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At the beginning, Nenjiang Formation in the south of Songliao basin was not considered as a favorable reservoir for hydrocarbon accumulation, which led to its low described and characterized degree. In recent years, many oil and gas bearing units have been found in this area, but the cognitive level of the reservoir is not enough to support a reasonable and efficient development strategy. Therefore, it is necessary to conduct detailed study on the sedimentary microfacies and reservoir characteristics. This paper aims to solve these problems effectively and provide a reliable conclusion of fine reservoir characterization. First, nine single lithofacies types and 5 combined lithofacies types were identified according to core sequence, and their characteristics were described in detail. Then, the sedimentary model of river delta front in the study area was established, which could be divided into four sedimentary microfacies: underwater distributary channel, mouth bar, sand sheet, and distributary. The distribution law of sandbodies was made clear, that is to say, they extend to the south in a tongue like form, and their thickness gradually decreases until they are pinched out. Finally, the influence degree of sedimentation on reservoir properties was analyzed by establishing the correlation between microfacies and reservoir physical parameters, such as porosity, permeability, pore radius, throat radius and clay minerals. It is revealed that the correspondence between reservoir physical properties and microfacies types is very good, and the control of microfacies types on reservoir physical properties is clear.

Shallow-water deltas are important reservoirs for hydrocarbon resources, and there are many oil and gas discoveries found in the sands in China. Many large shallow-water delta sedimentary systems were found in the Bohai Bay Basin in the Late Miocene. Several classic shallow-water deltas are developed in the early-stage sequence (SQmL2) of the lower part of Neogene Minghuazhen Formation in the Bohai Bay Basin which have attracted much attention in recent years. We choose the SQmL2 as an example to reveal the relationships between paleoenvironment and shallow-water delta facies and architecture. Analysis of 3D seismic data and logging data indicated that two types of sedimentary facies, including shallow-water delta and shallow lake facies, are developed during SQmL2. The shallow-water delta facies mainly consist of subaqueous distributary channel with mouth bar rarely developed. The deltas are mainly comprised of relatively thin (1–4 m) fine- to medium-grained sandstone. The combinations of distributary channels on planer view are mostly branch-shaped and lobe-shaped. The shallow-water deltas developed in SQmL2 are controlled by paleogeomorphology, sediment supply, and paleoclimate. The flat topography and sediment supply are favorable for sediments moving basinward for a long distance and forming channelized sand bodies. As the climate gets humid, the lake level rises and shallow lake area expands, resulting the sand bodies move landward and become much thinner. The lake level has changed from shallow to deep and to shallow, and correspondingly, sand body of subaqueous distributary channels has changed from lobe shape to branch shape and to lobe shape.

With the continuous deepening of exploration and development, it is urgent to develop the T structure in order to increase reserves and productions. The block contains 4 sets of oil-gas bearing strata, including LTAF, UTAF, BRF, and GUF. The reservoir types are mainly sandstone and carbonate rocks. However, there are many problems having to face in this structure, among which is the distribution of sedimentary facies. Based on the study of high frequency sequence stratigraphy, the study of sedimentary facies was conducted from the point-line-plane by comprehensively using cores, wells and seismic data. According to the coring data of adjacent areas, single well facies study was carried out, and core facies-logging facies-seismic facies interpretation plates were established. The plane distribution of seismic facies was studied by using seismic techniques such as seismic attribute, strata slice and waveform classification, and the distribution of sedimentary facies was finely delineated by well-seismic combination. The study shows that the provenance of T block is located in/to the northeast or east of the study area. The LTAF formation is mainly composed of alluvial fan and braided river deposits, and braided river delta is locally developed. The UTAF formation mainly consists of braided river, delta front and sheet sand, and alluvial fans and underwater distributary channels locally developed. BRF formation mainly consists of the coastal and offshore, reef flat, inter-reef and delta front. Underwater distributary channels and sheet sand are locally developed. The GUF formation is mainly composed of delta plain, distributary channels, underwater distributary channels, levee, and locally developed mouth bar.

Summary This work presents the facies-based petroleum system of the Tatau-Bintulu area in northern Sarawak, represented by the Belaga-Tatau-Nyalau formations. The Nyalau Formation exposures can be closely related to the offshore hydrocarbon-producing Balingian Province of Cycle I/II. Twelve facies associations are recognized from the formations, which form elements of larger-scale facies successions. The Belaga-Tatau-Nyalau formations are interpreted as mixed tide- and wave-influenced coastal to deep marine depositional system. The facies identified and the geological setting of the area are evaluated for potential elements in a petroleum system. Wave-dominated shoreface succession forms good reservoir-seal with shoreface sand overlain by muddy estuarine-bay. The fluvial channel forms good quality stacked reservoir enclosed by carbonaceous mud and coal bed, followed by the deposition of heterolithic-mud filled tidal channel sealed by muddy estuarine-bay, forming moderate-poor reservoir-seal potential. Tidal bar and mouth bar form broad amalgamated sand bodies with good horizontal and vertical flow properties, overlain either by muddy bay or prodelta mud. The distal turbidite sand forms moderate to poor reservoir with the interbedded basinal mud impeding the upward flow of hydrocarbon. As such, Belaga-Tatau-Nyalau formations possess a viable petroleum system depending on the facies that made up the geological element in a depositional environment.

Identifying the pattern of delta morphological change under decreasing sediment flux due to dam construction is essential for sustainable management in such densely populated coastal areas. In this study, we investigated the morphological processes of the Yangtze mouth bar and prodelta based on bathymetric data on a decadal-interannual scale (1958, 1978, 1997, 2002, 2007, 2010, 2013 and 2015). We found that strong accretion (205.1 Mm3 yr−1) occurred during 1958–1978, when a high sediment load (465 Mt yr−1) was supplied by the Yangtze. Afterwards, the net accumulation rate decreased to 31.9 Mm3 yr−1 in 1978–1997 and 114.6 Mm3 yr−1 in 1997–2002 as a result of riverine sediment loads decreasing to 390 Mt yr−1 and 314 Mt yr−1, respectively. Surprisingly, the net accumulation rate increased to 130.8 Mm3 yr−1 in 2002–2007, though the sediment load sharply decreased to 177 Mt yr−1. This anomaly was attributed to the construction of training walls within the mouth bar area, which induced significant accretion in groyne-sheltered areas and nearby regions. Along with a further decrease in sediment load, the entire study area converted to net erosion of −200.4 Mm3 yr−1 in 2007–2010 and −152.2 Mm3 yr−1 in 2010–2013. Stronger erosion in the former period was partly caused by intensive dredging activities in the mouth bar area. The critical sediment discharge for the Yangtze mouth bar and prodelta to retain net accretion was estimated to be ca. 218 Mt yr−1. If deducting the impacts of estuarine engineering projects on accretion/erosion during 1997–2010, the critical sediment discharge is adjusted to ca. 234 Mt yr−1. In combination with previously reported accretion-erosion conversion elsewhere in the Yangtze Delta, we inferred that most portion of the subaqueous delta has most likely converted from net accretion to net erosion in response to fluvial sediment decline, and the mouth bar area showed the latest conversion among portions of the delta. Integrated assessment and adaptive strategies are urgently required for the Yangtze Delta to survive the coming erosional stage.

Chu, A.; Tai, J.; Chen, Y., and Wang, B., 2020. Sediment budget of the mouth bar in the Yangtze Estuary response to the change of marine input conditions: A process-based model approach. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 36–41. Coconut Creek (Florida), ISSN 0749-0208.The transition of upstream or open sea conditions eventually leads to the change of sediment budget in estuaries and results in its evolution. In this paper, marine facies change for the Yangtze Estuary has been investigated based on statistics and harmonic analysis on the observed water-level time series at stations. The sea-level rise (SLR) rate and the main tidal constituent change were obtained for the estuary. Scenarios were designed to represent change of input conditions for the process-based model of the estuary. The net sediment budget of the mouth bar area in the estuary was calculated according to the cumulative flux through the predefined controlling cross-sections. The results reveal that (1) the SLR in the coming two decades results in sediment demand increase in the mouth bar area and restrains the seaward export sediment; (2) amplitude of the M2 component increase slightly enhances seaward sediment export; and (3) the combination of SLR and M2 increase responses for sediment demand increase in the mouth bar area, and 1.5% more sediment export to sea.

Detailed analysis of a typical wave-dominated delta beach bar sedimentary system of the Fenghe River, in Qingdao, China, concentrated on identifying the sedimentological characteristics of wave-dominated delta beach bar sedimentary system. The aim of the study was to establish a sedimentological facies model for similar deposits. Using well-established sedimentological criteria for recognizing the characteristic of wave-dominated delta beach bar. This modern sedimentary system mainly hosts front subfacies, as well as sedimentary microfacies like underwater snake-like channel, mouth bar, distal bar, and sheet sand. From the river entrance to the mouth bar, more than 80% of the area is occupied by sheet sand, which is distributed widely across a flat terrain. The sheet sand is dominated by wave-built sedimentary structures, plus a few current-formed sedimentary structures. The sheet sand can be divided into an underwater shoal parallel to the coastline and a stable crescent-shaped above-water bar. The underwater shoal is a long ellipse in the plan and an asymmetric shape that is gentle seawards and steep landwards in the vertical section. The sedimentary structures are dominated by wave-formed ripple marks and cross bedding, overlaid with swash bedding. The above-water bar is composed of two bars formed at different stages. The sedimentary structures are dominated by swash bedding, low-angle wedge bedding, and wind-formed sedimentary structure. Both underwater shoal and the above-water bar are resulted from the transformation and redistribution of the sediments on the delta front sheet sand by waves. The two parts reflect a sedimentary association of genetic significance in the sedimentary environment of wave-dominated delta front.

Wang, M.; Wu, Z.; Peng, C.; Fan, Q.Q.; Fu, B.; Ouyang, S.K.; Wang, Y.; Wan, D.F., and Yu, X.N., 2020. Delta sedimentary model of Shanxi Formation in Qingyang Gas field, Ordos Basin. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 425–434. Coconut Creek (Florida), ISSN 0749-0208.Qingyang gas field is a new exploration tight sandstone gas field in the southwest of Ordos Basin, with characteristics of thin production layer, low physical property of reservoir, Shan 1 member is the main production layer. Based on the analysis of field outcrop observation, core drilling and logging data, the Shan 1 member is divided into three sublayers according to cycle characteristics. Based on stratigraphic division, the sedimentary environment, sediment source and sand body distribution characteristics are defined through mineral petrology analysis, grain size analysis, sedimentary facies marker research and Paleogeomorphology restoration. The controlling factors of high-quality reservoir development were analyzed on the basis of comprehensive sedimentary analysis and structural recovery. During the deposition of the Shan 1 member, the meandering river delta is developed, and the sand body is distributed from southwest to northeast. Four main river channels are developed in the study area. The reservoir is mainly developed in the river bed residence, point bar of delta plain and the mouth bar, underwater distributary channel of delta front. Most of high productivity gas wells are distributed in the updip part of the slope. Sedimentation determines the spatial basis of reservoir formation, structural evolution controlling the migration and accumulation mode and the type of gas reservoir in the stage of hydrocarbon accumulation. The overlapping area of sand body development and the updip part of the slope is the favourable area for the gas reservoir.

Herein, we report field studies of the seasonal and daily dynamics of the mixing zone in the micro-tidal mouth of the Partizanskaya river. The position of the mixing zone was determined according to the volume of river run-off. The upper boundary of the mixing zone was observed at 5 (at a river run-off of 73.67 m3/s) to 12.5 km (at 7.7 m3/s) from the mouth bar. The estuary is characterized by a two-layer circulation of water, which results in a halocline with a salinity gradient of up to 30% per 1 m. Variations of salinity in the rifts caused by tides reaches 27% over 3 h.

Field studies of the seasonal and daily dynamics of the mixing zone were carried out in the microtidal estuary of the Partizanskaya River. The position of the mixing zone was determined by river runoff volume. The upstream boundary of the mixing zone was located at a distance from 5 (at river discharge of 73.67 m3/s) to 12.5 km (at 7.7 m3/s) from the mouth bar. The estuary features a two-layer water circulation, resulting in the formation of halocline with a gradient of water salinity of up to 30‰ per 1 m. Salinity variations at rifts, caused by tides, reach 27‰ over a 3-hour period.

Water and sediment are two of the most essential elements in estuaries. Their product, suspended sediment concentration (SSC), is involved in hydrology, geomorphology and ecology. This study was focused on the spatial and temporal variations of SSC in the Yangtze Estuary under new situations after the closure of ~50,000 dams in the Yangtze basin, including the Three Gorges Dam (TGD) in 2003. It was found that the SSC first exhibited an increasing and then a decreasing trend longitudinally from Xuliujing Station to the outer estuary with the Turbidity Maximum Zone located in the mouth bar area. Vertically, the SSC in the bottom layers averaged 0.96 kg/m3, about 2.4 times larger than the surface layers (0.40 kg/m3). During spring tides, the SSCs were always higher than those in neap tides, which was fit for the cognition law. As for the seasonal variations in the North Branch and mouth bar area, the SSCs in the dry season were higher than those in the flood season, while in the upper reach of the South Branch and outer estuary, the seasonal variation of SSCs reversed. This phenomenon primarily reflected the competition of riverine sediment flux and local resuspended sediment flux by wind-induced waves. As for the interannual changes, the SSCs demonstrated overall fluctuant downward trends, determined by riverine sediment flux and influenced by waves. This study revealed the new situation of SSC and can be a reference for other related researches in the Yangtze Estuary.

River-mouth bar is a fundamental element to constitute a delta system, and its internal facies architectures are vital to reconstruct delta evolution history and study high-resolution sequence stratigraphy. Changxing Island is a representative mouth-bar complex in the modern Changjiang Delta. Its vertical stacked strata produced by delta progradation were first studied by detailed facies analysis of core CX03, and then a general facies architecture and evolution history of mouth-bar complexes in the modern Changjiang Delta were discussed through a comparative study of 5 different cores and historical charts. A progradational deltaic sequence has generally a similar internal facies architecture, composed of massive muddy deposits of prodelta and delta-front slope facies at the bottom, sand-dominated deposits of delta-front platform, inter-bar channel and mouth-bar facies at the middle, and heterolithic deposits of tidal flat and saltmarsh facies at the top. There is a significant time lag for the initial formation of channel-mouth bar systems between Chongming and Jiuduansha Islands. Compared with subtidal flats, sedimentation rates on intertidal flats were highly accelerated, potentially resulting from weakening wave and tidal strength over extensive intertidal flats and increasing human embankment activities in the last few centuries. These findings provide some new clues to understand modern and ancient mouth-bar evolution and resultant sequence strata in tide-dominated deltas.

Integration of the sedimentological and ichnological characteristics of the Campanian-Maastrichtian succession of the Nkporo Formation, Afikpo Sub-basin, particularly in the Itigidi-Ediba area reveals a prograding deposit that is considered to record a river-dominated, wave-influenced and tide affected (Rwt ) delta. Facies analysis of the succession indicates six facies associations (FA 1 to 6) suggesting deposition in the shelf, prodelta, distal delta front, proximal delta front, distributary mouth bar and bay-fill sub-environments. These deposits are characterized by abundant carbonaceous detritus ; current-, storm-, wave-, and tide-generated sedimentary structures ; low to moderate diversity, sporadically distributed trace fossil assemblages dominated by depauperate Cruziana and Skolithos ichnofacies that suggest relatively stressed environmental conditions; coarsening upward of most individual facies and the overall succession, and the presence of soft-sediment deformation structures. Zoophycus ichnofacies occurs as opportunistic burrows in fully marine deposits. The frequent occurrence of Diplocraterion sp. indicates a high rate of sedimentation. These ichnofossils are dominantly dwelling and feeding structures with limited grazing behaviour constructed by suspension and deposit feeders .

Morphodynamics of world's river deltas are increasingly affected by human activities, which are of great ecological, economic and social implications. However, impacts of human interventions in deltaic regions are insufficientlyunderstood, especially superimposed upon diminishing sediment supplies. This study uses the heavily interfered Yangtze River delta as an example to address this issue. The morphodynamic impacts of the Deepwater Navigation Channel Project (DNCP) during 1997–2013 are investigated through process-basedmodeling approach (Delft3D) and bathymetric data analysis. The DNCP was implemented in the mouth bar area of the Yangtze River delta including the twin dikes and 19 groynes with the total length of 132.0 km. Hydrodynamic simulations indicate that the training walls resulted in weaker tidal flow and longer slack period at the East Hengsha Shoal (EHS) and stronger tidal flow at the subaqueous delta. Thus, the EHS is characterized as a sediment accumulation zone after the completion of the training walls. Subsequently, morphologicalmodeling shows enhanced accretion at the EHS and enhanced erosion at the subaqueous delta when the training walls are taken into account. Numerical experiments further demonstrate that the above changes are mainly attributed to the seaward half of the northern training walls constructed in 2002–2005. This is probably the reason for the observed accretion peak of the EHS in 2002–2007 and the gradual increase in the erosion rate of the subaqueous delta after 2002. The schematized paths of sediment transport after the DNCP indicate thatsediment eroded from the subaqueous delta serves as an important source for accretion of the mouth bar area. It is suggested that siltation promoting projects within the mouth bar area increased shallow shoal accretion and aggravated erosion at the subaqueous delta. With the overall erosion of the Yangtze River delta due to river sediment reduction, large-scale estuarine engineering projects substantially increase the complicacy of its morphodynamic pattern, which merits close attention for sustainable delta management.

The sandstone from the Oligocene Xiaganchaigou Formation (E3) in the Lengdong area, Qaidam Basin, China, is extensively distributed and acts as an effective regional reservoir for hydrocarbon accumulation. Based on thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD) image analysis and cathodoluminescence (CL), a comprehensive analysis of the sedimentology, petrography, diagenesis and reservoir quality of the Oligocene sandstone reservoirs of the Xiaganchaigou (E3) Formation in the Lengdong area, Qaidam Basin, are studied. The sandstones in the Lengdong area are classified as argillaceous sandstone, silty sandstone, fine sandstone, medium sandstone, pebbly sandstone, conglomeratic sandstone and conglomerate based on their grain sizes, degrees of sorting, and matrix contents. Five sedimentary facies were identified in the Xiaganchaigou Formation (E3) of the Lengdong area, Qaidam Basin: distributary channel, interdistributary bay, mouth bar, central bar and distal sand sheet facies. Their major diagenetic processes include compaction, carbonate cementation and feldspar and calcite cement dissolution. The porosity and permeability values of the fine sandstone, conglomerate, and conglomeratic sandstone are the highest, followed by those of the medium sandstone and silty sandstone, and the argillaceous sandstone and pebbly sandstone have the lowest porosity and permeability values. The diagenetic sequence in the study area ranges from the eodiagenesis B stage to the mesodiagenetic A stage. Compaction has significantly reduced the primary porosity. Carbonate cements, mainly calcite cements, occlude pores by precipitating in intergranular and intragranular spaces. Dissolution largely contributes to increasing the secondary porosity. The well-sorted and relatively coarser-grained sandstones that formed in higher-energy sedimentary facies (distributary channel, mouth bar and central bar) have a better reservoir quality than the poorly sorted, clay-rich sandstones that formed in low-energy environments (interdistributary bay and distal sand sheet). Based on the comprehensive analysis of petrographic data, diagenesis and sedimentary facies, the reservoir in the Lengdong area is classified into three types: type A, type B and type C. Type A, located in the center of the study area, is the most favorable reservoir, while type C sandstone is the last to consider when looking for a good reservoir. This study can guide hydrocarbon exploration in the Lengdong area, as well as in northwestern China and similar areas throughout the world.

The postrift stage in the pericratonic Kachchh Rift Basin of western India is represented by a thick sequence of a diachronous megadelta system. The deposition of this deltaic sequence was initiated during the mid-Kimmeridgian and ended in the Albian. The sedimentation was interrupted by two transgressive events demarcating three subcycles within the megadelta system. The present study addresses the older mid-Kimmeridgian to Tithonian “Jhuran Delta”. An attempt is made here to delineate the nature of the Jhuran Delta using the ichnological and sedimentological parameters. The Jhuran Delta, which consists of 14 lithofacies, is grouped into seven lithofacies associations corresponding to the prodelta, subaqueous gravity flow, delta front, distributary channel, distributary mouth bar, and shoreface depositional environments along with a transgressive unit overlapping the lower delta of the megadelta system. Three distinct stages of deltaic evolution are delineated along with the fourth stage of transgression and delta destruction. The prodelta environment of Stage I is characterized by moderate ichnodiversity represented by nine recurring ichnotaxa, suggesting alternating brackish and fully saline water conditions, which indicate river-dominated deltaic sedimentation. Stage II shows a marked increase in the influence of river (fresh water) water, as indicated by a submarine mass failure that includes debris flow, chaotic and contorted structures, sediment gravity-failure and water-escape structures and suggesting a higher rate of sedimentation. Ichnologically, this phase indicates low ichnodiversity with sporadic occurrences of Ophiomorpha and Palaeophycus. Stage III indicates the mixed dominance of river and wave processes. Sediments deposited in the delta front environment show moderate ichnodiversity with nine ichnotaxa. The distributary mouth bar environment comprises 6 recurring ichnotaxa including the ichnoassemblages of both river and marine wave environments. Integrated ichnological data suggest deposition in a mixed environment. The Jhuran Delta stage ended with a marine transgressive event and reworking of the deltaic sands, which were overlain by a thick shoreface deposit. Thus, the Upper Jurassic Jhuran Delta represents a river-dominated, wave-influenced delta.

Shim, W.J. and Kim, C.W., 2018. The necessity of coastal management in Busan Considering human and natural conditions: The case of barrier islands in Nakdong-estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp.1501–1505. Coconut Creek (Florida), ISSN 0749-0208. The Busan coasts have complex natural and human conditions including dynamic coastal, river processes and human activities. These complex natural and human factors have had direct and indirect impacts on the coastal areas of Busan, so a spatially integrated approach for management is required. Especially, the barrier islands located in the Nakdong River estuary are proper examples that show the effect of the sediment budget as natural and human conditions. This research aims to identify the effects of natural and human conditions on the barrier islands. The area of the barrier islands, sedi...

The Carnegie Quarry at Dinosaur National Monument was excavated in the Quarry Sandstone bed of the Brushy Basin Member of the Morrison Formation (Jurassic). The Quarry Sandstone is a discontinuous, lenticular, heterolithic unit that rests upon drab, greenish-gray claystones and is capped by reddish-brown mudstones. The underlying drab claystones are interpreted as being deposited in an overbank interfluvial wetland or lacustrine environment. By tracing the sandstone and studying detailed measured stratigraphic sections along its 1.8-km outcrop belt, this interval can be shown to be a complex of intergrading sandstone bodies and mudstone units. The Quarry Sandstone interval is reinterpreted as being deposited within a crevasse splay complex. The lowest part of this deposit is a laterally continuous, tabular unit composed of polymictic sandstone and granule conglomerate that directly overlies lacustrine claystones. This unit contains re-sedimented carbonate clasts from the surrounding Brushy Basin, displays a gradational to sharp basal contact, and is interpreted as the initial crevasse splay deposit. Overlying the tabular basal unit are numerous, laterally continuous, upward-coarsening sandstone bodies interpreted as distributary mouth bars. The interpreted distributary mouth bar deposits are cut by lenticular, trough cross-bedded, upward fining sandstone units exhibiting erosional bases. These sandstone lenses are interpreted as distributary channels within the crevasse splay. They, in turn, are overlain by discontinuous sandstone bodies that interfinger with, and are overlain by reddish brown and variegated, rooted mudstones containing calcic paleosols. The Carnegie dinosaur quarry was excavated in one of the main distributary channels of this splay complex.

The interpretation of tidal influence in a depositional system or stratigraphic interval buried deep in the subsurface is mainly based on sedimentary structures, fossils and trace fossils preserved in conventional cores. Studies of modern tidal depositional settings have shown that certain geomorphological features can be used as reliable tidal indicators. In this study we present evidence of tidal influence associated with Miocene channels in the Malay Basin, based on an integrated analysis of sedimentary facies from cores, well logs and high-quality 3D seismic data. Six facies associations identified in cores were interpreted as inter-distributary bay/offshore, tidal flat, subaqueous delta platform/prodelta, tide-influenced channel/bar, mouth bar, and mangrove/overbank deposits. Evidence for tidal influence include rhythmites, thick heterolithic successions, mud drapes, abundant bidirectional current indicators and the presence of an impoverished marine trace fossil assemblage. Channels identified in 3D seismic show unique geomorphological features indicative of tidal influence in the depositional system, such as flaring channel mouths, cuspate meanders, high-sinuosity, as well as dendritic and parallel channel networks comprising several orders of dead-end and through-flowing tributary channels. Identification of tidal geomorphological features in 3D seismic may help in predicting channel fill lithology in the subsurface, and in better planning of hydrocarbon exploration and development in basins with paralic channel-bearing reservoirs.

Digitate deltas consist of one or multiple separate bar fingers, which can form hydrocarbon reservoirs after burial. This paper focuses on digitate shallow-water deltas, which are commonly seen in modern and ancient deposits with similar downstream conditions. Four metrics were adopted to quantify their morphologies, including the average sinuosity, average nondimensional width (average width ratio between the bar fingers and distributary channels), nondimensional delta length (ratio between the delta length and average width of the distributary channels), and number of bar fingers. These metrics measured from 9 modern deposits and 21 Delft3D simulations exhibited wide-ranging values that were strongly affected by the upstream conditions. However, the effects of the upstream conditions remain unclear. The quantitative effects were revealed by performing Delft3D simulations: (1) the average sinuosity is proportional to the sediment cohesion and concentration and inversely proportional to the sand proportion and water discharge, and reaches equilibrium as sediment supply increases; (2) the average nondimensional width is proportional to the sediment concentration, is inversely proportional to the sediment cohesion and water discharge, has an inverse exponential relationship with the sand proportion, and is independent of the sediment supply; (3) the nondimensional delta length has a power-law relationship with the water discharge and is logarithmically related to the sediment supply; (4) the number of bar fingers is proportional to the sand proportion and sediment supply and inversely proportional to the sediment cohesion. Upstream conditions influence channel, mouth bar and levee growth, resulting in various bar finger morphologies. Empirical equations from Delft3D simulations were proven effective in examinations of nine modern deposits and applied to help predict the distribution of a digitate shallow-water delta reservoir. This work improves the fundamental understanding of the upstream controls in digitate shallow-water deltas and may help enhance the inter-well prediction of paralic reservoirs.

We conducted, for the first time, a study of the long-term evolution of an inner mouth bar in a microtidal environment that complements field observations with detailed numerical modelling of the same morphodynamics. Images collected by a video-monitoring station, from 2016 to 2019, were processed to study the evolution of a persistent inner mouth bar formed inside the highly engineered Misa River estuary (Senigallia, Italy) after years of reduced precipitation and discharges. We developed a semi-automatic procedure to detect the emerged area of this deposit. We seek to quantify the relationship between the long-term evolution of the bar and the forcing from the river, waves and tides. The observed high peaks in river discharge caused a strong downriver bar migration (i.e. almost twice the river width). Conversely, the observed sea storms produced an upriver bar migration smaller than one river width. A much slower and weaker (less than half the river width) upriver migration was also observed during periods of large area accretion and due to mild wave climate. Moreover, results showed that the sea water level variation did not directly impact the morphodynamics of the estuary, affecting the emerged portion of the bar only. Numerical simulations, run with Delft3D, were used to complete the information coming from field observations. After some checks on the proper use of the solver for the scenarios and environments of interest, some parametric simulations were run to highlight the role of the different forcing on the bed evolution. Simulations showed, as expected, erosion of the riverbed and significant downriver migrations (four river widths) during peaks of river discharge comparable to the 1-year return period discharges. Numerical results also showed upriver sediment transport when the wave forcing was dominant, with 10-years return period waves inducing an upriver bar migration in the order of one river width. Then, one real-life event was simulated to inspect the interaction of the various forcing and to compare their effects with the observations. Our analysis provides new insight into the complex morphodynamics in a microtidal estuary when weak river discharge is opposed by sea waves driving upriver sediment transport. A more thorough understanding of the morphodynamics is needed for future forecasting of the formation and evolution of sediment deposits inside estuarine channels that can inhibit both navigation and the flux of sediment from the river to the estuary.

The Erin modern marginal-marine depositional system sits along the Trinidad southwestern coastline. It is among the many unstudied and undocumented modern, dynamic coastal depositional systems around Trinidad. Our study defines the Erin system as being a deflected and asymmetric wave-dominated delta, and in so doing, elucidates the dynamics of the Erin system. This was done using a compendium of satellite images, temporal cross-shore elevation profiles, modern shallow sediment cores, and sediment samples. Geomorphologically, the Erin system comprises a vegetated delta plain and the unvegetated modern deposits. The delta plain has four amalgamated sand bars with intercalated lagoonal deposits. The unvegetated modern deposits is defined as the fifth bar of the system. These five bars were loosely correlated to the five 6th order eustatic cycles of the Holocene highstand. The modern, unvegetated deposit of the fifth bar is divided into an updrift segment and a downdrift segment relative to the inlet mouth. The updrift segment comprises a spit and beach depositional elements, while the downdrift segment comprises a barrier spit, back-barrier lagoon, rip-channels, and sometimes a bayhead delta at the Erin River mouth. The dynamic, annual evolution of the spit reflects a seasonally controlled, possibly cyclical evolution wherein the delta transitions from being asymmetric to deflected-asymmetric. This phenomenon is postulated to be brought on by seasonal changes in the wave regime, and not, as one might expect, seasonally controlled river discharge. That is, during the summer wave season, when net-deposition occurs, the system morphology is deflected as a consequence of increase sedimentation in the nearshore. During the winter wave season, when net-erosion is expected, the system morphology reflects that of a typical asymmetric delta, as a consequence of reduced sedimentation in the nearshore. This cyclical movement of sediment is also observed in cross-shore elevation profiles. Sedimentologically, six depositional elements were sampled using sediment cores: foreshore, updrift spit, channel bars, mouth bar, barrier spit (downdrift), and back-barrier lagoon. Physical sedimentary structures reflected wave energy dominance across the system with an increase in tidal signatures within the lagoon deposits and lower foreshores. Biogenic sedimentary structures were limited across much of the system, but the traces recorded were mostly isolated in the downdrift back-barrier lagoon deposits, and few in the upper barrier spit. Grainsize distributions showed an average grainsize of fine sand across the system with coarse-grained, poorly sorted, bio-clastic sands present as channel lag deposits. An increase in mud content was recorded in the downdrift segment of the delta. The geomorphological, sedimentological, and ichnological data described above provided sufficient evidence to define the Erin system as an asymmetric wave-dominated delta with seasonally controlled deflected morphology.

Investigations of syn‐sedimentary growth faults in the Last Chance delta (Ferron Sandstone, Utah, USA) show that fault‐bounded half‐grabens arrested high amounts of sand in the mouth bar and/or distributary channel areas. Fault‐controlled morphology causes changes in routing of the delta top to delta front drainage towards the long axis of half‐grabens. Faulting was spatially and temporally non‐systematic, and polyphase, with 3D cusp/listric fault geometries instigated by linkage of variously oriented segments. Hanging wall rollover folds consisting of wedge‐shaped syn‐kinematic sand attest to rapid

Research focussing on the morphology and morphodynamics of modern river deltas has contributed much to the understanding of reservoir geometry and prediction of hydrocarbon splays and deep geothermal aquifers. The interplay of allogenic and autogenic controls results in complex histories of modern river deltas comprising subsequent regressive and transgressive stages of delta formation. The application to ancient examples is still ambiguous and in particular the detailed morphological description of ancient deltas is often hampered by limited subsurface data. This basin-scale study employs a data set of 15 cored wells and more than 450 logged wells in combination with lithofacies, biofacies and architectural analysis to reconstruct high-resolution subsurface facies and sand thickness maps of the Toarcian–Bajocian deltaic system in the North German Basin. The results of this study show the evolution from smaller elongate river-dominated delta types in the Lower and Upper Toarcian (15,000 to 20,000 km²), and a larger lobate river-dominated delta in the Upper Aalenian (40,000 km²) to a cuspate mixed river-dominated and wave-modified delta in the Upper Bajocian (25,000 km²). The river-dominated parts are composed of subsequently formed of distributary deltaic channel belts and associated sheetsands of the delta plain and distributary mouth bar complexes with bar finger sand architectures of the delta front. Increasing marine processes in the Bajocian resulted in modification of delta complexes forming a shoreface setting with foreshoals, arc-like chains of ooid-bearing barrier shoals and back barrier lagoons. The complex history of the Toarcian–Bajocian deltaic system was mainly controlled by allogenic sea-level fluctuations that triggered the delta progradation and subordinately by allogenic basin reorganisation. Autogenic process change of channel avulsion led to locally reduced sediment flux and culminated in lobe abandonment and transgressive shorelines. Differential compaction of underlying deltaic deposits result in strong differences in accommodation space and contributed to much to large-scale delta shifts (>300 km). This article is protected by copyright. All rights reserved.

Based on outcrop, core, logging and mud logging data, and modern deposition analog, the sandbodies genetic types and spatial distribution in different facies belts of the shallow water delta in the first Member of Cretaceous Yaojia Formation (K2y1) of Qian'an area in Changling sag of southern Songliao Basin were analyzed, and the sedimentary model of shallow water delta was established according to deposition process. Active channel sandbodies, point bar sandbodies and bifurcation bar sandbodies in distributary channels and complex sandbodies formed the main sandbodies in the delta plain, while terminal distributary channels and mouth bar sandbodies formed the main sandbodies in the delta front. The delta prograded gradually under the construction of river mouth and reconstruction of river erosion, the early delta front evolved into delta plain and was reformed by distributary channels, and new delta fronts were formed at the river mouth ahead constantly. Under the control of the above deposition process, the size of main distributary channels in delta plain-delta front declined, while mouth bars developed increasingly. The sandbodies of different genetic types formed framework of river-dominated shallow water delta. The point bar and active channel sandbodies in main distributary channels of the delta, with the best reservoir quality, are lithologic reservoir targets in future exploration. Key words: Songliao Basin, Cretaceous, Yaojia Formation, shallow water delta, sandbody type, sedimentary model

The mechanism by which new deltaic wetlands form is a complex suite of biological and physical processes that can modify one another. Understanding these processes and their interactions is imperative to successful coastal restoration. This study investigated the relationship between belowground plant biomass and sediment cohesion. We hypothesized that greater root densities increase shear strength, variably across plant communities, and that these communities are associated with distinct inundation regimes. A significant relationship was found between belowground biomass and surface shear strength when accounting for sediment grain size, water content, and organic matter content. Sites dominated by native graminoids or woody species had significantly higher shear strengths than unvegetated areas. However, sites dominated by Phragmites australis or forbs did not differ significantly in shear strength from the unvegetated sites. Sites dominated by Phragmites australis were also subject to significantly higher inundation rates during the previous water year than any other vegetation type. These results suggest that vegetation community differences lead to differences in shear strength that result in locally differential erosion rates, in turn modifying future geomorphology, hydrology, sedimentation, and vegetation distribution. This feedback implies that certain vegetation communities in wetland restoration projects could not only impart immediate erosion resistance to the substrate, but affect the long-term potential for land creation.

River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that—despite the active morphodynamics in tidal channels and mouth bar regions—tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention. River deltas are shaped by interactions between fluvial and tidal processes. Tides act to stabilize delta morphology, but sediment depletion due to human activities disrupts the balance and leads to erosion and scour.

Understanding the decadal morphodynamic evolution of estuaries and deltas and their controls is of vital importance regarding management for estuarine function and sustainable development. This work addresses this issue by applying a process-based model system (Delft3D) to hindcast and then forecast the morphodynamic evolution of the Yangtze Estuary at a decadal timescale. Forced by the river and tides, the model considers sand-mud mixture and the variations of river water discharge and sediment discharge. The morphodynamic model is validated against three periods, i.e., an accretion period (1958–1978), an erosion period (1986–1997) and a recent accretion period with human activities (2002 − 2010). Model results show good performance with respect to spatial erosion and deposition patterns, sediment volume changes, and hypsometry curves. The model reveals quite different behaviors for mud transport between the dry and wet seasons, which is subject to the prescription of river boundary conditions and bed composition. We define six scenarios to project evolution to the year 2030 under decreased river inputs and increased relative sea level. The simulations reveal that overwhelming amount of erosion will likely occur in the inner and mouth bar area of the estuary. Particularly, the mouth zone will shift from net deposition before 2010 to net erosion by 2030, mainly because of decreasing sediment supply. Changes in water discharge have minor effects on the projected trend. Net erosion will be considerable when the sediment supply is extremely low (100 Mt yr − 1 ) due to the abundance of erodible modern sediment in the Yangtze Estuary. Erosion within the mouth bar area may be unexpected, including the deepening of the tidal inlet at East Chongming mudflat and the formation of a flood channel on the seaward side of Jiuduansha Shoal. Overall, the model results provide valuable information for sustainable delta management under changing conditions for both the Yangtze system and other similar estuaries and deltas with diminishing sediment supplies.

The Upper Triassic Xujiahe tight-sand reservoir is characterized by low porosity and ultra-low permeability as well as intense heterogeneity. Investigation on depositional facies and their impact on reservoir quality has been proven to be a powerful tool to predict high-quality reservoirs. This study attempted to explain impacts of depositional environment and diagenesis on Xujiahe tight-sand reservoir quality in Guang’an area by: (1) identifying petrofacies and wireline logs patterns and analyzing the spatial variation of sedimentary facies, (2) determining diagenesis through detrital components, rock properties and their spatially variation as well. The results suggest that (1) T3x2, T3x4 and T3x6 were mainly deposited in delta system, including braided river in delta plain, delta distributary channels, underwater distributary channel, and mouth bar, etc., (2) the Upper Triassic Xujiahe Formation in the Guang’an area is typical tight-sand reservoir with porosity of 0.68–15.94% and permeability of 0.001–274 mD. Poor reservoir quality is attributed to intense compaction and dissolution during middle diagenetic stage A2, which are dominated by feldspathic litharenite and lithic sandstone. (3) Potential high-quality reservoirs in T3x2, T3x4 and T3x6 are associated with delta plain distributary channel, delta front underwater distributary channel and mouth bar, since high-energy delta channel microfacies typically resulted in a large number of primary pores in sand body. Considerable secondary pores were resulted from organic acid derived from source rocks during middle diagenetic stage, improving reservoir quality significantly.

Video observations of depth-limited wave-breaking patterns at an ebb-tidal delta on the energetic west coast of New Zealand at Raglan were used to identify geomorphic features over a 5-year period. The terminal lobe, mouth bar, channel margin linear bars, and swash bars were identified and tracked over the duration. Morphodynamic response was related to environmental conditions by correlating observed movements with concurrent wave and tidal conditions. Movements occurred throughout the record with a slight tendency to occur more during the transition between seasonal forcing trends. Winter deltas were generally broader and extended further seaward than the summer deltas which were more cuspate. The formation of a double-barred ebb-shoal was observed, with the cross-shore position of the outer bar influenced by wave conditions while the inner bar was influenced by ebb-jet strength. Furthermore, swash bars were observed to constrict the seaward extent of the main channel during large wave events, which was subsequently eroded by tidal currents. These observations are consistent with the present consensus that ebb-shoal features are dependent upon competition between ebb-jet strength and opposing waves. Interannual morphological changes were not significantly correlated to any particular environmental forcing, suggesting that either some process or combination of processes not considered were influential, or that the system might be showing signs of emergent behaviour.

In recent years, oil reservoirs in the large-scale delta sedimentary system of a salty lake have been discovered in the Lower Ganchaigou Formation(E 3 1 ) and the Lower Youshashan Formation (N 2 1 ) in the western part of Qaidam Basin (referred to as WQ), constituting an oil and gas exploration breakthrough in Qaidam Basin. To expand the scale of exploration, a braided delta deposition model of the salty lake was developed, and the regular patterns of sand gathering from three source areas, Alar, Niubiziliang, and Tiemulike, were clarified. Based on the experimental simulation technique of large flume deposition under a background of salty lake, these areas were then chosen as sedimentary prototypes to carry out a physical simulation experiments to examine large flume deposition, the dynamic process of braided delta deposition, and the model of sand gathering. The results show that a braided delta has the sedimentary characteristics of a small delta front with a large delta plain and development of underwater distribution channels and a mouth bar in a saltwater environment. Lake salinity controlled not only grain size, thickness, spatial distribution regularity, and particle transport distance, but also the scale of development of the underwater distribution channels and the mouth bar. Because of the dynamic complexity of lake inputs due to the vertical stratification of salinity, the authors believe that the braided branch channels of the braided delta plain and the mouth bar of the braided delta front may hold good reservoirs.

Taking the Kumkol oilfield in the South Turgai Basin of Kazakhstan as an example, based on the quantitative statistics of permeability coefficient, grade difference and rush coefficient, the water driving dominant channel of the braided river sandstone, meandering river sandstone and delta sandstone under the same development mode are compared and analyzed, and finally determined water driving degree and remaining oil potential of different types of sandstones. The results show that the permeability heterogeneity of the braided river sandstone is weak and the water driving dominant channel in the reservoir is not developed, so the overall waterflooding and water driving degree is high with small remaining oil potential; in delta sandstone, the permeability heterogeneity is high and water driving dominant channels develop in underwater distributary channel and mouth bar single sand bodies, so the overall waterflooding and water driving degree are low with large remaining oil potential; While in meandering sandstone, the permeability heterogeneity is moderate and water driving dominant channels develop in point bar single sand bodies, the overall waterflooding and water driving degree as well as remaining oil potential are between the braided river sandstone and the meandering sandstone. Under the same development mode, the delta sandstone is the main target of the remaining oil potential tapping in the later stage.

River deltas are highly dynamical and valuable environments and often undergo strong natural changes and human-induced pressures that need careful observation and monitoring. However, the high dynamicity of submerged deltas makes it very hard to observe how sediment are distributed across the delta area, a crucial element in understanding their morpho-dynamic evolution. To fill this observational gap, in the last few years (2013-2016) repeated high-resolution multibeam bathymetry surveys were carried out for the first time at the Po della Pila delta, the recent-most delta lobe of the Po river. The collected bathymetric and acoustic reflectivity (backscatter), seabed samples and seismic profiler datasets provided insights on the short-term morphological and sedimentological evolution of the extremely dynamic submarine portion of the delta in the framework of the hydrodynamical, seismo-stratigraphical and environmental setting. A high variety of geomorphological features and depositional bodies at different scales were observed from the mouth bar to the prodelta slope such as the alongshore and radial bars under the effect of marine currents, gravitational-instability phenomena and collapse depressions driven by fluid expulsion. Concurrently, the analysis of the seabed reflectivity and sediment samples allowed the identification of two main classes of seafloor sediment, corresponding to dominantly sandy vs. muddy substrata. The comparison among time-lapsed, high-resolution DEMs in the time frame 2013-2016 showed that the main changes occurred on the northern side of the prodelta slope in front of the active channel: mainly as a consequence of the flood of November 2014, a new lobe-shaped fine-sediment deposit up to 4.5 m thick corresponds to a newly-added sediment volume of 1.16 Mm3. Other major morphological changes occurred in the prodelta slope, where radial depositional bars showed a net S-ward migration. Moreover, a generalized seafloor deepening was documented, accompanied by changes in seabed reflectivity with a general coarsening of the delta lobe sediment distribution from the first to the third survey. We document the morphological and sedimentological complexity and the rapidity of the geomorphological changes in the shallow reaches of the Po della Pila lobe. Given the high rates of sediment accumulation and rapid erosion related to storms and currents, this area represents as well a relevant site to study the Anthropocene short-term climate-driven variability of the coastal region including the possible interaction among human-induced changes in sediment supply, coastal erosion, alongshore sediment transport, local subsidence (both natural and anthropogenic) and submarine slope instability.

Coastline changes over some 24 years along the Ganjiang-Poyang Lake have allowed us to monitor the coastal morphological evolution, with its attendant social consequences. This study focuses on the coastal morphology changes controlled by the north and middle branches of the Ganjiang River as the lake delta prograded into the Poyang Lake. The north branch resulted in an elongated coastal headland with one sinuous channel complex, whereas the middle branch produced a prograding shoal-water river-dominated delta system with a distributary channel network. The main units of the north branch consist of a single channel and associated point bar and levee, whereas those of the middle branch consist of distributary channels and mouth bar. The evolution of the north branch was dominated by changes of the channel, while the middle branch became dominated by distributary channel bifurcation and mouth-bar formation. Changing morphology of both the branches of Ganjiang shows a decreased progradation rate from 1992 to 2015, which can be evidenced by a decreasing prograding rate from 0.875 to 0.21 km/year of the middle branch. The lakeward outbuilding process was characterized by an initial stage of strong progradation, whereas the subsequent stage was dominantly aggradation associated with weak progradation. Human activity such as dam building and forestation generated decrease of sediment input, resulting in the decrease in the prograding rate of the Ganjiang delta. Sediment grain-size variations control the geometry of the prograding body of the two branches. The finer sediment delivery of the north branch resulted in the elongated coastal headland, whereas the relatively coarser sediment of the middle branch resulted in the development of the lobate-shaped delta lobe. This study highlights the significant role of upstream factors, which can be evidenced by that the grain size and magnitude of supply that controls the construction and shape of the coastal morphology.