Tidal Ridges Research Articles

Alternating patterns of cross-shelf suspended sediment transport in the northern East China Sea in winter

Suspended sediment transport across the continental shelf is a key process for the materials exchange between coastal seas and the deep ocean. The cross-shelf transport through the Yangtze Shoal in the northern East China Sea (ECS) exhibits a unique pattern, which is characterized by alternations between high and low values in suspended sediment concentration (SSC). This study is conducted to reveal the underlying mechanisms and their effects on sediment fluxes. Surface SSC retrieved from GOCI data are combined with in situ observations of concentration and particle sizes of suspended sediment to study the temporal and spatial variations of the SSC in the Yangtze Shoal. Additionally, a numerical model for examining ocean circulation based on the FVCOM is established to display the hydrodynamic feature in the study area. The alternating SSC pattern is closely related to the topography of three ridges and two troughs. High SSC with fine particle size can be found over the ridge, while low SSC is detected at the surface layer of water in the trough. Even during the flood and ebb tides, this alternating pattern of high and low SSCs does not change, except for the expansion and contraction of coverage areas of high SSC. The high SSC near the tidal ridge should have resulted from the combined effect of resuspension and upwelling since the stronger bottom shear stress and a surface divergence that may induce an upwelling can be found in this area. Combined with the simulated current, the sediment transport flux between ridges and troughs is estimated. The sediment flux in the ridge is substantially increased than that in the trough, especially during the flood maximum and ebb maximum time. The contribution of suspended sediments from the Yangtze Shoal to the Southwestern Cheju Island Mud (SCIM) is relatively small during the normal weather in winter. However, cross-shelf transport can be remarkably strengthened by strong northerly winds in winter. This work puts forward a detailed cross-shelf transportation process induced by topography.

A new interpretation for the Pliensbachian Cook Formation (northern North Sea) as north–south-prograding tidal deltas and shelf ridges in the Early Jurassic Seaway: new model of linkage to the Norwegian Sea

Abstract The Lower Jurassic Cook Formation reservoir is a hydrocarbon-prolific unit that produces from several fields in the northern North Sea. For 40 years this formation has been interpreted as a westward-prograding deltaic unit sourced from Norway. Despite numerous discoveries, exploration targeting this unit has been hampered by well failures with lack of reservoir sand, discouraging companies from further exploration of this play. During a current re-evaluation of the process sedimentology of the Norwegian offshore basins, the Cook Formation is now interpreted as the middle to distal reaches of a very large, north-to-south-oriented delta system, variably confined within the Early Jurassic Seaway running from the Norwegian Sea into the northern North Sea. The Cook Formation is a subaqueous delta built southward during regression, whereas several internal transgressive phases produced sands that were reworked as north–south-oriented, shelf tidal ridges. The tidal ridges of the Cook Formation constitute some of the best reservoirs and are elongated with stacked, well-sorted, cross-bedded sandstone sets with mudstone drapes. Both the elongate tidal sand-ridges and intervening mudstone-rich, inter-ridge zones are proven by numerous well observations and illustrated by seismic amplitudes. In contrast to earlier eastern derivation models, these new results for the depositional system of the Cook Formation better explain the Cook well successes and failures in the northern North Sea. This work also strongly suggests that the tide-dominated subaqueous delta to transgressive-ridge system of the Cook Formation is spatially linked with the time-equivalent shorelines, subaerial tidal deltas and estuaries of the Tilje Formation in the Haltenbanken region to the north. The Tilje Formation deltas built into the Early Jurassic Seaway due to rift-initiation and rift-shoulder uplift, drained southwards and spilled eventually into the northern North Sea, becoming the entirely subaqueous Cook Formation. The relatively narrow seaway enhanced the tidal currents and suppressed wave activity, resulting in Cook subaqueous delta lobes and ridges without any delta-top facies. Overall, this elongate and extensive, Pliensbachian deltaic to estuarine system of the Early Jurassic Seaway off Norway competes in scale with some of Earth's largest present-day deltas.

Soil Physical Characteristics and Saturated Hydraulic Conductivity in the Landform of Barito Delta, Kalimantan, Indonesia

We explore the soil physical characteristics in wetland of Barito Delta from primary data of soil sample and electrical resistivity measurement with the support from some secondary data. We also estimate saturated hydraulic conductivity (Ks) in Barito Delta from soil physical characteristics applying Saxton and Rawls (1986) and Weynants et al. (2009). Soil texture profile is determined from interpolation of soil fraction in each layer applying Bayesian statistics to analyze soil physical characteristics in the landforms of Delta. Clay is the dominant soil fraction in the soil of Barito Delta. Clay fraction percentage decrease along the depth of soil profile as it reaches fine sand particles deriving from ancient sedimentation from the past. It is an opposite with soil organic matter content that has contrast value from 1st to 2nd soil depth, but a few discrepancy from 3rd depth to downward direction. The content of clay in the soil depends on the sedimentation activity in the landform. Clay is dominant soil particle in the Delta; in case, it is in flat area and there is no intensive of sea water sedimentation such as in Basin of Peat Anticline and Natural Levee. In more than 2 m depth of soil, loamy sand and silty clay textures are mostly in the landform that is influenced by sea water activity, while by river water is clay loam. Ks values from Saxton and Rawls (1986) are close to Ks values from the measurement of previous studies. Ks values are generally small in Barito Delta that is mostly ranging from 1.10−7 to 2 m s−1. Ks values are larger following the depth of soil profile. The values of Ks are smaller in Basin of Peat Anticline and Natural Levee than in Tidal Flat and Beach Ridge. It is because both landforms have clay as dominant soil particles.

New insights into the formation of submarine glacial landforms from high-resolution Autonomous Underwater Vehicle data

Autonomous Underwater Vehicles (AUVs) deployed close to the seafloor can acquire high-resolution geophysical data about the topography and shallow stratigraphy of the seabed, yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction. Here, we present multibeam echo-sounding, side-scan sonar, sub-bottom profiler and High-Resolution Synthetic Aperture Sonar (HISAS) data acquired during three AUV dives on the northeast Antarctic Peninsula continental shelf. These data enable glacial landforms, including mega-scale glacial lineations (MSGLs), grounding-zone wedges (GZWs) and iceberg ploughmarks, to be imaged at a horizontal resolution of a few tens of centimetres, allowing for the identification of subtle morphological features. We map tidal ridges that are interpreted as having been formed 1) along the ice-sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles, and 2) by the tidally driven motion of grounded or near-grounded icebergs. These data also enable the mapping of small GZWs that show the location of short-term still-stands or re-advances of the ice-sheet grounding zone. No meltwater channels are identified from our data, suggesting that free-flowing meltwater may not be essential for the formation of GZWs or MSGLs. The examples presented here show how high-resolution AUV-derived geophysical data provide a step-change in our ability to image seafloor glacial landforms, enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales.

Morphological Characteristics of Low-angle Dunes on a Tidal Ridge, the Jiangsu Macrotidal Coast, China

Wang, L.; Yu, Q.; Zhang, Y., and Gao, S., 2020. Morphological characteristics of low-angle dunes on a tidal ridge, the Jiangsu macrotidal coast, China. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 717-721. Coconut Creek (Florida), ISSN 0749-0208.Subaqueous dunes are typical flow-transverse rhythmic bedforms in fluvial, intertidal and marine environments. The low-angle dunes (LADs), commonly associated with a leeside angle of less than 15°, differ in terms of the formation mechanism from the high-angle dunes (HADs). Here, multibeam echosounder exploration and seafloor surficial sediment sampling were carried out on a tidal sand ridge off the Jiangsu coast, China, a macrotidal area with the spring tidal range exceeding 6 m. The spatial distribution of the dune morphological parameters, including wave height, wavelength, asymmetry, and lee-side angle, are analyzed in association with the water depth and seafloor sediment. The following results are obtained. (1) Two-dimensional linear dunes are superimposed on the tidal ridge, and a total of 3599 dunes detected are all LADs with an average maximum leeside angle of 5.46°. (2) The spatial distribution of the dune parameters is closely related to the topography of the ridge-swath system. The asymmetries and migration directions of the dunes on the northern and southern slopes of the tidal ridge are opposite, indicating a clockwise residual sand circulation, while the ridge represents the transition zone with relatively symmetrical dunes. (3) Water depth is the controlling factor for the dune geometry in shallow water places. In areas where water depth is below 7.5 m and the seafloor sediments are composed of pure sand, the scales of LADs are proportional to the water depth. (4) Bed sediment composition becomes important for the deeper water areas. For water depth more than 7.5 m, the ratio of cohesive particles (< 8 µm) of bed sediment, which increases with the water depth, inhibits the growth of the LADs. These observations reveal the behavior of LADs in association with sediment particle size and water depth.

Influencing factors and evaluation application of regional crustal stability in the Bohai Strait

ABSTRACT Due to the extremely complex geological conditions in the Bohai Strait, active faults is very developed and earthquake activity occurs frequently. It is of great importance to evaluate the regional crustal stability for the planning and construction of the Trans-straits Passage. In this study, the authors carry out the evaluation by means of buffer analysis, topology analysis and overlay analysis based on ArcGIS software. The evaluation mainly analyzed six assessment factors of Bohai Strait including neotectonic activity, active faults distribution, seismicity, tectonic stress fields, Bouguer gravity anomaly and geological disasters. In brief, the crustal stability of the eastern North Yellow Sea Basin is best, while that of the Bohai Basin and southwest Bohai Strait is poor. Meanwhile, small and frequent earthquakes in the southern Strait and geological disasters developed in the northern and central Strait such as tidal ridge and shallow gas which may adversely impact on the Trans-straits Passage construction.

Facies architecture of the Cambrian deposits of the Baltica shelf in the Lublin Basin, SE Poland

In the Cambrian, the Lublin Basin was a shallow-water area, located on the western edge of the Baltica palaeocontinent. The Cambrian sedimentary sequence, forming the lower part of the sedimentary cover of the North European Platform, is lithologically diversified and reflects dynamic variation in depositional environment. This paper presents the distribution of palaeofacies and sedimentary environments in the early Lublin Basin, including changes in their lateral extent during its evolution in the Cambrian. In order to evaluate the facies architecture of the Lublin Basin, a sedimentological analysis was carried out. On the basis of the detailed logging of drill cores, lithofacies made up of conglomerates, sandstones, mudstones and heterolithic deposits were distinguished; 16 lower-rank sublithofacies were identified. Their specific assemblages are indicative of shelf-type lithofacies associations, i.e. (1) tidal flat with muddy, mixed and sandy tidal plain sublithofacies including subtidal channels; (2) barrier – lagoon; (3) shoreface with lower, middle and upper shoreface subassociations; and (4) offshore with upper and lower offshore subassociations, including sandy tidal ridges. During the early Cambrian, the lateral variability and environmental succession indicate a transgressive, long-term trend and the migration of a lagoonal environment across wide tidal plains and the shoreface up to an offshore environment. The Lublin Basin reached its greatest lateral extent and maximum depth in the upper lower Cambrian. Next, an opposite trend began and during the middle Cambrian a regression cycle is recorded in successive changes in sedimentary environments that reflect a progressive shallowing. Multiple changes in adjacent environments indicate repeated and cyclical, lower-rank ingressions.

Tide-dominated deltas in active margin basins: Insights from the Guayas estuary, Gulf of Guayaquil, Ecuador

The Gulf of Guayaquil, Southern Ecuador, is the largest tidal system of the Pacific margin of South America. The incipient oceanic tide has a tidal range of over 1 m and is amplified on the continental shelf, which is widened in this area by the tectonic activity related to the northward escape of the North Andean Block. The head of this embayment connects to the Guayas River, roughly running along the dextral strike-slip fault bounding the North Andean Block. The Guayas River connects to the Gulf of Guayaquil through a tide-dominated delta, the supratidal part of which is composed of mangroves drained by a network of tidal channels. The river channels merge into the Jambelí Channel, a subtidal valley forming the main distributary channel of the delta. Very high resolution seismic profiles collected at the junction between the Jambelí Channel and the Gulf of Guayaquil show the architecture of several depositional sequences preserved in the first 0.1 s twt beneath the sea bed. These sequences mainly consist of a lowstand to transgressive systems tract comprised of fluvial to estuarine channels topped by a highstand systems tract of prodeltaic muds. The progradational muds volumetrically dominate the stratigraphic record and characterize the Guayas delta facies. By contrast, the near bed features close to the mouth of Jambelí Channel show the present dominance of tidal scour, forming hollows up to 50 m deeper than the surrounding area, reworking the underlying deposits and forming levees or, inside the subtidal valley, tidal ridges. The prodeltaic muds may reach and cover the tidal scour hollows during the late highstand only, in favor of a damping of tides due to the reduction of the tidal prism caused by the advance of the Guayas delta. The sequences preserved in the outer part of Jambelí Channel pinch out toward a hinge line located along the Puná - Santa Clara fault system. This fault system is responsible of the uplift and emergence of a topographic barrier at the entrance of the Jambelí Channel. As a result, the Estero Salado was progressively disconnected from the Gulf and the tidal flows were concentrated in the Jambelí Channel, bringing about tidal scour hollows. In the meantime, the tidal prism was maintained and subsidence took place in a sub-basin located landward of the uplifting barrier. This caused the Jambelí Channel to remain subtidal during most of the past sea-level highstands, in spite of the large amount of sediment supplied by the Guayas River.

Morphodynamics of a tidal ridge system in the southwestern Yellow Sea: HF radar study

A radial tidal ridge system is present throughout the coastal waters of the southwestern Yellow Sea (China) with varied and complicated ridges and channels between them. A newly designed ground-wave high-frequency (HF radar), with full-coverage and high spatial-temporal resolution, was employed in this study to measure the surface currents and bathymetric features correlated wave celerity in the study area from July 17 to August 6, 2011. We found that the spatial distribution pattern of the tidal channels is generally stable with periodic adjustments during a spring-neap tidal cycle and with higher degree of spatial orderliness from neap to spring tides than from spring to neap tides; the nearshore part of the channels is most stable in lateral, the middle part is relatively lateral unstable, and the offshore part changes complicatedly; flood-dominated channels and ebb-dominated ridges are identified using HF radar signals. The horizontal Kelvin number (Keh) is workable in lateral stability evaluation. This study reveals the potential of HF radar in morphodynamic studies on shallow coastal waters.

Shoal morphodynamics of the Changjiang (Yangtze) estuary: Influences from river damming, estuarine hydraulic engineering and reclamation projects

Concerns regarding estuarine shoal morphodynamics have increased worldwide because of intensive anthropogenic activities. To explore response of estuarine shoals to possible couplings of multiple artificial interferences in river basins and within estuaries, the link between the morphodynamic processes of the Nanhui Shoal (NHS), which is located along the southern margin of the Changjiang estuary, the largest estuary in Asia, and river damming, estuarine hydraulic engineering and reclamation projects, is discerned in this study. The results reveal that the NHS exhibited secular polarization during 1998–2013, with a significant accretion of 1.8×108m3 landward from the tidal ridge and an erosion of 0.3×108m3 on the seaward edge, respectively, forming a steep slope with an elevation between −2 and −3m. Meanwhile, the NHS morphodynamics could be divided into 3 stages: mild accretion with an undisturbed tidal channel during 1998–2002, strong sedimentation with a disrupted tidal channel during 2003–2008, and large-scale landward accretion with an infilled tidal channel after 2009. Moreover, the NHS's volume variations exhibited an 18-month cycle, even though an increased area of 35km2 above −2m and a decreased area of 45km2 between −2 and −5m were observed. The primary causes of theses periodic changes in the NHS's volume are determined as the fluctuating Changjiang water discharge and cyclically altered hydrodynamics of the South Passage. The Deep Waterway Project (DWP) and reclamation projects were responsible for the polarization of seaward erosion and landward accretion, respectively. Moreover, these reclamation projects dominated the staggered changes in NHS morphodynamics by inducing continuous accretion within the tidal channel. Compared to estuarine engineering, river damming induced dramatic declines in distal sediment may have played a minor role in flat changes of NHS.

Holocene sedimentary systems on continental shelves

The present knowledge of Holocene continental shelf deposits in relation to the processes for their formation, from the prospective of marine sediment dynamics, is examined. Over the last 50 years, various innovative techniques have been developed to measure and calculate currents, waves and suspended sediment concentrations. Thus, sediment transport rates can be defined by in situ observations, or numerical modeling. At the same time, sediment dynamics has been applied to morphodynamics, such that deposition rate and seabed morphological change can be predicted. On the continental shelf, tide–wave action, residual circulation and sediment gravity flow are the major sediment dynamic forcing mechanisms. The tidal current is often responsible for landward transport, waves can cause landward transport of sand and gravel but seaward transport of fine-grained sediment, and shelf circulation and sediment gravity flow favor the dispersal of suspended sediment towards offshore or even across the shelf. For the various types of the shelf, wide or narrow, sediment starved or supply abundant, prediction on the basis of processes is consistent with the observed spatial distribution of Holocene sedimentary systems, e.g., river deltas, beaches, barrier islands, lagoons, tidal ridges, tidal inlets, tidal flats and shelf muds. The sedimentary records associated with these systems often consist of high-resolution slices, i.e., each record tends to have a resolution within 101 years, but covers only a relatively short period of the Holocene. Nevertheless, if different records are connected, according to their chronological order, then the overall period covered by the records will be extended. In order to achieve this objective, a modeling approach to the formation of sedimentary records should be developed. Based upon an understanding of process–product relationships, simulation can be undertaken for: the formation of early Holocene reworking-induced deposits, during sea level rise; event beds due to extreme events; the preservation potential of the sedimentary sequences; the post-depositional modifications to the sedimentary records; the environmental settings during sedimentation; and the long-term effects of material budgeting processes on the sediment system behavior.

基于GIS技术的南黄海辐射沙脊群海域水质分布特征与评价

使用Arcgis软件对南黄海辐射沙脊群附近海域2007年春秋两季表层水样的水质进行了分析，包括砷(As)、汞(Hg)、铜(Cu)、锌(Zn)、镉(Cd)、铅(Pb)、铬(Cr)七种重金属的含量分布变化。用Hakanson潜在生态危害指数法(HPERI)对该海域7种重金属进行生态风险评价，旨在为江苏沿海辐射沙脊区水质健康和海域生态环境保护提供科学依据，并为江苏沿海的开发利用提出合理化建议。研究结果发现，春秋两季As、Cd、Cr、Cu 4种重金属含量均低于国家海水水质I类标准；Pb和Zn在部分区域符合II类标准，其余各处符合I类标准；Hg在沙脊沉积区含量较高，春季为IV类海水，秋季为超IV类海水，在潮流通道含量较低，春季为I类海水，秋季为II、III类海水。秋季重金属较春季普遍含量更高，且整体分布呈现南移趋势。Hakanson潜在生态危害指数法评价结果表明，春秋两季该海域均以Zn的潜在生态危害最大，除秋季Zn存在强生态危害以外，其余重金属在春秋两季均为轻微生态危害；综合潜在生态风险以沿岸河口、港口附近和沙脊沉积区处为最高，表明人类活动是影响该海域重金属分布的主要因素；春季潜在生态风险属轻微，秋季高值区属中等风险。We used Kriging modelling in Arcgis 10.1 to find out the distribution characteristics of water qual-ity in Radial Tidal Ridge in South Yellow Sea during spring and autumn in 2007, focusing on 7 heavy metals as As, Hg, Cu, Zn, Cd, Pb, Cr. Hakanson Potential Ecological Risk Index (HPERI) was used to assess extents of heavy metals in this area to propose better suggestions for Jiangsu coastal development. According to our study, contents of heavy metals were higher and more enriched in south in autumn than in spring. Monsoon had a significant impact on distribution of those heavy metals in surface water in study area. Zn was found to contribute the most to the pollution status while other heavy metals were found to cause only slight ecological risk based on HPERI method. RI was high in costal Estuary and port area, where human impacts were significant, or sedimentary area of sand ridges, where tidal dynamics were weaker, which suggested that there was a tendency that pollution caused by human activities had turned into the most important impacting factor of the water quality in the Radial Tidal Sand Ridge in South Yellow Sea. And RI showed that the potential ecological risk was low in spring while high in autumn.

Provenance Tracing of Indicative Minerals in Sediments of the Yalu River Estuary and its Adjacent Shallow Seas

Liu, Y.; Cheng, Y.; Li, H.X.; Liu, J.W.; Zhang, C.P.; Zhang, L.; Zheng, C.D., and Gao, J.H. 2013. Provenance Tracing of Indicative Minerals in Sediments of the Yalu River Estuary and its Adjacent Shallow Seas.Vitreous tuff, sphene, andalusite, staurolite, and kyanite are minerals indicative of source and are found in the Yalu River estuary and its adjacent shallow seas. After analyzing the longitudinal variation of content and characteristic index of these indicative minerals (including mineral maturity, source zone index, stability coefficient, ATi index, and ZTR index) in 58 representative surface sediment samples and discussing their trace significance, results were obtained. Surface sediments in the Yalu River estuary and its adjacent shallow seas are found to belong to different provenances. Douliupu and its surroundings represent the southern boundary of the Yalu River's bed load transportation. Surface sediments in shallow seas have moved inward toward land. Sediments in the West-river-way reveal contact with the deposition from shallow seas, retaining characteristics of the main channel before construction of the Shuifeng reservoir, upstream in the Yalu River. While the deposits in the Middle-river-way are similar to the Aihe River, they showed a greater content of modern river deposits. Most sediments in the Liaodong shoals originate from the Yalu River; some originate from the shallow seas via storm surge. Modern river deposits are unable to reach easily the deposition zone near underwater tidal ridges in the shallow seas.

Sedimentary Environment and Sequence Stratigraphy of Late Quaternary Deposits in the East China Sea

High-resolution (Chirp and Sparker system) seismic profiles were analyzed to investigate the sedimentary environment and sequence stratigraphy of the late Quaternary deposits in the East China Sea. Echo types in the study are divided into three major echo types which are classified as flat (transgressive sediment sheets, relict sands, and Holocene muds), mounded (tidal ridges), and irregular echoes (channels). Sequence analysis of high-resolution seismic profiles reveals that the shelf deposits form a succession of high-frequency (fifth-order) sequences consisting of three depositional sequences (DI, DII, and DIII) developed during the late Quaternary. The depositional sequence includes five sedimentary units, each with different seismic facies and geometry: (1) regressive estuarine/deltaic wedge (unit J1), (2) regressive deltaic/offshore deposits (unit J2), (3) low-stand deltaic wedge with incised-channel fill (unit J3), (4) transgressive estuarine/deltaic complex (unit J4-a) and sand ridges/sheet (unit J4-b), and (5) recent mud (unit J5). The results (correlation of echo types and depositional sequences, sedimentary features, and sequence stratigraphic interpretation etc.) of this study suggest that the late Quaternary deposits of the East China Sea were formed by complex sedimentary processes and systems under the influence of tidal action, sea-level change, and an enormous bulk of sediment inflow from adjacent rivers.

황해 중동부 경기만의 후기 제4기 순차층서 연구

황해 경기만은 제4기에 반복된 해침과 해퇴로 4개의 해침-해퇴 퇴적체(DS-1, DS-2, DS-3, DS-4)를 형성하였다. 본 연구는 황해 경기만 퇴적체의 형성을 6개 퇴적단계로 나누어 설명한다. A 단계는 MIS-6 저해수면 시기로서 큰 규모의 해수면 하강으로 인해 대부분의 지역이 대기에 노출되고 광범위한 하도 침식 및 풍화작용의 영향을 받았다. 이어지는 B 단계는 MIS-5e 까지 빠른 해수면 상승과정에서 MIS-5 시퀀스의 하부 해침퇴적체가 형성되었고, 다음에 이어지는 MIS-5d부터 MIS-4 저해수면 시기까지의 C 단계에서는 MIS-5 시퀀스의 상부인 해퇴퇴적체가 만들어졌다. 다음의 D 단계는 MIS-4 저해수면 시기부터 MIS-3c 고해수면 시기까지로 하도 침식 및 하도 충전 구조로 이루어진 MIS-3 해침 퇴적체가 형성되었다. 다음의 E 단계에서는 LGM 시기까지 계속적인 해수면 하강이 있었고 외해쪽에서는 천해 기원의 MIS-3 해퇴퇴적체가 만들어진 반면에, 내륙쪽에서는 노출된 환경에서 하도 충전 퇴적체나 범람원 퇴적체가 형성되었다. 마지막 단계인 F 단계는 황해 전체적으로 홀로세 해침이 발생하였고, 이 시기에 외해쪽에서는 대륙붕 사질 퇴적체와 조석사주 퇴적체가 형성되어 고해수면 시기인 현재까지 퇴적이 일어나고 있다. The Yellow Sea has sensitively responded to high-amplitude sea-level fluctuations during the late Quaternary. The repeated inundation and exposure have produced distinct transgression-regression successions with extensive exposure surfaces in Kyeonggi Bay. The late Quaternary strata consist of four seismic stratigraphic units, considered as depositional sequences (DS-1, DS-2, DS-3, and DS-4). DS-1 was interpreted as ridge-forming sediments of tidal-flat and estuarine channel-fill facies, formed during the Holocene highstand. DS-2 consists of shallow-marine facies in offshore area, which was formed during the regression of Marine Isotope Stage (MIS)-3 period. DS-3 comprises the lower transgressive facies and the upper highstand tidal-flat facies in proximal ridges and forced regression facies in distal ridges and offshore area. The lowermost DS-4 rests on acoustic basement rocks, considered as the shallow-marine and shelf deposits formed before the MIS-6 lowstand. This study suggests six depositional stages. During the first stage-A, MIS-6 lowstand, the Yellow Sea shelf was subaerially exposed with intensive fluvial incision and weathering. The subsequent rapid and high amplitude rise of sea level in stage-B until the MIS-5e highstand produced transgressive deposits in the lowermost part of the MIS-5 sequence, and the successive regression during the MIS-5d to -5a and the MIS-4 lowstand formed the upperpart of the MIS-5 sequence in stage-C. During the stage-D, from the MIS-4 lowstand to MIS-3c highstand period, the transgressive MIS-3 sequence formed in a subtidal environment characterized by repetitive fluvial incision and channel-fill deposition in exposed area. The subsequent sea-level fall culminating the last glacial maximum (Stage-E) made shallow-marine regressive deposits of MIS-3 sequence in offshore distal area, whereas it formed fluvial channel-fills and floodplain deposits in the proximal area. After the last glacial maximum, the overall Yellow Sea shelf was inundated by the Holocene transgression and highstand (Stage-F), forming the Holocene transgressive shelf sands and tidal ridges.

Sedimentological–ichnological model for tide‐dominated shelf sandbodies: Lower Cambrian Gog Group of western Canada

AbstractDunes and bars are common elements in tide‐dominated shelf settings. However, there is no consensus on a unifying terminology or a systematic classification for thick sets of cross‐stratified sandstones. In addition, their ichnological attributes have hardly been explored. To address these issues, the properties, architecture and ichnology of compound cross‐stratified sandstone bodies contained in the Lower Cambrian Gog Group of the southern Canadian Rocky Mountains are described here. In these transgressive sandstones, five types of compound cross‐stratified sandstone are distinguished based on foreset geometry, sedimentary structures and internal heterogeneity. These represent four broad categories of subtidal sandbodies: (i) compound‐dune fields; (ii) sand sheets; (iii) sand ridges; and (iv) isolated dune patches; tidal bars comprise a fifth category but are not present in the Gog Group. Compound‐dune fields are characterized by sigmoidal and planar cross‐stratified sandstone in coarsening‐upward and thickening‐upward packages (Type 1); these are mostly unburrowed, or locally contain representatives of the Skolithos ichnofacies, but are intercalated with intensely bioturbated sandstone containing the archetypal Cruziana ichnofacies. Sand‐sheet complexes, also composed of compound dunes, cover more extensive subtidal areas, and comprise three adjacent subenvironments: core, front and margin. The core is characterized by thick‐bedded sets of cross‐stratified sandstone (Type 2). A decrease of bedform size at the front is recorded by wedges of thinner‐bedded, low‐angle and planar cross‐stratified sandstone (Type 3) exhibiting dense Skolithos pipe‐rock ichnofabric. The margin is characterized by interbedded sandstone and mudstone, and hummocky cross‐stratified sandstone. Sand‐sheet deposits exhibit clear trends in trace‐fossil distribution along the sediment transport path, from non‐bioturbated beds in the core to Skolithos ichnofacies at the front, and a depauperate Cruziana ichnofacies at the margin. Tidal sand ridges are large elongate sandbodies characterized by large sigmoid‐shaped reactivation surfaces (Type 4). Sand ridges display clear ichnological trends perpendicular to the axis of the ridge, with no bioturbation or a poorly developed Skolithos ichnofacies in the core, a depauperate Cruziana ichnofacies in lee‐side deposits, and Cruziana ichnofacies at the margin. While both tidal ridges and tidal bars migrate by means of lateral accretion, the latter occur in association with channels while the former do not. Because tidal bars tend to occur in brackish‐water marginal‐marine settings, their ichnofauna are typically of low diversity, representing a depauperate Cruziana ichnofacies. Isolated dune patches developed on sand‐starved areas of the shelf, and are represented by lenticular sandbodies with sigmoidal reactivation surfaces (Type 5); they typically lack trace fossils, but the interfingering muddy deposits are intensely bioturbated by a high‐diversity fauna recording the Cruziana ichnofacies. The variety of sandbody types in the Gog Group reflects varying sediment supply and location on the inner continental shelf. These, in turn, governed substrate mobility, grain size, turbidity, water‐column productivity and sediment organic matter which controlled trace fossil distribution.

A tidal depositional model for the Carolina sand (Pliocene, Talparo Formation) of central Trinidad

A BSTRACT. — The Pliocene geological history of Trinidad’s Northern Basin is little known. The need for such knowledge is pressing; some rock units cropping out there yield hydrocarbons offshore in the Gulf of Paria, but the environments in which they were deposited have yet to be deciphered. As a first step towards unravelling this geohistory, this study examines the sedimentology of the Carolina sand, a small and informal member of the Pliocene Talparo Formation. From plan view the lenticular Carolina sand is concluded to comprise a tidal sand ridge that built up almost to sea level. This interpretation is supported by abundant sedimentary structures indicative of tidal influence (herringbone cross-bedding, mud couplets, clay drapes). Drape and ripple orientations show northward transport that is concluded to be indicative of ebb tide currents. For most of the succession, sediments alternate between two lithofacies (tabular cross-bedded sands with clay drapes, and interlaminated sands and silts). Comparison with tidal flats suggests these lithofacies indicate rapid cycling between different water depths. The depth changes are suggested to be related to outflow from the paleo-Orinoco River, which, like the present day Orinoco, is suggested to have raised sea levels around Trinidad during the annual rainy season. The cross-bedded sands were deposited as deeper-water megaripples on the tidal ridge surface during the rainy season, the interlaminated sands and silts under intertidal conditions when sea levels fell during the dry season. The Carolina sand was probably deposited during one of the eustatic sea level highstands hitherto noted farther east, in the offshore Columbus Basin. K EYWORDS. — tidal sand ridge , Orinoco , clay drapes , herringbone cross-bedding , mud couplets

서해 경기만에서의 고해상도 탄성파 탐사를 이용한 퇴적환경 및 퇴적층서 연구

High-resolution (Chirp and Sparker system) seismic profiles were analyzed to investigate the sedimentary sequence and distribution pattern of the late Holocene deposits in Gyunggi Bay, the Yellow Sea. The bay is located in the western part of Korea, east of the Yellow Sea. The sedimentary sequence divided into three units bounded by erosional bounding surface: (1) acoustically parallel to subparallel reflectors with cross bedding structures (Unit 1); (2) confused inner reflectors and top of unit exposed partially at the seafloor (Unit 2); and (3) approximately parallel reflections and regressive to transgressive incision-fills (Unit 3). On the basis of seafloor morphology, surface bedforms, and subbotom acoustic characters, echo types in the study area were identified following the schemes of Chough et al. (2002); (1) flat seafloor with sharp bottom echoes (echo types 1-1, 1-2 and 1-3; transgressive sediment sheets or relict sands), (2) mounded seafloor with either smooth surface or superposed bedforms (echo types 2-1 and 2-2; tidal ridges), and (3) various-scale eroded seafloor (echo types 3-1 and 3-2; channels). Suspect features of acoustic turbid zones which is related to gas charged sediment are reported.

Characteristics of modern sedimentation in Qingdao bays

With available survey data and 237 surface sediment samples, the modern sedimentation in Qingdao bays is studied. The research result shows that the east area is shallower (16.4 m) than that in the west (45.8 m). The geography was formed by a symmetric wave in a sequence of bank — offshore depression — platform — tidal channel — platform — offshore depression — foreshore from south to north. Flood sedimentary systems were formed from inlet of the Jiaozhou Bay in the west to the barrier bar in the east. Lateral sedimentation includes mainly tidal current ridges in two tidal channels. Gravel sandy sediments formed by wave lie in midland of from seashore to wave base. Dynamic functions are mainly tide and wave. Tidal current moves sediment in vertical and horizontal directions, sorting sediments and providing materials for coastwise beaches. The sources of sediment are mainly from eroded headland rocks. In general, grain sizes in this area from the inlet of the Jiaozhou Bay in the west (120°17′) to the barrier bar outside in the east (120°35′) are coarse-fine-coarse, forming gravel-gravelly sand (G-S), sand (S), gravel clay silt (G-YT), clay silt (YT), gravelly silty sand (G-TS), silty sand (TS), gravelly sandy silt (G-ST), and sandy silt (ST) in turn.

GRAIN SIZE CHARACTERISTICS OF SURFICIAL SEDIMENTS AND THEIR RESPONSE TO HYDRODYNAMICS OVER THE COASTAL WATERS OF NORTHERN JIANGSU PROVINCE

Surfical sediment samples were collected from the radial tidal ridge areas and tidal flats on the Jiangsu coast during September to November 2007.The moment grain size parameters(i.e.mean size,sorting coefficient,skewness and kurtosis) are obtained by grain size analysis,and cluster analysis was carried out for the parameters.The result indicates that water depth being shallower than 9 m,sediment samples can be grouped into the same type.Likewise,when the water depth is more than 20 m,sediments belong to another type.However,if the water depth is between 9 and 20 m,there are various types of sediments.Grain size trends obtained using the Gao-Collins model show that there is general trend of transporting towards the central part of the coast,except for the Waimaozhu sandbank.Such a pattern is consistent with the measured sediment transport pathways reported in literature.On the basis of an analysis using the Sternberg diagram,the effect of differential sorting during sediment transport is the main process for the distribution of surficial sediments.The sediments are almost entirely transported in suspension from the Sheyang estuary towards the Dafeng tidal flat,while only around 60% of the sediments are transported in suspension from the Xiaomiaohong channel to the Dongzao tidal flat.This process results in the unified sediment grain size parameters for the surfical sediments between the Sheyang estuary and the Dafeng tidal flat,and different sediment grain size parameters between the Xiaomiaohong channel and the Dongzao tidal flat.