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Notes: The Maesan fan-delta-fed slope system in the Miocene Pohang Basin occurs between two Gilbert-type fan deltas. Detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies. These facies can be organized into three facies associations, representing distinct depositional environments: alluvial fan (facies association I), steep-faced slope (facies association II), and basin plain (facies association III). Subaerial debris flows and dense, inertia-dominated currents were transformed into subaqueous sediment gravity flows in steep-faced slope environments. Further downslope, these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels (or chutes). Interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone, deposited by suspension settling of fine-grained materials. Part of the steep-faced slope deposits experienced large-scale slides and slumps. The chutes/channels, lobes and splays on the steep-faced slope of the Maesan system are similar to those in modern subaqueous coarse-grained fan-delta systems.

Notes: The Ilchulbong mount of Cheju Island, South Korea, is an emergent tuff cone of middle Pleistocene age formed by eruption of a vesiculating basaltic magma into shallow seawater. A sedimentological study reveals that the cone sequence can be represented by nine sedimentary facies that are grouped into four facies associations.Facies association I represents steep strata near the crater rim composed mostly of crudely and evenly bedded lapilli tuff and minor inversely graded lapilli tuff. These facies suggest fall-out from tephra finger jets and occasional grain flows, respectively. Facies association II represents flank or base-of-slope deposits composed of lenticular and hummocky beds of massive or backset-stacked deposits intercalated between crudely to thinly stratified lapilli tuffs. They suggest occasional resedimentation of tephra by debris flows and slides during the eruption. Facies association III comprises thin, gently dipping marginal strata, composed of thinly stratified lapilli tuff and tuff. This association results from pyroclastic surges and cosurge falls associated with occasional large-scale jets. Facies association IV comprises a reworked sequence of massive, inversely graded and cross-bedded (gravelly) sandstones. These facies represent post-eruptive reworking of tephra by debris and stream flows.The facies associations suggest that the Ilchulbong tuff cone grew by an alternation of vertical and lateral accumulation. The vertical buildup was accomplished by plastering of wet tephra finger jets. This resulted in oversteepening and periodic failure of the deposits, in which resedimentation contributed to the lateral growth. After the eruption ceased, the cone underwent subaerial erosion and faulting of intracrater deposits. A volcaniclastic apron accumulated with erosion of the original tuff cone; the faulting was caused by subsidence of the subvolcanic basement within the crater.

Notes: Abstract 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.

Notes: The lower part of the Jangki Group (Miocene), SE Korea consists of pyroclastic mass-flow-dominated facies and epiclastic stream-flow-dominated facies which reflect sedimentation during syn- and intereruption periods, respectively. On the basis of pyroclastic composition, sedimentary structures and bed geometry, they are organized into two facies associations: (1) dacitic and basaltic debris-flow and hyperconcentrated-flood-flow deposits of eruption periods, and (2) epiclastic stream-flow and interchannel deposits of intereruption periods. The lateral relationship between the syn- and intereruption deposits varies significantly over short distances (2 km). In the western part of the study area, syneruption deposits are predominant, and fluvial deposits occur as small-scale channel-fill gravelstone bodies encased within dacitic debris flow deposits. In the eastern part, however, intereruption deposits are dominated with thick sequences of interbedded channel and interchannel deposits. The abrupt lateral change indicates alternation of epiclastic axial fluvial system with pyroclastic-rich volcaniclastic aprons. The syneruption deposits are enriched in vitric ash but lack contemporary volcanic rock fragments (dacitic or basaltic). They are sharply differentiated from intereruption deposits that mostly consist of epiclasts and are deficient in vitric ash. The vertical transition suggests that streams drained a hinterland of igneous basement rocks during intereruption periods and became bulked with pyroclasts during syneruption periods.

Notes: A synthesis of high-resolution (Chirp, 2–7 kHz) seismic profiles in the South Korea Plateau reveals that large masses of wavy stratified sediment (≈60–90 m thick) cover broad, gently sloping (〈0·5°) ridges in water depths of 1000–2000 m. The wavy stratified sediment (WSS) is characterized by wavy (0·2–5 km in wavelength and 〈15 m in relief), continuous reflective layers with a basal deformed zone that overlies undeformed, strong reflectors. The WSS exhibits systematic variation in wave dimensions and thickness of internal reflective layers with changes in slope gradient. The troughs of the waves are commonly associated with internal growth faults, and wave amplitude generally increases with subbottom depth. On steep slopes around the ridges, the WSS masses are bounded downslope by slide and slump deposits including slightly translated or rotated WSS blocks. The acoustic and geometric characters, and association with downslope slides and slumps on the steeper slopes, suggest that the WSS masses were most probably formed by slow creep movement before slope failure. In the absence of significant sediment input to the South Korea Plateau, the deep (1000–2000 m in water depth) mass movements were probably triggered by earthquakes that have occurred frequently in this region. Some slightly displaced, intact WSS blocks in the associated slides and slumps downslope reflect a progressive evolution from submarine creep into slide and slump.

Notes: The Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south-western Korean Peninsula. It comprises an approximately 400-m-thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations.Facies association I is characterized by thick homogeneous brownish siltstone, wedge-shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining-upward cycles. Some facies units are low-angle trough cross-bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high- and low-concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism.The Uhangri sequence generally shows a fining-upward trend with a transition from alluvial fan fringe, coarse-grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the oblique-slip mobile zone.

Notes: The Songaksan mount in the southwestern part of Cheju Island, Korea, is a Taalian tuff ring produced by phreatomagmatic explosions at an aquifer. A detailed analysis of proximal-to-distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies; one lateral facies sequence (LFS) and three vertical facies sequences (VFS).The VFS 1 and 2 are representative of facies relationships in horizontal near-vent deposits. The VFS 1 comprises scour-fill bedded tuff, inversely graded tuff, massive tuff and laminated tuff from base to top. The VFS 2 is a variant of the VFS 1, replaced by an inversely graded lapilli tuff unit at the base. The sequences suggest traction carpet, suspension and minor traction sedimentation from a high-concentration near-vent base surge.The LFS 1 and the VFS 3 are distilled from outward-dipping flank deposits. Both sequences begin with disorganized lapilli tuff, followed successively by stratified (lapilli) tuff, dune-bedded (lapilli) tuff, very thinbedded tuff and accretionary lapilli. They are suggestive of waning base surge which decreases in particle concentration, suspended-load fall-out rate and flow regimes with an increase in traction and sorting.These facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space. A near-vent base surge is turbulent, uniformly mixed and highly concentrated and produces scour-fill bedded tuff. As capacity decreases, the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part (gravity transformation), depositing inversely graded, massive and normally graded (lapilli) tuff. Ensuing loss of sediment load and mixing of ambient air result in flow dilution (surface transformation). Stratified and dune-bedded units are produced by tractional processes of turbulent and low-concentration surge. Further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension.

Notes: Abstract A detailed analysis of high-resolution seismic data (Chirp, 2–7 kHz) in the Ulleung Basin reveals spatial variation in echo characteristics and geometry of large-scale debris lobes. In the proximal part, the debris lobes are dominated by hummocky surface echoes and gradually transitional downslope to seafloor-tangent hyperbolic and smooth prolonged bottom echoes, reflecting progressive decrease in size, spacing, and relief of surface forms. The strongly convex-upward upper surface with steep blunt margins in the proximal part is gradually transitional downslope to slightly convex- upward or nearly flat form with less blunt margins. The gradual downslope decrease in both scale and spacing of surface forms and convexity of upper surface within each debris lobe is suggestive of progressive dilution in flow concentration within a debris flow, probably due to mixing of ambient water and removal of suspended sediment by deposition during downslope movement.

Notes: Abstract Parallel laminated, graded, and homogeneous muds of turbidity current origin are the predominant facies in the non-fan slope-centered Ulleung marginal basin during the last glacial period. Dilute turbidity currents were probably generated from slumps, slides, and debris flows on the slope. A mid-slope core contains poorly sorted mud-clast muds of debris flow origin. During the period of 75,000 and 10,000 years BP, turbidity currents occurred approximately every 125 years, each depositing about 0.5 km3 of mud with an accumulation rate of up to 40 cm/103 years. The basin was largely suboxic with a rare incursion of bottom currents.

Notes: Abstract  Major variations in type and rate of tectonic movement in the southwestern margin of the Ulleung Basin coincide in time with changes in stratal patterns at succession boundaries, suggesting that the effect of tectonism was dominant for the development of sequence architecture. During the back-arc opening (16–12 Ma), the rise of relative sea level and the high rate of sediment supply gave rise to sequences with sigmoid progradational patterns. During the back-arc closing (12–6.5 Ma), fall- and rise-dominated relative sea-level fluctuations resulted in sequences with varying stratal patterns depending upon changes in deposition rate. The rise-dominated relative sea level has been prevalent during the later stage (6.5 Ma–Present) with low sedimentation rate.