Clay mineral distribution in surface sediments of the South China Sea and its significance for in sediment sources and transport

Clay minerals of surface sediments in the South China Sea (SCS) are analyzed with X-ray diffraction, and their transport is explored with a grain size trend analysis (GSTA) model. Results show that clay mineral types in various sedimentary environments have different sediment sources and transport routes. Sediments in the northern SCS (north of 20°N) between the southwest of Taiwan Island and the outer mouth of the Pearl River have high contents of illite and chlorite, which are derived mainly from sediments on Taiwan Island and/or the Yangtze River. Sediments from the Pearl River are characterized by high kaolinite and low smectite content, and most are distributed in the area between the mouth of the Pearl River and northeast of Hainan Island and transported vertically from the continental shelf to the slope. Characterized by high illite content, sediments from Kalimantan Island are transported toward the Nansha Trough. Sediments from Luzon Island are related with volcanic materials, and are transported westwards according to smectite distribution. On the Sunda Shelf, sediments from the Mekong River are transported southeast in the north while sediments from the Indonesian islands are transported northward in the south. Ascertaining surface sediment sources and their transport routes will not only improve understanding of modern transportation and depositional processes, but also aid paleoenvironmental and paleoclimatic analysis of the SCS.     

泥岩与页岩特征辨析

细粒沉积岩类型复杂,原因是其定义基于结构粒度概念,缺乏对矿物成分的有效约束,加之,不同学者是在不同尺度下对构造现象进行描述,使得细粒沉积岩缺乏较为科学、系统的分类。为辨析泥岩与页岩的特征,通过大量调研国内外沉积学教材及相关文献发现：细粒沉积物(粒径小于62.5μm)的概念自20世纪30年代进入人们的视野,后被广大研究人员广泛接受,且大多数学者普遍认为可依据粒度大小,进一步将细粒沉积物划分为黏土级颗粒(粒径小于3.9μm)和粉砂级颗粒(粒径介于3.9～62.5μm之间)。但是,国、内外沉积学界对细粒沉积物“泥”(泥级颗粒)的粒径划分不同,欧美学者一般将“泥”界定为粒径小于62.5μm,包括黏土级颗粒与粉砂级颗粒。在我国,自20世纪50年代开始,沿用了前苏联的方案,“泥”的粒径对应黏土级颗粒即小于3.9μm,这一分歧是导致泥岩与页岩等概念使用混乱的根本原因。概而言之,固结的泥岩具有与页岩相同的粒级结构和组分,但是不具备页岩的“纹层”或“页理”构造特征;辩证而言,“纹层”强调沉积过程所形成的垂向层理差异,而“页理”则是成岩过程受风化作用影响形成的力学薄弱面。从泥岩和页岩的矿物组成看,存在石英...     

Heavy mineral stratigraphy of sediments from the southern outer shelf of the East China Sea since the last glaciation using fuzzy C-means cluster method

Correspondence analysis and fuzzy C-means cluster methods were used to divide the stratigraphy of heavy mineral assemblages, and the sediment sources and depositional dynamics of the environment reconstructed. The assemblages were taken from marine sediments from the late Pleistocene to the Holocene in Core Q43 situated on the outer shelf of the East China Sea. Based on the variable boundaries of the mineral assemblage at 63 and 228 cmbsf (cm below sea floor), the core might have previously been divided into three sediment strata marked with units I, II and III, which would be consistent with the divided sediment stratum of the core using minor element geochemistry. The downcore distribution of heavy minerals divided the sedimentary sequence into three major units, which were further subdivided into four subunits. The interval between 0 and 63 cmbsf of the core (unit I), which spans the Holocene and the uppermost late Pleistocene, is characterized by a hornblende-epidote-pyroxene assemblage, and contains relatively a smaller amount of schistic mineral and authigenic pyrite. In comparison, the interval between 63 and 228 cmbsf (unit II), is representative of the Last Glacial Maximum (LGM), and features a hornblende-epidote-magnetite-ilmenite assemblage containing the highest concentrations of heavy minerals and opaque minerals. However, the interval between 228 and 309 cmbsf (unit III), which spans the subinterglacial period, is characterized by a hornblende-authigenic-pyrite-mica assemblage. Relative ratios of some heavy minerals can be used as tracers of clastic sediment sources. The lower part of the sediment core shows the highest magnetite/ilmenite ratio and relatively high hornblende/augite and hornblende/epidote ratios. The middle core shows the highest hornblende/augite and hornblende/epidote ratios, and the lowest magnetite/ilmenite ratio. The upper part exhibits a slightly higher magnetite/ilmenite ratio, and also the lowest hornblende/augite and hornblende/epidote ratios. The distribution of the mineral ratio is consistent with stratigraphic division in heavy mineral data using correspondence analysis and fuzzy C-means clustering. Variations in heavy mineral association and mineral ratio in core Q43 revealed changes in provenance and depositional environment of the southern outer shelf of the East China Sea since the late Pleistocene, well corresponding to interglacial and glacial cycles.     

Distribution and origin of sediments on the northern Sunda Shelf, South China Sea

ＩＮＴＲＯＤＵＣＴＩＯＮＯｎｅｏｆｔｈｅｍｏｓｔｅｘｔｅｎｓｉｖｅｓｈｅｌｖｅｓｏｆｔｈｅｗｏｒｌｄｌｙｉｎｇｗｉｔｈｉｎｔｈｅｓｏｕｔｈｅｒｎｐａｒｔｏｆｔｈｅＳｏｕｔｈＣｈｉｎａＳｅａｉｓｔｈｅ1850000ｋｍ2ＳｕｎｄａＳｈｅｌｆｌｏｃａｔｅｄｂｅｔｗｅｅｎｔｈｅｔｈｒｅｅｌａｒｇｅｉｓｌａｎｄｓｏｆＳｕｍａｔｒａ,Ｂｏｒｎｅｏ,ＪａｖａａｎｄｍａｉｎｌａｎｄＡｓｉａ(ＬａＦｏｎｄ,1966).ＴｈｅｎｏｒｔｈｅｒｎｐａｒｔｏｆｔｈｅＳｕｎｄａＳｈｅｌｆｉｓｓｅｐａｒａｔｅｄｆｒｏｍｔｈｅＪａｖａＳｅａｓ…     

The Mineral Composition and Sources of the Fine-Grained Sediments from the 49.6°E Hydrothermal Field at the SWIR

We used the X-ray diffraction method to determine systematically the mineral phases in bulk sediment samples and acid undissolved residuals of the fine-grained fraction of the surface sediments from the 49.6°E hydrothermal field at the Southwest Indian Ridge(SWIR)and discussed the mineral sources of the surface sediments.The results showed that the surface sediments in this region were composed of calcareous ooze,and calcite was the dominant mineral.The sediments also contained quartz,feldspar,clay minerals,pyroxene,sphalerite,barite,serpentine,and magnetite.The quartz,feldspar,and clay minerals were exogenous minerals that mainly originated from the Namib and Kalahari deserts in southern Africa.The pyroxene,serpentine,magnetite,sphalerite,calcite,and barite were endogenous minerals from weathering of seafloor basement rocks and seafloor hydrothermal activities.The sulfide particles in the sediments were mainly deposited from upwelling plumes.     

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

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

Statistical analysis of the material source and the modern sedimentary environment of the ferromanganese nodules enriched area of the North Pacific region

The source of elements and the modern sedimentary environment of the ferromanganese nodules enriched area of the North Pacific region were analysed statistically and discussed in detail. Cluster analysis shows the area's surface sediments are mainly brown clay and biogenic calcareous, calcsiliceous and siliceous ooze. Factor (principal component) analysis shows that the area's trace elements (Fe, Mn, Cu, Co, Ni, Zn, Cr, etc.) mainly come through adsorption of clay minerals and secondarily from authigenic sediments related to biochemical processes. Bao Gende, 1990. Characteristics of element geochemistry in sediments in the ferromanganese nodules enriched area of the North Pacific region.Acta Sedimentologica Sinica. (in press, in Chinese)     

Rare earth elements in sediments of the China continental shelf

Determination of the concentrations of, 15 rare earth elements (REE) in China continental shelf sediments by X-ray fluorescent spectral analysis of selected representative sediment samples showed that REE concentration in the sediments is 156 ppm, similar to that in China loess and Fujian granite, but different from that in Pacific sediments. The shelf REE have the characteristic distribution pattern of typical continental crust REE and evidently philo-continental property. The above findings suggest that weathered materials transported from the China continent are the main source of the REE in China continental shelf sediments. Experiments show that REE exist mainly in the crystal lattices of clay minerals (<2μ) as isomorphs and that REE have close relation with most elements (Al, Ti, K, Rb, Fe, etc.) related with clay minerals, but have negative correlation with the biophile elements Ca and Sr. Contribution No. 1520 from the Institute of Oceanology, Academia Sinica.     

青藏高原东北缘尖扎盆地沉积物矿物特征及其古环境意义

应用X射线衍射对青藏髙原东北缘尖扎盆地加让剖面11.8~5.8 Ma的地层沉积物进行矿物分析,结果表明加让剖面沉积物矿物组分主要包括碎屑矿物、碳酸盐矿物和黏土矿物。其中,以碎屑矿物居多,主要是石英、斜长石、云母类矿物(白云母、黑云母),及少量尖晶石、辉石类矿物(普通辉石、锰钙辉石及顽火辉石等)、金红石、刚玉、磁铁矿、钛磁铁矿、榍石、霞石,偶见锆石、石榴子石、锐钛矿;碳酸盐矿物以方解石居为主,白云石占比较少;黏土矿物中,绿泥石占比最高,还有少量赤铁矿、蛭石和沸石。以全岩矿物指标研究为主,结合加让剖面沉积相演化特点,并以磁化率变化为参考,进行系统的矿物学研究,获得了尖扎盆地在11.8~5.8 Ma蕴含的古气候环境演化大致可分为4个阶段:11.8~10.0 Ma,气候干冷期;10.0~8.6 Ma,气候暖湿波动期;8.6~6.2 Ma,气候温暖湿润期;6.2~5.8 Ma,气候干冷期。在约10.0、8.6、7.2 Ma附近,主要矿物占比及组合特征有明显改变,当时的古环境状况发生急剧变化,可能揭示青藏高原东北缘在10~8 Ma期间广泛发生了一系列较强烈的构造运动,来源于周边山脉的剥蚀使得研究区沉积的近源物质增多,约7.2 Ma之后的古环境演化过程主要受青藏高原构造隆升以及全球气候变冷协同影响。     

Sedimentary evolution of the Holocene subaqueous clinoform off the southern Shandong Peninsula in the Western South Yellow Sea

Based on the stratigraphic sequence formed since the last glaciation and revealed by 3000 km long high-resolution shallow seismic profiles and the core QDZ03 acquired recently off the southern Shandong Peninsula, we addressed the sedimentary characteristics of a Holocene subaqueous clinoform in this paper. Integrated analyses were made on the core QDZ03, including sedimentary facies, sediment grain sizes, clay minerals, geochemistry, micro paleontology, and AMS 14 C dating. The result indicates that there exists a Holocene subaqueous clinoform, whose bottom boundary generally lies at 15–40 m below the present sea level with its depth contours roughly parallel to the coast and getting deeper seawards. The maximum thickness of the clinoform is up to 22.5 m on the coast side, and the thickness contours generally spread in a banded way along the coastline and becomes thinner towards the sea. At the mouths of some bays along the coast, the clinoform stretches in the shape of a fan and its thickness is evidently larger than that of the surrounding sediments. This clinoform came into being in the early Holocene(about 11.2 cal kyr BP) and can be divided into the lower and upper depositional units(DU 2 and DU 1, respectively). The unit DU 2, being usually less than 3 m in thickness and formed under a low sedimentation rate, is located between the bottom boundary and the Holocene maximum flooding surface(MFS), and represents the sediment of a post-glacial transgressive systems tract; whereas the unit DU 1, the main body of the clinoform, sits on the MFS, belonging to the sediment of a highstand systems tract from middle Holocene(about 7–6 cal kyr BP) to the present. The provenance of the clinoform differs from that of the typical sediments of the Yellow River and can be considered as the results of the joint contribution from both the Yellow River and the proximal coastal sediments of the Shandong Peninsula, as evidenced by the sediment geochemistry of the core. As is controlled mainly by coactions of multiple factors such as the Holocene sea-level changes, sediment supplies and coastal dynamic conditions, the development of the clinoform is genetically related with the synchronous clinoform or subaqueous deltas around the northeastern Shandong Peninsula and in the northern South Yellow Sea in the spatial distribution and sediment provenance, as previously reported, with all of them being formed from the initial stage of the Holocene up to the present.     

The Sources and Transport Patterns of Modern Sediments in Hangzhou Bay: Evidence from Clay Minerals

Clay mineral compositions of 199 offshore surface sediment samples collected from the Hangzhou Bay have been analyzed. The clay minerals in the sediments from the Hangzhou Bay are dominated by illite(58.7%, on average), followed by chlorite(20.3%), kaolinite(16.9%) and smectite(4.1%). Two provinces were classified by Q-mode cluster analysis. Class Ⅰ with relatively low amounts of illite and smectite is widely distributed in the Hangzhou Bay, especially concentrated in the top and mouth of the bay, and the northern and southern nearshore areas. Class Ⅱ with comparatively high amounts of illite and smectite is mainly concentrated in the central part of the bay with the water depth of 8–10 m. By comparing clay mineral compositions with the neighbouring regions, we can find that the sediments in the Hangzhou Bay are mainly influenced by the resuspension and repeated deposition of particles from the Yangtze River due to the strong dynamic environment. In particular, the clay fraction of Class Ⅰ is mainly supplied by the Yangtze River, while the sediments of Class Ⅱ are mixture of the clay minerals carried by the Yangtze River and Qiantang River. In general, the distributions of clay minerals in the northern bay are affected by Yangtze River runoff, coastal current and flood tide together, and in the southern they are mainly affected by the Qiantang River runoff and ebb tide.     

Distributions of surface sediments surrounding the Antarctic Peninsula and its environmental significance

We analyzed grain size composition to provide information on the types and distributions as well as depositional varieties of marine surface sediments from the area surrounding the Antarctic Peninsula. The samples retrieved from the study area contain gravel, sand, silt and clay. As suggested by bathymetry and morphology, the study area is characterized by neritic, hemipelagic and pelagic deposits. The glacial-marine sediments can be divided into two types, residual paratill and compound paratill, which are primarily transported by glaciers and as ice-rafted debris. Ocean current effects on deposition are more obvious, and the deposit types are distributed consistently with terrain variations.     

黔北镇远地区三丘田剖面寒武系明心寺组上段滨岸相沉积特征及其地质意义

沉积环境分析是古地理重建的核心内容,黔北地区寒武系明心寺组沉积环境研究存在较大争议,以致对中上扬子地区明心寺组沉积期古地理格局的认识不能统一。选取寒武系明心寺组发育齐全、出露良好的黔北镇远地区三丘田剖面为研究对象,通过野外剖面观察、室内薄片鉴定及碎屑岩粒度分析等方法对三丘田剖面明心寺组岩石学特征、沉积构造、沉积演化序列、沉积相类型进行了详细分析。结果表明:黔北镇远地区三丘田剖面寒武系明心寺组上段发育大套的石英粉-细砂岩,沉积构造以低角度冲洗交错层理为主,碎屑颗粒的成分和结构成熟度均较高;三丘田剖面明心寺组上段砂岩以双次跳跃组分为主,悬浮组分含量较少,纵向剖面自下而上显示为浅水陆棚→临滨→前滨→后滨演化序列,呈典型的陆棚相向滨岸相变化。综上所述,黔北镇远地区三丘田剖面寒武系明心寺组上段的沉积相为滨岸相。黔北镇远地区明心寺组滨岸相沉积的出现,指示了黔北地区区域上重新认识明心寺组沉积相的必要性,将直接影响对黔北地区乃至中上扬子地区寒武纪古地理格局及其大地构造背景的认识。     

Discussion on origin of clay minerals in outcropped sandstone from Lower Cretaceous Chengzihe Formation and Muling Formation in Jixi Basin

Clay minerals in the outcropped sandstone from Lower Cretaceous Chengzihe Formation and Muling Formation in Jixi Basin were analyzed by X-ray diffraction. The results show that the clay minerals mainly consist of illite, kaollinite and illite/smectite, which can be divided into two types: kaolinite- and illite/smectite types. The outcropped sandstone occurred in middle diagenetic stage-A on the basis of the clay mineral composition. The development factor of the formation of kaolinite type clay mineral is caused mainly by the organic acid from the coal-bearing formation and mudstone during the diagenesis process in Lower Cretaceous Chengzihe Formation and Muling Formation in the Jixi Basin. The weak hydrodynamic force of sedimentary facies made the sandstone leaching condition poor, which is the reason forming the aggregation of clay minerals of the illite/smectite-and illite types.     

Sedimentary characteristics of silty clay facies in the South Yellow Sea shelf

ＩＮＴＲＯＤＵＣＴＩＯＮＳｔｕｄｙｏｆａｇｒｅａｔｑｕａｎｔｉｔｙｏｆｓｅｄｉｍｅｎｔｓａｎｄｈｉｇｈ ｒｅｓｏｌｕｔｉｏｎｓｅｉｓｍｉｃｐｒｏｆｉｌｅｓ (3 .5ｋＨｚ)ｄａｔａｃｏｎ ｆｉｒｍｅｄｔｈｅｅｘｉｓｔｅｎｃｅｏｆａｌａｒｇｅａｒｅａｏｆｍｕｄｄｙｓｅｄｉｍｅｎｔｓｗｈｏｓｅｄｉｓｔｒｉｂｕｔｉｏｎ ,ｆｏｒｍａｔｉｏｎｅｎｖｉｒｏｎｍｅｎｔａｎｄｏｒｉｇｉｎｈａｄｂｅｅｎｓｔｕｄｉｅｄｂｙｖａｒｉｏｕｓｒｅｓｅａｒｃｈｅｒｓ (Ｌｉｕｅｔａｌ.,1 987;ＰａｒｋａｎｄＫｈｉｍ ,1 990 ;Ａｌｅｘａ…     

Provenance of Sediments Filling a Paleo-Channel that Formed on the Western Yellow Sea Continental Shelf During the Last Glacial Period

Several buried paleo-channels are located on the continental shelf of the western Yellow Sea. Research on the paleochannels is significant for both theoretical studies and practical applications. In this paper, we analyse and discuss the mineralogy of sediments in a core (SYS-0803) recovered from a buried paleo-channel on the continental shelf of the western Yellow Sea. The aim is to determine the provenance of sediments that fill the paleo-channel. The heavy mineral assemblage of sediments in the core consists of schistose minerals, common hornblende, epidote, and ilmenite. The light mineral assemblage consists of plagioclase, quartz, lithic fragments, and K-feldspar. Analysis of the compositional maturity of the sand fraction revealed a quartz/feldspar ratio of < 1. A relatively high percentage of smectite is recorded throughout the entire paleo-channel fill, with the greatest percentage in the middle to lower parts. The detrital mineral assemblage and clay mineral content indicate that the paleo-channel sediments were sourced mainly from the Huanghe River during the last glacial period.     

Sedimentary facies of the subaqueous Changjiang River delta since the late Pleistocene

The sedimentary facies of the subaqueous Changjiang(Yangtze) River delta since the late Pleistocene was studied based on lithology and foraminifera analysis for two boreholes,CJK07 and CJK11,along with14C dating.Four sedimentary facies were identified,namely fluvial,tidal flat,offshore,and prodelta facies.The fluvial sedimentary facies is comprised of fluvial channel lag deposits,fluvial point bar deposits,and floodplain deposits,showing a fining-upward sequence in general with no benthic foraminifera.A layer of stiff clay overlies the fluvial deposits in core CJK07,indicating a long-term exposure environment during the Last Glacial Maximum(LGM).During the postglacial sea-level rise around 13-7.5 cal ka BP,the tidal flat facies was deposited in core CJK11,characterized by abundant silt-clay couplets.Euryhaline species dominate the subtidal flat foraminiferal assemblages,while almost no foraminifera was found in the intertidal flat.The offshore environment was the major sedimentary environment when the sea level reached its highest level around 7.5 cal ka BP,with a maximum accumulation rate of 10 mm/a found in core CJK11.Prodelta sediments have been deposited in core CJK11 since ~3 cal ka BP,after the formation of the Changjiang River delta.The difference in sedimentary facies between core CJK07 and CJK11 is due to their location: core CJK07 was in an interfluve while core CJK11 was in an incised valley during the LGM.Furthermore,AMS14C dating of core CJK07 shows poor chronological order,indicating that the sediments were reworked by strong tidal currents and that sediment deposited since ~7.7 cal ka BP in core CJK07 was eroded away by modern hydrodynamic forces caused by the southward shift of the Changjiang River delta depocenter.     

Change in Sediment Provenance Near the Current Estuary of Yellow River Since the Holocene Transgression

Sedimentary sequence and sediment provenance are important factors when it comes to the studies on marine sedimentation. This paper studies grain size distribution, lithological characteristics, major and rare earth elemental compositions, micropaleontological features and ~(14)C ages in order to examine sedimentary sequence and sediment provenance of the core BH6 drilled at the mouth of the Yellow River in Bohai Sea. According to the grain size and the micropaleontological compositions, 4 sedimentary units have been identified. Unit 1(0–8.08 mbsf) is of the delta sedimentary facies, Unit 2(8.08–12.08 mbsf) is of the neritic shelf facies, Unit 3(12.08–23.85 mbsf) is of near-estuary beach-tidal facies, and Unit 4(23.85 mbsf–) is of the continental lake facies. The deposits from Unit 1 to Unit 3 have been found to be marine strata formed after the Holocene transgression at about 10 ka BP, while Unit 4 is continental lacustrine deposit formed before 10 ka BP. The provenances of core BH6 sediments show properties of the continental crust and vary in different sedimentary periods. For Unit 4 sediments, the source regions are dispersed while the main provenance is not clear, although the parent rock characteristics of a few samples are similar to the Luanhe River sediments. For Unit 3, sediments at 21.1–23.85 mbsf have been mainly transported from the Liaohe River, while sediments above 21.1 mbsf are mainly from the Yellow River and partially from the Liaohe River. For Unit 2, the sediments have been mainly transported from the Yellow River, with a small amount from other rivers. For Unit 1, the provenance is mainly the Yellow River catchment. These results help in better understanding the evolution of the Yellow River Delta.     

Heavy mineral stratigraphy of sediments from the southern outer shelf of the East China Sea since the last glaciation using fuzzy C-means cluster method

Correspondence analysis and fuzzy C-means cluster methods were used to divide the stratigraphy of heavy mineral assemblages,and the sediment sources and depositional dynamics of the environment reconstructed.The assemblages were taken from marine sediments from the late Pleistocene to the Holocene in Core Q43 situated on the outer shelf of the East China Sea.Based on the variable boundaries of the mineral assemblage at 63 and 228 cmbsf (cm below sea floor),the core might have previously been divided into th...     

鲁北平原高氟深层地下水的探究

在山东省北部(鲁北)地区,当地群众由于长期饮用高氟深层地下水,极易导致地氟病,严重影响当地群众的身体健康。根据取样分析,研究区深层地下水氟离子含量大致呈现由南向北、由东向西依次增大的趋势,并且同一地段不同深度、不同岩性的氟离子含量也不尽相同,粘土中氟离子含量普遍大于粉砂层中的含量,高氟地下水多为弱碱性水,高氟地下水Na/Ca比高,高氟水与Na/Ca呈对数相关,相关性较好;高氟水水化学类型一般为HCO_3·Cl-Na型。从地质环境、水文地质环境、水文地球化学角度初探了鲁北平原深层高氟地下水的水文地球化学成因,认为鲁北深层高氟水的形成及分布规律主要受沉积环境、径流条件以及开采量的影响。由于沉积物来源的不同、水化学特征的迥异以及深层地下水的大量开采,粘土层压密释水过多补给,同时由于粘土层由南向北厚度逐渐增大,地下水径流进一步变缓,造成氟离子含量逐步增高,形成了南北部相差较大的氟离子分布特征。