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This paper focuses on the initial basin-fill processes in an extensional nonmarine back-arc basin. Sedimentary facies analysis in the southwestern part of the Gyeongsang Basin (Jinju Subbasin), Hapcheon area reveals that the succession consists of four facies assemblages. The assemblage I mainly consists of disorganized conglomerate deposited by flash floods in a streamflow-dominated alluvial fan. The assemblage II is dominated by stratified conglomerates and massive, stratified, and cross-stratified sandstones, showing architecture of stacked channels and bars. The assemblage III largely comprises massive, stratified to laminated, and trough cross-stratified sandstones, which are organized into channel-fill and bar-accretion structures. It most likely formed in sandy sinuous rivers. The assemblage IV comprises gray mudstone interlayered with fine sandstone, representing water-logged floodplains. Conglomerate and sandstone bodies formed in the fluvial systems appear to be randomly distributed within floodplain fines, displaying a great lateral and vertical lithologic variation. This study helps understand the complexity of basin-fill history, i.e., switching of fluvial networks in time and space, in contrast to the simple notion of margin-parallel stacking of lithostratigraphic units.

This paper discusses the equivocal nature of the refined definition of stratigraphic sequence for universal recognition. The current definition requires a couple of inferences to be drawn: diagnosis of “a full cycle of base-level change” and, in turn, evaluation of stratal lapout “systems tract”. In the initial depositional models, the inferences were made in vertically exaggerated seismic profiles of passive continental margins with condensed clinoform geometry and bounding surfaces. In ancient outcrop sections, which are devoid of the clinoforms, the inferences are practically implausible. On the other hand, the cycle change is not always in phase with the unconformity, especially with the upper unconformity affected by tectonic movements. For these reasons, a sequence is limited for universal recognition. Intercontinental correlation of stratigraphic sequence is implausible. An alternative sequence can be defined by “a basin-wide correlation of recurrent facies succession bounded at the base by distinctive lithologic discontinuity or erosion surface”. A sequence in alluvial deposits can be identified on the basis of its bounding discontinuities. The evolving definition of stratigraphic sequence signals the demise of the initial concept of sequence stratigraphy and leads to a new avenue for the recognition of stratigraphic sequence. A distinctive sequence can be recognized based on the descriptive characteristics and scale of the succession.

This paper focuses on the depositional processes and environmental changes during initial marine flooding recorded in the lower Cambrian succession of the North China Platform in Shandong Province, China. In order to understand imbalance of accommodation and sediment supply in the initial stage of basin-fill, a detailed analysis of sedimentary facies was made for the lowermost siliciclastic deposits of the Liguan Formation. It reveals ten siliciclastic lithofacies in three large-scale outcrops (Jinhe, Anqianzhuang, and Zhangjiapo sections). These facies are grouped into four facies associations, representing siliciclastic foreshore-shoreface (S1), siliciclastic offshore (S2), distributary mouth bars (S3), and coastal plain (S4). The siliciclastic components occur in a linear belt, emanating from a major drainage system in the northeastern part of the platform. Deposition of siliciclastic sediments was largely controlled by regional topography of the unconformable surface and shoreline configuration as well as strong effect of waves and currents. With ensued rise in sea level and decrease in siliciclastic sediment supply, carbonate sediments prevailed, filling the accommodation created by epeirogenic subsidence and sediment loading.

This study focuses on the initial subsidence mechanism of Korea Plateau in the East Sea. New interpretation of digitized multichannel seismic profiles (vertically unexaggerated) in the southern part of the South Korea Plateau delineates that acoustic basement comprises a number of normal-fault blocks, forming intra-plateau basins and troughs. In the western part of the plateau, the normal faults are oblique to the continental margin, whereas in the eastern part, they are bounded by an orthogonal transfer fault. The entire faults are suggestive of a large-scale dextral strike-slip fault system. The dextral fault system in the plateau was accompanied by a regional strike-slip fault along the North Korean continental margin, which offsets the prominent NE-SW granite belts on land and under the sea. The regional dextral strike-slip fault system activated during the late Oligocene/early Miocene to middle Miocene. The regional dextral strike-slip along the western continental margin of the sea was coupled with the complex dextral fault on the eastern margin from Sakhalin to Honshu. The regional strike-slip deformation was due to the changes in plate motion, i.e., southward drift (late Oligocene/early Miocene) and clockwise rotation (middle Miocene) of the Japanese Arc away from the Eurasian Plate.

The reefs of the middle–late Cambrian (Cambrian Epoch 3–Furongian) have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction. Thorough review of the reefs in these periods shows, however, that the Cambrian Epoch 3 and the Furongian actually yield different types of reefs. The Cambrian Epoch 3 reefs are dominated by thrombolites and dendrolites, largely constructed by the calcified microbes Epiphyton and Renalcis. On the other hand, the Furongian reefs consist mainly of maze-like maceriate reefs and columnar stromatolites. The maceriate reefs most likely formed by siliceous sponges and calcified microbes including Girvanella and Tarthinia, whereas the columnar stromatolites were mainly constructed by Girvanella, Tarthinia, and minor siliceous sponges. Other microbial reefs (e.g., non-columnar stromatolites) persisted during the Cambrian Epoch 3 and the Furongian, mainly as small patch reefs or reefal crusts. Lithistid sponge-microbial reefs initially formed in the Cambrian Epoch 3 and occurred throughout the Furongian, but occupied only a minor portion during these periods. Several geological events occurred across the boundary between the Cambrian Epoch 3 and the Furongian, including positive carbon and sulfur isotope excursions, a eustatic sea-level drop, major faunal turnover of trilobites, and diversification of new organisms. The coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events. Among the events, it is likely that sea-level change would have affected reefs, although further studies are required in order to test whether and how the other events influenced the reef transition. Epiphyton and Renalcis (and thrombolites and dendrolites formed by them) declined greatly most likely due to sea-level fall and thus decreased in shallow marine habitat at the end of Cambrian Epoch 3. The Cambrian Epoch 3 thrombolites and dendrolites were gradually replaced by a sponge-microbial association of the maze-like, maceriate reefs and the columnar stromatolites in the Furongian, coincident with a sea-level rise.

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 (

This paper focuses on the tectonic, sedimentary, and volcanic evolution of a unique back-arc basin (Ulleung Basin) in the southwestern part of the East Sea (Sea of Japan). The basin consists of thick extended continental (or transitional) crust and an overlying sedimentary succession (4–8 km thick), with interlayered volcanic flows and sills, defining a number of seismic units of variable reflection characteristics. The northern margin is bounded by faulted continental blocks (South Korea Plateau) with isolated basement lows and sub-basins with intruded and extruded volcanics, whereas the southern margin is underlain by deep-seated basement with a thick (> 8 km thick) sedimentary succession. The western margin is bounded by a series of strike-slip and normal faults produced by NNW–SSE-directed dextral movements. These structural features suggest a south–southeastward drift of the southwestern Japanese Arc away from the South Korea Plateau during the Early to Middle Miocene, involving large-scale right-lateral strike-slip deformation along the western margin, akin to pull-apart basin formation. During the back-arc opening, the thinned continental crust was largely modified by intrusive volcanics under tensional stress regime. The volcanics also extruded across the axis of extension as well as along the boundary faults on the west. In the Middle to Late Miocene, major faults in the southern and western margins were inverted, forming partial closure of the basin especially in the southern part, although the plateau in the northern margin experienced continuous subsidence. The Ulleung Basin thus provides an example of an immature back-arc basin which experienced a rather brief episode of rifting and extension followed by closure due to tectonic inversion.

This study focuses on the microbial reefs of the Zhushadong Formation (Cambrian Series 2) in Shandong Province, China in order to understand the evolution of calcified microbes in the North China Platform during the Cambrian Series 2 and 3. The microbial reefs occur in a thin unit, ca. 3 m thick, over an area of 1 km 2 . They consist of three types of thrombolite based on their mesostructures: rimmed, grainstone-patch, and dendritic. The thrombolites mainly occur in various coarse-grained carbonate facies, including crudely stratified oolitic grainstone, stromatolitic grainstone, and disorganized limestone conglomerate. Calcified microbes in the thrombolites include Epiphyton , Kordephyton , a tubiform microbe, Bija , Tarthinia , Renalcis , Amgaina , and Razumovskia . The Zhushadong thrombolites were formed within a grainstone shoal, and experienced repeated burial and exposure. The rimmed thrombolite and grainstone-patch thrombolite experienced abundant input of carbonate grains (forming grainstone patches). In contrast, the dendritic thrombolite formed solely by calcification of microbes that mainly include Epiphyton , Tarthinia , and the tubiform microbe. The outer crusts of the rimmed thrombolite were formed by Amgaina , under high energy conditions. The diverse calcified microbes of the Zhushadong Formation form the earliest assemblage of their type in the North China Platform. Their descendants, mostly Epiphyton , subsequently thrived, forming a ca. 180 m thick microbialite–oolite-dominated succession during the Cambrian Series 3 (Zhangxia Formation). Although the reefs in the Zhushadong Formation are much smaller than those of the overlying Zhangxia Formation, their calcified microbes are more diverse. This most likely reflects changes in depositional environments (e.g., abundant siliciclastic input and tidal effects vs. those of a stable carbonate platform), and/or global changes within reef environments (e.g., end-Cambrian Series 2 extinction of archaeocyaths and calcified microbes). A decrease in diversity of calcified microbes in the North China Platform, where archaeocyaths were absent, may help to account for evolutionary trends in calcified microbes that occurred independently of archaeocyath influence.

This study delineates the collision belt (late Permian-Triassic) between the Sino-Korean and South China blocks in the northeast Asian margin, based on correlation of endemic fossil components (corals) in shallow marine deposits of the Silurian and Devonian, identified in both south China and southwest and northeast Japan. The Qinling-Dabie Belt in China was offset by the left-lateral Tanlu Fault and contiguous to the Sulu Belt. The Imjingang Belt in the Korean peninsula was, in turn, offset by the right-lateral South Korean Tectonic Line, and extended eastward to the Namhae Belt (newly named). Further east, it extended to the Higo Belt and the Kitakami Terrane in Japan, prior to the opening of the East Sea in the Miocene. The collision in the northeastern Asian margin in the Triassic was superposed by contemporaneous subduction of the paleo-Pacific Plate.

In order to diagnose emplacement of discordant breccia body in carbonate platform, we here describe sedimentary structures and texture as well as bed geometry of two beds of the Chaomidian Formation (Frongian) in Shandong Province, China. Each breccia body consists of granule- to cobble-size clasts of peloidal grainstone and matrices of dolomitic marlstone and/or micritic limestone, showing a tunnel geometry. Marlstone in the matrix is homogeneous, whereas micritic limestone shows irregular and disoriented laminations. It is hypothesized that the breccia body formed by subsurface in situ fluidization and fragmentation and further injection into the ambient deposits. Subsurface sediment remobilization occurred most likely under cyclic loading of large storm waves. The laminated matrix is strongly suggestive of hydroplastic deformation (flowage) of fluidized material during injection. This study suggests that there exists a full spectrum of subsurface deformation from liquefaction/fluidization to injection flow.

This study focuses on the stratigraphic sequences and the bounding surfaces in the upper Cambrian Series 3 to Furongian Gushan and Chaomidian formations in the Shandong region, China. The bounding surfaces are compared with those of the coeval succession in the Taebaek area, Korea. According to the vertical arrangement of the facies associations and the identification of the bounding surfaces, three stratigraphic sequences are recognized, representing dynamic changes in accommodation versus sedimentation. The bounding surfaces can be traced in the Shandong region for about 6,000 km2 in area, but cannot be correlated with those of the Taebaek area (eastern margin of the platform, about 1,000 km apart). Surface 1 is characterized by an abrupt facies change from carbonate to shale, representing a distinct drowning surface. The drowning surface is also diagnosed in the Taebaek area but highly diachronous. Surface 2 is a cryptic subaerial unconformity, reflected by an erosion surface, missing of a trilobite biozone (Prochuangia Zone), and an abrupt increase in carbon isotope value. It is not identified in the Taebaek area where the Prochuangia Zone is present. Surface 3 is a marine flooding surface, indicated by a subtle transition from flat-bedded microbialite to domal microbialite (or grainstone). It may be correlated with that in the Taebaek area, which is, however, represented by an abrupt facies change from sandstone to limestone-shale alternation. The high variability of the sequence-bounding surfaces is indicative of variable regional factors such as topographic relief, carbonate production, siliciclastic input, and hydrodynamic conditions. It suggests that the sequence-bounding surfaces are invalid for a basin-scale correlation, especially in an epeiric carbonate platform.

This study focuses on an extensive biostromal microbialite (10–20 m in thickness and over 6,000 km2 in area) and the overlying grainstones in the Furongian Chaomidian Formation, Shandong Province, China in order to understand the demise of the microbialite. The microbialites are characterized by centimeter-to decimeter-scale maze-like maceria structures and/or chaotic mesostructures. According to the megastructures of microbialites and the proportion of non-microbial carbonate sediment, the biostromal microbialite is generally divided into the lower and the upper parts, separated by a distinct surface. The lower part is laterally continuous and generally flat-bedded, whereas the upper part shows variable domal megastructures and locally co-occurs with abundant non-microbial carbonate sediment. The entire microbialite bed is sharply overlain by grainstone-dominated deposits via an erosion surface which is either irregular with significant relief or flat with hematitic coating. The lower part of the biostromal microbialites with flat-bedded megastructures most likely deposited contemporaneously during sea-level highstand in the early middle Furongian, as evinced by well-correlated flat-bedded units separated by distinct bounding surfaces. The microbialites formed regional topographic variation, generally deepening toward southeast. The flat-bedded microbialites were drowned by subsequent rapid rise in sea level. In the topographic highs, the microbialites caught up with sea-level rise, forming large-scale domal megastructures. In the topographic lows, however, domal microbialites formed together with abundant non-microbial sediment, which were frequently reworked by storm-induced waves and currents. Subsequent deposition and migration of coarse-grained non-microbial sediment during sea-level rise terminated the entire microbialites.

To understand the depositional processes and environmental changes during the initial flooding of the North China Platform, this study focuses on the Lower to Middle Cambrian Zhushadong and Mantou formations in Shandong Province, China. The succession in the Jinan and Laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone, dolostone, stromatolite, thrombolite, purple and grey mudstone, and sandstone. A detailed sedimentary facies analysis of seven well-exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments, including local alluvial fans, shallowing-upward carbonate–siliciclastic peritidal cycles, oolite dominant shoals, shoreface and lagoonal environments. These facies associations successively show a transition from an initially inundated tide-dominated carbonate platform to a wave-dominated shallow marine environment. In particular, the peritidal sediments were deposited during a large number of depositional cycles. These sediments consist of lime mudstone, dolomite, stromatolite and purple and grey mudstones. These shallowing-upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea-level. The carbonate production was, however, interrupted by frequent siliciclastic input from the adjacent emergent archipelago. The depositional cycles thus formed under the influence of both autogenetic changes, including sediment supply from the archipelago, and allogenic control of relative sea-level rise in the carbonate factory. A low-relief archipelago with an active tidal regime allowed the development of tide-dominated siliciclastic and carbonate environments on the vast platform. Siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea-level. This study provides insights on how a vast Cambrian carbonate platform maintained synchronous sedimentation under a tidal regime, forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea-level during the early stage of basin development in the North China Platform.

This paper analyzes the growth patterns of dendrolite in the Zhangxia Formation (Middle Cambrian), Shandong Province, China, using the technique of 3-D computed tomographic reconstruction. Dendroids are classified into V-dendroids, columnar dendroids, and arborescent dendroids, based on morphological characteristics. The means of interconnection between dendroids are classified into trunks, nodules, shoots, and fingers. Stacking and tiering control the gross morphology and structural framework of dendrolite. Stacking is a process of vertical growth, in which V-dendroids create a staircase-like structure. Tiering occurs when a layer of dendroids is covered by sediment, and then partially eroded, allowing a new layer of dendroids to form. A comprehensive blueprint of the structural divisions of dendrolite is presented, according to scale, being divided into micro-, meso-, macro-, and megastructures. The mesostructure, which includes individual dendroids and their combined structures, is subsequently divided into primary (V-dendroid), secondary (columnar and arborescent dendroid), and tertiary (stair and tier) structures and a basic growth model is provided for V-dendroids. The stages of V-dendroid growth are: 1) trunk extension and base expansion, 2) divergence, 3) expansion and convergence, followed by repetition of stages 2 and 3, until 4) growth completion, followed by the subsequent emergence of a new dendroid by either stacking or tiering. This development of systematically ordered structures is suggestive of the reaction of microbial colonies to external environmental conditions.

In order to understand sequence development and sea-level fluctuations during the late Middle Cambrian to early Furongian on the North China epeiric platform, the present study focuses on a unique, subtle erosion surface of an extensive (approx. 100 km), strongly deformed limestone bed in the uppermost part of the Gushan Formation, Shandong Province, China. The Gushan Formation and the overlying Chaomidian Formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments (e.g., deep subtidal, shallow subtidal, shoreface/shoal, subtidal microbial flat, and restricted platform interior). Three third-order depositional sequences (S1–3) are identified, each of which comprises a thin transgressive systems tract (TST) and a relatively thick highstand systems tract (HST). Each sequence is bounded by a drowning unconformity (SB1), a subaerial unconformity (SB2), or a surface of submarine erosion (SB3). The upper sequence boundary (SB2) of sequence 1 (S1) is represented by a subtle erosion surface of an extensive, deformed limestone bed with a wide variety of soft-sediment deformation structures (e.g., lime mudstone breccias, chaotic wacke-packstone laminae and fragments, homogenized oolites, and clastic dykes), and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed. The deformed limestone was formed during early diagenesis by differential deformation processes (brecciation, liquefaction/fluidization, and injection) which were most likely induced by pore-water overpressure during the period of rapid sea-level fall. Despite the lack of subaerial exposure features (e.g., paleokarst, paleosol, etc.), the characteristics of the erosion surface (cutting well-lithified sediment below), the missing of a significant geological record (the Prochuangia biozone), and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment. The missing of the Prochuangia biozone is most likely due to non-deposition at a subaerial hiatal surface. The erosion surface was submerged as a result of subsequent rise in sea level, where sporadic microbial buildups formed under suitable conditions. Freshly deposited, winnowed, shell-dominated transgressive lag deposits (containing Chuangia trilobite fragments, brachiopod shells, and abundant glauconite grains) formed with continued rise in sea level, which became, in turn, overlain by shale-dominated facies. The unique combination of the subtle erosion surface ( sensu stricto a subaerial unconformity) and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms.

This study focuses on the unique occurrence of an extensive microbialite bed (10–20 m thick) in the Chaomidian Formation (Furongian) in Shandong Province, China in order to understand its paleoenvironmental implications. The microbialite bed can be traced for over 6000 km2 in area. The microbialites are characterized by centimeter- to decimeter-scale branching maze-like constituents (maceriae) of microbial and muddy sediments with chaotic texture, including tabular maceriate microbialite (type 1), columnar maceriate microbialite (type 2), and columnar chaotic microbialite (type 3). Within the bed, each microbialite unit is generally well correlated for tens of kilometers. The entire bed is bounded by limestone–marlstone alternation at the base, and an erosional surface at the top that is subsequently overlain by a grainstone bed of various thicknesses. The microbialite bed formed when the seafloor reached suitable water depth for the microbial growth during sea-level rise accompanied with carbonate production. The maze-like maceria structures formed to acquire a larger surface area under a relatively large input of lime mud. The tabular maceriate microbialites initially formed in relatively deep-water environments and flourished on broad and flat seafloor, whereas the columnar microbialites (types 2 and 3) developed under the influence of strong waves and currents. The microbialite bed was eroded and terminated by frequent storm events and buried under the reworked grainstone. Further rise in sea level and increased metazoan activities afterwards limited the resurgence of microbes in the late Furongian.

The Cambrian succession in the North China Platform comprises a mixed carbonate-siliciclastic sequence, superbly exposed in the southern part of Shandong Province, China. In order to refine the lithostratigraphy of the Cambrian succession, this paper presents detailed sedimentary logs of outcrop sections in the Jinan, Laiwu, Jining, and Linyi areas. The entire succession consists of six lithologic units: Liguan, Zhushadong, Mantou, Zhangxia, Gushan, and Chaomidian formations in ascending order. The upper boundary of the Zhushadong Formation is refined as the base of the first purple mudstone bed of the Mantou Formation. The Mantou Formation is, in turn, bounded at the top by a thick oolitic grainstone bed of the Zhangxia Formation. The upper boundary of the Gushan Formation is placed at the base of a distinct bioclastic grainstone bed of the Chaomidian Formation. The constituent members of the Zhushadong, Mantou, and Chaomidian formations are also refined. Seventeen trilobite biozones are recognized, representing the Cambrian Series 2 to the Furongian.

Microbes started constructing shallow marine stromatolitic bioherms in the Archean, but they transferred their role as a major buildup maker to metazoans in Phanerozoic. Microbial buildups often recovered their predominance in the carbonate platform when reefal metazoan communities collapsed. Epiphyton , an extinct taxon of calcified microbe that possessed branching filamentous trichomes, was an important reef builder in the shallow marine carbonate platform during Middle Cambrian, aftermath of an extinction of archaeocyath sponges which were major reef-building sessile organisms in the Early Cambrian. Here we present direct evidence of phototropism of Epiphyton , found from fossilized behavior in micro- and macro-structures of meter-scale microbial bioherms of the Zhangxia Formation (Middle Cambrian), North China Platform, Shandong Province, China. The bioherms consist of stacked growth layers with the inner and outer divisions divided by distinct boundary. The inner division of growth layers of the Epiphyton bioherm is dominated by dense uniform bush-shaped Epiphyton thalli, whereas the curved outer division has layered texture normal to the surface, comprised of elongated and chambered thalli. It suggests that photosynthetic Epiphyton reacted actively to the spatial changes in intensity of sunlight, controlled by angle of illumination on the curved growth surface of the bioherm. The inner and the outer divisions comprise different morpho-types of Epiphyton . The spatial distributions of different morpho-types in variously illuminated divisions of Epiphyton might have caused further speciation of Epiphyton .

This study analyzes the structural development of the Gunsan Basin in the central Yellow Sea, based on multi-channel seismic reflection profiles and exploratory well data. The basin comprises three depressions (the western, central, and eastern subbasins) filled with a thick (ca. 6000 m) Cretaceous to Paleogene nonmarine succession. It was initiated in the early Cretaceous due to intracontinental extension caused by oblique subduction of the Izanagi plate under the Eurasian plate and sinistral movement of the Tan-Lu fault. The basin appears to have undergone transtension in the late Cretaceous–Eocene, caused by dextral movement of the Tan-Lu and its branching faults. The transtension was accommodated by oblique intra-basinal normal faults and strike-slip (or oblique-slip) movement of a NE-trending bounding fault in the northern margin of the central subbasin. The entire basin was deformed (NE–SW contraction) in the Oligocene when tectonic inversion occurred, possibly due to the changes in strike-slip motion, from right- to left-lateral, of the Tan-Lu fault. During the early Miocene, extension resumed by reactivation of the pre-existing normal and transpressional faults. A combination of extension, uplift, and erosion resulted in differential preservation of the early Miocene succession. At the end of the early Miocene, extension ceased with mild contraction and then the basin thermally subsided with ensued rise in sea level.

Some examples of a funnel-shaped structure filled with both angular and rounded clasts occur in a peloidal grainstone bed of the Chaomidian Formation (Late Cambrian) in the Jiulongshan area (Shandong Province, China). The clasts consist of peloidal grainstone which is the same as that of the walls of the funnels. The structures are interpreted as dykes formed by upward escape of pore water and/or fluidized sediment through a narrow conduit which was gradually widened by the force of the intruding fluid/sediment. The erosional capacity of the pressurized fluid/sediment mixture consequently diminished upwards, which explains the gradual decrease in intensity of fragmentation from the adjoining walls in this direction.

This paper focuses on the formative processes of limestone pseudoconglomerates in the Gushan and Chaomidian Formations (Late Cambrian) of the North China Platform, Shandong Province, China. The Gushan and Chaomidian Formations consist mainly of limestone and shale (marlstone) interlayers, wackestone to packstone, grainstone and microbialite as well as numerous limestone conglomerates. Seventy-three beds of limestone pseudoconglomerate in the Gushan and Chaomidian Formations were analysed based on clast and matrix compositions, internal fabric, sedimentary structures and bed geometry. These pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes (i.e. flat to undulatory disc, blade and sheet), marlstone and/or grainstone matrix and various internal fabrics (i.e. intact, thrusted, edgewise and disorganized), as well as transitional boundaries. Limestone pseudoconglomerates formed as a result of soft-sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth. Differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates. Initial deformation (i.e. burial fragmentation, liquefaction and injection) and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates. Burial fragmentation resulted from mechanical rupture of cohesive carbonate mud, whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials (liquefied carbonate sand and water-saturated argillaceous mud) under increased stress. Storm-wave loading was the most probable deformation mechanism, as an external triggering force. Subsequent re-orientation and rounding of clasts were probably prolonged under normal compactional stress. Eventually, disrupted clasts, along with matrix materials, were transformed into pseudoconglomerates by progressive lithification. Soft-sediment deformation is prevalent in alternate layers of limestone and mud(marl)stone and/or grainstone, regardless of their depositional environments.

This paper presents detailed facies and architectural analyses and palaeoenvironmental reconstruction of the Sihwa Formation (Lower Cretaceous), mid-west Korea, which comprises an about 3-km-thick non-marine succession containing abundant dinosaur eggshells. Based on constituent facies, bedset geometry, stacking pattern, and bounding surface characteristics, the entire succession can be classified into three architectural elements. Element I occurs along the basin margin and shows a monotonous stacking of tabular or crudely stratified conglomeratic units. It represents alluvial-fan deposits of debris-flow-dominated fan and sheetflood-dominated fan. Element II is characterized by multi-storey, sheet or upward-widening, conglomeratic channel-fills whose maximum thickness exceeds 1.5 m. Each channel-fill unit is encased within red–brown silty sandstones of Element III with sharp erosional bases but diffuse gradational upper boundaries. It consists generally of (1) cut-and-fill deposit (trough cross-stratified or openwork conglomerate) in the lower part and (2) composite low-relief bar deposit (lenticular conglomerate and stratified gravelly sandstone) in the upper part. Shallowness of each cut-and-fill unit, absence of fining-upward lateral accretion package and the predominance of simple-bar deposit collectively suggest deposition from ephemeral braided streams. Element III typically shows a fining-upward stacking of (1) single- or multi-storey small-scale ( The entire sequence of the Sihwa Formation can be divided into the alluvial-fan and terminal-fan successions. The alluvial-fan succession displays a progradational stacking pattern and indicates a low rate of basin subsidence in the initial phase of rifting. The upper terminal-fan succession consists of proximal braided stream and distal floodplain deposits in the western and central parts of the basin and is characterized by an axial dispersal pattern and an aggradational stacking. It suggests rapid subsidence of the basin floor during the main phase of rifting. The asymmetrical cross-basin distribution of each architectural element reflects a half-graben structure of the basin with steep-gradient fault-bounded eastern margin (footwall block) and gently sloped, flexural western margin (hangingwall block). The predominance of ephemeral braided-stream deposits along with red–brown fine-grained floodplain deposits with common calcretes indicates arid to semi-arid palaeoclimates. Approximately 140 dinosaur eggs (Faveoloolithidae and Dendroolithidae) were identified mainly from the (gravelly) siltstones and small-scale channel fills of Element III deposits and partly from the cut-and-fill conglomerates of Element II deposits. The eggs commonly retain their original oval shape but are invariably breached and stuffed with the substrate of gravels and silt. They are either isolated or clustered, forming a circular concentration in plan view. The abundant yield of eggs, more than 20 eggs in 5 separate nests from a single depositional unit, suggests a dense population of the parental dinosaurs. The repetitive occurrence in many stratigraphic horizons reflects site preference as a nesting habitat of the near-channel or abandoned channel areas.

The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.

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. Bus...

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.

This study focuses on the development of depositional systems in the southeastern Yellow Sea during the postglacial transgression, based on the analysis of closely spaced high-resolution seismic profiles (Chirp) and piston cores. Transgressive deposits comprise the paralic component of estuarine channel fills, seaward prograding wedge, and along-shore prograding mound, and the marine component of sand veneer, mud blanket, and offshore ridge. These transgressive deposits were developed through three distinctive stages in terms of possible sea-level position. During the early stage, tidal sand ridges and sand veneer formed south of Jeju Island, resulting from shoreface erosion associated with a relatively slow transgression. The following transgression, in the middle stage, inundated subaerially formed interfluves along the central part of the sea, and affected development of estuarine environments with increasing tidal regime in the eastern part of the sea. Combined with the strong tidal reworking, insufficient sand supply enhanced the formation of erosional ridges. Short-period increase in fluvial discharge affected the deposition of coastal wedge in the western part. Fine-grained sediments from either fluvial discharge or tidal reworking were dispersed seaward to form mud blanket. The late stage was characterized by the deposition of veneered sands off the Jiangsu coast, which was due to relatively slow rise in sea level. Further offshore, along-shore prograding mound was constructed by Huanghe-derived sediment influx, and subsequently eroded and redeposited by wave and tide activities, thus detached from the proximal source. The depositional processes and variability of the transgressive deposits in the southeastern Yellow Sea were largely controlled by changes in rate of sea-level rise during the transgression, most likely related to the global flooding events triggered by melt water pulses. The changes in shoreline configuration and oceanographic regime have also influenced the distribution and morphology of the transgressive deposits. A short-period increase in riverine discharge caused the temporal sediment progradation off the Jiangsu coast.

This study focuses on the depositional and deformational features of quartzite-shale and phyllite beds in the lower part of the Seochangri Formation, Okcheon Group, mid-Korea. Each quartzite unit (25–320 cm thick) is massive, whereas the overlying laminated shale unit (0.5–10 cm thick) is either homogeneous or slightly laminated. Although these interbeds were strongly deformed under brittle-ductile conditions (ca. 300°C), the quartzite units show a thickening-upward trend. The quartzite-shale interbeds represent deposition from turbidity currents, i.e., Bouma-A and-D/E divisions. The thickening-upward quartzite-shale units are suggestive of progradation of sand lobes in the middle-outer fan. The overlying phyllite beds with thin quartz interlayers most likely represent outer fan and basinplain environments. The Seochangri Formation in the Bonghwajae section forms a thrust front against the limestone and dolomite beds of the Joseon Supergroup in which the quartzite-shale units are overlain by the phyllite beds and, in turn, underlain by the folded limestone beds. The phyllite and limestone beds were strongly deformed, showing upright isoclinal to tight folds, sheath folds, and boudins. The fold axes generally trend north-northeast with a low plunge angle. The thrust front represents part of the restraining bend of a dextral fault, the South Korean Tectonic Line. It is the major structural discontinuity between the Okcheon Group (Proterozoic) and the Joseon Supergroup (Lower Paleozoic). The collisional offset between the Gyeonggi Massif (South China Block) and the Yeongnam Massif (Sino-Korean Block) most likely occurred in the Jurassic prior to the emplacement of the mafic dyke and amphibolite.

This study focuses on the sequence stratigraphy of the Pyeongan Supergroup (Carboniferous-Permian), central-eastern Korea. The supergroup consists of about 1700-m-thick siliciclastic deposits, disconformably overlying the Joseon Supergroup (Cambro-Ordovician). The entire succession is represented by thirteen sedimentary facies which can be organized into seven facies associations (FAs) and, in turn, three sequence units. Sequence 1 constitutes FAs 1, 2, 3, and 4. FA 1 consists of conglomerate, sandstone and shale facies, and is bounded by a sequence boundary (SB 1) at the base. The overlying purple siltstone with interbedded massive sandstone and carbonate grainstone (FA 2) formed on a coastal plain during sea-level rise, which is transitional upward into black shale and patchy bioturbated carbonate packstone (FA 3) of lagoonal environments. The transition from FA 1 to 3 represents relative sea-level rise with small-scale fluctuations, i.e., transgressive systems tract. FA 4 consists of cross-stratified conglomerate and massive sandstone with black shale which prograded over lagoonal area, forming highstand systems tract (HST). Sequence 2 consists of FAs 5 and 6. Sequence boundary (SB 2) occurs at the transition between FAs 4 and 5. FA 5 is characterized by cross-stratified coarse sandstone and purple fine sandstone to siltstone of fluvial plain environments. It represents rapid change in depositional environments from shoreface to fluvial system. FA 6 comprises upward-fining units (massive sandstone to dark gray siltstone), suggestive of restricted bay environments during relative sea-level rise. Due to an abrupt fall in sea level, the basin was closed with thick fluvial deposits (FA7). Sequence 3 comprises planar and trough cross-stratified coarse sandstone and partly bioturbated purple fine sandstone to mudstone (FA 7). The entire succession represents deposition of a second order cycle of sea-level rise and fall during the period between the Carboniferous and the Permian. A reconstructed relative sea-level curve is concordant with eustasy in the Carboniferous, but discordant in the Permian, implying that the influence of local tectonic movements was dominant in the Permian.

This study focuses on the sequence stratigraphic implications of the Taebaek Group (Cambrian–Ordovician), a mixed carbonate–siliciclastic sequence (ca. 1200 m thick), in the mideastern part of the Korean peninsula. The group contains 11 lithologic units (formations) that can be partitioned into four packages (supersequences I–IV). Each package comprises alternation of siliciclastic and carbonate successions, corresponding to the second-order sequence (supersequence) formed in a period of 10–100 m.y. Supersequence I (Jangsan/Myeonsan, Myobong, and Daegi fms) represents the initial inundation and subsequent drowning during the late Early to middle Middle Cambrian. It experienced the drowning between the middle and late Middle Cambrian, forming type-3 sequence boundary. Supersequence II (Sesong and Hwajeol fms) was formed by prolonged marine flooding during the late Middle and Late Cambrian. It was terminated by a large supply of siliciclastics due to the rejuvenation of the drainage basin, and the subsequent shallowing at the Cambrian–Ordovician boundary (type-2 sequence boundary). Supersequence III (Dongjeom, Dumugol, and Makgol fms) comprises the lowstand coarse-grained siliciclastics, transgressive shale by marine flooding, and shallow platform carbonates by highstand progradation in the Early Ordovician. Following the large-scale eustatic fall of sea level in the earliest Middle Ordovician, supersequence IV (Jigunsan and Duwibong fms) formed on the subaerial exposure surface (type-1 sequence boundary) by resumed marine flooding in the Middle Ordovician. This study provides basis for basin-scale correlation with the coeval sequences in northeastern China.

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.

This study focuses on the cyclic successions of the Dumugol Formation (Early Ordovician), Taebaeksan Basin, mideast Korea. The successions consist of meter-scale cycles, represented by alternation of shale- and limestone-dominated beds, and can be grouped into three cycle types: shale-lime-mudstone, shale-wacke/packstone, and shale-grainstone cycles. The meter-scale cycles most likely formed in shoreface and offshore transition zone where there was abrupt change between the depositional environments with siliciclastic-dominated sediment supply and carbonate-dominated sediment supply. The change most likely resulted from variations in clastic input and carbonate productivity during fourth- or fifth-order sea-level fluctuations accompanied with climatic changes. The cycles can be stacked into four third-order transgressive-regressive sequences, showing a systematic change in cycle thickness, cycle type, and intracycle facies proportion within a sequence. Each sequence is characterized by an upward-thickening to-thinning trend in cycle thickness, an upward-fining to— coarsening trend in cycle type, and an upward increase to decrease in proportion of shale-dominated facies. Sequence boundaries are picked out by a distinct surface (or zone) that shows a turnaround from gradual upward decrease to abrupt increase in cycle thickness and an abrupt shift in cycle type from shale-grainstone cycle to shale-wacke/packstone cycle. The sequence can be divided into transgressive and highstand systems tracts. The transgressive cycles are characterized by upward-thickening in thickness, upward-fining in cycle type, and higher and upward-increasing proportion of shale-dominated facies, whereas the regressive cycles are by upward-thinning, upward-coarsening, and lower and upward-decreasing proportion of shale-dominated facies. The systematic change in cycle thickness, cycle type, and facies proportion helps deduce the stacking patterns of the cycle units in the Dumugol Formation. The stacking pattern analysis suggests that the cycles are retrograded during rapid increase in accommodation and prograded during slow increase in accommodation. During relative fall of sea level, the platform sediments were affected by intense submarine erosion and redistribution, forming submarine hiatus.

Records of redox-sensitive elements (Mo, Cd, Cu, V and U), δ18O of planktonic foraminifera (δ18Opf), and organic carbon and biogenic opal contents in dark laminated mud (DLM) layers of the East/Japan Sea reveal relative role of primary productivity versus bottom-water stagnation for the formation of these layers during the last 25,000 years. Enrichments of redox-sensitive elements in these layers indicate that bottom waters were reduced during the formation of the lower DLM (22,500-15,00014C yr B.P.) and the upper DLM (10,400-10,20014C yr B.P.), probably to a greater extent in the lower layer. Anomalous low δ18Opf values and minimal contents of both organic carbon and biogenic opal suggest that bottom-water stagnation due to density-stratified water column could be more important than primary productivity for the lower DLM formation. In contrast, the relatively high contents of the organic carbon in the upper DLM invoke a primary role of enhanced productivity in the formation. This inference is, however, questioned by the absence of comparable increase in biogenic opal contents which is expected from generally coupled production of organic carbon and opal in surface water. The discrepancy between the organic carbon and opal records suggests that a bottom-water stagnation, which might have caused the preferential preservation of organic carbon in the reducing bottom-water condition, could be also more important than primary productivity for the upper DLM formation.

The lower Paleozoic sedimentary rocks in Korea, Joseon Supergroup, are mainly exposed in the Taebaeksan Basin. The Joseon Supergroup is a siliciclastic-carbonate succession that ranges from late Early Cambrian to Middle Ordovician in age. It can be subdivided into the Taebaek, Yeongwol, Yongtan, Pyeongchang, and Mungyeong groups, based on lithologic characteristics and geographic distribution. The stratigraphy of the Taebaek and Yeongwol groups is relatively well established due to prolific occurrence of trilobites and conodonts, whereas the latter three groups are poorly understood. The Taebaek Group comprises in ascending order the Jangsan/Myeonsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol, Makgol, Jigunsan, and Duwibong formations. The Cambrian-Ordovician boundary in the Taebaek Group can be drawn within the lowermost part of the Dongjeom Formation. The Yeongwol Group consists of the Sambangsan, Machari, Wagok, Mungok, and Yeongheung formations in ascending order. The Cambrian-Ordovician boundary in the Yeongwol Group has been placed at the base of the Mungok Formation. The trilobite faunal assemblages of the Taebaek and Yeongwol groups display a profound contrast in faunal contents, which resulted in two separate biostratigraphic schemes. A total of 19 biozones are recognized in the Taebaek Group comprises in ascending order theRedlichia, Elrathia, Mapania, Bailiella, Megagraulos, Solenoparia, Olenoides, Stephanocare, Drepanura, Prochuangia, Chuangia, Kaolishania, Dietyites, Eoorthis, Pseudokainella, Asaphellus, Protopliomerops, Kayseraspis, andDolerobasilicus zones. However, most of these biozones have not been well defined. On the other hand, the biostratigraphy of the Yeongwol Group is well established: from oldest to youngest, theMetagraulos sampoensis, Megagraulos semicircularis, Tonkinella, Lejopyge armata, Glyptagnostus stolidotus, G reticulatus, Proceratopyge tenuis, Hancrania brevilimbata, Eugonocare longifrons, Eochuangia hana, Agnostotes orientalis, Pseudoyuepingia asaphoides, Fatocephalus hunjiangensis, Yosimuraspis vulgaris, Kainella euryrachis, Shumaridia pellizzarii, andKayseraspis zones. Little attention has hitherto been paid to the Cambrian-Ordovician chronostratigraphy of the Taebaeksan Basin. The Taebaek area includes the Iyeonnaeian and Homyeongian series for the Cambrian and the Mungogian and Yemisanian series for the Ordovician. Stages for the Cambrian-Ordovician of the Yeongwol area are the Eodungolian, Deokuan, Bundeokchian, Gonggirian, Garamian, and maepoan stages in ascending order. The refined biostratigraphy and chronostratigraphy provide an enhanced and more reliable correlation with coeval units elsewhere.

A detailed facies analysis of core sediments from the Ulleung Interplain Gap (UIG) reveals ten sedimentary facies which reflect a variety of sedimentary processes: volcaniclastic high-concentration sediment gravity flows, low-density turbidity currents, pelagic settling under either well or poorly oxygenated bottom-water conditions, marine fallout of tephra, hampered sedimentation by bottom currents, top-truncation of turbidites by bottom-current reworking, and Mn-carbonate precipitation under changing bottom-water oxygenation states. Distribution of the facies in the cores, integrated with echo characters of high-resolution subbottom profiles, delineates spatial and temporal changes in sedimentary processes, influenced by variations in bottom-current activity during the late Quaternary. The glacial (> ∼15 ka) sediment units from the Ulleung Interplain Channel (UIC), an erosional axial channel system in the UIG, consist mainly of manganiferous and muddy contourites, interbedded with coarse-grained volcaniclastic turbidites or debrites and non-bioturbated pelagites. This indicates prevalent activity of bottom currents, rarely interrupted by volcaniclastic high-concentration sediment gravity flows and deep-water stagnations which resulted in anoxic bottom-water conditions. On the other hand, the glacial units of the southeastern margin of the UIC, where upslope migrating sediment waves developed, are generally dominated by alternating fine-grained turbidites and bioturbated or non-bioturbated pelagites. This suggests that frequent turbidity currents derived from upslope mass wasting were responsible for the generation of the sediment waves. The post-glacial (

This review focuses on the depositional processes of late Quaternary sediments in the eastern Yellow Sea, an epicontinental sea with a flat and broad seafloor (less than 100 m in water depth) and extensive tidal flats along the southeastern coast. The Yellow Sea was subaerially exposed during the last glacial period when sea level was about 120 m below the present level. During erosional retreat of shorefaces and river mouths, sedimentation was largely controlled by high-amplitude rise in sea level, forming transgressive sheets (echo type 1–3a) and sediment ridges (echo types 2-1 and 2–2) with extensive development of ravinement surfaces. The distribution of surface sediments reflects an interplay of sediment input from the surrounding landmass and the hydrodynamic regime in response to sea-level rise. Muddy sediments in the central part represent the Huanghe-River source and form a highstand sheet (echo type 1–3b). Large birdfoot-like sand bodies off the Jiangsu coast also represent highstand deposits when sea level reached the present position at about 6 ka. In the southeastern part of the Yellow Sea, sediments are dominated by sand ridges (echo types 2-1, 2–2 and 2–3), largely shaped by tidal currents. The southwestern corner of the Korean Peninsula is dominated by a thick deposit of mud, the Heuksan mud belt. The muds largely originate from the Geum River, whose distribution is controlled by strong southward coastal currents. In the coastal regions of the southeastern Yellow Sea, sedimentation is controlled by a combined effect of waves and tides with distinctive season-alities in sedimentary facies owing to the monsoonal climate: tidedominated mud deposition in summer and wave-dominated sand deposition/erosion in winter: Winter storms play a role in sedimentation on intertidal flats. Quantitative monitoring of sediment transport suggests that the textural variation results from the overwhelming role of winter waves superimposed on tidal currents in pulling sands and resuspending muds. Due to low sedimentation rate, the tidal flats formed retrogradational, coarsening-upward pattern during the Holocene sea-level rise.

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.

The Ulleung Interplain Gap (UIG) is a deep (2300–2700 m) passage which has served as a conduit for deep-water circulation between the Ulleung and Japan basins. A detailed analysis of Chirp (2–7 kHz) subbottom profiles (ca. 6270 linekm) and nine sediment cores (8.6–11.4 m long) together with age data of tephra layers and four AMS 14 C from the UIG and the adjacent areas reveals complex sedimentation caused by an interaction between bottom currents and mass flows during the lastand post-glacial periods. From high-resolution subbottom data, rock basement, slide/slump/rock-fall deposits, mass-flow chutes/channels, mass-flow deposits, bottom-current deposits, and a large-scale bottom-current channel system are recognized. Core sediments consist of various deposits of turbidites, muddy contourites, manganiferous contourites, and pelagic/ hemipelagic sediments. Based on vertical distribution of sedimentary facies together with a chronostratigraphic framework, core sediments can be divided into Units I ( f15 ka). The extensive mass-flow deposits with slope failures on the entire slopes of topographic highs around the UIG and the dominant turbidites in Unit II (>f15 ka) suggest that a relatively large amount of sediment was delivered into the UIG by frequent mass flows (recurrence intervals of ca. 250–500 years in the upper Unit II) during the last-glacial period. Erosion or hampered sedimentation by bottom currents is indicated by the truncated reflectors of channel walls and muddy/manganiferous contourites in the Ulleung Interplain Channel (UIC) along the UIG. Interbedded turbidites in the UIC floor reflect that some large-scale mass flows intermittently entered into the UIC. The UIC has an asymmetric channel-flank geometry. The southeastern flank shows a gentle, wide mound morphology of mass-flow deposits derived from large-scale slope failures on the slopes of the Oki Bank, reflecting a dominance of downslope gravitational processes over alongslope bottom currents. In contrast, the northwestern flank is characterized by a narrow, steep geometry of mass-flow deposits, where a relatively small amount of sediment derived from the slopes of the South Korea Plateau could not overcome bottom-current activity. The dominant muddy and manganiferous contourites with rare turbidites in Unit I (

In a broader application of sequence stratigraphic concept to a tectonically active margin setting, this study presents a sequence model that considers all three controls on sequence development (i.e. eustasy, tectonic movement and sediment supply) as independent variables. The model introduces six sequence types (A to F) including type 1 and type 2 sequences defined in the original Exxon scheme. Each sequence shows a variety in number and stacking pattern of its constituent parasequence sets reflecting combined effects of accommodation change and sediment supply. This model is applied to a seismic sequence analysis of the shelf–slope system (middle to upper Miocene) in the southwestern margin of Ulleung Basin which has experienced significant crustal deformation during the Tertiary back-arc opening and subsequent closing of the East Sea (Sea of Japan). The model application delineates four sequence types whose development is closely associated with the tectonic evolution of the Ulleung Basin margin. During the back-arc opening (early to middle Miocene), type A and B sequences were emplaced as a result of steady creation of accommodation space due to a rapid subsidence combined with a tectonic-controlled high to moderate rate of sediment supply. The sequences associated with the extensional tectonism are characterized by active progradation and aggradation without forced regressive phases. In the initiation stage of back-arc closure (middle to late Miocene), subsidence rates were significantly reduced because of a widespread contractional deformation, while subaerial erosion of the uplifted thrust belt resulted in an increase in sedimentation rate. As a result, steady prograding type-E sequences were formed by alternating normal and forced regressions. During the quiescent phase of back-arc closure in the late Miocene, rise-dominant fluctuating relative sea-level change and moderate to low sediment supply gave rise to type-F sequences (similar to type-1 sequences of the Exxon group) reflecting a major control of eustatic sea-level change.

Isolated sponge bioherms are documented from the Lower Ordovician Makkol Formation of the Taebaek Group in the Taebaeksan Basin, mideast Korea. They are formed by an association of a lithistid spongeArchaeoscyphia, a receptaculidCalathium and stromatolitic algae, and share many features with the Lower Ordovician buildups known elsewhere. These bioherms were established in an incised bottom and reached up to about 1 m in height. As the bioherms grew upward, they were more severely affected by intense wave action and frequent storms, which eventually perished the bioherms. The occurrence ofArchaeoscyphia-Calathium association suggests a close biogeographic link between Korea and North China, supporting the paleogeographic model that the Taebaeksan Basin was connected through contiguous shallow waters to North China in the early Paleozoic.

The Kyokpori Formation (Cretaceous), south-west Korea, represents a small-scale lacustrine strike-slip basin and consists of an ≈ 290 m thick siliciclastic succession with abundant volcaniclasts. The succession can be organized into eight facies associations representing distinctive depositional environments: (I) subaqueous talus; (II) delta plain; (III) steep-gradient large-scale delta slope; (IV) base of delta slope to prodelta; (V) small-scale nested Gilbert-type delta; (VI) small-scale delta-lobe system; (VII) subaqueous fan; and (VIII) basin plain. Facies associations I, III and IV together constitute a large-scale steep-sloped delta system. Correlation of the sedimentary succession indicates that the formation comprises two depositional sequences: the lower coarsening- to fining-upward succession (up to 215 m thick) and the upper fining-upward succession (up to 75 m thick). Based on facies distribution, architecture and correlation of depositional sequences, three stages of basin evolution are reconstructed. Stage 1 is represented by thick coarse-grained deposits in the lower succession that form subaqueous breccia talus and steep-sloped gravelly delta systems along the northern and southern basin margins, respectively, and a sandy subaqueous fan system inside the basin, abutting against a basement high. This asymmetric facies distribution suggests a half-graben structure for the basin, and the thick accumulation of coarse-grained deposits most likely reflects rapid subsidence of the basin floor during the transtensional opening of the basin. Stage 2 is marked by sandy black shale deposits in the upper part of the lower succession. The black shale is readily correlated across the basin margins, indicating a basinwide transgression probably resulting from large-scale dip slip suppressing the lateral slip component on basin-bounding faults. Stage 3 is characterized by gravelly delta-lobe deposits in the upper succession that are smaller in dimension and located more basinward than the deposits of marginal systems of the lower succession. This lakeward shift of depocentre suggests a loss of accommodation in the basin margins and quiescence of fault movements. This basin evolution model suggests that the rate of dip-slip displacement on basin-margin faults can be regarded as the prime control for determining stacking patterns of such basin fills. The resultant basinwide fining-upward sequences deviate from the coarsening-upward cycles of other transtensional basins and reveal the variety of stratigraphic architecture in strike-slip basins controlled by the changes in relative sense and magnitude of fault movements at the basin margins.

A detailed analysis of Chirp (2–7 kHz) subbottom profiles and a long (ca. 10 m) piston core reveals origin of deep-water sediment waves in the Ulleung Interplain Gap (UIG). On the basis of acoustic and lithologic characters, the sediments are divided into two units: 1) upper transparent unit (UTU) and 2) lower wavy stratified unit (LWSU). The LWSU is characterized by a few regular wavy reflectors with upslope migration. Also, it gradually decreases downslope in wave height, wave asymmetry and thickness, and consists dominantly of fine-grained turbidites with subordinate pelagic and hemipelagic sediments. These sedimentary features indicate that the LWSU was most likely generated by turbidity currents, rather than bottom currents. The UTU, discordant to the reflectors of the underlying LWSU, mostly comprises muddy contourites and managniferous contourites with rare fine-grained turbidites, reflecting intensified bottom-current activity and infrequent input of turbidity currents from the slopes of the Oki Bank and Dok Island. Under these conditions, a thin (3–6 m thick), elongate mound of bottom-current deposits (UTU) formed on the fine-grained turbidity current waves (LWSU).

In the Hunghae Formation of the Pohang Basin, some heavily armored, calcareous mudstone balls (boulders) occur in a chaotic conglomerate bed which was deposited from debris flow on a steep slope. Sparsely armored or unarmored mudstone balls are also found in the same bed. Also some isolated armored mudstone boulders occur in a homogeneous mudstone bed of the formation which is interpreted as hemipelagite. The armored mudstone balls were most likely formed by retrogressive failures of submarine channel or scar wall and subsequent rolling over sand and pebble pavement along the submarine channel floor prior to incorporation into the debris flow. Their occurrence also suggests that a large-scale slumping should be happened on the upper slope apron or lower prodelta including the submarine channel and be evolved into debris flows, resulting in the corporation of the boulders into them. Some armored mud boulders rolled along and passed away the channelized gravel pavement, and deposited on hemipelagic mud in lower slope, not having been reworked.

Large amounts (45390 line km) of closely spaced (2.2–4.4 km) high-resolution subbottom profiles (Chirp, 2–7 kHz) made it possible to identify detailed echo types and their distribution in an epicontinental shelf environment. On the basis of seafloor morphology, surface bedforms and subbottom acoustic characters, 10 echo types were identified in the uppermost sedimentary sequence of the central-eastern Yellow Sea. Flat seafloor with sharp bottom echoes (echo types 1-1, 1-2 and 1-3a; transgressive sediment sheets or relict sands) is widespread in the offshore area and underlain to the west by an acoustically transparent wedge (echo type 1-3b; highstand muds). Mounded seafloor with either smooth surface or superposed bedforms (echo types 2-1, 2-2 and 2-3; tidal ridges) and flat seafloor with regularly spaced, wavy bedforms (echo type 1-4; large-scale dunes) are dominant in the eastern nearshore area. Large-scale mounds with continuous, inclined internal reflectors (echo type 2-4; giant mud bank) occur in the southeastern nearshore area. Various-scale eroded seafloor (echo types 3-1 and 3-2; channels) and flat seafloor with regularly spaced, wavy bedforms (echo type 1-4; large-scale dunes) are present in the northern part of the sea. The distribution pattern of echo types in the central–eastern Yellow Sea reflects depositional processes and sediment dispersal systems during the Holocene transgression and highstand period: (1) development of tidal ridges and large-scale dunes in response to strong tidal currents and waves in the eastern nearshore area; (2) construction of transgressive to highstand mud bank (Huksan mud belt) by deposition of muds derived from the Keum river in the southeastern nearshore area; (3) active erosion due to intensified currents in the northern part; and (4) highstand mud deposition derived from the Huanghe river on the transgressive sediment sheets in the offshore area.

This study presents an evolutionary history of the southwestern Ulleung Basin margin on the basis of sequence stratigraphic and structural analyses of multi-channel seismic reflection profiles. Ten sequences and geologic structures identified in the late Tertiary strate suggest three distinct stages of basin development in the early Miocene to Pliocene. In the early Miocene, the basin, bordered on the west by a steep basement fault with normal sense of offset, experienced a rapid subsidence giving rise to a deep-marine depositional setting. The movement of the basin-bordering fault ceased at the end of the early Miocene, then the basin subsidence progressively slowed, which, coupled with increased terrigenous sediment input, resulted in the development of prograding shelf margin. In the late middle to late Miocene time (12.5–5.5 Ma), the basin was characterized by compressional readjustment by thrusting and folding. The sequential effects of this tectonic event include local and regional angular unconformities, progradation-dominant shelf-margin depositional system and frequent triggering of large-scale mass-failures in front of the thrust belt. Since the early Pliocene, the basin has progressively subsided again, forming aggradation-dominant shelf-slope system.

In the mid-eastern Yellow Sea, late Pleistocene–Holocene glacio-eustatic sea-level fluctuations and a local subsidence regime have formed an aggradational set of high-resolution sequences (sequences I–V in descending order). Extensive tidal scour-and-fill processes during transgressions played a significant role in marked partitioning of non-marine to paralic clast-rich lowstand systems tract (LST) and tidal fine-grained transgressive–highstand systems tract (TST–HST) within each sequence. The lateral extent and thickness of sequences and component systems tracts reflect differences in magnitude and duration between eustatic sea-level cycles. Sequence V is characterized by extensive LST, indicating sea-level fall to the shelf-margin area. Sequences IV and III display a limited extent of LST, reflecting small-scale sea-level falls during the late Pleistocene. Sequence II displays seaward restriction of TST–HST owing to a small-scale sea-level rise prior to the last glacial maximum (LGM). Sequence I has formed since the LGM and is characterized by discontinuous TST–HST over the entire shelf area, reflecting rapid retreat of sediment sources during the post-glacial sea-level rise. Along with the predominant controls of local subsidence, glacio-eustasy and transgressive tidal dynamics on the overall stratal architecture, minor variations in architectural characteristics were added by other local factors such as changing sediment flux, antecedent topography and basin physiography.

The South Korea Plateau is a complex of ridges, seamount chains, troughs and a basin. Detailed analysis of 12 019 line-km Chirp (2–7-kHz) subbottom profiles from the South Korea Plateau and the eastern continental slope of Korea reveals a distinctive zonal distribution of echo types depending systematically on seafloor morphology. Pelagites/hemipelagites (type I-2) and basement highs (type III-1) prevail on the ridge summits, seamount chains and the upper to middle part of the eastern continental slope of Korea, and are commonly bounded downslope by creeps (type III-3) and slides/slumps (type IV-1) that occur extensively over the entire slope areas of the ridges, seamount chains and eastern continental slope. The mass-movement deposits change downslope to debrites and turbidites (types II, III-2, IV-2 and IV-3) in the troughs and Onnuri Basin, suggesting successive downslope evolution from slide and slump to debris flow and turbidity current. The voluminous creeps, slides and slumps over the entire slope areas of the plateau and eastern continental slope, deeper than 300 m in water depth, were most likely generated by frequent seismic shakings.