Increasing Water Depth Research Articles

Effect of multiple environmental conditions on the formation process and adhesion strength of ice on asphalt binder surface

Road icing caused by freezing rain significantly impacts driving safety. Since asphalt binder plays a pivotal role in pavement infrastructure, understanding the formation process and adhesion strength of ice on asphalt binder surfaces is crucial for assessing road icing risk. This work investigated the effect of different environmental conditions on asphalt-ice interface adhesion strength via a self-designed low-temperature adhesion testing system. In addition, the icing process on asphalt binder surfaces was observed to analyze the asphalt-ice adhesion strength formation mechanism. Results show that the completion time of water-ice phase transition signified the initial development of asphalt-ice adhesion strength. Moreover, as the internal structure of the ice evolved from transparent to needle-like fine lines to dense, the asphalt-ice adhesion strength gradually increased until it reached stability. At asphalt-ice adhesion began forming after 40 min and stabilized after 80 min, whereas at −8°C, adhesion strength started forming after 20 min and stabilized by 60 min. The growth rates of asphalt-ice adhesion strength for temperatures ranging from −2°C to −10°C were approximately 7.92 kPa/°C, 6.56 kPa/°C, 5.14 kPa/°C, 3.29 kPa/°C, and 1.49 kPa/°C, respectively, showing a positive correlation with temperature and a negative correlation with time. According to heterogeneous nucleation theory, the influence mechanism of temperature and water depth on the nucleation icing process and asphalt-ice adhesion strength is analyzed. lower temperatures lead to asphalt-ice adhesion strength increase originating from the larger supercooling, which reduces the critical nucleation energy and thus accelerates the ice nucleation rate. In addition, the increase in water depth promotes the formation of nucleation sites and further enhances the asphalt-ice adhesion strength. Finally, an asphalt-ice adhesion strength prediction model was developed, with PSO-SVM-G achieving over 90 % accuracy. These results provide insights for evaluating ice adhesion behavior on asphalt surfaces and designing anti-icing asphalt materials.

UAV-based LiDAR Bathymetry at an Alpine Mountain Lake

Abstract. LiDAR bathymetry provides an efficient and comprehensive way to capture the topography of water bodies in shallow water areas. However, the penetration depth of this measurement method into the water column is limited by the medium water and water turbidity, resulting in a limited detectability of the bottom topography in deeper waters. An increase of the analyzable water depth is possible by the use of extended evaluation methods, in detail full-waveform stacking methods. So far, however, this has only been investigated for water depths of up to 3.50 m due to water turbidity. In this article, the potential of these extended data processing methods is investigated on an alpine mountain lake with low water turbidity and thus high analyzable water depth. Compared to the standard data processing, the penetration depth could be significantly increased by 58%. In addition, methods for depth-resolved water turbidity parameter determination on the basis of LiDAR bathymetry data were successfully tested.

Numerical study on ignition start-up process of an underwater solid rocket motor across a wide depth range

Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets. In this paper, the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied. A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model. This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor, along with the gas jet evolution in the external water environment. The detailed flow field developments in the combustion chamber, nozzle, and wake field are carefully analyzed. The variation rules of the internal ballistics and thrust performance are also obtained. The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed. The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens. The development of the gas jet in water lags significantly compared with that in air. As the water depth increases, the ignition delay time of the motor is shortened, and the morphology evolution of the gas jet is significantly compressed and accelerated. Furthermore, the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified, resulting in stronger fluctuations in the wake pressure field and motor thrust.

Structural changes and assembly mechanisms of microbial communities during rapid sedimentation of Yellow River sediments

Microbial communities are essential for the biogeochemical cycles in aquatic ecosystems. The effects of sediment depositional processes on the microbial community characteristics in the Yellow River have not been extensively studied at the in-situ macroscopic scale. Since the Yellow River diversion reservoir has the sedimentation pond, it can be used as a natural experimental area. This study investigated changes in microbial community structures, functions, and assembly mechanisms under sediment deposition by analysing 26 water and sediment samples. The results showed that during rapid sediment deposition, different community structures formed between the water body and the sediment (Analysis of similarities, P<0.01), and the variability between them increased with increasing water depth. Sediments are more closely associated with carbon, nitrogen, and sulfur cycling processes, while water is more closely associated with light reactions. Under changing sediment concentrations, the microbial community diversities, community compositions, and functions changed significantly. Actinobacteria and Cyanobacteria were the species responsible for the significant differences in the microbial communities in the water, with linear discriminant analysis scores of 4.478–4.724 and 4.427–5.007, respectively. Water temperature, NH4+-N, and electrical conductivity were the most critical factors that affected the microbial community structures. During the rapid deposition of sediments, microbial community assembly was dominated by stochastic process. This study may provide a reference for exploring the mechanism of microbial community changes in reservoirs under the dynamic hydrological conditions of the Yellow River.

Wetland restoration enhances habitat for an endangered bat, Eumops floridanus

Restoring lost or degraded wetlands is a major challenge in contemporary conservation. Understanding how wetland restoration and changes in hydrology affect wildlife is increasingly urgent for endangered species conservation. This is especially pertinent for the endangered Florida bonneted bat (Eumops floridanus), whose range is almost entirely contained within one of the world's most iconic wetland systems, the Greater Everglades Ecosystem. We investigated how E. floridanus may respond to future hydrological and vegetation changes associated with current and planned Everglades hydrologic restoration efforts. We conducted acoustic surveys at 194 random points stratified across a restoration gradient (no hydrologic restoration, partial hydrologic restoration, full hydrologic restoration, and reference). Using generalized linear mixed models, we determined the most important predictors explaining variation in bat activity and foraging likelihood. Positive associations between bat activity and several hydrologic variables expected to increase with restoration (hydroperiod, water depth, distance to canals, and extent of freshwater forested wetlands, ecologically intact reference areas, and zones with full hydrological restoration) suggest that foraging habitat for this species will likely benefit from hydrologic restoration both in the near term (immediate increases in hydroperiod and water depth) and in the longer term (as freshwater forested wetlands expand). Our results inform immediate management decisions for this species and suggest the benefits of restoration for wildlife adapted to historically longer hydroperiods and greater water depths, which are anticipated to increase with the gradual return of natural hydrological regimes.

Longevity of subtidal mussel beds (Mytilus edulis) in eutrophic coastal areas

Mussel populations (Mytilus edulis) around the coasts of Europe and the North Atlantic are often ephemeral and have notably experienced a large decline in abundance. Since 1993, annual blue mussel stock surveys have been carried out in the Limfjorden, Denmark. We used the stock survey data combined with electronic monitoring fishing data and Mechanistic Models for the Limfjorden, providing environmental data to investigate the impact of various stressors. Multiple factors were found to affect the longevity of subtidal mussel beds in Limfjorden. Predation by starfish, fishing activities, shell length of the mussels, amplitude in summer temperature and consecutive days of oxygen depletion decreased the longevity of the beds. Conversely, increased biomass, multiple cohorts and increasing water depth demonstrate stabilising effects. Water column stratification had both a negative and positive impact on bed longevity depending on the duration. These analyses can help inform environmental, conservation, and fisheries managers on the long-term trends of population dynamics and gain a deeper understanding of what factors can affect mussel bed longevity in the context of declining stocks.

Sight and blindness: The relationship between ostracod eyes, water depth, and light availability in the Arctic Ocean

AbstractEye loss has been a long‐standing interest in evolutionary biology. Many organisms that inhabit environments without light penetration, for example the deep sea, exhibit eye loss and thus become blind. However, water‐depth distribution of eyes in marine organisms is poorly understood. Ostracods are widely distributed crustaceans, and many sighted marine ostracods have eye tubercles (lenses) on their shells. Since eye tubercles are visible on the shells illustrated in much literature, it is easy to determine their presence or absence via a literature survey. Here, we used a large Arctic‐wide ostracod census dataset (Arctic Ostracode Database) to calculate the eye index (the percentage of species with eyes), and compare them with water depth and light availability. As water depth increases, eye index values decrease and become constantly zero in water deeper than 1000 m. Similar decline of sighted species with increasing depth is also known in isopods and amphipods, suggesting that it may be common in other crustaceans and perhaps in deep‐sea organisms in general. We also show that eye index values increase as light availability increases. This study is the first to quantify how distributions of sighted and blind species change with light availability, giving baseline information on vision in the deep sea.

Experimental study of dynamic pressure and wave load on variform vertical cylinders under extreme waves

Extreme waves pose a significant threat to the proliferating marine structures, however, the impact on the vertical cylinder with different cross-sectional shapes remains inadequately evaluated. Herein, we carried out a physical experiment, comprising 45 scenarios generated by three water depths, three wave paddle velocities, and five vertical cylinder models, to measure the extreme wave-induced pressure and load on this type of structure. The wave load and dynamic pressure distribution in time and spatial domains under the influence of cross-sectional shapes and wave conditions have been fully discussed. The experimental results indicate that: 1) As the position turns from front to back side, the circumferential pressure of five models initially decreases and then increases. 2) The maximum differential pressure between the front and back side decreases with increased water depth and decreased velocity, and occurs earlier than the peak pressure on the front side. 3) The chamfered cross-section (round and right triangle) can significantly reduce the wave load compared to the rectangular section, and the circular section suffers the lowest force logically. The dynamic pressure and wave load in this experiment can serve to establish a more sophisticated load model and provide valuable insights for marine structural design and disaster prevention.

Research on the effect of shallow draft on the performance of azimuth thruster under bollard conditions

For the azimuth thruster installed on shallow draft ships, the shallow water effect leads to a decrease in propulsive performance, especially under the bollard condition. In order to accurately predict the bollard propulsion performance of the azimuth thruster under shallow draft conditions, this paper firstly obtains the bollard thrust performance in several waters through the shallow water test, and then analyzes the effect of hull wake and cavitation on the bollard thrust performance of the azimuth thruster by using the CFD method. The results are consistent with the test results under the open water. When the water depth is less than 1.0D, the thrust coefficient increases with the increase of water depth, when the water depth is greater than 1.0D, the thrust coefficient basically does not change; Considering the influence of hull wake, the axial inlet velocity of the azimuth thruster is 7.27% higher than that of the open water condition; meanwhile considering the influence of the hull wake and cavitation, the leading edge of the bottom of the azimuth thruster conduit and the back of the paddle blade are susceptible to cavitation, which leads to average decrease of the thrust coefficient and torque coefficient by 7.03% and 6.12%, respectively.

The resistance of Georgia coastal marshes to hurricanes

AbstractEcosystems vary broadly in their responses to disturbance, ranging from highly impacted to resilient or resistant. We conducted a large‐scale analysis of hurricane disturbance effects on coastal marshes by examining 20 years of data from 10 sites covering 100,000 ha at the Georgia Coastal Ecosystems Long‐Term Ecological Research site distributed across gradients of salinity and proximity to the ocean. We analyzed the impacts of Hurricanes Matthew (in 2016) and Irma (in 2017) on marsh biota (plants, crabs, and snails) and physical attributes (erosion, wrack deposition, and sedimentation). We compared these variables prior to the storms (2000–2015) to years with storms (2016, 2017) to those after the storms (2018–2020). Hurricanes generated storm surges that increased water depth and salinity of oligotrophic areas for up to 48 h. Biological variables in the marsh showed few effects of the hurricanes. The only physical variable affected was creek bank slumping; however, slumping had already increased a year before the hurricanes, suggesting that slumping could have a different cause. Thus, our study uncovered only minor, ephemeral impacts on Georgia coastal marshes, highlighting their resistance to hurricane disturbance of the lower magnitude that typically confronts this region of coastline.

An analytical study for predicting incipient motion velocity of sediments in ecological open channel flows

Sediment movements on the riverbeds are crucial in fluvial processes. Therefore, studying incipient sediment motion is valuable for predicting changes in sediment behavior. In this study, the influence of aquatic vegetation is introduced into the momentum balance equation under the condition of a bare bed. The presented model for incipient sediment motion in open channels covered by vegetation is derived, in consideration of vegetation density and relative submergence. This study simplifies the model format. The model and its coefficients demonstrate good applicability to various working conditions without requiring numerous changes. The predicted velocity determined by the proposed model is validated against experimental data. Results show excellent agreement between the two in various scenarios, including combinations of rigid or flexible conditions and submerged or emergent states. Additionally, the velocity for incipient sediment motion is observed to decrease with increasing vegetation density. However, a further increase in vegetation density may amplify vegetation resistance, hindering incipient sediment motion. Meanwhile, sediment movement becomes challenging as water depth increases, assuming that flow discharge and vegetation conditions remain constant.

Effects of multiple future environmental changes on flooding in coastal area: Case study in Qianshan River Basin, South China

Due to their unique geographical characteristics, coastal areas are not only impacted by climate change and urbanization but also by sea level rise-induced lower boundary jacking. This makes them vulnerable to rapid, intense, and short-duration flooding events. In this study, a comprehensive analysis was conducted considering future climate change, land use change, and sea level change. By employing a hydrological model, potential flood scenarios in Qianshan River Basin were simulated in efforts to understand the combined impact of multiple environmental changes on coastal flooding. The results indicate that the flood characteristics of Qianshan River Basin will increase due to multiple future environmental changes. Notably, Dachong experiences the most significant surge in peak discharge, while Hongwanchong and Guangchangchong experience the highest increase in peak water depth under normal and extreme conditions, respectively. The inundation area’s location remains predominantly situated in the southern part of the basin, with high-risk zones substantially increasing, particularly in Tanzhou Town and the outlet of Qianshanshuidao. The observed pattern of increasing flood characteristics follows a clear trend across future scenarios SSP126, SSP245, SPP370, and SSP585. The flood characteristics resulting from a design rainfall of grade n correspond to those produced by a design rainfall of grade (n + 1), (n + 2), (n + 3), and (n + 4) in the current period, respectively.

Uncovering extensive populations of the ‘threatened’ Black Crowned Cranes in Gambella, Ethiopia

A reliable assessment of the population size of threatened species is crucial for making informed decisions about their conservation and management. However, there is a lack of comprehensive knowledge on the population of the eastern Black Crowned Crane (Balearica pavonina ceciliae), which is globally recognized as a threatened taxon experiencing a declining population trend. Here, we investigated the density, abundance and factors that influence flock size in the wetlands of the Gambella region in Ethiopia. We used line transects to collect data during dry and wet seasons. Population density and abundance were estimated using DISTANCE software, whereas factors influencing crane flock size were evaluated using a generalized linear model. We found that crane density ranged from 444 to 965 birds per sq km in the dry season and from 62 to 105 individuals per sq km in the wet season. We estimated that the population size within the designated survey areas as 7634 during the dry season and 866 during the wet season. Furthermore, for the broader survey region that encompasses permanent wetlands, the estimated population ranged from 9138 to 19,849 individuals in the dry season and from 1272 to 2166 individuals in the wet season. We found that grazing intensity and proximity to woodlands and rivers had significant positive impacts on crane flock size, whereas an increase in wetland water depth and grass height remarkably reduced flock size. As a result, wetland habitat degradation-related problems are not currently a threat to cranes in this region, but are likely to increase in the future due to large-scale agricultural expansion. The crane population size we estimated in Gambella is high, three to four times higher than the estimate from the entirety of Ethiopia. Our research underscores the global significance of Gambella wetlands as an important habitat for cranes. However, to obtain an accurate population estimate in this region, it is imperative to include seasonal wetlands, savannah grasslands, farmlands and the extended wetlands of South Sudan, which are hydrologically connected to the wetlands of Gambella region. To achieve this, comprehensive surveys and estimations should incorporate various techniques, such as aerial surveys, satellite telemetry, and high-resolution satellite imagery.

Load Calculation and Strength Analysis of the Deepwater Landing Drill Pipe-Lowering Operation

A landing string is directly exposed to seawater and subjected to significant stresses and complex deformations due to environmental loads such as wind, waves, and ocean currents during the phase in which the drill string carries the casing to the wellhead. Meanwhile, as the water depth increases, the weight of the drill string increases, leading to an increase in the tensile loads borne by the drill string, which can easily cause a risk of failure. Therefore, a quasi-static load calculation model for the deepwater insertion of the pipe column was established. Using the Ansys platform, simulations were conducted for average wind, wave, and ocean current conditions during different months throughout the year. The ultimate loads and stress distributions of the string were derived from theoretical analyses and numerical simulations for different operational sea states, and the suggested safe operating window and desired BOP trolley restraining reaction force for landing strings’ lowering are given according to the existing industry standards. The research findings can help in identifying the potential risks and failure modes of the deepwater landing string under different working conditions.

Informing the Conservation of Ephemerally Flooded Wetlands Using Hydrologic Regime and LiDAR-Based Habitat Assessments

Integrated assessments of wetland hydrologic regimes and other environmental factors are key to understanding the ecology of species breeding in ephemerally flooded wetlands, and reproductive success is often directly linked to suitable flooding regimes, both temporally and spatially. We used high-resolution Light Detection and Ranging (LiDAR) data to develop bathymetric stage–flooded area relationships, predict spatial extent of flooding, and assess vegetation structure in 30 pine flatwoods wetlands. For a subset of wetlands with monitoring wells, we then integrated bathymetric and water level data to create multi-year time series of daily flooded areas. We then related the observed flooded areas to topographic and landscape metrics to develop models predicting flooded extents in wetlands without monitoring wells. We found that stage–area curves varied depending on wetland size and bathymetry, such that a one-cm increase in water depth could generate flooded area increases ranging from hundreds to thousands of square meters. Flooded areas frequently fragmented into discrete flooded patches as wetlands dried, and there was a weak positive correlation between hydroperiod and mean flooded area across multiple years (r = 0.32). To evaluate the utility of using LiDAR-derived data to support the conservation of wetland-breeding species, we combined metrics of flooding and vegetation to map potentially suitable habitat for the imperiled reticulated flatwoods salamander (Ambystoma bishopi). Overall, projects focusing on the ecology of wetland-breeding species could gain a broader understanding of habitat effects from coupled assessments of bathymetry, water level dynamics, and other wetland characteristics.

Variability in Symbiont Chlorophyll of Hawaiian Corals from Field and Airborne Spectroscopy

Corals are habitat-forming organisms on tropical and sub-tropical reefs, often displaying diverse phenotypic behaviors that challenge field-based monitoring and assessment efforts. Symbiont chlorophyll (Chl) is a long-recognized indicator of intra- and inter-specific variation in coral’s response to environmental variability and stress, but the quantitative Chl assessment of corals at the reef scale continues to prove challenging. We integrated field, airborne, and laboratory techniques to test and apply the use of reflectance spectroscopy for in situ and reef-scale estimation of Chl a and Chl c2 concentrations in a shallow reef environment of Kāne‘ohe Bay, O‘ahu. High-fidelity spectral signatures (420–660 nm) derived from field and airborne spectroscopy quantified Chl a and Chl c2 concentrations with demonstrable precision and accuracy. Airborne imaging spectroscopy revealed a 10-fold range of Chl concentrations across the reef ecosystem. We discovered a differential pattern of Chl a and Chl c2 use in symbiont algae in coexisting corals indicative of a physiological response to decreasing light levels with increasing water depth. The depth-dependent ratio of Chl c2:a indicated the presence of two distinct light-driven habitats spanning just 5 m of water depth range. Our findings provide a pathway for further study of coral pigment responses to environmental conditions using field and high-resolution airborne imaging spectroscopy.

Rapid sea level rise causes loss of seagrass meadows

As global declines in seagrass populations continue to cause great concern, long-term assessment of seagrass meadows show promise in furnishing valuable clues into fundamental causes of seagrass loss and drivers of environmental change. Here we report two long-term records of seagrass presence in western Gulf of Mexico coastal waters (Laguna Madre) that provided insight into their rapid decline in a relatively pristine ecosystem. Coincident with unprecedented increases in water depth starting in 2014 (14–25 mm y−1), monthly measurements at a deep edge fixed station revealed that two ubiquitous seagrass species (Halodule wrightii and Syringodium filiforme) vanished altogether in just five years; a subsequent basin-wide assessment revealed that seagrasses disappeared at 23% of 144 sentinel stations. Models that incorporate differing sea level rise scenarios and water depth thresholds reveal potential global losses of seagrass habitat (14,000 km2), with expansion into newly created shallow habitats constrained by altered natural shorelines.

Development of a hazard risk map for assessing pedestrian risk in urban flash floods: A case study in Cúcuta, Colombia

AbstractThe rapid growth of impervious areas in urban basins worldwide has increased the number of impermeable surfaces in cities, leading to severe flooding and significant economic losses for civilians. This trend highlights the urgent need for methodologies that assess flood hazards and specifically address the direct impact on pedestrians, which is often overlooked in traditional flood hazard analyses. This study aims to evaluate a methodology for assessing the risk to pedestrians from hydrodynamic forces during urban floods, with a specific focus on Cúcuta, Colombia. The methodology couples research outcomes from other studies on the impact of floodwaters on individuals of different ages and sizes with 1D/2D hydrological modeling. Advanced computational algorithms for image recognition were used to measure water levels at 5‐s intervals on November 6, 2020, using drones for digital elevation model data collection. In Cúcuta, where flood risk is high and drainage infrastructure is limited, the PCSWMM (Computer‐based Urban Stormwater Management Model) was calibrated and validated to simulate extreme flood events. The model incorporated urban infrastructure details and geomorphological parameters of Cúcuta's urban basin. Four return periods (5, 10, 50, 100), with extreme rainfall of 3 h, were used to estimate the variability of the risk map. The output of the model was analyzed, and an integrated and time‐varying comparison of the results was done. Results show that the regions of high‐water depth and high velocity could vary significantly along the duration of the different extreme events. Also, from 5 to 100 years return period, the percentage of area at risk increased from 9.6% to 16.6%. The pedestrian sensitivity appears much higher than the increase in velocities or water depth individually. This study identified medium to high‐risk locations, which are dynamic in time. We can conclude dynamics are spatiotemporal, and the added information layer of pedestrians brings vulnerability information that is also dynamic. Areas of immediate concern in Cúcuta can enhance pedestrian safety during flash flood events. The spatiotemporal variation of patterns requires further studies to map trajectories and sequences that machine learning models could capture.

Study on the resistance characteristics of layered vegetation to overland flow

AbstractDifferent types of plants in the vegetation community near the surface of the basin coexist, forming a layered vegetation distribution with high and low plants in the morphology. In order to research the characteristics of flow resistance generated by layered vegetation on slope runoff, a flume experiment was carried out by simulating layered vegetation. The Manning roughness coefficient n was used to characterize the flow resistance of vegetation. Three kinds of vegetation with height combinations of 5 and 7 cm, 6 and 8 cm, and 7 and 9 cm were used for this experiment. By studying the relationship between Manning roughness coefficient n and water depth, it is found that the change of flow resistance of layered vegetation is closely related to the submerged state. The distribution of n shows an inverted “J” type with the increase of water depth. Under the condition of nonsubmerged state and transitional submerged state, n increases with the increase of water depth. The critical point n values of the two states will plummet, and the growth rate of n in the nonsubmerged state is greater than that in the completely submerged state. In the transitional submerged state and completely submerged state, the higher the plant height below the water surface, the higher the corresponding n value and the greater the change rate of n. Formula for predicting overland flow resistance of layered vegetation was established by considering the influence of combined vegetation height and Reynolds number.

The Lower Silurian Longmaxi rapid-transgressive black shale and organic matter distribution on the Upper Yangtze Platform, China

The characteristics and formation of maximum flooding (MF) black shales are important aspects in defining the geology of fine-grained reservoirs. The MF black shales are located at the bottom of the Longmaxi Formation on the Upper Yangtze Platform, corresponding to graptolite zone LM1. Seismic interpretation, X-ray diffraction entire rock analysis, total organic carbon (TOC) tests, and field emission scanning electron microscopy analysis indicate that the MF black shales have an average content of 49.3% quartz (85% clay size), 10.5% calcite, 8.4% dolomite, and 23.4% clay minerals. The quartz content increases basinward, whereas the clay mineral content decreases. The shale has developed during rapid sea level rise, with a thickness of 0.5–2.8 m that gradually thickens basinward. The TOC content, averaging 5.4%, gradually decreases basinward, with four distinct stacking patterns. The mineral composition and thickness of the Longmaxi shale are related closely to rapid transgression, biology, and volcanism during the period of sedimentation. Rapid transgression has led to a decrease in terrestrial input and shale thickness. In addition, biological activity and volcanism have caused the prevalence of microcrystalline quartz. Shales with high TOC content are related to anoxic conditions, along with low sedimentation rates and high primary productivity. The combination of an anoxic water column, weak dilution, and enhanced organic matter (OM) supply have enhanced the preservation of the OM. The four TOC stacking patterns are related to the water depth. The supply of clay minerals decreases with increasing water depth, whereas the degradation and recycling of OM decrease the TOC content. The sediment accommodation increases with increasing water depth, resulting in four TOC stacking patterns.