Groundwater nitrate pollution in the Essaouira Basin (Morocco)

The Essaouira Basin (Morocco) contains a multi-layered aquifer situated in fractured and karstic materials from the Middle and Upper Cretaceous (the Cenomanian, Turonian and Senonian). Water percolates through the limestone and dolomite formations of the Turonian stage either through the marls and calcareous marls of the Cenomanian or through the calcareous marly materials of the Senonian. The aquifer system may be interconnected since the marl layer separating the Turonian, Cenomanian and Senonian aquifers is thin or intensively fractured. In that case, the water is transported through a network of fractures and stratification joints. This paper describes the extent of the nitrate pollution in the area and its origin. Most of the wells and drillholes located in the Kourimat perimeter are contaminated by nitrates with some concentrations over $\text{400 }\text{mg}\text{l}{}^{\mathrm{?1}}$. Nitrate contamination is also observed in the surface water of the Qsob River, which constitutes the natural outlet of the multi-layered complex aquifer system. In this area, agriculture is more developed than in the rest of the Essaouira Basin. Diffuse pollution of the karstic groundwater body by agricultural fertiliser residues may therefore partially explain the observed nitrate pollution. However, point pollution around the wells, springs and drillholes from human wastewater, livestock faeces and the mineralisation of organic debris close to the Muslim cemeteries cannot be excluded.     

Late Cretaceous paleoenvironmental evolution of the Tarfaya Atlantic coastal Basin,SW Morocco

Lithological evidence, benthic foraminiferal census counts, and X-ray fluorescence (XRF) scanner-derived elemental data were integrated with planktonic foraminiferal biostratigraphy and bulk carbonate stable isotopes to retrace the Turonian to early Campanian paleoenvironmental evolution and sea-level history of the Tarfaya Atlantic coastal basin (SW Morocco). The lower Turonian is characterized by laminated organic-rich deposits, which contain impoverished benthic foraminiferal assemblages, reflecting impingement of the oxygen minimum zone on the shelf during a sea-level highstand. This highstand level is correlated to the global transgressive pulse above the sequence boundary Tu1. The appearance of low-oxygen tolerant benthic foraminiferal assemblages dominated by Gavelinella sp. in the middle to upper Turonian indicates an improvement in bottom water oxygenation, probably linked to offshore retraction of the oxygen minimum zone during a regressive phase. This interval is marked by major regressive events expressed by a series of erosional truncations associated with the prominent sequence boundaries Tu3 and/or Tu4. Dysoxic–anoxic conditions recorded in the upper Santonian of the Tarfaya Basin coincide with the eustatic sea-level rise prior to Sa3 sequence boundary. The lower Campanian transgression, only recorded in the southern part of the Tarfaya Basin, coincided with substantial deepening, enhanced accumulation of fine-grained clay-rich hemipelagic sediments and improved oxygenation at the seafloor (highest diversity and abundance of benthic foraminiferal assemblages). Stable isotope data from bulk carbonates are tentatively correlated to the English Chalk carbon isotope reference curve, in particular the Hitch Wood Event in the upper Turonian, the Navigation Event in the lower Coniacian, the Horseshoe Bay Event in the Santonian and the Santonian/Campanian Boundary Event.     

Processes of water–rock interaction in the Turonian aquifer of Oum Er-Rabia Basin, Morocco

Possible water–rock interaction processes, in the Moroccan basin of Oum Er-Rabia, were discussed by a geochemical study of groundwater from the Turonian limestone aquifer, the most important water resource in the region. Different types of water according to the classification of Piper were defined. Waters have shown an evolution from dominant CHO₃–Ca–Mg type through mixed to SO₄–Cl–Ca–Mg type. The use of geochemical diagrams and chemical speciation modeling method has shown that water–rock interaction is mainly controlled by carbonate and anhydrite dissolution, ion exchange and reverse ion exchange processes. Water–rock equilibrium conditions are favorable for the precipitation of calcite, dolomite, kaolinite and magnesian smectite.     

Modelling groundwater flow of the Trifa aquifer, Morocco

Trifa is the most productive agricultural plain of north-eastern Morocco. The development of agricultural activities during the last few decades has been mainly based on imported water for irrigation. However, irrigation requirements have become so large that groundwater is used as a secondary source to supply the agricultural and domestic water needs, causing a depletion of the groundwater resources, especially during dry periods. A hydrological and a hydrogeological model for the Trifa plain have been developed, which yield information on relevant parameters such as groundwater recharge, and estimate the amount of pumped groundwater needed to meet the irrigation needs. The models (MODFLOW and WetSpass) provide insight into the status and evolution of the groundwater reserves. The results of the study are useful to predict the sustainability of the groundwater resources in the Trifa plain and to evaluate possible management actions. A reduction in groundwater abstraction by at least 25% may be necessary to achieve sustainable conditions.

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Resumen Trifa es la planicie agrícola más productiva del noreste de Marruecos. El desarrollo de las actividades agrícolas durante las últimas décadas se ha basado principalmente en agua importada para riego. Sin embargo, los requerimientos de riego han llegado a ser tan grandes ocasionando que se utilice el agua subterránea como una fuente secundaria para abastecer las necesidades de agua para uso doméstico y agrícola, lo que causa un agotamiento de los recursos de agua subterránea, especialmente durante periodos secos. Se ha desarrollado un modelo hidrogeológico e hidrológico para la planicie Trifa el cual aporta información de parámetros relevantes tal como recarga de agua subterránea y estima la cantidad de agua subterránea que necesita bombearse para satisfacer las necesidades de riego. Los modelos (MODFLOW y WetSpass) aportan una idea acerca del estado actual y la evolución de las reservas de agua subterránea. Los resultados de este estudio son útiles para predecir la sostenibilidad de los recursos de agua subterránea en la planicie Trifa y para evaluar posibles acciones de gestión. Puede ser necesario reducir la explotación de agua subterránea en por lo menos 25% para alcanzar condiciones sostenibles.

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Résumé Trifa est la plaine agricole la plus productive du Nord-Est marocain. Le développement de l’activité agricole durant ces dernières décennies a essentiellement reposé sur l’irrigation. Néanmoins les besoins de l’irrigation sont devenus tels que l’eau souterraine est utilisée comme ressource secondaire, pour combler la demande en eau domestique et agricole, induisant un rabattement d’autant plus important durant les périodes sèches. Un modèle hydrologique et hydrogéologique de la plaine de Trifa a été développé sur base des paramètres les plus importants, tels la recharge, et permet d’estimer le pompage nécessaire des eaux souterraines pour combler les besoins de l’irrigation. Les modèles (MODFLOW et WetSpass) apportent une bonne connaissance de l’état et de l’évolution des réserves souterraines. Les résultats de l’étude sont utiles pour prédire la longévité des ressources et pour évaluer différents scénarios de gestion. Une réduction de l’extraction de 25% serait nécessaire pour atteindre un état durable.

     

Kriging of water levels in the Souss aquifer,Morocco

Universal kriging is applied to water table data from the Souss aquifer in central Morocco. The procedure accounts for the spatial variability of the phenomenon to be mapped. With the use of measured elevations of the water table, an experimental variogram is constructed that characterizes the spatial variability of the measured water levels. Spherical and Gaussian variogram models are alternatively used to fit the experimental variogram. The models are used to develop contour maps of water table elevations and corresponding estimation variances. The estimation variances express the reliability of the kriged water table elevation maps. Universal kriging also provides a contour map of the expected elevation of the water table (drift). The differences between the expected and measured water table elevations are called residuals from the drift. Residuals from the drift are compared with residuals obtained by more traditional least-squares analysis.     

基于岩相的鄂尔多斯白垩系盆地含水层系统结构的研究

依据岩性岩相研究、孔隙度研究、物探洲井解译等成果,对鄂尔多斯白垩系盆地含水层系统的结构进行了划分与研究.结果袁明:盆地北部沙漠高原区含水层系统为单一结构,表现为强富水与中等富水含水层在垂向上叠置与组合,无区域性连续稳定的隔水层,由下到上构成含水统一体;南部黄土高原区为多层结构,表现为含水层与隔水层上下叠置,垂向水文地质分层明显:盆地南、北含水层的结构类型明显不同.利用孔隙度、渗透系数、单位涌水量3个参数,对含水层的富水性级别进行了划分,盆地中共划分出7个强富水含水层、7个中等富水含水层和2个弱富水舍水层.盆地南、北比较,北部含水层孔隙度大,富水性强,地下水主要富集于盆地北部地区.垂向上比较,盆地北部由上到下,孔隙度由大变小,富水性由强变弱,地下水主要富集于浅层和中层:南部上部罗汉洞组和下部洛河组孔隙度较大,富水性好,中部环河组相对较差.地下水主要富集于罗汉洞组和洛河组.     

Mapping of groundwater quality in the Turonian aquifer of Oum Er-Rabia Basin, Morocco: a case study

This study takes the groundwater of the Moroccan limestone aquifer of Oum Er-Rabia as an example of statistical and cartographical approaches in water resources management. Statistical analyses based on frequency distribution and PCA methods revealed the homogeneity of waters with the existence of abnormal points and have helped to assess correlations between the studied variables. The mapping approach illustrated that waters are influenced by the lithology of the surrounding rocks and are of Ca–Mg–HCO₃, Ca–Mg–Cl–SO₄, and mixed types according to the Piper classification. The quality of water is of high to medium, north of the basin, but it is of medium to bad, NE and south, due to excessive contents of chloride, sulfate and nitrate. According to the US Salinity Laboratory classification, water used for irrigation in the eastern and the southern parts of the basin should take into consideration the drainage conditions, the nature of plants and the addition of gypsum doses.

基于岩相的鄂尔多斯白垩系盆地含水层系统的结构研究

依据岩性岩相研究、孔隙度研究、物探测井解译等成果,对鄂尔多斯白垩系盆地含水层系统的结构进行了划分与研究。结果表明：盆地北部沙漠高原区为单一结构,表现为强富水与中等富水含水层在垂向上叠置与组合,无区域性连续稳定的隔水层,由下到上构成含水统一体;南部黄土高原区为多层结构,表现为含水层与隔水层上下叠置,垂向水文地质分层明显;盆地南、北含水层结构的结构类型明显不同。利用孔隙度、渗透系数、单位涌水量3个参数,对含水层的富水性级别进行了划分,盆地中共划分出7个强富水含水层、7个中等富水含水层和2个弱富水含水层。盆地南、北比较,北部含水层孔隙度大,富水性强,地下水主要富集于盆地北部地区。垂向上比较,盆地北部由上到下,孔隙度由大变小,富水性由强变弱,地下水主要富集于浅层和中层;南部上部罗汉洞组和下部洛河组孔隙度较大,富水性好,中部环河组相对较差,地下水主要富集于罗汉洞组和洛河组。     

Late Cretaceous lithoevents in the Bohemian Cretaceous Basin, Czechoslovakia

Facies evolution and vertical changes within the Late Cretaceous sequence of the Bohemian Cretaceous Basin reveal fluctuations of intra- and extrabasinal circumstances. Evidence of periodic oscillations is recognized and two categories of aperiodic event indications are distinguished according to their significance and lateral persistence. Several lithoevents may be related to eustatic changes, while others indicate the independent evolution of the basin, influenced by epeirogenetic movements of segments of the Bohemian Massif.     

Present recharge of an aquifer in a semi-arid region: an example from the Turonian limestones of the Errachidia basin, Morocco

 The Errachidia basin is composed of three superposed aquifers (Senonian, Turonian limestones and Infracenomanian). The Liassic limestone of the upper Atlas borders the northern part of the basin. The piezometric map of the Turonian aquifer displays a north-south flow, with an inflow area from the Atlas. This recharge hypothesis is demontrated by a discriminant analysis performed on chemical data: the majority of the spots are of sodium choride and hydrogenocarbonate types, while several boreholes are assigned to a calcium hydrogenocarbonate type Jurassic component. ¹⁸O measurements, using the Atlasic gradient δ¹⁸O=–4.18–0.0027 x elevation to estimate the recharge areas, confirm that the recharge area is the basin itself (<1100 m) on the Turonian outcrops, while in the confined part, the Turonian is recharged higher than 1400 m (corresponding to the Atlas). This contribution ranges from 56 to 85%, according to the situation versus the piezometric inflow area. The remainder represents infiltration and vertical leakage from the Senonian layers.     

鄂尔多斯盆地都思兔河流域白垩系含水层特征及供水前景分析

在鄂尔多斯盆地都思兔河流域供水水文地质详查的基础上,通过水文地质钻探、抽水试验、样品分析等手段,查明了流域含水层的结构、埋深以及含水层和隔水层在水平和垂直方向上的变化规律,探讨了各含水层之间的水力联系,并求取了含水层的水文地质参数;对比圈定了包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区;采用地下水流数值模拟方法对上述3处富水区地下水开采量进行计算,提出了27种地下水开采方案,并经过对比得到地下水开采推荐方案。结果表明：包乐浩晓、巴彦布拉格、好勒包勒吉3处富水区主要补给为侧向径流及大气降水入渗补给,排泄方式以潜水面蒸发及向河流排泄为主;在地下水浅埋区,结合含水层单井涌水量的大小,确定采用管井开采方式、中段悬挂式非完整井结构,平均布井,井深300m,单一开采白垩系环河组的地下水,最大限度夺取潜水蒸发排泄量;根据推荐方案,上述3个富水区总开采量达到123500m3／d,可为该地区地下水资源开发与利用提供技术保障。     

松嫩盆地扶余地区白垩系嫩江组岩石地层与沉积环境

松嫩盆地白垩纪地层发育,其嫩江组沉积厚度大,呈盆地演化后期的沉积特征。本文从扶余地区嫩江组岩石组合、韵律变化、厚度及区域分布入手讨论其特点,对其影响因素(泥质、粉砂质、细砂质岩石)进行分析总结。根据岩石组合,该区嫩江组可划分成三段:下段黑色泥(页)岩—粉砂质泥岩互层;中段灰绿色粉砂质泥岩、泥质粉砂岩、细砂岩互层;上段杂色粉砂质泥岩互层。分析沉积岩石颜色、构造及韵律组合特征,推测嫩江组由下而上为半深湖—深湖—半深湖(浅湖)相交替变化—滨湖(湖滩)相演化过程。     

鄂尔多斯盆地下白垩统含水层储水岩石特征与介质结构研究

本文采用沉积学与水文地质学交叉研究的思路,对鄂尔多斯盆地下白垩统含水层储水岩石特征与含水介质结构进行了研究。下白垩统是由宜君-洛河、华池-环河、罗汉洞-泾川三套含水岩组组成的一个厚达1300m、具多层结构的巨型碎屑岩地下水系统,发育以长石砂岩、长石石英砂岩为主的多类型储水砂岩,其沉积形成于以河流、沙漠为主的多种陆相沉积环境。由于受沉积、成岩及后期剥蚀等作用的控制,各含水岩组储水岩石的类型、厚度及分布,以及储水空间的类型和发育程度、储水孔隙介质结构均有明显变化;在与其它水文地质条件的共同影响下,下白垩统地下水赋存和富集条件总体呈现"盆地北好南差、北部上好下差、南部下好上差"的宏观分布规律。     

Evolution of groundwater salinity in the unconfined aquifer of Bou-Areg, Northeastern Mediterranean coast, Morocco

The Bou-Areg plain in the Mediterranean coast at the North-eastern of Morocco is characterized by a semi-arid climate. The aquifer consists of two sedimentary formations of Plio-quaternary age: the upper formation of fine silts and the lower one of coarse silts with sand and gravels. The aquifer is underlain by marly bedrock of Miocene age that dips toward the coastal lagoon of Bou-Areg. The hydrodynamic characteristics vary between 10⁻⁴ and 10⁻³ m/s; and transmissivities range between 10⁻⁴ and 10⁻¹ m²/s. The general direction of flow is SW to NE, toward the lagoon. The aquifer is crossed by the river Selouane, which also ends in the lagoon. The groundwater is characterized by a high salinity that can reach 7.5 g/l. The highest values are observed in the upstream and in the downstream sectors of the aquifer. The temporal evolution of the physico-chemical parameters depends on the climatic conditions and piezometric variations. The analysis of the spatio-temporal distribution of the physico-chemical parameters suggests different sources of groundwater salinization: the seawater intrusion, the influence of marly gypsum-bearing terrains, and the influence of anthropogenic products as the agricultural fertilizers, which cause great nitrate concentrations that vary between 80 and 140 mg/l.     

Groundwater pollution risk mapping for the Eocene aquifer of the Oum Er-Rabia basin, Morocco

Sustainable development requires the management and preservation of water resources indispensable for all human activities. When groundwater constitutes the main water resource, vulnerability maps therefore are an important tool for identifying zones of high pollution risk and taking preventive measures in potential pollution sites. The vulnerability assessment for the Eocene aquifer in the Moroccan basin of Oum Er-Rabia is based on the DRASTIC method that uses seven parameters summarizing climatic, geological, and hydrogeological conditions controlling the seepage of pollutant substances to groundwater. Vulnerability maps were produced by using GIS techniques and applying the “generic” and “agricultural” models according to the DRASTIC charter. Resulting maps revealed that the aquifer is highly vulnerable in the western part of the basin and areas being under high contamination risk are more extensive when the “agricultural” model was applied.     

松辽盆地红岗地区下白垩统储层沉积与隐蔽油气圈闭预测

对松辽盆地红岗地区中部含油组合的储层沉积学研究表明:研究区砂岩类型以长石砂岩为主,成熟度低,分选好-中等,磨圆中-差,杂基含量低;沉积构造类型多样,准同生变形构造十分发育;自西向东依次出现(扇)三角洲/浅湖、半深湖、深湖沉积,可划分为三种沉积体系,有利沉积相为(扇)三角洲前缘及浊积岩;成岩作用较弱,次生孔隙发育,属中孔中-低渗型储层。笔者应用对储层沉积学的研究成果进行了隐蔽油气圈闭识别,指出了研究区隐蔽圈闭类型及其在平面上和纵向上的分布规律。     

Integrated Reservoir Characterization and Petrophysical Analysis of Cretaceous Sands in Lower Indus Basin,Pakistan

The reservoir character of the Cretaceous sand is evaluated in Lower Indus Basin, Pakistan where water flooding is very common. Thus, prediction of subsurface structure, lithology and reservoir characterization is fundamental for a successful oil or gas discovery. Seismic reflective response is an important tool to detect sub-surface structure. Seismic reflection response is not enough to highlight geological boundaries and fluids in the pore space therefore, the use of integrated approach is vital to map sub-surface heterogeneities with high level of confidence. Based on seismic character and continuity of prominent reflectors four seismic horizons are marked on the seismic sections. All the strata is highly disturbed and distorted with presence of a network of fault bounded horst and graben structures, which indicate that the area was under compressional tectonic regime. These fault bounded geological structure formed structural traps favorable for the accumulation of hydrocarbon. The petrophysical analysis reveals that the Cretaceous sand formation has four types of sand: Sand A, B, C and D with good porosity (15 % average) and low volume of shale. Although complete petroleum system is present with structural traps and reservoir character of sand interval is very good but these sands are highly saturated with water thus are water flooded, which is the main reason of the abundant wells in the study area.     

羌塘盆地那底岗日地区上侏罗统—下白垩统碳酸盐岩稀土元素地球化学与古气候

通过对羌塘盆地那底岗日地区上侏罗统—下白垩统索瓦组碳酸盐岩稀土元素丰度、分布模式及稀土总量(ΣREE)的分析,结合总有机碳(TOC)含量、EFMn、Sr/Cu的变化特征,探讨了稀土元素纵向变化与气候环境之间的关系。结果表明:那底岗日地区碳酸盐岩中稀土元素总丰度值平均为45.3μg/g(不包括Y)。稀土元素与总有机碳(TOC)之间存在较好的相关性,与EFMn和Sr/Cu值的变化呈反向对应关系。ΣREE的高值段代表相对湿润的气候环境,ΣREE的低值段代表干热的气候环境。根据稀土元素分布与沉积环境的关系,推断晚侏罗世—早白垩世那底岗日地区经历了干热和相对温湿频繁交替变更的气候演化过程。     

Cretaceous synsedimentary tectonics in the Atlas system of Central Morocco

Cretaceous sediments in Central Morocco were deposited in various depositional environments and comprise an undetermined Lower Cretaceous base up to Maastrichtian. The sedimentary columns show a similar facies evolution. Basal unconformities, conglomeratic layers and significant differences in thicknesses reflect pre- and synsedimentary vertical tectonic movements. These tectonic movements took place along large NE/SW striking fault systems, one of the major features of the present tectonic framework. Permanent displacement of the subsidince maxima in time and space indicate the development of small tectonic blocks which were tilted and/or compressed between the fault zones. High sedimentation rates in areas of strong subsidence, however, prevented the evolution of intraplatformbasins. Although tectonic influence was important, eustatic sea level changes ruled the whole sedimentary regime.

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Zusammenfassung Im Mittleren Atlas und der Haute Moulouya reichen die Kreidesedimente von nicht genauer datierbarer Unterkreide bis ins Maastricht. Sie entstanden unter ständig wechselnden Ablagerungsbedingungen. Die einzelnen Sedimentsäulen weisen jeweils große Ähnlichkeiten in ihrer Faziesentwicklung auf, welche hauptsächlich den eustatischen Meeresspiegelschwankungen folgten. Basale Diskordanzen, Konglomeratlagen und signifikante Unterschiede in den Sedimentmächtigkeiten zeigen ständige synsedimentäre Vertikalbewegungen an. Diese erfolgten hauptsächlich an ausgedehnten, NE-SW streichenden Störungssystemen. Die ständigen, sowohl räumlichen als auch zeitlichen Verschiebungen der Subsidenzmaxima deuten auf die Entstehung von kleinräumigen tektonischen Blöcken hin, die zwischen den Störungszonen entweder gefaltet oder gekippt wurden. Dabei verhinderten die hohen Sedimentationsraten und die geringe räumliche Ausdehnung der Subsidenzzonen die Entstehung von tieferen Becken. Trotz der permanenten tektonischen Bewegungen waren eustatische Meeresspiegelschwankungen bestimmend für die Faziesentwicklung im gesamten Sedimentationsraum.

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Résumé Dans le Moyen Atlas et la Haute Moulouya, la sédimentation crétacée s'est effectuée dans des environnements variables depuis l'Eo-Crétacé jusqu'au Maastrichtien. Les colonnes sédimentaires dans les différentes localités sont caractérisées par une grande analogie d'évolution de faciès. Les discordances basales, les niveaux conglomératiques et la différence des épaisseurs d'une localité à une autre traduisent les mouvements verticaux pré- et synsédimentaires; ceci est surtout clair le long des failles de direction NE-SW qui ont constamment influencé la sédimentation. Les variations de la subsidence dans le temps et dans l'espace trouvent leur explication dans un modèle de basculement ou de plissement de petits blocs entre les zones de failles. Dans les zones à subsidence élevée, le taux de sédimentation était également élevé, ce qui a empêché la formation de bassins profonds. Ainsi, en dépit de l'action tectonique, les changements eustatiques du niveau de la mer ont déterminé tout le régime sédimentaire.

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