Muddy Deposits Research Articles

The origin and internal structures of submarine-slide deposits in a lower Pleistocene outer-fan succession in the Kazusa forearc basin on the Boso Peninsula of Japan

This study investigates the internal geometry and formation processes of submarine-slide deposits in a lower Pleistocene outer-fan succession in the Kazusa forearc basin on the Boso Peninsula of Japan. The submarine-slide deposits are ~40m thick, with a minimum length of ~900m and a width of ~700m. Both the submarine-slide deposits and host deposits comprise siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds. Based on the sequence-stratigraphic framework of the submarine-fan succession, we conclude that the submarine-slide deposits formed during a glacioeustatic sea-level lowstand at about 1.16Ma.The submarine-slide deposits are characterized by thrust sequences with a ramp anticline in the frontal part. A basal slide plane in the lower part of the deposits is developed at a horizon located 2–4cm below the base of a coarse volcanic ash bed and is associated with sheared deposits. Slide planes are sealed in the upper part of the submarine-slide deposits in association with drag folds and chaotic deposits. Finally, the submarine-slide deposits are transitionally overlain by ~3-m-thick chaotic muddy deposits, and are finally overlain by siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds, which show lithofacies features similar to those of the submarine-slide deposits. The variations in the deformation styles indicate that sliding occurred as a synsedimentary process in the outer-fan environment, and the basal slide plane formed when the porosity of the muddy deposits was reduced to ~55% or less.Based on the empirical relationship between the submarine-fan length and lower-fan slopes from modern examples, the gradient of the outer-fan is estimated at 0.31°–0.46°, which is lower than the threshold gradient of 1.2° for a 40-m-thick submarine slide with the estimated basal porosity. Based on the distribution of deformed deposits within the lower-fan host deposits, the minimum volume and runout distance of the submarine-slide deposits are estimated to be ~3×107m3 and ~5km, respectively. Furthermore, based on data from modern submarine slides, the elevation difference between the failed mass in both the starting and depositional areas is estimated to be 80–170m. Thus, the initiation of a submarine slide in the outer-fan environment was likely influenced by a combination of external forces, such as seismic shaking and increased pore-water pressure in association with the seepage of gas and water from underlying deposits in the Kazusa forearc basin. This study suggests that submarine slides occur in distal and low-gradient deep-water environments in active-margin basins.

Distinction and grain-size characteristics of intertidal heterolithic deposits in the middle Qiantang Estuary (East China Sea)

The routine sampling procedure for grain-size analysis of intertidal heterolithic deposits runs a high risk of inadvertent mixing of two or more different sedimentation units, which would consequently complicate data interpretation. Traditionally, sedimentologists pay less attention to muddy layers due to a lack of internal structures, although the grain-size populations of such layers should encode more information on fine-mud flocculation processes than sandy layers. In this paper, individual muddy and sandy layers of nine short cores from the Da-Jian-Shan tidal flats of the middle Qiantang Estuary in the East China Sea, which experiences tidal bores, were sampled separately for grain-size analysis. A core taken at Huang-Jia-Yan from the lower estuary, not affected by tidal bores, served for comparison. A curve-fitting method was employed to decompose each grain-size distribution into two Gaussian populations. Cumulative plots indicate that intertidal sediments are mostly dispersed as intermittent and uniform suspension loads, traction loads being absent or very subordinate. This is conceivably linked to flows agitated by tidal bores, and to the highly dynamic nature of fine sand and coarse silt particles. Selective transport and deposition have produced three distinct sedimentation units, namely, tidal-bore deposits, tidal sandy deposits, and tidal muddy deposits. These can also be discriminated on bivariate plots of any two textural parameters. Shoreward attenuation of tidal flows is reflected in the gradual fining and thinning of sandy layers from lower-flat massive sands, through middle-flat hybrid deposits (alternations of massive sands and tidal rhythmites), to upper-flat tidal rhythmites. This gradient is also well represented in slightly decreasing (increasing) sorting and decreasing (increasing) proportions of the coarser (finer) hydraulic populations in the muddy layers. Although no corresponding trends are discernible in the hydraulic populations of the sandy layers, these can be distinguished on the basis of characteristic sedimentary structures. The floc limit and floc volume fraction, estimated from the modes and proportions of the finer hydraulic populations, are 8~10 μm (16 μm) and on average 41.73% (26.41%) for muddy (sandy) layers, respectively. The most plausible explanation is that the floc limit sensitively responds to subtle changes in the suspended sediment composition and the ambient hydraulic and hydrochemical settings. In comparison, the Huang-Jia-Yan core features blurred bedding and higher contents of fine mud and flocs, these being consistent with the weaker energy on the upper tidal flat of the lower estuary where neither tidal bores nor bigger waves occur.

Large-scale dam removal on the Elwha River, Washington, USA: Coastal geomorphic change

Two dams on the Elwha River, Washington State, USA trapped over 20millionm3 of mud, sand, and gravel since 1927, reducing downstream sediment fluxes and contributing to erosion of the river's coastal delta. The removal of the Elwha and Glines Canyon dams, initiated in September 2011, induced massive increases in river sediment supply and provided an unprecedented opportunity to examine the geomorphic response of a coastal delta to these increases. Detailed measurements of beach topography and nearshore bathymetry show that ~2.5millionm3 of sediment was deposited during the first two years of dam removal, which is ~100 times greater than deposition rates measured prior to dam removal. The majority of the deposit was located in the intertidal and shallow subtidal region immediately offshore of the river mouth and was composed of sand and gravel. Additional areas of deposition include a secondary sandy deposit to the east of the river mouth and a muddy deposit west of the mouth. A comparison with fluvial sediment fluxes suggests that ~70% of the sand and gravel and ~6% of the mud supplied by the river was found in the survey area (within about 2km of the mouth). A hydrodynamic and sediment transport model, validated with in-situ measurements, shows that tidal currents interacting with the larger relict submarine delta help disperse fine sediment large distances east and west of the river mouth. The model also suggests that waves and currents erode the primary deposit located near the river mouth and transport sandy sediment eastward to form the secondary deposit. Though most of the substrate of the larger relict submarine delta was unchanged during the first two years of dam removal, portions of the seafloor close to the river mouth became finer, modifying habitats for biological communities. These results show that river restoration, like natural changes in river sediment supply, can result in rapid and substantial coastal geomorphological responses.

Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula, Japan

AbstractThe canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.

Evidence for ca. 7‐ka maximum Holocene transgression on the Peninsular Malaysia east coast

ABSTRACTIn situ fossil coral and shelly marine deposits occur up to 50 cm above mean sea level in north‐east Peninsular Malaysia. The fossil reef comprises over 15 coral species and associated molluscs. Radiocarbon ages of corals range from 7238 to 6909 cal a BP. The reef occurs adjacent to bedrock hills that formed a mainland peninsula when the coral was living. Abundant well‐preserved fossil molluscs with bivalves commonly articulated occur in ditch tailings from coastal plains flanking these hills. Landward, a sand ridge represents part of the maximum transgression shoreline. When alive, the fossil coral reef required clear water and full marine conditions seaward of the peninsula. The maximum transgression here occurred ca. 7 ka with stable environmental conditions persisting long enough for diverse coral reef development. Assuming a similar tidal range to today, relative sea level ca. 7 ka would have been between 1.4 and 3 m above present. Between then and ca. 6 ka, abundant sediment supply resulted in barrier‐beach construction seaward of the coral reef, converting the area to a lagoonal environment unsuitable for coral and burial by muddy deposits. Assuming that regional relative sea‐level data indicate maximum Holocene highstand up to +5 m between 6 and 4 ka are correct, then the maximum transgression preceded maximum sea level by at least 1000 years.

Geoacoustic character, sedimentology and chronology of a cross-shelf Holocene sediment deposit off Cabo Frio, Brazil (southwest Atlantic Ocean)

The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8–4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73–7.70 ka BP) to generally very low values (<0.11 cm/century) over the last thousand years in all cores. Over the last 6 ka there appear to have been three distinct sedimentation peaks, one between 6 and 5 ka BP, another between 4 and 3 ka PB, and one around 1 ka BP. Due to different time intervals between dates, not every peak is equally well resolved in all four cores. Based on the similar sedimentology of the inner and outer shelf cores, an essentially identical sedimentation model is proposed to have been active in both cases, albeit at different times. Thus, already during the last glacial maximum, alongshore sediment transport was deflected offshore by a change in shoreline orientation caused by the Cabo Frio structural high. The source of terrigenous material was probably a barrier-island complex that was subsequently displaced landward in the course of sea-level rise until it stabilized some 6.5 ka BP along the modern coast.

Spatial thickness variability of the 2011 Tohoku-oki tsunami deposits along the coastline of Sendai Bay

Soon after the 2011 Tohoku-oki event, approximately 1300 tsunami deposit thickness data were collected spatially by the governors to cover the entire tsunami affected area (Sendai Plain) along the Sendai Bay coastline. This dataset, along with high-resolution and high-precision data of flow depth and pre-tsunami and post-tsunami elevation, enables us first to conduct a direct comparison of the sedimentation and erosion volumes as well as the tsunami hydrodynamic features (e.g., flow depth) and sediment thickness. The total balance of sedimentation and erosion volumes revealed that the volume of tsunami-deposited sediments can be explained roughly using the erosion volumes at the beach and sand dunes for sandy deposits and at rice paddy fields for muddy deposits. Both the flow depth and sediment thickness showed positive correlations with the distance from the shoreline while sediment thickness is no correlation to the elevation except in the zone closest to the shoreline where erosion is present. In addition, a statistical relation was found between the flow depth and sediment thickness. In fact, the frequency distribution of sediment concentration, defined here as the sediment thickness divided by the maximum flow depth at each survey site, fits well with the logarithmic normal distribution with geometric average of about 2%. This fit indicates that the tsunami deposits on the Sendai Plain can be explained generally if we simply assume that the saturated level of the sediment concentration in the flow is limited to about 2% on average, irrespective of the grain size. Such a simple explanation might be applicable only for the tsunami deposits on the Sendai Plain because the topography is remarkably flat and low. Therefore, the tsunami inundation process is relatively simple. Nevertheless, a possible relation between tsunami flow depth and sediment thickness suggested here would be very useful to consider the ideal sedimentary process of the tsunami deposits and to improve forward and inverse modelings.

Dispersal of the Zhujiang River (Pearl River) derived sediment in the Holocene

High-resolution Chirp profiling and coring reveals an elongated (ca. 400 km) Holocene Zhujiang River (Pearl River)-derived mud area (maximum thickness > 20 m) extending from the Zhujiang River Delta, southwestward off the Guangdong coast, to the Leizhou Peninsula. Two depo-centers, one proximal and one distal, are identified. On the continental shelf off the west Guangdong Province, the mud is deposited in water depth shallower than 50 m; while to the southeast of the Zhujiang River Estuary, the mud area can extend to the −120 m isobath. A combined analysis with the stratigraphic sequences of other muddy deposits in the Western Pacific marginal seas (mainly Changjiang (Yangtze) and Huanghe (Yellow) Rivers derived) indicates that the initiation of the Zhujiang River muddy deposit can be further divided into two stages: Stage 1 is before the mid-Holocene sea-level highstand (ca. 7.0 cal. ka BP), the proximal mud was mostly deposited after 9.0 cal. ka BP, when the sea-level rose slowly after the Meltwater Pulse −1C; Stage 2, after the mid-Holocene sealevel highstand, clinoform developed on the continental shelf off the west Guangdong Province, extending ca. 400 km from the Zhujiang River Estuary. The proximal clinoform thins offshore, from ca. 10 m thickness around 5–10 m water depth to less than 1–2 m around 20–30 m water depth. In addition, we also find a developed distal clinoform in the east of the Leizhou Peninsula.

Characteristics of tidal-bore deposits and facies associations in the Qiantang Estuary, China

Abstract The characteristics of tidal-bore deposition in the Qiantang Estuary are studied on the basis of core strata and grain-size data, and lateral and longitudinal associations with other sedimentary facies are synthesized. A typical depositional package by tidal bores and associated flows is generally initiated with (1) an undular/planar erosion base, overlain by (2) a massive sandy bed, and (3) a sandy bed with parallel laminations or some thinly heterolithic beds. The depositional units, especially the parallel laminations, are prone to deformation into convolute bedding, flames, and boiled sand patches with water-escape structures. In the middle estuary, tidal-bore deposits (TBDs) at the main channel and the lower tidal flat transit laterally into alternative beds of TBDs andz heterolithic beds at the middle tidal flat, and then toward incomplete tidal rhythmites on the higher tidal flat. TBDs are generally coarser and less sorted than tidal sandy deposits (TSDs), and tidal muddy deposits (TMDs) have finer grains, less sorting and lower positive skewness than either TSDs or TBDs. Therefore, bivariate plotting of size parameters is a useful tool to differentiate between these three genetic sedimentary bed types. Along the axis, three facies divisions are obvious and consist of: (1) linear depositional ridges and erosion troughs at the outer estuary, (2) TBDs at the middle estuary, and (3) coarse fluvial deposits at the upper estuary. The tripartite facies model of the Qiantang Estuary is similar to other well-known tide-dominated estuarine facies models, but it is the first to stress tidal-bore deposition in the sedimentary facies using detailed discriminative textural and structural characteristics. The approaches offer the potential to better understand tidal-bore processes and their important role in sediment dispersion and facies formation within modern and ancient macrotidal to hypertidal estuaries.

Depositional environments of the Plio-Pleistocene Upper Valdarno Basin (Tuscany, Italy)

The Upper Valdarno Basin is located about 35 km SE of Florence between the Chianti Mountains and the Pratomagno Ridge. The basin fill is made of four synthems named as Castelnuovo dei Sabbioni, Montevarchi, Fosso Salceto and Torrente Ciuffenna synthems. The Castelnuovo dei Sabbioni Synthem (Late Pliocene) consists of coarse-grained, stream gravels grading upwards into sheet-like, alluvial sand. These sands are overlain by a muddy lacustrine unit bearing, at its base, two well-developed lignitiferous seams accumulated in a coastal marsh setting. The lacustrine mud grades upwards into deltaic sand accumulated in a shallow-water delta under repeated lake-level oscillations. The Montevarchi Synthem (Late Pliocene to Early Pleistocene) consists of two portions separated by an unconformity surface passing basinward into a correlative conformity. The lower portion of the Montevarchi Synthem is made of alluvial fan gravel and sand passing upwards into fluvio-aeolian sandsheet deposits, consisting of aeolian-reworked, alluvial sand bearing isolated channels. Fluvio-aeolian sandsheet deposits are covered by mollusc-rich, alluvial sand which makes lateral transition into lacustrine muddy deposits. The upper portion of the Montevarchi Synthem consists of fluvial and alluvial fan deposits. Fluvial deposits occupy the axial part of the basin and are referred to sandy channels wandering through a muddy floodplain hosting shallow lakes and swamps. Alluvial fan deposits occur along the basin margins and consist of proximal gravels grading downfan into gravelly sand and a variety of sandy facies. Floodplain lakes deposits are well-developed in the middle part of the upper Montevarchi Synthem and in the Palazzolo sub-basin (Fosso Salceto Synthem), where they are overlain by alluvial-fan gravels. The Torrente Ciuffenna Synthem (Early to Middle Pleistocene) consists of fluvial sediments in axial part of the basin and alluvial fans deposits along the basin margins. The axial fluvial deposits were accumulated by the paleoArno River and consist of gravel and overlying sand. The basal gravels were deposited by low-sinuosity channels, whereas sandy deposits were formed by moderate to high-sinuous channels. The alluvial fan deposits consist of proximal gravels passing downfan into gravelly sand and sandy facies.

Clay fabric of fluid-mud deposits from laboratory and field observations: Potential application to the stratigraphic record

Abstract The clay fabric of fluid-mud deposits was investigated with the aim of identifying characteristic features that potentially apply to the recognition of fluid-mud deposits in the stratigraphic record. We examined both experimentally formed and natural fluid-mud deposits. The clay fabric of experimentally formed fluid-mud deposits is characterized by aggregates of clay particles in face-to-face contact with each other (herein termed ‘FF-aggregates’), with long-axis lengths of up to 20 μm. Some flocs that formed in fluid with a high initial suspended sediment concentration (ISSC), such as fluid mud, would have a high preservation potential as FF-aggregates; once they have settled to the sea floor, to distinguish them from flocs that form in fluids with a lower ISSC. Aggregates that are similar to FF-aggregates are also observed in natural fluid-mud deposits that formed in a modern tide-dominated estuary at the mouth of the Rokkaku River in Kyushu, Japan. Thus, in conjunction with formally proposed lithofacies and ichnofacies features of fluid-mud deposits, the observation of FF-aggregates is potentially useful in identifying fluid-mud deposits when examining limited volumes of muddy samples or thin- to very thin-bedded muddy deposits in the stratigraphic record.

Sedimentation Patterns of Fine-Grained Particles in the Dam Area of the Three Gorges Project: 3D Numerical Simulation

AbstractThis paper is focused on the sedimentation processes of fine-grained particles in a 14-km-long section upstream of the Three Gorges Dam, referred to as the dam area, during the period from March 2003 to October 2006. Field measurements indicated that sediment deposits in the dam area were mostly found at the bottom of the main channel, where a new river bed was formed with a flat, nearly horizontal surface. In contrast, very little deposits could be found on the bank slopes of the channel. The observations disagree with the previous predictions based on numerical models, which suggested more evenly distribution of deposits over the cross section. This paper explains the discrepancy by identifying the motion of muddy deposits by gravity as a key process in the dam area. A three-dimensional (3D) full Reynolds-Averaged Navier-Stokes (RANS) model is applied to calculate the flow and sediment transport processes. A critical slope method (CSM) is used to estimate the downslope movement of muddy deposits...

Delivery, reworking and export of fine-grained sediment across the sandy Skagit River tidal flats

Tidal flats with fluvial input can have ample fine-grained sediment supply, and yet the Skagit River tidal flats remain mostly sandy. Therefore, hydrodynamic mechanisms must efficiently export mud off the flats. This study evaluates short-term deposition and long-term burial of mud on an intertidal flat and links seabed deposits to sediment-transport processes. To investigate the fine-grained sediment-transport mechanisms within the sandy Skagit River tidal flats, seabed and water-column observations were collected seasonally from 2008 to 2009 under varying river discharge conditions. Little mud was observed deposited on the seabed. Spatially, mud was most common near channels and on the seaward flat edge. Its presence was temporary, and was typically observed following high river discharge. Strongest current velocities and high suspended-sediment concentrations were measured during spring tidal cycles with peaks in the late ebb. Maximum velocities were observed within channels, permitting for rapid transport of fine-grained particles to the seaward edge of the flat and export beyond. These physical processes also act to mobilize the mostly sandy seabed, which is reworked at various frequencies: on a semi-diurnal tidal timescale, both channel and flat seabeds are reworked to 1–2cm; and over a decadal timescale, lateral channel migration acts to rework the seabed to 1–2m, making the limited mud deposits available for export. Overall, channel networks on sandy tidal flats with fluvial input not only deliver fine-grained sediment to the flat, but also aid in the export of suspended sediment at ebb tides and in the release of muddy deposits through reworking of the seabed.

The impact of the Three Gorges Dam on the downstream distribution and texture of sediments along the middle and lower Yangtze River (Changjiang) and its estuary, and subsequent sediment dispersal in the East China Sea

The grain size of river sediments changes systematically downstream from source to sink, and is influenced by catchment lithology, geomorphology, hydrology, oceanography and, in modern settings, anthropogenic impacts. Compared with small, gravel-bedded river systems, less is known about large, sandy‐bed rivers, particularly from the river source to marine sink. In the present study, we examine longitudinal changes in sediment grain size along the middle and lower Yangtze River, downstream of the Three Gorges Dam (TGD), and along the major sediment dispersal pathway into the East China Sea, over a total length of 2100km. We also examine the spatial patterns of seabed sediment grain size in the East China Sea adjacent to the Yangtze Estuary (70,000km2 in area). In particular, we consider the impact of the TGD on the grain size of the riverbed and seabed sediments. Before the construction of the TGD, the relationship between median grain size and distance along the sandy bed of the middle and lower Yangtze showed a downstream fining trend that was exponential in form. After the TGD was built, erosion caused an abrupt gravel–sand transition to develop in the section immediately downstream of the TGD. In the Yangtze Estuary, flocculation and subsequent deposition of suspended riverine mud during the slack water period between flood and ebb tides led to the formation of an abrupt sand–mud transition. Muddy deposits along the major longshore sediment dispersal route also show an exponential fining trend. However, towards the open East China Sea, the modern riverine muds are replaced seawards by older sands. The mud margin there was found to have retreated landward significantly over the post-TGD period due to erosion driven by the significant decrease in sediment supply from the Yangtze River. We expect that the impact of the TGD on the grain size of bed sediments in the Yangtze River and the East China Sea will continue for some time, and the change in the grain size of bed sediments there will become more pronounced.

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.

Peduncular attached secondary tiering acrotretoid brachiopods from the Chengjiang fauna: Implications for the ecological expansion of brachiopods during the Cambrian explosion

Brachiopods are usually thought to contribute little to the tiering complexity from the Paleozoic to the Recent, mainly due to the fact that their recent representatives live primarily in lower tiers directly above or below the water–sediment interface. Here we present the first and oldest record of varied levels of secondary tiering in minute brachiopods attached by exceptionally preserved thread-like pedicles around the branched fronds of the algae-like Malongitubus kuangshanensis Hu, 2005. The specimens illustrated herein were recovered from the Chengjiang fauna (Series 2, Stage 3) in the Lower Cambrian Heilinpu Formation at the Kuangshan section in Malong County, Yunnan Province, southern China. The micro-morphology and oval outline of the attached brachiopods demonstrate that they can be assigned to acrotretoid brachiopods (Linguliformea, Lingulata, Acrotretoidea), described here as Kuangshanotreta malungensis gen. et sp. nov. This is the first report on the occurrence of acrotretoid brachiopods in the Lower Cambrian muddy deposits from southern China. The posterior margins of the Kuangshanotreta shells are invariably either in direct contact with, or directed towards, and then in situ attached to the algal frond of M. kuangshanensis, indicating a secondary tiering in the ecological structure of Early Cambrian brachiopods. The acrotretoid Kuangshanotreta/algae malongitubus association represents both the first and oldest evidence into the enigmatic paleoecology of the diverse acrotretoid linguliformean stock that comprises an important component of the Cambrian evolutionary fauna, and sheds light on medium-high levels of secondary tiering (+5 to +10cm) Cambrian soft substrate suspension-feeding communities. When compared to other Chengjiang brachiopods, the miniature morphology and concomitant weight reduction of the shell of K. malungensis may be a good adaption to a suspended epifaunal tiering life style. We infer that the diversification of micromorphic and miniaturized acrotretoids that occurred from the Middle Cambrian to Early Ordovician may be the result of the increased availability of habitable surfaces provided by high levels of tiering in new types of ecological spaces.

Farmlands Damaged by Huge Tsunami and Countermeasures

A strong earthquake hit eastern Japan on March 11th, 2011 and it lasted for 6 minutes. It triggered huge tsunami and the tsunami damaged not only houses and residents but also farmlands. There are several types of interactions between the tsunami and the farmlands. If there was a muddy (sometimes contains sulfidic materials) and/or sandy deposit under the shallow seawater or in the nearshore zone, it was transported inland. Pyrite was found in the sulfur-rich muddy deposits. There are narrowly eroded places along a road and a ridge where tsunami fell down from these micro-high sites. Moreover, the plow layer soil was lost at least partly. Thus, the deposits on the farmlands are the mixtures of the eroded plow layer soil and transported materials from the nearshore zone. The chemical interactions include the exchange reaction between Na+ in seawater and exchangeable cations in the plow layer soil, and precipitation of gypsum (CaSO4 .2H2O) as well as halite (NaCl) when the soils dry. Debris of various materials and halite, at least, must be removed to restore the damaged farmlands.

Sedimentary evolution since the late Last Deglaciation in the western North Yellow Sea

To decipher the sedimentary evolution and environmental changes since the late Last Deglaciation, two gravity cores were analyzed from the western North Yellow Sea (NYS). The two cores (B-L44 and B-U35) were sampled for grain size, clay minerals, detrital minerals, and 14C dating. They are comparable in lithofaies, and the observed succession was divided into four depositional units based on lithology and mineral assemblages, which recorded the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized with enrichment in sand, and was interpreted as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5–9.6 ka) displayed a fining-upward succession composed of sediments from local rivers, such as the Huanghe (Yellow) River, and from coastal erosion, which clearly were related to the Early Holocene transgression. Stable muddy deposition (DU 2) in NYS began to form at about 9.6 ka, which received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of fine sediment deposition in DU 1 (after 6.4 ka) after the sea level maximum.

Depositional Characteristics and Distribution of Lake-Floor Fan of Paleogene Lower Member 3 of Shahejie Formation in Northwestern Part of Huanghekou Sag, Bohai Bay Basin

The lake-floor fan, as an important deposition of Paleogene in Huanghekou Sag, is characterized with both good physical character of reservoir and oil-bearing property, thus it has higher values for petroleum exploration. The lower Member 3 of Shahejie Formation, rich in sandstone, can be divided into lowstand system tract, extensive system tract and highstand system tracts based on seismic reflection signature, and core and logging data clearly. The sand bodies in the study area belonged to two kinds of lake-floor fan deposition formed under semi-deep-lake to deep-lake environment: deposition of the deep-water turbidite fan corresponded to lowstand system tract; deposition of the slump turbidite fan corresponded to extensive system tract and highstand system tract, which was formed by slumping fan delta front sand. Viewed from spatial distribution, the deep-water turbidite fan was mainly developed in the second-order fault downthrown of the basin, while the slump turbidite fan was distributed in the abrupt slope which located in the south of study area. The complex of lake-floor fan consists of various sediments’gravity flow deposits, including:(1)turbidity current deposit with characteristics of Bouma sequences; (2)mud-bearing sandy debris flow deposits with characteristics of dominated sand and mixed by mud; (3)sand-bearing muddy debris flow deposits with characteristics of dominated mud and mixed by sand; (4)gritty debris flow deposits with characteristics of massive gravel accumulation;(5)sandy slump deposits with characteristics of deformed sedimentary structure. During lower water level period(LSTs3L), most of the study area were erosion or sediment pass-by areas, and terrigenous clastic matters were directly transported into deep-water area under the second-order faulted belt, and then formed the deep-water turbidite fan. During higher water level period (ESTs3L, HSTs3L), the slump tuibidite fan, which resulted from various sediments’gravity flows, mainly developed in front of fan dalta in south. The sandstones of the lake-floor fan are the main reservoirs of oil in the northwestern part of the Huanghekou sag.

Self-similar long profiles of aggrading submarine leveed channels: Analytical solution and its application to the Amazon channel

Many submarine fans are coursed by well-defined leveed channels constructed by turbidity currents. The channels aggrade in time, typically accumulating sandy deposits in their beds and muddy deposits in their levees. Periodic channel avulsion acts to build up the fan as a whole. Here a first theory for the long profile of leveed channels is offered. The theory is based on the assumption that there exists a time period, well after channel initiation but before incipient avulsion, during which the channel and its levees are in a quasi-equilibrium state, concurrently aggrading and prograding onto the surrounding fan. The currents are assumed to deposit sand on the channel bed and mud on the levees. The formulation uses a steady uniform flow assumption and a sediment transport relation inherited from rivers and yields a partial differential equation for the evolution of the channel starting from any initial condition. For the ideal case of a channel forming on an initially unchannelized sloping fan, the theory predicts self-similar long profiles for the down-channel variation of channel bed slope, bed elevation, and width, as well as flow discharge and sand/mud discharges. The time evolution of the channel then amounts to a simple rescaling of the self-similar profile as it aggrades and progrades down fan. The theory, when tested against data from the Amazon channel of the Amazon Submarine Fan, shows encouraging comparisons. The generality and shortcomings of the model assumptions are discussed based on a comparative study of mud-rich and relatively sand-rich submarine fan systems.