Fine-grained gravity flow sedimentation and its influence on development of shale oil sweet sections in lacustrine basins in China

The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.

Effects of loose deposits on debris flow processes in the Aizi Valley, southwest China

Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.

Deposition Morphology of Non-homogeneous Debris Flow and Its Energy Characteristics

Non-homogeneous two-phase debris flows are widely found in the western mountainous regions of China. To investigate the characteristics of the debris flow deposition process related to the morphology and extent of the debris fan, a series of physical experiments were carried out using an experimental flume. Some useful relationships were obtained to link the flow velocity with the geometric characteristics of deposition morphology and the corresponding area or volume. Based on these, some expressions about energy dissipation process in both the transport-deposition zone and deposition zone are presented, and improved equations describing solidliquid two-phase energy transformations in the specific deposition zone are also established. These results provide a basis for further investigating the underlying mechanisms of non-homogeneous debris flows, based upon which effective disaster control measures can be undertaken.

Sedimentary Microfacies and Porosity Modeling of Deep-Water Sandy Debris Flows by Combining Sedimentary Patterns with Seismic Data： An Example from Unit I of Gas Field A, South China Sea

Sandy debris flow deposits are present in Unit I during Miocene of Gas Field A in the Baiyun Depression of the South China Sea. The paucity of well data and the great variability of the sedimentary microfacies make it difficult to identify and predict the distribution patterns of the main gas reservoir, and have seriously hindered further exploration and development of the gas field. Therefore, making full use of the available seismic data is extremely important for predicting the spatial distribution of sedimentary microfacies when constructing three-dimensional reservoir models. A suitable reservoir modeling strategy or workflow controlled by sedimentary microfacies and seismic data has been developed. Five types of seismic attributes were selected to correlate with the sand percentage, and the root mean square （RMS） amplitude performed the best. The relation between the RMS amplitude and the sand percentage was used to construct a reservoir sand distribution map. Three types of main sedimentary microfacies were identified： debris channels, fan lobes, and natural levees. Using constraints from the sedimentary microfacies boundaries, a sedimentary microfacies model was constructed using the sequential indicator and assigned value simulation methods. Finally, reservoir models of physical properties for sandy debris flow deposits controlled by sedimentary microfacies and seismic inversion data were established. Property cutoff values were adopted because the sedimentary microfacies and the reservoir properties from well-logging interpretation are intrinsically different. Selection of appropriate reservoir property cutoffs is a key step in reservoir modeling when using simulation methods based on sedimentary microfacies control. When the abnormal data are truncated and the reservoir properties probability distribution fits a normal distribution, microfacies-controlled reservoir property models are more reliable than those obtained from the sequence Gauss simulation method. The cutoffs for effective porosity of the debris channel, fan lobe, and natural levee facies were 0.2, 0.09, and 0.12, respectively; the corresponding average effective porosities were 0.24, 0.13, and 0.15. The proposed modeling method makes full use of seismic attributes and seismic inversion data, and also makes the property data of single-well depositional microfacies more conformable to a normal distribution with geological significance. Thus, the method allows use of more reliable input data when we construct a model of a sandy debris flow.

GIS-based Numerical Modelling of Debris Flow Motion across Three-dimensional Terrain

The objective of this study is to incorporate a numerical model with GIS to simulate the movement, erosion and deposition of debris flow across the three dimensional complex terrain. In light of the importance of erosion and deposition processes during debris flow movement, no entrainment assumption is unreasonable. The numerical model considering these processes is used for simulating debris flow. Raster grid networks of a digital elevation model in GIS provide a uniform grid system to describe complex topography. As the raster grid can be used as the finite difference mesh, the numerical model is solved numerically using the Leap-frog finite difference method. Finally, the simulation results can be displayed by GIS easily and used to debris flow evaluation. To illustrate this approach, the proposed methodology is applied to the Yohutagawa debris flow that occurred on 20th October 2010, in Amami- Oshima area, Japan. The simulation results that reproduced the movement, erosion and deposition are in good agreement with the field investigation. The effectiveness of the dam in this real-case is also verified by this approach. Comparison with the results were simulated by other models, shows that the present coupled model is more rational and effective.

The Disastrous 23 July 2009 Debris Flow in Xiangshui Gully, Kangding County, Southwestern China

On 23 July 2009, a catastrophic debris flows were triggered by heavy rainfall in Xiangshui gully, Kangding county, southwestern China. This debris flow originating shortly after a rainstorm with an intensity of 28 mm per hour transported a total volume of more than 480×103 m3 debris, depositing the poorly sorted sediment including boulders up to 2-3 m in diameter both onto an existing debris fans and into the river. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the debris supply conditions, and to estimate debris-flow volume, mean velocity, and discharge. A comparison with adjacent rain-gage records indicates that debris flows in this setting can be produced in response to as little as 17 mm/hour or 3.5 mm/10-minute of rainfall intensity with relatively lower amount of cumulative antecedent rainfall. The field measurement and the interpretation of the Worldview image indicate that abundant landslides occurred on steep slopes within areas underlain by highly weathered granite. Using empirical equations that combine flow depth and channel slope, the mean velocity and discharge of the debris flow were estimated to be 9.2 m/s and 2150 m3/s, respectively. The results contribute to a better understanding of the conditions leading to catastrophic debris flows.

Theoretical Study on the Confluence of Debris Flow and the Main River

Because of the high momentum of debris flow,when it confluences with the Main River,the water level in the upstream of the conjunction point will increase and a portion of sediment will deposit in the con- junction area.The discharge of downstream will be less then the summation discharge of main river and side channel,and the density of downstream will be difference from both the density of the fluid of main river and tributary.Based on momentum theory,and with the transport coefficient and deposit coef...

Quantitative evaluation of eco-geotechnical measures for debris flow mitigation by improved vegetation-erosion model

Eco-geotechnical measures for debris flow mitigation and control have attracted wide attention,but the mitigation effect is lack of quantitative evaluation of coordinated measures.In order to evaluate the debris flow mitigation effect in the combinations of geotechnical engineering and ecological engineering,this study investigated the different trends of debris flows behaviour based on the sediment deposition on the gully bed and the loose material on the hillslope.Besides,this research proposed a new model involving vegetation coverage,source gravity energy and debris flow volume based on vegetation-erosion model.The new model validated that the debris flow volume was proportional to the gravity energy of gravel and rock fragments on the hillslope and inversely proportional to the vegetation coverage in a dry-hot valley setting.Furthermore,a typical area in the valley of the Xiaojiang River in Yunnan Province,China was quantified with the new model.The results showed that under different gravity energy conditions,the implementation order of check dam construction and afforestation was important for debris flow mitigation.

A hyperspectral detection model for permeability coefficient of debris flow fine-grained sediments, Southwestern China

Fine-grained sediments are Quaternary sediments with grain sizes of not more than 2 mm.They startfirst when meeting water,their stability is related to the initial water volume triggering debrisflow,and thus plays an important role in debrisflow hazards early warning.The permeability coefficient is the inter-controlled factor offine-grained sediment stability.However,there is no hyperspectral model for detecting thefine-grained sediment permeability coefficient in large areas,which seriously affects the progress of debrisflow hazards early warning.Therefore,it is of great significance to establish a hyperspectral detection model for the permeability coefficient offine-grained sediments.Taking Beichuan County,Southwestern China as the case,a permeability coefficient hyperspectral detection model was established.The results show that eight bands are sensitive to the permeability coefficient with correlation coefficient(R)of 0.6343.T-test on the model shows that P-a values for sensitive bands are all less than 0.05,indicating the established model has a good prediction ability with a precision of 85.83%.These sensitive bands also indicate the spectral characteristics of the permeability coefficient.Therefore,it provides a scientific basis forfine-grained sediment stability detection in large areas and lays a theoretical foundation for debrisflow hazards’early warning.

Numerical Simulation of the Mass Movement Process of the 2018 Sedongpu Glacial Debris Flow by Using the Fluid-Solid Coupling Method

In the context of global warming and intensified human activities,glacier instability in plateau regions has increased,and glacier debris flows have become active,which poses a significant threat to the lives and property of people and socioeconomic development.The mass movement process of glacier debris flows is extremely complex,so this paper uses the 2018 Sedongpu glacier debris flow event on the Qinghai-Tibet Plateau as an example and applies a numerical simulation method to invert the whole process of mass movement.In view of the interaction between phases in the process of motion,we use the fluid-solid coupling method to describe the mass movement.The granular-flow model and drift-flux model are employed in FLOW3D software to study the mass movement process of glacier debris flows and explore their dynamic characteristics.The results indicate that the glacier debris flow lasted for 700 s,and the movement process was roughly divided into four stages,including initiation,scraping,surging and deposition;the depositional characteristics calculated by the fluid-solid coupling model are consistent with the actual survey results and have good reliability;strong erosion occurs during the mass movement,the clear volume amplification effect,and the first wave climbs 17.8 m across the slope.The fluid-solid coupling method can better simulate glacier debris flows in plateau regions,which is helpful for the study of the mechanism and dynamic characteristics of such disasters.

Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study, significant achievements have been made in terms of classification schemes, genetic mechanisms, and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages： incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently, three primary classification schemes based on the sediment support mechanism, the rheology and transportation process, and the integration of sediment support mechanisms, rheology, sedimentary characteristics, and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows, sandy debris flows, and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents （hyperpycnal flows）. Sustainable sediment supplies mainly generate muddy debris flows, sandy debris flows, and hyperpycnal flows. Deep-water fans, which are commonly controlled by debris flows and hyperpycnal flows, are triggered by sustainable sediment supply; in contrast, deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from fine- grained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes, transformation between different types of gravity flow deposit, and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.

Deep-water gravity flow deposits in a lacustrine rift basin and their oil and gas geological significance in eastern China

The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.

The Effect of Grain Size on the Viscosity and Yield Stress of Fine-Grained Sediments

In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size on the rheology of fine-grained sediments associated with yielding.When looking at the relationship between shear stress and shear rate before yielding,a high-viscosity zone(called pseudoNewtonian viscosity) towards the apparent yield stress exists.After yielding,plastic viscosity(called Bingham viscosity) governs the flow.To examine the effect of grain size on the rheological characteristics of fine-grained sediments,clay-rich materials(from the Adriatic Sea,Italy; Cambridge Fjord,Canada; and the Mediterranean Sea,Spain),silt-rich debris flow materials(from La Valette,France) and silt-rich materials(iron tailings from Canada) were compared.Rheological characteristics were examined using a modified Bingham model.The materials examined,including the Canadian inorganic and sensitive clays,exhibit typical shear thinning behavior and strong thixotropy.In the relationships between the liquidity index and rheological values(viscosity and apparent yield stress),the effect of grain size on viscosity and yield stress is significant at a given liquidity index.The viscosity and yield stress of debris flow materials are higher than those of low-activity clays at the same liquid state.However the viscosity and yield stress of the tailings,which are mainly composed of silt-sized particles,are slightly lower than those of low-activity clays.

Influence of rheological characteristics on the fluidization catastrophe of tailings flows

Limited by mining technology,mineral exploitation can produce large amounts of tailings.Heavy summer rainfall or seasonal freeze-thaw can lead to physical and chemical modification of tailing material in mountainous areas,resulting in fluidized tailings flow and severe disaster losses.Therefore,aiming at the problem of tailings fluidization catastrophe,this paper tried to reveal the rheological mechanism of tailings fluidization transformation by combining rheological tests and theoretical analysis.The results show that the yield stress increases with decreasing temperature,and when the density of debris flow(ρ)is more than 1.9 g/cm~3,this behavior becomes more pronounced as the density increases.The storage modulus decreases by at least two orders of magnitude at the solid-fluid transition under amplitude test sweep.Storage and loss modulus in the linear viscoelastic range and yield stress have an exponential growth relationship with sediment concentration.In addition,a stress constitutive relation and a new exponential law describing the evolution of yield stress required for solid-liquid transformation were proposed,and the relationship is further strengthened through a comprehensive analysis of existing results,which expands the evaluation application of the rheological characteristics of tailings flow.This paper provides a new insight into the rheological properties of tailing and how they occur through solid-liquid transition under different environments,which is beneficial to geological hazard prevention and the ecological remediation of the mining area.

泥石流停淤工程应用现状与思考

泥石流综合防治体系主要由稳固、拦挡、排导和停淤工程组成,其中停淤工程发挥重要的减灾作用。在查阅国内外泥石流停淤工程相关资料的基础上,对已建的停淤工程开展野外调查,总结停淤工程在设计和运行过程中存在的问题。具体表现在:1)停淤场内缺乏泥石流分流、导流及均衡停淤措施,导致停淤空间未合理利用;2)停淤工程设计仍以经验设计为主,尤其是停淤量以经验估算为主,计算结果与实际停淤量偏差大;3)停淤场内缺乏快速停淤和减速耗能措施,导致结构受损;4)传统停淤挡墙设计未考虑泥石流冲击力;5)停淤场占地面积与人类使用土地之间的矛盾等。基于以上问题,作者提出泥石流停淤工程均衡停淤的理念,并对以后泥石流停淤工程的设计和研究提出停淤空间优化配置、停淤挡墙结构型式和设计参数优化等方面的思考。

叠覆堆积过程中泥石流偏移的实验研究

泥石流堆积扇经过多期叠覆堆积,其在空间和时间分布上有随机性,存在主流偏移和堆积摆动等各向异性现象,给合理规划与利用泥石流滩地带来困难。本文在野外调查四川平武县碓窝梁子沟堆积扇的基础上,开展室内水槽模型实验,结合3D扫描技术和基底压力传感器,探讨泥石流在叠覆堆积过程中的阶段性流态变化以及主流偏移的成因和发展。实验发现:(1)泥石流密度差异导致不同的偏移形式,高密度泥石流易出现层面整体偏移;低密度泥石流易形成插入式的叠覆堆积。(2)泥石流多期堆叠过程中偏移行为并不一定是沿地势更低处,而是取决于后期来流的性态。(3)泥石流偏移角度和距离依赖于流体密度、流速和堆积体几何特征,可以建立以上述参数为变量的堆积偏移角度与偏移距离的计算公式。本研究成果可以为了解泥石流堆积扇的形成机制、致灾范围和演化趋势提供依据。

Effects of river flow velocity on the formation of landslide dams

Natural dams are formed when landslides are triggered by heavy rainfall during extreme weather events in the mountainous areas of Taiwan.During landslide debris movement,two processes occur simultaneously:the movement of landslide debris from a slope onto the riverbed and the erosion of the debris under the action of high-velocity river flow.When the rate of landslide deposition in a river channel is higher than the rate of landslide debris erosion by the river flow,the landslide forms a natural dam by blocking the river channel.In this study,the effects of the rates of river flow erosion and landslide deposition(termed the erosive capacity and depositional capacity,respectively)on the formation of natural dams are quantified using a physics-based approach and are tested using a scaled physical model.We define a dimensionless velocity index vde as the ratio between the depositional capacity of landslide debris(vd)and the erosive capacity of water flow(ve).The experimental test results show that a landslide dam forms when landslide debris moves at high velocity into a river channel where the river-flow velocity is low,that is,the dimensionless velocity index vde>54.Landslide debris will not have sufficient depositional capacity to block stream flow when the dimensionless velocity index vde<47.The depositional capacity of a landslide can be determined from the slope angle and the friction of the sliding surface,while the erosive capacity of a dam can be determined using river flow velocity and rainfall conditions.The methodology described in this paper was applied to seven landslide dams that formed in Taiwan on 8 August 2009 during Typhoon Morakot,the Tangjiashan landslide dam case,and the Yingxiu-Wolong highway K24 landslide case.The dimensionless velocity index presented in this paper can be used before a rainstorm event occurs to determine if the formation of a landslide dam is possible.

中国湖盆细粒重力流沉积作用及其对页岩油“甜点段”发育的影响

通过分析中国陆相湖盆细粒重力流沉积作用的地质条件和过程,建立湖盆细粒重力流沉积模式,揭示细粒沉积和源储发育规律,识别页岩油“甜点段”。研究表明:细粒重力流是深湖环境中重要的沉积作用之一,能把浅水细粒碎屑和有机质搬运到深湖,有利于形成优质烃源岩和页岩油的“甜点段”。中国湖盆深水环境发育的细粒重力流沉积主要是细粒浓缩密度流、细粒浊流(包括浪涌状浊流和细粒异重流)、细粒黏性流(包括细粒碎屑流和泥流)和细粒过渡流沉积。温暖湿润的气候条件下,湖平面升降、洪泛事件和湖底古地貌控制欠补偿型湖盆细粒重力流的沉积分布。湖平面上升期,洪水引发的细粒异重流在湖盆地形平坦的深湖区形成“细粒水道—堤岸—朵叶”体系。湖平面下降期,坳陷湖盆的挠曲坡折及沉积斜坡部位、断陷湖盆的陡坡带发育非限定水道为主的湖底扇体系,断陷湖盆的缓坡及轴向发育限定或非限定水道湖底扇体系,湖底扇扇缘可发育细粒重力流沉积。湖盆四级沉积层序水进可形成富有机质页岩和细粒异重流的沉积,水退可引起细粒浓缩密度流、浪涌状浊流、细粒碎屑流、泥流和细粒过渡流沉积。二叠纪以来中国湖盆页岩层系多个四级层序水进-水退旋回形成了多套源储组合,中国湖盆多样的细粒重力流沉积作用形成了由细粒浓缩密度流、细粒异重流、浪涌状浊流沉积形成的薄层粉砂岩“甜点段”,由细粒过渡流形成的泥岩与粉砂互层的“甜点段”,由细粒碎屑流、泥流沉积等形成的含粉砂屑和泥屑的水平层理泥页岩“甜点段”。湖盆细粒重力流沉积模式的建立,对科学评价页岩油“甜点段”和优质烃源岩具重要意义。

Coarse grain deposit feature of Guantao formation in western depression Shuyi area of Liaohe basin

The extensive distribution of coarse-grained clastic rock of Guantao formation in Shuyi area of Liaohe basin was considered as a result of fluvial deposit. According to the comprehensive analysis of seism data, well log, core observation and experimental data, this kind of clastic rock is composed of pebblestone-cobblestone, microconglomerate, sand conglomerate, medium-coarse grained sandstone and fine-sandstone. According to the clast composition, sedimentary texture, structure and rock type, 3 kinds of sediment facies can be recognized ie the mixed accumulation-conglomerate dominated debris flow, pebblestone-cobblestone dominated gradient flow and sandstone dominated braided stream. Vertically, the bottom gradient current deposit and top braided stream deposit form fining-upward sediment sequence, and the debris flow deposit distributes in them at random. The sedimentary feature of coarse grain clastic of Guantao formation in Shuyi area is accordant with proximal wet alluvial fan deposited in wet climate at foreland and this kind of alluvial fan is different from the traditional one.

蒙山峨峪口砾石堆积堤的年代学研究

准确界定蒙山峨峪口砾石堆积堤的形成时代,对于探明其成因、澄清山东中低山丘陵第四纪冰川有无之争,是一个需要解决的科学问题。峨峪口堆积垄岗砾石组构、沉积构造、地貌组合等标志,均指向其为山洪泥石流堆积物,且为暴发频率极低、发展周期较长的水石流或稀性泥石流堆积。其下伏第四纪沉积物OSL埋藏年龄和AMS14C年龄可作为砾石堆积堤形成时代的最老约束参考年龄,当地村民迁居此地的历史可作为最小约束参考年代。OSL测年结果为2.1~2.3 ka BP,AMS14C测年结果为951~1522 cal AD,证明砾石堆积堤为数百年前形成的历史泥石流遗迹。