Dolomitization in the Carbonate Rocks of the Upper Turonian Wata Formation, West Sinai, NE Egypt: Petrographic and Geochemical Constraints

Anan, Tarek; Wanas, H.A.

doi:10.1016/j.jafrearsci.2015.07.015

Cited by 15 publications

(12 citation statements)

References 28 publications

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“…The Sr concentration in the present dolomite samples ranges between 144 and 234 ppm (average = 187 ppm) and is comparable with the proposed value of Veizer () and Warren () for typical meteoric‐seawater mixing carbonates. The low concentration of Sr (<300 ppm) in the studied dolostone succession would have been possible as a result of freshwater input, thus suggesting the meteoric‐marine mixing mechanism of dolomitization (e.g., Anan & Wanas, ; Veizer, ; Warren, ). The Na content in the studied dolostones ranging between 206 and 529 ppm (avg.…”

Section: Discussionmentioning

confidence: 98%

“…The petrographic examination of the studied dolostone shows a dominance of medium‐grained, unimodal, zoned, planar, and mostly euhedral (idiotopic) dolomite rhombs. The prevalence of planar (euhedral and subhedral) dolomite texture and the absence of non‐planar (anhedral) one indicates that dolomitization occurred under low salinity and temperature conditions (e.g., Anan & Wanas, ; Sibley & Gregg, ). The absence of spheroidal, spindle, and dumbbell‐shaped dolomite textures, thus, disfavour the microbial and/or groundwater origin.…”

Section: Discussionmentioning

confidence: 99%

“…Other possible sources for Mg would have been the leaching of high Mg‐calcite grains (micrite), aggrading neomorphism of the high Mg‐calcitic matrix, and aragonite shells of the precursor limestone, as evidenced in the thin‐section study (Figure ). In addition, the leaching of Mg adsorbed on clay minerals of the associated wackestone and mudstone facies of the Fulra Limestone Formation would have been acted as a possible source for Mg carried by meteoric water (e.g., Anan & Wanas, ).…”

Section: Discussionmentioning

confidence: 99%

“…At the same time, the mixing zone dolomitization (also called Dorag dolomitization; Badiozamani, ) has been discredited by several earth scientists, keeping in view the kinetic and thermodynamic hindrances to dolomite precipitation (e.g., Hardie, ; Luczaj, ; Machel & Mountjoy, ). However, recent studies by Anan and Wanas (), Land (), Roberts, Bennett, Gonzàlez, Macpherson, and Miliken (), Sumrall et al (), Vasconcelos et al (), and Wright and Wacey () emphasized the role of meteoric water along with microbial processes in lowering of such kinetic and thermodynamic obstacles to dolomitization. They promote dolomitization at relatively low temperature (~25°C), salinity and Mg/Ca conditions in the meteoric‐marine mixing zone, as they lower the ionic strength of seawater in the surrounding of Mg 2+ cations.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the middle Eocene dolostone of the Kachchh Basin, western India, precipitated at comparatively lower temperatures associated with a major regression at this stage (B. P. Singh et al, ). This regression was responsible for the exposure of the shelf for more freshwater input from the continental part and precipitation of dolomite as a result of meteoric‐marine mixing (e.g., Anan & Wanas, ).…”

Section: Discussionmentioning

confidence: 99%

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Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

2018

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Dolostones form by many processes, and their origins are enigmatic. The present study focuses on the origin of the newly recorded 16.5‐m‐thick late middle Eocene dolostone succession of the Kachchh Basin, western India. To achieve this target, a comprehensive field, petrographic, scanning electron microscopy and geochemical studies have been carried out. This dolostone succession shows a sharp contact with the underlying middle Eocene Fulra Limestone Formation. The petrographic study shows a dominance of unimodal, planar‐euhedral idiotopic mosaics of dolomite rhombs along with replacement texture. The X‐ray diffraction pattern confirms it as non‐stoichiometric type dolomite (average molar% MgCO3 = 47.19). SEM‐EDS study deciphers perfectly developed zoned planar‐e dolomite rhombs (40–100 μm) with minor variation in the concentrations of elemental Mg (47.67% to 43.33%) and Ca (52.33% to 56.67%). Among the major oxides, CaO and MgO are the dominant components, indicating that the major mineral phase is dolomite. The positive correlation of CaO with SiO2, Al2O3, and Fe2O3 and a negative correlation of MgO and ∑REE with them suggest that the CaO was mainly contributed from the rivers, while the MgO was contributed from the lagoonal brine/seawater. The low concentration of Sr (144–234 ppm) in the studied dolostone is compatible with the marginal marine mixing origin. The ∑REE content in the dolostones is comparatively lower (18.22 ppm) than the average value of typical marine carbonates (28 ppm), thus suggesting meteoric mixing conditions. The superchondritic Y/Ho values (35.21–100) and Post‐Archaean Australian Shale‐normalized REY patterns of the dolostone facies exhibit typical shallow (bathymetry <50 m) seawater‐like patterns. A strong positive correlation between ΣREE and Y, and low Er/Nd ratios (~0.1) in the dolostone facies indicate incorporation of minor terrigenous influx during dolomitization in a meteoric‐marine mixing condition. The authigenic uranium (0.4–1.7) and slightly negative Ce anomaly suggest that the dolostone succession was precipitated in oxic to dysoxic conditions. The prevalence of planar (euhedral and subhedral) dolomite texture indicates that the dolomitization occurred in a shallow marine environment under low salinity and temperature conditions. Thus, the absence of evaporitic association and physical compaction or deep burial features and the presence of large channelized vugs, mouldic pores along with partially replaced shallow marine fossils, anhydrite cement, and marginal‐marine values of Sr, Na, Ba, Mn, and Fe support the meteoric‐marine mixing model of dolomitization under shallow marine condition of this dolostone succession.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

2018

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Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives

Hussein

El‐Rahman

2019

Geological Journal

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This paper tries to elucidate the origin of the siliceous rocks (cherts) within the Turonian flint‐bearing chalky limestone member of Abu Roash Formation, Abu Roash area, north Western Desert, Egypt. Understanding the formation mechanism of the studied chert was gained through field and petrographic investigations, supplemented by geochemical analyses of both cherts and host Turonian carbonates. The field observations reveal that the chert is found in two forms: banded and nodular. The microscopic investigation determined that the cherts exhibit two types of silica: replacive silica (cryptocrystalline and microcrystalline quartz) and silica cement (length‐fast chalcedony and megaquartz). The chert texture corroborates that the examined authigenic silica was formed diagenetically by the replacement and void‐filling of the host carbonate rocks. The silica was most likely derived from the biogenic opal‐A of the siliceous radiolarian tests. The silica‐phase transformation started with the dissolution of the biogenic opal‐A and precipitation of opal‐CT. Subsequently, opal‐CT was recrystallized into crypto‐ and microquartz at low pH and high temperature. The length‐fast chalcedony and megaquartz occur later as infill to the cavities and pore spaces. The formation of chert is interpreted to be a result of mixing marine–meteoric waters. The effect of the freshwater diagenesis on carbonates is manifested by the dissolution of the allochems, precipitation of granular, drusy, and blocky calcite (meteoric cements), aggrading neomorphism of matrix, and calcitization of the skeletal particles. Geochemical analyses of the host carbonates indicate nearly flat REE patterns and absence of a negative Ce anomaly. This confirms the deviation from the typical seawater and supports the effect of phreatic meteoric water in the chert formation. The paragenetic relationships reveal that the chertification process was performed after dolomitization and before the carbonate meteoric cementation.

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Origin of dolomite of the lower Cambrian Longwangmiao Formation, eastern Sichuan Basin, China

Ren

Gao

Sun

et al. 2017

Carbonates Evaporites

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Dolomitization in the Carbonate Rocks of the Upper Turonian Wata Formation, West Sinai, NE Egypt: Petrographic and Geochemical Constraints

Cited by 15 publications

References 28 publications

Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives

Origin of dolomite of the lower Cambrian Longwangmiao Formation, eastern Sichuan Basin, China

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