Geochemical characteristics of the mud volcano fluids in southwestern Taiwan and their possible linkage to elevated arsenic concentration in Chianan plain groundwater

Fluid and mud samples were collected from Wushanting (WST), Hsiaokunshui (HKS), Yenshuikeng (YSK), Kuantzeling (KZL), and Kunshuiping (KSP) mud volcanoes of southwestern Taiwan. Concentrations of major ions and trace elements in mud volcanic fluids were analyzed to find the possible linkage to elevated arsenic (As) concentrations in the Chianan plain groundwater. The elevated Na⁺, K⁺, and Cl⁻ concentrations indicated possible marine origin of the fluids. The trace element concentrations in the mud volcanic fluids were generally low, but the As concentrations were up to 0.12 mg/L. High contents of As, Fe, and Mn were observed in the mud samples. Saturation index calculations indicated that both carbonate and oxide minerals acted as potential sinks for As in the mud volcanic fluids. Arsenic in the dewatering fluids and muds may be transported by the subsurface flow and surface streams as suspended solids and eventually deposited in the Chianan plain aquifers. Under reducing conditions, As may be released from the host minerals (such as Fe- and Mn-oxides/hydroxides), thereby causing widespread groundwater As pollution.     

Recharge and sustainability of a coastal aquifer in northern Albania

The River Mati in Albania has formed a coastal plain with Holocene and Pleistocene sediments. The outer portion of the plain is clay, with three underlying aquifers that are connected to an alluvial fan at the entry of the river into the plain. The aquifers supply water for 240,000 people. Close to the sea the aquifers are brackish. The brackish water is often artesian and found to be thousands of years old. Furthermore, the salinity, supported by δ¹⁸O results, does not seem to be due to mixing with old seawater but due to diffusion from intercalated clay layers. Heavy metals from mines in the upstream section of River Mati are not an immediate threat, as the pH buffering of the river water is good. Moreover, the heavy metals are predominantly found in suspended and colloidal phases. Two sulphur isotope signatures, one mirroring seawater sulphate in the brackish groundwater (δ³⁴S >21 ‰) and one showing the influence of sulphide in the river and the fresh groundwater (δ³⁴S <10 ‰), indicate that the groundwater in the largest well field is recharged from the river. The most serious threat is gravel extraction in the alluvial fan, decreasing the hydraulic head necessary for recharge and causing clogging of sediments.     

新疆喀什三角洲地下水流系统的水化学和同位素标记

新疆喀什三角洲地下水“水质型”缺水问题较为突出，开展地下水流系统研究具有实际意义.采用水化学和环境同位素年龄测试法，在对喀什三角洲地下水含水系统划分基础上，对地下水化学和循环更新特征进行了分析研究.结果表明:三角洲含水系统由山前倾斜冲洪积平原潜水、河流冲积平原潜水和河流冲积平原承压水构成.沿地下水流向，水化学类型演化为HCO₃·SO₄-Ca→SO₄-Ca→SO₄·Cl-Mg·Na→SO₄·Cl-Na，TDS增高，水质趋向盐化.山前倾斜冲洪积平原为溶滤-径流区，河流冲积平原为径流-累盐区.研究区地下水更新速率为0.03%~16.35%·a-1，具有山前倾斜冲洪积平原潜水>河流冲积平原潜水>河流冲积平原承压水的特征.利用3H估算得出，山前倾斜冲洪积平原潜水年龄为8~49 a，平均值为29 a；河流冲积平原潜水年龄为14~>50 a，其中上部潜水平均年龄为24 a，下部潜水平均年龄大于50 a.利用14C估算得出，河流冲积平原潜水为476~33 623 a，平均值为8 106 a；河流冲积平原承压水为5 186~34 578 a，平均值为30 043 a，与潜水比为“更古老”的水.综合以上特征得出，喀什三角洲地下水含水系统可以划分为2个更新速率较快的局部水流系统（Ⅰ₁和Ⅰ₂）和一个循环滞缓的区域水流系统（Ⅱ）.      

A study on groundwater recharge in the Anyanghe River alluvial fan,North China Plain,based on hydrochemistry,stable isotopes and tritium

Studies on groundwater recharge are essential for sustainable exploitation of groundwater resources, especially in areas of extensive groundwater exploitation such as the Anyanghe River alluvial fan (ARAF) in the North China Plain (NCP). However, the recharge sources and processes and the contribution of each recharge flow component remain unclear. This study used hydrochemistry, stable isotopes, and tritium to investigate sources and underlying processes of groundwater recharge, along with the steady flow Mixing Cell Model (MCMsf) to quantify the proportion of each source flow for the shallow confined groundwater system in the medial fan. The results showed that groundwater mainly originates from precipitation occurring on the eastern Taihang Mountain area with average elevation estimated at 700–1,000 m above sea level during the East Asia summer monsoon period since 1952. Recharge mechanisms are: (1) river water seepage for the unconfined aquifers of the proximal and medial fan; (2) lateral flow for the confined aquifers of the medial and distal fan; and (3) precipitation infiltration for the phreatic water system. The MCMsf simulation showed that the shallow confined groundwater system in the central zone of the medial fan mainly recharged by the lateral flow from the proximal fan, a constant and considerable recharge flow from the southwestern and southern hills, and river water seepage in the medial fan; the lateral recharge flow from the Zhanghe alluvial aquifer was insignificant by comparison. The results of this study can act as a valuable reference for sustainable groundwater management in the ARAF.

     

黄河冲积扇平原浅层地下水中氮循环对砷迁移富集的影响

黄河冲积扇平原浅层地下水砷含量超标情况严重,豫北平原的主体是黄河冲洪积扇平原.全面了解豫北平原浅层地下水氮循环驱动下砷的富集模式,对地下水资源的可持续利用和居民健康至关重要.本文采集豫北平原513组浅层地下水样品,采用原子荧光光谱法测定砷含量,原子吸收光谱和离子色谱等方法进行全分析及微量元素分析,对该地区高砷地下水的水...     

黄河三角洲地区地下淡水（微咸水）的形成与演化

黄河三角洲地区地下淡水（微咸水）资源贫乏，咸水广布。南部冲洪积平原受第二次海侵层位的影响形成大面积咸水，后被逐渐淡化。近年来由于开采量加大，又使北部咸水南侵。海积冲积平原随着黄河河道的变迁，仅在黄河现行河道两侧和充水的黄河故道带分布有淡水（微咸水）。近代，现代黄河三角洲古河道带和决口扇淡水体已被咸化。     

Spatial characteristics of water quality,stable isotopes and tritium associated with groundwater flow in the Hutuo River alluvial fan plain of the North China Plain

The groundwater flow system and the flow velocity in the alluvial fan plain of the Hutuo River, China, have been studied, with an emphasis on relating geochemical characteristics and isotopes factors. Seven stretches of one river, six springs and 31 wells, with depths ranging from 0 m (river waters) to 150 m, were surveyed. The groundwater has a vertical two-layer structure with a boundary at about 80–100 m depth, yielding an upper and a lower groundwater layer. The δ¹⁸O and δD values range from ?10.56 to ?7.05‰ and ?81.83 to ?59‰, respectively. The groundwater has been recharged by precipitation, and has not been subjected to significant evaporation during infiltration into the aquifer in the upper layer. Using a tritium model, the groundwater flow in the alluvial fan plain showed horizontal flow velocity to be greater than vertical velocity. Groundwater in the upper layer is characterized by Ca–HCO₃ type. From the spatial distribution characteristics of the stable isotope and chemical composition of the groundwater, agricultural irrigation was considered to have an influence on the aquifer by causing excessive groundwater abstraction and irrigation return.     

Geochemical characterization of arsenic-affected alluvial aquifers of the Bengal Delta (West Bengal and Bangladesh) and Chianan Plains (SW Taiwan): Implications for human health

Major ion and trace element analyses were performed on groundwater samples collected from the Bengal Delta (Chakdaha municipality, West Bengal and Manikgonj town, Bangladesh) and Chianan Plains (SW Taiwan) to compare geochemical characteristics. Results showed that concentrations of Na, K, Mg, Cl and SO₄ were generally higher in Chianan Plain (CNP) groundwaters, while high Ca was observed in Bengal Delta Plain (BDP) groundwater. Measured As concentrations in groundwaters of BDP and CNP showed large variations, with mean As concentrations of 221 μg/L (range: 1.1-476 μg/L) in Chakdaha, 60 μg/L (range: 0.30-202 μg/L) in Manikgonj, and 208 μg/L (range: 1.3-575 μg/L) in CNP groundwater. The Fe-reduction mechanism was found to be the dominant geochemical process in releasing As from sediment to groundwater in Chakdaha, West Bengal, however the Mn-reduction process was dominant in groundwaters of Manikgonj, Bangladesh. In Chianan Plain groundwater, a combination of geochemical processes (e.g., bacterial Fe-reduction, mineral precipitation and dissolution reactions) controlled release of As. Fluorescence spectral patterns of the groundwater showed low relative fluorescence intensity (RFI) of dissolved humic substances in BDP groundwater (mean: 63 and 72 QSU, Chakdaha and Manikgonj, respectively), while high RFI was observed in CNP groundwater (mean: 393 QSU). The FT-IR spectra of the extracted humic acid fractions from sediments of Chianan Plain showed a stronger aliphatic band at 2850-3000 cm⁻¹ and a higher resolved fingerprint area (from 1700 to 900 cm⁻¹) compared with BDP sediments. The geochemical differences between the study areas may play a crucial role in the clinical manifestation of Blackfoot disease observed only in Chianan Plain, SW Taiwan.     

Multi-tracer investigation of river and groundwater interactions: a case study in Nalenggele River basin,northwest China

Environmental tracers (such as major ions, stable and radiogenic isotopes, and heat) monitored in natural waters provide valuable information for understanding the processes of river–groundwater interactions in arid areas. An integrated framework is presented for interpreting multi-tracer data (major ions, stable isotopes (²H, ¹⁸O), the radioactive isotope ²²²Rn, and heat) for delineating the river–groundwater interactions in Nalenggele River basin, northwest China. Qualitative and quantitative analyses were undertaken to estimate the bidirectional water exchange associated with small-scale interactions between groundwater and surface water. Along the river stretch, groundwater and river water exchange readily. From the high mountain zone to the alluvial fan, groundwater discharge to the river is detected by tracer methods and end-member mixing models, but the river has also been identified as a losing river using discharge measurements, i.e. discharge is bidirectional. On the delta-front of the alluvial fan and in the alluvial plain, in the downstream area, the characteristics of total dissolved solids values, ²²²Rn concentrations and δ¹⁸O values in the surface water, and patterns derived from a heat-tracing method, indicate that groundwater discharges into the river. With the environmental tracers, the processes of river–groundwater interaction have been identified in detail for better understanding of overall hydrogeological processes and of the impacts on water allocation policies.     

Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO₃ type water with depleted δ¹⁸O and δD (mean value of −8.8‰ δ¹⁸O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO₃–Cl–SO₄ type), and heavier δ¹⁸O and δD were observed (around −8‰ δ¹⁸O). Before the surface water with mean δ¹⁸O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ¹⁸O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO₃, Na–HCO₃, to Na–SO₄. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.     

内蒙古河套平原浅层高铁高氟地下水分布与成因

为了查明内蒙古河套平原高铁高氟地下水的分布与形成原因,通过实地调查、监测、资料分析和试验测试等方法手段,详细研究了地下水中铁、氟的分布、地球化学特征及其来源。结果表明:高铁水主要分布在平原中部的冲湖积平原,地势低洼和地下水的排泄地带含量最高;高氟水主要以条带状分布在山前的冲洪积扇地带;在调查研究区12510.83 km2的范围内,深度在10~40 m的浅层地下水中,分布有高铁水9310.66 km2,高氟水2308.35 km2,分别占调查研究区总面积的74.40%和18.45%;研究认为,河套平原高铁高氟地下水的形成主要是由自然地质环境所致,是不同地质环境条件下环境水文地球化学作用的结果;地下水中的铁主要来源于由黄河携带来的大量的第四系沉积物,而溶出的主要原因是地下氧化还原条件的变化;地下水中的氟主要来源于平原周边的山区,气候、地质构造、水文地质和水化学条件是氟富集的主要因素;研究表明河套平原高铁水与高氟水不存在正相关关系。     

黑河干流浅层地下水与地表水相互转化的水化学特征

通过分析黑河干流地表水与地下水的水化学特征,识别沿黑河干流不同地带地下水与地表水的相互转化关系.研究结果表明:(1)在祁连山区,地下水与地表水的转化以地下水向河流排泄为主.(2)南部盆地,在山前戈壁带,出山河水入渗转化为地下水;溢出带地下水以泉的形式转化为地表水;进入细土平原后,汛期河水补给地下水,非汛期地下水补给河水;在农灌区引河水通过田间入渗补给地下水.(3)北部盆地,在金塔灌区,地下水主要接受引水灌溉入渗补给;在金塔灌区到额济纳旗,河流入渗转化为地下水.     

北京平原区地下水位预警初步研究

借鉴美国地质调查局在宾夕法尼亚的地下水位预警方法,从统计学的角度,探索了北京平原区地下水预警方法。对监测井多年长期监测资料进行百分位统计分析,把同一时间(月平均、旬平均、日平均)地下水水位(头)标高值的最小值至百分位5、百分位5至百分位10、百分位10至百分位25、百分位25至百分位75范围内的地下水位分别定义为红色、橙色、黄色和蓝色预警,形成地下水位预警判据。根据地下水水位实时监测数据,实时判定监测井代表区域的地下水预警等级,同时修正和完善地下水位预警判据,称之为监测井单点预警,监测井代表的同一层位的区域的集合,构成不同含水层的地下水位区域预警。对北京平原区2009年12月的地下水位预警结果为:潮白河冲洪积扇顶部和中部潜水含水层地下水位为红色预警,前缘为黄色预警,冲洪积平原为蓝色预警区;城区以南地区为红色预警,海淀山后的西北部地区为红色预警,永定河冲积扇和冲积平原大部分地区黄色和蓝色预警,大石河冲洪积扇地区均为蓝色预警;承压水含水层在潮白河冲洪积扇的前缘为红色预警,冲洪积平原为蓝色预警,北运河山前地带均为橙色预警,城区东、东南地区为橙色和黄色预警,少数地区为橙色预警,除上述地区以外,承压水均为蓝色预警。北京市平原区主要地下水开采地区地下水位已经处于历史的较低水位处,特别是潮白河冲积扇中上部地区以及平谷盆地,地下水位几乎全部处于红色预警区。该预警方法原理明确,方法简便,有望在地下水主要开采区推广应用。     

鄂尔多斯盆地及周缘地区下二叠统沉积特征*

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川—榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达—杭锦旗—鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心—庆阳一线发育三角洲前缘沉积,盆地南部彭阳—泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡—义马一带为潟湖沉积。     

川西前陆盆地中侏罗统千佛岩组沉积体系研究

千佛岩组发育冲积扇、曲流河、三角洲和湖泊沉积。曲流河发育洪泛平原和河道两个亚相;三角洲发育三角洲前缘、三角洲平原及前三角洲三个亚相;湖泊相则发育浅湖和滨湖亚相;冲积扇分出扇中和扇端两个亚相。龙门山系周期性推覆构造活动是川西前陆盆地沉积作用及层序发育的主控因素。     

Depositional character of a dry-climate alluvial fan system from Palaeoproterozoic rift setting using facies architecture and palaeohydraulics: Example from the Par Formation,Gwalior Group,central India

The ∼20 m thick coarse-grained clastic succession in the basal part of Palaeoproterozoic Par Formation, Gwalior Group has been investigated using process-based sedimentology and deductive palaeohydraulics. Bounded between granitic basement at its base and shallow marine succession at the top, the studied stratigraphic interval represents products of an alluvial fan and its strike-wise co-existent braided river system that possibly acted as a tributary for the fan. Detailed facies, facies association analysis allowed identification of two anatomical parts for the fan system viz. proximal and mid fan. While thin proximal fan is represented by products of rock avalanche and hyperconcentrated flows with widely varying rheology, the mid fan is represented by products of sheet floods and flows within streamlets. The interpretation found support from palaeoslope estimation carried out on the fluvial part of the mid fan that plot dominantly within the alluvial fan field demarcated by Blair and McPherson (1994). Dry climatic condition suggested from dominance of stream flow over mass flow deposition within the Par alluvial fan. Strike-wise, the fan is discontinuous and juxtaposed with a braid plain system. In contrast to the fluvial part of fan system, the palaeoslope data from the braid plain system dominantly plot within the ‘natural depositional gap’ defined by Blair and McPherson. A raised palaeoslope for the river systems, as suggested from Proterozoic braid plain deposits around the Globe, is found valid for the Par braid plain system as well. From preponderance of granular and sandy sediments within the alluvial fan and braid plain systems and a pervasive north-westward palaeocurrent pattern within the fluvial systems the present study infers a gently sloping bevelled source area in the south-southeast of the basin with occurrence of steep cliffs only locally.     

台湾浊水溪冲积扇地下水位变化及地面沉降对高铁之影响

浊水溪冲积扇是台湾水资源最为丰富但也是地面沉降最严重地区。近年来该区域的地面沉降因有可能威胁高铁行车安全而备受关注。本文整合历年累积的地下水位及地面沉降等相关监测数据,验证了地下水位变化与含水层补给之机制,探讨了地下水周期性波降条件下土层压缩特性以及高铁路堤与桩基础工程结构的沉降行为。认为对于设置桩基础的线型高架结构而言,区域性地下水位波降不致增加桥墩间的差异沉降,但桩基础若承受邻近局部的额外载重,则可能伴随地下水位波降产生持续性的差异沉降,其长期效应将对线型交通结构物的平整度及安全性造成负面影响。     

Contamination of shallow aquifers by arsenic in upper reaches of Tista river at Siliguri–Jalpaiguri area of West Bengal, India

Arsenic is present in groundwater at Siliguri–Jalpaiguri area, West Bengal, India. This is the place where Tista river descending from the Himalayas meets the alluvial plain. The area represents alluvial fan and floodplains of Tista, Mahananda-Balasan, Jaladhaka and its tributaries. In the river sediment samples, para- and ferro-magnetic minerals within 0.3–0.05 mm fraction contain 9–80 ppm of arsenic. The study indicates that iron bearing minerals viz. biotite, hornblende as well as iron coated grains of the sediment are major contributors towards arsenic budget. Though magnetite as a mineral shows maximum arsenic content (22 ppm), it is volumetrically not of much significance. Measurement of groundwater collected from tube wells shows up to 0.05 ppm of arsenic. These arsenic contaminated tube wells occur in a linear fashion along the course of the rivers. Moreover, localization of contaminated tube wells coincides with the change of channel gradient as observed in longitudinal section. The study enumerates a cause–effect relationship of arsenic occurrence with river gradient and fluvial sedimentation.     

Arsenic enrichment in groundwater in the middle Gangetic Plain of Ghazipur District in Uttar Pradesh,India

Groundwater with high geogenic arsenic (As) is extensively present in the Holocene alluvial aquifers of Ghazipur District in the middle Gangetic Plain, India. A shift in the climatic conditions, weathering of carbonate and silicate minerals, surface water interactions, ion exchange, redox processes, and anthropogenic activities are responsible for high concentrations of cations, anions and As in the groundwater. The spatial and temporal variations for As concentrations were greater in the pre-monsoon (6.4–259.5 μg/L) when compared to the post-monsoon period (5.1–205.5 µg/L). The As enrichment was encountered in the sampling sites that were close to the Ganges River (i.e. south and southeast part of Ghazipur district). The depth profile of As revealed that low concentrations of NO₃⁻ are associated with high concentration of As and that As depleted with increasing depth. The poor relationship between As and Fe indicates the As release into the groundwater, depends on several processes such as mineral weathering, O₂ consumption, and NO₃⁻ reduction and is de-coupled from Fe cycling. Correlation matrix and factor analysis were used to identify various factors influencing the gradual As enrichment in the middle Gangetic Plain. Groundwater is generally supersaturated with respect to calcite and dolomite in post-monsoon period, but not in pre-monsoon period. Saturation in both periods is reached for crystalline Fe phases such as goethite, but not with respect to poorly crystalline Fe phases and any As-bearing phase. The results indicate release of arsenic in redox processes in dry period and dilution of arsenic concentration by recharge during monsoon. Increased concentrations of bicarbonate after monsoon are caused by intense flushing of unsaturated zone, where CO₂ is formed by decomposition of organic matter and reactions with carbonate minerals in solid phase. The present study is vital considering the fact that groundwater is an exclusive source of drinking water in the region which not only makes situation alarming but also calls for the immediate attention.     

河北省唐山地区古滦河冲积扇第四纪以来演化与变迁

古滦河冲积扇研究的关注点更多在全新世,对其更新世的演化与变迁一直没有进行过系统研究。根据古滦河冲积扇上PZK10、PZK20钻孔的磁性地层学、年代地层学、沉积学、测井沉积学、岩芯色度分析等,对古滦河冲积平原的第四纪三维地质结构、冲积扇体的规模以及迁移规律进行综合研究,结果表明：PZK10孔揭露了上新世时沉积的巨厚洪积成因“泥包砾”地层,早更新世时发育两个冲积扇-湖相旋回,中更新世时发育辫状河沉积,晚更新世发育湖相、冲积扇相、辫状河相沉积。PZK20孔上新世沉积了一套巨厚“泥包砾”层,早更新世为扇前平原-辫状河相沉积,中更新世为辫状河-冲积扇相沉积,晚更新世为辫状河沉积。古滦河发育两期冲积扇,第一期为早更新世早期,在沙流河镇一带出山口形成的规模较大的冲积扇;第二期为早更新世中期,古滦河在现今丘庄水库一带发生分流,在丰润区一带出山口形成的冲积扇。中更新世,第一期冲积扇开始萎缩,第二期冲积扇继续发育,形成巨厚砾石层;晚更新世,古滦河在迁西县城以北发生袭夺,东流迁移出研究区,在西峡口进入迁安盆地,形成以西峡口为顶点的冲积扇。