Stratigraphic Setting, Facies Types and Depositional Environments ...

Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02

Stratigraphic Setting, Facies Types and Depositional Environments of Haddat Ash Sham Ironstones, Western Arabian Shield, Saudi Arabia. Rushdi J. Taj Abstract-The ironstone-bearing Tertiary succession in Haddat Ash Sham area consists of conglomerates, sandstones, siltstones, mudstones and ironstones arranged in upward coarsening-and fining cycles of intermittent depositional environments ranging from fluvial coastal plain to shallow marine. The studied ironstones are enclosed within the middle shallow marine member of this succession. This middle ironstones-bearing member consists of repeated coarsening and shallowing-upward cycles representing deposition during general upward increasing in the current and wave activities as a result of the gradual progradation of linear tidal sand/ooid bars on basal shelf muds. The ironstones are classified according to their stratigraphic setting, depositional environments and lithology into the following types: chamositic, silty chamositic, lean oolitic, true oolitic, silty, chamositic silty and sandy ironstones. Most of these ironstones are recorded within the middle and upper parts of small-scale shallowing and coarsening-upward cycles reflecting intermittent short-lived periods of sea regression and transgression. The chamositic ironstones are recorded in the middle parts of the cycles while the oolitic and sandy ironstones are recorded in the middle and upper parts of the cycles. The mineralogical compositions and textural parameters of these ironstones vary according their stratigraphic positions and depositional environments. The different ironstone are composed mainly from: a) extra-basinal components i.e. quartz, intermixed with amorphous clays and Fe-oxyhydroxides, b) intra-basinal components i.e. chamosite and Fe-oxyhydroxides flasers, ooids and peloids, and c) diagenetic components formed by the hematitization of the precursor amorphous Fe-oxyhydroxides as well as the green chamositic clays and the formation of goethite and hematite mineral phases of different morphological forms (cements, coating, ooids and peloids). Index Terms- Haddat Ash Sham area, green marine clays, ooid bars. Phanerozoic oolitic ironstones, Saudi Arabia iron ores.

I. INTRODUCTION AND GEOLOGIC SETTING

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ADDAT Ash Sham area lies about 70km N to NE of Jeddah city (Fig. 1). It lies between latitude from 21º 50´ 00‖ to 21 º 50´ 19‖N and longitude 39 º 43´ 38‖ to 39 º 44´ 00‖ E (Fig. 1A, B, C). It comprises small isolated landforms of

crystalline Precambrian Arabian shield rocks overlained by the Tertiary sedimentary succession of the red sea coast, west central Saudi Arabia. The area contains many NE and NW small wadies. The aims of this study are to give a detailed description of stratigraphic setting, sedimentologic and petrographic characters of the different types of ironstones encountered within the Tertiary succession in Haddat Ash Sham area. To achieve these purposes, a detailed stratigraphic section was measured in the ironstone-bearing units and the petrographic characters of the ironstones are deduced. The study area comprises Precambrian-Cambrian basement complex, Cretaceous-Tertiary sedimentary succession enclosing the studied ironstones, the Tertiary-Quaternary basaltic lava flows, and the Quaternary-Recent alluvial deposits. A. Precambrian Rocks The Precambrian rock units in the study area have been studied by different workers of the Directorate General of Mineral Resources [1]. The basement rocks in the study area consist of Late-Proterozoic basaltic to rhyolitic volcanic and volcanoclastic and epiclastics of primitive island-arc type, that have been multiply deformed and metamorphosed and injected by intrusive bodies of different ages and compositions [2]. According to the Arabian Shield map [3] the Precambrian rock units (Fig. 1D) are represented by: 1) The Cryogenian layered rocks which are represented by the Samran Group (sa) which includes mafic to felsic lavas and volcaniclastic rocks, graywacke, polymict conglomerate, shale, siltstone, chert, marble, and quartzofeldspathic schist, mica schist and amphibole schist. Chlorite schist and subordinate interlayered sericite schist and andesitic tuff are locally common, representing fine-grained distal volcanic deposits,

Manuscript received March 29, 2011 Rushdi Jamal Taj. Faculty of Earth Sciences, King Abdulaziz University P.O. BOX 80206, Jeddah, 21589, Saudi Arabia [email protected]

ATBAS-40110025 ©Asian-Transactions

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Fig. 1. A= General location map for Saudi Arabia, B, C= Google image (B) and geologic map of Jeddah-Wadi Fatima area (C), D= Detailed geologic map of Haddat As Sham area


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 2) The Cryogenian intrusive rocks which are represented by: A) The Hishash granite (ig) which is an irregularly shaped pluton that intrudes the Kamil suite and Samran group in the western part of the Jeddah terrane. The pluton is composed of monzogranite and subordinate granodiorite [2]; B) The Kamil suite (km) which consists of mafic, intermediate, and felsic plutonic rocks of calc-alkalic and locally trondhjemitic affinities widely exposed in the southwestern part of the Jiddah terrane between the Bi’r Umq suture on the north and the Makkah area on the south. The suite includes tonalite and trondhjemite, diorite and quartz diorite, lesser amounts of granodiorite and quartz monzonite, and minor monzogranite, and

middle and an upper member. The lower member consists of shale, mudstone, marlstone, sandstone, limestone and dolomite. Raindrops imprints occur on top of the lime mudstone bed. The middle member consists of very fine-tofine quartz sandstone and an upper part of conglomerate layers. The upper member consists of remarkably finer sediments composed of very fine-grained sandstone, siltstone and shale. This upper member is covered by almost horizontal sheets of basaltic lava flows. The Maastrichtian age (upper most Cretaceous) to the Usfan Formation was assigned by [5], [6].

3) The Edicarian layered rocks which are represented by Shayma Nasir Group crops out in small exposures at the western edge of Harrat Rahat in the west-central part of the shield. They include polymictic conglomerate; basaltic, andesitic, dacitic, and rhyolitic lava, tuff, and agglomerate; and red-brown arkosic, volcaniclastic, and calcareous sandstone.

Cenozoic lava fields occupy large surface areas in western Saudi Arabia. One of the largest lava fields occurs in Harrat Rahat, which extends from Al-Madinah Al-Munawarah southward for about 310 km. into the study area. These basaltic rocks were mapped and assigned as Rahat group [9]. These harrat rocks are mainly formed of flat- lying alkali basalts surrounded by a few pyroclastic cinder cones. The lavas either rest on peneplains or have infilled ancient wadies (buried channels).

B. Cretaceous-Tertiary Sedimentary Succession The Cretaceous-Tertiary sedimentary rocks are exposed beneath a cover of flat-lying lavas and Quaternary deposits in the study area. The names Shumaysi and Usfan formations to these sedimentary sequences after [4], [5], [6]. The Shumaysi Formationis subdivided into the Haddat Ash Sham, Shumaysi, Khulays, and Buraykah formations [7]. In the study area, the Tertiary sequence is represented only by the haddat Ash Sham and Usfan Formation [Taj and Mesaed, personal communications]. Haddat Ash Sham Formation consists of clastic rocks dominated by sandstones, shale, mudstones, oolitic ironstones, and occasionally conglomerates. The formation has been divided into three members [8]: a lower, middle and an upper member. The lower member rests on a peneplained surface of Precambrian rocks and is clearly visible in the southernmost part of the study area where it is marked by a basal conglomerate. The middle member overlies the lower member conformably. The most distinctive lithological feature of this member is the oolitic ironstone deposits and the dominant red beds. The upper member rests conformably on the middle member. It is characterized by fine-grained sediments mainly shale and siltstone with a minor proportion of very fine to fine- grained sandstone. The member is terminated by a 1m thick bed of red shale. A middle Cretaceous age has been assigned to Haddat Al-Sham Formation.

C. Tertiary-Quaternary Basaltic Lava Flows

D. Quaternary Deposits The deposits cover large parts of the study area (Fig. 1D). They are composed of terrace gravel, alluvial fan deposits, tallus deposits, alluvial sands and gravels and some eolian sand deposits.

II. STRATIGRAPHY OF TERTIARY SUCCESSION OF HADDAT ASH SHAM AREA

The present detailed field investigations and measurements in Haddat Ash Sham area revealed that the Tertiary succession in the study area is composed mainly of three members (Fig. 2): Lower fluvio-lacustrine clastic member, Middle oolitic ironstones-carbonate member and Upper tidal flat fluviolacustrine clastic member (Fig. 2). A. The Lower Fluvio-Lacustrine Clastic Member This is present overlying highly weathered Arabian Shield granite with a characteristic quartz pebble lag and disorganized conglomerates. This member is composed mainly from two main channels of characteristic three finingupward cycles (Fig. 3, Column A). Each of these cycles began by massive disorganized conglomerates grades upwards into trough and tabular cross-bedded kaolinitic and ferruginous

Usfan Formation lies conformably on Haddat Al-Sham Formation and it is characterized by its carbonate ledge. The formation has been divided into three members [8]: a lower,


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Fig. 2. Detailed geologic map of the study area showing the different members of the Tertiary succession of the study area

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conglomerates and pebbly sandstones then into tabular crossbedded to cross-laminated fine-grained sandstone and siltstone. The fining-upward cycles are terminated by parallel bedded fine-grained sandstone/siltstone and ferruginous mudstones.

The quartz lag beds at the contact between the Arabian Shield granite and the conglomerates of the lower member indicate deposition in the proximal reaches of braided streams. The grain-supported organized conglomerate facies is similar to the organized conglomerate facies which is interpreted as gravel sheets or longitudinal gravel bars. Weak internal


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 stratification within the lower parts of these deposits probably represents waxing and waning of individual flood flows. B. The Middle Oolitic Ironstone-Carbonate Member Three scales of cyclicity have been recognized in the measured stratigraphic section in the middle oolitic ironstonescarbonate member in Haddat Ash Sham area (Figs. 3, 4). These are: Large-Scale-Coarsening-Upward Cycle (LC); Medium-Scale Coarsening-Upward Cycle (MC) and SmallScale Coarsening-Upward Cycle (SC). The middle member (Fig. 2, upper parts of column A and lower part of column B) attains up to 150m thick and consists of characteristic 11 shallowing and coarsening-upward cycles (Pl. 1A, B). This member is ironstone-bearing and is represented in the field by gentle slope unit where it contains thick mudstone units. Also, it is characterized by the presence of red ironstone beds and rhythmic beds of bench-like protruded sandstone and slopeforming mudstone. The middle member comprises three main units (Figs. 2 and 3): 1) the oolitic ironstone unit which contains the large cycles from 1 to 8, 2) thick tidal sandstone unit (cycles 9 and 10), and 3) phosphatic carbonate unit (Cycle 11). The large-scale-coarsening-upward cycles (LC) of this middle member are subdivided into medium and small-scales cycles (Figs. 3 and 4) which represent a general shoaling regime of a delimited time period that began by general transgression and deposition of thick mudstone dominated unit. This was followed upward by a transitional unit of rhythmic alternations of mudstone-siltstone-sandstone and oolitic ironstone comprising medium and small-scale coarseningupward cycles representing deposition during somehow stable period of very short and repeated sea level falls and rises (regression and transgression).

ironstone-bearing member are shown in figure 6. The description of this member is shown below as follows: A. First Large Cycle This cycle forms the first mudstone dominated unit overlying the sandstones and conglomerates of the lower fluvio-lacustrine clastic member (Fig. 4, column A, Pl. 1C). This cycle is subdivided according to the thickness of the mudstone of the lower parts of the shallowing-upward cycle into three medium-scale cycles: The first medium-scale cycle is composed of four small-scale cycles of rhythmic alternations of mudstone and ferruginous fine-grained sandstone/siltstone. The second medium scale cycle is chamositic clays-bearing and it is characterized by its green color (Pl.1D). It begins by thinly laminated green chamositic mudstone which grades upward into thinly bedded green chamositic siltstones and terminated by cross-laminated chamositic sandstone (sandy chamositic ironstone, Pl.1E). The third medium-scale cycle attains up to 5m thick and it is composed of 12 small-scale cycles. The lower part of this cycle is composed of green bioturbated chamositic mudstone which grades upward into reddish green hematitized green chamositic siltstone/silty chamositic ironstone and terminated by the first protruded oolitic ironstone bed (Pl.1F). After this oolitic ironstone bed, this medium-scale cycle becomes composed from different types of chamositic, chamositic silty, silty chamositic and oolitic ironstones (Table 1) stacked in successive small-scale cycles. The third medium-scale cycle is terminated by a characteristic chamositic sandstone unit. The fourth medium-scale cycle is ironstone-free and it represents the light color protruded sandstone unit terminating the first large-scale cycle (Fig. 4, top of column A). It attains up to 7m thick and it begins by thinly bedded light green chamositic fine-grained sandstone (Pl. 1F) which grades upwards into cross-laminated to cross-bedded medium-grained sandstone (Pl. 1G) and terminated by tabular cross-bedded tidal flat sandstone and pebbly sandstone (Pl. 1H).

C. The Upper Tidal Flat Fluvio-Lacustrine Clastic Member B. Second Large Cycle This upper member forms the thick mudstone, sandstone and conglomerates stacked in fining and coarsening-upward cycles. This member represents the upper parts of the Tertiary succession in the study area just overlying the middle ironstone-bearing member (the aim of the present study) and underlying the black basaltic flows (harrat). It is composed of red clays components of high economic potential for brick clays factories. III. STRATIGRAPHIC SETTING OF HADDAT ASH SHAM IRONSTONES

This cycle attains up to 10.5m thick (Fig. 4, lower part of column B). This cycle is also similar to the first cycle where it is composed from thick grey mudstone unit in its lower parts and a middle green chamositic clays, chamositic ironstones and chamositic siltstone/ sandstone unit and a characteristic reddish white (bench-like) tabular cross-bedded sandstone unit (Pl. 2A, B). Detailed field description of this cycle in the field led to the recognition of two medium-scale cycles in this second cycle (Fig. 4, lower part of column B, red cycle no. 2).

The middle-ironstone-bearing member is composed mainly of 11 successive shallowing-upward cycles (Figs. 4 & 5). The symbols used in the drawing and presentation of this


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Fig. 3. Detailed stratigraphic section of the Tertiary succession in Haddat Ash Sham area showing the middle oolitic ironstone-carbonate member (red color tap, for legend see Fig. 5).


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Plate 1: A, B= The shallowing-upward cycles (arrows) of the middle ironstone-carbonate member of the Tertiary section in Haddat Ash Sham area, C= Close up view of the oolitic ironstone-bearing (arrows) shallowing-upward cycle; D, E= The green chamositic clays (arrows) of the middle part of the first large-scale shallowing-upward cycle; F= Thick bench-like red oolitic ironstone bed (arrows) terminating the small-scale cycles; G= Cross-laminated to cross-bedded medium-grained sandstone, top of the first large cycle; H= Tabular cross-bedded tidal flat sandstone and pebbly sandstone, top of the first large cycle.


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 The first medium-scale cycle begins by thick grey mudstone which grades upward into green chamositic mudstone/siltstone and terminated by a characteristic two oolitic ironstone beds alternating with green chamositic mudstone (forming the uppermost two small-scale cycles terminating the first medium-scale cycle (Pl. 2C, D). The second medium-scale cycle begins by intercalations of green chamositic clays and thin oolitic and chamositic ironstone beds forming the lower four small-scale cycles in the lower part of this secondmedium-scale cycle (Pl. 2E). This medium-scale cycle is terminated by small cycle begins by cross-laminated to crossbedded ferruginous sandstone and terminated by thick crossbedded protruded tidal flat sandstone (Pl. 2F). Horizontally aligned ferruginous mudstone-siltstone and ironstone clasts are observed distributed along the bedding planes (Pl. 2F). C. Third Large-Cycle This cycle attains up to 30m thick and it forms a remarkable unit in the ironstone-bearing succession (Fig.4, column B). It begins by very thick grey mudstone (Pl. 2G) and terminated by remarkable bench-like sandstone horizon. This third large-cycle is composed of two medium-scale cycles; the lower one begins by thick thinly laminated mudstone and terminated by cross-laminated fine-grained sandstone (Pl. 2H). The second medium-scale cycle is composed of two smallscale cycles, the lower one begins by ferruginous fine-grained sandstone and terminated by bioturbated sandy/silty ironstone (Fig. 4, top of column B, Pl. 3A). The second small-scalecycle begins by fine-grained sandstone and terminated by sandy/silty ironstone beds (Pl. 3B). D. Fourth Large Cycle The fourth, fifth, sixth, seventh, and eighth large cycles (Fig. 4, lower and middle parts of column C) form a characteristic slope-forming thinly bedded unit in the ironstone-bearing middle member (Pl. 3C, D). The fourth cycle attains up to 9m thick and it consisting of lower ironstone-free unit consists of interbedded mudstone and finegrained sandstone stacked in successive small-scale cycles (Pl. 3E). The middle part of this cycle is composed of successive small-scale cycles which are composed of a lower green chamositic clays and chamositic siltstone and terminated by red and reddish green chamositic and oolitic ironstones (Table 1, Pl. 3F). The ironstone beds show gradational contacts with the alternated red hematitic mudstone and green chamositic mudstones of the lower parts of the shallowing-upward cycles. The main red oolitic ironstone bed of the middle part of this cycle (Pl. 3E) is overlained by thin oolitic ironstones beds with thin mudstone intercalations (Pl. 3E).

This cycle attains up to 2.5m thick and it consists mainly of green chamositic clays which grades upward into protruded slightly hematitized chamositic siltstone/silty chamositic ironstone (Pl. 3G, H). F. Sixth Large Cycle This cycle attains up to 3m thick and it consists of three small-scale cycles (Fig. 4, middle part of column C, Pl. 4A). The lower small-scale cycle is relatively thicker than the overlying other two small-scale cycles. It begins by thick grey mudstone which grades upward into green chamositic mudstone/siltstone and terminated by a characteristic red oolitic ironstone bed (Pl. 4B). The second cycle is composed from a basal red oolitic mudstone and terminated by ferruginous cross-laminated to cross-bedded siltstone/finegrained sandstone (middle part of photo of Pl. 4B). The upper small scale-cycle is similar to the aforementioned cycle where it begins by red oolitic mudstone and terminated by protruded cross-laminated to cross-bedded ferruginous sandstone (Pl. 4B). G. Seventh Large Cycle This cycle attains up to 10 m thick. It is ironstone-free and composed of a thick grey mudstone which is followed upward by green chamositic clays, siltstone and sandstone and terminated by ferruginous cross-laminated to cross-bedded fine-to medium grained sandstone (Pl. 4C). H. Eighth Large Cycle This cycle attains up to 9m thick and it is composed of successive seven small scale cycles. Cycles 3, 4 and 6 are terminated by red /reddish green oolitic and chamositic ironstone beds (Fig. 4, top of column C, Pl. 4D). The first small cycle begins by laminated mudstone and terminated by cross-laminated fine-grained sandstone, the second cycle begins by mudstone and terminated by green chamositic finegrained sandstone. The third small cycle begins by mudstone and terminated by oolitic ironstone. The fourth small cycle begins by mudstone and terminated by hematitic chamositic ironstone. The fifth cycle is terminated by sandstone. The sixth cycle is terminated by thick oolitic ironstone beds while the seventh cycle is terminated by cross-laminated to crossbedded fine-to medium-grained sandstone. I. Ninth Large Cycle This cycle is characterized in the field by the presence of very thick tidal flat cross-bedded sandstone in its uppermost part (Fig. 4, lower part of column D). It begins by mudstone

E. Fifth Large Cycle


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Fig. 4. Detailed stratigraphic section of the ironstone-bearing interval within the middle oolitic ironstone-carbonate member (For legend see Fig. 5). The abbreviations of the ironstone types are as follows: Chamositic ironstones include: Chamositic ironstones (ChIs I1), Silty Chamositic ironstones (Silty Ch IS I2) and Hematitic Chamositic Sandstone (H Ch S.S. I3).The oolitic ironstones include: Lean Oolitic Ironstones (L O IS II1) and True Oolitic ironstones (T O IS II2). The silty ironstones includes: Silty Ironstones (Silty IS III1) and Chamositic Silty Ironstones (Ch Silty IS III2). The Sandy Ironstones (sandy IS IV). The abbreviations are used in Figs 4 and 5.

and contains two thin chamositic and sandy ironstone beds in its middle part.

K. Eleventh Large Cycle This cycle consists mainly of small-scale cycles of mudstone, sandy and silty ironstone, dolostone and dolomitic sandstone (Fig. 4, Column E).

J. Tenth Large Cycle Which begins by mudstone and terminated by crosslaminated to cross-bedded reddish white fine-to medium grained sandstone.

V. CLASSIFICATION OF THE HADDAT ASH SHAM IRONSTONES Based on the lithologic, sedimentologic aspects and composition, the Haddat Ash Sham ironstones, are classified


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 into four main groups which are further subdivided into nine types (Table 1). The stratigraphic setting of these ironstone groups and types reveal their general upward arrangement and their intimate association with certain levels within the largescale coarsening- upward cycles. The terms used in the description of the studied ironstones are adopted from [10]. The terms Chamositic: Chamosite-bearing or chamosite-rich are used to refer to berthierine. The term chamosite and green chamositic clays are equivalent to Fe-rich chlorites with definite 14 A° basal spacing [11]. The detailed field description augmented with microscopic investigations of the different ironstone types led to the recognition of different types of ironstones (Table 1). The distribution of these ironstones within the measured section and their microscopic description is given below as follows: A. Chamositic Ironstones These types of ironstones are mainly recorded within the middle parts of the shallowing-upward cycles overlying the grey mudstones of the lower parts of the cycles and underlying the red horizons of the oolitic, silty and sandy ironstones. According to the predominant mineral phases and the textures, the chamositic ironstones are classified into: Chamositic Ironstones (Ch IS I1) This subtype of chamositic ironstones is the most common in the described Ch IS. It is present in three main horizons: The first bed is recorded in the topmost part of the third Medium-Scale Cycle (MC) of the first large cycle. It consists mainly of slightly hematitized chamositic peloids (Pl. 4E). The hematitization of green chamositic clay peloids led to the formation of blood red Fe- oxyhydroxides and goethite. The formation of hematite by the diagenetic oxidation of green chamositic clays was previously described by Cooter and Link [12] in the ironstones of Pennsylvania and also in the oolitic ironstones of the area east of Aswan, Egypt [13], [14], [15] . The second horizon of chamositic ironstones is described in the fourth small cycle in the fourth large cycle (Fig. 4). This horizon of chamositic ironstones is composed of slightly and highly hematitized massive and peloidal green chamositic clays (Pl. 4F), with very rare silty-sized quartz grains. There are microscopic evidences that support the formation of the blood red Fe-oxyhydroxides, red goethite and black hematite patches and domains by diagenetic hematitization (oxidation) of the green chamositic clays matrix, patches and peloids (Pl. 4G, H). The third horizon of the chamositic ironstones is present just overlying the aforementioned one in the small scale cycle (small cycle 7) in the uppermost part of the seventh large cycle (Fig. 4, Column C). This type of chamositic ironstone is composed mainly of black (hematitic) and blood red

(goethitic) irregular patches and domains within the slightly hematitized Fe-oxyhydroxides groundmass formed by the hematitization of massive green chamositic clays (Pl. 5A, B). The irregular forms and the gradational contacts between the black patches and domain and the enclosing blood red amorphous Fe-oxyhydroxides groundmass support their formation by the hematitization of green chamositic clays (Pl. 5B). Silty chamositic Ironstones (Silty Ch IS I2) This subtype of chamositic ironstones is almost recorded only overlying the proper chamositic ironstones in the shallowing-upward cycles. It is observed in two horizons: The first horizon is recorded in the fifth small cycle of the third medium cycle of the first large cycle (Large Cycle 1, Medium Cycle 3, Small Cycle 5, Table 1). This type is similar to the chamositic ironstones instead of the presence of siltysized quartz grains (Pl. 5C). The interstitial green chamositic clay matrix show stages of hematitization and formation of blood red amorphous Fe-oxyhydroxides (ferrihydrites), goethite and finally into black hematite (Pl. 5D). Similar mechanisms of hematitization of the green chamositic clays are described by [12], [13], [14] and [15] and green glauconitic clays [16] and [17]. The hematitization processes resulted in the formation of rounded to subrounded diagenetic in situ formed peloids (Pl. 5D). The second horizon is described in the fourth small scale cycle of the eighth cycle (Fig. 4). Microscopically, this horizon of silty chamositic ironstones is composed mainly of amorphous Feoxyhydroxides, goethite groundmass contains very small relicts of yellowish green chamositic clays (Pl. 5E) in addition to very rare highly corroded and embayed quartz grains (Pl. 5E). During the progressive diagenetic dehydration and recrystallization, the amorphous Fe-oxyhydroxides becomes dehydrated and recrystallized giving rise to the formation of shrinkage cracks of hematite and goethite instead of the blood red amorphous Fe-oxyhydroxides (Pl. 5F, G). Hematitic Chamositic Sandstone (H Ch S.S. I3) The hematitic chamositic sandstone is present in six main horizons: The first horizon is recorded in first small cycle of the first medium cycle of the first large cycle (Fig. 4, column A). It consists of angular to subrounded quartz grains admixed with green chamositic clay peloids. Sporadically distributed within slightly hematitized yellowish green chamositic clay matrix (Pl. 5H). Some black hematite patches and domains are present in between the slightly hematitized yellowish green chamositic matrix.


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Fig. 5. Legend of the symbols used in Figs. 3, 4, 6 and 7; for ironstone types see Fig. 4.


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Plate 2: A=Complete succession of the second large-scale shallowing-upward cycle; B, C, D= Red oolitic ironstone beds (arrows) in the middle part of the second large cycle; E= Green chamositic clays (arrows) underlying the oolitic ironstone beds (red), second large cycle; F= Cross-laminated to cross-bedded ferruginous sandstone in the topmost part of the second large cycle; G= Thick grey mudstone in the base of the third large cycle; H= Bioturbated sandy/silty ironstone (arrows) terminated the third large cycle.


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Plate 3: A, B= Bioturbated sandy/ silty ironstones (arrows) in the topmost part of the third large cycle; C, D= The ironstone (arrows) -bearing fourth, fifth, sixth, seventh and eighth large cycles; E= The fourth cycle that consists of interbedded mudstone and fine-grained sandstone and red oolitic ironstone bed in its middle part (arrows), F= The middle part of fourth large cycle terminated by red and reddish green chamositic and oolitic ironstones (arrows); G, H= The fifth large cycle terminated by hematitized chamositic siltstone/silty chamositic ironstone (arrows).


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 TABLE 1 CLASSIFICATION AND DISTRIBUTION OF HADDAT ASH SHAM IRONSTONES WITHIN THE MIDDLE IRONSTONE-CARBONATE MEMBER

Ironstone Facies

Symb ol/No.

Petrographic Names

Composition

Chamositic Ironstones

Fresh and oxidized green chamositic clay peloids , and ooids embedded in goethite and hematite

Silty Chamositic Ironstones

Fresh and oxidized green chamositic clay peloids , and ooids and silt-sized quartz grains embedded in goethite and hematite

Hematitic Chamositic Sandstone

Quartz grains, hematitized chamositic clay peloids in hematitized chamositic clays and hematite

Lean Oolitic Ironstones

Sporadically distributed goethite and hematite ooids in Feoxyxhydroxides matrix and /or goethite-hematite cement.

TO IS II2

S.L1, M3, S3 L1, M2, S4 L2, M1, S1 L1, M1, S2 L4 S5

True Oolitic Ironstones

Tightly spaces goethite and hematite ooids in Feoxyxhydroxides matrix and /or goethite-hematite cement.

Silty IS III1

L1, M3 L1, M3 last S L3 S2

Silty Ironstones

Silty-sized quartz grains goethite and hematite

Chamositic Silty Ironstones

Silty-sized quartz grains and hematitized chamositic clay peloids in goethite and hematite

Ch IS I1

Chamositic Ironstones

Stratigraphic position within the measured section (Fig. 4).

Silty Ch IS I2

H Ch S.S I3

L1, M3, S1 L4 S4 L4 S7 L1, M3, S5 L8, S4

L1, M1, S1 L1, M3 last S L1, M3 Top of 3 rd M L3, Top of 1st S L4, S4 L6 S1

LO IS II1 S.L1, M3, S3

Oolitic Ironstones

Silty Ironstones

Sandy Ironstones

Ch Silty IS III2

L1, M2, S1 L1, M3, S1

Sandy IS IV

L8 S3 L8 S7

Sandy Ironstones

Sand-sized quartz hematite cement

grains

in

in

LC 1, 2, 3 = number of large cycle; MC1, 2, 3= number of medium cycle; SC1, 2, 3= number of small cycle of figure 4).

The second horizon is recorded in the topmost small cycle of the third medium scale cycle of the first large scale cycle (Pl. 6A) and the third horizons is observed in the first small cycle of the six large cycle (Fig. 4 column c, Pl. 6B). The hematitic sandstone of both horizons is composed mainly of angular to subrounded fine-to medium grained quartz grains admixed with slightly hematitized chamositic clays peloids. These constituents are embedded in hematitic chamositic clay matrix.

B. Oolitic Ironstones This ironstone type is the most economic and is present as a marked red oolitic ironstone beds within the middle part of the shallowing-upward cycles. It is subdivided into two main types according to the percentage of iron ooids relative to the enclosing goethitic/ hematitic matrix/ cement.


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Plate 4: A= The small-scale cycles of the sixth large cycle; B= The lower small-scale cycle begins by thick grey mudstone which grades upward into green chamositic mudstone/siltstone and terminated by a characteristic red oolitic ironstone bed (arrows); C= The seventh large cycle terminated by ferruginous cross-laminated to cross-bedded fine-to medium-grained sandstone (arrows); D= Cycles 3, 4 and 6 of the eighth large cycle terminated by red /reddish green oolitic and chamositic ironstone beds (arrows).; E= Slightly hematitized chamositic peloids (arrows) in the chamositic ironstones; F= Slightly and highly hematitized massive and peloidal green chamositic clays (arrows) in the chamositic ironstones; G, H= Fe-oxyhydroxides (Blood red), goethite (red) and hematite (black) patches and domains in the chamositic ironstones; T. S.= Thin section; O.L.= Ordinary Light; C.N.= Crossed Nicols.


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Plate 5: A, B= black (hematitic) and blood red (goethitic) irregular patches and domains within the slightly hematitized Fe-oxyhydroxides groundmass; C= Silty chamositic Ironstones, D= Hematitization of green chamositic clays and formation of blood red amorphous Fe oxyhydroxides (ferrihydrites), goethite and finally into black hematite; E= amorphous Fe-oxyhydroxides, goethite groundmass contains very small relicts of yellowish green chamositic clays (arrows); F, G= Amorphous Fe-oxyhydroxides dehydrated and recrystallized giving rise to the formation of shrinkage cracks of hematite and goethite instead of the blood red amorphous Fe-oxyhydroxides; H= Hematitic chamositic sandstone composed from quartz grains(white) admixed with green chamositic clay peloids.


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 Lean Oolitic Ironstones This type of oolitic ironstone is almost present t underlying the true oolitic ironstone beds. It consists mainly of widely spaced goethitic, hematitic or goethitic-hematitic ooids and silty-sized quartz grains. These components are present in Feoxyhydroxides/goethite matrix-hematite cement (Pl. 6C, D). This ironstone type is present in the third small cycle of the third medium-scale cycle of the first large cycle.

laterally and vertically changed into cross-laminated chamositic siltstone (Pl.7E). The hematitic black domains show evidences for their formation by diagenetic hematitization of the precursor green chamositic clay peloids and matrix. The progressive corrosion of the quartz grains by the enclosing hematite cement led to the formation of black hematite domains contain small highly corroded and embayed quartz grains (Pl. 7F).

True oolitic ironstone This type of ironstone is the most economic and is composed mainly of Fe-ooids embedded within very small narrow area of hematite cement (Pl. 6E). The hematite /goethite ooids are moderately to well sorted of ill defined internal structure and mostly of gradational contacts with the enclosing hematite cement/goethite matrix (Pl. 6E, F). Some of the iron ooids show well defined zones of blood red goethitic and black hematitic domains and white kaolinitic domains (Pl. 6G). Some oolitic ironstone fragments are seen admixed with the iron ooids (Pl. 6H). Some ooids are similar to peloids where they are of ill defined internal structure and show a characteristic zonation (Pl.7A) of dark Fe-rich massive zones and light Fe-poor , kaolinite-rich zones (Pl.7A).

D. Sandy Ironstones

C. Silty Ironstones

Many theories have been currently postulated exploring the mode of formation of the ironstone-bearing coarseningupward progradation cycles or sequences. The factors controlling the development of such prograding sequences differ from one basin to another [18]. The mudstone units seem to be deposited during new periods of sea transgression following periods of sea regression. Similar green or black mudstones of prograding coarsening-upward cycles have been previously described [19], [18], [20], [21], [10], [12] and [13]. Most of these authors used this green or dark mudstone as a good indication of new transgressive cycles.

This ironstone type is present either underlying the oolitic ironstone or laterally intertounged with the chamositic ironstones. It is subdivided into silty ironstones and chamositic silty ironstones.

Silty Ironstones The silty ironstones are mainly localized in the third medium cycle of the first large cycle and also in the second small cycle of the third large cycle of the measured stratigraphic section (Fig. 4, Table 1). The silty ironstones are composed mainly of highly corroded and embayed silt-sized quartz grains embedded in highly hematitized Feoxyhydroxides matrix/ hematite cement (Fig. 7B). This ironstone type shows a characteristic mottling where some black hematitic domains are present close to the blood red goethitic Fe-oxyhydroxides-hematite domains (Pl. 7B). Chamositic Silty Ironstone This ironstone type is located mainly within the second and the third medium cycles of the first large cycle of the measured section (Fig. 4, Table 1). It is similar in composition to the silty ironstones instead of the presence of hematitized green chamositic clays peloids (Pl.7C). The silty sized quartz grains and the hematitized chamositic peloids are embedded in hematitic / goethitic matrix and/or cement which show microscopic criteria supporting their formation by the diagenetic hematitization of the green chamositic clay peloids and matrix (Pl.7D). The chamositic silty ironstones are

This ironstone type is recorded in the eight large cycles and it is composed of angular to subrounded quartz grains, rounded to subrounded slightly and highly hematitized green chamositic clay peloids (Pl. 7G, H). These components are embedded in the slightly to highly hematitized green chamositic clays giving rise to black hematite cement. V. DEPOSITIONAL ENVIRONMENTS AND ORIGIN OF IRONSTONES

A. The Shallowing-Upward Cycles

The coarsening-upward tendency of the studied ironstonebearing succession is similar to that described in the Coniacian-Santonian oolitic ironstones of Aswan Area, Egypt by [22], [13], [14] and [15] where they related these cycles to shoaling. The studied ironstone-bearing coarsening-upward cycles are characterized by a sharp contact against the underlying one and starts with mudstone dominant unit, being formed of laminated green mudstone represent deposition in low energy environment within inter-bar areas (troughs) of migrated sand bars. The oolitic ironstone beds and the associated sandstone and mudstone interbeds of the described large-scale coarseningupward cycles seem to be deposited in a shallow marine


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Plate 6: A, B= Hematitic chamositic sandstone composed from quartz grains (white) admixed with slightly hematitized chamositic clays peloids (arrows); C, D= Lean oolitic ironstones composed from goethitic, hematitic or goethitic-hematitic ooids (arrows) and silty sized quartz grains (white); E, F= True oolitic ironstones composed from hematite /goethite ooids (blood red) of ill defined internal structure and mostly of gradational contacts with the enclosing hematite cement/goethite matrix; G = Fe-ooids of well defined zones of blood red goethitic and black hematitic domains and white kaolinitic domains; H= Oolitic ironstone fragments (arrows) embedded with the iron ooids (red).


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Plate 7: A= Ooids of ill defined internal structure similar to peloids and composed from dark Fe-rich massive zones and light Fe-poor, kaolinite-rich zones; B= Silty ironstones composed of silt-sized quartz grains (white) embedded in highly hematitized Fe-oxyhydroxides matrix/ hematite cement; C= Chamositic silty ironstone contains hematitized green chamositic clays peloids (arrows); D= Silty-sized quartz grains (white) and hematitized chamositic peloids (black) embedded in hematitic / goethitic matrix; E= Cross-laminated chamositic siltstone changed into chamositic silty ironstones; F= Hematitic black domains formed by hematitization of the precursor green chamositic clay peloids and matrix; G, H= Sandy ironstones composed from quartz grains (white) hematitized green chamositic clay peloids (arrows) embedded in black hematite cement.


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 moderately to highly agitated environment. This is supported by: a) The rippled cross-bedded, frequently burrowed and texturally mature sands of this unit which reflect a high-energy depositional environment of probably wave swept subaqueous coastal barrier or swipt, and b) The abundance of horizontal and ripple cross- laminations and also symmetrical ripples in the sandstone beds and the associated oolitic ironstones which reflect the importance of upper flow regime processes, producing the horizontal laminations and the role of wave generated oscillation, producing symmetrical ripples in the lower foreshore or upper shoreface [12]. B. Formation of Oolitic Ironstones The stratigraphic positions of the described ironstone types reflect their intimate genetic relation with the short-lived transgressive-regressive events which are expressed by the small- and medium- scale coarsening-upward cycles developed during the long-lived progradation or coarseningupward regimes. Ferriferous ooid accumulation after the waning of coarsening-upward cycles has been also documented by [23], [24], [25], [26], [27]. The oolitic ironstones are commonly described as condensed deposits that accumulated during a transitional stage which developed either at the end of a regional regression [19] or the beginning of renewed transgression while thicker correlative marine sediments were deposited elsewhere. The stratigraphic setting of Haddat Ash Sham oolitic ironstones, their composition, textural maturity, internal sedimentary structures and lateral facies changes strongly emphasize the concentration of the ferruginous ooids in highly agitated conditions along bar flanks and bar crests during the regressive events which terminate the short- lived (smallscale) prograding regimes. During the regressive events, winnowing, transportation and redeposition of the formed ooids take place and the coarse sediments including quartz grains and/or iron ooids prograde gradually on the interbar shelf muds. This is indicated by the graded bedding, rippling and burrowing of the oolitic ironstone beds. A similar bar (shoal) progradation model is recently suggested by [12] for the Clinton oolitic ironstones of Pennsylvania. Association of ooid development with reduced influx of detritus is clearly expressed by the rarity of detrital grains in the true oolitic ironstone beds and the lateral replacement of these beds by oolitic sandy ironstones or sandstones in areas received much influx of detritus.

associated amorphous Fe-oxyhydroxides in addition to the detrital quartz grains. In the dysaerobic environment, green chamositic and glauconitic clays were formed along or below the sediments /water interface during periods of low clastic input and of high Mg2+ and Fe 2+ activities. The syndepositional chamositization of the detrital clays and the intimately associated Fe-oxyhydroxides either along or below the sediments/water interface and the formation of the green chamositic clays have been previously discussed by many theories [10]. The most common and accepted one of these theories is the processes of progressive greening and conversion of the precursor kaolinite and the associated Feoxyhydroxides into green clays [28], [29], [30], [31], [32], [13], [15], [14] which suggest the conversion of Fe3+ into Fe2+ within the marine water and its reaction with Mg (from the marine water) and Si and Al (resulted from the destruction of detrital clays) forming green chamositic clays (mostly berthierine). During the post-depositional (diagenetic) processes, the precursor kaolinitic clays become converted into the green chamositic clays during early anoxic diagenesis with Mg from the entrapped pore water and Fe2+, Si and Al released from the interstitial iron-rich clay particles. Most of the observed green chamositic clays are of patchy nature within the light kaolinitic clay matrix and they are of gradational contacts with them. This suggests the intimate genetic relation between these clays and the enclosing lighter unchamositized clay patches. The Fe-oxyhydroxides, goethite and hematite of the different ironstone types of Haddat Ash Sham ironstones are mostly formed during the diagenetic hematitization of the formed green chamositic clay constituents i.e. peloids, ooids, flasers and laminae during the late stages of diagenesis. The formation of the hematite of the worldwide Phanerozoic oolitic ironstones by the diagenetic hematitization of the associated green chamositic clays have been previously confirmed by [33], [34], [35], [36], [20], [37], [38], [39] and [40]. The formation of the hematite of ferruginous sandstone and/or red beds by the progressive hematitization of the associated detrital yellow or brown Fe-oxyhydroxides have been also previously confirmed by [41], [42], [43], [44]) and [45]. VI. DEPOSITIONAL MODEL

C. Mechanism of formation of Fe-minerals In discussing the depositional history of Haddat Ash Sham ironstones, two main processes will be clarified as follows: the syn-depositional and diagenetic processes. The syn-depositional processes which began by the input of the fine detrital materials i.e. allogenic clays and the

The Tertiary succession of Haddat Ash Sham area begins by the deposition of the Fluviatil to fluvio-lacustrine clastic member by braided stream system (Fig. 6A). The middle oolitic ironstone-carbonate member was deposited during the marine transgression (Fig. 6B). During this time periods the basin becomes stable and suffered from progressive shoaling


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 following the major transgression. After the deposition of the oolitic ironstone-bearing shallowing-upward cycles during the general upward shallowing in the basin, another fluviolacustrine regim led to the deposition of the upper clastic member of the sequence (Fig. 6C). The ironstones are associated with fine-grained quartz sandstone and mudstone. This association suggests that ironstones were generated on the flanks of sand shoals located in the transition between the shoreface and the inner platform environments [46]. The redistribution of ooids by intense storms and their concentration as lags on shoal crests and as storm beds in deeper water in the Clinton ironstones is also confirmed by [12]. Within the large-scale cycles, the basal mudstone units are thinly laminated and it represents a Transgressive System Tract. This thick mudstone is present underlying a rhythmically bedded unit representing the High and Lowstand System Tracts. The peloidal and ooidal ironstone beds are almost located overlying the Transgressive System Tract and underlying the High and Lowstand System Tracts within the large-scale shallowing-upward cycles. This well-defined situation of these ironstone types indicate that, they represent Maximum Flooding Surface (MFS) or Condensed Sequence (CS) formed during interval in which all the required synsedimentary physico-chemical conditions for their synthesis are present. It is concluded that, water depth represents the main factor in the formation of these ironstone beds where it depends on the vertical distribution of the different geochemical zones of [47] within the depositional environment. The absence of black pyritic mudstone in the lowermost parts of the shallowing-upward cycles indicate that, the depositional environments does not reach the highly reducing environment (the anaerobic zone of [47]) during the transgressive pulses (Fig. 7A). This indicates the formation of the present ironstones in the transitional zone between the lower shoreface and the inner shelf environments under the effect of wave base on the shoal flanks. The slightly reducing to oxidizing conditions (the dysaerobic zone) are dominant during periods of low clastic input, high organic activities, and low oxygen contents. During these periods, syndepositional chamositization and greening of the detrital allogenic clays and the associated Fe-oxyhydroxides was carried out along or below the sea floor. These processes were carried out during the progressive decaying of organic matter and conversion of Fe3+ to Fe2+ with Mg from the marine water and Al & Si from the decayed amorphous clays and Fe-oxyhydroxides (Fig. 7A).

During the progressive and subsequent phases of shoaling and lowering of sea level, the already formed green chamositic clays suffer from intermittent periods of intra-basinal brecciation, breakage, reworking and transportation giving rise to green chamositic clay peloids, intraclasts, flasers and laminae of variable shapes and mineralogical composition (Fig. 6B; 7B). The wide variation in the types of Fe- ooids from the geometric and mineralogical points of views can be related to the variation in: i) waves and current intensities and directions controlling to a large extent of the observed very small variations in the dimension parameters of the ooids, ii) rate of sediment input which control in the time, rate and mechanism of oolitization either by stationary or mechanical accretion [48]. The subsequent steps of intra-basinal brecciation, reworking, and redeposition of these constituents led to the formation of peloidal, ooidal, peloidal ooidal and ooidal peloidal ironstone beds with or without very small amount of extra-basinal components, i.e. quartz and heavy mineral grains. In shallower depositional sites (Fig. 7C), i.e. shoal crests and upper shoreface environments, the depositional environments become more oxidized [dysaerobic or lower part of aerobic zone of [47], therefore the chance for synthesis of iron silicate intra-basinal constituents become very rare. The main constituents deposited in these sites are extra-basinal i.e. detrital quartz grain, detrital (allogenic) clays admixed with amorphous Fe-oxyhydroxides with very small amounts of intra-basinal components reworked from remote deeper areas (shoal flanks) and deposited in close association with these extra-basinal constituents forming the sandy and silty ironstone beds. In the shallowest areas (the uppermost parts of the shallowing-upward cycles), siliciclastic facies free from any type of ironstones are accumulated (Fig. 7D). This is related to the deposition of extra-basinal components free from any ironbearing components in these highly agitated depositional sites. VII. SUMMARY AND CONCLUSIONS The stratigraphic positions of the oolitic ironstones reflect their intimate genetic relation with short-lived transgressiveregressive events which are expressed by the small and medium scale cycles, developed during the long-lived progradation or coarsening-upward cycles. The lithologic characteristics and sedimentary structures of the green laminated sandstones and mustones suggest deposition during the transgressive periods in a relatively calm conditions along lower bar flanks or within interbar areas (bar troughs),


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Fig. 6. Schematic model of the depositional stages of the Tertiary succession in Haddat Ash Sham area showing the location of ironstones in the middle shallow marine member, for legend see Fig. 5.


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Fig. 7. Schematic diagrams showing the progressive steps and possible situations for ironstone accumulation during the depositional history of Haddat Ash Sham ironstones; for legend see Fig. 5.

affected by an interment current activities. The stratigraphic setting of the true oolitic ironstones, their composition, textural maturity, internal sedimentary structures and lateral facies changes strongly emphasize the concentration of their ferruginous ooids in highly agitated conditions along bar flanks and bar crests during the regressive events which terminate the short-lived (small-scale) prograding regimes. After the deposition of the middle member of the Tertiary succession in Haddat Ash Sham area and the associated

ironstones, the sea retreated and the fluvial clastics of the upper member were deposited. The syn-and post-depositional microfabric evolution as well as the mineral paragenesis of the studied ironstones types of Haddat Ash Sham area are still under investigations by the author and will be submitted for publications as soon as possible. The mineral chemistry of the Fe-mineral phases .i.e. green chamositic clays, Fe-oxyhydroxides, goethite and hematite are still under study by the author.


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Asian Transactions on Basic & Applied Sciences (ATBAS ISSN: 2221-4293) Volume 01 Issue 02 REFERENCES [1] A. M. S. Al-Shanti, ―Oolotic iron ore deposits in Wadi Fatima between Jeddah and Mecca, Saudi Arabia.‖ Saudi Arabian directorate General of Mineral Resources, Bulletin 2, 51p., 966. [2] T. A. Moore, and H. Ar-Rehaili, ―Geologic map of the Makkah quadrangle, sheet 21D, Kingdom of Saudi Arabia‖: Saudi Arabian Deputy Ministry for Mineral Resources Geoscience Map GM 107, 62 p, 1989. [3] P. R. Johnson, ―Proterozoic geology of western Saudi Arabia, west-central sheet‖: Amended May 2005: Saudi Geological Survey Open-File Report SGS-OF-2005-6, 59 p, 2006. [4] Brown, G.F., Jackson, R.O., Bogue, R.G., and MacLean, W.H. (1963) Geology of the Southern Hijaz quadrangle, Kingdom of Saudi Arabia: Saudi Arabian Dir. Gen. Min. Res. Misc. Geologic Invest. Map I - 210A, 1:500,000 scale. [5] R. Karpoff, ―Esuuisse geologique de l Arabie Seoudite‖: bull. Soc. Geol. Fr. 6. ser.; 7, 653-667, 1957a. [6] R. Karpoff, ―Sur l existence du Maestrichtiane au Nord de D Jeddah‖ (Arabia Seoudite: Compt. Rend. Séance Acd. Science, 245, 1322-1324, 1957b. [7] C. H. Spincer, and P. L. Vincent, ―Bentonite resource potential and geology of the Cenozoic sediments, Jeddah region‖: Saudi Arabian Deputy Ministry for Mineral Resources, Open-File Report BRGM-O-F-02-34, 34 p, 1984 [8] R. Zeidan and K. Banat, ―Petrology, Mineralogy and Geochemistry of the Sedimentary Formations in Usfan, Haddat Ash-Sham and Shumaysi Areas, and their Associated Oolitic Ironstone Interbeds, North East and East of Jeddah Saudi Arabia.‖ King Abdulaziz University, Directorate of Research Projects 035/406, 264 p, 1989. [9] E. A. Smith, ―Reconnaissannce geologic map of the Wadi Hammah quadrangle, sheet22/40C, Kingdom of Saudi Arabia‖: Saudi Arabian Deputy Ministry for Mineral Resources Geologic Map GM-65, 1:100,000 scale, with text, 19 p, 1982. [10] T.P. Young, ―Phanerozoic ironstones: an introduction and review‖. In: Young, T.P. and Taylor, W.E.G. (eds.) Phanerozoic ironstones. Geol. Soc. London, Spec.Publ., v.46: pp.19-30, 1989 [11] G.W. Brindley, ―Chemical compositions of berthierines—a review‖. Clays and Clay Minerals 30:153–155, 1982. [12] E. Cotter and, J. E., Link, ―Deposition and diagenesis of Clinton ironstones (Silurian) in the Appalachian Foreland Basin of Pennsylvania‖. Geol. Soc. Am. Bull. v. 105: pp. 911922, 1993. [13] A. A. Mesaed, ―Geological, mineralogical and geochemical studies on the ironstones and related lateritic products of Aswan region, Egypt‖. Ph. D. Thesis, Faculty of Science, Geology Department, Cairo University, 289p, 1995. [14] M. M. El Sharkawi, M. M. El Aref, and, A. A Mesaed., ―Stratigraphic setting and paleoenvironment of the Coniacian-Santonian ironstones of Aswan, South Egypt.‖ Geol. Soc. Egypt. Spec.Publ.No.2: pp.243-278, 1996.

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Dr. Rushdi J. Taj is Associate Professor in Petroleum Geology & Sedimentology Department, Faculty of Earth Sciences, King Abdullaziz university, Jeddah, Saudi Arabia. B. SC. Geochemistry 1980, FES-KAAU, Saudi Arabia; M. SC. Sedimentology 1986, FES-KAAU, Saudi Arabia; Ph. D. Sedimentology 1991, GlasgowScotland, U K. He is interested in the economic potential of paleo-laterites and fine-grained clastic sediments and in the textural analysis, mineralogy & palaeoenviroments interpretation. He has many publications (20 papers, the most recent three papers are: Mesaed, A. A. Taj, R. J. & Harbi, H. (2010): Stratigraphic Setting, Facies Types, Depositional Environments and Mechanism of Formation of the Ash Shumaysi ironstones, Wadi Ash Shumaysi, Jeddah District, West Central Saudi Arabia. (Accepted for publication in the Arabian Journal of Geosciences). Taj, R. and Mesaed, A. A. and (2011): Facies analysis and Depositional Environments of Al Shumaysi Formation, Jeddah- Makkah District, W. Al Shumaysi, West Central Saudi Arabia. (Arabian journal of sciences and engineering). Taj, R. J. and Aref, A. M. (2009). Sediments characteristics and petrography of marginal marine ephemeral saline pans, Shuaiba lagoons, Red Sea coast, Saudi Arabia. Sedimentology of Egypt, vol. 17, p27-44. Dr. Taj is Former Chairman of Petroleum Geology & Sedimentology Department (2000- 2004), Former Chairman of Technical Training Department (2006-2007); Vice Dean for Postgraduate Studies & Scientific Research (2008 – till now) and Member of Saudi Society for Geosciences (SSG) since 1992.


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