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Fifth International Conference on the Geology of the Tethys Realm, South Valley University, January 2010, P. 179-196 MINERALOGY AND GEOCHEMISTRY OF THE ECONOMIC CLAY BEDS OF ASWAN AREA, SOUTHERN EGYPT E. S. Khedr*, E. A.A. Youssef**, A. A. Refaat**, K. Abu Elmagd*, and H. M. Khozyem* *Geology Department, Aswan Faculty of Sciences, South Valley University, Aswan, Egypt ** Geology Department, Faculty of Sciences, Cairo University, Giza, Egypt ABSTRACT The studied sedimentary section at Aswan area (~ 170 m. thick) consists mainly of sandstone intercalated with six clay beds. The section encloses nine stratigraphic formations, ranging in age between Cambrian and Paleocene, separated by four unconformity planes. Two types of rock weathering, glacial and lateritic, are indicated. The upward increase of alumina and iron oxide in Kalabsha weathering profile suggested lateritization in hot humid weather (tropical). Even as the weathered profile east and southeast of the study area is a character of upward increases in the oxides of Si, Ti, Mg, and Na accompanied with depletion in the oxides of Al, Fe, Mn, Ca, K, and P, the weathering processes could have been occurred in very cold region. The economic kaolin SW of the study area are developed by weathering of the Precambrian crystalline basement rocks. The contradiction in types of the weathering processes (very cold versus tropical condition) on the crystalline Basement Rocks is attributed to changeability of different climatic zones in the study area during Paleozoic and Mesozoic Eras. The weathering zone in the basement is disconformably covered by the Cambrian Araba Formation east and southeast of the study area. The Araba Formation is devoid of economic clay and unconformably overlain by the Carboniferous Gilf Formation which consists of three clay-beds namely; lower, middle, and upper clay beds, all are in use for ceramics industry. After deposition of the Gilf Formation in the study area, deep peneplanation prevailed and the remnant of the Gilf Formation as well as the scoured surfaces of the basement crystalline rocks are subjected to lateritization followed by deposition of the Abu Ballas Formation (Late-Jurassic-Early Cretaceous) which unconformably overlies by Temsah Formation (Late Cretaceous) followed by Taref Formation, the Maastrichtian Qusier variegated shale and Dakhla shale formations. Both Qusier and Dakhla shale are not in use for ceramics industry. The average size grade of the economic clay beds of the Gilf Formation in Aswan area is the silty clay, while the shale beds of Qusier and Dakhla formations are sandy-siltstone. There is a general upward increase in oxides of Fe, Si, Mg, Ca, and P from the older Carboniferous clay beds of the Gilf Formation to the relatively younger Qusier and Dakhla shale deposits. However, the sequence of the three economic shale-beds of Carboniferous age demonstrates upward enrichment in alumina and loss in silica. This criterion is in harmony with the gradual rise in temperature of the regional climate in Egypt due to the northward drift of Africa faraway from the Ordovician polar region into the equatorial region in Jurassic-Cretaceous times. The most dominant clay minerals in the studied samples are kaolinite, illite, smectite, and regular stratified mica- montmorilonite, whilst the non clay minerals are represented by quartz as the most dominated mineral with subordinate iron oxides (hematite, and goethite), calcioferrite, pyrite, calcite, gibbsite, and kleberite. The economic clay beds of the Temsah Formation (Late Cretaceous) formed in area characterized by calm reducing lake-water supplied by ephemeral meanders deriving their suspended loads from elevated land located to the north of the studied Wadi Abu Aggag localities. INTRODUCTION Many authors apply granulometry as a tool for interpretation of the depositional environments of sediments (Friedman, 1961; Folk, 1966;, 1967; Moila & Weiser, 1968; Visher, 1976; Mansour, 1984; and Boggs, 1987). Pipette method is applied by Krumbian and Pettijohn, (1961); Galehouse, (1971); and Folk, (1974) for the granulometric analyses of fine- grained sediments. Present usage of granulometry is limited, and interpretation based on the granulometric parameters are scarce as the subject is almost absent in papers. The present authors suggest further-statistical treatments for the granulometric functions of Folk and Ward (1957), which enable comparisons between size-parameters of different formations in the stratigraphic sequence of southern Egypt. The study area is located south of Egypt between latitudes 23° 30` and 24° 15` and longitudes 32° 30` and 33° 30` covering an area of about 7500 km 2 (Fig. 1). The generalized stratigraphic section of Aswan Area (about 170m thick) is made-up of three vertical stratigraphic groups containing eight formations disconformably developed over weathering zone of the Precambrian basement rocks (Fig.2). From base upwards the three vertical groups forming the sedimentary sequence at-issue are “Infra Nubia Group (Cambrian-Pre Jurassic), Nubia Group (Late-Jurassic-Maastrichtian), and the Ultra Nubia Group (Maastrichtian–Paleocene; Khedr et. al., 2007). The analyzed shale samples are taken from the Carboniferous Gilf Formation (three set of clay beds), Qusier clastics of the “Nubia-Group”, and from the Dakhla Formation of the “Ultra Nubia Group”. Samples taken from both Qusier Formation and the Dakhla Formation are not in use for ceramics industry at the time being. However, all the chosen samples form together a complete stratigraphic sequence representing east Aswan area. Additionally, the three clay beds of the Gilf Formation (lower, middle, and upper clay-bed) are separated by cross-bedding sandstone dipping southerly (Khedr, 1985). The lower-shale-bed includes pyrite nodules attaining 40 cm in diameter with multiple peat festoons and coal streaks millimeter in thickness, whilst the upper-shale-bed of the Gilf Formation includes oolitic iron concretions at Km-6 of Wadi Abu Aggag, to the east of Aswan (Khedr, 1991). In Wadi Abu Soubaera north of Wadi Abu-Aggag at the east bank of the River Nile, the upper clay bed of the Carboniferous the Gilf Formation is a character of the so called Ball-clay shale, currently of economic use in ceramics industry. This bed,
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Petrology, Mineralogy and Geochemistry of the Economic Shale Beds of Aswan Area, Southern Egypt.

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Page 1: Petrology, Mineralogy and Geochemistry of the Economic Shale Beds of Aswan Area, Southern Egypt.

Fifth International Conference on the Geology of the Tethys Realm, South Valley University, January 2010, P. 179-196

MINERALOGY AND GEOCHEMISTRY OF THE ECONOMIC CLAY BEDS OF ASWAN AREA, SOUTHERN EGYPT

E. S. Khedr*, E. A.A. Youssef**, A. A. Refaat**, K. Abu Elmagd*, and H. M. Khozyem* *Geology Department, Aswan Faculty of Sciences, South Valley University, Aswan, Egypt

** Geology Department, Faculty of Sciences, Cairo University, Giza, Egypt

ABSTRACT The studied sedimentary section at Aswan area (~ 170 m. thick) consists mainly of sandstone intercalated with six

clay beds. The section encloses nine stratigraphic formations, ranging in age between Cambrian and Paleocene, separated by four unconformity planes. Two types of rock weathering, glacial and lateritic, are indicated. The upward increase of alumina and iron oxide in Kalabsha weathering profile suggested lateritization in hot humid weather (tropical). Even as the weathered profile east and southeast of the study area is a character of upward increases in the oxides of Si, Ti, Mg, and Na accompanied with depletion in the oxides of Al, Fe, Mn, Ca, K, and P, the weathering processes could have been occurred in very cold region. The economic kaolin SW of the study area are developed by weathering of the Precambrian crystalline basement rocks. The contradiction in types of the weathering processes (very cold versus tropical condition) on the crystalline Basement Rocks is attributed to changeability of different climatic zones in the study area during Paleozoic and Mesozoic Eras.

The weathering zone in the basement is disconformably covered by the Cambrian Araba Formation east and southeast of the study area. The Araba Formation is devoid of economic clay and unconformably overlain by the Carboniferous Gilf Formation which consists of three clay-beds namely; lower, middle, and upper clay beds, all are in use for ceramics industry. After deposition of the Gilf Formation in the study area, deep peneplanation prevailed and the remnant of the Gilf Formation as well as the scoured surfaces of the basement crystalline rocks are subjected to lateritization followed by deposition of the Abu Ballas Formation (Late-Jurassic-Early Cretaceous) which unconformably overlies by Temsah Formation (Late Cretaceous) followed by Taref Formation, the Maastrichtian Qusier variegated shale and Dakhla shale formations. Both Qusier and Dakhla shale are not in use for ceramics industry. The average size grade of the economic clay beds of the Gilf Formation in Aswan area is the silty clay, while the shale beds of Qusier and Dakhla formations are sandy-siltstone. There is a general upward increase in oxides of Fe, Si, Mg, Ca, and P from the older Carboniferous clay beds of the Gilf Formation to the relatively younger Qusier and Dakhla shale deposits. However, the sequence of the three economic shale-beds of Carboniferous age demonstrates upward enrichment in alumina and loss in silica. This criterion is in harmony with the gradual rise in temperature of the regional climate in Egypt due to the northward drift of Africa faraway from the Ordovician polar region into the equatorial region in Jurassic-Cretaceous times.

The most dominant clay minerals in the studied samples are kaolinite, illite, smectite, and regular stratified mica-montmorilonite, whilst the non clay minerals are represented by quartz as the most dominated mineral with subordinate iron oxides (hematite, and goethite), calcioferrite, pyrite, calcite, gibbsite, and kleberite.

The economic clay beds of the Temsah Formation (Late Cretaceous) formed in area characterized by calm reducing lake-water supplied by ephemeral meanders deriving their suspended loads from elevated land located to the north of the studied Wadi Abu Aggag localities.

INTRODUCTION

Many authors apply granulometry as a tool for interpretation of the depositional environments of sediments (Friedman, 1961; Folk, 1966;, 1967; Moila & Weiser, 1968; Visher, 1976; Mansour, 1984; and Boggs, 1987). Pipette method is applied by Krumbian and Pettijohn, (1961); Galehouse, (1971); and Folk, (1974) for the granulometric analyses of fine-grained sediments. Present usage of granulometry is limited, and interpretation based on the granulometric parameters are scarce as the subject is almost absent in papers. The present authors suggest further-statistical treatments for the granulometric functions of Folk and Ward (1957), which enable comparisons between size-parameters of different formations in the stratigraphic sequence of southern Egypt.

The study area is located south of Egypt between latitudes 23° 30` and 24° 15` and longitudes 32° 30` and 33° 30` covering an area of about 7500 km2 (Fig. 1). The generalized stratigraphic section of Aswan Area (about 170m thick) is made-up of three vertical stratigraphic groups containing eight formations disconformably developed over weathering zone of the Precambrian basement rocks (Fig.2). From base upwards the three vertical groups forming the sedimentary sequence at-issue are “Infra Nubia Group (Cambrian-Pre Jurassic), Nubia Group (Late-Jurassic-Maastrichtian), and the Ultra Nubia Group (Maastrichtian–Paleocene; Khedr et. al., 2007). The analyzed shale samples are taken from the Carboniferous Gilf Formation (three set of clay beds), Qusier clastics of the “Nubia-Group”, and from the Dakhla Formation of the “Ultra Nubia Group”. Samples taken from both Qusier Formation and the Dakhla Formation are not in use for ceramics industry at the time being. However, all the chosen samples form together a complete stratigraphic sequence representing east Aswan area. Additionally, the three clay beds of the Gilf Formation (lower, middle, and upper clay-bed) are separated by cross-bedding sandstone dipping southerly (Khedr, 1985). The lower-shale-bed includes pyrite nodules attaining 40 cm in diameter with multiple peat festoons and coal streaks millimeter in thickness, whilst the upper-shale-bed of the Gilf Formation includes oolitic iron concretions at Km-6 of Wadi Abu Aggag, to the east of Aswan (Khedr, 1991). In Wadi Abu Soubaera north of Wadi Abu-Aggag at the east bank of the River Nile, the upper clay bed of the Carboniferous the Gilf Formation is a character of the so called Ball-clay shale, currently of economic use in ceramics industry. This bed,

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2.5 meter thick, gradually changes upward into thin iron-oxide band, 6-10 cm thick, covered by 20-40 cm thick horizon of siliceous-shale forming the seal of the Ball-clay quarries in Wadi Abu Soubaera .

Fig. 1: Lithostratigraphic map of the study area showing the different lithologic units.

Stratigraphy and sedimentology of the claystone and shale beds east and west of Aswan area is the main goal of

the present study. Integral studies including granulometry, mineralogy and geochemistry; all are necessary to decipher the depositional history of the considered succession in the study area. The present work is planed with the intention of erecting three geochemical models, two of which are models of in-situ-weathering profiles of the residual claystone developed from the underlying fresh granitic rocks due to weathering either in tropical conditions or in very cold condition (Khedr, 2007). The third geochemical model is a character of the vertical variation on elemental composition of the shale bed along the Carboniferous-Paleocene time intervals in Aswan area. Fourth sedimentological (petrologic) model of the vertical and lateral variation in size grades of the shale beds is also proposed to achieve. Methods of Study:

One hundred and eight samples representing different shale beds occurring in the sedimentary sequence of the study area are mechanically analyzed to elucidate depositional environments of the shale samples in the study area. Among these number 82 shale samples represents the shale beds of the Infra Nubia Group, and 26 shale samples represent the shale beds of the Nubia Group and the overlying ultra Nubia Group. Seventy seven representative samples are chosen for geochemical investigation. Care has been taken to choose the samples with reference to both of their stratigraphic position in the studied section (Fig. 2) as well as their petrologic types. The analyzed elements are the oxides of (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P), in addition to H2O, and LOI. Mutual relationships between the elemental compositions are also achieved to explain the technical properties of the shale materials, their validity for use in industrial application, and to build up a model of variation in chemical composition of the shale beds along the Carboniferous-Paleocene time intervals in Aswan area (Khozyem, 2006).

Conventional screen analyses using set of sieves, followed by pipette analyses for the fine-grained particles have been achieved for 108 clastic samples and granulometric parameters of Folk and Ward (1957) are computed. Vertical variation in granulometric composition is planed by plotting percent frequency of sand, silt, and clay of the analyzed shale

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samples from different formations against the composite section of the study area. Consequently, a new statistical method is suggested and the vertical changes in granularity of the shale beds since the Carboniferous to Paleocene times have been applied. On the other hand, lateral variation showing the spatial distribution of mean percent frequencies of sand, silt, and clay of each individual shale bed of the study area are plotted in a series of contour maps. Seventy seven samples are selected and have been subjected to Shapero`s (1956) procedures for "Rapid Chemical Analysis". Twenty two samples representing the exposed weathering zone and the overlying shale beds are chosen for XRD mineralogical identification of the clay minerals, hence, the area under beaks in every diffractogram is measured and proportions of the identified minerals are calculated. The obtained mineralogical and geochemical results of the different shale samples were used to recognize their environments of deposition and the geological history of the study area.

Fig. 2: Generalized stratigraphic section of the studied area.

GRANULOMETRY

The lowermost clay bed of the Gilf Formation (Fig. 3) ranges in size-grade between silty-shale and clayey-siltstone. There is a general upward increase in the clay fraction accompanying with decreasing in silt and sand fractions in columnar sections. The spatial distribution of the clay fraction shows tendency to increase in the southwest direction accompanied with general decrease of the silt and sand ratios in the same direction. However, the analyzed shale samples from the lowermost clay bed of the Gilf Formation are currently in use for the brick industry.

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The middle shale bed of the Gilf Formation indicates that most of the analyzed samples are clayey-silt (40.82%), silty-clay (26.53%), or silt (20.41%). The rest of the analyzed samples (12.24%) are sandy-silt (8.16%), and clay (4.08%). All the analyzed samples from the middle clay bed of the Gilf Formation are used in ceramics industry. The vertical and lateral variations in grain size are portrayed in. Laterally the shale ratio increases either in the west or in the southwest direction, whereas the silt and sand percent increases northeasterly. Samples possessing the highest value of clay ratios are those collected from Wadi Abu Aggag.

The upper clay bed of the Gilf Formation indicates that about 71.43% of the analyzed economic shale are made up

mainly of clayey siltstone whilst the rest of the analyzed samples (28.57%) is either clay, loom, or silty-clay. There is a general upward increase of the clay fraction in the columnar section accompanying by general upward decreasing in both of the silt and sand fractions. Regional distribution of either the clay and the sand ratios of the Gilf Formation shows lateral westward increase, with an antagonized behavior of the silt fraction. The analyzed samples of the Qusier Formation are sandy siltstone with few amounts of shale. Most (66.67%) of the analyzed shale samples of the Dakhla formation are either silty-clay (38.89%) or clayey-silt (27.78%). These are followed by siltstone samples (22.22%).

The pure claystone sample makes about (11.11%) of the analyzed samples. There is a general upward decrease of the clay fraction in the columnar sections accompanying by a general upward increase in both the silt and the sand fractions. Laterally there is a general increase in the clay ratio in both the east and the northeast directions accompanied by eastward decrease in the silt-sized fraction. Moreover, ratios of the sand-sized fraction decrease towards the south and the southeast directions of the study area.

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Vertical changes in granularity of the shale beds since the Carboniferous to Paleocene times: To shed more light on the granulometric changes of the shale beds of the study area through the Carboniferous to

Paleocene times, the vertical granularity changes of the different formations in different sections are categorized; every category represents one individual bed. The mean values of the obtained parameters are listed in Tables (1 to 5). Hence, the vertical changes in mean size parameters of the different stratigraphic formations are plotted in Figure (4). From this figure, comparison between the shale beds which were deposited in the time span between the Carboniferous and the Paleocene can be evaluated. The following remarks can be delineated:

Fig. 4: Summary of vertical variation in grain size statistical parameters (in Ø units) against the composite section of the study area

a) Starting from base upwards, the lower two shale beds of the Carboniferous Gilf Formation pointed out to two

separate cycles of coarsening upward deposits (Fig. 3). These followed upwards by third shale bed possessing a cycle of fining upward deposition, all the three beds are separated by cross-bedded sandstone. The gradual upward coarsening in lower two clay beds of the Gilf Formation can be attributed to reworking and rapid deposition of previously formed mudstone beds. Moreover, cross-bedding direction measured in the sandstone bed below and above the shale beds (Khedr, 1985) indicated that the lower two shale beds were derived by streams from relatively higher elevated areas located further to the north of the study area. Once the sequence was sited the topmost clay bed of the Gilf Formation took place in calm water (pools or lakes), judged by its fining upward character. However, the absence of evaporite deposits from the economic Gilf-shale materials suggests that deposition of the shale grains occurred during cold to temperate weather implying deposition of the shale materials in subordinate area appropriate for deposition of deltas prior to the prevalence of the hot climate in the Cretaceous (Briden et. al., 1974). In Maastrichtian time the shale bed of the Qusier Formation changed upward into relatively coarser shale materials of the Dakhla Shale

b) The occurrence of pyrite concretions in the base of the lower clay bed of the Gilf Formation suggests a reducing condition during the early phase of deposition of the shale beds in pool environments. The source of sulfur forming the sulfide of iron is not quit easily to explain but it could be related to exhalation of gaseous-solutions passed through deep seated fissures below the pools bottom. The presence of black shale deposits with coal streaks in the lower shale beds at the escarp face opposite to the Nile north of Wadi Abu Aggag east of Aswan explains the rule of the plant remains as reducing agent which could facilitate the formation of pyrite nodules in the base of the clay bed of the Gilf Formation. In

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short, the environment of deposition of the clay beds of the Carboniferous Gilf Formation took place during fair weather to cold weather in calm reducing lake-water supplied by annual meanders driving their suspended loads from elevated land located to the north of the studied Wadi Abu Aggag sections. The presence of iron-bands covered by silica on top of the Ball-clay horizon has been attributed (by Khedr et. al., 2007) to previous long-term exposure of this horizon to lateritic weathering in alternative wet and dry periods. Alternatively, the iron and the overlying silica bands forming the sealing of the Ball-clay mines in Abu Soubaera valley could have been derived by small meteoric streams derived from juxtapose province experiencing volcanic activity.

Table 1: Calculated grain size parameters of the analyzed samples of the lower clay bed of the Gilf Formation

Table 2: Calculated grain size parameters of the analyzed samples of trhe upper clay bed of the Gilf Formation

Transport and depositional mechanisms of the shale beds: Following Passega (1957, 1964), the analyzed samples of lowermost clay bed of the Gilf Formation were deposited

from a uniform suspension of the fluvial environment (Fig. 5) and both of the lower and the upper clay beds of the Gilf Formation are deposited in the range of uniform suspension to graded suspension. Whilst, the analyzed samples of the Qusier Formation are deposited from a uniform suspension material. However, the uniform suspension transport requires a uniform sediment concentration through the suspension and minimal turbulence in the near bottom waters (Passega, 1957 and 1964).

The average size grade of the economic clay beds of the Gilf Formation in Aswan area is the clayey-silt. The shale beds of the Qusier Formation are a character of sandy-siltstone and they are not validated for used in the ceramic industry. Despite the similarity in mean-size of the Dakhla Shale and other shales from the Gilf Formation, the Dakhla shale is not validated for use in the ceramics industry. The enigmatic problem of the inapplicability of both the Qusier Shale and the Dakhla Shale in ceramics industry could be explained by the following data on geochemistry and mineralogy.

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Table 3: Calculated grain size parameters of the analyzed samples of the middle clay bed of the Gilf Formation

Table 4: Calculated grain size parameters of the analyzed samples of the Quseir Formation

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Table 5: Calculated grain size parameters of the analyzed samples of the Dakhla Shale Formation

Fig. 5: Transport mechanism of the clastic sediments according to CM diagram of Passega (1957, 1964)

GEOCHEMISTRY The chief point of interest about the residual claystone and the directly overlying sedimentary cover is the evidence

that provides the original order of deposition of the clastic sequence in southern Egypt. Correlation of elemental

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composition of the residual claystone as well as the transported shale of the sedimentary cover is not fairly clear. However, the following paragraphs will shed some lights on the geochemistry of the residual claystone and the overlying transported shale.

Geochemistry of the residual claystone. The generalized stratigraphic section of Aswan area reveals two weathering zones developed in different geological

periods over the hard basement rocks judged by types and ages of the sediment / basement interface (Khedr et. al., 2007). Glacial weathering is indicated in Alaqi area overlaid with tillite of Cambrian age Araba Formation (Osman, 2002; Issawi, 2002, 2005; Kozayem, 2006). Contrarily, lateritic weathering of the exposed Jurassic surface of the Precambrian basement rocks is indicated by Khedr (1985) and reinvestigated by Khozyem (2006) and concerned herein. The analyzed weathering profiles can discriminate between lateritic weathering and glacial weathering sometimes with hydrothermal alteration. Lateritic weathering has relatively thick iron-crust more than ten cm in thickness (carapace of McFarlane, 1976), taking place at the top of the complete weathering profile, whilst the glacial weathering could possess a thin lamina, less than one centimeter of iron pigment at the top of the weathering profile formed by downward infiltration from the above basal conglomerate sediments (Khedr, 1978).

Downward progressive weathering of the parent rocks can be inferred for the analyzed samples of glacially weathered profile developed over pink granite in Wadi-Allaqi (Fig. 6) as well as for the lateritic profile developed over syano-granite in Kalabsha kaolin mine (Fig. 7). Values of concentration ratio of the detected nine oxides are computed with respect to Al2O3 in the parent rock assuming that it equals to unity in both of the mother rock and the resulted weathering materials. However, from Figs (6 and 7) the following remarks can be delineated:

Fig. 6: Vertical variations in chemical composition of the Allaqi weathering profile (Glacial weathering).

Fig. 7: Vertical variations in chemical composition of the Kaolin weathering profile (Tropical weathering).

Behavior of chemical elements during glacial weathering of pink granite. The analyzed samples of glacial; weathered profile (Allaqi-3) show a general upward increase in the oxide of Si, Ti,

Mg, and Na with upward decrease in oxides of Al, Fe, Mn, Ca, K, and P (Fig. 6). The upward decreasing behavior of iron and Alumina oxides in this profile suggested that the chemically analyzed materials have not been subjected to lateritization. The presence of glacial sediments transected with volcanogenic materials arisen the possible access of ferruginous materials as an outcome of hydrothermal alteration of the basement rocks and the overlying materials belong to the basal

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part of the Infra Nubia Group. Figure (8A), shows enrichment in the oxides of Ti, Mn, and Na in the transitional horizon of the weathered profile then impoverished in the upper horizon. The oxide of Mn also shows slight increase in the lower part of the weathering profile but remains so in the upper clayey horizon. However, figure (8B) shows that most of major oxides analyzed are impoverished in the transitional horizon relative to Al2O3 in parent rocks. However, the oxides of Ca, Si, and P are slightly enriched in the middle horizon, accompanied with impoverishment of all other oxides. Oxides of Fe and Ti show steady upward decrease relative to Al2O3 in the parent rocks. This behavior of major elements for residual weathering profiles can be used as a predictable tool for weathering processes of silicate rock in very cold climate.

Fig. 8: Concentration ratios of major oxides against weathered products over granit in Wadi Allaqi (A) and East Bank of River Nile (B).

Behavior of chemical elements during Tropical weathering of syano-granite.

There is a general upward loss in the oxides of (Si, K, Na, Ca, and Mg) from the weathering materials through the profile, and general gain in the oxides of (Fe and Ti) relative to their quantities in the mother fresh-rocks (Syano-granite). The lower horizon of the weathering profile indicates removal of earth alkaline elements from the mother rock. Oxides of Fe, P, and Mn are still enriched with gradual upward depletion of other oxides. The middle horizon has enriched in SiO2, TiO2, and MnO and impoverished in both of the Fe2O3 and earth alkaline oxides. The uppermost part of the weathering profile enriched in SiO2, TiO2 and iron oxides forming iron crust (carapace).

Geochemistry of the transported shale.

The transported shale beds of the Infra Nubia Group represented in the study area by five beds the lower three of which belong to the Carboniferous Gilf Formation namely, lower, middle, and upper shale beds. This is followed upwards by the upper-Cretaceous Qusier Formation and the Paleocene Dakhla Formation. The following paragraphs will deal with the lateral and vertical variation of chemical composition of the five transported shale beds. Forty four shale samples covering the "five" different shale horizons have been chemically analyzed for major oxides and listed in five consequential Tables (6 to 10). Mean chemical composition of shale of every formation has been calculated and represented graphically in figure (9). Data of the chemical analysis of shale samples of the lower bed of the Gilf Formation (section of Abu Aggag No.15, and Aswan Airport No.26) are shown in Table 6. The mean values of elemental composition in the stratigraphic sequence indicate upward increasing in values of the oxides of Si, Fe, and Mn accompanied with decreases in values of Al2O3, TiO2, MgO, CaO, Na2O, K2O, and P2O5 (Fig. 9). Laterally in the study area, there are northeast increase in Al2O3, TiO2, MgO, CaO, Na2O, K2O, and P2O5, where values of SiO2, Fe2O3, and MgO show an opposed behavior i.e. decreasing in northeast direction. Within the middle shale-bed of the Gilf Formation (Table 7) there are general upward increasing in values of the oxides of Si, Ti, Mg, K, and P associated with upward decreasing in oxides of Al, Mn, Fe, Ca, Na (Fig. 9). Silica confirms westward lateral increase in the study area, whilst values of TiO2, Al2O3, MnO, and Na2O demonstrate east and northeastwards increases. The oxides of Fe, and Ca show northward increasing, whilst the oxides of Mg, K, and P exhibit southwest ward increasing.

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Fig. 9: Mean vertical variation in chemical composition of shale beds from the older Carboniferous clay beds of the Gilf Formation to the

relatively younger Paleocene Dakhla Shale in Aswan area.

The upper shale beds associated with the Gilf Formation (Table 8) show upward decreasing in SiO2 accompanied with increasing of all other major elements analyzed (Fig. 9). Laterally, SiO2, and TiO2 show westward increasing, whilst the oxides of Al, Fe, Mg, Ca, Na, K, and P are increasing eastwardly, and MnO increases in northwest ward. The analyzed shale samples of Qusier Formation (Table 9) indicate upward decreasing in mean values of the oxides of Si, Ti, and K whereas the oxides of Al, Fe, Mg, Ca, Na, and P behave inversely i.e. show general upward increasing (Fig. 9).

Mean values of the analyzed shale samples from a vertical sequence of Dakhla Formation (Table 10) demonstrate that there is a general upward increase in all analyzed major elements in the expenses of values of silica. Laterally, the oxides of Si, Ti, Ca, K, and P prove southeastward increase, whereas oxides of Al, Fe, Mn, Mg, and Na behave inversely i.e. validate northwest ward increasing. The collective picture of the chemical analysis of the different shale beds indicates that, there is a general upward increase in oxides of Al, Fe, Mn, Mg, Ca, and P from the older Carboniferous clay beds of the Gilf Formation to the relatively younger Paleocene Dakhla Shale deposits. This is accompanying with upward increase in oxides of Al and loss in Si at the top of Carboniferous shale beds (Fig.10).

Table 6: Chemical composition of samples from lower clay bed of the Gilf Formation

(Section of Abu Aggag No. 15 and Aswan Airport No.26) Section name Abu Aggag- 15

Bottom Top Aswan airport- 26

Bottom Top Sample .No. 234 236 239 240a 240b 241 394 395 397 399 404 408

SiO2 54.30 55.70 57.40 43.90 51.60 50.50 52.87 56.89 57.30 54.40 56.30 68.60 TiO2 1.28 1.29 2.49 2.61 1.01 1.75 1.49 1.27 1.40 1.40 1.10 0.94 Al2O3 24.51 23.3 22.1 36.5 27.9 29.36 26.9 23 22.6 23.11 23.4 12.7 Fe2O3 4.91 3.2 3.1 3.05 3.1 2 3.1 3.1 2.4 6.2 3.9 2.4 MnO 0.2 0.2 0.25 0.25 0.3 0.25 0.25 0.2 0.25 0.43 0.25 0.2 MgO 0.07 1.1 0.31 0.15 0.7 0.05 0.25 0.16 0.66 0.1 0.12 0.38 CaO 0.69 0.83 0.06 0.03 0.07 0.06 0.22 0.12 0.17 0.06 0.12 0.09 Na2O 0.9 0.73 0.62 1.01 0.81 0.8 0.78 0.82 0.87 0.82 0.63 0.4 K2O 4.5 3.6 2.1 2.4 3.8 3.7 2.6 3.71 2.1 3.1 2.3 2.01 P2O5 0.13 0.13 0.09 0.07 0.12 0.11 0.12 0.11 0.12 0.01 0.13 0.11 H2O 0.99 1.4 1.46 1.13 0.3 0.75 0.89 1 0.62 1.17 0.91 0.55 L.O.I 7.21 7.95 9.8 8.78 9.74 9.91 9.8 9.3 11.08 9.03 10.4 11.5 Total 99.69 99.43 99.78 99.88 99.45 99.24 99.27 99.68 99.57 99.83 99.56 99.88

Calculations K2O/ Na2O 5 4.93 3.39 2.38 4.69 4.63 3.33 4.52 2.41 3.78 3.65 5.03

Func.1* 2.54 0.04 -0.41 8.14 3.18 3 3.94 0.7 0.97 3.69 3.54 -3.99 Func.2* 2.22 -0.08 -1.34 0.91 0.67 1.96 -0.36 0.97 -1.6 -0.57 -1.52 -3.03

Notes: * = after Roser and Karsch (1988)

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Table (7): Chemical composition of samples from middle clay bed of the Gilf Formation (Section of Abu Aggag Nos. 16, 17, 18, and 19) Section

name Abu Aggag- 16

Bottom Top Abu Aggag-17

Bottom Top Abu Aggag-19

Bottom Top Abu Aggag- 18

Bottom Top Sample .No. 247 250 253 254 269d 271 290a 291c 294 282 284 285b

SiO2 57.20 66.20 67.00 72.40 75.30 68.40 60.40 55.70 75.50 79.60 81.70 86.20 TiO2 0.20 0.31 0.37 0.32 0.76 0.40 0.51 0.62 0.42 0.24 0.14 0.17 Al2O3 26.7 15.4 16.11 15.86 15.4 17.9 26.1 28.22 10.8 10.2 8.4 2.1 Fe2O3 2 1.7 1.2 1.7 1.3 0.5 1.8 1.7 0.3 0.5 1.3 2.1 MnO 0.1 0.3 0.21 0.25 0.231 0.3 0.5 0.12 0.36 0.2 0.24 0.11 MgO 0.1 0.04 0.14 0.1 0.07 0.03 0.15 0.03 0.47 0.14 0.28 0.88 CaO 0.87 0.24 0.44 0.34 0.14 0.19 0.22 0.26 0.13 0.09 0.17 0.11 Na2O 0.2 0.18 0.17 0.19 0.17 0.17 0.17 0.21 0.18 0.17 0.16 0.14 K2O 0.085 0.089 0.1 0.1 0.12 0.1 0.11 0.088 0.13 0.11 0.13 0.17 P2O5 0.03 0.161 0.196 0.041 0.014 0.201 0.19 0.242 0.298 0.036 0.338 0.289 H2O 2.27 8.9 8.61 6.6 5.51 6.92 6.63 8.31 4.95 0.69 1.88 3.07 L.O.I 8.81 6.15 4.73 1.97 0.95 4.57 3.18 3.91 6.35 6.77 4.54 3.96 Total 98.57 99.67 99.27 99.87 99.96 99.68 99.96 99.41 99.88 98.75 99.28 99.3

Calculations K2O/ Na2O 0.43 0.49 0.59 0.53 0.71 0.59 0.65 0.42 0.72 0.65 0.81 1.21

Func.1* 8.67 1.07 0.97 1.30 -0.18 1.48 7.08 8.35 -3.74 -3.15 -3.64 -7.91 Func.2* -4.66 -5.56 -5.38 -5.52 -5.31 -5.05 -4.86 -4.46 -5.96 -5.82 -6.30 -7.61

Notes: * = after Roser and Karsch (1988)

Table (8): Chemical composition of samples from the upper clay bed of the Gilf Formation (section of Abu Soubaera No. 11and 13) Section name Abu Soubaera - 11

Bottom Top Abu Soubaera - 13

Bottom Top Sample .No. 187 189 191a 191b 207a 208a

SiO2 55.94 53.59 51.58 48.15 56.02 53.15 TiO2 0.12 0.13 0.13 0.14 0.18 0.15 Al2O3 24.3 25.6 29.31 31.9 26.4 26.8 Fe2O3 1.2 1.6 1.1 3.9 0.9 1.3 MnO 0.12 0.23 0 0 0 0 MgO 1.09 0.32 1.20 0.42 0.18 0.69 CaO 0.05 0.21 0.32 0.21 0.13 0.05 Na2O 0.3 0.4 0.7 0.9 0.08 0.6 K2O 1 1.1 1.3 1.45 0.8 1.5 P2O5 0.332 0.337 0.376 0.298 0.24 0.31 H2O 1.75 2.39 0.09 1.42 0.67 1.77 L.O.I 13.55 13.96 13.41 10.44 13.53 13.06 Total 99.75 99.87 99.82 99.44 99.34 99.6

Calculation K2O/ Na2O 3.33 2.75 1.86 1.61 10.00 2.50

Func.1* 3.69 5.95 6.47 11.18 6.17 5.37 Func.2* -4.70 -3.47 -3.31 -2.47 -3.99 -2.93

Notes: * = after Roser and Karsch (1988)

Table (9): Chemical composition of shale samples from Qusier Formation (section of Idfu-Marsa Alam No.27).

Notes: * = after Roser and Karsch (1988)

Section name Idfu – Marsa Alm Road- 27 Top Bottom

Sample .No. 411 412 417 422 427 433 SiO2 48.59 53.75 57.94 49.85 55.09 52.66 TiO2 0.91 0.83 0.96 1.28 1.34 1.27 Al2O3 16.17 11.44 12.67 18.44 15.25 17.42 Fe2O3 4.93 3.71 7.88 4.56 3.42 7.09 MgO 1.6 1.31 1.11 1.22 1.04 1.71 CaO 1.48 0.6 0.94 0.24 0.19 0.13 Na2O 3.15 1.68 1.24 1.38 1.38 1.81 K2O 0.91 1.09 1.05 1.55 1.56 2.98 P2O5 0.244 0.453 0.673 0.202 0.494 0.041 L.O.I 20.47 25 15.24 21.1 19.95 14.49 Total 98.454 99.863 99.703 99.822 99.714 99.601

K2O/ Na2O 0.29 0.65 0.85 1.12 1.13 1.65

Func.1* -0.58 -2.25 0.43 1.15 -2.87 1.86 Func.2* -1.76 -2.83 -3.12 -4.98 -3.76 -1.73

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Table (10): Chemical composition of samples from shale bed associated with Dakhla Formation Section name Kurkur-section No 29 Kurkur- No 28 Sample .No. 450 452 454 459 472 437 438 439

SiO2 59.44 54.87 58.6 46.06 72 66.45 81 52.7 TiO2 0.14 0.1 0.12 0.18 0.21 0.19 0.11 0.17 Al2O3 14.2 17.3 14 21 7 13 6 19 Fe2O3 3.70 4.20 0.40 3.60 0.60 2.70 1.80 0.10 MnO 0.23 0.15 0.18 0.29 0.24 0.11 0.12 0.20 MgO 0.5 0.42 1.05 0.46 0.85 0.36 0.18 0.15 CaO 0.23 0.14 3.1 0.13 0.55 0.15 0.09 4.13 Na2O 2.1 2.4 2.2 4.1 1.2 2.1 0.36 4.2 K2O 0.3 0.2 0.25 0.6 0.1 0.2 0.8 0.1 P2O5 0.356 0.301 0.34 0.378 0.36 0.3 0.405 0.427 H2O 2.94 3.19 2.75 3.97 2.94 1.77 1.93 2.61 L.O.I 15.28 16.28 16.61 18.9 13.86 12.9 6.46 15.93 Total 99.42 99.55 99.90 99.37 99.41 99.73 99.355 99.817

Calculations K2O/ Na2O 0.14 0.08 0.11 0.15 0.08 0.10 2.22 0.02

Func.1* 2.19 4.86 0.83 6.64 -5.51 0.59 -5.22 6.61 Func.2* -3.61 -3.19 -2.09 0.26 -5.22 -3.48 -5.27 2.56

Notes: * = after Roser and Karsch (1988)

Fig. 10: Vertical variation of the mean chemical composition (%) of the shale materials of different formations along Carboniferous to

Paleocene time in Aswan area. (A): SiO2, Al2O3, Fe2O3, TiO2 and K2O, (B): MnO, MgO, Na2O and P2O5 Tectonic setting of deposition of the studied shale beds

According to the discrimination diagram of Roser and Karsch (1986), the shale samples of the lower clay beds of the Gilf Formation are most probably formed in active continental margin, whereas the middle clay beds of the Gilf Formation are most probably formed in area situated between island arcs and active continental margins. The shale samples of the upper bed of the Gilf Formation could be formed in area situated in active continental margins. Moreover, the analyzed shale samples of Qusseir Formation are most probably formed at island arc region. The Dakhla Formation is formed in the area situated in island arc to passive continental margin (Fig. 11)

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Khedr, E. S. et al. 192

Provenance of the studied shale beds. Values of the elemental composition of the shale beds (Tables 6 to 10) are used to calculate the discrimination

functions of Roser and Karsch (1988). The obtained results have been plotted on the discrimination diagrams (Fig. 12) and applied on the model sited by Roser and Karsch (1988). Consequently, the lower clay beds of the Gilf Formation can be derived from felsic to intermediate igneous provenances Roser and Karsch (1988)., whereas the middle and the upper clay bed of the Gilf Formation have been derived from mafic igneous rock. The fact that mafic rock is scarce in the study area led to postulate derivation of the shale beds from near by provenance. However, vector amounts of dip and direction of cross-bedding of the sandstone beds underneath and above the shale-beds of the Gilf Formation indicate their derivation from the north direction. However, volcanic exhalative materials as swarms and vein filling fault plans are recorded in Dehmite locality juxtaposed to Umm-Hubal. These dykes are injected into conglomerate and quartzitic sandstone of the Araba Formation of Cambrian-Ordovician age, sometimes bear out flows over the surface. On the other hand, the analyzed shale samples of Qusier Formation have been derived from multi-sources. The samples of Dakhla Formation also seem to be derived from three different provenances mafic, intermediate, and quartzose sedimentary provenance, and deposited afterwards into marine environments. The probable provinces and tectonic setting of the studied shale beds are summarized in Table (11).

Fig. 11: Tectonic setting of the studied shale beds based on K2O/Na2O ratio vs. SiO2 results according to discrimination diagrams of

Roser and Karsch (1986).

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Fig. 12: Provenance signature of the studied shale sediments using major elements plotted on discrimination function diagrams of Roser

and Karsch (1988)

Table (11): The probable provinces and tectonic setting of the studied shale samples according to Roser and Karsch (1986 and 1988). Shale beds Provenance Tectonic setting of deposition

Dakhla Shale Mafic, intermediate and quartzose sedimentary rocks Passive continental margin

Qusier Formation Mafic, intermediate and quartzose sedimentary rocks Island Arc

Upper clay bed Mafic igneous rocks Active continental margin

Middle clay bed Mafic to quartzose sedimentary rocks Island arc to active continental margin Gilf Formation

Lowe clay bed Felsic to intermediate igeneous rocks Active continental margin.

MINERALOGY

The XRD results of the studied sediments indicated that the most dominant clay minerals in the study samples are kaolinite, illite, smectite, and regular stratified mica-montmorillonite. Whilst the non clay minerals are represented by quartz as the most dominated mineral with iron oxides (hematite, and goethite), calcioferrite, pyrite, calcite, gibbsite, and kleberite. Percentages of these minerals are listed in Table (12). Generally, the clay mineral can be generated by three mechanisms, inheritance, neoformation, and transformation (Eberl, 1984). These three processes could occur in three geological environments; weathering, sedimentary, and diagenetic-hydrothermal. The mineralogy of neoformed clays in the weathering environment is a function of solution chemistry, with the most dilute solutions favoring formation of the least

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Khedr, E. S. et al. 194

soluble clays (Smirnov, 1976). However, Brasahad, (1966) stated that smectite is formed in an arid climate, gibbsite formed in wet climate, and kaolinite is formed in semi-wet climate. Thompson et al. (1982) suggested that acidic reducing medium sometimes associated with pyrite is most appropriate medium of deposition of kaolinite, whereas Illite can be formed in neutral oxidizing medium, while smectite (montmorillonite) acquiring a weakly alkaline oxidizing medium of deposition (Khedr and Moufty, 2000), and (Khedr, 2002). The chemical and mineralogical composition of the Kalabsha kaolin-deposits showing kaolinite as a principal clay minerals in Kalabsha Kaolin, which suggested that the deposits has been formed in acidic medium with pH ranging between 3.5 up to 5.7 in wet, hot climate (Barshad, 1966). The presence of pyrite at the lower part of Kalabsha Kaolin and at the base of the Gilf Formation demonstrates their formation in reducing conditions with gradual upward change to oxidizing environment which tolerates deposition of hematite crust at the top of both of Kalabsha kaolin profile and the Gilf shale deposits.

Table (12): Percentage frequencies of identified minerals from different claystone horizons and shale beds of Aswan area.

Rock unit

Fm.

Sample No.

Kaolinite

Illite

Smectite

Mica - Mont

Illite-smectite

Quartz

Hematite

Goethite

Calcite

Gibbsite

Calcioferrite

Kleberite

Pyrite

Albite

22 10.37 12.76 11.64 15.63 - 25.84 6.7 9.89 7.18 - - - - - (NG) Dakhla Fm.

21 34.29 12.47 - 17.79 - 22.47 7.92 - 5.06 - - - - -

20 56.41 6.08 - - - 21.22 - 5.17 - - - - - -

19 41.96 8.67 - - - 31.91 - 7.54 5.15 - - 4.77 - -

18 38.05 10.79 - 17.8 - 28.72 - 7.43 8.16 - - 6.85 - -

17 36.2 7.69 - - - 38.31 - - - - - - - -

Upper clay bed of the

Gilf Formation

16 75.42 - - - - 24.58 - - - - - - - -

15 35.5 10.94 - - - 39.3 - - - - 14.26 - - -

14 41.24 15.77 - - - 34.3 - - - - - - 8.68 -

13 35.29 15.57 - - - 41.18 - - - 7.96 - - - -

12 40.54 13.01 - - - 29.65 8.57 8.47 - - - - 8.32 -

11 31.28 12.03 - 10.83 - 26.74 - - - 19.12 - - - -

Middle clay bed of the

Gilf Formation

10 51.05 - - - - 25.74 - - - - 11.11 - - -

9 37.35 - - - 15.03 38.89 8.78 8.78 - - - - - -

Infra Nubia Group

Lower clay bed of the

the Gilf Formation

8 49.65 - - - 9.87 29.2 11.28 11.28 - - - - - -

7 13.27 - - - - 80.97 - - - - - - - -

6 15.64 - 9.87 - - 74.49 - - - - - - - -

5 40.08 - 20.34 - - 26.46 - - - - - - - -

Abu Aggag weathering

zone 4 25.33 - - - - 74.67 - - - - - - - -

3 61.25 12.87 - - - 16.64 - - - - - - -

2 45.87 7.33 - - - 16.31 - - - - - - - 8.72

Weathering zone Kalabsha

Kaolin 1 69.38 9.43 - - - 12.34 - - - - - - 8.58 -

The presence of albite (K-Feldspar) in the middle part of Kalabsha Kaolin could take place during lateritic processes

due to inverse reaction of KCO3 and kaolinite to form antigenic feldspars, or it can be developed from K-illite. Alternatively, albite could be inherited from the mother rock (Khedr, 2002). The studied weathering profile of Wadi Abu Aggag is developed over granitic rock. It shows upward gradation from fresh basement rocks to kaolinized basement rocks then to silty kaolin. In many localities along Wadi Abu-Aggag, peneplanation of the weathering zone was deep enough to erode the whole materials of the weathering products. Thus, the basal conglomerate bands overlying the weathering zone mostly are mingled in many places with kaolin and sometimes with red pigment of iron oxides; both are most probably derived by infiltration from above (eluviation) into the Cambrian sandstone sequence at the base of the Infra Nubian Group at issue. Collectively, the above observable facts suggest the prevalence of a wet, cold weather during weathering of the basement hard rocks at Abu Aggag valley, in well drained acid environment (Paquet, 1961). Moreover, the identified smectite and hematite in the weathering zone of Wadi Abu Aggag most probably could attribute to the prevalence of alkaline oxidizing medium in latter phase during their formation. To sum up it is now possible to state that conditions possibly responsible for the weathering of the basement crystalline rocks prior to deposition of the sandstones are differ from place to place in the study area. It was hot, hummed climate in Kalabsha area but in Abu Aggag and Allaqi areas the climate was wet cold

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weather. Hence, the basal conglomerate of the Sandstone sequence can be formed in different ages, late Jurassic-early Cretaceous in Kalabsha area and probably Cambrian-Ordovician in age in Abu Aggag and Umm Hubal localities. This conclusion is in harmony with situation of the study area during the phases of continental drifts since Cambrian to Cretaceous time-span (Briden et. al., 1974). In the study area, the spatial distribution of mean compositional values of different types of clay minerals is achieved using Surfer Computer program. The transported shale beds of both of the Gilf Formation and Dakhla Formation are characterized by northward increases of illite accompanied by eastward decreases in the mean percentage of kaolinite.

SUMMARY AND CONCLUSIONS There are two different types of weathering processes formed in two different times but both of them are developed

over the Precambrian basement rocks. The first of them is associated with cold climate in Paleozoic time (Cambrian to Silurian). The analyzed samples of glacially weathered profile of Wadi Allaqi area show a general upward increase in the oxide of Si, Ti, Mg, and Na with upward decrease in oxides of Al, Fe, Mn, Ca, K, and P. These weathering materials are recorded underneath rocks of Cambrian Araba Formation in Wadi Abu Aggag and also recorded in Wadi Allaqi area southeast of Aswan (Khedr et. al., 2007). This conclusion is in harmony with the cold weather prevailed during Cambrian-Ordovician and probably Silurian times in the northern part of Africa (Briden et. al., 1974). The second type of weathering developed over granitic hard basement rocks shows concentration of silica at the basal part, alumina in the central part and iron in the topmost part of weathering profile which substantially formed due to lateritization in hot hummed climate during Triassic-Jurassic and Cretaceous times (Khedr, 1987, and 2002). Lateritization represented in the study area by Kalabsha profile. The Kalabsha kaolin profiles had been developed in upper Jurassic-Lower Cretaceous time in lateritic environment (Youssef, 1996, and Khedr, 2002)), and validate the upward enrichments of the oxides of Fe, Al, and Ti and depletion in K, Na, Ca, Mg, and Mn.

The studied shale beds of the idealized sequence indicate general vertical increase in mean grain-size i.e. passing from relatively finer shale of the Carboniferous Gilf Formation to coarser Paleocene Dakhla Shale. Starting from base upwards, the lower and the upper shale beds of the Carboniferous Gilf Formation pointed out to two separate coarsening upward sequences, implying inverse graded deposit, which can safely be attributed to recycling of these beds. The middle clay bed of the Gilf Formation indicates upward fining products. Following Passega (1957, 1964), the analyzed samples of the lowermost clay bed of the Gilf Formation were deposited from a uniform suspension of the fluvial environment. Both of the lower and the upper clay beds of the Gilf Formation are deposited in the range of uniform suspension to graded suspension. In short, the environment of deposition of the shale beds of the Gilf Formation took place during fair weather to cold weather in calm reducing lake-water supplied by ephemeral meanders driving their suspended loads from elevated land located to the north of the studied Wadi Abu Aggag localities.

The analyzed shale of Qusier Formation shows gradual upward increase in grain size, implying inverse graded bedding and reflects deposition of the shale bed in calm lake water (pools) supplied with small meanders. The analyzed samples representing the lower part of the Dakhla Formation show a general upward decrease in grain size, suggesting deposition in shallow marine environment of transgressive sea encroached on old land areas marked by relatively stable conditions with gentle rates of subsidence (Elliot, 1981, and Johnson, 1981).

There is a general upward increase in oxides of Fe, Si, Mg, Ca, and P from the older Carboniferous clay beds of the Gilf Formation to the relatively younger Dakhla shale deposits, accompanied with upward increase in alumina and loss in silica at the upper shale bed of Carboniferous age. Peneplanation of the Cambrian and Carboniferous Formations led to projection of the surface of the basement crystalline rocks which re-weathered in hot-humid condition and covered underneath Late Jurassic-Early Cretaceous Six-Hills Formation. The Triassic-Jurassic volcanogenic dykes recorded cross-cutting Cambrian-Ordovician tillite arises the possible access of ferruginous materials as an outcome of hydrothermal alteration along deep seated channels of the basement hard rocks and the overlying basal clastics. In places sheltered against peneplanation, the Carboniferous Gilf Formation has been subjected to lateritic weathering judged by the occurrence of iron carapace covered by silicified shale horizons at the top of the Ball-clay shale in Wadi Abu-Soubaera, with consequent upward enrichment in alumina and iron in the whole sedimentary sequence at issue, "mantel of waste" of Strakhov (1962). According to the discrimination diagram of Roser and Karsch (1986) clay beds of the Gilf Formation are most probably formed in area situated between island arcs to active continental margins. Whilst, shale of the Qusier Formation most probably is formed at island arc region, and those of the Dakhla Formation is formed in the area situated at island arc to passive continental margin.

The identified minerals using XRD technique are categorized into two groups, clay minerals and non clay minerals. The most dominant clay minerals in the studied samples are kaolinite, illite, smectite, and regular stratified mica-montomorilonite, whilst the non clay minerals are represented by quartz as the most dominated mineral with iron oxides (hematite, and goethite), calcioferrite, pyrite, calcite, gibbsite, and kleberite. The presence of kaolinite as principal clay minerals in the investigated samples suggested that the deposits have been initiated in acidic medium with pH ranging between 3.5 up to 5.7 in wet, hot climate (Barshad, 1966). The presence of pyrite in the lower part of Kalabsha Kaolin and in the base of the Gilf Formation demonstrates their formation in reducing conditions with gradual upward change to oxidizing environment which tolerates deposition of hematite crust at the top of both of Kalabsha kaolin profile and on top of the Carboniferous Ball-clay in Wadi Abu Soubaera.

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The illite content in the shale beds of the study area shows northward increase, whilst the kaolinite content decreases in the same direction. Parham (1966) suggested that kaolinite decrease away from the shore and illite increase towards the basin direction. This result agrees with the results of the mechanical analysis of the studied claystone horizons where grain size decreases and sorting worsens towards the north and east. In these directions, the sedimentary basin of the economic shale beds of Aswan area clearly becomes deeper.

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