Mineralogical transformations in the Fe-laterite profiles of Saudi Arabia: A study of weathering dynamics and secondary lateritization Rami A. Bakhsh, , Ali A. Mesaed, , and International Journal of Advanced and Applied Sciences, 2024 This study examines an iron-rich laterite profile, 4 to 9 meters thick, located between the ancient Precambrian Arabian Shield rocks and the younger Phanerozoic layers in Saudi Arabia. The profile begins with hard parent rocks composed of quartz diorite and gabbro containing iron-silicate. As these rocks weather, they become progressively softer and more clay-like, forming slightly and highly weathered argillaceous rocks. The Fe-laterite profile includes three main layers: the original parent rocks, the slightly altered rocks (saprolite), and the highly altered argillaceous rocks at the top. Samples from different layers of the weathering profile were collected and analyzed for their mineral content. The original quartz diorite and gabbro primarily consist of feldspars, hornblende, chlorite, and quartz. In the slightly altered layer, the hornblende and chlorite expand and peel apart, while the feldspar crystals transform into kaolinite and sericite. In the highly altered top layer, the remaining iron-silicate minerals show significant curling and breaking apart, and the surrounding clay becomes more uniform, composed mainly of mixed dark iron-oxyhydroxides and a light aluminum- and silicon-rich gel with small amounts of quartz. The study explores the progressive stages of weathering, including: a) Initial breakdown of iron-silicate minerals through hydrolysis and oxidation, b) Further destruction of these minerals and the formation of goethite, hematite, and kaolinite, c) Final stages where kaolinite and small microcrystalline quartz aggregates form from silica leached from higher layers, a process known as secondary lateritization.
Mineral paragenesis and stratigraphic setting of the Neoproterozoic volcano-sedimentary succession of Samran Group, Jabal Farasan Area, West central Arabian Shield, Saudi Arabia A. A. Mesaed, A. R. Sonbulc Indian Journal of Geo Marine Sciences, 2021 Jabal Farasan is located in the west central part of the Arabian Shield. The present study aims to reveal the stratigraphic setting and mineral paragenesis of the exposed volcano-sedimentary succession of the Samran Group in Jabal Farasan area. The succession of Samran Group is composed of three successive facies: the lower interbedded andesitic tuffs and tuffaceous andesites and trachyte’s (F1), the middle-altered quartz diorite/andesite (F2) and, an upper interbedded andesitic tuff, tuffaceous andesites and trachytes (F3). The vertical variations in the petrographic lithotypes depend mainly on the position of the depositional sites relative to the volcanic centers (proximal and distal). Both the volcanic rocks and the associated units are subjected to syn-and post-depositional diagenetic/metamorphic processes. These processes include the formation of the Fe 2+ -silicates: ( i.e ., chlorite instead of the volcanic ashes and the formation of plagioclase minerals). Post diagenetic recrystallization of the tuffaceous mudstones and the formation of microcrystalline quartz. The diagenetic oxidation of the Fe 2+ -silicates led to the formation of volcaniclastic red beds in certain stratigraphic horizons.
Stratigraphic setting, facies types, and mineral paragenesis of the carbonate-bearing succession of Jabal Farasan Area, West Central Arabian Shield, Saudi Arabia Abdullah R. Sonbul, Ali A. Mesaed Arabian Journal of Geosciences, 2021 The studied carbonates are present within the topmost part of Jabal Farasan, 150 km NE Jeddah city, west-central Arabian Shield. These carbonates overlie thick dark slightly metamorphosed basic volcanic and related volcaniclastic deposits of the Samran group. The present stratigraphic and petrographic investigations revealed the presence of nine main intercalated units (units I to IX). The carbonate (marble) units are presently intercalated with green slightly metamorphosed basic to intermediate volcaniclastic deposits. Five carbonate units (units I, III, V, VII, IX) are intercalated with four green volcaniclastic units. There are very characteristic vertical and lateral lithologic variations within the carbonate deposits where the carbonate facies just overlying the green volcaniclastic intercalations are thinly laminated and of gray and green colors. Microscopically, these carbonate facies are composed of hard devitrified tuffs which contain many mafic minerals, i.e., chlorite and wollastonite with less frequent calcite laminae and patches. Going towards the upper parts of the marble-bearing horizons, the carbonates are composed of white and reddish-white thickly bedded zones and composed mainly of fine and coarse crystalline calcite without and silicate green minerals. It is concluded that many quarrying problems in Farasan marble deposits are related to the very complicated lithologic composition of the marble deposits. This is original related to horizontal and vertical variations in paleo-depositional environments and the location of the depositional sites (proximal or distal) within the general frame of the island arc situation. The volcaniclastic input controls to a large extent the purity of the deposited carbonates and also the type of marble deposits.
Geochemical variation of the groundwater characters along Wadi Qudaid, northeast Jeddah, westcentral Arabian Shield, Saudi Arabia Mohamed A. Sharaf, Abdullah R. Sonbul, Ali A. Mesaed Arabian Journal of Geosciences, 2018 Wadi Qudaid is present about 120 km northeast of Jeddah, Saudi Arabia. The area includes Precambrian Arabian Shield, Tertiary sedimentary rocks, Tertiary basic volcanics (harrat), and finally Quaternary wadi deposits which represent the main aquifer of Wadi Qudaid area. The present study indicates the presence of pronounced geochemical variations in the groundwater characters along the main channel of Wadi Qudaid from the southwestern part (downstream) to the northeastern (upstream) part. The groundwater-bearing horizon is thicker in the downstream part than the upstream part. The study also revealed that the groundwater is of good quality in the upstream (NE) part than the downstream (SW) part. This is related to the addition and depletion of many elements during the groundwater trip from NE to SW and the addition and depletion of some elements. The downstream part is of high hardness and TDS when compared with the upstream part. Also, the downstream part is of high bisnous element (As, Co, Ni) than the upstream part. The groundwater of the southwestern part of Wadi Qudaid are free from the following elements: i.e., Al, Mn, Fe, Ni, Cu, Zn, and Pb.
Origin and mechanism of formation of the Oligo-Miocene ironstones of Umm Himar Formation, Turabah area, southwestern Arabian Shield, Saudi Arabia Rushdi J. Taj, Ali A. Mesaed, Mohamed I. Matsah, Mohamed Gameil Arabian Journal of Geosciences, 2017 Turabah area is located in the southwestern Arabian Shield of Saudi Arabia. The present study aims to shed light on the origin and mechanism of formation of the ironstones of the Tertiary sedimentary succession of the Umm Himar Formation in Turabah area. These ironstones are enclosed within mudstones and carbonates with less frequent sandstone. These lithologies show lateral and vertical facies changes and thickness variations and are stacked in cyclic nature within seven sedimentary units. The studied ironstones are present in two main horizons within the lower part of the succession as follows. (1) Lower massive and oolitic hematitic ironstones which are present as thin continuous and discontinuous bands and laminae within the varicolored tuffaceous mudstone unit of the lower part of the succession. The oolitic ironstones are present in successive small cycles. The lower parts of these cycles are composed of ferruginous friable mudstones. The middle parts are composed of hard ferruginous mudstones with abundant vertical and inclined burrows. The upper parts of these cycles are composed of indurated oolitic hematitic ironstones. The iron ooids of these ironstones were formed during successive and subsequent stages of diagenetic ferruginization of the precursor tuffaceous materials. (2) Upper bedded peloidal hematitic-magnetitic ironstones which are present in the hematitic-magnetitic ironstone unit no. 6 just overlying the bedded basalt unit no. 5. These ironstones were formed during subsequent stages of diagenetic ferruginization of precursor tuffaceous materials. These stages include the formation of green clays, devitrification, and finally ferruginization of the tuffaceous materials. This ironstone type is laterally changed into the penecontemporaneous bedded tuffaceous basalt.
Origin and geochemistry of the Late Proterozoic intra-arc rift-related volcaniclastic red and green beds of Tayibit El Esm area, Ablah district, south central Arabian shield, Saudi Arabia Asaad M. Moufti, Ali A. Mesaed Arabian Journal of Geosciences, 2015 The volcaniclastic red beds of the study area are present overlying the rhyolite-dolostone succession of wadi Girshah area, Ablah district. It is composed of seven shallowing-upward cycles. The lower part of this sequence is dominated by gray tuffaceous mudstone which grades upward into mudstone/siltstone. The middle part is dominated by red hematitic volcaniclastic siltstone-sandstone while the upper part is dominated by thinly to thickly bedded silicified stromatolitic dolostone. This vertical distribution reflects the gradation from deeper conditions of high volcaniclastic input into shallower conditions of very low volcaniclastic input into more shallower and highly silicified restricted depositional environments dominated during the deposition of the uppermost silicicfied dolostones of the upper parts of the succession. The field, mega, microscopic, and geochemical results conclude the formation of the present volcaniclastic red beds during the following stages, these are: (1) deposition of the basic and intermediate volcanic ashes in slightly deeper back-arc setting, (2) the degradation of the deposited volcanic ash and the diagenetic authigenesis of green celadonitic clays either along the sediment/water interface or beneath the sea floor by the interaction between Fe2+, Mg2+, Si4+, and Al3+, (3) the diagenetic hematitization of the formed green celadonitic clays of the cycles of the middle and upper parts of the succession and the formation of the iron-oxyhydroxide mineral, i.e., goethite and hematite as a result of the change in the pore water sediments from reducing to oxidizing conditions, and (4) finally, the direct hematitization of the original tuffaceous materials and formation of iron minerals especially in the upper parts of the volcaniclastic red bed succession.
Mechanism of formation of Haddat Ash Sham ironstones (Oligo-Miocene), Makkah Al Mokaramah District, West Central Arabian Shield, Saudi Arabia Rushdi J. Taj, Ali A. Mesaed Arabian Journal of Geosciences, 2013 The present study aims to shed light on the mechanism of formation of the Oligo-Miocene oolitic ironstones of Haddat Ash Sham area, Saudi Arabia. These ironstones are enclosed within the middle part of the Oligo-Miocene siliciclastic succession of the western part of the Arabian Shield, western Saudi Arabia. The ironstone beds were formed during marine incursion and creation of short-lived starved time periods of high organic matter activities, ferrous iron, and low clastic input. The depositional and diagenetic processes involved in the formation of Haddat Ash Sham ironstones are summarized here as follows: (1) the deposition of detrital components (i.e., amorphous iron-bearing clays admixed with silt and sand-sized quartz grains) and their distribution by the waves and current actions in areas of different water depths (bars and inter-bar areas); (2) the deposition of the iron-bearing clays in slightly reducing transgressive conditions (dysaerobic zone) led to the authigenesis of green marine chamositic clays of variable mineralogical and chemical compositions according to the predominated depositional environments; and (3) in the upper parts of the depositional cycles, the iron-bearing clays become admixed with detrital quartz grains which resulted in the formation of silty and sandy ironstones of low iron content. The diagenetic processes led to the oxidation of the green chamositic clays and formation of amorphous Fe-oxyhydroxides, ferrihydrites, goethite, and hematite. These iron mineral phases are related to each other and show progressive steps of transformation during the diagenetic processes. The iron ooids represent in situ formed irregular domains formed during the diagenetic crystallization and dehydration of the amorphous iron oxyhdroxides resulted from the diagenetic oxidation of green chamositic clays. This is supported by the absence of detrital cores of the iron ooids, the gradational contact between the iron ooids and the enclosing matrix and also by the presence of many ooids of unclear and ill-defined internal structure.
Stratigraphic setting, facies types, depositional environments and mechanism of formation of Ash Shumaysi ironstones, Wadi Ash Shumaysi, Jeddah district, West Central Saudi Arabia Ali A. Mesaed, R. Taj, H. Harbi Arabian Journal of Geosciences, 2013 The ironstones of Wadi Ash Shumaysi are mainly enclosed within the middle part of the fluvio-lacustrine siliciclastic succession of Ash Shumaysi Formation (Oligo-Miocene). This succession is composed mainly of conglomerates, sandstones, siltstones, muddy, sandy and glauconitic ironstones, fresh water carbonates, tuffaceous mudstone and basalts in descending order. The study aims to determining the stratigraphic setting, facies types, depositional environments, and mechanism of formation of the succession and the associated ironstones, through field and petrographic investigations. The succession comprises the following four main facies associations arranged according to their predominance from the lower to the upper parts of the succession of Ash Shumaysi Formation: I: Proximal (Conglomerate Facies) Braided Streams, II: Distal (Sandstone Facies) Braided Streams, III: Floodplain facies association, including ironstones, IV: Lacustrine delta, including ironstones. The ironstones of facies associations III and IV represent the following types: 1. Sandy ironstones (ironstone type 1 (IST 1)): which formed by the deposition of water laid detrital quartz grains and Fe-bearing clays under different water depth and currents. 2. Glauconitic muddy ironstones (ironstone type 2 (IST 2)): which formed by the deposition of Fe-bearing clays within slightly agitated starved lakes. During periods of low clastic input, the deposited Fe-bearing clays become converted into green glauconitic clays as a result of the high Fe, Mg, K, Al, and Si activities. During ultimate stages of oxidized diagenetic alterations, the green glauconitic clays become hematitized into glauconitic ironstones. 3. Oolitic muddy ironstones-oolitic ferruginous sandstone (IST 3): which is represented by lacustrine successive shallowing-upward cycles. Each of these cycles begins by friable ferruginous in situ oolitized muddy ironstone which grades upward into oolitic sandy ironstone/oolitic ferruginous sandstone. The second interval is recorded overlying the fining-upward cycle of facies F5. 4. Flaser laminated silty ironstone/ferruginous siltstone (IST 4): which consists of small-scale shallowing-upward cycles of parallel laminated hematitic siltstone and flaser laminated silty ironstone/ferruginous siltstone. In this ironstone type, the inputted depositional components are composed mainly from silt-sized detrital quartz grains embedded within Fe-bearing clays. These components are vertically and laterally distributed within the depositional environments by the impact of the currents and wave actions. The diagenetic processes play an important role in the petrographic and mineralogic evolution of ironstone type IST 1. These processes includes: (a) the diagenetic recrystallization and dehydration of the precursor amorphous Fe-bearing clays and the intimately associated Fe-oxyhydroxies and formation of ferrihydrites, goethite. and hematite; (b) corrosion and embayment of the quartz grains by the enclosing different Fe mineral phases; and (c) in situ pellitization and oolitization throughout the tangential growth of the Fe-oxhyhdroxides during their dehydration and recrystallization and formation of pseudo-ooids. The diagenetic processes in ironstone type IST 2 includes glauconitization of the remained unglauconitized clays during the depositional stages, hematitization and the related oolitization, and pelletization processes. The main diagenetic processes involved in the formation of ironstone type IST 3 are: (a) hematitization of the amorphous Fe-clays and formation of goethite and hematite cement, (b) in situ pelletization and oolitization. The most important diagenetic process in ironstone type IST 4 is the dehydration and recrystallization of the amorphous Fe-clays and formation of goethite and hematite cement.
Facies Analysis and Depositional Environments of Ash Shumaysi Formation (Oligocene-Miocene), Makkah Quadrangle, Wadi Ash Shumaysi, West Central Arabian Shield, Saudi Arabia Rushdi J. Taj, Ali A. Mesaed Arabian Journal for Science and Engineering, 2012 Ash Shumaysi Formation represents Oligo-Miocene fluvio-lacustrine succession consisting mainly of conglomerates, sandstones, siltstones, muddy, sandy and glauconitic ironstones, fresh water carbonates, tuffaceous mudstone and basalts in descending order. It shows the transition from proximal to distal parts of the depositional environments of braided streams into floodplain and finally into lacustrine facies. This succession comprises four main facies associations arranged according to their predominance from the lower to the upper parts of the succession of Ash Shumaysi Formation as follows: (1) proximal (conglomerates facies association I) braided streams which includes four facies of sandstones and conglomerates (F1, F2, F3 and F4), (2) distal (sandstones facies association II) braided streams which comprises three facies (F5, F6 and F7), (3) meandering streams (facies association III) which include the thinly bedded muddy, glauconitic and sandy ironstones–ferruginous sandstone facies (F8), (4) lacustrine delta (facies association IV) which includes three facies (F9, 10 and 11). The Oligo-Miocene siliciclastic sections of Ash Shumaysi represent deposition in mid to distal parts of alluvial fans formed as a result of interplay between climatic conditions, tectonic and sedimentation. In the extreme distal parts of these alluvial fans, river lakes were filled rapidly with conglomerates, sandstones, mudstones and finally fresh water carbonated were formed during arid periods of low siliciclastic input.
