally thinning towards the growth fold but, only a few kilometres along‐strike, thickening towards the surface‐breaking fault. Despite displaying the classic early syn‐rift stratigraphic motif recording net upward‐deepening, extensional forced folding rather than surface faulting played a key role in controlling basin physiography, accommodation development, and syn‐rift stratal architecture and facies development during the early stages of extension. This structural and stratigraphic observations required to make this interpretation are relatively subtle and may go unrecognized in low‐resolution subsurface data sets.
Abstract Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of foss... more Abstract Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of fossilised keratose sponges (keratolites) and microbial carbonates, are reported from the Tremadocian Mungok Formation, Yeongwol, Korea. The stromatolite-like columns, which are up to 10 cm wide and high, consist of an inner core with low-angled (10–45°) layers that are covered by high-angled (>45°) layers. The inner core is made up of millimetric layers of alternating keratolite and microbial carbonate, and microbial carbonate dominantly comprises the outer cover. The entire columns are surrounded by bioclastic packstone to grainstone. The thrombolite-like mounds are domes a maximum of 100 cm high and 40–60 cm wide embedded within lime mud and shale. These mounds consist of keratolite–microbial carbonate clots and minor lithistid sponge–microbial carbonate clots. The stromatolite-like columns were formed in a high-energy subtidal setting, in which laminoid keratolite and microbial carbonate formed the tight laminar frame columns. Continued growth of the column narrowed the intercolumnar space, resulting in higher-energy hydrodynamic conditions that limited the growth of sponges but promoted growth of microbial organisms. In contrast, thrombolite-like mounds developed in a low-energy environment below fair-weather wave base, where irregular to bulbose keratose sponges with minor lithistid sponge–microstromatolite associations formed cluster reefs. There appear to have been ecological and/or environmental factors that affected the distribution of these sponges; keratose and lithistid sponges rarely occur together in the Mungok reefs, whereas lithistids are pervasive within coeval intermediate-energy microbial reefs elsewhere. These results demonstrate the importance of hydrodynamic controls on overall reef morphology and configurations during the Early Ordovician, and suggest that keratosan–microbial consortia may have been an integral component of the Great Ordovician Biodiversification Event, together with the lithistid sponge–microbial consortium.
DESAPROPRIAÇÃO -JUROS -CORREÇÃO MONET ARIA -E devida a correção da dívida, ainda que por mais de ... more DESAPROPRIAÇÃO -JUROS -CORREÇÃO MONET ARIA -E devida a correção da dívida, ainda que por mais de uma vez, se o atraso na satisfação do quantum debeatur deu-se por culpa do expropriante. Precedentes. Recurso provido.
The Lower Ordovician mixed carbonate–shale Dumugol Formation of Korea was analysed to compare the... more The Lower Ordovician mixed carbonate–shale Dumugol Formation of Korea was analysed to compare the stratal thickness and facies proportion of measured and decompacted successions and to assess the effect of compaction on the interpretation of cyclicity. Metre-scale cyclic units (MSUs) in the formation consist in part of outer-shelf shale, distal to intermediate mid-ramp limestone–shale couplets, and proximal mid-ramp lime mudstone facies. A total of 119 MSUs were recognised in the studied section. Thickness reduction was estimated based on petrographic evidence, including compressed to uncompressed burrows, firm- to hardground surfaces and differentially compacted laminae, and supplementary values of decompaction factors taken from the literature. Five oscillatory units in the apparent Fischer plots consist of thickening- to thinning-upward packages composed of shallowing- to deepening-upward MSUs. Similar thickness–facies relationships were observed in the lower two oscillatory unit...
Cryptic ecosystems of modern and ancient reefs contain substantial amounts of biodiversity. It re... more 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.
A potentially new type of non-reef sponge-bearing micritic limestone is reported from the Upper O... more A potentially new type of non-reef sponge-bearing micritic limestone is reported from the Upper Ordovician Xiazhen Formation of southeastern China. The sponges are preserved as incomplete skeletons that consist of curved bifurcated and trifurcated spicules embedded in dark micrite, and can only be recognized under a petrographic microscope. The characteristics of the spicule networks suggest that the sponges are probably belonging to demosponges. However, based on the absence of features such as desma, zygome, a distinct dermal layer, and a canal system, they are not considered to be lithistids. The majority of the sponges are found in a lime mudstone facies, together with some micritic portions of wackestone to grainstone facies, comprising approximately 13% of the 50-m thick micritic limestone successions. It is interpreted that the non-lithistid demosponges flourished on soft substrates over shallow marine carbonate platform. Such sponge-bearing carbonates are similar to spiculites and spongolites in terms of being a major constituent of the sedimentary rocks and their potential contribution as sediment producers, but affinity and modes of preservation of the Xiazhen sponges are significantly different to those of the spiculites and spongolites. In light of the present finding, it is suggested that non-lithistid demosponges may have been more widespread in early Palaeozoic non-reef carbonates than has previously been recognized, thus indicating the critical need for further detailed studies if we are to understand their distributions and sedimentological contributions.
ABSTRACT The Early Ordovician witnessed an increased influence of skeletal organisms on the const... more ABSTRACT The Early Ordovician witnessed an increased influence of skeletal organisms on the construction of microbial-dominant reefs, which preceded the Middle to Late Ordovician expansion of skeletal-dominant reefs. Skeletal frameworks of Early Ordovician reefs built by stromatoporoids, bryozoans, pelmatozoans and calathiids have recently been reported. In this study, we document the occurrence of localized Archaeoscyphia frameworks and additional unidentified non-anthaspidellid spiculate sponges that played diverse roles in the construction of microbial–siliceous sponge reefs preserved in the Early Ordovician Dumugol Formation, Korea which have not been previously described in coeval reefs elsewhere. Two types of boundstone textures are recognized: microbial-dominated boundstone and sponge–microbial boundstone. Microbialites were primarily responsible for reef construction (making up about one third of reefs), both as framework builders and as encrusters of other reef components. The Archaeoscyphia and spiculate sponges contributed in various ways to reef development. Archaeoscyphia, constituting about one fourth of the Dumugol reefs, mainly constructed sponge–microbial boundstone, together with encrusting microbialites. Clusters of Archaeoscyphia individuals sporadically formed centimeter-sized sponge framestone (3% of reefs) with primary cryptic spaces. Spiculate sponges (4% of reefs), a previously unknown component of Early Ordovician reefs, also played diverse roles, such as encrusting other constituents, dwelling in cryptic spaces, stabilizing reef-flank sediments and even building frameworks. Such framework-building siliceous sponges, together with previously reported skeletal frameworks in other Early Ordovician reefs, reflect an early phase of the transition from microbial- to skeletal-dominated reefs in the early Paleozoic.
Episodes does not have to share the same opinion as reviewers and we do not take responsibility f... more Episodes does not have to share the same opinion as reviewers and we do not take responsibility for reviews and comments.
The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergr... more The Ordovician succession of the Korean Peninsula is part of the Cambro-Ordovician Joseon Supergroup exposed in the Taebaeksan Basin of South Korea and the Pyeongnam Basin of North Korea. This review summarises the advances made on these successions during the past two decades, focusing on the Taebaeksan Basin. The Ordovician succession in the Taebaeksan Basin comprises the Taebaek, Yeongwol, Yongtan, Pyeongchang, and Mungyeong groups, of which the Taebaek and Yeongwol groups have been studied in detail. These strata are mixed carbonate-siliciclastic deposits formed in peritidal to deep-subtidal environments. Sedimentological and palaeontological studies show that the Korean Ordovician succession represents local variations of the Great Ordovician Biodiversification Event, exemplified by reef evolution, changes in sedimentary systems, and changes in invertebrate fossil assemblages. Recent studies on the Yongtan, Pyeongchang, and Mungyeong groups have demonstrated that these units ar...
The thickness and distribution of early syn‐rift deposits record the evolution of structures acco... more The thickness and distribution of early syn‐rift deposits record the evolution of structures accommodating the earliest phases of continental extension. However, our understanding of the detailed tectono‐sedimentary evolution of these deposits is poor, because in the subsurface, they are often deeply buried and below seismic resolution and sparsely sampled by borehole data. Furthermore, early syn‐rift deposits are typically poorly exposed in the field, being buried beneath thick, late syn‐rift and post‐rift deposits. To improve our understanding of the tectono‐sedimentary development of early syn‐rift strata during the initial stages of rifting, we examined quasi‐3D exposures in the Abura Graben, Suez Rift, Egypt. During the earliest stage of extension, forced folding above blind normal fault segments, rather than half‐graben formation adjacent to surface‐breaking faults, controlled rift physiography, accommodation development and the stratigraphic architecture of non‐marine, early syn‐rift deposits. Fluvial systems incised into underlying pre‐rift deposits and were structurally focused in the axis of the embryonic depocentre, which, at this time, was characterized by a fold‐bound syncline rather than a fault‐bound half graben. During this earliest phase of extension, sediment was sourced from the rift shoulder some 3 km to the NE of the depocentre, rather than from the crests of the flanking, intra‐basin extensional forced folds. Fault‐driven subsidence, perhaps augmented by a eustatic sea‐level rise, resulted in basin deepening and the deposition of a series of fluvial‐dominated mouth bars, which, like the preceding fluvial systems, were structurally pinned within the axis of the growing depocentre, which was still bound by extensional forced folds rather than faults. The extensional forced folds were eventually locally breached by surface‐breaking faults, resulting in the establishment of a half graben, basin deepening and the deposition of shallow marine sandstone and fan‐delta conglomerates. Because growth folding and faulting were coeval along‐strike, syn‐rift stratal units deposited at this time show a highly variable along‐strike stratigraphic architecture, locally thinning towards the growth fold but, only a few kilometres along‐strike, thickening towards the surface‐breaking fault. Despite displaying the classic early syn‐rift stratigraphic motif recording net upward‐deepening, extensional forced folding rather than surface faulting played a key role in controlling basin physiography, accommodation development, and syn‐rift stratal architecture and facies development during the early stages of extension. This structural and stratigraphic observations required to make this interpretation are relatively subtle and may go unrecognized in low‐resolution subsurface data sets.
Abstract Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of foss... more Abstract Lower Ordovician stromatolite-like columns and thrombolite-like mounds, composed of fossilised keratose sponges (keratolites) and microbial carbonates, are reported from the Tremadocian Mungok Formation, Yeongwol, Korea. The stromatolite-like columns, which are up to 10 cm wide and high, consist of an inner core with low-angled (10–45°) layers that are covered by high-angled (>45°) layers. The inner core is made up of millimetric layers of alternating keratolite and microbial carbonate, and microbial carbonate dominantly comprises the outer cover. The entire columns are surrounded by bioclastic packstone to grainstone. The thrombolite-like mounds are domes a maximum of 100 cm high and 40–60 cm wide embedded within lime mud and shale. These mounds consist of keratolite–microbial carbonate clots and minor lithistid sponge–microbial carbonate clots. The stromatolite-like columns were formed in a high-energy subtidal setting, in which laminoid keratolite and microbial carbonate formed the tight laminar frame columns. Continued growth of the column narrowed the intercolumnar space, resulting in higher-energy hydrodynamic conditions that limited the growth of sponges but promoted growth of microbial organisms. In contrast, thrombolite-like mounds developed in a low-energy environment below fair-weather wave base, where irregular to bulbose keratose sponges with minor lithistid sponge–microstromatolite associations formed cluster reefs. There appear to have been ecological and/or environmental factors that affected the distribution of these sponges; keratose and lithistid sponges rarely occur together in the Mungok reefs, whereas lithistids are pervasive within coeval intermediate-energy microbial reefs elsewhere. These results demonstrate the importance of hydrodynamic controls on overall reef morphology and configurations during the Early Ordovician, and suggest that keratosan–microbial consortia may have been an integral component of the Great Ordovician Biodiversification Event, together with the lithistid sponge–microbial consortium.
DESAPROPRIAÇÃO -JUROS -CORREÇÃO MONET ARIA -E devida a correção da dívida, ainda que por mais de ... more DESAPROPRIAÇÃO -JUROS -CORREÇÃO MONET ARIA -E devida a correção da dívida, ainda que por mais de uma vez, se o atraso na satisfação do quantum debeatur deu-se por culpa do expropriante. Precedentes. Recurso provido.
The Lower Ordovician mixed carbonate–shale Dumugol Formation of Korea was analysed to compare the... more The Lower Ordovician mixed carbonate–shale Dumugol Formation of Korea was analysed to compare the stratal thickness and facies proportion of measured and decompacted successions and to assess the effect of compaction on the interpretation of cyclicity. Metre-scale cyclic units (MSUs) in the formation consist in part of outer-shelf shale, distal to intermediate mid-ramp limestone–shale couplets, and proximal mid-ramp lime mudstone facies. A total of 119 MSUs were recognised in the studied section. Thickness reduction was estimated based on petrographic evidence, including compressed to uncompressed burrows, firm- to hardground surfaces and differentially compacted laminae, and supplementary values of decompaction factors taken from the literature. Five oscillatory units in the apparent Fischer plots consist of thickening- to thinning-upward packages composed of shallowing- to deepening-upward MSUs. Similar thickness–facies relationships were observed in the lower two oscillatory unit...
Cryptic ecosystems of modern and ancient reefs contain substantial amounts of biodiversity. It re... more 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.
A potentially new type of non-reef sponge-bearing micritic limestone is reported from the Upper O... more A potentially new type of non-reef sponge-bearing micritic limestone is reported from the Upper Ordovician Xiazhen Formation of southeastern China. The sponges are preserved as incomplete skeletons that consist of curved bifurcated and trifurcated spicules embedded in dark micrite, and can only be recognized under a petrographic microscope. The characteristics of the spicule networks suggest that the sponges are probably belonging to demosponges. However, based on the absence of features such as desma, zygome, a distinct dermal layer, and a canal system, they are not considered to be lithistids. The majority of the sponges are found in a lime mudstone facies, together with some micritic portions of wackestone to grainstone facies, comprising approximately 13% of the 50-m thick micritic limestone successions. It is interpreted that the non-lithistid demosponges flourished on soft substrates over shallow marine carbonate platform. Such sponge-bearing carbonates are similar to spiculites and spongolites in terms of being a major constituent of the sedimentary rocks and their potential contribution as sediment producers, but affinity and modes of preservation of the Xiazhen sponges are significantly different to those of the spiculites and spongolites. In light of the present finding, it is suggested that non-lithistid demosponges may have been more widespread in early Palaeozoic non-reef carbonates than has previously been recognized, thus indicating the critical need for further detailed studies if we are to understand their distributions and sedimentological contributions.
ABSTRACT The Early Ordovician witnessed an increased influence of skeletal organisms on the const... more ABSTRACT The Early Ordovician witnessed an increased influence of skeletal organisms on the construction of microbial-dominant reefs, which preceded the Middle to Late Ordovician expansion of skeletal-dominant reefs. Skeletal frameworks of Early Ordovician reefs built by stromatoporoids, bryozoans, pelmatozoans and calathiids have recently been reported. In this study, we document the occurrence of localized Archaeoscyphia frameworks and additional unidentified non-anthaspidellid spiculate sponges that played diverse roles in the construction of microbial–siliceous sponge reefs preserved in the Early Ordovician Dumugol Formation, Korea which have not been previously described in coeval reefs elsewhere. Two types of boundstone textures are recognized: microbial-dominated boundstone and sponge–microbial boundstone. Microbialites were primarily responsible for reef construction (making up about one third of reefs), both as framework builders and as encrusters of other reef components. The Archaeoscyphia and spiculate sponges contributed in various ways to reef development. Archaeoscyphia, constituting about one fourth of the Dumugol reefs, mainly constructed sponge–microbial boundstone, together with encrusting microbialites. Clusters of Archaeoscyphia individuals sporadically formed centimeter-sized sponge framestone (3% of reefs) with primary cryptic spaces. Spiculate sponges (4% of reefs), a previously unknown component of Early Ordovician reefs, also played diverse roles, such as encrusting other constituents, dwelling in cryptic spaces, stabilizing reef-flank sediments and even building frameworks. Such framework-building siliceous sponges, together with previously reported skeletal frameworks in other Early Ordovician reefs, reflect an early phase of the transition from microbial- to skeletal-dominated reefs in the early Paleozoic.
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